research into good design practice for reels

MSc SUBSEA ENGINERING

NAME: TEICA FLORIAN TEICA

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RESEARCH INTO

GOOD DESIGN PRACTICE FOR

REELS

MSc Subsea Engineering 2011-2012

University of Aberdeen

Student Name: Mircea Florian Teica

Supervisors

Academic: Dr. Mohammed Salah-Eldin Imbabi

Industry: Marius Popa



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Abstract

This dissertation proposes a study of the current design methods relevant to reels (LRFD and WSD) and discusses their particularities, limitations and how a reel could be designed according to each of them. The design method limitations are discussed in light of recent studies and findings in areas and for equipment similar to reels (i.e. winches).

In the second part, a reel is designed according to both design methods and the 2 sets of results are compared.

Finally, the “Conclusions and Recommendations” chapter summarizes the most important aspects of reel design, the areas where the accuracy of current standards needs improvement and highlights some areas where further studies may improve the current design practices.



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Table of contents

Chapter 1: Introduction 5

1.1 Scope of Work 8

Chapter 2: Design Methods 9

2.1 LRFD (Load Resistance Factor Design) Method 9

2.2 WSD (Work Stress Design) Method 10

2.3 Additional Standards 10

2.4 Comments 11

Chapter 3: Design by LRFD Method 12

3.1 Load Types 12

3.2 Load Combinations 14

3.3 Comments 16

Chapter 4: Design by WSD Method 17

4.1 Load Types 18

4.2 Load Cases 20

Chapter 5: Discussion on LRFD and WSD Methods 21

5.1 Load Combination Factors for LRFD Method 21

5.2 Utilization Factors for LRFD and WSD Methods 23

5.3 Hoop Stress and Flange Pressure 25

5.4 Rope Factor (C) 29

5.4.1 “Large Wire Rope Mooring Winch Drum Analysis and Design Criteria” Study 29

5.4.2 “Problems Related to the Design of Multilayer Drums for Synthetic and Hybrid Ropes” Study 30



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5.5 Spooling Tension – Friction Factor Relationship; Friction between Product Layers 31

5.5.1 “AM16 Improvement in the Design of Winches” Study 34

5.5.2 “Improvement in Winch Design Guide AM11” Study 35

5.6 Comments 36

Chapter 6: FEA Analysis 37

6.1 Reel Design 37

6.2 Boundary Conditions 38

6.3 Load Scenarios 42

6.4 Operational Limitations 44

6.5 Load Cases 47

6.6 Load Combinations 54

Chapter 7: Results and Interpretation 55

7.1 Results of the Analysis 55

7.1.1 Flange Spokes 55

7.1.2 Drum Staves 56

7.2 Comments 57

Chapter 8: Conclusions and Recommendations 59

Bibliography 61

Appendix 1: Load Cases 63

Appendix 2: Risk Assessment 72

Plagiarism Cover Sheet 74



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Chapter 1: Introduction

The need for fast and undisrupted communication and transportation of resources (i.e.

electricity, oil, gas, etc.) over large distances, between continents or countries separated by seas

could be solved, as technology evolved through the use of pipelines and electric cables.

For example, during World War II, after allied forces disembarked in Normandy, their

planned advance into German occupied territories could have been granted to a halt if they had

ran out of fuels. Since oil tankers would have been easy targets for enemy bombers, a different

solution should have been found.

Military engineers came up with the solution of building a pipeline that could link oil

supply reservoirs on British soil with unloading stations on the French coast, thus ensuring a safe,

quick and continuous supply of fuels. But how to build and lay pipelines in a very short period of

time, in war conditions and in some

of the most unfriendly waters – the

English Channel? The answer was

to build the pipe onshore, the

transport it offshore and lay it to the

seabed. Transportation would have

been possible by spooling the

innovative flexible pipelines onto

giant floating “conundrums” [21]

that could be tugged behind vessels,

so that the pipe could be unspooled

as they approached France. Figure 1.1 Floating Reel Towed by Allied War Ship [21]

The laying of the pipe went according to plan and the idea proved so good, that allied

decided to continue “Operation Pluto” and lay a second pipe.[1][2]

Making a step forward in time, up to present days, the need for transporting products,

energy and information increased exponentially, especially in the Oil and Gas industry. As easily

accessible oil reserves have mostly been depleted, industry now focuses on the deep water fields.



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Deep waters mean larger depths, increased distances to be covered, longer pipes and umbilicals

to be laid and larger vessels and equipment need for their transportation and installation.

Reels have remained the only way of transporting long sections of umbilicals and cables

and started to play an increasingly important role, as flexible pipe became more popular due to

its advantages over traditional pipe systems: controlled fabrication onshore and increased laying

speeds offshore.

But what exactly are reels and what makes them so important?

Reels are objects around which long, flexible products are winded for storage [1]. Their

storage capacity can vary from a few hundred kilograms to more than 300 tones, so the larger

ones can be more than 11 meters high and 9 meters wide. They are made up of a horizontal,

cylindrical drum, on which the product is spooled and 2 side, vertical flanges that help keeping

the product in place.

Reels that make the object of this study are the larger ones, used for transporting

increased lengths and weights of product offshore, being able to resist many spooling/unspooling,

lifting and transportation cycles for an extended period of time. Therefore, they can be described

as portable offshore units that must comply with structural and safety regulations.

Figure 1.2, Courtesy of Forsyths [20]



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Even though their role is primarily simple and they can be described as simple as “dumb

pieces of metal”, in reality things are a little bit different: often used to carry payloads exceeding

300 tones, their design must be flexible enough to accommodate further improvements or

different types of products, with different material characteristics that would require larger

spooling tensions or that could be laid at higher speeds. For instance, large reels are not designed

specifically for one job or to operate just in a certain location. Often, the rating of a reel can be

increased just by adding some extra stiffeners. Or their drum can be fitted with intermediate

spacers – partitions – (as shown in figure 1.3) to be able to transport 2 or 3 products at a time,

sometimes with different characteristics: weight, rigidity, etc. Furthermore, they need to be able

to be operated throughout a long service life: due to their size and weight, they are quite difficult

to build and transport and, most important, expensive.

Figure 1.3, Courtesy of Oceaneering [17]

Their design must also make best use of the material characteristics; design concepts and

features must ensure a final product that is not too heavy or too flexible. Overdesigning has

serious implications especially for large pieces of equipment where 1mm of additional wall

thickness could mean 1 tone or more when applied to the whole structure. This does not affect

only the material price and building costs (i.e. a plate too thick will be more expensive to buy,

manufacture and will require and increased force to be bend in the final cylinder shape), but also

its service life. The thick plate would add more weight to the reel, which, in turn, will lead to



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reduced payload or increased transport costs on service ships. This means money lost at each trip

or, worse, other reels to be used for their more efficient design.

All these and other issues could be avoided through a good design. But the problem is

that there is no unified standard that could provide accurate and well documented guidance to an

engineer. They must consult numerous standards and recommended practice guides in order to

produce a design. This means that a coherent design, based on design factors and load cases

specifically adapted to reel particularities is almost impossible to achieve. The standards used for

reel design are mostly for general use or only marginally related to reels, and this often leads to

overly conservative solutions. Furthermore, the third party verifier’s job is even more difficult

and most of the times summarizes in just checking calculations and correct application of

designer’s assumptions, but cannot refer to an industry generally accepted set of rules that

regulate this grey area. In absence of these rules, the interpretation of the numerous existing

standards is highly subjective and dependent on the understanding of each engineer.

1.1 Scope of Work

So, in light of those written above, the scope of this dissertation is to summarize the

design approaches for reels based on 2 design methods (LRFD and WSD), point out the

differences, comment on the results and present its conclusions to the public. The final purpose

of this study would be to provide a good starting point for further researches that could

ultimately lead to the development of a “recommended design practice” for reels.



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Chapter 2: Design methods

The most utilized design methods used for reel design are LRFD and WSD. None of

them applies directly to reels. However, engineers have designed reels based on these 2

methodologies until now and are likely to do so in the future, so why the need for a new design

code?

2.1 LRFD (Load Resistance Factor Design) Method

In LRFD method, the safety of the design is obtained by multiplying the loads and

dividing the resistances with safety factors. Material resistances are divided with material safety

factors (i.e. γm= 1.15 in DNV standards), while loads are multiplied with factors higher than 1.

The value of these factors depends on the safety class desired (e.g. high, medium or low). [3][4]

The design approach is described in detail in DNV-OS-H102 “Marine Operations, Design

and Fabrication” and DNV-OS-C101 “Design of Offshore Steel Structures, General (LRFD

Method)”. However, for the purposes of this dissertation, from all load cases described in the 2

standards, only the Ultimate Limit State (ULS) and the Serviceability Limit State (SLS) will be

analyzed, particularly the way how the load factors are chosen in the load combinations.

SLS represents the normal operational mode for the offshore structure, in this case the

reel. The designers must ensure that during normal operation, the structure will not experience

loads that will cause high stresses (close to or above yield) or deformations, thus the structure

will not become unsuitable to perform its intended job. Usually, a deformations check (actual

deformations are compared with allowable ones) is performed to ensure the suitability of the

design.

ULS checks will ensure that the structure will not collapse under the worst case scenario

load combination that could be experienced during its service life. Basically, the ULS dictates

the strength requirements a structure must have, directly influencing its design. Thus, choosing

too conservative load factors will lead to an overdesigned structure that would do the job, but in

an uneconomical manner.



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So, it is of great importance to understand how the structure works, how it is going to be

loaded and operated, how to use the material and, in case of reels, the payload’s characteristics in

the benefit of the overall design.

LRFD method is used as a general design method, described in the 2 DNV standards.

They provide a general design methodology applicable to all structures involved in marine

operations

2.2 WSD (Work Stress Design) Method

WSD is a design method where safety is achieved by limiting equivalent Von Misses

stresses to a decreased value of the material’s characteristic strength. DNV’s no. 2.22 “Lifting

Appliances” standard is built around WSD method; the maximum allowable stresses should be

equal or lower than 85% of the yield strength of the material. In other words, the usage factor of

the material is limited to 0.85. [5][6]

This standard is specifically built on industry experience and good design practices for all

structures that can be defined as lifting appliances: cranes and their components, spreader beams,

lifting sets, etc. The part relevant for reel design is the one dedicated to winches. Although

winches and reels basically share the same constructive principles, the size difference and the

way they work during operation (from a structural perspective) makes them so different.

Lifting Appliances 2.22 standard provides a design procedure for winches and is

calibrated according to winch operating requirements and particularities. Reel designers can only

use to the part referring to drum and flange design.

2.3 Additional Standards

Additional design tools are borrowed from Eurocode 3, DNV-RP-C202 “Buckling

Strength of Shells” or other recognized and industry accepted design standards in order to cover

the necessary strength requirements of the new design.



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2.4 Comments

But all these existing standards do not cover the specifics of reels and their transported

products. For instance, none of the design methods take into account the increased number of

layers the product is spooled onto the drum and the benefic influence the layers have on the

overall drum strength; or how spooling tension in the product is transferred to the drum.

Recent studies lead to interesting conclusions that could help to improve the current way

of designing reels. Further on, in this paper there will be analyzed 2 of the most commonly used

reel designs. Also, there will be analyzed and explained the loads action on the reel, the various

load combinations identified during lifting, transportation and operation.

