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TMR4225 Marine Operations, 2009.01.27

• Lecture content:– Linear submarine/AUV motion equations

• Dynamic stability (stick-fixed stability)

• Neutral point

• Critical point

– AUV hydrodynamics – Hugin operational experience

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Linear motion equations

• Linear equations can only be used when– The vehicle is dynamically stable for motions in horisontal and

vertical planes

– The motion is described as small perturbations around a stable motion, either horisontally or vertically

– Small deflections of control planes (rudders)

– For axi-symmetric bodies the 6DOF equations can be split in two sets of equations

• 2 DOF for coupled heave and pitch

• 3 DOF for sway, yaw and roll

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Dynamic stability

• Characteristic equation for linear coupled heave - pitch motion:– ( A*D**3 + B*D**2 + C*D + E) θ = 0

• Dynamic stability criteria is:– A > 0, B > 0 , BC – AE > 0 and E>0

• Found by using Routh’s method

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Roots of stability for a submarine

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Speed variation of damping ratio for a submarine

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Transient response for vertical motion – variation of the damping ratio

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Neutral point position (from Hoerner ”Fluid Dynamic Lift”)

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Critical point – variation with forward speed

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Dynamic stability (cont)

• For horizontal motion the equation (2.15) can be used if roll motion is neglected

• The result is a set of two linear differential equations with constant coefficients

• Transform these equations to a second order equation for yaw speed

• Check if the roots of the characteristic equation have negative real parts

• If so, the vehicle is dynamically stable for horizontal motion

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Traditional approach

• Manoeuvring problem– Calm water

– Large vessel motions in the horizontal plane only

– Problem formulated in a body-fixed coordinate system

• Seakeeping problem– Incident waves

– Focus on vertical motions (heave and pitch)

– Body motions assumed small about mean position of vessel

– Problem formulated in a coordinate system fixed with respect to the mean position of vessel

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New formulation including manoeuvring in waves

• The asymptotic solution of the sea keeping formulation when ω -> 0 will NOT give the traditional manoeuvring equations

• Seakeeping model will also give time-independent forces

• Use of rudder and propulsive forces will introduce dynamic forces in the sea keeping model

Inconsistent behaviour if hydrodynamic model is based on traditional approach

• The traditional maneuvering equations must be obtained by setting the frequency to zero

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The different reference frames

• The north-east-down reference frame (NED frame)– Main coordinate system of ship simulator– Wave/wind/current environment

• The hydrodynamic reference frame (HYDRO frame)– Fixed with respect to mean position of ship– Seakeeping formulation

• The body-fixed reference frame (BODY frame)– Manoeuvring formulation

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Unified formulation – Development steps

• Establish transformations between the BODY and NED frames

• Establish transformations between the BODY and HYDRO frames

• Formulate unified formulation in the BODY frame in the frequency-domain (ie transform the sea keeping formulation from the HYDRO frame to the BODY frame).

• Formulate the unified formulation in the time-domain

• Calculate 2D hydrodynamic coefficients and exciting forces

• Calculate frequency dependent added mass and damping coefficients in unified formulation

• Calculate retardation functions

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AUV overview

• AUV definition:– A total autonomous vehicle which carries its own power and does

not receive control signals from an operator during a mission

• UUV definition:– A untethered power autonomous underwater vehicle which

receives control signals from an operator

– HUGIN is an example of an UUV with an hydroacoustic link

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AUV/UUV operational goals

• Military missions– Reconnaissance

– Mine hunting

– Mine destruction

• Offshore oil and gas related missions– Sea bed inspection

– Pipe line inspection

• Sea space and sea bed exploration and mapping– Mineral deposits on sea floor

– Observation and sampling

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Generic axis system for AUV

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Vector definitions

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6 DOF matrix equation for AUV motion

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Mass matrix

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HUGIN history

• AUV demo (1992-3)– Diameter: 0.766 m Length: 3.62/4.29 m

– Displacement: 1.00 m**3

• HUGIN I & II (1995-6)– Diameter: 0.80 m Length: 4.8 m

– Displacement: 1.25 m**3

• HUGIN 3000C&C and 3000CG (1999-2003)– Diameter: 1.00 m Length: 5.3 m

– Displacement: 2.43 m**3

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HUGIN family

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Initial HUGIN design

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Hugin UUV

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Forebody pressure drag (Hoerner)

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Resistance coefficient – aft body

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Drag coeffient variation with slenderness ratio

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Radius effect on drag for 2D bodies (Hoerner)

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Drag measurement – Hugin prototype

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Panels for added mass calculation

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Added mass matrix for HUGIN prototype

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Stinger for AUV testing in cavitation tunnel

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Heave force variation with pitch angle

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Offshore oil and gas UUV scenario

• Ormen Lange sea bed mapping for best pipeline track

• Norsk Hydro selected to use the Hugin vehicle

• Hugin is a Norwegian designed and manufactured vehicle

• Waterdepth up to 800 meters

• Rough sea floor, peaks are 30 – 40 meter high

• Height control system developed for Hugin to ensure quality of acoustic data

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Phases of an AUV/UUV mission

• Pre launch• Launching• Penetration of wave surface (splash zone)• Transit to work space• Entering work space, homing in on work task• Completing work task• Leaving work space• Transit to surface/Moving to next work space• Penetration of surface• Hook-up, lifting, securing on deck

