Experimental hydrodynamics and simulation of manoeuvring of an axisymmetric underwater vehicle

Azarsina, Farhood (2009) Experimental hydrodynamics and simulation of manoeuvring of an axisymmetric underwater vehicle. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Experimental study of the hydrodynamics of an underwater vehicle requires state-of-the-art facilities, precise design of the experiment and careful analysis of the results. This thesis presents hydrodynamic observations resulting from experiments that were performed on a series of five bare-hull configurations of slender axisymmetric underwater vehicles and also reports a simulation code to predict the manoeuvring behaviour of a real underwater vehicle: MUN Explorer. The main aim is to find the correct form of the physically-based expressions for the hydrodynamic loads that are exerted on completely-submerged underwater vehicles during various manoeuvres and use this improved knowledge to obtain a better prediction of the manoeuvring of an underwater vehicle. -- Straight-ahead resistance tests and static-yaw runs up to 20 degrees yaw angle for the axisymmetric bare-hull configurations that were performed in the 90 metre towing tank at the Institute for Ocean Technology, National Research Council, Canada, provided empirical formulae for the drag force, side force and turning moment that are exerted on such axisymmetric torpedo-shaped hull forms. The empirical formulae were then embeded in a numerical code to simulate the constant-depth planar manoeuvres of the MUN Explorer AUV. The simulation code was first calibrated using the sea-trials data, and then was used to study the turning manoeuvres and compare the simulation results with theoretical formulae based on the linearized equations of motion. -- Dynamic captive-model tests including pure sway and pure yaw runs were the other part of the experiments on the five bare-hull configurations. The sway force that is exerted on the bare-hull during lateral accelerations, according to the pure sway test data, was observed to have a variation over manoeuvring frequency and amplitude. Also, empirical formulae were proposed to estimate the magnitude and phase of the hydrodynamic loads: sway force and yawing moment that are exerted on the axisymmetric torpedo-shape bare-hull of an underwater vehicle during a rapid zigzag manoeuvre. -- Finally, in order to obtain further insight into the origin and distribution of the hydrodynamic loads during underwater manoeuvres, pressure measurement experiments were proposed and as an initial step towards the aim of performing such measurements over the surface of an underwater vehicle, a re-analysis of the old airship data was presented. The re-analysis of the airship pressure test results provided an estimate of the normal pressures that may be experienced by an underwater vehicle during manoeuvres.

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