One of the designs will be chosen and analyzed in an FEA program according to load

cases built on LRFD and WSD principles and the 2 sets of results will be compared.

Ultimately, the conclusions and recommendations chapter will try to comment on the

ways the design of reels could be improved considering recent studies and findings and on the

results from the FEA analysis.



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Chapter 3: Design by LRFD Method

Design by LRFD method is covered by DNV-OS-H102 “Marine Operations, Design and

Fabrication” and DNV-OS-C101 “Design of Offshore Steel Structures, General (LRFD

Method)”. Since these standards provide general rules, applicable to all types of offshore

structures and installations, only the information relevant to reel design will be selected and

discussed.

3.1 Load Types

Every structure, regardless of its nature, will be likely to be subject to the combined effect of

at least 2 of the following load types:

� Permanent loads (G)

� Variable functional loads or Live loads (Q)

� Deformation loads (D)

� Environmental loads (E)

� Accidental loads

These loads will be combined into load combinations relevant to the function of each

individual structure and their effect on the proposed design will be analyzed. The suitability of

the design is confirmed as long as it is not prone to failure in any of the load situations

considered (the design load effect – Sd – does not exceed the design resistance – Rd). Of course,

a design is considered to be efficient in both economical and engineering terms when Sd is just

below Rd in ULS or resistance limit state. This ensures a rational and efficient way of using

material characteristics in favor of the overall design and avoids the overdesign of the

structure.[3][4]

The load types presented above will be grouped into load combinations (also called limit

states): ULS, SLS, FLS (fatigue limit state) and ALS (accidental limit state). Each load type will

be multiplied by a safety factor according to the possibility of that load type to occur during that

particular limit state and the impact it will have on the structure. [3][4]



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Although each load type includes many subcategories of loads to be considered, only

subcategories considered relevant to reels will be discussed:

• Permanent loads (G) – fixed loads that will not vary over the entire service life of the

structure

o Self weight of structure

o Weight of permanent installed equipment that cannot be removed (i.e. drum

partitions)

Weight estimate and weight distribution (thus an accurate estimation of the relative

position of the center of gravity) is of great importance especially for structures and

equipments subject to lifting operations.

• Variable functional loads (Q) – these loads can vary during the service life of the

structure; they can be defined as:

o Payload – stored materials, equipment (i.e. umbilicals, pipes, wires, etc.)

o Operation forces generated by reeling/unreeling of product

Again, the weight of the payload shall be accurately measured for the purposes of lifting

operations. The maximum value of the payload shall be considered for dimensioning the

structural elements.

• Deformation loads (D) – not relevant for reels

• Environmental loads (E) – loads generated by environmental factors, such as:

o Wind

o Waves,

that generate dynamic effects.

In the case of reels, wind loads shall be considered during lifting operations onshore.

Combined wind and wave effects will affect the transport vessel and that will translate into

vessel motions. These motions will generate inertia forces and should be considered when

designing the sea fastening arrangements (including the sea fastening geometry and structural

components that will need to handle the load induced stresses), as well as assessing their impact

on the reel structure and auxiliary equipment (towers, rollers) and their connections with the ship.

[3][4]



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• Accidental loads (A) – due to occurrence of unexpected events

o Dropped objects

Since reels can be considered pieces of equipment with transportation purposes and rather

simplistic operational function, the accidental loads considered relevant could only cause

damages that would endanger their good operation (large deformations of flanges or severe

damage to the flange-drum connection caused by large and heavy dropped objects).

Sea fastenings should be able to cope with sudden loads associated to minor ship

collisions (very unlikely).

3.2 Load Combinations

The load types described in 3.1 will be grouped into load combinations. The design loads

used in the load combinations are obtained by multiplying the characteristic loads with design

load factors. [3][4]

Relevant for reels are the following load combinations:

1. Onshore spooling – loads to be considered:

o Self weight of reel

o Weight of payload

o Spooling tension

2. Onshore storage – same as onshore spooling, only spooling tension will vary; because of

deformations in the anchoring devices (e.g. steel wires will increase in length due to

tension) that will hold the end part of the product after spooling, part of the spooling

tension in the last layers of product will decrease.

3. Onshore lifting:


o Weight of payload

o Storage tension

o Loads generated by wind



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4. Offshore operation – this load combination is defined as “ULS a)” in DNV-OS-H102; it

can also considered as SLS


o Weight of payload

o Spooling/unspooling tension

o Dynamic effects

5. Transit survival – this load combination is defined as “ULS b)” in DNV-OS-H102;


o Weight of payload

o Storage tension

o Increased dynamic effects compared to ULS a)

The most relevant load combinations that will be further considered are “Offshore

Operation” and “Transit Survival”. These will determine the overall strength requirements the

reel design must comply with.

The FLS will not be covered by this dissertation; ALS is not considered to be relevant to

reel design in general. [3][4]

DNV standards (OS-C101 and OS-H102) provide a table for the load factors to be used

for the 2 relevant ULS load combinations:

Load factors for ULS

Load

Condition

Load Categories

G Q D E A

a 1.3 1.3 1 0.7 N/A

b 1 1 1 1.3 N/A

Table 5-1 in DNV-OS-H102



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3.3 Comments

The standard allows for a decrease of the load factors applicable to G and Q loads in load

combination a) to a value of 1.2 if these load types are well defined. This lower value is usually

adopted by industry in reel design, as the self-weight of reels, spooling tension and payload are

clearly stated. [DNV OS-C101, Section 2, B402]

Also, according to DNV OS-C101, Section 2, B404, the load factors for the

environmental loads in combination b) can be lowered to a more permissive 1.15 value for

unmanned structures during extreme environmental loads. Since “ULS b)” will be associated to

“Transit survival” load case, it is assumed that the reel will not be in operation during severe

weather conditions, therefore can be considered as unmanned. [3]

LRFD standards propose a 10-2 annual return probability for ULS combinations. This

translates into a level of safety based on the “100 year storm” occurrence. This can be considered

somewhat exaggerated, since reels are transported offshore by ships (more rarely on barges),

which according to ship design rules, are designed for loads with 10-8 (or 20 years) probability of

exceedance, hence much lower than the 10-2 return probability requirements in OS-C101 or OS-

H102.[3][4]



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Chapter 4: Design by WSD Method

Similarly as the LRFD method, the WSD method and standards propose rules and general

principles on how to select relevant load types for different structures and equipment, the way to

calibrate them using design load factors and, ultimately, these combined loads will generate

stresses on the structural elements that would be divided with the material allowable resistance

and compared to agreed usage factors. The usage (or utilization) factors are precisely calibrated

so that they would allow the design to achieve a certain level of safety according to the role of

the structure/equipment will perform during its service life. [5][6]

Table E-1 in DNV-OS-C201 gives the basic usage factors for each of the load conditions

considered. The analysis must be conducted for the “worst case scenario” generated by the

relevant load combinations.

Loading conditions

a) b) c) d) e)

η0 0.60 1) 0.80 1) 1.00 1.00 1.00

1) For units unmanned during extreme environmental conditions,

the usage factor η0 may be taken as 0.84 for loading condition b).

Table E1 Basic usage factors η0 [5]

DNV-OS-C201 is a design standard similar with DNV-OS-C101, the difference being

that one is built on the WSD method (OS-C201) and the other on the LRFD method. They both

provide general design rules for offshore steel structures. However, also based on the WSD

method is DNV no. 2.22 “Lifting Appliances” standard for certification. DNV 2.22 is written

based on general WSD principles, but tailored on the specific requirements and studied behavior

of lifting equipment. Relevant to this study is the section related to the design if winches, to

which, as previously mentioned, reels could be associated.

The advantage of having a dedicated standard is that it is calibrated to the equipment’s

needs. For instance, studies were conducted on specific pieces of machinery (e.g. winches), their

behavior was observed during their service life in all types of environments, failures were

documented, the causes of failure were identified and lessons could have been learned,



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experiments were conducted and designs could have been improved. All these activities

generated conclusions which were analyzed and compared with the existing general design rules.

Once it was understood how specific equipment actually perform in real situations, the overall

design could have been improved.

The results were further translated into specific design rules. For the specific case of

winches, that meant that the usage factor was increased from lower values – 60% – to 85% of

yield strength (for both drum and flange) for functional loads. This is a huge improvement,

allowing structures to become lighter, carry more payload or operate at higher tensions. [6]

4.1 Loads Types

Just like DNV-OS-C101, DNV 2.22 lists load types relevant to the design of lifting

appliances that should be used for design/design verification. For reels, the following loads will

be selected:

� Principal loads

� Loads due to motion of the vessel on which the crane is mounted

� Loads due to climatic effects

1. Principal loads – define loads given by self-weight of components, payload and loads due to

pre-stressing. In case of reels, the pre-stressing load can be translated into reeling tension, or the

tension that will be applied to the product (e.g. umbilical, wire, etc.) during spooling in order to

obtain a tight, well arranged product on the reel drum, that will not become tangled and will be

easy to unspool.

Reels are not subject to horizontal loads as described in DNV 2.22 standard, as they only

rotate around their longitudinal axis. These forces are considered to be the consequence of loads

induced by movement of cranes on rails (generated by acceleration and braking), therefore not

applicable to reels. [6] Therefore, they will be disregarded from the load combination.

2. Loads due to motion of vessel – are represented by the inertia forces that act on the

equipment (reel). The inertia forces are generated by the ship’s motions (pitch, roll, etc.).

The ship’s motions will be calculated with DNV Ship Rules Part 3, Chapter 1, Section 4 for

a 10-8 probability of repeatability; this corresponds to a once in 20 years probability of



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occurrence, and the values are less than the once in 100 years (or 10-2 return probability) defined

in LRFD standards.[7]

There are 3 types of vessel motions:

- Vertical (V)

- Longitudinal (L)

- Transversal (T)

Due to the fact that the vessel has a major axis (longitudinal axis), the ship theory

demonstrates that not all motions are in phase (at their maximum intensity). The 3 motions are

combined as in the ship rules – DNV Rules for Ships Part 3, Chapter 1, Section 4 C500). The

factor for various motions shall account the targeted level of probability). The possible motion

combinations are:

i. V g±av

ii. V + T g/(±at)

iii. V + L (g±av)/ al

where:

g – acceleration of gravity (g ≈ 9.81m/s2)

av – vertical acceleration of ship

at – transversal acceleration of ship

al – longitudinal acceleration of ship [7]

Depending on the ship’s characteristics and weight, the loads due to vessel motions can be

calculated and then the most unfavorable can be applied to the design of the reel.

3. Loads due to climatic effects – loads due to wind (especially)

They are particularly important for lifting of reels onshore; offshore, high winds will

generate high waves, thus increased vessel motions, and so the predominant loads will still be

those generated vessel motions.



