TMR4225 Marine Operations, 2006.02.09 Lecture content: AUV hydrodynamics and Hugin operational experience What are you expecting to learn from todays lecture?

Dynamic stability 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 constant motion, either horisontally or vertically Small deflections of control planes (rudders)

Dynamic stability (cont) For horisontal 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 horisontal motion

Dynamic stability (cont) 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

Methods for estimating forces/moments Theoretical models Potential flow, 2D/3D models Lifting line/lifting surface Viscous flow, Navier-Stokes equations Experiments Towing tests (resistance, control forces, propulsion) Oblique towing (lift of body alone, body and rudders) Submerged Planar Motion Mechanism Cavitation tunnel tests (resistance, propulsion, lift) Free swimming

Methods for estimating forces/moments Empirical models Regression analysis based on previous experimental results using AUV geometry as variables

Submarine motion equations 6 degrees of freedom equations Time domain formulation Simplified sets of linear equations

EUCLID Submarine project MARINTEK takes part in a four years multinational R&D programme on testing and simulation of submarines, Euclid NATO project “Submarine Motions in Confined Waters”. Study topic: Non-linear hydrodynamic effects due to steep waves in shallow water and interaction with nearby boundaries.

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AUV overview AUV definition: UUV 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

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

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

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

Hugin UUV

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

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

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

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

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

AUV – Experimental techniques Submerged resistance and propulsion tests Towing tank Cavitation tunnel Submerged Planar Motion Mechanism tests Oblique towing test Lift and drag test, body and control planes

AUV – Experimental techniques Free sailing tests Towing tank Ocean basin Lakes Coastal waters Free oscillation tests/ascending test Water pool/ Diver training pool

HUGIN history AUV demo (1992-3) HUGIN I & II (1995-6) 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

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

NTNU/MARINTEK HUGIN involvement 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

HUGIN field experience Offshore qualification seatrials (1997) Åsgard Gas Transport Pipeline route survey (1997) Pipeline pre-engineering survey (subsea condensate pipeline between shorebased process plants at Sture and Mongstad) (1998) Environmental monitoring – coral reef survey (1998) Fishery research – reducing noise level from survey tools (1999)

HUGIN field experience Mine countermeasures research (1998-9) Ormen Lange pipeline route survey (2000) Gulf of Mexico, deepwater pipeline route survey (2001 ->)

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)

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)

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

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

Hugin deployment video Video can be downloaded from Kongsberg homepage

TMR4225 Marine Operations, 2006.02.09 Sum up the 3 most important learning outcomes of todays lecture Have your expectations been fulfilled? If not, why not?