Minimization of thrust and sideforce fluctuations of a two-segment ichthyoid propulsor for autonomous underwater...

This study deals with the problem of optimizing the geometry and motion of a two-segment articulated ichthyoid propulsor for autonomous underwater vehicles. The considered propulsor mimics the undulating body and caudal fin motion of a swimming fish; thus, the thrust and sideforce that are generated exhibit undesirable oscillations. The formulas for these hydrodynamic forces, which were derived in the author's previous work, are presented. For selected values of the mean thrust and the swimming speed, two problems of minimizing the thrust (1) and the sideforce (2) variance are solved by systematically searching the set of feasible solutions. Two considered objective functions lead to quite different results regarding the optimal geometry and motion of the propulsor. The propulsor minimizing the thrust variance should have the first segment shorter than the second one, and the propulsive fin should spread over almost the entire length of the second segment. When the objective is minimizing the sideforce variance, the first segment should be described by a length greater and the amplitude smaller than that of the second segment, and the propulsive fin should be small. For both objective functions, the optimal motion of the propulsor strongly depends on the swimming speed and generated thrust. Generating greater thrust at higher swimming speeds requires reducing the vibration period.