TMR4225 Marine Operations, 2004.02.21 UUV/AUV definitions Critical design parameters for a seabed mapping system Critical parameters for vehicles used for intervention tasks on subsea structures Linear motion equations

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 Reconnecaince 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 piperoute trace Norsk Hydro selected to use the Hugin vehicle Waterdepth up to 800 meters Rough sea floor, peaks are 30 – 40 meter high Height control of Hugin to ensure quality of acoustic data

C & C Technologies – Track record Operational areas Gulf of Mexico West coast Africa Brazil Mediterranean More than 18000 survey line kilometers Waterdepths down to 2850 m Cost 33-50% of traditional deep-tow system

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

Group work no. 1 Describe physical factors to be considered when analysing different phases of an AUV/UUV mission Select on of the following missions: Mapping seabed for selection of optimal pipeline track Inspection of a subsea gas export pipe Seabed mapping for deep sea mining Select the three phases you rank as most critical for a successful mission

Group work no. 1 – Student feedback (2004) Launching Launching arrangement; A-Frame, crane etc Readiness for operation, eg. various equipment on board All openings on the hull surface must be closed (watertightness)

Group work no. 1 – Student feedback (2004) Penetration of splash zone Impact loads Hydro-elasticity Relative motion; phase, amplitude, frequency Change of parametres from air to water (buoyancy, eigenfrequency, etc.) Wire tensions

Group work no. 1 – Student feedback (2004) Transit to work space Navigation/control system (current/flow/(diving)), DP Buoyancy during transit ( different layers of salinity in the sea) Resistance/propulsion/endurance/power supply Material/hullform ( the vehicle has to withstand high external pressure)

Group work no. 1 – Student feedback (2004) Completing work task Battery capacity Check if mission is completed Check the current conditions Safe manoeuvring to avoid collisions, damage of propellers Interaction between thrusters

Group work no. 1 – Student feedback (2004) Transit to surface/Moving to next work place Changing buoyancy (pressure/gravity) Resistance forces (transit between workfields) Current forces Wave influence near surface

Group work no. 1 – Student feedback (2004) Penetration of surface Movements induced by: Waves Current (viscous forces) Buoyancy/gravity Reaching the surface -> change of: Wetted surface (viscous) Buoyancy (volume) According to the sea state, we can have very unstable system

Group work no. 1 – Student feedback (2004) Hook-up, lifting, securing on deck Sea state; ship motion, AUV motion Effect of wind in the crane Centre of gravity of AUV Lifting Splash zone, wind, safety distance Securing on deck Safe bed, fastening devices, operation in heavy seas

Motion equation for AUV Read Chapter 2 in project work of Jon E. Refnes For small perturbation of a constant speed motion, motions can be described by two sets of linear equations Heave and pitch Sway, roll and yaw Studying streamlined AUVs the horisontal plane motion can be reduced to coupled sway and yaw See equations 3.2 - Horisontal motion 3.3 – Vertical motion

Dynamic stability For horisontal plane motion, see section 2.4 in course note Final criteria is G1 > 0 (or C >0 in blackboard notes) No speed dependence on stability criteria Vertical motion, see section 2.3.2 in course note Note that the characteristic equation is of third order More complex stability criteria Stability criteria is speed dependent Characteristic equation has to be solved for all possible operational speeds of the vehicle

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