טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGuy Kagan
SubjectPropulsion System for Autonomous Vessels using Oscillating
Foils
DepartmentDepartment of Autonomous Systems and Robotics
Supervisor Research Professor E Weihs Daniel


Abstract

 

Millions of years of evolution have improved and adapted marine animals to an elegant and efficient water motion. Many of them use body movement and tail fin to create forward motion. Studies have shown that propulsion systems based on an oscillating foil are equal to or better than propulsion systems based on screw propeller, both in terms of efficiency and in their ability to provide power for propulsion.


Fish form schools to facilitate swimming efficiency of each individual. This phenomenon has served as the basis for many studies and was implemented in experimental systems. Foils oscillating in a side-by-side (SBS) configuration have been found to have better propulsion properties than a single oscillating foil due to their use of the "neighbor effect" or "ground effect".


The purpose of this project is to design, build and calibrate an experimental system consisting of two foils oscillating in a SBS configuration in order to extract propulsion properties.


The experimental system consists of two hydrofoils with a symmetric NACA0012 section, constructed from anodized aluminum with a chord length 60 mm and span of 210 mm. The foils oscillate in two degrees of freedom. The system allows controlling the maximum angle of attack, the amplitude of the heaving motion and the oscillation's frequency. It is also possible to control the phase difference and the minimum distance between the two foils. The experimental propulsion system allows measuring the forces, and enables calculating the thrust produced and efficiency.


The results show that the thrust coefficient obtained for one foil in a two foil set is higher than that of a single foil system by up to 210%. System boundaries were explored by changing the distance between the foils. Most of the results show a clear downward trend in the value of the thrust coefficient obtained as the distance between the foils increases, and in contrast, getting maximum value for minimum foil distance. These results are consistent with the assumption that increasing the distance between the foil reduces the mutual influence between them. However, some results show that for maximum distance between the foils there is an increase in the thrust coefficient. This phenomenon is assumed to be caused by edge effects. We further found that the value of thrust coefficient for the two foil system grows faster when increasing the amplitude of heaving relative to a single foil. No changes in thrust coefficient were observed by minimizing the distance.


The development of the various configurations predicted the desire to improve the system as much as possible, both in terms of the quality of the results, and in the human engineering aspect. The selected configuration was based on minimum mechanics and electronic control in order to change the desired parameters, including the angle of attack, the frequency of movement, the heaving and the pitching amplitude, and the minimum distance between the two foils. A Parametric examination of the forces due to motion of the foils was compared to the values obtained from a single oscillating foil.