offshore structure design, sigve hamilton aspelund
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Offshore Structure Design Sigve Hamilton Aspelund
Day 1:
• Introduction to offshore structures• Different types of offshore structure• Loads effects on offshore structure• Design Parameters Specifications• General Design Considerations• Basics design of offshore platforms
Jack up
• Retractable legs that can be lowered to the sea bed.
• The legs support the drilling rig and keep the rig in position.
Jack up
• Unaffected by the weather during the drilling phase
• The safety valve is located on deck
• It does not need anchoring system
• It does not need heave compensator
• (permanent installation in the drilling phase)
• It has removable drill tower
• Depth limit is 150 meters
• It is unstable under the relocation
• It depends on the tug for moving
Semi submersible
• Portable device that consists of a deck placed on columns attached to two or more pontoons.
• During operation tubes are filled with water and lowered beneath the sea surface.
Semi submersible
• The vessel normally kept in position by anchors, but may also have dynamic positioning equipment (DP).
• Usually have their own propulsion machinery (max. depth approx. 600 to 800 meters).
• The most common type is the "semi-submersible drilling rig".
Drilling ship
• In very deep water (2300m) drill ships are used for drilling the well.
• A drillship is easy to move and is therefore well suited for drilling in deep waters, since it is well suited for dynamic positioning.
• It requires relatively little force to remain in position.
Condeep platform
• Condeep platform is the denomination of a series of oil platforms that were developed in Norway to drill for oil and gas in the North Sea.
• The name comes from the English“concrete deep water structure", or deep structure of concrete.
• The platforms rest on thick concrete tanks that are on the ocean floor and acts as an oil stock.
• From these sticks it as one, three or four slender hollow columns, which is about 30 feet above the surface.
Condeep platform
• It was Stavanger company Norwegian Contractors who developed the concept of Condeep platforms in 1973, after the success of the concrete tank at the Ekofisk field.
• Condeep platforms are not produced anymore.
• The large concrete platforms are out competed by new, cheaper floating rigs and remote-controlled underwater installations.
Jacket platform
• The most widely used platform in the North Sea bearing structure is built as framed in steel
• Platform are poles fixed to the bottom
• The construction is susceptible to corrosionHas no storage tank, but must be associated pipeline network.
• Edvard Grieg Project Update - May 2015
Tension leg platform
• A tension leg platform is a floating and vertically anchored platform or buoy which is normally used for offshore production of oil or natural gas, and is especially suitable for water depths exceeding 300 meters. We usually use rods or chains to keep the platform in place.
Tension leg platform
• Affordable solution
• Quick to install
• Can be equipped entirely by countries
• Can be used on very deep
• Can be moved when a field is empty
• Because of movement of water requiredcompensation equipment
Well head plattform
• Can be an alternative to production facilities on the seabed, especially where water depth is small, as in the southern part of the north sea.
• The wellhead platform is an unmanned small platform, which we can remotely control from a “mother platform".Valve tree is dry.
FPSO
• What is FPSO (Floating Production Storage and Offloading) System?• The FPSO (Floating Production Storage and Offloading) system is used
extensively by oil companies for the purpose of storing oil from the oil rigs in the middle of the ocean and in the high seas.
• It is one of the best devised systems to have developed in the oil exploration industry in the marine areas.
• The FPSO, as its name suggests, is a floating contraption that allows oil rigs the freedom not just to store oil but also to produce or refine it before finally offloading it to the desired industrial sectors, either by way of cargo containers or with the help of pipelines built underwater.
• The use of this system ensures that shipping companies do not have to invest even more money by ferrying the raw and crude oil to an onshore refinery before transferring it to the required industrial areas.
• In simple terms, the FPSO saves time and money effectively.
• Understanding FPSO• The following steps will elaborate on the different functions
performed by the FPSO as a system:
• Production: The ‘P’ in the FPSO stands for production. • Production means evolving the crude oil obtained from the deeper
parts of the ocean. • The FPSO is enabled and fitted with equipments that would act as a
refinery of sort to distil the oil obtained from the ocean along with the gases that are emitted.
• This is the main feature of a FPSO as only with the help of this feature can a FPSO attain the reliability that it enjoys in today’s times.
• Storage: This is the second most important feature and the ‘S’ in the acronym FPSO.
• Second-most important because just as it is important to filter the excavated oil from its oceanic reservoirs, it is equally important to store it well.
• For this purpose, the FPSO is built in such a way that the tubes and the pipes and the tanks are perfect for storing the distilled product from the crude raw-material.
• They are safe and sturdy so as to resist any chances of unwanted oil spillage and thus contamination of the marine life-forms.
• Offloading: This is ‘O’ in the concept of FPSO. • The offloading aspect is important when the FPSO has
to transfer its contents into ships designed as oil carriers or to pipelines that act as transfer agents.
• In simple terms, offloading refers to removing the cargo in a FPSO and transferring it to another cargo-carrying vessel or equipment.
• The offloading part is very tricky as the process is carried out in the middle of the sea and thus requires a lot of concentration and focus in order to avoid any sort of spillage.
• Important Information• It has to be noted that even while the entire working process of a
FPSO is very intriguing, the designing aspect is very amazing. • This is because the system has to be constructed in such a way that it
remains invulnerable to the constant changes that take place in the middle of the ocean or the seas.
• The various tubes and pipes have to be built in such a way that they do not affect the pureness of the oil obtained and the same time do not get broken because of heavy storms or tide-currents.
Conclusion• The FPSO as a system has been in use from the seventies when major-
scale oil exploration began in the oceans and seas. • In these past four decades, given the way oil exploration industry has
been on the rise, the use and relevance of a FPSO has increased even more.
• The system is fool proof, enables cost efficiency and thus becomes a very major asset when it comes to excavating oil in the marine areas.
Spar Platforms• For drilling wells beyond 10,000 feet, naval architects have designed a
type of drilling and production platform which has a hollow cylindrical hull that can descend up to a sea depth of 200 meters.
• This are called Spar Platforms. • It is secured to the ocean floor by a complex network of cables and
tendons.• The weight of the cylindrical hull stabilises thedrilling platform and caters for the drilling risers to descend up to the drilling well on the sea floor.
Subsea Production System
• As the name suggests, this system is based on the idea where wellheads are mounted on the sea floor after the wells have been drilled by one of the many deep sea drilling platforms.
• Shell Ormen Lange - a journey in energy
• The wellheads are remotely controlled and their automated system is so designed that it allows for transporting the oil or gas directly to the production facilities using a network of undersea pipelines and risers.
• Apart from those mentioned above, shuttle tankers are also used in offshore oil production systems.
• As technology advancements are progressively made, deep water exploration possess superior challenges for all the operating parties.
• These massive structures are home to some highly improved and advanced systems, machineries and equipments for carrying out the coveted job of offshore drilling.
The Guyed Tower
• ABSTRACT
The guyed tower is an offshore platform that rests on a spud can or bearing foundation and is held upright by multiple guylines.
• A simplified procedure for calculating the wave-induced dynamic response of this compliant tower is presented.
• Also, the dynamic characteristics that allow the structure to safely resist large ocean waves is discussed.
• A large scale test model of the tower has been installed in 300 feet of water in the Gulf of Mexico to verify the validity of the conclusions drawn.
• INTRODUCTION
A new compliant offshore structure, the guyed tower, has been proposed as a deep water production and drilling platform.
• The concept as proposed has two major advantages over other proposed schemes; first, the structure can be fabricated and installed using presently available equipment and technology; second, this production platform is anticipated to be less expensive to build, and maintain than present alternatives proposed for water depths from 600 to 2000 feet.
• This paper describes the basic guyed tower concept and illustrates the design procedures used to insure that the compliant structure will safely withstand severe environmental forces and yet be slender, lightweight and economical.
• Prototype Guyed Tower
The guyed tower is a trussed structure that rests on the ocean floor, extends upward to a deck supported above the waves, and is held upright by multiple guylines.
• The base of the tower is supported on a truss reinforced shell foundation called a spud can.
• During installation the spud can is forced into the ocean bottom until the desired load carrying capability is attained.
• The amount of design penetration is of course dependent on the load to be carried and the site soil parameters.
• The main truss of the tower as currently proposed would have four equally spaced legs connected primarily with x-bracing.
• However, other geometric configurations could be used. • For a structure supporting 24 wells in 1500 feet of water, the legs would be spaced
100 feet apart and range in size from 5 to 8 feet in diameter. • Ideally the deck would be designed to support all the equipment to drill and
produce a large number (20 to 40) of wells. • The deck for the 24 well 1500 ft structure would have two levels 150 feet on a side
and would support 7500 tons deck payload, which is adequate for many areas of the world.
• To carry larger payloads, the support capacity of the tower truss, spud can, and guying system would have to be increased proportionally.
Deep-water guyed tower concept
1, 2) Conventional fixed platforms; 3) Compliant tower; 4, 5) Vertically moored tension leg and mini-tension leg platform;6) Spar; 7,8) Semi-submersibles; 9) Floating production, storage, and offloading facility; 10) Sub-sea completion and tie-back to host facility.
Loads
Offshore structure shall be designed for following types of loads:• Permanent (dead) loads• Operating (live) loads • Environmental loads • Wind load • Wave load • Earthquake load• Construction - installation loads• Accidental loads• The design of offshore structures is dominated by environmental loads, especially
wave load
Permanent Loads
• Weight of the structure in air, including the weight of ballast.• Weights of equipment, and associated structures permanently
mounted on the platform. • Hydrostatic forces on the members below the waterline. • These forces include buoyancy and hydrostatic pressures.
Operating (Live) Loads
• Operating (Live) Loads: • Operating loads include the weight of all non permanent equipment
or material, as well as forces permanent equipment or material, generated during operation of equipment.
• The weight of drilling, production facilities, living quarters, furniture, life support systems, heliport, consumable supplies, liquids, etc.
• Forces generated during operations, e.g. drilling, vessel mooring, helicopter landing, helicopter landing, crane operations.
• Following Live load values are recommended in BS6235:• Crew quarters and passage ways: 3.2 KN/m²• Working areas: 8,5 KN/m²
Wind Loads:
• Wind load act on portion of platform above the water level as well as on any equipment, the water level as well as on any equipment, housing, derrick, etc.
• For combination with wave loads, codes recommend the most unfavorable of the following two loadings:
• 1 minute sustained wind speeds combined with extreme waves • 3 second gusts
• When, the ratio of height to the least horizontal dimension of structure is greater than 5, then API-RP2A requires the dynamic effects of the wind to be taken into account and the flow induced cyclic wind loads due to vortex shedding must be investigated.
Wave load:
• The wave loading of an offshore structure is usually the most important of all environmental loadings.
• The forces on the structure are caused by the motion of the water due to the waves
• Determination of wave forces requires the solution of,• a) Sea state using an idealization of the wave surface profile and the
wave kinematics by wave theory • b) Computation of the wave forces on individual members and on the
total structure, from the fluid motion.
• Design wave concept is used, where a regular wave of given height and period is defined and the forces due to this wave are calculated using a high-order wave theory.
• Usually the maximum wave with a return period of 100 years, is chosen.
• No dynamic behavior of the structure is considered.• This static analysis is appropriate when the dominant wave periods
are well above the period of the structure.• This is the case of extreme storm waves acting on shallow water
structures.
Wave theories
• Wave theories describe the kinematics of waves of water• They serve to calculate the particle velocities and accelerations and
the dynamic pressure as functions of the surface elevation of the waves.
• The waves are assumed to be long-crested, i.e. they can be described by a two dimensional flow field, and are characterized by the parameters: wave height (H), period (T) and water depth (d).
Wave forces on structural members
• Structures exposed to waves experience forces much higher than wind loadings.
• The forces result from the dynamic pressure and the water particle motions.
• Two different cases can be distinguished: • Large volume bodies, termed hydrodynamic compact structures,
influence the wave field by diffraction and reflection. The forces on these bodies have to be determined by calculations based on diffraction theory.
• Slender, hydro-dynamically transparent structures have no significant influence on the wave field. The forces can be calculated in a straight-forward manner with Morison's equation. The steel jackets of offshore structures can usually be regarded as hydro-dynamically transparent.
• As a rule, Morison's equation may be applied when D/L < 0.2, where D is the member diameter and L is the wave length.
• Morison's equation expresses the wave force as the sum of, • An inertia force proportional to the particle acceleration • A non-linear drag force proportional to the square of the particle velocity
Earthquake load:
• Offshore structures are designed for two levels of earthquake intensity.
• Strength level: Earthquake, defined as having a "reasonable likelihood of not being exceeded during the platform's life" (mean recurrence interval ~ 200 - 500 years), the structure is designed to respond elastically.
• Ductility level: • Earthquake, defined as close to the "maximum credible earthquake"
at the site, the structure is designed for inelastic response and to have adequate reserve strength to avoid collapse. strength to avoid collapse.
• Ice and Snow Loads: • Ice is a primary problem for marine structures in the arctic and sub-
arctic zones. • Ice formation and expansion can generate large pressures that give
rise to horizontal as well as vertical forces. • In addition, large blocks of ice driven by current, winds and waves
with speeds up to 0,5 to 1,0 m/s, may hit the structure and produce impact loads.
• Temperature Load:• Temperature gradients produce thermal stresses. • To cater such stresses, extreme values of sea and air temperatures
which are likely to occur during the life of the structure shall be estimated.
• In addition to the environmental sources, accidental release of cryogenic material can result in temperature increase, which must be taken into account as accidental loads.
• The temperature of the oil and gas produced must also be considered.
• Marine Growth: • Marine growth is accumulated on submerged members. Its main
effect is to increase the wave forces on the members by increasing exposed areas and drag coefficient due to higher surface roughness. It is accounted for in design through appropriate increases in the diameters and masses of the submerged members.
• Installation Load • These are temporary loads and arise during
fabrication and installation of the platform or its components.
• During fabrication, erection lifts of various structural components generate lifting forces, while in the installation phase forces are generated during platform load out, transportation to the site, launching and upending, as well as during lifts related to installation.
• All members and connections of a lifted component must be designed for the forces resulting from static equilibrium of the lifted weight and the sling tensions.
• Load out forces are generated when the jacket is loaded from the fabrication yard onto the barge.
• Depends on friction co-efficient.
Accidental Load Accidental Load : • According to the DNV rules , accidental loads are loads, which may
occur as a result of accident or exceptional circumstances. • Examples of accidental loads are, collision with vessels, fire or
explosion, dropped objects, and unintended flooding of buoyancy tanks.
• Special measures are normally taken to reduce the risk from accidental loads.
Load Combinations Load Combinations: • The load combinations depend upon the design method used, i.e.
whether limit state or allowable stress design is employed. • The load combinations recommended for use with allowable stress
procedures are: • Normal operations
• Dead loads plus operating environmental loads plus maximum live loads.• Dead loads plus operating environmental loads plus minimum live loads.
• Extreme operations• Dead loads plus extreme environmental loads plus maximum live loads. • Dead loads plus extreme environmental loads plus minimum live loads
• Environmental loads, should be combined in a manner consistent with their joint probability of occurrence.
• Earthquake loads, are to be imposed as a separate environmental load, i.e., not to be combined with waves, wind, etc.
Design Parameters Specifications
General Design Considerations
Design of offshore fixed platforms
• The most commonly used offshore platforms in the Gulf of Mexico, Nigeria, California shorelines and the Persian Gulf are template type platforms made of steel, and used for oil/gas exploration and production (Sadeghi 1989, 2001).
• The design and analyses of these offshore structures must be made in accordance with recommendations published by the American Petroleum Institute (API).
• The design and analysis of offshore platforms must be done taking into consideration many factors, including the following important parameters:
• Environmental (initial transportation, and in-place 100-year storm conditions)
• Soil characteristics • Code requirements (e.g. American Institute of Steel Construction “AISC”
codes) • Intensity level of consequences of failure • The entire design, installation, and operation must be approved by the
client.
Different analyses needed for template platforms• Different main analyses required for design of a template (jacket) type
platform are as follows (Sadeghi 2001): • In-place analysis • Earthquake analysis • Fatigue analysis • Impact analysis • Temporary analysis • Loadout analysis • Transportation analysis • Transportation analysis
• Appurtenances analysis • Lift/Launch analysis • Upending analysis • Uprighting analysis • Unpiled stability analysis • Pile and conductor pipe drivability analysis• Cathodic protection analysis • Installation analysis
Software used in the platforms design• To perform a structural analysis of platforms, the following software
may be used (Sadeghi 2001): Structural analysis:• SACS• FASTRUDL• MARCS • OSCAR• StruCAD • SESAM
Pile analysis:• Maxsurf Hydromax • Seamoor for hydrodynamics calculations• GRLWEAP • PDA• CAPWAP
Day 2:
• Design methodology for floating structure • Different types of floating structure• Basic concept and dynamic analysis• Structure optimum configuration• Structure Reliability
Different types of floating structure
Basic concept and dynamic analysis
• Basic Concepts of Analysis• The software uses the Finite Element Method (FEM). • FEM is a numerical technique for analyzing engineering designs. • FEM is accepted as the standard analysis method due to its generality
and suitability for computer implementation. • FEM divides the model into many small pieces of simple shapes called
elements effectively replacing a complex problem by many simple problems that need to be solved simultaneously.
• Elements share common points called nodes. • The process of dividing the model into small pieces is called meshing.• The behavior of each element is well-known under all possible support and load scenarios. • The finite element method uses elements with different shapes.• The response at any point in an element is interpolated from the response at the element nodes. • Each node is fully described by a number of parameters depending on the analysis type and the
element used. • For example, the temperature of a node fully describes its response in thermal analysis. • For structural analyses, the response of a node is described, in general, by three translations and
three rotations. • These are called degrees of freedom (DOFs). • Analysis using FEM is called Finite Element Analysis (FEA).
• The software formulates the equations governing the behavior of each element taking into consideration its connectivity to other elements.
• These equations relate the response to known material properties, restraints, and loads.
• Next, the program organizes the equations into a large set of simultaneous algebraic equations and solves for the unknowns.
• In stress analysis, for example, the solver finds the displacements at each node and then the program calculates strains and finally stresses.
The software offers the following types of studies:Static (or Stress) Studies. • Static studies calculate displacements, reaction forces, strains, stresses, and
factor of safety distribution. • Material fails at locations where stresses exceed a certain level. • Factor of safety calculations are based on one of four failure criterion.• Static studies can help you avoid failure due to high stresses. • A factor of safety less than unity indicates material failure. • Large factors of safety in a contiguous region indicate low stresses and that
you can probably remove some material from this region.
Frequency Studies. • A body disturbed from its rest position tends to vibrate at certain frequencies
called natural, or resonant frequencies. • The lowest natural frequency is called the fundamental frequency. • For each natural frequency, the body takes a certain shape called mode shape. • Frequency analysis calculates the natural frequencies and the associated
mode shapes.• In theory, a body has an infinite number of modes. • In FEA, there are theoretically as many modes as degrees of freedom (DOFs). • In most cases, only a few modes are considered.
• Excessive response occurs if a body is subjected to a dynamic load vibrating at one of its natural frequencies.
• This phenomenon is called resonance. • For example, a car with an out-of-balance tire shakes violently at a certain
speed due to resonance. • The shaking decreases or disappears at other speeds. • Another example is that a strong sound, like the voice of an opera singer, can
cause a glass to break.• Frequency analysis can help you avoid failure due to excessive stresses caused
by resonance. • It also provides information to solve dynamic response problems.
Dynamic Studies. • Dynamic studies calculate the response of a model due to loads that
are applied suddenly or change with time or frequency.• Linear dynamic studies are based on frequency studies. • The software calculates the response of the model by accumulating
the contribution of each mode to the loading environment.
• In most cases, only the lower modes contribute significantly to the response.
• The contribution of a mode depends on the load’s frequency content, magnitude, direction, duration, and location.
• The objectives of a dynamic analysis include: • (a) the design of structural and mechanical systems to perform
without failure in dynamic environments, and • (b) the reduction of vibration effects.
Buckling Studies. • Buckling refers to sudden large displacements due to axial loads. • Slender structures subject to axial loads can fail due to buckling at
load levels lower than those required to cause material failure. • Buckling can occur in different modes under the effect of different
load levels. • In many cases, only the lowest buckling load is of interest.• Buckling studies can help you avoid failure due to buckling.
Thermal Studies. • Thermal studies calculate temperatures, temperature gradients, and
heat flow based on heat generation, conduction, convection, and radiation conditions.
• Thermal studies can help you avoid undesirable thermal conditions like overheating and melting.
Design Studies. • Optimization design studies automate the search for the optimum design based on a
geometric design. • The software is equipped with a technology to quickly detect trends and identify the
optimum solution using the least number of runs. • Optimization design studies require the definition of the following:
• Goals or Objectives. State the objective of the study. For example, minimum material to be used.• Design Variables. Select the dimensions that can change and set their ranges. For example, the
diameter of a hole can vary from 0.5” to 1.0” while the extrusion of a sketch can vary from 2.0” to 3.0”.
• Constraints. Set the conditions that the optimum design must satisfy. For example, you can require that a stress component does not exceed a certain value and the natural frequency to be within a specified range.
• NOTE: For the non-optimization design study, do not define any goals.
Nonlinear Studies. • When the assumptions of linear static analysis do not apply, you can
use nonlinear studies to solve the problem. The main sources of nonlinearity are: • Large displacements, nonlinear material properties, and contact. • Nonlinear studies calculate displacements, reaction forces, strains,
and stresses at incrementally varying levels of loads and restraints. • When inertia and damping forces can not be ignored, you can use
nonlinear dynamic analysis.