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AUV – Theoretical models

• Potential theory– Deeply submerged, strip theory

– VERES can be used to calculate

• Heave and sway added mass

• Pitch and yaw added moment of inertia

– VERES can not be used to calculate

• Surge added mass

• Roll added moment of inertia

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AUV- Theoretical models

• Viscous models

• Solving the Navier Stokes equations– Small Reynolds numbers (< 1000) : DNS

– Medium Reynolds numbers (< 10**5) : LES – Large Eddy Simulation

– High Reynolds numbers (> 10**5) : RANS – Reynolds Average

Navier Stokes

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AUV – Theoretical models

• 3D potential theory for zero speed - WAMIT– All added mass coefficients

– All added moment of inertia coefficients

– Linear damping coefficient due to wave generation

• Important for motion close to the free surface

• More WAMIT information– http://www.wamit.com

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NTNU/Marine Technology available tools:

• 2 commercial codes– Fluent

– CFX

• In-house research tools of LES and RANS type

• More info: Contact Prof. Bjørnar Pettersen

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AUV – Experimental techniques

• Submerged resistance and propulsion tests– Towing tank

– Cavitations tunnel

• Submerged Planar Motion Mechanism tests– Towing tank

• Oblique towing test– Towing tank

• Lift and drag test, body and control planes– Cavitations tunnel

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AUV – Experimental techniques

• Free sailing tests– Towing tank

– Ocean basin

– Lakes

– Coastal waters

• Free oscillation tests/ascending test– Water pool/ Diver training pool

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NTNU/MARINTEK HUGIN involvement

• AUV demo (1992-3)– Model test in cavitation tunnel, open and closed model, 2 tail

sections (w/wo control planes)• Resistance, U = {3,10} m/s

• Linear damping coefficients for sway, yaw, heave and pitch, yaw/trim angles {-10, 10} degrees

– 3D potential flow calculation • Added mass added moment of intertia

– Changes in damping and control forces due to modification of rudders

– Student project thesis

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NTNU/MARINTEK HUGIN involvement

• HUGIN 3000– Resistance tests, w/wo sensors

• Model scale 1:4

• Max model speed 11.5 m/s

• Equivalent full scale speed?

– Findings• Smooth model had a slightly reduced drag coefficient for increasing

Reynolds number

• Model with sensors had a slightly increased drag coefficient for increasing Reynolds numbers

• Sensor model had some 30% increased resistance

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HUGIN 1000 layout

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Hugin navigation system

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HUGIN navigation system - items

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HUGIN communication system

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HUGIN sub system overview

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HUGIN information

• New vessels have been ordered late 2004 and 2005– One delivery will be qualified for working to 4500 m waterdepth

• New instrumentation is being developed for use as a tool for measuring biomass in the water column

• Minecounter version HUGIN 1000 has been tested by Royal Norwegian Navy

• More Hugin information: see Kongsberg homepage for link

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HUGIN field experience

• Offshore qualification sea trials (1997)

• Åsgard Gas Transport Pipeline route survey (1997)

• Pipeline pre-engineering survey (subsea condensate pipeline between shore based process plants at Sture and Mongstad) (1998)

• Environmental monitoring – coral reef survey (1998)

• Fishery research – reducing noise level from survey tools (1999)

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HUGIN field experience• Mine countermeasures research (1998-9)• Ormen Lange pipeline route survey (2000)• Gulf of Mexico, deepwater pipeline route survey (2001 ->)• Raven, West Nile Delta, Egypt, area of 1000 km**2 was

surveyed late 2005 by Fugro Survey– Sites for subsea facilities– Route selection for flowlines, pipelines & umbilicals– Detect and delineate all geo-hazards that may have an impact on

facilities installation or well drilling– Survey area water depth: 16 – 1089 m (AUV used for H > 75 m)– Line spacing of 150 m and orthogonal tie-lines at 1000 m intervals– Line kilometers surveyed by AUV: 6750 km – Distance to seabed (Flying height): 30-35 m– Operational speed: 3.6 knots

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Fugro survey pictures

http://www.fugrosurvey.co.uk/

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Actual HUGIN problems

• Inspection and intervention tasks– Adding thrusters to increase low speed manoeuvrability for

sinspection and intervention tasks• Types, positions, control algorithms

– Stabilizing the vehicle orientation by use of spinning wheels (gyros)

• Reduce the need for thrusters and power consumption for these types of tasks

– Docking on a subsea installation• Guideposts

• Active docking devices on subsea structure (robotic arm as on space shuttle for capture of satelittes)

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Actual HUGIN problems

• Roll stabilization of HUGIN 1000– Low metacentric height– 4 independent rudders – PI type regulator with low gain, decoupled from other regulators

(heave – pitch – depth, sway – yaw, surge)– Task: Keep roll angle small ( -> 0) by active control of the four

independent rudders• Reduce the need for thrusters and power consumption for these types of

tasks

– Docking on a subsea installation• Guideposts

• Active docking devices on subsea structure (robotic arm as on space shuttle for capture of satelittes)

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Future system design requirements

• Launching/ pick-up operations up to Hs = 5 m when ship is advancing at 3-4 knots in head seas

• Increasing water depth capability

• Increased power capability– Operational speed 3- 4.5 knots

– Mission length 3- 4 days

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Hugin deployment video

• Video can be downloaded from Kongsberg homepage