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DNV 2.22 gives 3 load cases, similar with the ones in DNV-OS-C201. Relevant to the

reels, these load cases will be translated into:

Reel DNV2.22 DNV-OS-C201

Operation in

standard conditions

Case I

(Crane without wind) Load condition a)

SG + ψSL (payload + spooling tension)

Environmental

dynamic operation

Case II

(Crane working with

wind)

Load condition b)

SG + ψSL +SW *) maximum combination of

environmental loads and associated

functional loads

Transit survival

Case III

(Crane subjected to

exceptional loadings)

Load condition c), d), e)

SG+SL+SM **) - *) in the case of reels, the maximum operational accelerations are assumed to be the vessel

motions during operation (so lower vessel motions calculated based on a 10-4 probability to be

exceeded – or 1 day return period)

in the case of reels, Ψ is considered to be 1 **) extreme loading conditions when the reel is not in operation, but inertia due to vessel motions

are extremely high and calculated based on the “20 year storm” scenario (or 10-8 probability)

where:

SG – self weight of reel;

SL – loads due to payload and spooling tension;

SW – loads due to wind;

SM – loads due to vessel motion. [6]



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Chapter 5: Discussion on LRFD and WSD Methods

5.1 Load Combination Factors for LRFD Method

If an engineer would want to design a reel base on the LRFD method, then he would have

to refer to DNV-OS-C101 for guidance regarding the load cases and load combinations to be

considered. The load factors that will need to be applied to each load type can be found in Table

5-1. As previously discussed, the load combinations that would ultimately dictate the strength

requirements of the reel would be those corresponding to the Ultimate Limit State (ULS).

Load factors for ULS

Load

Condition

Load Categories

G Q D E A

a 1.3 1.3 1 0.7 N/A

b 1 1 1 1.3 N/A

Table 5.1 (DNV-OS-H102, Table 5-1)

For “Load condition a)”, which corresponds to the “Environmental dynamic operation”

case, the load factor 1.3 for G (self-weight of structure) and Q (live loads) may seem to be too

high because:

• The overall weight of the reel should be accurately estimated for lifting purposes;

• G is fixed – the self-weight of the reel is well controlled;

• The self-weight of the spooled product (i.e. umbilical) cannot be easily monitored and

should be the full responsibility of the end user not to exceed the maximum value;

however, there are reduced chances to exceed the maximum value, as only an increase in

length would generate additional product weight.

• The spooling tension (T): it is assumed that the maximum value is not exceeded and that

systems to prevent the overcome are arranged – i.e. tensioners;

• The loads developed on the reel drum and flanges during spooling (pressure loads as a

function of T) can only be estimated by using DNV 2.22 formulas for hoop stress and

flange pressure [6, Chapter 2, Section 3, B207 and B208]. These can be considered

conservative, as they already have built-in safety factors (i.e. the rope layer factor – C).



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Having in mind that these loads are constant or with quasi-constant effect, the 1.3 load

factor may be considered over conservative and a decreased value of 1.0 for the load factor

might be applicable.

Assuming that this case reflects the operational condition, the 0.7 load factor used for

environmental loads (E) is hard to explain as long as accelerations or wind speeds indicated as

the upper limit for the operational criteria are expected.

For “Load condition b)”, which corresponds to the “Transit survival” condition, the

extreme environmental load factor of 1.3 applied to the environmental loads (E) does not seem to

be in accordance with the expected accelerations and wind speeds indicated for a 10-8

probability to be exceeded as indicated in DNV Rules for ships Part 3 Chapter 1 Section4.

Based on the above assumptions, this paper would suggest the following values for the

load factors:

Proposed load factors for ULS

Load

Condition

Load Categories

G Q D E A

a 1.0 1.0 1.0 1.0 N/A

b 1.0 1.0 1.0 1.3or 1.0 N/A

For “Load condition a)”:

• A 1.0 load factor applicable to the self-weight of the reel and product and spooling

tension (G, Q, T respectively)

• A 1.0 load factor applicable to environmental loads (E) corresponding to the ship’s

maximum accelerations in operational condition (i.e. during spooling/unspooling

operations)

Note: If there are doubts regarding the values for T and E, the corresponding values for the load

factors can be estimated with other reliable methods e.g. CN 30-6 - Structural reliability analyze

of marine structures.



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For “Load condition b)”:

• A 1.0 load factor applicable to the self-weight of the reel and product and spooling

tension (G, Q, T respectively)

Note: If there are doubts regarding the value for T, the corresponding value for the load factor

can be estimated with other reliable methods e.g. CN 30-6 – “Structural reliability analyze of

marine structures”.

• A 1.3 load factor applicable for the ship’s dynamic in transit/survival conditions with

accelerations at 10-4 probability to be exceed (DNV Ships Rules Part 3, Chapter 1,

Section 4, C500)

or

• A 1.0 load factor applicable for the ship’s dynamic in transit/survival conditions with

accelerations at 10-8 probability to be exceed (DNV Ships Rules Part 3, Chapter 1,

Section 4)

Summarizing the analysis listed above:

The operational conditions of the reel could analyzed as LRFD “Load condition a)” with

a general 1.0 load factor for every load type, where environmental loads are associated with the

ship’s maximum motions for operational conditions.

The “Transit survival” conditions could be analyzed as LRFD “Load condition b)” with a

load factor of 1.0 for the self-weight of the reel, product and spooling tension and an

environmental load factor of 1.3 or 1.0 depending on the probability level of the environmental

loads (dynamic of the ship and wind speed).

5.2 Utilization Factors for LRFD and WSD Methods

After analyzing the behavior of the proposed structure under all these load scenarios, the

stresses resulted must be compared with allowable utilization factors. Confusions appear when

dimensioning the reel’s structural elements, since each standard gives different values for the

usage factors (however, the differences are not that high)



24

Load case DNV 2.22 DNV-OS-C201

1 � = 11.5 = 0.67 a) 0.6

2 � = 11.33 = 0.75 b) 0.8

3 � = 11.1 = 0.91 c), d), e) 1.0

Usage factors according to table C-1 in DNV 2.22

(permissible stresses for elastic analysis) and E-1 in DNV-OS-C201

But the load combinations proposed are made of a summation of different load types,

each multiplied with a safety factor. The functional loads are represented by self-weight loads,

payload and spooling tension. This spooling tension will be used to calculate the hoop stress on

the drum. The thickness of the drum can then be easily obtained by dividing the hoop stress with

the material resistance and comparing it to a maximum usage factor of 85% of yield strength. [6]

It can logically be assumed that by adding the Tare and Payload to the equation,

combined with the 85% utilization from spooling tension, the overall utilization will be greater

than 85%. So, a safe conclusion would be that the entire functional load combination should be

limited to an 85% utilization factor. But then both DNV 2.22 and OS-C201 give a U value of

0.67 and 0.6 respectively for this load combination. Which one is to be used?

Similarly, for the Dynamic Operation load case, to the functional loads will be added the

inertia loads from the vessel motions, and again, the overall utilization will be higher than 85%.

Therefore, the utilization from the functional loads will then need to be further lowered

so all the 3 loads (SG+SL+SM) will not exceed 0.85 allowable utilization. But then how to comply

with proposed 0.75 and 0.8 utilization in DNV 2.22 and OS-C201 respectively?

LRFD method only gives load types and load combinations. It does not provide any tools

that would enable the calculation of the stresses in the structural elements, therefore enabling

their dimensioning. So, for reel design, hoop stress and flange pressure are calculated based on

the same formulas found in DNV 2.22 (so similarly to the WDS method), and comparing results

with 0.85 allowable utilization factor.



25

If the engineer then combines his loads according to the LRFD method:

• ULS a): 1.3 x F + 0.7 x E, just by multiplying 0.85 with 1.3 the usage factors will exceed

1

(0.85 x 1.3 = 1.105 > 1). Then how can be fulfilled the safety requirement of 0.86

utilization in DNV-OS-C101? (� = ��

= ��.�� = 0.86)

- γM = material factor according to DNV C-101 Section 5, B100

�� < ��; �� = 1

γ��

where:

Sd = design load

- Rd = resistance factor

- fy = yield strength of material [3]

5.3 Hoop Stress and Flange Pressure

When trying to establish the reel’s drum wall thickness, the methodology used is the one

proposed by DNV 2.22 standard. Basically, the hoop stress in the drum will be calculated by

considering the pressure resulting from on-spooling the product stored on the reel (umbilical,

risers, etc.).

As the product will be spooled onto the reel under a well-controlled tension, the pressure

applied onto it will try and squeeze the drum, thus forcing it to expand on longitudinal direction.

The outer flanges of the reel will try to restrict the drum from expanding, thus generating

longitudinal stresses into the drum’s walls. The simple equilibrium of forces is achieved by

considering only 1 layer of product (umbilical, wire, etc.), so the equations need to be calibrated

for the effect of multi-layering.

Multi-layering of product onto the drum of the reel or winch involves a much more

complex array of forces than the simple case of 1 layer, where only tension is to be considered.

This is the reason for the rope layer factor (C) present in the DNV 2.22 hoop tension formula:



26

�� = � ∙ �� ∙ !"

#$. [5.1]

where:

- S = spooling tension

- P = pitch of product (wire, etc.)

- tav = plate thickness

- C = rope layer factor:

o C = 1 for 1 layer

o C = 1.75 for 2 layers

o C = 3 for more than 5 layers [6]

It can be easily observed that the hoop stress value is governed by 2 parameters: spooling

tension (S) and rope factor (C).

DNV 2.22 is built on the assumption that the product will be spooled under maximum

allowable and uniform tension. Therefore, the wire will experience the same tension all across its

cross section and the entire product will be spooled at a constant, well controlled tension. This is

logic and perfectly achievable in the case of steel wire (where the exact material characteristics

are known and only one material is used for the wire fabrication) spooled onto winches. But

what happens when synthetic fiber rope or composite products (like umbilicals), made up from 5

or more different materials, with different properties, prone to internal slippage between

components, for which their behavior under tension is not entirely made public by their

manufacturers or simply unknown? [8]

Furthermore, umbilical storage reels are extremely large structures, built with high

tolerances, even at the drive hub. So, based on reel designers and fabricators information,

accuracy is not one of reels’ strengths, especially when talking about spooling. If the tension can

be more accurately controlled when using a tensioner, in case of spooling when the reel is

mounted on rollers (and the rotation of the reel is achieved due to friction between the rollers and

the outer edge of the flange) or by hub drive (i.e. when the reel is mounted between 2 massive

towers like in figure xxx. for tower driven systems), correct product spooling is often



27

acknowledged not by measuring the spooling tension employed, but by visual confirmation that

the product is properly arranged onto the reel drum. [8]

Sometimes, due to product tension limitations (especially umbilicals) or restrictive

crushing pressures imposed by product fabricator or because of umbilical end terminations that

would make attaching the product to the reel more difficult and not as strong as originally

intended, then the spooling tension will no longer be uniform, neither it will have significant

values, so the hoop stress generated will be low. [8]

So, what degree of accuracy do the DNV 2.22 formulas have in these cases? If the hoop

stress is low, then the pressure acting onto the flanges (which is directly dependent on the hoop

stress value, as it can be seen in Equation 5.2), will be even lower, especially if considering the

industry preferred arrangement (the product layers carefully winded ones on top of the others as

shown in Figure 5.1).

Figure 5.1 Product Arrangement on the Reel Drum



28

�' = 2 ∙ !"3 ∙ ) ∙ ��#$[5.2]

where:

- Φ = drum diameter

- tav = average drum thickness of drum barrel [6]

A logical question could be why the product crushing pressure is not considered to be a

suitable design parameter? [8]

Would the provided formulas still ensure a safe design or should there be a static (based

primarily on self-weight of structure and product) design method provided as back-up, just for

such situations?