• Nonlinear studies refer to nonlinear structural studies. • For thermal studies, the software automatically solves a linear or nonlinear
problem based on material properties and thermal restraints and loads.• Solving a nonlinear problem requires much more time and resources than
solving a similar linear static study.• The principle of superposition does not apply for nonlinear studies. • For example, If applying force F1 causes stress S1 and applying force F2 causes
stress S2 at a point, then applying the forces together does NOT necessarily cause a stress (S1+S2) at the point as is the case for linear studies.
• Nonlinear studies can help you assess the behavior of the design beyond the limitations of static and buckling studies.
• Solving a nonlinear problem requires much more time and resources than solving a similar linear static study.
• The principle of superposition does not apply for nonlinear studies. • For example, If applying force F1 causes stress S1 and applying force F2
causes stress S2 at a point, then applying the forces together does NOT necessarily cause a stress (S1+S2) at the point as is the case for linear studies.
• Nonlinear studies can help you assess the behavior of the design beyond the limitations of static and buckling studies.
• Static studies offer a nonlinear solution for contact problems when you activate the large displacement option.
Drop Test Studies. • Drop test studies evaluate the effect of dropping the design on a rigid floor. • You can specify the dropping distance or the velocity at the time of impact in addition
to gravity. • The program solves a dynamic problem as a function of time using explicit integration
methods. • Explicit methods are fast but require the use of small time increments. • Due to the large amount of information the analysis can generate, the program saves
results at certain instants and locations as instructed before running the analysis.• After the analysis is completed, you can plot and graph displacements, velocities,
accelerations, strains, and stresses.
Fatigue Studies. • Repeated loading weakens objects over time even when the induced stresses
are considerably less than allowable stress limits. • The number of cycles required for fatigue failure to occur at a location
depends on the material and the stress fluctuations. • This information, for a certain material, is provided by a curve called the S-N
curve. • The curve depicts the number of cycles that cause failure for different stress
levels. • Fatigue studies evaluate the consumed life of an object based on fatigue
events and S-N curves.
Structure optimum configuration
• Reinforced Concrete walls, which include lift wells or shear walls, are usual requirements of Multistory Buildings.
• Constructing the Shear wall in tall, medium and even short buildings will reinforce the significantly and either more economic than the bending frames.
• By the Shear walls, we can control the side bending of the structure, much better than other elements like closed frames and certainly the shear walls are more flexible than them.
• However, on many occasions the design has to be based on the off center position of the Lift and stair case walls with respect to the centre of mass.
• The design in these cases results into an excessive stresses in most of the structural members, unwanted torsional moments and sways.
• Design by coinciding Stiffness centre and mass of the building is the ideal for a structure. • In this case there is no eccentricity, but as per IS 1893(1):2002 the minimum eccentricity is to be considered. • The lateral force in a wall due to rotational moment is given by, Fir =• ri = Radial distance of shear wall “i”• F = Design Shear force ed = Design eccentricity
• From the above equation, it is observed that the distance of any shear wall from the centre of stiffness increases, the Shear generated in the Shear wall is decreased.
• The distance of Shear wall from the Centre of Stiffness is also an important Criteria for the Stresses generated in the Structural members and overall behavior of the whole structure.
• The nature of stresses generated in the Shear wall according to its position is also different.
• The shear wall kept at very near to the Centre of stiffness act as a Vertical bending element and the shear wall kept at corner of the building are may be in axial compression or in axial tension according to the direction of the Lateral Force.
• In the bending nature of the wall the drift generated is more compare to shear walls kept at the corner of the building.
• So it is necessary and important to know, what should be the exact location of the shear walls that can results in minimum stresses in all the structural members of the multistoried building.
To locate shear wall at radial distance from the centre of mass for optimum configuration of a multi storey building, by keeping the features of shear wall constant. 1. To Study the operation of computer aided software “STRUD” 2. Validation of “STRUD” by designing a model building having existing
design data3. Preparation of problem building drawing from the data4. Model generation of problem building in “STRUD” 5. Comparison of analysis and design data of four different cases having
various radial position of shear wall generated in the “STRUD”
1) To Study the operation of computer aided software STRUD• When any type of high-rise structure is going to be design, it should
be analyze as the space frame rather than plain frame or plain grid. • As the analysis of the high-rise structure as a space frame is very
difficult or it seems to be impossible manually, so we need computer aided software which helps us to analyze the high-rise structure
• So we are going to use the computer aided software “STRUD” • And for this we are first of all going to study the operation by the
tutorial of the software
2) Whenever any structure is to be analyzing in any type of computer aided software first of all validation should be done about the software that the result given by the software are fair? For this purpose we are going to take one identical problem whose design have been done by manually or by any other means and we are going to input the same data into the above software and compare the result.
3) We will develop an identical model by using Auto CA 2008 in the computer. We have taken a structure having six bays in both the horizontal direction. From these drawing we have created four different cases by placing the shear wall radically away from the centre of the stiffness in sequence. Also we will generate the centerline plan in AutoCAD 2008.
4) After generating the centerline plan in AutoCAD 2008, we will input the above data in computer aided Structure Designing software. • The input in the software is done in sequence from bottom to top. • The design of structure is done in descending order from slab-beam-
column-footing sequence.
• 5) After inputting the data in software and after attaching all the sections / after doing all the preliminary data the analysis is carried out.
• With the help of this analysis of all the four different cases we will find the bending moment, shear force, axial force and sway in various elements of the structure.
• After obtaining the final results from all the above four cases we are going to make the comparison of ……
• Beam moments. • Column axial forces. • Storey displacement & drift. • Percentage of steel in beams. • Percentage of steel in column. • Percentage of steel in footings. • Overall economy of each case.
• A typical building (G+8) having three various position of shear wall and one without shear wall having following data Floor to Floor height = 3000mm Height of Plinth = 450mm above ground level.
• Depth of Foundation = 2100mm below ground level. • External Walls =230 mm Internal Walls =115 mm
• Roof: Roof Finish = 1.5 KN/m2 • Live Load = Variable parameter • Floor : Floor Finish = 1.0 KN/m2 • Live Load = Variable parameter • EQ load generation method = Response Spectrum Method • Seismic Zone = Zone 3 • Soil Type = Medium Soil • Percentage Damping = 5 % • Modal Combination method = SRSS
• Concrete = M20 • Steel: Main & Secondary = Fe 415 • Unit Weight of Concrete = 25 KN/m2 • Unit Weight of Bricks Masonry = 19 KN/m2 • Design Basis: =Limit State Method based on IS: 456-2000 • Live Load = 2 KN/m2 • Preliminary Beam Size = 230 x 450 mm
• When live load 2 KN/m² and beam size is 230 x 450mm, quantity of steel is increase (approx 17%) at location of shear wall near to the center of building, compare to shear wall at corner of building.
• When the shear wall kept near to the center with live load is 2KN/m² and preliminary dimension of beam is 230 x 300mm, quantity of steel in beam increase (approx 15%), while quantity of steel in column is decrease (approx 8.77%) as compare to shear wall at corner of building.
• When live load 3 KN/m² and beam size is 230X300mm, quantity of steel is increase (approx 13%) at location of shear wall near to the center of building, compare to shear wall at corner of building.
• When live load 3 KN/m² and beam size is 230 x 300mm, quantity of steel is decrease (approx 22%) at location of shear wall near to the center of building, compare to building without shear wall.
• The location of shear wall at corners of building is much effective while increasing live load 3 KN/m² with preliminary dimension of beam 230 x 300mm.
• The shear wall gives beneficial effect of more clear head way in case of providing it at corners of building or away from the center of building.
• Quantity of steel and concrete is less in case of without shear wall so it is said that for G+8 building with 2 KN/m² live load and preliminary beam size is 230 x 450 mm or 250 x 300mm, there is no economical beneficial effect of shear wall.
• Here the G+8 building is taken one can take higher no. of floor as G+15 or G+20 more than that, it may be given.
• More effective beneficial effect of shear wall. • The problem building is only symmetric square building; one can take
rectangle, L-shape, C-shape building with eccentricity. • Identical building of (6 bay x 6 bay) is taken in problem for simplicity,
but commercial and residential building irregular shape in plan can also take for further work for implementation to this project.
• Shape of shear wall is taken in this building is “L shape”; one can take different shape for further work.
Structure Reliability
Reliability engineering
• Reliability engineering is engineering that emphasizes dependability in the lifecycle management of a product.
• Dependability, or reliability, describes the ability of a system or component to function under stated conditions for a specified period of time.
• Reliability engineering represents a sub-discipline within systems engineering. • Reliability is theoretically defined as the probability of success (Reliability=1-
Probability of Failure), as the frequency of failures, or in terms of availability, as a probability derived from reliability and maintainability.
• Maintainability and maintenance is often defined as a part of "reliability engineering" in Reliability Programs.
• Reliability plays a key role in the cost-effectiveness of systems.
• Reliability engineering deals with the estimation and management of high levels of "lifetime" engineering uncertainty and risks of failure.
• Although stochastic parameters define and affect reliability, according to some expert authors on Reliability Engineering, e.g. P. O'Conner, J. Moubray and A. Barnard, reliability is not (solely) achieved by mathematics and statistics.
• "Nearly all teaching and literature on the subject emphasize these aspects, and ignore the reality that the ranges of uncertainty involved largely invalidate quantitative methods for prediction and measurement"
• Reliability engineering relates closely to safety engineering and to system safety, in that they use common methods for their analysis and may require input from each other.
• Reliability engineering focuses on costs of failure caused by system downtime, cost of spares, repair equipment, personnel and cost of warranty claims.
• Safety engineering normally emphasizes not cost, but preserving life and nature, and therefore deals only with particular dangerous system-failure modes.
• High reliability (safety factor) levels also result from good engineering, from attention to detail and almost never from only re-active failure management (reliability accounting / statistics).
Scope and techniques to be used within Reliability Engineering• Reliability engineering for complex systems requires a different, more
elaborate systems approach than for non-complex systems. Reliability engineering may in that case involve:• System availability and mission readiness analysis and related
reliability and maintenance requirement allocation• Functional System Failure analysis and derived requirements
specification• Inherent (system) Design Reliability Analysis and derived
requirements specification: for both Hardware- and Software design• System Diagnostics design• Predictive and Preventive maintenance (e.g. Reliability Centered
Maintenance)• Human Factors / Human Interaction / Human Errors
• Manufacturing and Assembly induced failures (non 0-hour Quality)• Maintenance induced failures• Transport induced failures• Storage induced failures• Use (load) studies, component stress analysis and derived requirements specification• Software(systematic) failures• Failure / reliability testing• Field failure monitoring and corrective actions• Spare-parts stocking (Availability control)• Technical documentation, caution and warning analysis• Data and information acquisition/organisation (Creation of a general reliability development
Hazard Log and FRACAS system)
Effective reliability engineering requires understanding of the basics of failure mechanisms for which experience, broad engineering skills and good knowledge from many different special fields of engineering, like:• Tribology• Stress (mechanics)• Fracture mechanics / Fatigue (material)• Thermal engineering• Fluid mechanics / shock loading engineering• Electrical engineering• Chemical engineering (e.g. Corrosion)• Material science
DefinitionsReliability may be defined in the following ways:• The idea that an item is fit for a purpose with respect to time• The capacity of a designed, produced or maintained item to perform as required
over time• The capacity of a population of designed, produced or maintained items to
perform as required over specified time• The resistance to failure of an item over time• The probability of an item to perform a required function under stated conditions
for a specified period of time• The durability of an object.
Basics of a Reliability AssessmentMany engineering techniques are used in reliability risk assessments, such as reliability hazard analysis, failure mode and effects analysis (FMEA), fault tree analysis (FTA), Reliability Centered Maintenance, material stress and wear calculations, fatigue and creep analysis, human error analysis, reliability testing, etc. Because of the large number of reliability techniques, their expense, and the varying degrees of reliability required for different situations, most projects develop a reliability program plan to specify the reliability tasks that will be performed for that specific system.
Consistent with the creation of a safety cases, for example ARP4761, the goal of reliability assessments is to provide a robust set of qualitative and quantitative evidence that use of a component or system will not be associated with unacceptable risk. The basic steps to take are to:• First thoroughly identify relevant unreliability "hazards", e.g. potential conditions,
events, human errors, failure modes, interactions, failure mechanisms and root causes, by specific analysis or tests
• Assess the associated system risk, by specific analysis or testing• Propose mitigation, e.g. requirements, design changes, detection logic, maintenance,
training, by which the risks may be lowered and controlled for at an acceptable level.• Determine the best mitigation and get agreement on final, acceptable risk levels,
possibly based on cost-benefit analysis
• Risk is here the combination of probability and severity of the failure incident (scenario) occurring.
• In a deminimus definition, severity of failures include the cost of spare parts, man hours, logistics, damage (secondary failures) and downtime of machines which may cause production loss.
• A more complete definition of failure also can mean injury, dismemberment and death of people within the system (witness mine accidents, industrial accidents, space shuttle failures) and the same to innocent bystanders (witness the citizenry of cities like Bhopal, Love Canal, Chernobyl or Sendai and other victims of the 2011 Tōhoku earthquake and tsunami) - in this case, Reliability Engineering becomes System Safety.
• What is acceptable is determined by the managing authority or customers or the effected communities.
• Residual risk is the risk that is left over after all reliability activities have finished and includes the un-identified risk and is therefore not completely quantifiable.
Reliability and availability program plan• A reliability program plan is used to document exactly what "best practices"
(tasks, methods, tools, analysis and tests) are required for a particular (sub)system, as well as clarify customer requirements for reliability assessment.
• For large scale, complex systems, the reliability program plan should be a separate document.
• Resource determination for manpower and budgets for testing and other tasks is critical for a successful program.
• In general, the amount of work required for an effective program for complex systems is large.
• A reliability program plan is essential for achieving high levels of reliability, testability, maintainability and the resulting system Availability and is developed early during system development and refined over the systems life-cycle.
• It specifies not only what the reliability engineer does, but also the tasks performed by other stakeholders.
• A reliability program plan is approved by top program management, which is responsible for allocation of sufficient resources for its implementation.
• A reliability program plan may also be used to evaluate and improve availability of a system by the strategy on focusing on increasing testability & maintainability and not on reliability.
• Improving maintainability is generally easier than reliability. • Maintainability estimates (Repair rates) are also generally more accurate. • However, because the uncertainties in the reliability estimates are in most cases
very large, it is likely to dominate the availability (prediction uncertainty) problem; even in the case maintainability levels are very high.
• When reliability is not under control more complicated issues may arise, like manpower (maintainers / customer service capability) shortage, spare part availability, logistic delays, lack of repair facilities, extensive retro-fit and complex configuration management costs and others.
• The problem of unreliability may be increased also due to the "domino effect" of maintenance induced failures after repairs.
• Only focusing on maintainability is therefore not enough. • If failures are prevented, none of the others are of any importance and therefore reliability
is generally regarded as the most important part of availability. • Reliability needs to be evaluated and improved related to both availability and the cost of
ownership (due to cost of spare parts, maintenance man-hours, transport costs, storage cost, part obsolete risks, etc.).
• But, as GM and Toyota have belatedly discovered, TCO also includes the down-stream liability costs when reliability calculations do not sufficiently or accurately address customers' personal bodily risks.
• Often a trade-off is needed between the two. • There might be a maximum ratio between availability and cost of ownership.
• Testability of a system should also be addressed in the plan as this is the link between reliability and maintainability.
• The maintenance strategy can influence the reliability of a system (e.g. by preventive and/or predictive maintenance), although it can never bring it above the inherent reliability.
• The reliability plan should clearly provide a strategy for availability control.
• Whether only availability or also cost of ownership is more important depends on the use of the system.
• For example, a system that is a critical link in a production system – e.g. a big oil platform – is normally allowed to have a very high cost of ownership if this translates to even a minor increase in availability, as the unavailability of the platform results in a massive loss of revenue which can easily exceed the high cost of ownership.
• A proper reliability plan should always address RAMT analysis in its total context.
• RAMT stands in this case for reliability, availability, maintainability/maintenance and testability in context to the customer needs.
Reliability requirements• For any system, one of the first tasks of reliability engineering is to adequately specify the reliability
and maintainability requirements derived from the overall availability needs and more importantly, from proper design failure analysis or preliminary prototype test results.
• Clear (able to design to) Requirements should constrain the designers from designing particular unreliable items / constructions / interfaces / systems.
• Setting only availability (reliability, testability and maintainability) allocated targets (e.g. max. Failure rates) is not appropriate.
• This is a broad misunderstanding about Reliability Requirements Engineering. • Reliability requirements address the system itself, including test and assessment requirements, and
associated tasks and documentation. • Reliability requirements are included in the appropriate system or subsystem requirements
specifications, test plans and contract statements. • Creation of proper lower level requirements is critical.
• Provision of only quantitative minimum targets (e.g. MTBF values/ Failure rates) is not sufficient for different reasons.
• One reason is that a full validation (related to correctness and verifiability in time) of an quantitative reliability allocation (requirement spec) on lower levels for complex systems can (often) not be made as a consequence of
• 1) The fact that the requirements are probabalistic • 2) The extremely high level of uncertainties involved for showing compliance with all these
probabalistic requirements • 3) Reliability is a function of time and accurate estimates of a (probabalistic) reliability number
per item are available only very late in the project, sometimes even only many years after in-service use.
• Compare this problem with the continues (re-)balancing of for example lower level system mass requirements in the development of an aircraft, which is already often a big undertaking.
• Notice that in this case masses do only differ in terms of only some %, are not a function of time, the data is non-probabalistic and available already in CAD models.
• In case of reliability, the levels of unreliability (failure rates) may change with factors of decades (1000's of %) as result of very minor deviations in design, process or anything else.
• The information is often not available without huge uncertainties within the development phase. • This makes this allocation problem almost impossible to do in a useful, practical, valid manner,
which does not result in massive over- or under specification. • A pragmatic approach is therefore needed. • For example; the use of general levels/ classes of quantitative requirements only depending on
severity of failure effects. • Also the validation of results is a far more subjective task than for any other type of requirement. • (Quantitative) Reliability parameters -in terms of MTBF - are by far the most uncertain design
parameters in any design.
• Furthermore, reliability design requirements should drive a (system or part) design to incorporate features that prevent failures from occurring or limit consequences from failure in the first place!
• Not only to make some predictions, this could potentially distract the engineering effort to a kind of accounting work.
• A design requirement should be so precise enough so that a designer can "design to" it and can also prove -through analysis or testing- that the requirement has been achieved, and if possible within some a stated confidence.
• Any type of reliability requirement should be detailed and could be derived from failure analysis (Finite Element Stress and Fatigue analysis, Reliability Hazard Analysis, FTA, FMEA, Human Factor analysis, Functional Hazard Analysis, etc.) or any type of reliability testing.
• Also, requirements are needed for verification tests e.g. required overload loads (or stresses) and test time needed.
• To derive these requirements in an effective manner, a systems engineering based risk assessment and mitigation logic should be used.
• Robust hazard log systems are to be created that contain detailed information on why and how systems could or have failed.
• Requirements are to be derived and tracked in this way. • These practical design requirements shall drive the design and not only be used for verification
purposes. • These requirements (often design constraints) are in this way derived from failure analysis or
preliminary tests. • Understanding of this difference with only pure quantitative (logistic) requirement specification
(e.g. Failure Rate/ MTBF setting) is paramount in the development of successful (complex) systems.
• The maintainability requirements address the costs of repairs as well as repair time.
• Testability (not to be confused with test requirements) requirements provide the link between reliability and maintainability and should address detectability of failure modes (on a particular system level), isolation levels and the creation of diagnostics (procedures).
• As indicated above, reliability engineers should also address requirements for various reliability tasks and documentation during system development, test, production, and operation.
• These requirements are generally specified in the contract statement of work and depend on how much leeway the customer wishes to provide to the contractor.
• Reliability tasks include various analyses, planning, and failure reporting.
• Task selection depends on the criticality of the system as well as cost. • A safety critical system may require a formal failure reporting and
review process throughout development, whereas a non-critical system may rely on final test reports.
• The most common reliability program tasks are documented in reliability program standards, such as MIL-STD-785 and IEEE 1332.
• Failure reporting analysis and corrective action systems are a common approach for product/process reliability monitoring.
Reliability culture / Human Errors / Human FactorsPractically, most failures can in the end be traced back to a root causes of the type of human error of any kind. For example, human errors in:• Management decisions on for example budgeting, timing and required tasks• Systems Engineering: Use studies (load cases)• Systems Engineering: Requirement analysis / setting• Systems Engineering: Configuration control• Assumptions• Calculations / simulations / FEM analysis• Design
• However, humans are also very good in detection of (the same) failures, correction of failures and improvising when abnormal situations occur.
• The policy that human actions should be completely ruled out of any design and production process to improve reliability may not be effective therefore.
• Some tasks are better performed by humans and some are better performed by machines.• Furthermore, human errors in management and the organization of data and information or
the misuse or abuse of items may also contribute to unreliability. • This is the core reason why high levels of reliability for complex systems can only be
achieved by following a robust systems engineering process with proper planning and execution of the validation and verification tasks.
• This also includes careful organization of data and information sharing and creating a "reliability culture" in the same sense as having a "safety culture" is paramount in the development of safety critical systems.
Reliability prediction and improvement• Reliability prediction is the combination of the creation of a proper
reliability model (see further on this page) together with estimating (and justifying) the input parameters for this model (like failure rates for a particular failure mode or event and the mean time to repair the system for a particular failure) and finally to provide a system (or part) level estimate for the output reliability parameters (system availability or a particular functional failure frequency).
• Some recognized reliability engineering specialists – e.g. Patrick O'Connor, R. Barnard – have argued that too much emphasis is often given to the prediction of reliability parameters and more effort should be devoted to the prevention of failure (reliability improvement).
