Design and Simulation of a Towed Underwater Vehicle

Abstract

Oceanographers are currently investigating small-scale ocean turbulence to understand how to better model the ocean. To measure ocean turbulence, one must measure fluid velocity with great precision. The three components of velocity can be used to compute the turbulent kinetic energy dissipation rate. Fluid velocity can be measured using a five-beam acoustic Doppler current profiler (VADCP). The VADCP needs to maintain a tilt-free attitude so the turbulent kinetic energy dissipation rate can be accurately computed to observe small-scale ocean turbulence in a vertical column. To provide attitude stability, the sensor may be towed behind a research vessel, with a depressor fixed somewhere along the length of the towing cable. This type of setup is known as a two-part towing arrangement.

This thesis examines the dynamics, stability and control of the two-part tow. A Simulink simulation that models the towfish dynamics was implemented. Through this Simulink simulation a parametric study was conducted to see the effects of sea state, towing speed, center of gravity position, and a PID controller on the towfish dynamics. A detailed static analysis of the towing cableâ s effects on the towfish enhanced this dynamic model. The thesis also describes vehicle design and fabrication, including procedures for trimming and ballasting the towfish.