DNV current practices and latest recommendations (that are included in the 2011 updated

version of the 2.22 standard), based on studies and industry experience, speak of a linear

increase of the value for C from 1.75 for 2 layers to 3 for more than 5 layers of product.

According to DNV, some winch and crane manufacturers have even confirmed that the new

increased value of C=3.0 matched the results from full scale testing of their products. However,

DNV allows decreasing the value for the C factor after special considerations. [9]

How relevant and what positive influence can this increase of C have on umbilical reels?

Did they consider a large number of materials with different characteristics or just various steel

wire ropes? Why is this apparent contradiction in conclusions between DNV and other public

studies?



29

5.4 Rope Factor (C)

But why is C factor so important?

By multiplying the spooling tension with a higher than 1 coefficient, the hoop stress will

increase rapidly, thus leading to the need of a thicker drum wall. Basically, since the spooling

tension cannot be modified due to proper spooling and winding reasons, a logical and relevant-

to-the-design value of C is very important. Understanding the reasons behind a certain value for

C and how they can be manipulated into the benefit of the design (thus enabling a decrease in

the wall thickness of drum) is crucial.

It has been observed that rope stiffness has a direct impact on how the loads are

distributed on the drum. Tough, very stiff steel wire ropes will push harder into the surface of

the drum, thus almost cutting into its shell. A softer, less rigid product like an umbilical will

deform more under the spooling tension loads that a steel wire, and will act like a damper.

Combined with the increased lateral area, the pressure will be distributed more evenly onto a

larger surface, thus lowering the loads at the drum’s surface. [9][10]

Another important aspect is related to how much load will experience the first (inner

layer) of the product. If the designers can confirm that the first layer of the product will be

subject to a reduced load than the next layers, then DNV guidelines allow the use of a reduced

value for the C factor.

5.4.1 “Large Wire Rope Mooring Winch Drum Analysis and Design Criteria”

Study

The “Large Wire Rope Mooring Winch Drum Analysis and Design Criteria” study

supports the above DNV conclusions and proves by calculation the direct relationship between

lateral modulus of elasticity and load transfer for the reel drum. [9]

The study concentrates on investigating how the stiffness of the wire, spooling tension

and number of layers influence the load transfer to the drum. Although well known by

manufacturers, from previous experience and analysis conducted over the years by design

engineers that got repeating results, it was observed that rope characteristics (diameter, stiffness,



30

etc.), number of layers and spooling tension dictate the impact on the reel barrel, but no study

could show in what proportion each of the 3 affect the overall result. Flange and drum design are

directly influenced by product stiffness, yet few have thoroughly investigated this aspect,

although accurate results and clear conclusions could lead to more economical winch/reel design.

The research results showed 2 important aspects:

1. The wire tension decreases towards the middle layers (possibly due to friction? Fig xxx – no

explanation provided);

2. High loads on the flange thrust if products with lower stiffness (products that would deform

more) are spooled at high tensions [10]

5.4.2 “Problems Related to the Design of Multilayer Drums for Synthetic and

Hybrid Ropes” Study

Similar results were obtained and recorded in the study conducted at the University of

Clausthal by P.Dietz, A. Lohrengel and others on the “Problems Related to the Design of

Multilayer Drums for Synthetic and Hybrid Ropes”. The study revealed that winches carrying

products with reduced Young’s modulus in transversal direction will experience lower pressures

on the drum, but increased loads on the flanges. This happens because of the deformation of the

product’s cross section from circular to oval, thus the pressures on the drum will decrease

because of increased product footprint on the drum and because the deformation of the product

will act as a damper, consuming energy until the forces will no longer be able to deform the

product. In the same time, on transversal direction, the cross section of the squeezed product will

increase in width, thus generating additional loads on the flanges. [11]

In this case, the way flange pressure is calculated in DNV 2.22, based on the hoop stress

will no longer match the actual way the loads are distributed on the drum and flange, leading to

the possibility that the flanges will be under-designed.

Although their study was conducted on fiber rope, the results can be considered relevant,

as umbilicals also have a reduced Young’s modulus in transverse direction, being prone to

deformation.



31

The rope factor gives a generic value, applicable to all types of products. It is not shown

how those values were obtained and based on what assumptions. Does it consider the benefic

influence of friction? How does the rigidity of the product influence the overall loads that act on

the drum?

5.5 Spooling Tension – Friction Factor Relationship; Friction between

Product Layers

The standards do not provide any information regarding the positive (or negative)

influence the friction between product layers has on load transfer to the reel drum. DNV 2.22

provides a 0.1 friction coefficient for the drum; does that cover accurately the friction between

the layers of an umbilical?

The following equations and logic was developed with the help and under the guidance of

my industry supervisor, Mr. Marius Popa. Based on his experience working with reels, by

understanding the general forces that act upon the product and stresses that develop within the

product during the spooling process and corroborating them with product rigidity and friction

between the product layers, we managed to transfer into equations his way of seeing the state of

efforts that act on the product during spooling operations.

Figure 5.5.1 Forces in Spooled Product

Spooled product (i.e. umbilical)

Drum Center



32

From Figure 5.5.1 it can be observed that:

*+ = , ∙ -. ∙ � [Eq. 5.5.1]

-� = *' = / ∙ (1�) [Eq. 5.5.2]

� ∙ -. + 1� − *+ = 0 ⟹ *+ − � ∙ -. = 1� [Eq. 5.5.3]

If we assume K = 0, then the equations will become:

*+ = 0 [Eq. 5.5.4]

Eq. 5.5.2 will remain the same

� ∙ -. + 1� = 0 ⟹ � ∙ -. = −1� [Eq. 5.5.5]

By substituting Eq. 5.5.5 in Eq. 5.5.2 we obtain:

-5 = −/ ∙ � ∙ -. ⟹ 6768 = −/ ∙ � [Eq. 5.5.6]

By integrating and rearranging, Eq. 5.5.6 will become:

� = �9 ∙ :;<8 [Eq. 5.5.7]

By substituting Eq. 5.5.3 in Eq. 5.5.2 we obtain:

-� = /(*+ − � ∙ -.) ⟹ 6768 = / ∙ , ∙ = − / ∙ � [Eq. 5.5.8]

From equation 5.5.7 and by integrating Eq. 5.5.8 we obtain the equation that governs the

spooling tension as a function depending on rigidity and friction.

� = / ∙ , ∙ = ∙ . + �9 ∙ :;<8 [Eq. 5.5.9]



33

Figure 5.5.2 Spooling Tension Curve According to Eq. 5.5.9

Where:

- S = spooling tension

- S0 = initial spooling tension

- Fe = elastic force

- k = rigidity coefficient

- Ff = friction force

- μ = friction coefficient

- ΔR = compressive force

- r = radius from drum center to product layer

- φ=the angular travel of the free end

When evaluating the tensions in the spooled product and the pressures on the drum

(Figure 5.5.1, 5.5.2 and Equation 5.5.9), we can observe that the tension is decreasing with the

increase of the friction (this happens because tension is consumed by friction) up to a point

(point P on figure 5.5.2) where, due to the product rigidity, the tension required to keep the

product from uncoiling becomes larger than the friction force. [22]

Same thing was observed by other engineers conducting FEA analysis on winches:

pressure on the drum increasing with the number of wire layers and then starting to decrease as

the drum began to fill. The overall conclusion was that the “lower layer’s friction was

preventing the upper layers from constricting the drum any further”. [12] Although this

S=µ·k·r·φ+S0·e-µφ

S=µ·k·r·φ

S0·e-µφ

P



34

observation is not included in any scientific study or official report, it should be taken into

consideration as evidence that engineers involved in different fields of activities, when analyzing

the behavior of spooled wires on winches, seem to get similar results and conclusions.

Furthermore, it is well known that cables are suffering from wear and tear caused by

friction during their service life (phenomenon highlighted in the Australian standard AS2759-

2004 “ Steel Wire Rope“ [13]) and it is common knowledge that a very fast unwinding of a

winch will lead to the overheating of the wire. This can only be explained by high friction

between the product layers.

Reel designers have confirmed that they consider in their calculations that the wire

tension (i.e. laying tension) will dissipate within 5 layers, therefore acknowledging and using

friction in their benefit, although it is not specifically taken into account in the design codes.

All these come and support the idea that friction plays a much more important role when

talking about multi layered reels/winches and its impact to the overall design must be

investigated more seriously.

5.5.1 “AM16 Improvement in the Design of Winches” Study

Back in 2005, a bachelor degree thesis written at the University of Singapore, “AM16

Improvement in the Design of Winches”, compared the way in which hoop stress is calculated

by DNV 2.22 and an Australian standard (AS 1418-1977 “Crane Code”). These standards were

found to be the only ones (to that date) to provide ways of calculating the hoop stress (i.e.

formulas) for a multi-layered winch drum.

To summarize their study, they calculated the hoop stress based on each of the 2

standards for the same loads. Even if the formulas were similar, the results were quite different

because of the differences in calculating the rope factor. The derived drum wall thickness from

the hoop stress was greater for the Australian standard then the DNV one and both showed that

the assumed drum design will fail during service. But the drum was already in service for more

than 10 years without any kind of structural failures.



35

So they undertook a series of experiments to show that the current ways of designing the

drum for a winch are too conservative. They observed 2 things:

1. The current DNV rope factor (C) and AS 1418-1977 (K) for multi-layered systems were far

too conservative. DNV C factors were found to be between 1.5 to 2.5 times larger than their

experimental readings.

2. For drums which are never fully unspooled, the first inner layers behave as part of the drum,

thus contributing to the increase of the effective drum’s wall thickness. They named this

phenomenon “rope relaxation”.[14]

5.5.2 “Improvements in Winch Design Guide AM11” Study

The same researchers conducted another study one year later (“Improvements in Winch

Design Guide AM11”). The experiments conducted by them showed not only that wire tension

decreased as product layers were spooled one on top of the other, but also that wire tension

decreased with each turn within the same layer. Their research comes as a scientific proof, based

on measurements, that even in the most controlled environment (i.e. University laboratory) the

spooling tension is not uniform, therefore the assumption on which the DNV and Australian

standards are built on (that spooling tension is uniform and constant) are unrealistic and too

conservative.

The final result of their work was to provide correction factors that could be used for

calibrating the rope factors provided by the 2 standards. [15]

The validity and accuracy of their correction factors will not be discussed in this paper,

but their observations regarding the fact that spooling tension is not uniform and has a

decreasing tendency will be considered relevant to the idea that current application of the design

standards for the design of reels offers too generalized design rules that may lead to “over-

conservative” designs.



36

5.6 Comments

In absence of relevant tests and studies made on products that could behave as close as

possible to umbilicals, results from studies made on other types of products and materials will

have to be considered and analyzed. However, because of the mixed nature of umbilicals (they

are made up of so many different materials – elastomers, plastics, steel, other metal alloys, etc.)

that perform in all but similar ways, the conclusions and assumptions have a decreased level of

accuracy and reel design will suffer, as it rather rely on guessing than on proven facts.