• Failures can and should be prevented in the first place for most cases. • The emphasis on quantification and target setting in terms of (e.g.) MTBF might provide the
idea that there is a limit to the amount of reliability that can be achieved. • In theory there is no inherent limit and higher reliability does not need to be more costly in
development. • Another of their arguments is that prediction of reliability based on historic data can be very
misleading, as a comparison is only valid for exactly the same designs, products, manufacturing processes and maintenance under exactly the same loads and environmental context.
• Even a minor change in detail in any of these could have major effects on reliability.
• Furthermore, normally the most unreliable and important items (most interesting candidates for a reliability investigation) are most often subjected to many modifications and changes.
• Engineering designs are in most industries updated frequently. • This is the reason why the standard (re-active or pro-active) statistical methods and
processes as used in the medical industry or insurance branch are not as effective for engineering.
• Another surprising but logical argument is that to be able to accurately predict reliability by testing, the exact mechanisms of failure must have been known in most cases and therefore – in most cases – can be prevented!
• Following the incorrect route by trying to quantify and solving a complex reliability engineering problem in terms of MTBF or Probability and using the re-active approach is referred to by Barnard as "Playing the Numbers Game" and is regarded as bad practise.
• For existing systems, it is arguable that responsible programs would directly analyse and try to correct the root cause of discovered failures and thereby may render the initial MTBF estimate fully invalid as new assumptions (subject to high error levels) of the effect of the patch/redesign must be made.
• Another practical issue concerns a general lack of availability of detailed failure data and not consistent filtering of failure (feedback) data or ignoring statistical errors, which are very high for rare events (like reliability related failures).
• Very clear guidelines must be present to be able to count and compare failures, related to different type of root-causes (e.g. manufacturing-, maintenance-, transport-, system-induced or inherent design failures).
• Comparing different type of causes may lead to incorrect estimations and incorrect business decisions about the focus of improvement.
• To perform a proper quantitative reliability prediction for systems may be difficult and may be very expensive if done by testing.
• On part level, results can be obtained often with higher confidence as many samples might be used for the available testing financial budget, however unfortunately these tests might lack validity on system level due to the assumptions that had to be made for part level testing.
• These authors argue that it can not be emphasized enough that testing for reliability should be done to create failures in the first place, learn from them and to improve the system / part.
• The general conclusion is drawn that an accurate and an absolute prediction – by field data comparison or testing – of reliability is in most cases not possible.
• An exception might be failures due to wear-out problems like fatigue failures. • In the introduction of MIL-STD-785 it is written that reliability prediction should be used with
great caution if not only used for comparison in trade-off studies.• See also: Risk Assessment#Quantitative risk assessment – Critics paragraph
Design for reliability• Reliability design begins with the development of a (system) model. • Reliability and availability models use block diagrams and Fault Tree Analysis
to provide a graphical means of evaluating the relationships between different parts of the system.
• These models may incorporate predictions based on failure rates taken from historical data.
• While the (input data) predictions are often not accurate in an absolute sense, they are valuable to assess relative differences in design alternatives.
• Maintainability parameters, for example MTTR, are other inputs for these models.
• The most important fundamental initiating causes and failure mechanisms are to be identified and analyzed with engineering tools.
• A diverse set of practical guidance and practical performance and reliability requirements should be provided to designers so they can generate low-stressed designs and products that protect or are protected against damage and excessive wear.
• Proper Validation of input loads (requirements) may be needed and verification for reliability "performance" by testing may be needed.
• One of the most important design techniques is redundancy. • This means that if one part of the system fails, there is an alternate
success path, such as a backup system. • The reason why this is the ultimate design choice is related to the fact
that high confidence reliability evidence for new parts / items is often not available or extremely expensive to obtain.
• By creating redundancy, together with a high level of failure monitoring and the avoidance of common cause failures, even a system with relative bad single channel (part) reliability, can be made highly reliable (mission reliability) on system level.
• No testing of reliability has to be required for this. • Furthermore, by using redundancy and the use of dissimilar design
and manufacturing processes (different suppliers) for the single independent channels, less sensitivity for quality issues (early childhood failures) is created and very high levels of reliability can be achieved at all moments of the development cycles (early life times and long term).
• Redundancy can also be applied in systems engineering by double checking requirements, data, designs, calculations, software and tests to overcome systematic failures.
• Another design technique to prevent failures is called physics of failure. • This technique relies on understanding the physical static and dynamic failure
mechanisms. • It accounts for variation in load, strength and stress leading to failure at high level of
detail, possible with use of modern finite element method (FEM) software programs that may handle complex geometries and mechanisms like creep, stress relaxation, fatigue and probabilistic design (Monte Carlo simulations / DOE).
• The material or component can be re-designed to reduce the probability of failure and to make it more robust against variation.
Another common design technique is component derating: • Selecting components whose tolerance significantly exceeds the expected stress, as
using a heavier gauge wire that exceeds the normal specification for the expected electrical current.
• Another effective way to deal with unreliability issues is to perform analysis to be able to predict degradation and being able to prevent unscheduled down events / failures from occurring.
• RCM (Reliability Centered Maintenance) programs can be used for this.
• Many tasks, techniques and analyses are specific to particular industries and applications.
Commonly these include:• Built-in test (BIT) (testability analysis)• Failure mode and effects analysis (FMEA)• Reliability hazard analysis• Reliability block-diagram analysis• Dynamic Reliability block-diagram analysis• Fault tree analysis• Root cause analysis• Statistical Engineering, Design of Experiments - e.g. on Simulations / FEM models or with
testing• Sneak circuit analysis• Accelerated testing
• Reliability growth analysis (re-active reliability)• Weibull analysis (for testing or mainly "re-active" reliability)• Thermal analysis by finite element analysis (FEA) and / or measurement• Thermal induced, shock and vibration fatigue analysis by FEA and / or measurement• Electromagnetic analysis• Avoidance of single point of failure• Functional analysis and functional failure analysis (e.g., function FMEA, FHA or FFA)• Predictive and preventive maintenance: reliability centered maintenance (RCM) analysis• Testability analysis• Failure diagnostics analysis (normally also incorporated in FMEA)• Human error analysis• Operational hazard analysis• Manual screening• Integrated logistics support
• Results are presented during the system design reviews and logistics reviews.
• Reliability is just one requirement among many system requirements. • Engineering trade studies are used to determine the optimum
balance between reliability and other requirements and constraints.
Quantitative and Qualitative approaches and the importance of language in reliability engineering• Reliability engineers could concentrate more on "why and how" items
/ systems may fail or have failed, instead of mostly trying to predict "when" or at what (changing) rate (failure rate (t)).
• Answers to the first questions will drive improvement in design and processes.
• When failure mechanisms are really understood then solutions to prevent failure are easily found.
• Only required Numbers (e.g. MTBF) will not drive good designs.
• The huge amount of (un)reliability hazards that are generally part of complex systems need first to be classified and ordered (based on qualitative and quantitative logic if possible) to get to efficient assessment and improvement.
• This is partly done in pure language and proposition logic, but also based on experience with similar items.
• This can for example be seen in descriptions of events in Fault Tree Analysis, FMEA analysis and a hazard (tracking) log.
• In this sense language and proper grammar (part of qualitative analysis) plays an important role in reliability engineering, just like it does in safety engineering or in general within systems engineering.
• Engineers are likely to question why?• Well, it is precisely needed because systems engineering is very much about finding the
correct words to describe the problem (and related risks) to be solved by the engineering solutions we intend to create.
• In the words of Jack Ring, the systems engineer’s job is to “language the project.” [Ring et al. 2000].
• Language in itself is about putting an order in a description of the reality of a (failure of a) complex function/item/system in a complex surrounding.
• Reliability engineers use both quantitative and qualitative methods, which extensively use language to pinpoint the risks to be solved.
• The importance of language also relates to the risks of human error, which can be seen as the ultimate root cause of almost all failures - see further on this site.
• As an example, proper instructions (often written by technical authors in so called simplified English) in maintenance manuals, operation manuals, emergency procedures and others are needed to prevent systematic human errors in any maintenance or operational task that may result in system failures.
Reliability modelling• Reliability modelling is the process of predicting or understanding the reliability of a
component or system prior to its implementation. • Two types of analysis that are often used to model a complete system availability
(including effects from logistics issues like spare part provisioning, transport and manpower) behavior are Fault Tree Analysis and reliability block diagrams.
• On component level the same type of analysis can be used together with others. • The input for the models can come from many sources: Testing, Earlier operational
experience field data or data handbooks from the same or mixed industries can be used. • In all cases, the data must be used with great caution as predictions are only valid in
case the same product in the same context is used. • Often predictions are only made to compare alternatives.
For part level predictions, two separate fields of investigation are common:• The physics of failure approach uses an understanding of physical
failure mechanisms involved, such as mechanical crack propagation or chemical corrosion degradation or failure.
• The parts stress modelling approach is an empirical method for prediction based on counting the number and type of components of the system, and the stress they undergo during operation.
• Software reliability is a more challenging area that must be considered when it is a considerable component to system functionality.
Reliability theory• Main articles: Reliability theory, Failure rate and Survival analysis• Reliability is defined as the probability that a device will perform its
intended function during a specified period of time under stated conditions. Mathematically, this may be expressed as,
Where is the failure probability density function and is the length of the period of time (which is assumed to start from time zero).
There are a few key elements of this definition:1. Reliability is predicated on "intended function:" • Generally, this is taken to mean operation without failure. • However, even if no individual part of the system fails, but the system
as a whole does not do what was intended, then it is still charged against the system reliability.
• The system requirements specification is the criterion against which reliability is measured.
• 2. Reliability applies to a specified period of time. In practical terms, this means that a system has a specified chance that it will operate without failure before time Reliability engineering ensures that components and materials will meet the requirements during the specified time. Units other than time may sometimes be used.
• 3. Reliability is restricted to operation under stated (or explicitly defined) conditions. This constraint is necessary because it is impossible to design a system for unlimited conditions. A Mars Rover will have different specified conditions than a family car. The operating environment must be addressed during design and testing. That same rover may be required to operate in varying conditions requiring additional scrutiny.
Quantitative system reliability parameters – theory• Quantitative Requirements are specified using reliability parameters. • The most common reliability parameter is the mean time to failure (MTTF), which can
also be specified as the failure rate (this is expressed as a frequency or conditional probability density function (PDF)) or the number of failures during a given period.
• These parameters may be useful for higher system levels and systems that are operated frequently, such as most vehicles, machinery, and electronic equipment. Reliability increases as the MTTF increases.
• The MTTF is usually specified in hours, but can also be used with other units of measurement, such as miles or cycles.
• Using MTTF values on lower system levels can be very misleading, specially if the Failures Modes and Mechanisms it concerns (The F in MTTF) are not specified with it.
• In other cases, reliability is specified as the probability of mission success. • For example, reliability of a scheduled aircraft flight can be specified as a dimensionless
probability or a percentage, as in system safety engineering.• A special case of mission success is the single-shot device or system. These are devices or
systems that remain relatively dormant and only operate once. • Examples include automobile airbags, thermal batteries and missiles. Single-shot reliability
is specified as a probability of one-time success, or is subsumed into a related parameter. • Single-shot missile reliability may be specified as a requirement for the probability of a hit. • For such systems, the probability of failure on demand (PFD) is the reliability measure –
which actually is an unavailability number. This PFD is derived from failure rate (a frequency of occurrence) and mission time for non-repairable systems.
• For repairable systems, it is obtained from failure rate and mean-time-to-repair (MTTR) and test interval.
• This measure may not be unique for a given system as this measure depends on the kind of demand.
• In addition to system level requirements, reliability requirements may be specified for critical subsystems.
• In most cases, reliability parameters are specified with appropriate statistical confidence intervals.
Reliability testing• The purpose of reliability testing is to discover potential problems
with the design as early as possible and, ultimately, provide confidence that the system meets its reliability requirements.
• Reliability testing may be performed at several levels and there are different types of testing.
• Complex systems may be tested at component, circuit board, unit, assembly, subsystem and system levels [1]
• (The test level nomenclature varies among applications.) For example, performing environmental stress screening tests at lower levels, such as piece parts or small assemblies, catches problems before they cause failures at higher levels.
• Testing proceeds during each level of integration through full-up system testing, developmental testing, and operational testing, thereby reducing program risk.
• However, testing does not mitigate unreliability risk.• With each test both a statistical type 1 and type 2 error could be made and
depends on sample size, test time, assumptions and the needed discrimination ratio.
• There is risk of incorrectly accepting a bad design (type 1 error) and the risk of incorrectly rejecting a good design (type 2 error).
• It is not always feasible to test all system requirements. • Some systems are prohibitively expensive to test; some failure modes
may take years to observe; some complex interactions result in a huge number of possible test cases; and some tests require the use of limited test ranges or other resources.
• In such cases, different approaches to testing can be used, such as (highly) accelerated life testing, design of experiments, and simulations.
• The desired level of statistical confidence also plays an role in reliability testing. • Statistical confidence is increased by increasing either the test time or the
number of items tested. • Reliability test plans are designed to achieve the specified reliability at the
specified confidence level with the minimum number of test units and test time. • Different test plans result in different levels of risk to the producer and
consumer. • The desired reliability, statistical confidence, and risk levels for each side
influence the ultimate test plan. • The customer and developer should agree in advance on how reliability
requirements will be tested.
• A key aspect of reliability testing is to define "failure". • Although this may seem obvious, there are many situations where it is not clear
whether a failure is really the fault of the system. • Variations in test conditions, operator differences, weather and unexpected
situations create differences between the customer and the system developer. • One strategy to address this issue is to use a scoring conference process. • A scoring conference includes representatives from the customer, the developer, the
test organization, the reliability organization, and sometimes independent observers. • The scoring conference process is defined in the statement of work. • Each test case is considered by the group and "scored" as a success or failure. • This scoring is the official result used by the reliability engineer.
• As part of the requirements phase, the reliability engineer develops a test strategy with the customer.
• The test strategy makes trade-offs between the needs of the reliability organization, which wants as much data as possible, and constraints such as cost, schedule and available resources.
• Test plans and procedures are developed for each reliability test, and results are documented.
• Reliability testing is common in the Photonics industry. • Examples of reliability tests of lasers are life test and burn-in. • These tests consist of the highly accelerated ageing, under controlled conditions, of a
group of lasers. • The data collected from these life tests are used to predict laser life expectancy under the
intended operating characteristics.
• Reliability test requirements• Reliability test requirements can follow from any analysis for which the first
estimate of failure probability, failure mode or effect needs to be justified. • Evidence can be generated with some level of confidence by testing. • With software-based systems, the probability is a mix of software and hardware-
based failures. • Testing reliability requirements is problematic for several reasons. • A single test is in most cases insufficient to generate enough statistical data. • Multiple tests or long-duration tests are usually very expensive. • Some tests are simply impractical, and environmental conditions can be hard to
predict over a systems life-cycle.
• Reliability engineering is used to design a realistic and affordable test program that provides empirical evidence that the system meets its reliability requirements.
• Statistical confidence levels are used to address some of these concerns. • A certain parameter is expressed along with a corresponding confidence
level: for example, an MTBF of 1000 hours at 90% confidence level. • From this specification, the reliability engineer can, for example, design
a test with explicit criteria for the number of hours and number of failures until the requirement is met or failed.
• Different sorts of tests are possible.
• The combination of required reliability level and required confidence level greatly affects the development cost and the risk to both the customer and producer.
• Care is needed to select the best combination of requirements – e.g. cost-effectiveness.
• Reliability testing may be performed at various levels, such as component, subsystem and system.
• Also, many factors must be addressed during testing and operation, such as extreme temperature and humidity, shock, vibration, or other environmental factors (like loss of signal, cooling or power; or other catastrophes such as fire, floods, excessive heat, physical or security violations or other myriad forms of damage or degradation).
• For systems that must last many years, accelerated life tests may be needed.
Accelerated testingThe purpose of accelerated life testing (ALT test) is to induce field failure in the laboratory at a much faster rate by providing a harsher, but nonetheless representative, environment. In such a test, the product is expected to fail in the lab just as it would have failed in the field—but in much less time. The main objective of an accelerated test is either of the following:• To discover failure modes• To predict the normal field life from the high stress lab life
An Accelerated testing program can be broken down into the following steps:• Define objective and scope of the test• Collect required information about the product• Identify the stress(es)• Determine level of stress(es)• Conduct the accelerated test and analyze the collected data.
Common way to determine a life stress relationship are• Arrhenius model• Eyring model• Inverse power law model• Temperature–humidity model• Temperature non-thermal model
Software reliabilityFurther information: Software reliability• Software reliability is a special aspect of reliability engineering. • System reliability, by definition, includes all parts of the system, including
hardware, software, supporting infrastructure (including critical external interfaces), operators and procedures.
• Traditionally, reliability engineering focuses on critical hardware parts of the system.
• Since the widespread use of digital integrated circuit technology, software has become an increasingly critical part of most electronics and, hence, nearly all present day systems.
• There are significant differences, however, in how software and hardware behave. • Most hardware unreliability is the result of a component or material failure that results in
the system not performing its intended function. • Repairing or replacing the hardware component restores the system to its original
operating state. • However, software does not fail in the same sense that hardware fails. • Instead, software unreliability is the result of unanticipated results of software operations. • Even relatively small software programs can have astronomically large combinations of
inputs and states that are infeasible to exhaustively test. • Restoring software to its original state only works until the same combination of inputs
and states results in the same unintended result. • Software reliability engineering must take this into account.
• Despite this difference in the source of failure between software and hardware, several software reliability models based on statistics have been proposed to quantify what we experience with software: the longer software is run, the higher the probability that it will eventually be used in an untested manner and exhibit a latent defect that results in a failure (Shooman 1987), (Musa 2005), (Denney 2005).
• As with hardware, software reliability depends on good requirements, design and implementation. • Software reliability engineering relies heavily on a disciplined software engineering process to
anticipate and design against unintended consequences. • There is more overlap between software quality engineering and software reliability engineering
than between hardware quality and reliability. • A good software development plan is a key aspect of the software reliability program. • The software development plan describes the design and coding standards, peer reviews, unit tests
, configuration management, software metrics and software models to be used during software development.
• A common reliability metric is the number of software faults, usually expressed as faults per thousand lines of code.
• This metric, along with software execution time, is key to most software reliability models and estimates.
• The theory is that the software reliability increases as the number of faults (or fault density) decreases or goes down.
• Establishing a direct connection between fault density and mean-time-between-failure is difficult, however, because of the way software faults are distributed in the code, their severity, and the probability of the combination of inputs necessary to encounter the fault.
• Nevertheless, fault density serves as a useful indicator for the reliability engineer. Other software metrics, such as complexity, are also used.
• This metric remains controversial, since changes in software development and verification practices can have dramatic impact on overall defect rates.
• Testing is even more important for software than hardware. • Even the best software development process results in some software
faults that are nearly undetectable until tested. • As with hardware, software is tested at several levels, starting with
individual units, through integration and full-up system testing. • Unlike hardware, it is inadvisable to skip levels of software testing. • During all phases of testing, software faults are discovered, corrected,
and re-tested. • Reliability estimates are updated based on the fault density and other
metrics.
• At a system level, mean-time-between-failure data can be collected and used to estimate reliability.
• Unlike hardware, performing exactly the same test on exactly the same software configuration does not provide increased statistical confidence.
• Instead, software reliability uses different metrics, such as code coverage.• Eventually, the software is integrated with the hardware in the top-level
system, and software reliability is subsumed by system reliability. • The Software Engineering Institute's capability maturity model is a
common means of assessing the overall software development process for reliability and quality purposes.
Reliability engineering vs safety engineering• Reliability engineering differs from safety engineering with respect to the
kind of hazards that are considered. • Reliability engineering is in the end only concerned with cost. • It relates to all Reliability hazards that could transform into incidents with a
particular level of loss of revenue for the company or the customer. • These can be cost due to loss of production due to system unavailability,
unexpected high or low demands for spares, repair costs, man hours, (multiple) re-designs, interruptions on normal production (e.g. due to high repair times or due to unexpected demands for non-stocked spares) and many other indirect costs
• Safety engineering, on the other hand, is more specific and regulated. • It relates to only very specific and system safety hazards that could potentially lead to
severe accidents and is primarily concerned with loss of life, loss of equipment, or environmental damage.
• The related system functional reliability requirements are sometimes extremely high. • It deals with unwanted dangerous events (for life, property, and environment) in the
same sense as reliability engineering, but does normally not directly look at cost and is not concerned with repair actions after failure / accidents (on system level).
• Another difference is the level of impact of failures on society and the control of governments.
• Safety engineering is often strictly controlled by governments (e.g. nuclear, aerospace, defense, rail and oil industries).
• Furthermore, safety engineering and reliability engineering may even have contradicting requirements.
• This relates to system level architecture choices. • For example, in train signal control systems it is common practice to use a fail-safe
system design concept. • In this concept the Wrong-side failure need to be fully controlled to an extreme low
failure rate. • These failures are related to possible severe effects, like frontal collisions (2* GREEN
lights). • Systems are designed in a way that the far majority of failures will simply result in a
temporary or total loss of signals or open contacts of relays and generate RED lights for all trains.
• This is the safe state. • All trains are stopped immediately. • This fail-safe logic might unfortunately lower the reliability of the
system. • The reason for this is the higher risk of false tripping as any full or
temporary, intermittent failure is quickly latched in a shut-down (safe)state.
• Different solutions are available for this issue. • See chapter Fault Tolerance below.
Fault tolerance• Reliability can be increased here by using a 2oo2 (2 out of 2) redundancy on part or
system level, but this does in turn lower the safety levels (more possibilities for Wrong Side and undetected dangerous Failures).
• Fault tolerant voting systems (e.g. 2oo3 voting logic) can increase both reliability and safety on a system level.
• In this case the so-called "operational" or "mission" reliability as well as the safety of a system can be increased.
