Design and commissioning of a computer controlled oscillating hydrofoil dynamometer

Greening, David L. (1996) Design and commissioning of a computer controlled oscillating hydrofoil dynamometer. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (22MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

High propulsive efficiencies can be realised from oscillating foil propulsors. Information on these propulsors can be obtained by systematically studying the geometry's and motions of manufactured foils and the fins and flukes of cetacean mammals and fast swimming fish, which propel themselves through oscillations of a high aspect ratio lunate fin or fluke. -- The development of a dynamometer for studying the flow patterns and propulsive characteristics of oscillating foil propulsors is described. The dynamometer was designed to measure the effect of variations in foil parameters such as planform, sweep back, foil section, pitching axis location, and foil flexibility for a series of oscillating motions. It was designed primarily for use in a cavitation tunnel, to study the flow over the foils and their cavitational characteristics and, secondarily, for use in a towing/wave tank, to study the propulsion efficiency of the foils. Two foils were mounted in a central mounting pod which in turn was connected to the drive system. Mounting the foils in this manner did not disturb the flow over the tips of the foils which are thought to play a prime role in the propulsive performance of the foils. The drive system consisted of two numerically controlled direct current servo motors connected to a 80286 computer through a Unidex 14 series multi-axis motion controller. The system was programmed to produce a small sine wave oscillating motion and to allow the oscillating motion to be modified easily. -- The dynamometer was capable of producing a series of motions which were obtained by modifying the motion subroutine in the Unidex control program. The first motion programmed for use with the dynamometer was a small pitch angle sine wave motion with a constant phase angle of 90° between pitch and heave. -- This thesis project was the first in a series of thesis projects aimed at developing a fully functional oscillating foil dynamometer to 1) Oscillate test foils with a substantial variety of oscillating motions; 2) Study the development of the flow over the test foils; 3) study the formation of cavitation on the test foils; and 4) To determine the propulsion efficiency of the test foils. The aim of this thesis was 1) design and fabricate the prototype dynamometer, 2) program its control system to produce the initial oscillating motion, 3) conduct a series of tests to determine the systems abilities and limitations, and 4) make recommendations on how to overcome its limitations. The implementation of the recommendations is left as part of the next thesis project in this series. -- The performance and evaluation of the dynamometer in a series of preliminary tests is described. These tests were aimed at evaluating the performance of the dynamometer and its computer control system and not as a complete study of the foils. The foils which were used in the initial tests had a rectangular planform with an aspect ratio of six and a NACA 0019 section (this section is similar to the section through the flukes of a fin whale). -- The initial test consisted of running the dynamometer with a sine wave motion for a series of pitch and heave amplitudes, pitching axis locations, oscillating frequencies, and water flow velocities. These tests demonstrated the operational capabilities of the dynamometer, the accuracy of the obtained motion compared with the requested motion and the quality of the data retrieved from the data acquisition system.

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