Furthermore, no standard regulates the matter of testing. Based on what rules should

designers take into account the implications that pressure testing of spooled products will have

on the reel’s structure? Who should take responsibility in case of reel structural failure during

testing, although the structure was designed in full compliance with existing standards? The fact

that no failures occurred up to date does not mean that they might not occur in the future.

All these grey areas and unaccounted aspects in the design information may lead to

overdesign and may be translated into increased reel weights. In consequence, the chance to lead

to increased costs for manufacture processes, lifting and transportation operations is significant.



37

Chapter 6: FEA Analysis

6.1 Reel Designs

Although they are not complex pieces of equipment, due to their increased size and

relative limited use, reels are designed and produced, at least in the UK, by a few manufacturers.

Basically, a reel is made of 3 main components: a horizontal cylinder (the drum), on which the

product is spooled, and 2 vertical members – the flanges – placed at each of the 2 ends of the

drum. There are several designs used by the various companies, but these can be grouped into 2

large categories:

1. Reels with the drum made from thick plate that is rolled and then welded to form a

cylinder. This drum cylinder is reinforced with 1 to 3 inner stiffeners, perpendicular to

the cylinder plane, that enable the drum to keep its shape during spooling/unspooling of

product and transportation operations, thus preventing it to buckle under the combined

loads from the hoop stress and pressures due to spooling.

2. Reels with the drum structure made from hollow sections or I beams, distributed on the

outer perimeter of the drum cylinder as generators. These are held together by several

perpendicular rings or hoops (2 – 4 depending on the drum’s size and payload); the

structure skeleton looks like a wooden barrel, but with fewer staves. Everything is

wrapped with a plate, thinner than the one used for the design described in 1, which

forms the support on which the product will be spooled onto.

So, the main differences between the 2 designs would be the fact that the first drum

design would be made just from bend plate, with internal stiffeners that would partition the drum

inside into 3 or more small “chambers”; these inner stiffeners look very similar with the reel

flanges, resembling a wagon wheel. The second design that will lead to a structure resembling a

barrel, with all the structural members placed at the exterior of the drum.

The flange design resembles the design of a wagon’s wheel: a small inner rim (on which

the drive mechanism would couple in case of hub-driven reels during spooling/unspooling) from

which radially distributed spokes will extend and connect to an outer rim (on which the reel



38

would be stored during transport or would rotate during spooling/ unspooling operations in the

case of rim-driven reels).

Sometimes, in the spacing between the spokes, steel gussets can be fitted (thus the

flanges would look almost like a disc) to rigidize the flanges. This measure can be necessary

when the weight of the payload is high or the spooling tension of the product will induce high

pressures to the drum and flanges.

Usually, for the reels with the drum designed as described in the first case, the connection

between the flanges and the drum is made through bolts. The resulting structure will be

considerably lighter than the one with hoops and staves, the downside being that this design is

limited to weights not exceeding 300t (payload + reel self-weight). For reels with rating

exceeding 300t, this design will no longer be used. Instead, a similar arrangement as described in

the second case will be chosen and the connection between the flanges and the drum will be

made via full penetration welds [8].

For the purposes of this dissertation, the second reel design type will be chosen, as it is

the more general and common of the 2. Based on the design reports and fabrication drawings

studied, a 10m diameter reel design was chosen. An overall view of the chosen reel design can

be seen in Figure 6.1.

Outer Rim

Flange Spoke

Drum Spoke (Stave)

Drum Stiffening Ring (Hoop)

Inner Rim (Hub)

Drum Plate

Figure 6.1 Reel Primary Structure



39

The structural elements are:

Element Number of

elements Section Material

Drum hoop 4 203x203x71

S355

Drum stave 18 203x203x71

Drum plate 1 15mm plate

Inner rim (hub) 2 250x250x8

Flange Spoke 18 305x305x118

Outer rim 2 250x250x8

6.2 Boundary conditions

For each of the 2 scenarios considered – storm (transit/survival) and operational – the reel

will be supported in different ways. During transport, it is assumed that the reel will rest on

cradles on the back deck of the service ship. It will be stored in upright position and the only

contact points (between the reel and the cradles) will be located at the lower part of the flanges,

on the outer rim. All the loads will be

transmitted to the cradles through the outer

rim and the flange spokes that would be

directly supported by the cradle. In the

considered situation, the cradles are long

enough to offer direct support only for 3

spokes. Therefore, the FEA model will only

have 3 supports at the lower part of each of

the 2 flanges, beneath 3 of the spokes, as

shown in Figure 6.2.1. Translations on all of

the 3 directions will be restrained, but the

rotations will be permitted.

Figure 6.2.1 Reel Flange Supports



40

Usually, reels are also tied down to the deck with wire ropes. This method is called sea

fastening and it ensures a better way of preventing the reel to move during transport. For the

purposes of this dissertation, sea fastenings are not considered.

Figure 6.2.2 Reel On Cradles and Sea Fastened On Deck of Ship

(Courtesy of Marine Well Containment Company) [18]

During operation, reels can either be put on rollers and unspooled, thus being rim-driven,

or they can be lifted and positioned between 2 towers. The towers have special supports on

which the reel will rest and a drive mechanism that couples to the hub of the reel. If the reel is

operated (spooled/unspooled) in this way, then it is called hub-driven. The contact points

between the reel and the tower supports are located on both sides of the reel, at the flange center,

where the reel hub (or inner rim) is located.

Cradle

Hub Support and

Drive Coupling

Figure 6.2.3 Reel Towers (Courtesy of

Aquatic) [19]



41

Figure 6.2.4 Reel Mounted Between Towers (Drive Side) Towers

(Courtesy of Aquatic) [19]

For the FEA model, supports that only allow rotations on all of the 3 directions are

selected. They will be fitted on the upper half of the hub, at the intersection between the hub and

the flange spokes, as shown in Figure 6.2.4.

Figure 6.2.4 Reel Hub Supports



42

6.3 Load Scenarios

An FEA model was built and loaded according to the WSD (DNV 2.22 and DNV OS-

C201 standards) and LRFD (DNV OS-101) requirements. The load combinations studied

correspond to the Ultimate Limit States (as these are considered to be the ones that would dictate

the overall design strength requirements. For each of the 2 scenarios selected (transport and

operational), the final orientation of the reel on the transport ship cannot be known from the

design stage, therefore the 2 possible orientations for each scenario must be analyzed to see

which one is the most unfavorable:

Transit survival

(transportation the ship deck on cradles)

Environmental Dynamic operation

(hub driven reel on the ship deck)

Storm LRFD Storm WSD Operational LRFD Operational WSD

longitudinal

direction

transversal

direction

longitudinal

direction

transversal

direction

longitudinal

direction

transversal

direction

longitudinal

direction

transversal

direction

load

combination 1xG + 1xQ + 1.3xE SG+SL+SM

1.3xG + 1.3xQ +

0.7xE SG + SL +SW

where:

SG – self weight of reel;

SL – loads due to payload and spooling tension;

SW – loads due to wind;

SM – loads due to vessel motion

G – permanent loads (self weight of structure)

Q – live loads (payload)

E – environmental loads

As previously discussed, since the LRFD method does not provide any formulas to

determine the pressures that act on the flanges and drum from spooling operations, these forces



43

were calculated using the methodology from DNV 2.22 “Lifting Appliances” Standard – Chapter

2 Section 3 B200 “Drums”.

Therefore, the only difference between the 2 methods is represented by the way in which

the load cases are combined to form the load combinations.

The conclusions and discussions regarding the results for each of the 2 methods can be

found in Chapter 7.2.



44

6.4 Operational Limitations

Operational limitations and specified loads:

Usually, reel designers specify certain values for the maximum ship accelerations under

which a reel can be operated or safely transported. In this way, by choosing lower values they

can obtain a lighter design. However, the acceleration values provided by the designers must be

somehow correlated with the values used for ship design. It can be assumed that the accelerations

for operational case could be chosen in a more permissive approach if the operational limitations

are very strict: the reel can be operated only in a calm sea and low winds, thus ensuring that the

ship accelerations with 1 day return period (or 10-4 probability to be exceeded) will not be

exceeded. In other words, the reel could only be operated as long as the weather conditions are

very good and the probability of the ship to experience accelerations close to its 1 day design

accelerations is minimal. This would drastically limit the operational window for the reel, but it

can be achieved under ideal conditions.

However, for transport conditions, especially if the reel is to be transported on a long

journey or if the transporting ship cannot avoid the storm, then the reel should be designed taking

Self-weight of reel 58t

Umbilical weight 252t

Number of layers 18

Product diameter 120mm

Reeling tension 10t

Environmental conditions

storm operational

Heave av = 1.9g av = 1.45g

Longitudinal

acceleration al = 0.75g al = 0.5g

Transversal

acceleration at = 0.75g at = 0.5g

Wind load 800 N/mm2 Figure 6.4.1 Assumed Ship Directions



45

into account the ship accelerations during storm conditions so that it will survive and still be in

operating condition once the storm passes. Therefore, its design accelerations should be

correlated to the ones specified in DNV’s “Rules for Ships” January 2012, Part 5, Chapter 7,

Section 2 E400 or with other similar standards. If the accelerations corresponding to the “Storm”

scenario are selected and applied to the reel for the “Transit Survival” case, if using LRFD

design method, then the accelerations should be multiplied with a safety factor of 1.3. [3] This

will lead to a reel design able to withstand greater motions than the carrying ship itself, which

does not make sense in a reality.

Therefore, using LRFD for the design of reels seems to be more challenging and requires

a very good understanding of the standards used and how their requirements correlate with the

requirements for other equipments and means of transportation (i.e. ships), but also the ability to

make solid judgments on how to interpret and chose the appropriate design factors – in this case

accelerations – so that the standard’s requirements are fulfilled and the final product (the reel)

will be designed in a coherent and realistic manner.

For this dissertation, the accelerations for the reel operation and transport cases were

selected based on the DNV “Rules for Ships” January 2012, Part 5, Chapter 7, Section 2 E400

(for storm/transit survival case) and DNV “Rules for Ships” January 2012, Part 3, Chapter 1,

Section 4 C500 (for operational conditions). [16][7]



46

Service Ship less than 100m Long (L < 100m)

20 Year Storm (10-8 probability of exceedance) Operating Conditions (10-4 probability of

exceedance or 1 day return period)

DNV “Rules for

Ships” January 2012,

Part 5, Chapter 7,

Section 2 E400

requirements

Design

Value

DNV “Rules for

Ships” January

2012, Part 3,

Chapter 1, Section 4

C500 requirements

Design

Value

av = 0.9g* av = 0.9g* av = (0.9/2)g =

0.45g* av = 0.45g*

at = 0.75g maximum

of at and

al will be

chosen

at = al =

0.75g

at = 0.75g x 0.67 =

0.5g

maximum

of at and

al will be

chosen

at = al =

0.5g al = 0.6g

al = 0.6g x 0.67 =

0.4g *) the reel and product self-weights will be added (1g) to the vertical accelerations

where:

g – acceleration of gravity (g ≈ 9.81m/s2)

av – vertical acceleration of ship

at – transversal acceleration of ship

al – longitudinal acceleration of ship [7]



47

6.5 Load Cases

The load cases considered for the FEA analysis are described below. Their values will be

summarized in a table at the end of this section. The calculations showing how the values for

each load case were obtained can be found in Appendix 1.