• This is also common practice in Aerospace systems that need continued availability and do not have a fail safe mode (e.g. flight computers and related electrical and/ or mechanical and/ or hydraulic steering functions need always to be working.
• There are no safe fixed positions for rudder or other steering parts when the aircraft is flying).
Basic reliability and mission (operational) reliability• The above example of a 2oo3 fault tolerant system increases both mission reliability
as well as safety. • However, the "basic" reliability of the system will in this case still be lower than a non
redundant (1oo1) or 2oo2 system! • Basic reliability refers to all failures, including those that might not result in system
failure, but do result in maintenance repair actions, logistic cost, use of spares, etc. • For example, the replacement or repair of 1 channel in a 2oo3 voting system that is
still operating with one failed channel (which in this state actually has become a 1oo2 system) is contributing to basic unreliability but not mission unreliability.
• Also, for example, the failure of the taillight of an aircraft is not considered as a mission loss failure, but does contribute to the basic unreliability.
Detectability and common cause failures• When using fault tolerant (redundant architectures) systems or
systems that are equipped with protection functions, detectability of failures and avoidance of common cause failures becomes paramount for safe functioning and/or mission reliability.
Reliability versus Quality (Six Sigma)• Six-Sigma has its roots in manufacturing and Reliability engineering is more
related to systems engineering. • The systems engineering process is a discovery process that is quite unlike a
manufacturing process. • A manufacturing process is focused on repetitive activities that achieve high
quality outputs with minimum cost and time. • The systems engineering process must begin by discovering the real (potential)
problem that needs to be solved; the biggest failure that can be made in systems engineering is finding an elegant solution to the wrong problem (or in terms of reliability: "providing elegant solutions to the wrong root causes of system failures").
• The everyday usage term "quality of a product" is loosely taken to mean its inherent degree of excellence.
• In industry, this is made more precise by defining quality to be "conformance to requirements at the start of use".
• Assuming the product specifications adequately capture customer (or rest of system) needs, the quality level of these parts can now be precisely measured by the fraction of units shipped that meet the detailed product specifications.
• But are (derived, lower level) requirements and related product specifications validated?
• Will it later result in worn items and systems, by general wear, fatigue or corrosion mechanisms, debris accumulation or due to maintenance induced failures?
• Are there interactions on any system level (as investigated by for example Fault Tree Analysis)?
• How many of these systems still meet function and fulfill the needs after a week of operation?
• What performance losses occurred? • Did full system failure occur? • What happens after the end of a one-year warranty period? • And what happens after 50 years (a common lifetime for aircraft,
trains, nuclear systems, etc...)? • That is where "reliability" comes in.
• Quality is a snapshot at the start of life and mainly related to control of lower level product specifications and reliability is (as part of systems engineering) more of a system level motion picture of the day-by-day operation for many years.
• Time zero defects are manufacturing mistakes that escaped final test (Quality Control).
• The additional defects that appear over time are "reliability defects" or reliability fallout.
• These reliability issues may just as well occur due to Inherent design issues, which may have nothing to do with non-conformance product specifications.
• Items that are produced perfectly - according all product specifications - may fail over time due to any single or combined failure mechanism (e.g. mechanical-, electrical-, chemical- or human error related).
• All these parameters are also a function of all possible variances coming from initial production.
• Theoretically, all items will functionally fail over infinite time. • In theory the Quality level might be described by a single fraction defective. • To describe reliability fallout a probability model that describes the fraction
fallout over time is needed. This is known as the life distribution model.
• Quality is therefore related to Manufacturing and Reliability is more related to the validation of sub-system or lower item requirements, (System or Part) inherent Design and life cycle solutions.
• Items that do not conform to (any) product specification in general will do worse in terms of reliability (having a lower MTTF), but this does not always have to be the case.
• The full mathematical Quantification (in statistical models) of this combined relation is in general very difficult or even practical impossible.
• In case manufacturing variances can be effectively reduced, six sigma tools may be used to find optimal process solutions and may thereby also increase reliability.
• Six Sigma may also help to design more robust related to manufacturing induced failures.
• In contrast with Six Sigma, Reliability Engineering Solutions are generally found by having a focus into a (system) design and not on the manufacturing process.
• Solutions are found in different ways, for example by simplifying a system and therefore understanding more mechanisms of failure involved, detailed calculation of material stress levels and required safety factors, finding possible abnormal system load conditions and next to this also to increase design robustness against variation from the manufacturing variances and related failure mechanisms.
• Furthermore reliability engineering use system level solutions, like designing redundancy and fault tolerant systems in case of high availability needs (see chapter Reliability engineering vs Safety engineering above).
• Next to this and also in a major contrast with Reliability Engineering, Six-Sigma is much more measurement based (quantification).
• The core of Six-Sigma thrives on empirical research and statistics where it is possible to measure parameters (e.g. to find transfer functions).
• This can not be translated practically to most reliability issues, as reliability is not (easy) measurable due to the function of time (large times may be involved), specially during the requirements specification and design phase where reliability engineering is the most efficient.
• Full Quantification of reliability is in this phase extremely difficult or costly (testing).
• It also may foster re-active management (waiting for system failures to be measured).
• Furthermore, as explained on this page, Reliability problems are likely to come from many different (e.g. inherent failures, human error, systematic failures) causes besides manufacturing induced defects.
• Quality (manufacturing) Six Sigma and Reliability (design) departments should provide input to each other to cover the complete risks more efficiently.
Reliability operational assessment• After a system is produced, reliability engineering monitors, assesses
and corrects deficiencies. • Monitoring includes electronic and visual surveillance of critical
parameters identified during the fault tree analysis design stage. • Data collection is highly dependent on the nature of the system. • Most large organizations have quality control groups that collect
failure data on vehicles, equipment and machinery.
• Consumer product failures are often tracked by the number of returns. • For systems in dormant storage or on standby, it is necessary to establish a formal
surveillance program to inspect and test random samples. • Any changes to the system, such as field upgrades or recall repairs, require additional
reliability testing to ensure the reliability of the modification. • Since it is not possible to anticipate all the failure modes of a given system, especially
ones with a human element, failures will occur. • The reliability program also includes a systematic root cause analysis that identifies
the causal relationships involved in the failure such that effective corrective actions may be implemented.
• When possible, system failures and corrective actions are reported to the reliability engineering organization.
• One of the most common methods to apply to a reliability operational assessment are failure reporting, analysis, and corrective action systems (FRACAS).
• This systematic approach develops a reliability, safety and logistics assessment based on Failure / Incident reporting, management, analysis and corrective/preventive actions.
• Organizations today are adopting this method and utilize commercial systems such as a Web-based FRACAS application enabling an organization to create a failure/incident data repository from which statistics can be derived to view accurate and genuine reliability, safety and quality performances.
• It is extremely important to have one common source FRACAS system for all end items. • Also, test results should be able to be captured here in a practical way. • Failure to adopt one easy to handle (easy data entry for field engineers and repair shop
engineers) and maintain integrated system is likely to result in a FRACAS program failure.
Some of the common outputs from a FRACAS system includes: • Field MTBF, MTTR, Spares Consumption, Reliability Growth,
Failure/Incidents distribution by type, location, part no., serial no, symptom etc.
• The use of past data to predict the reliability of new comparable systems/items can be misleading as reliability is a function of the context of use and can be affected by small changes in the designs/manufacturing.
Reliability organizations
• Systems of any significant complexity are developed by organizations of people, such as a commercial company or a government agency.
• The reliability engineering organization must be consistent with the company's organizational structure.
• For small, non-critical systems, reliability engineering may be informal. As complexity grows, the need arises for a formal reliability function.
• Because reliability is important to the customer, the customer may even specify certain aspects of the reliability organization.
• There are several common types of reliability organizations. The project manager or chief engineer may employ one or more reliability engineers directly.
• In larger organizations, there is usually a product assurance or specialty engineering organization, which may include reliability, maintainability, quality, safety, human factors, logistics, etc. In such case, the reliability engineer reports to the product assurance manager or specialty engineering manager.
• In some cases, a company may wish to establish an independent reliability organization.
• This is desirable to ensure that the system reliability, which is often expensive and time consuming, is not unduly slighted due to budget and schedule pressures.
• In such cases, the reliability engineer works for the project day-to-day, but is actually employed and paid by a separate organization within the company.
• Because reliability engineering is critical to early system design, it has become common for reliability engineers, however the organization is structured, to work as part of an integrated product team.
Reliability engineering education• Some universities offer graduate degrees in reliability engineering. Other reliability
engineers typically have an engineering degree, which can be in any field of engineering, from an accredited university or college program.
• Many engineering programs offer reliability courses, and some universities have entire reliability engineering programs.
• A reliability engineer may be registered as a professional engineer by the state, but this is not required by most employers.
• There are many professional conferences and industry training programs available for reliability engineers.
• Several professional organizations exist for reliability engineers, including the IEEE Reliability Society, the American Society for Quality (ASQ), and the Society of Reliability Engineers (SRE)
See also• Brittle systems• Burn-in• Cauchy stress tensor• Factor of safety• Failing badly• FMEA• Fault-tolerant system• Fault tree analysis• Fracture mechanics• Solid mechanics• Highly accelerated life test• Highly accelerated stress test• Risk assessment• Safety engineering
• Human reliability• Industrial engineering• Integrated logistics support• Logistic engineering• Performance engineering• Product qualification• Professional engineer• Quality assurance• RAMS• Redundancy (engineering)• Redundancy (total quality management)• Reliability (disambiguation)• Reliability, availability and serviceability (computer hardware)• Reliability theory• Reliability theory of aging and longevity• Reliable system design
• Safety integrity level• Security engineering• Single point of failure (SPOF)• Software engineering• Software reliability testing• Spurious trip level• Structural fracture mechanics• Strength of materials• Systems engineering• Temperature cycling
Day 3:
• Design methodology for Tension Legged Platform • Different types of Tension Legged Platform• Basic concept and dynamic analysis for Tension Legged Platform• Structure optimum configuration• Structure Reliability
Tension-leg platform• Tension-leg platform (TLP) or extended tension leg platform (ETLP) is a vertically
moored floating structure normally used for the offshore production of oil or gas, and is particularly suited for water depths greater than 300 metres (about 1000 ft) and less than 1500 metres (about 4900 ft).
• Use of tension-leg platforms has also been proposed for wind turbines.• The platform is permanently moored by means of tethers or tendons grouped at each of the
structure's corners. • A group of tethers is called a tension leg. A feature of the design of the tethers is that they have
relatively high axial stiffness (low elasticity), such that virtually all vertical motion of the platform is eliminated.
• This allows the platform to have the production wellheads on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor.
• This allows a simpler well completion and gives better control over the production from the oil or gas reservoir, and easier access for downhole intervention operations.
• TLPs have been in use since the early 1980s. The first tension leg platform was built for Conoco's Hutton field in the North Sea in the early 1980s.
• The hull was built in the dry-dock at Highland Fabricator's Nigg yard in the north of Scotland, with the deck section built nearby at McDermott's yard at Ardersier.
• The two parts were mated in the Moray Firth in 1984.• The Hutton TLP was originally designed for a service life of 25 years in Nord Sea depth
of 100 to 1000 metres. • It had 16 tension legs. Its weight varied between 46,500 and 55,000 tons when
moored to the seabed, but up to 61,580 tons when floating freely. • The total area of its living quarters was about 3,500 square metres and
accommodated over a 100 cabins though only 40 people were necessary to maintain the structure in place.
• The hull of the Hutton TLP has been separated from the topsides. • Topsides have been redeployed to the Prirazlomnoye field in the
Barents Sea, while the hull was reportedly sold to a project in the Gulf of Mexico (although the hull has been moored in Cromarty Firth since 2009).
• Larger TLPs will normally have a full drilling rig on the platform with which to drill and intervene on the wells.
• The smaller TLPs may have a workover rig, or in a few cases no production wellheads located on the platform at all.
• The deepest (E)TLPs measured from the sea floor to the surface are:
• 4,674 ft (1,425 m) Magnolia ETLP. Its total height is some 5,000 feet (1,500 m).
• 4,300 ft (1,300 m) Marco Polo TLP• 4,250 ft (1,300 m) Neptune TLP• 3,863 ft (1,177 m) Kizomba A TLP• 3,800 ft (1,200 m) Ursa TLP. Its height above surface is 485 ft (148 m)
making a total height of 4,285 ft (1,306 m).[4]
• 3,350 ft (1,020 m) Allegheny TLP• 3,300 ft (1,000 m) W. Seno A TLP
A tension-leg platform (gray) under tow with seabed anchors (light gray) held up by cables (red) on left-hand side; platform with seabed anchors lowered and cables lightly tensioned on right-hand side
Tension leg platform (gray) free floating on left-hand side; structure is pulled by the tensioned cables (red) down towards the seabed anchors (light-gray) on right-hand side (very simplified, omitting details of temporary ballast transfers)
• Oil platform• Magnolia (oil platform)• Mars (oil platform)• Olympus tension leg platform
Structure optimum configuration
Structural Optimization• Perform structural optimization analysis during design using CAD-
embedded SOLIDWORKS Simulation to reach the best available strength-to-weight, frequency, or stiffness performance for your designs, and cut costly prototypes, eliminate rework and save time and development costs.
Structural Optimization Overview• SOLIDWORKS Simulation simplifies structural optimization with a
goal-driven design approach to parametrically alter a design so that it meets defined structural goals. You specify design goals at the beginning of design to:
• Have SOLIDWORKS software alert you during the design process if goals are violated
• Use goals in a design study where SOLIDWORKS Simulation automatically changes allowable model dimensions to maximize or minimize adherence to the design goal
• Structural optimization uses multiple constraints to limit the scope of the optimization process, ensuring that any design study optimization meets the primary design goal without violating the supporting design requirements.
• Advanced structural reliability• Civil engineers aim at designing reliable structures i.e. structures that attain an acceptably small
failure probability. • The evaluation of the probability of failure can be a highly demanding task, especially when the
structural system is described by complex numerical models, typically finite element models. • The problem becomes even more involved when the time variability of loading conditions or
the spatial variability of material parameters needs to be accounted for through a random process/field representation.
• The numerical treatment of these quantities may lead to a large number of random variables, hence increasing the dimensionality of the problem, which poses problems for most existing solution strategies.
• We are active in the development of advanced structural reliability methods for application to high dimensional reliability problems involving computationally demanding finite element models.
Subset simulation for efficient evaluation of small failure probabilities.
Day 4:
• Topsides and jacket design• Different types of jacket• Basic concepts of dynamic analysis• Platform optimum configuration• Platform construction (Case study)• Structural Reliability
Topsides and jacket design
DESIGN & OPERATION OF TOPSIDE PROCESSING FACILITIES FOR GAS FIELDS
CONTENTS
• TYPES OF GAS FIELD TOPSIDES
• DESIGN ENGINEERING FOR TOPSIDES
• DESIGN OF OFFSHORE PROCESSING FACILITIES
• FACTORS OF CONSIDERATION FOR DESIGN OF TOPSIDES PROCESSING FACILITIES
• PROCESS FLOW
• FLOWCHART FOR GAS TREATMENT AND PROCESSING
• SEQUENCE AND OPERATION
TYPES OF GAS FIELD TOPSIDES
GAS FIELD TOPSIDES
FIXED JACKET (TOPSIDE) COMPLIANT TOWER(TOPSIDE)
1500 ft 3000 ft
GAS FIELD TOPSIDES
TENSION LEG PLATFORM (TOPSIDE)
SPAR(TOPSIDE)
5000 ft 8000 ft
GAS FIELD TOPSIDES
SEMI SUBMERSIBLE(TOPSIDE)
FLOATING PRODUCTION STORAGE & OFFLOADING VESSEL
10000 ft More than 10000 ft
DESIGN & ENGINEERING FOR TOPSIDES
DESIGN ENGINEERING FOR OFFSHORE PROCESSING FACILITIES
• FEED phase: It is more critical for determining the feasibility of specific well area development. An economic analysis on the development of a specific well area is performed based on the outputs of the FEED phase.
• Detailed engineering phase: Based on the results of this analysis, the detailed engineering phase is executed if the value of the development is sufficiently large.
• In other words, the FEED phase is the basis of the detailed engineering phase and of the feasibility of development on specific well areas.
• The final outputs of the FEED phase are: the total costs, the weight, and the layout of an offshore plant. The feasibility of offshore plant projects is determined by these final outputs.
DESIGN OF OFFSHORE PROCESS FACILITIES
DESIGN OF OFFSHORE PROCESSING FACILITIES Design of offshore processing facility consist of two main systems: topside system and a hull system.
• Topside systems, which are those that take place on the decks of offshore plants, are used for the production of oil and gas.
• Hull systems, which are located on the lower decks of offshore plants, are used for the storage of oil and gas.
• The importance of topside systems is far greater than that of hull systems when considering the main function of an offshore platform.
• Fields of engineering related to topside systems include offshore process engineering, piping engineering, mechanical engineering, instrumentation engineering, electrical engineering, and outfitting engineering
FACTORS OF CONSIDERATION FOR DESIGN OF PROCESSING
FACILITIES
DESIGN OF TOPSIDES PROCESSING FACILITIES- Factors of consideration
• Minimize the effects of possible liquid misdistribution
For the main pieces of equipment, such as a compressor, expander, gas turbine, column, heat exchanger, and separator etc.
• LNG storage
Design factors to minimize the loss of containment and the effect of sloshing must be carefully studied when considering hull fabrication.
• LNG offloading
Feasibility studies have been conducted to establish offshore LNG transfer techniques and appropriate methods associated with side-by-side offloading; tandem offloading and flexible loading arms may be suggested in the near future.
EQUIPMENT LAYOUT & PROCESS FLOW
PROCESS FLOW OF TOPSIDE FOR GAS FIELD
FLOWCHART FOR GAS TREATMENT
FLOW CHART FOR GAS TREATMENT
SEQUENCE & OPERATION
Reservoir
Separator
Stabilizer & Condenser
Dehydrator
Active Gas Extractor
Mercury Extractor
Nitrogen Ext.
Demethanizer
Fractionator
NGLs to Different Pipe Lines
SEQUENCE & OPERATION FOR GAS TREATMENT AND PROCESSING
Removal of oil, gas & water by Gravity Action
Stabilization by maintaining RVP & Solid Content Removal
Removal of water contents
Used for removal of CO2, H2S & Other Sulphur Gases in gaseous
form
Used for removal of Mercury in liquid form
Used for removal of Nitrogen in gas form
Used for removal of Methane in gas form
Extraction of different NGLs
Field Sp. Part
Liquefaction Part
Different types of jacket
Dynamic Analysis• Dynamic analysis using SOLIDWORKS Simulation enables designers
and engineers to quickly and efficiently determine the impact of time varying loads on the structural response of their product design to ensure performance, quality, and safety.
• Tightly integrated with SOLIDWORKS CAD, dynamic analysis using SOLIDWORKS Simulation can be a regular part of your design process, reducing the need for costly prototypes, eliminating rework and delays, and saving time and development costs.
Dynamic Analysis Overview• Dynamic analysis can incorporate frequency, impact, and drop tests. • The primary unknown in a dynamic analysis is component displacement over
time, but with this calculated, stresses, velocities, and accelerations can also be determined together with the natural modes of vibration.
SOLIDWORKS Simulation uses one of two methods for dynamic analysis:• Linear modal analysis determines the natural modes of vibration and then the
displacements, stresses, strains, velocities, and accelerations.• Nonlinear dynamic analysis calculates the displacement field at every time step,
given the applied loads and initial component velocities. From this field, the nonlinear stresses, strains, velocities, and accelerations are calculated.
Plot translations versus time (dynamic response) at specified locations due to time-varying loads
Platform optimum configuration
Optimizing rig performance through NPT reduction• Rig performance is the key factor for meeting or exceeding the business
plan. • Drilling capital expenditure represents significant proportion of any oil and
gas project. • Typically, drilling investment is 30-50% of the total project expenditure for
the well and therefore rig performance has considerable influence on well costs.
• A literature review on previous studies have shown the implementation of different practices such as adopting certain rig monitoring systems to help improve the overall rig performance.
• Nevertheless, the challenges also consist of poor teamwork, inexperienced rig crews, equipment failure, an increase in flat times, etc.
• The methodology follows the analysis of statistical data through Company X’s archives for the documented operational incidents & Halliburton’s drilling engineering software, “OpenWells,” with emphasis on Non Productive Time (NPT) records as the performance history from 2009-2012.
• The study focus is particularly on the amount of time lost that could be reduced with general and particular solutions, which correlates to how much money can be saved.
• There will also be a further examination on what Company X has changed over the years to reduce NPT as well as Invisible Lost Time (ILT) to meet the company’s business plan and Key Performance Indicators (KPI).
• What was effective or ineffective from different optimization methods over the years’ NPT?
• Understanding the issues will help in creating solutions in order to enhance the rig performance for Company X and for other oil & gas operators.
• Furthermore, the solutions will be different proven ideas and practical possibilities that can be contributed in the rig site to sustain and improve the company’s integrity in the phases of the drilling operations.
Case Study: North Sea Platform Contract Creates more than 1,000 Engineering and Manufacturing Jobs• OGN Group of Newcastle-upon-Tyne is delivering engineering,
procurement, construction and installation services to the offshore oil and gas and renewable energy industries.
• At its 75 acre Hadrian Yard, OGN has the capability to construct and load out decks in excess of 10,000 tonnes and jackets or substructures weighing up to 7,000 tonnes.
• In September 2010, Apache North Sea Ltd awarded a £150 million contract to OGN to provide conceptual and detailed engineering design, materials and equipment procurement, fabrication and construction, commissioning and hook-up services for a new oil production platform for its Forties field.
• Scheduled for onshore completion in July 2012, the new platform will be bridge-linked to the existing Forties Alpha installation.
