TMR4225 Marine Operations, 2004.02.12 - ROV intro AUV Types HUGIN development Motion equations Force and moment estimation Exercise

AUV – UUV definitions AUV UUV An Autonomous Underwater Vehicle which carries its own power and does not receive control signals from an operator during a mission UUV An Untethered Underwater Vehicle carrying its own power and receiving control signals from an operator (hydroacoustic or fibre optic cable)

Two characteristic shapes Torpedo shape Originally military application, also used for scientific vehicles Tactical Acoustic System Mine Search System Remote Surveillance System Low drag shape Pearson form Basic shape used for initial development studies of HUGIN

Torpedo shape - Autosub

Low drag shape – HUGIN 3000

AUV examples

Important AUV web sites www.freesub.soton.ac.uk www.ausi.org www.cs.nps.navy.mil/research/auv/auvframes.htm www.dosc.uu.se~robmil/AUV/AUV_links.htm www.oe.fau.edu/AMS/auv.htm www.scss03.org

AUV design challenges Suspension in air Centre of gravity Lifting arrangements Penetration of sea surface Resistance – propulsion – energy capacity Steering and manoeuvring Dynamic stability Control units (thrusters, rudders) Control system design

Mathematical model SNAME axis system Nielsen (chapter 4) + X forwards + Z downwards Nielsen (chapter 4) + X aftwards + Z upwards Refnes (chapter 2)

6 Degree of freedom motion equations Nielsen Second order partial differensial equations with constant coefficient Frequency dependent hydrodynamic coefficients Matrix form Refnes First order nonlinear partial differential equations with constant coefficients (state space formulation)

6 Degree of freedom motion equations Gertler and Hagen – Submarine equations Second order, nonlinear partial differensial equation Constant coefficients (some may be speed dependent) Component form Simplified models Decoupled equations for motions in vertical and horizontal plane Linear equations for study of dynamic stability and small perturbations around a steady state condition

Group work A: Discuss the statements on forces/moments on pages 5 – 8 in Refnes, Chapter 2 B: Discuss methods to estimate forces/moments C: Present the results for the other groups Group 1: Inertial forces Group 2: Coriolis and centripetal forces Group 3: Hydrodynamic damping and lift forces Group 4: Restoring forces and moments due to gravity/buoyancy Group 5: Control forces Group 6: Environmental forces (waves and currents) Group 7: Interaction forces

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

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 – 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

HUGIN 3000 Characteristics Operational depth: 3000 m Mission lenght: 58 hours Nominal speed: 4 knots Position accuracy: 2-3 m for water depths > 2000 m Costs: 30 – 45 mill NOK (2002) Number produced 3 (2002)

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

Actual HUGIN problems Norwegian Defence Research Institute (FFI) and Kongsberg Simrad are looking for talented students that would like to work on problems related to design, control and operational performance of AUVs/UUVs

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

Exercise no. 4 Linear equations for horizontal plane motion of an AUV Dynamic stability check Calculation of yaw response using zigzag tests

Additional reading B. Jalving, K. Vestgård and N. Størkersen: - Detailed seabed surveys with AUVs (27 pages) M. Mandt, K. Gade and B. Jalving: - Integrating DGPS-USBL position measurements with inertial navigation in the HUGIN 3000 AUV (9 pages)

TMR4225 Marine operations, 2004.02.12 Sum up the most important learning outcome(s) of this lecture Forward your summary to Toreinar.berg@marintek.sintef.no Feedback will presented as a separate Word document