1. Self-weight of structure.

2. Product load – the entire product load will act only on the top half of the reel drum as

shown in Figure 6.5.1 (left flange removed for clarity).

Figure 6.5.1



48

3. Drum pressure due to reeling tension.

In DNV no. 2.22 Standard, the hoop stress formula in Chapter 2, Section 3, B207

requirements for the C factor for 5 layers and above is 3. However, this will lead to increased

pressure values on both the drum and flanges. In the industry, the value for C is usually taken as

1.75. [6] However, in this dissertation both values were considered and the results will be

commented in the following chapters.

Figure 6.5.2 Drum Pressure Due to Reeling Tension

(left flange removed for clarity)

4. Flange force due to reeling tension.

In DNV no. 2.22 Standard, in Chapter 2, Section 3, B208 the flange “pressure is assumed

to be linearly increasing from zero at the top layer to the maximum value of

�' = 2 ∙ !"3 ∙ A ∙ ��

near the barrel surface”. Designers consider the load to be

linearly distributed on the spoke and have a triangular shape,

with the maximum value near the barrel surface. In reality, the

pressure is distributed on the whole flange area which have a

circular shape. The spokes are radially extending from the inner

rim towards the outer rim and the area from which the pressure

is unloaded to the spoke is a circle sector. Since the pressure



49

decreases as the corresponding spoke area increases (there is an inverse relationship between

them), probably a more accurate distribution of the pressure on the spokes would be a parabolic

one, with the maximum value towards the middle of the spoke.

For the purposes of this dissertation, a similar simplifying assumption as the one used by

the industry will be considered, thus a triangular load distribution will be modeled on each spoke.

The pressure at the drum surface will be considered linearly distributed on each of the

staves and the value will be 3 times greater than the one acting on the flange. [6]

Figure 6.5.3 Flange Pressure Due to Reeling Tension

5. Transverse load on flange under transverse accelerations.

Under transverse accelerations (generated by the ship’s motions), depending on the

reeling tension, a portion of the product or the entire product will slide, thus the flange will have

to support an additional load.

As the reel tilts under transverse accelerations, if the product is not spooled with a

sufficient tension, then the force that keeps the product attached to the drum and prevents it from

sliding might be exceeded by the force generated by the mass of the product combined with the



50

transverse acceleration. A simple check whether the minimum required friction coefficient

(µ=0.1 in DNV 2.22 Chapter 2, Section 3, B513) is exceeded or not (detailed calculations in

Appendix 1). In this particular case, the entire product will not slide.

Therefore, a common industry practice is to consider a conical shaped portion of the

product to slide and act on the flange. In cross section, the load distribution has a triangular

shape, increasing from 0, near the drum surface, and linearly increasing towards a maximum

value at the outer layers of the product (Figure 6.5.4). The angle made by the flange and assumed

product sliding plane is usually considered to be 30° (Figure 6.5.5).

If the spooling tension cannot generate a drum pressure large enough, then the whole

product might slide, thus the entire weight of the product will have to be supported by the flange.

Figure 6.5.5 Proportion in which

Sliding Product Pressure Will Be

Supported by Flange and Drum

Figure 6.5.4 Flange Pressure Due to Partial Product Slide



51

5a. For the purposes of this design exercise, a special, extreme case will be considered when

the spooling tension will be taken as 0 and the effects will be analyzed. However, the drum and

flange pressures due to spooling tension will then become 0, so it should be interesting to see

what actually happens in an extreme case.

6.5.6 Flange Pressure Due to Full Product Slide

6. Forces on the hub under transverse accelerations.

The remaining payload after the product slide assumed in the previous load case will still act

as pressure on the drum. Therefore, each of the drum staves will be subjected to a pressure

generated by the remaining payload, but this pressure will be acting as friction force, along the

local X axis of each stave.

Note: Load cases 5 and 6 are always applied simultaneously.



52

7. Forces on the hub under longitudinal accelerations.

Figure 6.5.7 Forces on the Hub Under Longitudinal Accelerations

8. Transverse loads generated by the wind (on the flange).

9. Longitudinal loads generated by the wind (on the drum).

10. Reeling tension



53

Load cases that would be applied to the FEA model

Model Load Cases

no name load axis value

C = 1.75 C = 3

LC1 self-weight x 58t

LC2 self-weight y 58t

LC3 self-weight z 58t

LC4 product z 252t

LC5 spooling pressure on drum perpendicular to

local x axis of each stave

500 N/mm 855.77 N/mm

LC6 spooling pressure on flange y

linearly varying from 0

to 233.21 N/mm

linearly varying from 0 to 399.79

N/mm

LC7 flange force from transversal

accelerations y 23.88 N/mm

LC7a flange force from transversal accelerations when product

slides (S=0) y 63.58 N/mm

LC8 drum force from transversal

accelerations in line with stave

local x axis 19.56 N/mm

LC9 drum force from longitudinal

accelerations x 252t

LC10 transverse wind load y 800 N/mm2

LC11 longitudinal wind load x 7.78 N/mm

LC12 reeling tension point load 10t



54


*) During transport, a reduced value for the spooling tension is usually considered by industry designers, thus lowering the pressures

on the drum and flange. [8] In this instance, it is assumed that only half of the spooling tension will still act on the reel components

during transport.

G

LCC1

Q

LCC2

E

LCC3

G

LCC1

Q

LCC2a

E

LCC4a

G

LCC1

Q

LCC2

E

LCC4

LC1 self-weight x 0.75 0.75 0.5 0.5

LC2 self-weight y 0.75 0.75 0.75 0.75 0.5 0.5

LC3 self-weight z 1 0.9 1 0.9 1 0.9 1.9 1.9 1.9 1 0.45 1 0.45 1.45 1.45

LC4 product z 1 0.9 1 0.9 1 0.9 1.9 1.9 1.9 1 0.45 1 0.45 1.45 1.45

LC5spooling pressure on

drum

perpendicular

to local x axis

of each stave

0.5* 0.5* 0.5* 0.5* 1 1 1 1

LC6spooling pressure on

flangey 0.5* 0.5* 0.5* 0.5* 1 1 1 1

LC7

flange force from

transversal

accelerations

y 0.75 0.75 0.5 0.5

LC7a

flange force from

transversal

accelerations when

product slides (S=0)

y 0.75 0.75

LC8

drum force from

transversal

accelerations

in line with

stave local x

axis

0.75 0.75 0.75 0.5 0.5

LC9

drum force from

longitudinal

accelerations

x 0.75 0.45 0.5

LC10 transverse wind load y 1 1 1 1 1 1

LC11 longitudinal wind load x 1 1 1 1

LC12 reeling tension point load 1 1 1 1

ULS a) 1.3G + 1.3Q + 0.7EULS b) 1G + 1Q + 1.3E

Load Combinations

Longitudinal

LCC15

Transversal

LCC16

Longitudinal

LCC5

Storm LRFD

G

LCC9

Q

LCC10

E

LCC11

G

LCC9

Q

LCC10

E

LCC12

Storm - accelerations: av = 1.9g, at = 0.75g, al = 0.75g Operational - accelerations: av = 1.45g, at = 0.5g, al = 0.5g

Operational LRFD

S = 0

LCC8a

S = 10t

LCC8

Longitudinal

LCC7

Transversal Transversal

S = 0 LCC6a S = 10t LCC6

Storm WSD Operational WSD

Longitudinal LCC13 Transversal LCC14Load

Case

Number

Name Axis



55

Chapter 7: Result Interpretation

The initial analysis considered loads calculated with a rope factor C=1.75. The models were run

under the relevant load combinations and the results compared. For both design methods were recorded

failures – utilization factors higher than allowable – for the flange spokes and for the drum staves. Code

checks were made based on Eurocode 3 (for LRFD method) and AISC ’89 (for WSD method), which are

built-in the FEA program used. For each of the two methods, the structure of the reel was strengthened, by

increasing the cross section of the spokes and staves to the next larger standard profile available in BS4

Part 1 1993 standard for structural sections. Eventually, the final weight of the 2 new reels was compared

and the results were commented.

The section increase could not be done just for the failing elements, but for all similar elements, as

the reel does not have an upright specific position in which it can be stored, thus all spokes could in turn

fail, not just the ones supporting the reel weight on the cradles at a specific moment in time; a similar logic

was followed in the case of the failing drum staves.

7.1 Results of the analysis

7.1.1 Flange Spokes

The analysis showed that the reel spokes will fail during transport for both design methods. The

initial assumption that the weight of the reel will be supported

only by 3 spokes on each flange was considered unrealistic as the

utilization in those spokes was almost 4 times the allowable

(allowable = 0.85 << 3.38 actual). Furthermore, no sea

fastenings were considered, so the length of the supporting cradle

was increased, thus providing support for 4 spokes on each flange.

The utilization ratios decreased to a more reasonable value of

1.36 for the LRFD method. For WSD, the utilizations in the same

spokes were around 1.05, so almost 30% lower.

Figure 7.1.1 Flange Spokes with

Highest Utilization



56

As expected, the spokes suffered failures only during transport, under increased vessel accelerations.

The case in which the reel tilts along its longer axis (transversal load situation considered in the model) is

more unfavorable that the longitudinal load situation.

The extreme scenario when the product spooling tension was assumed to be 0, thus determining the

entire product to slide and all its weight to be supported by the flange, did not show higher utilizations that

the case when only a percentage of the product slides. The utilization values were similar

- 0.49 and 0.5 for full product slide and partial product slide, respectively for the LRFD;

- 0.40 and 0.53 for full product slide and partial product slide, respectively for the WSD.

This might be explained by the fact that the spooling pressure on the flange due to reeling tension,

although reduced to half of its operational value during transport, still has an important impact on the

behavior of the flange spokes.

7.1.2 Drum Staves

Although there were recorded failures of the staves in the Transport Scenario, the failures were

small compared to the ones from the Operational Case.

Almost all the drum staves had utilization ratios above 0.85, the highest being up to 1.79 for the

LRFD and 1.47 for WSD. Again, a difference of over 20% between the two methods.

Probably an interesting point is that the parts of the

staves with highest stressed were located at the connection

between the flanges and the drum, highlighted in red in

Figure 7.1.2. This aspect could be of significant importance,

especially in the case of the reel design where the flanges

connected to the drum through bolts.

The drum hoops did not appear to have a utilization

factor higher than allowable.

Figure 7.1.2 Drum Staves with Highest Utilization



57

7.2 Comments

Overall, the spokes and the drum staves had to be increased up to the where their maximum

utilization did not exceed the allowable. Along with the section increase came also an increase in weight.

The new sections and weight of the reel according to the design methods considered are shown in Table 7.2.

Initial Sections

Final Sections

C=1.75 C=3

WSD LRFD LRFD

Spoke UC 305x305x118 UC 305x305x158 UC 305x305x240 UC 305x305x240 Hoop UC 203x203x71 UC 203x203x71 UC 203x203x71 UC 203x203x71 Stave UC 203x203x71 UC 254x254x132 UC 254x254x176 UC 305x305x240

Reel Self-weight 58t 71.26t 88.63t 102.61t

Weight Difference (%) 24.40% 44%

Table 7.2.1 New Sections for the Structural Members

It can be easily observed that by considering a higher value for the rope factor, as per DNV 2.22

requirements, could lead to a dramatic weight increase. Therefore, at least in case of reels transporting

lengthy products that have to be spooled in many layers, based on previous experiences that did not point

out reel structural failures, a lower value for C=1.75 or less can be considered more appropriate.