• The iconic Forties field, the first of the UK’s large oil fields and originally developed by BP, is still going strong after more than 35 years of production, with at least another 20 years’ life left which this project will help sustain.
Impact on Employment• From its Tyneside base, OGN is providing full manufacturing and administration
services for the design and construction of the facility, known as Forties Alpha Satellite Platform (FASP).
• The contract award has led to the creation of more than 1,000 jobs over a period of 20 months at the Hadrian Yard, with additional jobs being generated at various engineering design offices and supply chain firms throughout the UK.
• During peak activity, direct employment has been provided at the Hadrian Yard for:
• 700 of OGN’s skilled fabrication workforce (platers, welders, riggers and pipe-fitters)• 150 of OGN’s project management and design professionals.
• Work outsourced to subcontractors, working on-site, has provided employment for 200 to 300 sub contractor staff (outfitting trades including electrical, control room instrumentation, non-destructive testing, painting, load out etc.)
• In addition, work outsourced to a total of 24 supply chain companies has generated 1,000 to 1,500 jobs across an extensive supply chain for off-site manufacture of materials and equipment (e.g. transformers, cranes, valves)
• Some 80% of the construction materials for FASPhave been sourced from the UK, amounting to almost £40 million in value.
Technical details• The dimensions of the platform are: topsides – 40m x 45m x 25m;
jacket – 125m x 35m x 35m; linking bridge structure – about 100m long.
• Topside facilities: 5,575 tonne with full oil and gas processing, gas compression, gas dehydration, sand wash facilities, produced water treatment, pumps, polishing unit, chemical injection, power generation, 50-man lifeboat, local equipment room, high and low voltage switchboard, uninterrupted power supply unit, heating ventilating and air conditioning plant, and platform crane.
• Jacket: 5,900 tonne, four legged jacket with 12 skirt piles and 18 well slots, configured to allow a jack-up rig access from the west side, and incorporating two risers and two umbilical J-tubes for future subsea tie-backs. It is also designed to accommodate a future 2,000 tonne mobile drilling unit.
• Bridge: 100m long, 450 tonne bridge linking FASP to the existing Forties Alpha platform. All interconnecting pipework, power and controls cabling are being installed onshore to minimise the offshore work. The sliding end of the bridge is located at FASP.
• The overall project is scheduled for overall completion by OGN (offshore hook-up and commissioning) in September 2012.
Employment• The oil and gas sector continues to be a major source of often highly
paid employment and, thereby, a significant contributor to the national economy.
• This is re-affirmed by analysis previously commissioned through Experian which uses data from the Office of National Statistics (ONS) to provide an update of the employment generated by the industry.
• Based on this insight, it is estimated that in 2010 some 440,000 jobs across the United Kingdom were supported by the activity on the UKCS and the export of oil and gas related goods and services around the world.
Experian calculates that exploration for and extraction of oil and gas from the UKCS accounts for around 340,000 of these: • 32,000 directly employed by oil and gas companies and the major oil and gas
service companies, 207,000 throughout the wider supply chain (“indirect” in Figure 41) and 100,000 jobs which are estimated to be supported by the economic activity induced by employees’ spending.
• Furthermore, Oil & Gas UK has estimated that there were an additional 100,000 jobs supported by the oil and gas supply chain’s growing export business, bringing the total employment provided by the sector to about 440,000 jobs in 2010.
• Given the Industry’s continued activity, the number employed is likely to remain at least as many in 2011.
• The employment generated by the industry is directly related to the rate of investment in new production and continuing expenditure on existing operations.
• Whilst this has sometimes been reflected in the swings in employment witnessed over the last decade, other factors such as price inflation (which reduces purchasing power) also has an impact on employment trends.
• The industry provides employment across the whole of the United Kingdom, with Scotland having the largest share which is clearly seen in Figures 42 and 43.
• Around 45% of the 340,000 UKCS related jobs are located in Scotland, but it should not be over-looked that this means 55% of the jobs lie elsewhere in the UK.
• This is not a purely Aberdeen centric industry and the benefits of the oil and gas industry in terms of employment are widespread, not just in major cities, but also in the more remote areas of the country (see Figures 39 and 45).
• Other regions in the rest of Britain which have sizable employment proportions are London and South-East England (21%), North-West England (6%), West Midlands (5%) and Eastern England (5%).
• The latest analysis demonstrates that each £billion spent by the industry in the UKCS currently delivers between 15,000 and 20,000 jobs, depending on the balance of spending between operations and capital investment.
• There is a wide range of industries which benefit from the economic activity of the oil and gas sector. • Using the ONS’s Standard Industrial Classification (SIC) codes, Experian has analysed the expenditure
of the industry and used the data to map which industrial sectors gain the largest employment from the economic activity.
• A large proportion of employment is provided by construction (16%), structural metal products (12%) and architectural activities and technical consultancy (10%) which together account for 45% of the total capital expenditure on the UKCS.
• There is also significant employment within nontechnical areas such as business services (8%), legal activities (6%) and banking and finance (6%).
• The nature of the categories used by the ONS tends to group a wide range of companies under a fairly small number of SIC codes; Oil & Gas UK believes that this does not do justice to the diversity of employment and skills found across the sector and its supply chain.
• A broad summary of employment in UK oil and gas related work by industry is provided in Figure 44 which shows oil and gas related employment in different industrial sectors, where the area of each bubble is directly proportional to the number of jobs represented by that bubble.
• The demographics of the industry have in the past raised concerns about an increasingly ageing work force.
• However, recent studies have revealed a more optimistic picture than is commonly perceived, with the average age of the offshore workforce being 41 years which is the expected average for a workforce generally in a range from 20 to 60 years.
• Figure 45 shows the distribution of ages of all offshore workers and female workers, in particular. Whilst females make up a small percentage of the offshore workforce, their average age is lower than that of males, indicating that in recent years, more women have been attracted to working offshore.
• The oil and gas fields of the UKCS are widely distributed along the length of the North Sea, with much smaller numbers in the east Irish Sea (Morecambe and Liverpool Bays) and to the west of Shetland.
• Helicopters from Aberdeen, Humberside and the Norwich area are used to transport the workforce to the North Sea’s fields.
• Analysis of the home addresses of such personnel has been carried out from data held on the Vantage Database and the results have been plotted on the map in Figure 45.
• This shows their residential locations and, the larger the diamond, the greater the number of offshore personnel from that area.
• As expected, there are clear concentrations around the main oil and gas service centres but, more interestingly, there are offshore personnel travelling from home locations stretching from the Scilly Isles to the Shetland Isles, including Northern Ireland.
• The industry is drawing on people from the length and breadth of the country.
• The extraction of oil and gas from beneath the seabed and its delivery to onshore terminals, for onward transport to refineries, requires a large amount of infrastructure.
• Some of the biggest structures ever built and moved by mankind have been installed in the very inhospitable waters around the United Kingdom.
• As well as being the means for producing oil and gas, these provide the daily working environment and accommodation for thousands of men and women and they operate round the clock.
• Most UKCS production platforms are fixed to the seabed, but some are mobile (such as semi-submersible and jackup rigs, as are used for drilling wells, or floating production, storage and offtake vessels, known as FPSOs).
• However, all must be designed, constructed, installed, and eventually decommissioned.
• While the UK had a long tradition of heavy engineering, such as shipbuilding, mining and power generation, the discovery of gas in the 1960s followed by oil in the 1970s required the transformation of these skills into a new body of expertise to design and build the platforms now installed throughout the UKCS, starting with the West Sole gas field in the southern North Sea (SNS).
• The earliest SNS platforms were based on shallow water (up to 30 metres) Gulf of Mexico designs, but the move into deeper waters (100 – 200 metres) with oil in the 1970s represented a step change; it had never been done before on this scale anywhere in the world, never mind in such stormy waters.
• Various projects and technologies stood out as defining stages in this engineering revolution:
• Forties, the first of the very large steel structures;• Brent with its ultra-large concrete base units (known as Condeeps);• Hutton’s tension leg platform (TLP);• FPSOs such as on the Schiehallion and Captain fields and subsea
production with long distance flow-lines, as in the Jura field and the currently being developed Laggan and Tormore fields.
• Together, these form multi-choice solutions for the extraction of the UK’s oil and gas reserves which, to a considerable degree, were designed and constructed by companies resident in this country.
• Fabrication yards were built along the coasts of Scotland and England, sometimes on the sites of former shipyards, to cope with the volume of work.
• In the majority of cases, platform jackets (the steel substructures) and the various modules comprising the topsides facilities (drilling, production, process, utilities and accommodation units) were split into separate packages for fabrication purposes which were then transported offshore and assembled in situ to create a complete production platform.
• More than 6.5 million tonnes of concrete and steel have been installed to date, with 290 operational platforms currently in place and, based on the projected developments over the next ten years, another such 40 structures potentially still to be fabricated and installed.
• Historical experience indicates that fabrication typically accounts for between 10 and 40% of capital expenditure, depending on the nature of the project.
• This would imply a fabrication market in excess of £6 billion over the next 10 years, a significant prize for the fabrication companies to pursue.
• The UK’s yards retain the capability to serve this anticipated activity, but how many of these projects will be awarded to them remains to be seen.
• Recent awards of jackets and various topside modules have been to yards in Europe and the Far East, indicating how attractive and competitive they have become.
• However, there have some notable successes at home, such as OGN in Newcastle and Hereema in Hartlepool.
• The benefits of these awards are highlighted in a case study in this report which describes the impact on direct jobs and the associated spread of activity to other parts of the country.
• Work for projects is usually tendered and awarded on a number of criteria, but invariably including cost, quality, safety, past performance and time schedule.
Such work will involve manufacturing and construction of a range of structures and components for the oil and gas and other energy related industries:• Jackets• Topside Modules• Subsea Templates/Manifolds• FPSOs• Flotels (floating accommodation vessels)• Renewables• Nuclear• Mining
• Figure 48 indicates where the major capacity is located but there are, in addition, numerous smaller facilities around the country that are well able to deliver specialist units to the size and quality demanded by the industry.
• Over 4 million square metres of yard space are still available and engaged in fabrication projects, despite the apparent downturn in fabrication activity since the heydays of the 1970s, 1980s and 1990s.
• In a recent survey completed by Subsea UK, forecasts indicated that planned subsea oil and gas projects around the world will require around 90 platforms, over 1,000 Christmas trees (production valves that sit at well heads), 80 subsea templates or manifolds and around 12,000 kilometres of pipelines and flow-lines.
• These future projects will require a very large amount of high quality steel and an ability to turn that steel into fabricated products.
• As oil and gas projects move into increasingly deeper waters around the world and exploit ever more difficult reservoirs, the technical challenges increase substantially.
• Backed by experience of the UKCS and a reputation for excellent engineering, especially in subsea technology, companies based here can target these new opportunities with confidence.
• The challenge for the supply chain is to secure an equitable share of these international projects.
• A specific subset of the upstream oil and gas supply chain is the well services contractors, a group of companies providing a wide range of specialist services outlined in Figure 52.
• All the services required to complete, test, and maintain an oil, gas or water or gas injection well, with the exception of actually drilling the borehole, are provided by this group.
• This sector of the industry comprises companies of many different sizes, from small companies focusing on high technology solutions to specific down-hole requirements, to large international, multiservice contractors that can provide of all categories of services.
• The UKCS has always been seen as a key testing and developing ground for new technology that is subsequently exported to the global market.
• Compared with many other parts of the industry, the well services contractors have a lot of capital invested in hardware and it is important that investment in research and development is sustained to ensure that this equipment is continually refreshed, improved and available to adapt to the challenges faced in the mature province of the UKCS.
• While many of the services provided are well proven and conventional, it is through the introduction of new technologies that the life of the province will continue to be extended by promoting economic extraction of previously inaccessible or small reserves.
• Since the dawn of North Sea operations, over 11,000 wells have been drilled in the UKCS; Figure 50 indicates their scale in terms of their internal length measured along the bore (otherwise known as “total depth” (TD)).
• The length of a well and the geology of the rock formation can create their own technical challenges, but the necessity of drilling being both safe and economic is paramount.
• Figure 51 illustrates an example of a system of production wells drilled from a rig as if it were located in Trafalgar Square in central London, showing the spread of the wells.
• Oil & Gas UK has recently canvassed the opinions of drilling managers in the UK, asking what they consider to be the biggest advances in drilling in the last 10 years and seeking their opinions of possible game changers in the next decade.
• For almost all of them, the top four of the past 10 years were technologies leading to:• Better control of drilling direction with rotary steerable bottom hole assemblies;• Better understanding of the nature of the reservoir through down-hole measurement;• Increased rate of progress of drilling, whilst reducing risk to personnel by the introduction of
enhanced top-drive capability;• Enhanced durability and reliability through improved drill bit design.• However, with the exception of coiled tubing / continuous pipe drilling, there was little
consensus as to what the game-changers for the next 10 years might be, though a constant theme to every suggestion was new technology that would save time and money, thus allowing the UKCS to continue to be an attractive investment proposition.
• Case Study: Using Down-Hole Flow Equipment with Intelligent Electronic Technology to Reduce Interventions during Complex Subsea Well Operations and to Enhance Safety
• Red Spider Technology, a well services specialist based in Aberdeen, provides clients with the ability to programme down-hole flow control valves, using remote control open and close technology, to monitor and respond to actual conditions in a well.
• This reduces the need to implement well interventions or use control lines which are time consuming and expensive.
• Clients can programme the tool, known as eRED®, to respond to a number of activation “triggers” such as time pressure windows, temperature and hydrostatic pressure.
Requirement• BP had used an eRED® down-hole valve on several of its platform and subsea
operations in the UK and Norway as an intelligent computer programmed tool to equalise pressures during well interventions.
• As a process, well interventions can be labour intensive and time consuming requiring teams offshore to erect scaffolding, carry out heavy lifts and rig up surface pressure control equipment which introduces additional risk and HSE exposure.
• These operations can be delayed by difficult weather conditions, leading oil and gas operators to seek technology that enables them to carry out completions more safely and which may reduce, or eliminate, the need for well interventions.
Solution• With experience of deploying eRED® down-hole valves on previous intervention projects, BP
saw the potential for adapting the tool in its Machar field. • Machar is a subsea well which is tied back to the ETAP platform (Eastern Trough Area Project,
operated by BP), which produces oil and gas from one of four separate fields, Marnock, Mungo, Monan and Machar, all part of ETAP.
• For the well completion on Machar, BP first executed a lower well completion and then, for the upper completion, used two eRED® valves, instead of the traditional plugs or barriers normally used by the industry.
• Each valve was programmed by BP to respond to its own unique command of a predefined pressure being applied over a specific time period.
• The valves were pre-installed in well tubing, one as a deep-set barrier below the production packer while the other was located higher up in the tubing hanger, and fully tested onshore prior to being shipped out to Machar.
• Method• BP carried out the upper completion of the well with both eREDs fully open allowing fluid to bypass
the valves and pressure to gain access to the lower completion for well control. • With the completion at depth, the tubing hanger was landed and locked in place. In order to pressure
test the production packer, BP instructed the deep-set eRED valve to close with a pre-programmed pressure and time command of 750 psi (500-1,000psi window) applied to the tubing for ten minutes.
• A delay of five minutes was programmed into the tool (to allow tubing pressure bleed down prior to the eRED closing.)
• BP set the production packer hydraulically by applying pressure against the deep-set eRED valve, but the first attempt to pressure test the production packer was unsuccessful.
• Having programmed the eRED to respond to repeating triggers, BP opened the valve with the same pressure and time command of 750 psi (500-1,000psi window) but this time excluding the five minute delay.
• After closing the eRED valve once more BP was then able to achieve a successful pressure test.
• The eRED in the tubing hanger was then instructed to close with its own pre-programmed pressure and time command of 1,750psi (1,500-2,000 psi window) applied to the tubing for ten minutes, with a time delay of five minutes. With both eREDs closed, providing a fully testable dual barrier, BP was able to remove the drilling blow-out preventer as well as installing and testing the subsea tree.
• On completing these operations, BP remotely opened the tubing hanger eRED using its command trigger. Positive feedback that the valve had opened successfully was observed at surface in the form of a tubing pressure drop and the same process was repeated successfully for the deep set eRED.
Outcome• During the operations to prepare the Machar well for production, BP was able to carry out multiple
tests using eRED technology to eliminate a total of six deep and four shallow wireline runs, so reducing exposure to risks associated with rigging up slickline for interventions and exposure to potential delays caused by adverse weather offshore. Pre-installation of the eRED valves onshore also enabled BP to reduce slickline runs from ten to two minimising risks to personnel as well as time spent operating equipment offshore.
Supply Chain Exports• The current supply chain was originally developed to supply and service
North Sea oil and gas activities and has a number of major companies with head offices in the UK, but it is increasingly reaching out into international markets.
• It also continues to diversify into other parts of the wider energy industry, both at home and overseas, with shale gas, coal bed methane and renewable energies all forming a valuable part of the business mixture.
• While a complete picture of export activity across the whole country is lacking, a reasonably representative view can be obtained from Scottish companies and, particularly those based in the north east of Scotland.
• The Scottish Council for Development and Industry (SCDI) has systematically tracked the growth of exports and international sales by Scottish oil and gas supply chain companies over the last decade. SCDI’s latest survey covering the calendar year 2009 again provides valuable insights into the continuing growth of the Scottish oil and gas activity with the following highlights:
• International activity has risen from £1.8 billion in 2000 to £7.24 billion in 2009, of which £2.5 billion came from direct exports and £4.74 billion came from sales via overseas subsidiaries;
• In 2009, international activity increased to account for more than 45% per cent of total Scottish oil and gas supply chain sales, compared with 27 per cent in 2000;
• Sales via overseas subsidiaries increased by 16% compared with 2008 of which 93% were from services;
• The value of direct exports only increased by 1% compared with 2008 with services comprising 44% of that total;
• Africa was the top geographic region for direct exports attracting 27% of sales, followed by Western Europe with 10%; North America was the largest market for overseas subsidiaries attracting 44% of total sales by overseas subsidiaries;
• Australasia and Western Europe had the highest year-on-year growth with increases of 83% and 75% respectively;
• The top five international markets for direct exports and subsidiaries’ sales combined were the United States, Canada, Angola, Norway and Australia;
• Sales activity from the supply chain was recorded in 107 different country markets.
• The SCDI survey also assesses the size of the Scottish supply chain revealing that domestic sales dropped slightly to £8.7 billion in 2009.
• Total domestic and international sales by the Scottish oil and gas supply chain have grown steadily over the last decade, reaching £15.9 billion in 2009, with international markets more than making up for a less expansionary domestic one.
• It is estimated that the total international activity by the supply chain across the whole of the United Kingdom is approximately double that achieved in Scotland, based on correlations with employment (our research shows that Scotland has approximately 45% of direct and indirect employment within the oil and gas sector).
• This implies that total exports from the UK by the whole supply chain were £5-6 billion in 2009, although the growth may have slowed somewhat in 2010 as the rate of international investment eased over the year.
• On a wider perspective, UK Trade & Investment (UKTI) has recently carried out research that explores the developing trends in international trade, particularly with respect of small to medium sized businesses (SMEs).
• Research among companies that already export found that most firms (over 90%) sell directly to businesses as part of their overseas strategy.
• It is clear that a permanent presence – often in the form of agents and distributors – remains an essential part of doing business overseas, with more than two in five exporters using local agents or distributors to sell their products or services abroad.
• Interestingly, it is larger and more experienced exporting companies that tend to use agents or distributors to the greatest extent, with 61% of larger firms (more than 50 employees) using them compared with only 34% of small firms (less than 10 employees).
• The research also showed that those companies with ambitions for substantial growth are more likely to use agents or distributors, 47% of them, compared with 27% of firms whose growth plans were simply to stay the same.
• The results suggest that this method of doing business internationally is one that stands the test of time.
• More young companies are taking international opportunities from an early stage; almost one in five (17%) of new companies currently active abroad are classified as “born global”, i.e. have been doing business overseas from the outset.
• Firms classed as “innovative” – those that devote resources to R&D or development of new products or services – tend to benefit most from doing business abroad and many international firms experience a virtuous circle where exporting leads to more innovation, with those innovations leading to further exporting.
• Over half of all firms (53%) said that a new product or service evolved because of their business overseas.
Export business is being won in a variety of areas such as:• Subsea engineering where the UK is recognised as a world leader;• High pressure, high temperature (HPHT) field developments;• Oil and gas process machinery, equipment and technology;• Deep water oil and gas developments;• Design, project management and delivery of new field developments;
• Integrated services for the operation and maintenance of fields;• Late life operation of mature fields;• Light weight, slim line structures;• Wind power generation (offshore and onshore);• Economic and technology led consultancy services;• Legal, financial and insurance services;• Health, safety and environmental expertise.
Future of the Supply Chain• During the past 40 or more years of operations to find and extract oil and gas from the waters around
the United Kingdom, a world class supply chain has been developed, rooted within this country. • However, with other nations bolstering their efforts to secure a major share of international business,
it is imperative that the UK continues to compete wholeheartedly on the world stage. • This will occur against a backdrop of declining but technology dependent UKCS production, and
growing global opportunities.• The supply chain must fight not to lose its attractiveness, not only in the domestic oil and gas market,
but also in the international arena which continues to drive ever growing exports. The supply chain will need to adapt to these evolving circumstances and, to do so, it will need to be encouraged and incentivised to maintain its momentum.
This may entail:• Moving beyond project specific decisions to strategic supplier/customer relationships;• Encouragement of foreign inward investment for goods and services;
• Ensuring that, when SMEs and larger companies grow internationally, they see the UK as a place in which to anchor themselves, for excellence in project management, design, support, technology, R&D, skills, training and development;
• Customers pooling projects and developing new contract strategies and business models.
