8/3/2019 Disain Bentuk Kendaraan Media Gerak Fluida_Marine Transport_Rutherford_Kieran

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K. Rutherford

School of Engineering Sciences, University of Southampton, UK

Evolution of an AUV Design StrategyFluid Structure InteractionsResearch Group,

School of EngineeringSciences

Southampton University Engineering Doctorate

IntroductionResearch Progressrevious work examined an alternative energy source, and modelled different AUV hull shapes using computational fluid dynamics. These two subsystemsave a large effect on the design and performance of the AUV, but there are other areas which affect the AUV design. Current work explores these areas,

etailing how they affect the AUV, energy source or hull shape. All these design areas, including their constraints and effects, are then integrated by a designmethodology to produce a conceptual AUV.

Pressure VesselsThe pressure vessel provides a space at Atmospheric pressure, protectingpressure sensitive components. The mass of the pressure vessel increaseswith diving depth, such that for a deep diving AUV, the pressure vessel isnegatively buoyant and requires additional buoyancy.

nergy Sourcel energy for powering the AUV has to come from an onboard energy

ource. Improved endurance can be achieved by increasing energy densitykg-1) or decreasing protective structural mass. Lithium polymer batteries

ave a high energy density and do not require a protective pressure vessel.

Selection of AUV Envelopeor different conceived missions, internal arrangement of sub-systems and foam to fulfil required constraints haseen completed. Next the outer shape of the vehicle is determined. Hydrodynamics will impose furtheronstraints on the AUV external shape and location of the sub-systems and foam. For example, placing a largeameter sub-system near the motor will impose a sharp stern gradient, and so may lead to adverse pressureradients and flow separation, increasing the drag of the vehicle.

Acknowledgements

Academic Supervisor: Prof. Grant Hearn.Industrial Supervisor: Prof. Gwyn Griffiths.

The Design Processrom a list of sub-systems, including payload, pressure sensitive components, energy source, structuralomponents, and their constraints, the design engineer has to arrange, balance and select a candidate AUV toulfil intended purpose. Organising all the sub-systems into a minimum volume becomes a packing problem. As

n AUV is a 3D problem with irregular shapes, it is outside the scope of linear programming problems. A newmethodology was created that could be automated given a set of rules.

i. Axial constraint: To make a rotationally symmetric AUV, each sub-system will be placed along a single axis.

ii. Maximum radius: The sub-system with the largest radius will define the AUV maximum radius.

iii. Maximum length: Each sub-system will touch another, such that the maximum length is given by a end on end string ofsubsystems.

he overall centre ofravity of the vehicle muste directly below theverall centre ofuoyancy, else the vehicle

will roll or pitch. The foams assumed to surround aSub-system, so foam cangnore constraint i, but notlter constraint ii, and

must fulfil constraint iii.

Subsystem arrangement with unique Centreof Buoyancy and Centre of Gravity.

Shapeless volume of foam to be addedat an unknown position (LeverFoam).

Leverfoam

Sub-system list

Mission objectives

Payload and

and navigationcomponents

Select energysource and size

Create pressurevessel forsensitive

components

Findbuoyancy

volume andposition

Generatepossible sub-

systemarrangements

Applyhydrodynamic

constraints

Filtered sub-system arrangements

Select arrangementand test against

mission objectives

If AUV fulfils Mission objectives,

move to detailed design.

If not, iterate design andreconsider constraints

nternal StructureUV space frame facilitatesounting of motors, controlanes and pipe work.hese Items can be very

mited in terms of theiracement position withine AUV.

NavigationSensors are required forthe AUV to be aware of itssurroundings. For example

an Echosounder needs tobe at the bottom of the

AUV to detect the seabed.

A Matlab script has been created that will create all possible arrangements from a finite list of sub-systems.The volume of foam is then calculated and the required axial position of the foam found (Fig.1.)

Fig. 1. Finding position of Foam given unique arrangement of sub-systems

Buoyancy FoamAn AUV has to displace the same mass of water as AUV mass. There is amass budget associated with a given AUV volume. The hull shape willoften include free flooding areas, such that the displacement is the sum ofinternal components, not the outer hull shape.

ayloadhe AUV has to carry a payload in order to fulfil its mission. This payload willquire power from the energy source, have a finite mass, and be packed

ependant on its purpose. For example a CTD will require water interaction,d bottom profilers require separation between transmitter and receiver.