With respect to the design method, since LRFD does not provide formulas to estimate hoop stress,

nor drum and flange pressures due to reeling tensions, then the input formulas for both methods is provided

by WSD method through DNV 2.22. For ultimate limit states, both methods have a similar allowable

utilization factor around 0.85 of the yield strength of the material (for LRFD U = 0.87, for WSD U = 0.85).

So, basically, in the particular case of reels, the main difference between the 2 design methods is the way in

which the load combinations are built. In other words, the safety factors applied to each of the load types

(self-weight loads – G, live loads – Q and environmental loads – E).

For the particular case of reels, if the LRFD is applied as per DNV-OS-H102 Table 5-1

Load factors for ULS Load

Condition Load Categories

G Q D E A a 1.3 1.3 1 0.7 N/A b 1 1 1 1.3 N/A

Table 7.2.2 (DNV-OS-H102, Table 5-1)



58

without considering any of the allowed reduced safety factors (as stated in DNV-OS-C101 Section 2 B402

and B404 and discussed in Chapter 3 Section 3.3 “Comments” of this paper), then the LRFD method

proves to be too conservative, thus leading to a heavier overall reel, which in turn could prove to be at least

uneconomical in terms of offshore transportation and lifting.

Another grey area for LRFD could be considered the way in which the safety factors for the

environmental loads are chosen, especially in the “Load case b)”; if the designer specified accelerations for

the reels are chosen according to DNV’s “Rules for Ships” January 2012, Part 5, Chapter 7, Section 2 E400,

then accelerations are already similar with the ship’s design accelerations for storm conditions and a further

multiplication for the reel’s accelerations could lead to a reel that is designed to survive in weather

conditions that the transport vessel will not.

The governing load combinations that were found to dictate the overall strength of the reel were the

Operational load cases for both LRFD and WSD. With respect to the safety load factors in LRFD for G and

Q, it can be stated that by increasing by 30% an already heavy structure and equipment (so for a 300t reel

plus product an addition of 100t plus a 30% increase of the already high spooling pressures on the drum

and flanges) could prove too conservative for a structure where these parameters can and are easily and

accurately controlled. Therefore, the weight difference highlighted in Table 7.2.1 can now be explained.

WSD appears to be the more economical of the 2 methods. Also, the reels designed according to

this method have been in service for long periods of time without known structural failure, so it also seems

to be confirmed by reality as suitable for reel design.

Both methods rely on the hoop stress and drum and flange pressure equations in DNV no. 2.22

(equations 5.1 and 5.2 in this paper) in order to determine the loads to be applied on the reel’s structural

members. Therefore, choosing the adequate value for the rope factor (C) should be carefully correlated

with the specifics of each design (i.e. payload type, etc.). The increase of the rope factor in the latest edition

of the DNV 2.22 standard from 1.75 to 3 for winches with more than 5 layers of product “for subsea

retrieval operations with the full load from the first layer” [6], which sometimes is applicable to reels if

they have to retrieve umbilicals form subsea, might prove to be over conservative, as long as these

operations were also done in the past when reels have been designed according to older editions of the

DNV 2.22 standard which did not have this requirement and the rope factor could be considered C=1.75.



59

Chapter 8: Conclusions and Recommendations

This paper tried to give a better understanding of the 2 design methods (LRFD and WSD) used for

reel design. The 2 methods discussed and compared from their requirements point of view and their

limitations were discussed in light of the latest studies regarding winch design and spooled product (i.e.

wire, rope, etc.) behavior when subjected to reeling tension (i.e. rope relaxation, friction between layers,

etc.). FEA models were built based on the specific requirements of each of the 2 methods and the results

obtained were commented upon.

All in all, there are a lot of grey areas and situations where further research on products with similar

characteristics as umbilicals is needed in order to reduce the amount of unknowns and give a better

understanding on how loads actually act within the product layers and what is their overall combined effect

on the reel structure. Friction between product layers that would lead to a reduction in the actual spooling

tension (maybe close to 0 in some layers) and the damping effect under spooling tension of products with

reduced lateral rigidity on the drum and flange pressures are just 2 areas where further research and solid

results could prove that lower values for these loads could be considered, thus lighter designs could be

obtained.

Reels in general seem to be one of the least studied equipment in the Offshore and Oil and Gas

industry. The assumption that they could be considered and designed as winches has its limitations,

especially when it comes to determining the loads generated by product spooling. Both design and design

review is difficult because there is no specific set of design rules or a recommended practice guide, so it

comes down to each engineer’s way of interpreting the general design requirements of both LRFD and

WSD methods. Although that, from discussions with reel designers, some engineers prefer the WSD

method which, together with DNV no. 2.22 standard, provide a more “calibrated-to-winch/reel-design” set

of rules, maybe others use LRFD which only provides general design rules and a lot of areas where

assumptions have to be made. This might lead to the fact that, although all the assumptions are according to

the standard requirements, the overall result could not be in accordance with the specifics of reels.

From the design exercise performed, the results and relative easier way of designing and identifying

load cases and building load combinations, but also the fact that WSD is more calibrated to winch design,

which is assumed similar to a certain point with reel design, WSD seems to be more suitable for reel design



60

than LRFD. Probably, if a new standard based on LRFD, but focused on the specifics of reels were to be

created, then the methods might be at least similar.

Finally, the delicate matter of testing is not covered by any of the standards and this is considered to

be an important area that needs to be regulated.

The overall conclusion, not just by analyzing the current situation in terms of design standards

available, but also from discussions with people from the industry, there is a need of a “Recommended

Practice Guide” built on one of the 2 design methods that would summarize the general design rules to be

used, how and what loads to be considered, to offer standard solvings for various details of the structure

(i.e. what type drive connection will be more suitable for a certain dimension of reel, etc.), what load tests

to be performed, etc., but calibrated on the particularities of reels and based on studies directly relevant to

reels and the products they transport.



61

Bibliography

1. Wikipedia

2. Subsea Construction lecture notes, University of Aberdeen, 2012

3. DNV-OS-C101 “Design of Offshore Steel Structures, General (LRFD Method)”, October 2008

4. DNV-OS-H102 “Marine Operations, Design and Fabrication”, January 2012

5. DNV-OS-C201 “Structural Design of Offshore Units (WSD Method)”, October 2008

6. DNV No. 2.22 “Lifting Appliances”, October 2011

7. DNV Ship Rules, Part 3, Chapter 1”Hull Structural Design – Ships with Length 100 Meters and

Above”, January 2011

8. Discussions with people from the industry (DNV, Aquatic, Forsyths and others), June – September

2012

9. DNV presentation on “Hoop Stress in Multi-layer Drums”,18th January 2011

10. Song, K.K., ODECO Engineers Inc.; Rao, G.P., Childers, Mark A., “Large Wire Mooring Winch Drum

Analysis and Design Criteria” 8548-PA, April 1980

11. P. Dietz, A. Lohrengel, T. Schwarzer and M. Wächter, “Problems Related to the Design of Multilayer

Drums for Synthetic and Hybrid Ropes”, Technical University of Clausthal, Fritz-Süchting-Institute of

Mechanical Engineering, OIPEEC Conference / 3rd International Ropedays - Stuttgart - March 2009

12. Forum “Winch Design Rules of Thumb” http://www.eng-tips.com/viewthread.cfm?qid=135428,

accessed august 2012

13. AS2759-2004 “Steel Wire Rope”, 2004

14. Lim Buan Teck, Danny, AM16 “Improvement in the Design of Winches”, National University of

Singapore, Session 2004/2005

15. Poon, Jiaen, AM11 “Improvements in Winch Design Guide”, National University of Singapore, April

2006

16. DNV “Rules for Ships” January 2012, Part 5, Chapter 7 “Offshore Service Vessels, Tugs and Special

Ships”, January 2012

17. Oceaneering http://large.stanford.edu/publications/coal/references/ocean/projects/reel/, accessed

September 2012

18. Marine Well Containment Company http://marinewellcontainment.com/expanded_system.php,

accessed September 2012



62

19. Aquatic http://www.aquatic.co.uk/equipment/powered-reel-systems/aqpr_02b_400-62, accessed

September 2012

20. Forsyths http://www.forsyths.com/oil-and-gas-equipment/reels/, accessed September 2012

21. American Oil & Gas Historical Society http://aoghs.org/offshore/secret-pipeline-offshore-technology/



63

Appendix 1 – Load Cases

1. Self-weight of structure (x axis): 58t

2. Self-weight of structure (y axis): 58t

3. Self-weight of structure (z axis): 58t

Note: 3 “self-weight” load cases were created in order to simplify the addition of the reel self-

weight multiplied with the relevant horizontal ship acceleration (longitudinal or transversal)

to the final load combinations.

4. Product load – acts only on the top half of the reel drum

*B = 252 ∙ 1000 ∙ C = 2472120E[1]

F = ) ∗ π ∗ H = 5400 ∙ π ∙ 5700 = 96698221.88IIJ[2]

�=KI[1]LM�[2]N = *BF = 0.02556 E

IIJ [3]

Where:

Fp = force generated by the product on the drum

A = drum overall area

Φ = drum diameter

L = drum length = stave length

l = product load distributed over the entire drum surface

Not all the drum staves will be subjected to the same amount of load: the loads on the

top staves will be significantly higher than the ones acting on the staves closer to the drum

Equator.

�O = P ∙ CH ∙ sin TO

U [4]

U = Vsin TO [5]W

OX�

Where:

Pi = pressure from product force on each stave

M = product mass = 252t Reel

Drum



64

g = acceleration of gravity (g ≈ 9.81m/s2)

xi = angle between stave and horizontal (18 staves distributed at a constant angle at the outer

edge of the drum; angle between 2 consecutive staves = 20°)

n = number of staves = 18

VsinTOW

OX�= 2 ∙ (YZM80 + YZM60 + YZM40 + YZM20 + YZM0)

= 2 ∙ (0.985 + 0.866 + 0.642 + 0.342 + 0) ⟹ Vsin TOW

OX�= 5.67

�� = 252 ∙ 1000 ∙ 9.815.67 ∙ 5700 ∙ YZM80 = 76.49 ∙ 0.985 = 75.33E/II

�J = 76.49 ∙ YZM60 = 76.49 ∙ 0.866 = 66.24E/II

�\ = 76.49 ∙ YZM40 = 76.49 ∙ 0.642 = 49.17E/II

�] = 76.49 ∙ YZM20 = 76.49 ∙ 0.342 = 26.16E/II

2 ∙ V�O = 2 ∙ 216.9 = 433.8E/II

^ℎ:^,: 433.8 ∙ 57009.81 ∙ 1000 = 252

5. Drum pressure due to reeling tension

�� = � ∙ �� ∙ !"