• In order to meet this challenge, it is not solely the companies involved that must foresee these new demands; both the government and operators, the ultimate customers, must help create the right environment for the supply chain to rise to this global contest.
• There is little doubt that the standards which are applied on the UKCS are among the most demanding in the world. An ability to meet these puts our offshore oil and gas supply chain in a unique position to take advantage of these international opportunities.
Common Data Access• Common Data Access (CDA) is a wholly-owned subsidiary of Oil & Gas UK. • The company was established by industry in 1995 with the aim of sharing
the costs and importantly also the benefits associated with managing geo-scientific exploration and production (E&P) data through collaborative working.
• CDA is funded independently from Oil & Gas UK by annual subscription income received from more than 50 operating companies.
• Other participating organisations include DECC, academia and several service companies.
• Information about the geology underlying the UKCS is critical to the understanding of the subsurface, in finding potential hydrocarbon accumulations, in modelling reservoirs and maximising recovery of oil and gas.
• The quality of almost all decisions taken by E&P companies depends directly upon the availability of sufficient and reliable well and seismic data.
• The volume of this information is in the order of petabytes1 and the cumulative acquisition costs amount to a sum of money almost beyond contemplation.
• A recent CDA study which involved more than 20 senior executives from oil companies in the UK found that 70% of the value generated by oil companies’ E&P activities relies on their understanding of the subsurface.
• The study then estimated that data and its effective management contributed more than one-third of this understanding (see Figure 56).
• Figure 56: Value of Data and Data Management
Leading E&P Data Management• CDA’s Well DataStore holds a wide range of digital information for more than 11,000 wells. • It has more than 500 active users who in aggregate download more that 65,000 items and
load approximately 3,000 new items of well data every month over the internet. • CDA’s Seismic DataStore holds data for more than 1,000 seismic surveys securely and
confidentially and is expected to show a ten-fold increase in data volumes by the end of 2011.
• CDA is leading cooperation on E&P data management in the UKCS in several other ways. • CDA has developed and published several important guidelines and best practices which
have improved the standards of data management and which contribute towards operating efficiency and safety on the UKCS.
• CDA is also exploring the case for widening industry collaborative initiatives to include other types of technical information including production data, for example.
• Information held by CDA on behalf of UKCS licensees is shared between participating companies literally at the click of a button and (where applicable) is also made available to the public.
• CDA’s DEAL website (see an extract, Figure 57) provides up-to-date details of all wells, platforms, pipelines and seismic surveys on the UKCS and links the user to various public and private sources of information for these features.
• The information about infrastructure that is collected from operators for DEAL is made available to British fishermen for use on their onboard plotters and is vitally important in the prevention of accidents and damage to equipment.
Regulatory Compliance• Licensees must retain the information they acquire over their licences in perpetuity and
must provide copies of these data to DECC for their use and for publication by them. Under a ‘deed’ between CDA and DECC, the storage of E&P data with CDA gives participating companies relief from these obligations (which are met by CDA on their behalf).
• The National Data Repository (NDR) for the UKCS promotes and facilitates the exploitation of national hydrocarbon resources through the collection, storage and dissemination of reliable geo-scientific data related to oil and gas exploration and production activities.
• The NDR is based upon a distributed model which relies on a network of commercial and other agreements that has evolved into an effective private/public partnership. CDA’s contribution as a strategic partner for DECC and its agents is very significant to this arrangement. Set within the context of important initiatives on data management standards and good practice, CDA’s Well DataStore, Seismic DataStore and the DEAL website are central and essential components of the NDR, contributing towards the sustained competitiveness of the UKCS.
Contributing Towards the Success of the UKCS• The effective management of subsurface data is crucial to the
successful and efficient exploitation of the hydrocarbon resources in the UKCS.
• CDA makes a very significant contribution in this domain by protecting this valuable information and making it available to geoscientists for them to take informed decisions quickly and reliably.
• Perhaps the ultimate test is to consider what the industry would do without these services.
• The offshore oil and gas industry is the most highly taxed business in the country.
• Fields developed since March 1993 are taxed at 62%, being liable for both Corporation Tax at 30% and a Supplementary Charge at 32% (before March 2011’s Budget, these three rates were 50%, 30% and 20% respectively).
• The marginal tax rate rises to 81% (75% pre-Budget 2011) for fields which received development consent before mid-March 1993, these also being liable for Petroleum Revenue Tax at 50%.
Corporation Tax and Supplementary Charge• Oil and gas exploration and production companies are subject to
Corporation Tax (CT) which is applied to company profits at a rate of 30%. The industry has been excluded from the general reductions in the rate of CT from 30% to 28% in April 2008, 28% to 26% in April 2011 and 26% to 25% planned for April 2012.
• The Supplementary Charge (SCT) was originally introduced at a rate of 10% in 2002’s Budget which also saw the introduction of 100% First Year Allowances for UKCS capital expenditure in recognition of the higher tax rate. Since the introduction of 100% First Year Allowances, all capital costs are effectively tax deductible as incurred.
• SCT was raised to 20% from 1 January 2006 and, in the Budget of March 2011, it was raised again to 32%. In conjunction with this latest increase, it was announced that from 2012 the government would restrict the ability to claim tax relief for decommissioning, capping relief against SCT at 20%.
• Furthermore, taxable profits derived from the extraction of oil and gas from the UKCS are “ring fenced” so that losses from other activities cannot be offset against these ring fenced profits. Stringent rules are also applied to ensure that only interest relating to UKCS projects is deductible within the ring fence. However, taxable profits for SCT differ from CT in that finance costs are not deductible.
• The 2009 Budget introduced a new field allowance for small fields and challenging HPHT (high-pressure, high-temperature) and heavy oil fields. These fields will be able to claim an allowance (a fixed amount depending on the type of development) which can be offset against SCT once in production, reducing the rate of tax paid. In January 2010, this allowance was extended to remote, deep water gas fields to the west of Shetland.
• In July 2011, a further change was announced when the ring fenced expenditure supplement was increased from 6% to 10%, with effect from January 2012.
• This allows companies with losses arising from E&A drilling, development or operational expenditure to reduce their profits chargeable to tax in up to six accounting periods.
• It is designed to benefit new investors with insufficient tax cover from production and could affect 24 of the 82 companies with commercial fields in the UKCS, improving the economics of their portfolios, according to Wood Mackenzie.
• It does not, however, compensate for the value wiped off companies’ assets by the SCT increase in 2011’s Budget.
Petroleum Revenue Tax• Petroleum Revenue Tax (PRT) is applied to all fields which received
development consent before 16 March 1993 and to tariff arrangements prior to 9 April 2003 relating to pipeline systems and other facilities which in some part service a field paying PRT.
• Tariff contracts arranged on or after this date are exempt from PRT, as addressed in the Finance Act 2004. PRT is applied at a rate of 50% to profits, field by field, in six-month chargeable periods. If losses arise, the ability to surrender losses to other fields is extremely limited.
• PRT is deductible for CT and SCT. Capital and operating costs are also deductible. No deduction is allowed for interest, but most capital incurred pre-payback (see below) qualifies for an additional deduction of 35% (uplift). As most fields subject to PRT are past payback, the significance of this relief is now very limited.
• “Payback” is the period in which total cumulative income exceeds total cumulative expenditure. This period not only determines the cut-off for uplift, but also dictates the number of six-month periods for which safeguard applies (see next paragraph).
• “Safeguard” was introduced as a safety net for the benefit of the less profitable fields, essentially to ensure that, in the early years of a field’s life, the PRT cannot exceed an amount that would reduce the participants’ after-tax profit below a minimum return on investment in the field.
• It limits PRT in each six-month chargeable period to 80% of the excess profits over 15% of cumulative capital which has qualified for uplift. It applies to the period from the start of production to the period of payback plus half as long again. It will not apply if it calculates PRT in excess of the “normal” calculation.
• An “Oil Allowance” can be applied to fields with development consent on or before 31 March 1982 which makes the first 250,000 tonnes per six month period, up to a cumulative total of 5 million tonnes, PRT free.
• From 1 April 1982, for southern fields the amounts are 125,000 and 2.5 million tonnes and for all other fields 500,000 and 10 million tonnes respectively.
• A “Tariff Receipts Allowance” is available for some income streams. This makes the first 250,000 tonnes of throughput per six month period PRT free for each field using the infrastructure.
• Gas sold under contracts entered into before 30 June 1975 is exempt from PRT.
• As mentioned above, new tariff business for transportation, processing and other services provided through the use of UKCS infrastructure which is transacted under contracts entered into on or after 9 April 2003 will be exempt from PRT, provided the infrastructure is used in relation to:
• A field receiving development consent on or after 9 April 2003; or• An existing field using a new evacuation route, but only if that field has not
to date made use of non-field assets which have qualified for PRT relief.• While the exemption covers new tariff business contracted on or after 9
April 2003, it only applies to income and expenditure received and incurred under such contracts since 1 January 2004.
• Glossary of Terms and Abbreviations
BAF best alternative fuel
bbl barrel (of oil) (1 barrel = 0.16 m3)
BBL Balgzand (in the Netherlands) to Bacton (in Norfolk, England) gas pipeline
bcm billion cubic metres (1 metre3 = 35.3 cubic feet)
bcm/y billion cubic metres per year (of gas)
BIS Department for Business, Innovation and Skills, previously called Department for Business, Enterprise and Regulatory Reform (BERR) billion one thousand million or 109
boe barrel of oil equivalent: this includes oil, gas and other hydrocarbons and equates all of these with oil, so that a common measure can be made of any of them, or of two or more of them in combination (1 boe = 164 m3 or 5.8 thousand cubic feet of gas)
bpd barrels per day
boepd barrel of oil equivalent per day
brown-field an oil or gas field already in production
BTU British Thermal Unit (of energy)
capex capital expenditure
CCGT combined cycle (gas + steam) gas turbine
CCS carbon capture and storage
CDA Common Data Access (a subsidiary of Oil & Gas UK)
CfD contract for difference
CHP combined heat and power
CNG compressed natural gas
CNS central North Sea
CO2 carbon dioxide (one of the six “greenhouse gases” under the Kyoto protocol) condensate low density, liquid hydrocarbon usually associated with natural gas which, depending on temperature and pressure, can be gaseous
CoP Cessation of Production (from a field)
CT Corporation Tax
DECC Department of Energy & Climate Change, formed in autumn 2008, by combining BERR’s previous responsibilities for energy and DEFRA’s for climate change and incorporating the Office of Climate Change
DEFRA Department for the Environment, Food and Rural Affairs
DSA Decommissioning Securities Agreement
E&A exploration and appraisal (drilling)
EEA European Economic Area (the EU plus Norway, Iceland and Liechtenstein)
EIA Energy Information Administration (of the USA)
EMR electricity market reform (by DECC)
EOR enhanced oil recovery
E&P exploration and production
EU European Union (the 27 member states)
EU ETS European Union’s Emissions Trading Scheme
FiT Feed-in Tariff (for electricity)
FPAL First Point Assessment Ltd, an organisation providing a registration, qualification and performance monitoring system of the industry’s suppliers and contractors
FPSO floating production, storage and offtake (vessel)
GHG greenhouse gas (of which there are six under the Kyoto protocol)
GTL gas to liquids
GVA Gross Value Added
GW Giga Watt (of electricity): one billion watts
HH Henry Hub (the principal trading point for gas in the USA)
HMRC Her Majesty’s Revenue and Customs (sometimes known as “the Exchequer”)
HMT Her Majesty’s Treasury
HPHT high pressure, high temperature (of reservoirs)
IEA International Energy Agency (part of the OECD)
ITF Industry Technology Facilitator, a not-for-profit, industry owned body
JOA Joint Operating Agreement (between partners in a field)
kms kilometres
KW Kilo Watt (of electricity) – unit of power: one thousand watts
KWh Kilo Watt hour – unit of energy
LTC long term contract
LNG liquefied natural gas
mboepd million barrels of oil equivalent per day
mbopd million barrels of oil per day
mcm/d million cubic metres per day (of gas)
MS Member State (of the EU)
mtoe million tonnes of oil equivalent
mt/y million tonnes per year
MVA market value analysis
MW Mega Watt (of electricity): one million watts
NBP National Balancing Point (fictional location in Britain where the NTS is notionally in balance and at which the trading of gas takes place)
NGL natural gas liquid (e.g. butane, propane)
NGO non-governmental organisation
NNS northern North Sea
NTS National Transmission System (high pressure gas transmission system in Britain operated by National Grid – the “motorway” network for gas)
OCGT open cycle gas turbine
OECD Organisation of Economic Co-operation and Development
OGP International Association of Oil and Gas Producers
ONS Office of National Statistics
OPEC Organisation of Petroleum Exporting Countries
opex operating expenditure
OTC over the counter
PILOT joint oil and gas industry – government task force chaired by the Secretary of State of DECC
PRT Petroleum Revenue Tax
p/th pence per therm (for gas)
REMIT Regulation of Energy Market Integrity and Transparency (EU)
ROV remotely operated vehicle (sub-sea)
SCDI Scottish Council for Development and Industry
SCT Supplementary Charge to Corporation Tax
SIC Standard Industrial Classification (ref ONS) side-track description of a well that is started from the bore of an existing well, but is then deviated to create a new well
SME small to medium (sized) enterprise
SNS southern North Sea (sometimes referred to as “southern gas basin”)
trillion one million million or 1012
UKCS United Kingdom Continental Shelf
UKTI UK Trade & Investment
UOC unit operating cost
WoS west of Shetland (sometimes referred to as “Atlantic margin”)
Structural Reliability
• Structural limit states are often defined as a difference between Strength ( ) and Load ( ):
• Probability of failure can be defined as
Reliability Analysis • Uncertainty propagate through physical system
Day 5:
• Wave Theories; Spectral Analysis Application• Wind and Wave Forces, Computational Hydrodynamics• Buoyancy and Stability• Geotechnical Engineering for offshore structure• Offshore design philosophy• Codes, Standards and Regulations
Wave• This article is about waves in the scientific sense. For waves on the surface of
the ocean or lakes, see Wind wave. For other uses, see Wave (disambiguation).
• In physics, a wave is an oscillation accompanied by a transfer of energy that travels through space or mass. Frequency refers to the addition of time.
• Wave motion transfers energy from one point to another, which may or may not displace particles of the medium—that is, with little or no associatedmass transport.
• Waves consist, instead, of oscillations or vibrations (of a physical quantity), around almost fixed locations.
• There are two main types of waves. Mechanical waves propagate through a medium, and the substance of this medium is deformed. The deformation reverses itself owing to restoring forces resulting from its deformation.
• For example, sound waves propagate via air molecules colliding with their neighbors.
• When air molecules collide, they also bounce away from each other (a restoring force). This keeps the molecules from continuing to travel in the direction of the wave.
• The second main type of wave, electromagnetic waves, do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles, and can therefore travel through a vacuum.
• These types of waves vary in wavelength, and include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
• Waves are described by a wave equation which sets out how the disturbance proceeds over time. The mathematical form of this equation varies depending on the type of wave.
• Further, the behavior of particles in quantum mechanics are described by waves. In addition, gravitational waves also travel through space, which are a result of a vibration or movement in gravitational fields.
• A wave can be transverse or longitudinal depending on the direction of its oscillation. Transverse waves occur when a disturbance creates oscillations that are perpendicular (at right angles) to the propagation (the direction of energy transfer).
• Longitudinal waves occur when the oscillations are parallel to the direction of propagation. While mechanical waves can be both transverse and longitudinal, all electromagnetic waves are transverse in free space.
Surface waves in water
General features• A single, all-encompassing definition for the term wave is not
straightforward. A vibration can be defined as a back-and-forth motion around a reference value. However, a vibration is not necessarily a wave.
• An attempt to define the necessary and sufficient characteristics that qualify a phenomenon to be called a wave results in a fuzzy border line.
• The term wave is often intuitively understood as referring to a transport of spatial disturbances that are generally not accompanied by a motion of the medium occupying this space as a whole.
• In a wave, the energy of a vibration is moving away from the source in the form of a disturbance within the surrounding medium (Hall 1980, p. 8).
• However, this notion is problematic for a standing wave (for example, a wave on a string), where energy is moving in both directions equally, or for electromagnetic (e.g., light) waves in a vacuum, where the concept of medium does not apply and interaction with a target is the key to wave detection and practical applications.
• There are water waves on the ocean surface; gamma waves and light waves emitted by the Sun; microwaves used in microwave ovens and in radar equipment; radio waves broadcast by radio stations; and sound waves generated by radio receivers, telephone handsets and living creatures (as voices), to mention only a few wave phenomena
• It may appear that the description of waves is closely related to their physical origin for each specific instance of a wave process.
• For example, acoustics is distinguished from optics in that sound waves are related to a mechanical rather than an electromagnetic wave transfer caused by vibration.
• Concepts such as mass, momentum, inertia, or elasticity, become therefore crucial in describing acoustic (as distinct from optic) wave processes.
• This difference in origin introduces certain wave characteristics particular to the properties of the medium involved.
• For example, in the case of air: vortices, radiation pressure, shock waves etc.; in the case of solids: Rayleigh waves, dispersion; and so on.
• Other properties, however, although usually described in terms of origin, may be generalized to all waves.
• For such reasons, wave theory represents a particular branch of physics that is concerned with the properties of wave processes independently of their physical origin.
• For example, based on the mechanical origin of acoustic waves, a moving disturbance in space–time can exist if and only if the medium involved is neither infinitely stiff nor infinitely pliable.
• If all the parts making up a medium were rigidly bound, then they would all vibrate as one, with no delay in the transmission of the vibration and therefore no wave motion.
• On the other hand, if all the parts were independent, then there would not be any transmission of the vibration and again, no wave motion.
• Although the above statements are meaningless in the case of waves that do not require a medium, they reveal a characteristic that is relevant to all waves regardless of origin: within a wave, the phase of a vibration (that is, its position within the vibration cycle) is different for adjacent points in space because the vibration reaches these points at different times.
Mathematical description of one-dimensional wavesWave equation• Main articles: Wave equation and D'Alembert's formula• Consider a traveling transverse wave (which may be a pulse) on a
string (the medium). Consider the string to have a single spatial dimension. Consider this wave as traveling
in the direction in space. E.g., let the positive direction be to the right, and the negative direction be to the left.with constant amplitude with constant velocity where is
• independent of wavelength (no dispersion)• independent of amplitude (linear media, not nonlinear).• with constant waveform, or shape• This wave can then be described by the two-dimensional functions
or, more generally, by d'Alembert's formula:
representing two component waveforms and traveling through the medium in opposite directions.
• A generalized representation of this wave can be obtained as the partial differential equation
• General solutions are based upon Duhamel's principle.
Wavelength λ, can be measured between any two corresponding points on a waveform
Animation for 2 wavelength, green wave traverse to the right while blue wave transverse left, the net red wave amplitude at each point is the sum of the amplitudes of the individual waves. Note that f(x,t) + g(x,t) = u(x,t)
Wave forms• The form or shape of F in d'Alembert's formula involves the argument x − vt. • Constant values of this argument correspond to constant values of F, and these
constant values occur if x increases at the same rate that vt increases. • That is, the wave shaped like the function F will move in the positive x-direction at
velocity v (and G will propagate at the same speed in the negative x-direction).• In the case of a periodic function F with period λ, that is, F(x + λ − vt) = F(x − vt), the
periodicity of F in space means that a snapshot of the wave at a given time t finds the wave varying periodically in space with period λ (the wavelength of the wave).
• In a similar fashion, this periodicity of F implies a periodicity in time as well: F(x − v(t + T)) = F(x − vt) provided vT = λ, so an observation of the wave at a fixed location x finds the wave undulating periodically in time with period T = λ/v.
• Amplitude and modulation• Main article: Amplitude modulation• See also: Frequency modulation and Phase modulation• The amplitude of a wave may be constant (in which case the wave is
a c.w. or continuous wave), or may be modulated so as to vary with time and/or position.
• The outline of the variation in amplitude is called the envelope of the wave. Mathematically, the modulated wave can be written in the form:
• where is the amplitude envelope of the wave, is the wavenumber and is the phase. If the group velocity (see below) is wavelength-independent, this equation can be simplified as:
showing that the envelope moves with the group velocity and retains its shape. Otherwise, in cases where the group velocity varies with wavelength, the pulse shape changes in a manner often described using an envelope equation.
Phase velocity and group velocity• Main articles: Phase velocity and Group velocity• See also: Envelope (waves) § Phase and group velocityThere are two velocities that are associated with waves, the phase velocity and the group velocity. To understand them, one must consider several types of waveform. For simplification, examination is restricted to one dimension.The most basic wave (a form of plane wave) may be expressed in the form:
Sine, square, triangle and sawtooth waveforms.
Amplitude modulation can be achieved through f(x,t) = 1.00*sin(2*pi/0.10*(x-1.00*t)) and g(x,t) = 1.00*sin(2*pi/0.11*(x-1.00*t)) Only the resultant is visible to improve clarity of waveform
• which can be related to the usual sine and cosine forms using Euler's formula. Rewriting the argument,
• , makes clear that this expression describes a vibration of wavelength traveling in the x-direction with a constant phase velocity
• The other type of wave to be considered is one with localized structure described by an envelope, which may be expressed mathematically as, for example:
• where now A(k1) (the integral is the inverse fourier transform of A(k1)) is a function exhibiting a sharp peak in a region of wave vectors Δk surrounding the point k1= k.
• In exponential form:
• with Ao the magnitude of A. For example, a common choice for Ao is a Gaussian wave packet:
• where σ determines the spread of k1-values about k, and N is the amplitude of the wave.
• The exponential function inside the integral for ψ oscillates rapidly with its argument, say φ(k1), and where it varies rapidly, the exponentials cancel each other out, interfere destructively, contributing little to ψ.