[6]

where:

- σh = hoop stress

- S = spooling tension = 10t

- P = pitch of product (umbilical) = 120mm

- tav = drum plate thickness =15mm

- C = rope layer factor:

o C = 1 for 1 layer

o C = 1.75 for 2 layers

Staves Figure A.1.1



65

o C = 3 for more than 5 layers [6]

The product on the considered reel is spooled in 18 layers, therefore a rope factor C =

3 should be considered. However, designers have usually based their calculations on a value

for C = 1.75 and industry practice and experience have proven that such a value would

ensure a safe design. 2 FEA models will be built with pressures calculated with both values

and the results will be discussed.

C = 3:

�� = 3 ∙ 10 ∙ 1000 ∙ 9.81120 ∙ 15 = 163.5E/IIJ

Pressure on drum calculated with the equation for thin-walled pressure vessels:

�� = �� ∙ 2 !") [7]

where:

- pd = pressure on the drum from spooling tension

- Φ = drum diameter

�� = 163.5 ∙ 2 ∙ 155400 = 0.908E/IIJ

Pressure on each stave:

�a = �� ∙ b ∙ )18 = b ∙ 5400

18 = 855.77E/II



66

C = 1.75:

Hoop stress:

�� = 93.375E/IIJ

Pressure on drum:

�� = 0.53E/IIJ

Pressure on each stave:

�a = 500E/II

6. Flange force due to reeling tension

C = 3:

�' = 2 ∙ !"3 ∙ ) ∙ �� = 2 ∙ 15

3 ∙ 5400 ∙ 163.5 = 0.303E/IIJ

The triangular load distribution will be transformed into equivalent uniform distributed load

(UDL) to simplify the calculation.

Total loaded area:

- Product diameter = 120mm

- Number of layers = 18

- Height of product = 18 · 120 = 2160mm

L=:L = b ∙ AJ − )J

4 = b ∙ (5400 + 2160)J − 5400J

4= 5.13 ∙ 10cIIJ

Total load:

5N = 0.1515 ∙ 5.13 ∙ 10c = 7771.95 ∙ 10\E

Load on each of the 18 flange spokes:

*N = 7771.95 ∙ 10\

18 = 431.775 ∙ 10\E

Force at drum surface:



67

*d = 431.775 ∙ 10\

2160 ∙ 2 = 399.79E/II

C = 1.75:

Flange force due to reeling tension:

�' = 0.177E/IIJ

Total load:

5N = 4533.64 ∙ 10\E

Load on each of the 18 flange spokes:

*N = 251.87 ∙ 10\E

Force at drum surface:

*d = 233.21E/II

7. Load on flange due to transverse acceleration

Annular area of product:

F = b ∙ (5400 + 2160)J − 5400J

4 = 5.13 ∙ 10cIIJ

Product volume:

e = F ∙ H = 5.13 ∙ 10c ∙ 5700 = 2.92 ∙ 10��II\

Calculated product density:

f = Pe = 252 ∙ 10\

2.92 ∙ 10J = 863,C/I\



68

Check if the product slides under transverse acceleration:

Transverse force:

*g = �P ∙ Lg = Lg ∙ (�F ∙ 2160 ∙ f)[8]

Friction force generated by the product mass and

spooling tension:

*' = �F ∙ h ∙ /[9]

where:

- P = product load +pressure on drum due to reeling tension (for C = 1.75)

- µ = friction coefficient = 0.1 [6]

�=KI[3]LM�[7]h = 0.02556 + 0.53 = 0.555E/IIJ

*g = 0.5 ∙ 2160 ∙ 863 ∙ C = 0.0091E/IIJ < 0.0555E/IIJ = 0.1 ∙ 0.555 = *'

⇒ product will not slide

For the “Storm” case, at = 0.75 and a reduced reeling tension will be considered

(Sstorm = 0.5 · S = 5t) ⇒

⇒ *g = 0.75 ∙ 2160 ∙ 863 ∙ C = 0.0137E/IIJ < 0.029E/IIJ = *'

Transverse load distribution:

Triangle area:

FgjO!Wkl+ = 2160 ∙ 12472 = 2693520IIJ

Annular volume of sliding product:

ealO�+ = 5.5 ∙ 10�9II\

⇒ 18.8 % of product volume will slide on the flange.



69

Load on each spoke:

Product slide load = 47.37t

Load on each of the 18 flange spokes = 25.80 kN

Load at top of spoke = 23.88 N/mm

5a. For S = 0, the entire product will slide, thus the entire payload will be supported by

the flange spokes

Payload = 252t

Load on each of the 18 flange spokes = 14t = 137.34 kN

Spoke loaded length = 2160mm

Load on each spoke = 63.58 N/mm

8. Forces on the hub under transverse acceleration

Remaining payload to be supported by the drum = 204.63t = 2007.42 kN

Drum surface area:

F = ) ∗ π ∗ H = 5400 ∙ π ∙ 5700 = 96698221.88IIJ

Drum pressure (similarly calculated as in [3]) = 0.0207 N/mm2

Distance between staves (each stave will collect loads from a surface as long as the stave’s

length and as wide as 2 halves of the distance between 2 consecutive staves – 2 x (d/2))

� = b ∙ )M = b ∙ 5400

18 = 942.477IIJ[10]

where:

- d = distance between staves (refer to Figure A.1.1)

- n = number of staves

Pressure on each of the 18 drum staves:



70

�ag = 0.0207 ∙ 942.477 = 19.56E/II

9. Product load due to longitudinal accelerations

Using same principle of calculations and equations [4] and [5], the load on each of the drum

staves will be obtained. This load will be modeled parallel with the ship deck plane.

�� = 252 ∙ 1000 ∙ 9.815.67 ∙ 5700 ∙ YZM90 = 76.49 ∙ 1 = 76.49E/II

�m = 76.49 ∙ YZM70 = 71.90E/II

�c = 76.49 ∙ YZM70 = 56.2E/II

�n = 76.49 ∙ YZM70 = 38.24E/II

�o = 76.49 ∙ YZM10 = 14.28E/II

�� + 2 ∙ V�O = 76.49 + 2 ∙ 178.605 = 433.7E/II

^ℎ:^,: 433.7 ∙ 57001000 ∙ 9.81 = 252

10. Transverse wind load

Fwind = 800 N/mm2

load on outer rim 0.44 N/mm

load on spoke 0.244 N/mm

load on inner rim 0.344 N/mm

11. Longitudinal wind load

- Product diameter = 120mm

- Number of layers = 18

- Height of product = 18 · 120 = 2160mm

- drum diameter = 5400mm

- Drum circumference = π · 5400 = 18221.23mm

- Sail area:

Fa!Ol = () + 2 ∙ �=K��^ ℎ:ZCℎ ) ∙ H = (5400 + 2 ∙ 2160) ∙ 5700 = 55404000IIJ

- Total wing force:



71

pZM� = Fa!Ol ∙ *qOW� = 44.32,E

Using same principle of calculations and equations [4] and [5], the load on each of the

drum staves will be obtained. This load will be modeled parallel with the ship deck plane.

��9 = 44.32 ∙ 10005.67 ∙ 5700 ∙ YZM90 = 1.37 ∙ 1 = 1.37E/II

�� = 1.37 ∙ YZM70 = 1.29E/II

��J = 1.37 ∙ YZM50 = 1.055E/II

��\ = 1.37 ∙ YZM30 = 0.685E/II

��] = 1.37 ∙ YZM10 = 0.23E/II

��9 + 2 ∙ V�O = 1.37 + 2 ∙ 3.205 = 7.778E/II

^ℎ:^,:7.778 ∙ 5700 = 44.32,E



72

Appendix 2 – Risk Assessment

School Of Engineering Risk Assessment (Guidance notes to be read prior to completing risk assessment)

PROCEDURE: • Experimenter completes Risk Assessment in consultation with Supervisor and technical staff as appropriate. • Risk assessment is checked and signed by Supervisor • Experimenter scans copy to Safety Advisor • Places a paper copy of the signed document with the lab technician. • Safety Advisor sends copy to School Administrative Officer & academic supervisor

NOTES: • No laboratory work is to commence without a risk assessment signed by the Supervisor. • The risk assessment must be reviewed when any changes are made to the equipment, materials, procedure or personnel. • Technical staff can stop work if no risk assessment is in place or if, in their opinion, there is a risk to safety.

Title of project

Research into Good Design Practice for Reels

Description of work

Writing

Names of persons carrying out work

Florian Mircea Teica

Name of Supervisor

Marius Popa (Industry) Dr. Mohammed Salah-Eldin Imbabi (academic)

Location of work

DNV Aberdeen Office

Start date 12.06.2012 Predicted end date 12.09.2012

List of major equipment, materials and facilities involved.

Laptop



73

Record details of the hazards and who could be harmed.

-

Record the precautions which will be taken.

-

Prepared by Signature Date

Florian Mircea Teica 11.09.2012

Supervisor Signature Date

Marius Popa 11.09.2012

Copy with Safety Advisor? -

Copy in Laboratory? (to be retained for 1 year after completion of work)

-



74

Date received: 12.09.2012

SCHOOL OF ENGINEERING

COVER SHEET FOR CONTINUOUSLY ASSESSED WORK

Course Code EG59G9 SECTION 1: Student to complete SURNAME/FAMILY NAME: Teica

FIRST NAME: Mircea Florian ID Number: 51124435 Date submitted: 12.09.2012 Please:

• Read the statement on “Cheating” and definition of “Plagiarism” contained over page. The full Code of Practice on Student Discipline, Appendix 5.15 of the Academic Quality Handbook is at: www.abdn.ac.uk/registry/quality/appendices.shtml#section5

• attach this Cover Sheet, completed and signed to the work being submitted

SECTION 2: Confirmation of Authorship The acceptance of your work is subject to your signature on the following declaration: I confirm that I have read, understood and will abide by the University statement on cheating and plagiarism defined over the page and that this submitted work is my own and where the work of others is used it is clearly identified and referenced. I understand that the School of Engineering reserves the right to use this submitted work in the detection of plagiarism. Signed: ___Mircea Florian Teica___________________________________________ Date:________11.09.2012____________________________ Note: Work submitted for continuous assessment will not be marked without a completed Cover Sheet. Such work will be deemed ‘late’ until a completed cover Sheet is submitted and will be subject to the published penalty for late submission.



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Cheating in any assessment, whether formative or summative, can result in disciplinary action being taken under the University’s Code of Practice on Student Discipline. For these purposes “Cheating” includes: (a) Possession in an examination of material or electronic device which has not been authorised in writing by the relevant Course Co-ordinator. Students whose first language is not English may, however, refer to a dictionary where this is approved by the Head of the School responsible for the examination; (b) Copying from another student in an examination; (c) Removing an examination book from an examination room; (d) Impersonating another candidate in relation to any assessment; (e) Permitting another person to impersonate oneself in relation to any assessment; (f) Paying or otherwise rewarding another person for writing or preparing work to be Submitted for assessment; (g) Colluding with another person in the preparation or submission of work which is to be assessed. This does not apply to collaborative work authorised by the relevant course coordinator. (h) Plagiarism. Plagiarism is the use, without adequate acknowledgment, of the intellectual work of another person in work submitted for assessment. A student cannot be found to have committed plagiarism where it can be shown that the student has taken all reasonable care to avoid representing the work of others as his or her own.

research into good design practice for reels

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