• However, an exception occurs at the location where the argument φ of the exponential varies slowly.
• (This observation is the basis for the method of stationary phase for evaluation of such integrals.)
• The condition for φ to vary slowly is that its rate of change with k1be small; this rate of variation is:
• where the evaluation is made at k1 = k because A(k1) is centered there. • This result shows that the position x where the phase changes slowly, the position
where ψ is appreciable, moves with time at a speed called the group velocity:
• The group velocity therefore depends upon the dispersion relation connecting ω and k.
• For example, in quantum mechanics the energy of a particle represented as a wave packet is E = ħω = (ħk)2/(2m).
• Consequently, for that wave situation, the group velocity is
• Showing that the velocity of a localized particle in quantum mechanics is its group velocity.
• Because the group velocity varies with k, the shape of the wave packet broadens with time, and the particle becomes less localized.
• In other words, the velocity of the constituent waves of the wave packet travel at a rate that varies with their wavelength, so some move faster than others, and they cannot maintain the same interference pattern as the wave propagates.
Illustration of the envelope (the slowly varying red curve) of an amplitude-modulated wave.
The fast varying blue curve is the carrier wave, which is being modulated.
Frequency dispersion in groups of gravity waves on the surface of deep water.
The red dot moves with the phase velocity, and the green dots propagate with the group velocity.
This shows a wave with the Group velocity and Phase velocity going in different directions.
Sinusoidal wavesMathematically, the most basic wave is the (spatially) one-dimensional sine wave (or harmonic wave or sinusoid) with an amplitude described by the equation:
Where is the maximum amplitude of the wave, maximum distance from the highest point of the disturbance in the medium (the crest) to the equilibrium point during one wave cycle.
• In the illustration to the right, this is the maximum vertical distance between the baseline and the wave.
is the space coordinate is the time coordinate is the wavenumber is the angular frequency is the phase constant
• The units of the amplitude depend on the type of wave. • Transverse mechanical waves (e.g., a wave on a string) have an
amplitude expressed as a distance (e.g., meters), longitudinal mechanical waves (e.g., sound waves) use units of pressure (e.g., pascals), and electromagnetic waves (a form of transverse vacuum wave) express the amplitude in terms of its electric field (e.g., volts/meter).
• The wavelength is the distance between two sequential crests or troughs (or other equivalent points), generally is measured in meters. A wavenumber , the spatial frequency of the wave in radians per unit distance (typically per meter), can be associated with the wavelength by the relation
• The period is the time for one complete cycle of an oscillation of a wave. The frequency is the number of periods per unit time (per second) and is typically measured in hertz.
• These are related by• In other words, the frequency and period of a wave are reciprocals.
• The angular frequency represents the frequency in radians per second. It is related to the frequency or period by
• The period is the time for one complete cycle of an oscillation of a wave. The frequency is the number of periods per unit time (per second) and is typically measured in hertz. These are related by:
• In other words, the frequency and period of a wave are reciprocals.• The angular frequency represents the frequency in radians per second.
• It is related to the frequency or period by
• The wavelength of a sinusoidal waveform traveling at constant speed is given by:
• where is called the phase speed (magnitude of the phase velocity) of the wave and is the wave's frequency.
• Wavelength can be a useful concept even if the wave is not periodic in space.
• For example, in an ocean wave approaching shore, the incoming wave undulates with a varying local wavelength that depends in part on the depth of the sea floor compared to the wave height.
• The analysis of the wave can be based upon comparison of the local wavelength with the local water depth.
• Although arbitrary wave shapes will propagate unchanged in lossless linear time-invariant systems, in the presence of dispersion the sine wave is the unique shape that will propagate unchanged but for phase and amplitude, making it easy to analyze.
• Due to the Kramers–Kronig relations, a linear medium with dispersion also exhibits loss, so the sine wave propagating in a dispersive medium is attenuated in certain frequency ranges that depend upon the medium.
• The sine function is periodic, so the sine wave or sinusoid has a wavelength in space and a period in time.
• The sinusoid is defined for all times and distances, whereas in physical situations we usually deal with waves that exist for a limited span in space and duration in time.
• Fortunately, an arbitrary wave shape can be decomposed into an infinite set of sinusoidal waves by the use of Fourier analysis.
• As a result, the simple case of a single sinusoidal wave can be applied to more general cases.
• In particular, many media are linear, or nearly so, so the calculation of arbitrary wave behavior can be found by adding up responses to individual sinusoidal waves using the superposition principle to find the solution for a general waveform.
• When a medium is nonlinear, the response to complex waves cannot be determined from a sine-wave decomposition.
Sinusoidal waves correspond to simple harmonic motion.
• Plane waves• Main article: Plane wave• Standing waves• Main articles: Standing wave, Acoustic resonance,
Helmholtz resonator and Organ pipe
• A standing wave, also known as a stationary wave, is a wave that remains in a constant position.
• This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions.
• The sum of two counter-propagating waves (of equal amplitude and frequency) creates a standing wave.
• Standing waves commonly arise when a boundary blocks further propagation of the wave, thus causing wave reflection, and therefore introducing a counter-propagating wave.
• For example when a violin string is displaced, transverse waves propagate out to where the string is held in place at the bridge and the nut, where the waves are reflected back.
• At the bridge and nut, the two opposed waves are in antiphase and cancel each other, producing a node.
• Halfway between two nodes there is an antinode, where the two counter-propagating waves enhance each other maximally.
• There is no net propagation of energy over time.
Standing wave in stationary medium. The red dots represent the wave nodes
One-dimensional standing waves; the fundamental mode and the first 5 overtones.
A two-dimensional standing wave on a disk; this is the fundamental mode
A standing wave on a disk with two nodal lines crossing at the center; this is an overtone.
Physical properties• Waves exhibit common behaviors under a number of standard
situations, e. g.• Transmission and media• Main articles: Rectilinear propagation, Transmittance and
Transmission medium• Waves normally move in a straight line (i.e. rectilinearly) through a
transmission medium. Such media can be classified into one or more of the following categories:
• A bounded medium if it is finite in extent, otherwise an unbounded medium
• A linear medium if the amplitudes of different waves at any particular point in the medium can be added
• A uniform medium or homogeneous medium if its physical properties are unchanged at different locations in space
• An anisotropic medium if one or more of its physical properties differ in one or more directions
• An isotropic medium if its physical properties are the same in all directions
Light beam exhibiting reflection, refraction, transmission and dispersion when encountering a prism.
Absorption• Main articles: Absorption (acoustics) and
Absorption (electromagnetic radiation)• Absorption of waves mean, if a kind of wave strikes a matter, it will
be absorbed by the matter. • When a wave with that same natural frequency impinges upon an
atom, then the electrons of that atom will be set into vibrational motion.
• If a wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the wave and transform it into vibrational motion.
Light beam exhibiting reflection, refraction, transmission and dispersion when encountering a prism
Reflection• Main article: Reflection (physics)• When a wave strikes a reflective surface, it changes direction, such that the
angle made by the incident wave and line normal to the surface equals the angle made by the reflected wave and the same normal line.
Interference• Main article: Interference (wave propagation)• Waves that encounter each other combine through superposition to create
a new wave called an interference pattern. • Important interference patterns occur for waves that are in phase.
Refraction• Main article: Refraction• Refraction is the phenomenon of a wave changing its speed.
Mathematically, this means that the size of the phase velocity changes. • Typically, refraction occurs when a wave passes from one medium into
another. • The amount by which a wave is refracted by a material is given by the
refractive index of the material. • The directions of incidence and refraction are related to the refractive
indices of the two materials by Snell's law.
Diffraction• Main article: Diffraction• A wave exhibits diffraction when it encounters an obstacle that bends
the wave or when it spreads after emerging from an opening. Diffraction effects are more pronounced when the size of the obstacle or opening is comparable to the wavelength of the wave.
Sinusoidal traveling plane wave entering a region of lower wave velocity at an angle, illustrating the decrease in wavelength and change of direction (refraction) that results.
• Polarization• Main article: Polarization (waves)• A wave is polarized if it oscillates in one direction or plane. • A wave can be polarized by the use of a polarizing filter. • The polarization of a transverse wave describes the direction of
oscillation in the plane perpendicular to the direction of travel.• Longitudinal waves such as sound waves do not exhibit polarization.
For these waves the direction of oscillation is along the direction of travel.
Dispersion• Main articles: Dispersion (optics) and Dispersion (water waves)• A wave undergoes dispersion when either the phase velocity or the
group velocity depends on the wave frequency. Dispersion is most easily seen by letting white light pass through a prism, the result of which is to produce the spectrum of colours of the rainbow.
• Isaac Newton performed experiments with light and prisms, presenting his findings in the Opticks (1704) that white light consists of several colours and that these colours cannot be decomposed any further.
Schematic of light being dispersed by a prism.
Mechanical waves• Waves on strings• Main article: Vibrating string• The speed of a transverse wave traveling along a vibrating string ( v )
is directly proportional to the square root of the tension of the string ( T ) over the linear mass density ( μ ):
where the linear density μ is the mass per unit length of the string.
• Acoustic waves• Acoustic or sound waves travel at speed given by
• or the square root of the adiabatic bulk modulus divided by the ambient fluid density (see speed of sound).
Water waves• Main article: Water waves• Ripples on the surface of a pond are actually a combination of transverse and
longitudinal waves; therefore, the points on the surface follow orbital paths.• Sound—a mechanical wave that propagates through gases, liquids, solids and
plasmas;• Inertial waves, which occur in rotating fluids and are restored by the Coriolis
effect;• Ocean surface waves, which are perturbations that propagate through water.
Seismic waves• Main article: Seismic wavesShock waves• Main article: Shock wave• See also: Sonic boom and Cherenkov radiation• Other• Waves of traffic, that is, propagation of different densities of motor vehicles, and so forth,
which can be modeled as kinematic waves• Metachronal wave refers to the appearance of a traveling wave produced by coordinated
sequential actions.• It is worth noting that the mass-energy equivalence equation can be solved for this form:
Electromagnetic waves• Main articles: Electromagnetic radiation and Electromagnetic spectrum• (radio, micro, infrared, visible, uv)• An electromagnetic wave consists of two waves that are oscillations of the electric and
magnetic fields. • An electromagnetic wave travels in a direction that is at right angles to the oscillation
direction of both fields. • In the 19th century, James Clerk Maxwell showed that, in vacuum, the electric and magnetic
fields satisfy the wave equation both with speed equal to that of the speed of light. • From this emerged the idea that light is an electromagnetic wave. Electromagnetic waves
can have different frequencies (and thus wavelengths), giving rise to various types of radiation such as radio waves, microwaves, infrared, visible light, ultraviolet and X-rays.
Quantum mechanical waves• Main article: Schrödinger equation• See also: Wave function• The Schrödinger equation describes the wave-like behavior of
particles in quantum mechanics. • Solutions of this equation are wave functions which can be used to
describe the probability density of a particle.
de Broglie waves• Main articles: Wave packet and Matter wave• Louis de Broglie postulated that all particles with momentum have a
wavelength
A propagating wave packet; in general, the envelope of the wave packet moves at a different speed than the constituent waves.
• where h is Planck's constant, and p is the magnitude of the momentum of the particle. This hypothesis was at the basis of quantum mechanics. Nowadays, this wavelength is called the de Broglie wavelength. For example, the electrons in a CRT display have a de Broglie wavelength of about 10−13 m.
• A wave representing such a particle traveling in the k-direction is expressed by the wave function as follows:
• where the wavelength is determined by the wave vector k as:and the momentum by:
• However, a wave like this with definite wavelength is not localized in space, and so cannot represent a particle localized in space. To localize a particle, de Broglie proposed a superposition of different wavelengths ranging around a central value in a wave packet, a waveform often used in quantum mechanics to describe the wave function of a particle.
• In a wave packet, the wavelength of the particle is not precise, and the local wavelength deviates on either side of the main wavelength value.
• In representing the wave function of a localized particle, the wave packet is often taken to have a Gaussian shape and is called a Gaussian wave packet. Gaussian wave packets also are used to analyze water waves.
• For example, a Gaussian wavefunction ψ might take the form:
• at some initial time t = 0, where the central wavelength is related to the central wave vector k0 as λ0 = 2π / k0.
• It is well known from the theory of Fourier analysis, or from the Heisenberg uncertainty principle (in the case of quantum mechanics) that a narrow range of wavelengths is necessary to produce a localized wave packet, and the more localized the envelope, the larger the spread in required wavelengths.
• The Fourier transform of a Gaussian is itself a Gaussian. Given the Gaussian:
• the Fourier transform is:
• The Gaussian in space therefore is made up of waves:
• That is, a number of waves of wavelengths λ such that kλ = 2 π.• The parameter σ decides the spatial spread of the Gaussian along
the x-axis, while the Fourier transform shows a spread in wave vector k determined by 1/σ. That is, the smaller the extent in space, the larger the extent in k, and hence in λ = 2π/k.
Gravity waves• Gravity waves are waves generated in a fluid medium or at the
interface between two media when the force of gravity or buoyancy tries to restore equilibrium. A ripple on a pond is one example.
• Gravitational waves• Main article: Gravitational wave• Researchers believe that gravitational waves also travel through
space, although gravitational waves have never been directly detected. Gravitational waves are disturbances in the curvature of spacetime, predicted by Einstein's theory of general relativity.
• WKB method• Main article: WKB method• See also: Slowly varying envelope approximation• In a nonuniform medium, in which the wavenumber k can depend on
the location as well as the frequency, the phase term kx is typically replaced by the integral of k(x)dx, according to the WKB method.
• Such nonuniform traveling waves are common in many physical problems, including the mechanics of the cochlea and waves on hanging ropes.
Animation showing the effect of a cross-polarized gravitational wave on a ring of test particles
• Audience wave• Beat waves• Capillary waves• Cymatics• Doppler effect• Envelope detector• Group velocity• Harmonic
• Inertial wave• Index of wave articles• List of waves named after people• Ocean surface wave• Phase velocity• Reaction-diffusion equation• Resonance• Ripple tank
• Rogue wave• Shallow water
equations• Shive
wave machine• Sound wave• Standing wave• Transmission
medium• Wave turbulen
ce• Waves in plas
mas
Spectral analysisSpectral analysis or Spectrum analysis is analysis in terms of a spectrum of frequencies or related quantities such as energies, eigenvalues, etc. In specific areas it may refer to:• Spectroscopy in chemistry and physics, a method of analyzing the
properties of matter from their electromagnetic interactions• Spectral estimation, in statistics and signal processing, an algorithm
that estimates the strength of different frequency components (the power spectrum) of a time-domain signal. This may also be called frequency domain analysis
• Spectrum analyzer, a hardware device that measures the magnitude of an input signal versus frequency within the full frequency range of the instrument
• Spectral theory, in mathematics, a theory that extends eigenvalues and eigenvectors to linear operators on Hilbert space, and more generally to the elements of a Banach algebra
• In nuclear and particle physics, gamma spectroscopy, and high-energy astronomy, the analysis of the output of a pulse height analyzer for characteristic features such asspectral line, edges, and various physical processes producing continuum shapes
• Wind and Wave Forces, Computational Hydrodynamics
Extreme wave impact on offshore platforms and coastal structures• Extreme waves and their impact loading on fixed and floating structures, like production and
offloading platforms, coastal protection systems and offshore wind farms, have long been subjects that could only be studied with experimental methods.
• The complex, highly non-linear wave kinematics could not be predicted with existing numerical methods (CFD).
• However, recent research by the partners of this proposal has shown that new hydrodynamic models based on the Navier–Stokes equations, in combination with a VOF-based method for the description of the free-surface dynamics, are able to predict such effects.
• In two foregoing projects a two-phase flow model has been developed. • Good progress has been made in predicting load forces for flow phenomena like sloshing, green
water loading and wave run-up; also the cushioning effects of entrapped air is included in the model. • On the other hand, experimental validation has revealed aspects in the numerical model that need
further extension and improvement.
This relates to the physical and mathematical aspects of: • Extreme waves and their propagation (to better model the oncoming waves until impact).• Effect of viscosity in shear layers (to model small-scale flow details of the endangered
construction). • Interactive vessel-wave dynamics (to describe the coupled dynamics of wave and vessel
motion). • Although first priority is on accurate description of physical phenomena, i.e. the functionality
of the simulation method, for its daily use also computational efficiency is relevant. • Thus another action will be:
• Speed-up through local grid refinement (to limit the number of grid points) and parallelization. • The proposalwill focus on these vitaland complex modelling issues, and to their computational
implementation. • Experimental validation with respect to the above-mentioned physical phenomena will also form part
of the project.
• Utilization The 2004/2005 hurricanes Ivan, Katrina and Rita in the Gulf of Mexico have refocussed attention to extreme waves and their consequences for coastal defense systems and offshore structures.
• These hurricanes created huge devastations both on land and at sea, causing many casualties and huge economic damage.
• A better understanding of the consequences of these forces of nature is urgently needed.
• Even without hurricane conditions, the impact of extreme waves can be a serious threat to the land behind the dikes and its inhabitants.
• Also the safety and operability of offshore vessels and the well-being of their crews are jeopardized.
• As indicated, hydrodynamic wave loading on structures plays an important role in areas such as coastal protection, harbour design, offshore constructions (production and offloading platforms, offshore wind farms), and mooring systems.
• In these areas there is a need for knowledge on the prediction and predictability of hydrodynamic loading, which can be required up to a very detailed level (max./min. pressures, duration of pressure peaks, shear stresses, etc.).
• In close cooperation with MARIN (Wageningen) and Deltares (formerly Delft Hydraulics, Delft) two application areas are envisaged in this project.
• On the one hand, the simulation methods to be developed will be applied in predicting impact forces on coastal protection structures.
• On the other hand, the simulation methods will be applied to predict the wave forces on offshore platforms and offloading vessels.
Generic examples of the physical phenomena encountered are: • Wave run-up against fixed and floating platforms and coastal protection systems. • Wave impact loading on breakwaters and dikes. • Sloshing of the cargo inside the hull (e.g. LNG carriers). • Green water loading: sudden and extremely violent water motions on the deck. • The proposal will be a further step forward from the ComFLOW-2 joint-industry project (JIP) that is
currently being carried out with 20 industrial partners from the offshore industry (oil companies, ship yards, etc.), under coordination of MARIN.
• Recently Deltares (then Delft Hydraulics) also joined this consortium to cover coastal protection applications.
• Currently a follow-up JIP is being defined: ComFLOW-3. • It will focus on the validation of the developed numerical models for advanced engineering applications
by improved functionality and speed-up of the algorithms. • The forelying proposal will be strongly intertwined with the ComFLOW-3 project.
Engineering challenge Offshore industry • Now that the use of ship-type offshore units for the production and storage of oil has become common, these
units should be able to survive the most critical environmental conditions occurring as they are unable to flee for approaching storms.
• This requires an adequate mooring system, but also attention to the potential problem of green water on the deck.
• While tankers have an almost empty deck, decks of these floating production and offloading platforms (FPSOs) carry a lot of sensitive equipment.
• Consequently green water can cause damage to the vessel’s superstructure and equipment, such as the fluid swivels, piping, turret structure, control valves, emergency systems, fire detection/protection systems, and cable trays.
• Similar problems can occur due to wave loading on offshore windmills, often gathered together in large wind farms.
• Extreme hydrodynamic loads may cause severe damage to their support structures, and herewith jeopardize their operability.
• Studies show a steady increase of these green water incidents in offshore operations.
• The recent hurricanes in the Gulf of Mexico have put broad attention to these forces of nature.
Some major incidents: • An exampleis waveimpact damageto the bowofthe Schiehallion FPSO in
November 1998 resulting in an evacuation of the personnel and expensive offshore hull repairs and an upgrade of the complete bow structure.
• Estimated costs are 87 mill. Euro (78 mill. Euro loss of oil production, 6 mill. Euro damage reparation costs and 3 mill. Euro operational costs without income).
• – Hurricanes Ivan, Katrina and Rita have had a devastating influence, not only on land but also at sea.
• Many offshore platforms were thrown from their anchors and severely damaged. E.g. the Ensco offshore platform (Fig. 1) was found 40 miles from where it was originally anchored after Ivan.
• As another example, the damage from Katrina on the Shell Mars tension leg platform is shown in Fig. 11.
• The problems associated with the behavior of floating structures in extreme wave conditions are experienced by all operatorsof such vesselsin open seas.
• As such, the industry has recognized that, being a problem affecting all operators, it should be addressed jointly.
• This is reflected in the high degree of interest which is being shown by industry with respect to joint industry projects (JIP) in this field.
• As a first attempt, in 1997, a JIP on ‘FPSO Green Water Loading’ was initiated by MARIN.
• The problem was studied in detail using an extensive series of model tests. • The main objective of this study, supported by a wide range of companies in the
offshore industry, was to develop methods for evaluating green water on ship-type offshore structures based on a clear description of the green water physics.
• It was concluded that in all phases of the green water problem non-linear and highly complex phenomena occur.
• As a follow-up, the already described SAFE-FLOW JIP (in 2000) and ComFLOW-2 JIP (in 2004) were defined to develop methodology to numerically simulate the highly non-linear green water events and the consequences of these green water loadings (see Section 3.1.2).
• The present proposal is intended to contribute significantly towards the solution of outstanding issues resulting from the above-mentioned JIPs.
• As such, the proposal will be complementary to the third-phase JIP project ComFLOW-3 (see Section 4.3.1) for which support is being sollicited from the offshore industry.
• Many of the ComFLOW-2 participants have already expressed their interest to contribute to the continuation of this research and a project proposal has been issued for their consideration and comments.
Buoyancy and Stability
Buoyancy and Stability• What is the vertical force acting on a body which is completely submerged in a
fluid? • Answer to such a question can be very well found in the theory developed in
the previous section. • Archimedes seems to have discovered the laws concerning submerged bodies
as well as floating bodies. • What is well known as Archimedes principle states • The vertical buoyant force experienced by a body immersed in a fluid is equal
to the weight of the fluid displaced.• A floating body displaces its own weight of the fluid.
• Proof is straight forward. Consider an elemental volume within the immersed body as shown in Fig.2.16 . Now the buoyant force is given by,
• where is the area of cross section of the elemental volume chosen. We have from Eq. 2.48
• It can be shown that the buoyant force, passes through the centroid of the displaced volume as shown in Fig.2.17. The point where this force acts is called "Center of Buoyancy", denoted as
• The above result holds good even in the case of a partially submerged body i.e., a floating body. It is assumed that part of the body above the liquid level is in air. The weight of air displaced as a consequence is ignored. (Fig. 2.18). For this case as well,
• The theory developed so far does hold good in case of a fluid for which specific gravity is not a constant, a layered fluid for example. However now the buoyant force may not act at the centroid of the displaced volume.
• The theory developed is also applicable where the fluid involved is a gas, say air.
• Convection currents established in atmosphere depend upon the buoyant forces generated.
Geotechnical Engineering for offshore structure
• Offshore geotechnical engineering is a sub-field of geotechnical engineering.
• It is concerned with foundation design, construction, maintenance and decommissioning for human-made structures in the sea.
• Oil platforms, artificial islands and submarine pipelines are examples of such structures.
• The seabed has to be able to withstand the weight of these structures and the applied loads.
• Geohazards must also be taken into account.
• The need for offshore developments stems from a gradual depletion of hydrocarbon reserves onshore or near the coastlines, as new fields are being developed at greater distances offshore and in deeper water, with a corresponding adaptation of the offshore site investigations.
• Today, there are more than 7,000 offshore platforms operating at a water depth up to and exceeding 2000 m.
• A typical field development extends over tens of square kilometers, and may comprise several fixed structures, infield flowlines with an export pipeline either to the shoreline or connected to a regional trunkline.
Platforms offshore Mexico.
Differences between onshore and offshore geotechnical engineering.• An offshore environment has several implications for geotechnical
engineering. These include the following:• Ground improvement (on the seabed) and site investigation are expensive.• Soil conditions are unusual (e.g. presence of carbonates, shallow gas).• Offshore structures are tall, often extending over 100 metres (330 ft)
above their foundation.• Offshore structures typically have to contend with significant lateral loads
(i.e. large moment loading relative to the weight of the structure).
• Cyclic loading can be a major design issue.• Offshore structures are exposed to a wider range of geohazards.• The codes and technical standards are different from those used for
onshore developments.• Design focuses on ultimate limit state as opposed to deformation.• Design modifications during construction are either unfeasible or very
expensive.• The design life of these structures often ranges between 25–50 years.• The environmental and financial costs in case of failure can be higher.
The offshore environment• Offshore structures are exposed to various environmental loads: wind
, waves, currents and, in cold oceans, sea ice and icebergs. • Environmental loads act primarily in the horizontal direction, but also
have a vertical component. • Some of these loads get transmitted to the foundation (the seabed).
The nature of the soilFollowing are some to the features characterizing the soil in an offshore environment:• The soil is made up of sediments, which are generally assumed to be in a saturated
state – saline water fills in the pore space.• Marine sediments are composed of detrital material as well as remains of marine
organisms, the latter making up calcareous soils.• Total sediment thickness varies on a regional scale – it is normally higher near the
coastline than it is away from it, where it is also finer grained.• In places, the seabed can be devoid of sediment, due to strong bottom currents.• The consolidation state of the soil is either normally consolidated (due to slow
sediment deposition), overconsolidated (in places, a relic of glaciation) or underconsolidated (due to high sediment input).
Metocean aspects• Wave forces induce motion of floating structures in all six degrees of freedom – they are a major
design criterion for offshore structures. • When a wave’s orbital motion reaches the seabed, it induces sediment transport. This only
occurs to a water depth of about 200 metres (660 ft), which is the commonly adopted boundary between shallow water and deep water.
• In shallow water, waves may generate pore pressure build-up in the soil, which may lead to flow slide, and repeated impact on a platform may cause liquefaction and loss of support.
• Currents are a source of horizontal loading for offshore structures. Because of the Bernoulli effect, they may also exert upward or downward forces on structural surfaces and can induce the vibration of wire lines and pipelines.
• Currents are responsible for eddies around a structure, which cause scouring and erosion of the soil. There are various types of currents: oceanic circulation, geostrophic,tidal, wind-driven, and density currents.
• Wind, wave and current regimes can be estimated from meteorological and oceanographic data, which are collectively referred to as metocean data.
• Earthquake-induced loading can also occur – they proceed in the opposite direction: from the foundation to the structure. Depending on location, other geohazards may also be an issue.
• All of these phenomena may affect the integrity or the serviceability of the structure and its foundation during its operational lifespan – they need to be taken into account in offshore design.
Geohazards• Geohazards are associated with geological activity, geotechnical features and
environmental conditions. Shallow geohazards are those occurring at less than 400 metres (1,300 ft) below the seafloor.
• Information on the potential risks associated with these phenomena is acquired through studies of the geomorphology, geological setting and tectonic framework in the area of interest, as well as with geophysical and geotechnical surveys of the seafloor.
• Examples of potential threats include tsunamis, landslides, active faults, mud diapirs and the nature of the soil layering (presence of karst, gas hydrates, carbonates). In cold regions, gouging ice features are a threat to subsea installations, such as pipelines.
• The risks associated with a particular type of geohazard is a function of how exposed the structure is to the event, how severe this event is and how often it occurs (for episodic events). Any threat has to be monitored, and mitigated for or removed.
Two types of seismic profiles (top: chirp; bottom: Water gun) of a fault within the seabed in the Gulf of Mexico.
Worldwide distribution of gas hydrates, which are another potential hazard for offshore developments.
• Site investigation• Offshore site investigations are not unlike those conducted onshore
(see Geotechnical investigation). They may be divided into three phases:• A desk study, which includes data compilation.• Geophysical surveys, either shallow and deep seabed penetration.• Geotechnical surveys, which includes sampling/drilling and in situ
testing.
Desk study• In this phase, which may take place over a period of several months
(depending on project size), information is gathered from various sources, including reports, scientific literature (journal articles, conference proceedings) and databases, with the purpose of evaluating risks, assessing design options and planning the subsequent phases.
• Bathymetry, regional geology, potential geo hazards, seabed obstacles and metocean data are some of the information that are sought after during that phase.
An example of a side scan sonar, a device used to survey the seabed.
A 3-D image of the Monterey Canyon system, an example of what can be obtained from multibeam echosounders.
Geophysical surveys• Geophysical surveys can be used for various purposes. • One is to study the bathymetry in the location of interest and to
produce an image of the seafloor (irregularities, objects on the seabed, lateral variability, ice gouges, …).
• Seismic refraction surveys can be done to obtain information on shallow seabed stratigraphy – it can also be used to locate material such as sand and gravel for use in the construction of artificial islands.
• Geophysical surveys are conducted from a research vessel equipped with sonar devices and related equipment, such as single-beam and multibeam echosounders, side-scan sonars, ‘towfish’ and remotely operated vehicles (ROVs).
• For the sub-bottom stratigraphy, the tools used include boomers, sparkers, pingers and chirp.
• Geophysical surveys are normally required before conducting the geotechnical surveys; in larger projects, these phases may be interwoven.
Geotechnical surveys• Geotechnical surveys involve a combination of sampling, drilling, in situ testing as well
as laboratory soil testing that is conducted offshore and/or onshore. • They serve to ground truth the results of the geophysical investigations; they also
provide a detailed account of the seabed stratigraphy and soil engineering properties. • Depending on water depth and metocean conditions, geotechnical surveys may be
conducted from a dedicated geotechnical drillship, a semi-submersible, a jackup rig, a large hovercraft or other means.
• They are done at a series of specific locations, while the vessel maintains a constant position.
• Dynamic positioning and mooring with four-point anchoring systems are used for that purpose.
• Shallow penetration geotechnical surveys may include soil sampling of the seabed surface or in situ mechanical testing.
• They are used to generate information on the physical and mechanical properties of the seabed.
• They extend to the first few meters below the mudline. • Surveys done to these depths, which may be conducted at the same
time as the shallow geophysical survey, may suffice if the structure to be deployed at that location is relatively light.
• These surveys are also useful for planning subsea pipeline routes.• The purpose of deep penetration geotechnical surveys is to collect
information on the seabed stratigraphy to depths extending up to a few 100 meters below the mudline.
• These surveys are done when larger structures are planned at these locations.
• Deep drill holes require a few days during which the drilling unit has to remain exactly in the same position (see dynamic positioning).
Sampling and drilling• Seabed surface sampling can be done with a grab sampler and with a
box corer. • The latter provides undisturbed specimens, on which testing can be
conducted, for instance, to determine the soil’s relative density, water content and mechanical properties.
• Sampling can also be achieved with a tube corer, either gravity-driven, or that can be pushed into the seabed by a piston or by means of a vibration system (a device called a vibrocorer).
• Drilling is another means of sampling the seabed. It is used to obtain a record of the seabed stratigraphy or the rock formations below it.
• The set-up used to sample an offshore structure's foundation is similar to that used by the oil industry to reach and delineate hydrocarbon reservoirs, with some differences in the types of testing.
• The drill string consists of a series of pipe segments 5 inches (13 cm) in diameter screwed end to end, with a drillbit assembly at the bottom.
• As the dragbit (teeth extending downward from the drillbit) cut into the soil, soil cuttings are produced.
• Viscous drilling mud flowing down the drillpipe collects these cuttings and carry them up outside the drillpipe.
• As is the case for onshore geotechnical surveys, different tools can be used for sampling the soil from a drill hole, notably "Shelby tubes", "piston samplers" and "split spoon samplers".
Box corer for extracting soil samples from the seabed.
A gravity-driven soil sampler, used for coring the seabed.
Two types of drilling systems: a semi-submersible (left) and a drillship (right).
In situ soil testing• Information on the mechanical strength of the soil can be obtained in
situ (from the seabed itself as opposed to in a laboratory from a soil sample).
• The advantage of this approach is that the data are obtained from soil that has not suffered any disturbance as a result of its relocation.
• Two of the most commonly used instruments used for that purpose are the cone penetrometer (CPT) and the shear vane.
• The CPT is a rod-shaped tool whose end has the shape of a cone with a known apex angle (e.g. 60 degrees).
• As it is pushed into the soil, the resistance to penetration is measured, thereby providing an indication of soil strength.
• A sleeve behind the cone allows the independent determination of the frictional resistance. Some cones are also able to measure pore water pressure.
• The shear vane test is used to determine the undrained shear strength of soft to medium cohesive soils.
• This instrument usually consists of four plates welded at 90 degrees from each other at the end of a rod.
• The rod is then inserted into the soil and a torque is applied to it so as to achieve a constant rotation rate.
• The torque resistance is measured and an equation is then used to determine the undrained shear strength (and the residual strength), which takes into account the vane’s size and geometry.
Diagram showing the principle of a cone penetrometer to obtain the soil's strength profile.
Diagram showing the principle of a shear vane to measure the soil's peak strength and residual strength.
• Offshore structures and geotechnical considerations• Offshore structures are mainly represented by platforms, notably jackup rigs,
steel jacket structures and gravity-based structures.
• The nature of the seabed has to be taken into account when planning these developments.
• For instance, a gravity-based structure typically has a very large footprint and is relatively buoyant (because it encloses a large open volume).
• Under these circumstances, vertical loading of the foundation may not be as significant as the horizontal loads exerted by wave actions and transferred to the seabed.
• In that scenario, sliding could be the dominant mode of failure.
• A more specific example is that of the Woodside "North Rankin A" steel jacket structure offshore Australia.
• The shaft capacity for the piles making up each of the structure's legs was estimated on the basis of conventional design methods, notably when driven into siliceous sands.
• But the soil at that site was a lower capacity calcareous sand. • Costly remediation measures were required to correct this oversight.• Proper seabed characterization is also required for mooring systems. • For instance, the design and installation of suction piles has to take into
account the soil properties, notably its undrained shear strength. • The same is true for the installation and capacity assessment of plate anchors.
Submarine pipelines• Main article: Submarine pipeline• Submarine pipelines are another common type of man-made
structure in the offshore environment. These structures either rest on the seabed, or are placed inside a trench to protect them from fishing trawlers, dragging anchors or fatigue due current-induced oscillations. Trenching is also used to protect pipelines from gouging by ice keels. In both cases, planning of the pipeline involves geotechnical considerations.
• Pipelines resting on the seabed require geotechnical data along the proposed pipeline route to evaluate potential stability issues, such as passive failure of the soil below it (the pipeline drops) due to insufficient bearing capacity, or sliding failure (the pipeline shift sideways), due to low sliding resistance.
• The process of trenching, when required, needs to take into account soil properties and how they would affect ploughing duration.
• Buckling potential induced by the axial and transverse response of the buried pipeline during its operational lifespan need to be assessed at the planning phase, and this will depend on the resistance of the enclosing soil.
• Civil engineering• Earth materials• Floating wind turbine• Geohazard• Geotechnical engineering• Geotechnical investigation• Geotechnics
• Ocean• Offshore construction• Offshore drilling• Offshore (hydrocarbons)• Oil platform• Seabed• Seabed gouging by ice
• Sediment• Soil• Soil mechanics• Submarine pipeli
ne• Subsea
Offshore design philosophy
• Delta House has potential to enhance offshore design philosophy• 'One-size-fits-most' approach could transform platform design
Delta House is a semisubmersible FPS that will have an initial production capacity of 80,000 b/d of oil and 200 MMcf/d of gas. (Photos courtesy Audubon Engineering Solutions)
• Another revolution is in the works for offshore oil and gas production - one caused by a new semisubmersible production platform named after the home of the boisterous college fraternity in the 1978 comedic film, "Animal House."
• The 21st-century Delta House is a deepwater floating production system, built to extract hydrocarbons from the Mississippi Canyon area in the Gulf of Mexico.
• Average water depth is approximately 4,500 ft (1,372 m), and reservoirs range from 12,000 to 18,500 ft (3,658 to 5,629 m).
• The facility was designed for a production rate of 80,000 b/d of oil, 200 MMcf/d (5.7 MMcm/d) of gas, and 40,000 b/d of water. First oil is expected in mid-2015.
• The field development is an example of how independent, privately-held companies that once focused on shallow-water opportunities are now wading into deeper waters.
• Moreover, these companies seem to be taking their fast-moving, "shallow-water" ways with them into water depths that have long been the domain of the deep-pocketed majors.
• Reasons for the transformative nature of Delta House go back to early 2010, when a group of joint venture partners began to realize the potential of their recently-acquired portfolio of leases.
• The challenge was how to drill them in less than 36 months before the 20 or so deepwater leases timed out.
• The one-time presidential lease suspension of operations reset the clock to give more time, but it would still require a big effort to maintain the leases.
Getting a head start• One of the distinctions used in the case of Delta House was project scheduling. • In addition to the leasehold considerations, participating company LLOG Exploration Co. • (LLOG) has long had a priority of generating a speedy return on investment (ROI). To meet its
ROI goals and secure future investments elsewhere, the company developed an accelerated production schedule for the project.
• It also had to meet the requirements of regulatory authorities, including the Bureau of Safety and Environmental Enforcement and the US Coast Guard as well as the classification requirements of Det Norske Veritas.
• To accomplish this, LLOG worked with external resources, such as Audubon Engineering Solutions, which served as the topsides engineering contractor on the project.
• Most major oil and gas companies active in offshore activities will take the time-honored approach, which involves discovery, delineation wells, and studies of the reservoir characteristics.
• This is followed by front-end engineering and design (FEED), requesting several bids for production platform types, which may include provision for a drilling rig included on the production platform.
• Only then, detailed design and construction would begin.
• The goal of LLOG's approach was to shorten the timeline for faster production.
• This included starting work on the engineering of the production platform even before a discovery was made.
• The designers' purpose was to develop a platform that could be expected to work within a range of reservoir characteristics.
• It was expected that the platform would be working with more than one field, combining hydrocarbons from a variety of wells.
The single-lift of the topsides was required to achieve LLOG's accelerated project schedule.
• Delta House's design can work with crude ranging from 28 to 37° API. The platform and its equipment could work slightly outside that range with some cost to capacity.
• The company felt that the benefits of getting to production faster was worth the potential downside of having a platform that was not customized exactly to the characteristics of the reservoirs from which it would be extracting hydrocarbons.
• LLOG and Audubon Engineering Solutions estimated that production could start three years sooner than with the traditional "Big Oil" approach.
• Another reason the company was able to shorten the timeline compared to the usual approach taken by the major oil companies is the extreme detailed requirements that the larger companies have for their deep water platforms.
• While many of these specifications have their value, they also have the tendency to slow down the design and construction of platforms. As a smaller, newer company, LLOG does not have this legacy of requirements and was able to develop its own specifications for the project.
• These specifications meet or exceed industry standards as well as the regulations of all applicable authorities.
One-size-fits-most• When the platform was in the design phase, LLOG did not possess the
specific characteristics of the reservoirs, particularly the profile of the hydrocarbons.
• If the processing requirements were greater than the Delta House name plate of 80,000 b/d, LLOG decided it would be better to build a second production platform than to revise plans in order to build a single larger-capacity platform.
• If the hydrocarbon flow turned out to be less than expected, the company would be able to shop the platform's capacity around so other companies' wells in the area could be tied into the facility.
• As such, Audubon Engineering Solutions used the "one-size-fits-most" design that would work with a wide range of hydrocarbons and sizes of reservoirs and be able to meet LLOG's stringent timeline.
• During the design, Audubon Engineering Solutions' project team collaborated with the fabricators and vendors to ensure equipment construction was completed on time and in accordance with specifications.
• The one-size-fits-most design has other benefits as well. • With a platform design that can work in a wide range of circumstances,
the company can use the same design on future platforms. • Because detailed design has already been done and areas for possible
improvement noted, a second similar platform will be relatively easy to build.
• Delta House was designed for the demanding environment of the Gulf of Mexico, where the risk of hurricanes sets a high standard for safety.
• Lessons learned in its design can be applied to other offshore environments with fewer weather-related risks.
Single-level topsides• The Delta House integrated structural deck and topsides facility was
designed as a single-level platform, unlike the three-level configuration of many offshore platforms.
• On a multi-level platform, if a piece of equipment for a lower level is delayed, it is impossible to float over that area of the deck until that item arrives and can be installed.
• A single, "Texas-style" deck means that there were fewer items on a critical path.
• Accordingly, Audubon Engineering Solutions designed the topsides so the construction could be completed entirely on the ground and then hoisted into place on the columns in a single lift.
• Being able to perform the equipment installation and the fitting of utilities, such as pipes and cabling, on the ground made construction easier- and thus cheaper - than having to do it 75 ft (23 m) above the water.
• The topsides also required complex calculations to ensure that the structure had a center of gravity (CG) that was very close to the geographic center of the platform, so the structure could be hoisted evenly and then lowered onto the columns.
• To do this, Audubon Engineering Solutions worked closely with hull designer EXMAR Offshore to check for design accuracy.
• Through the use of its plant design management system model and weight control program, Audubon Engineering Solutions was able to closely monitor the CG and make equipment location adjustments as required to maintain the CG within the acceptable tolerances.
• The company's design team also worked with Kiewit Offshore Services, the topsides' fabrication and integration contractor, to keep the topsides deck within the limited 10,000-ton (9,072-metric ton) lifting requirements of the heavy-lift device booms. 4 Kiewit Offshore Services and other equipment vendors supplied actual equipment weights during construction, and these weights were fed back into the weight control program.
• Simplification also applied to the chosen equipment. • Selections were made based on the ease of maintenance for
approximately 25 Delta House crew members. • This is in contrast to many platforms from major companies that may
have more than 100 personnel, particularly if the platform includes a drilling rig.
• In Delta House's case, the structure is only designed to be a production platform.
• Another benefit to the single-deck design is how the design can be applied to future projects.
• For example, if there is a need for a different size of quarters on a subsequent platform, the design will be relatively easy to modify in order to fit the quarters on the platform.
• Innovations such as these will not work for all circumstances. However, the lessons learned from the Delta House project may help usher in some advances that will make offshore oil and gas production more flexible in meeting changing conditions.
Codes, Standards and Regulations
Oil & Gas Projects Standards & Construction Codes & Standards
The ISO 9001 family - Global management standards (International Organization for Standardization)
Questions
1. Describe 7 different offshore structures2. What effect has wind and sea waves on load on offshore structures?3. Describe structure reliability for offshore structures4. Mention important basics for design for offshore structures5. Describe design methodology for floating structures
Question X Y Z
A Jack Up: Depth limit 100 m 150 m 200 m
B Condeep plattform was invented Stavanger Aberdeen Dubai
C FPSO Production ship Drilling ship Production plattform
D Software used in the platforms design Olav Oscar Harald
E FEED Final End Engineering Design
Front End Engineering Development
Front End Engineering Design
F NPT Non Productive Time Non Progressive Time Non Process Time
Question X Y Z
G KPI Key Productive Indicators
Key Performance Indicators
Key Presentation Indicators
H PRT Petroleum Reserve Tax
Petroleum Royal Tax
Petroleum Revenue Tax
I Capex Capital expenditure Capital expences Complete expenditure
J E&P Enhancement Production
Exploration and production
Exploration and petroleum
K OPEC Organisation of Petroleum Exporting
Countries
Organisation of Petroleum Exporting
Companies
Organisation of Petroleum Equipment Countries
L ROV Remotely Operation Venue
Remotely Operated Vehicle
Real Organisation Vehicle