Date

8-1-2019

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Mechanical Engineering

First Adviser

Keith W. Moored

Abstract

Inspired by the advanced capabilities of fish and other aquatic swimmers, in this thesis, a greater understanding of fish-like propulsion has been sought in terms of morphology and kinematics. Unsteady potential flow simulations on real cetacean flukes reveal that the effect of shape and gait on the swimming performance are not intertwined and are in fact independent. There is one fluke shape that maximizes the propulsive efficiency regardless of the gait and vice versa. It is also determined that the shape and the gait of the fluke have a considerable influence on the wake topology and in turn the Strouhal number. Evolutionary optimization is used to isolate the shape effects and study optimum conditions when the kinematic features of the animals are varied. Searching the optimum swimmer in terms of swimming gait is performed by considering the three main aspects of the swimming performance: swimming speed, swimming range, and efficiency. Optimum conditions are found when i) the swimmer keeps the duty cycle low and uses sinusoidal-like motion by maintaining higher pitching amplitudes to provide higher thrust and swimming range; ii) the swimmer uses square-like waveform shapes by increasing the duty cycle and using small pitching amplitudes which decrease the swimming range but increase the swimming speed. In all combinations, swimming efficiency is maintained at the maximum achievable level. Scaling laws are presented to predict thrust production and power consumption of the swimmers by accounting for three-dimensionality with shape and gait variations. The scaling laws presented here provide insight into the flow physics that drive thrust production, power consumption, and efficient swimming when the morphology and kinematics are varied.

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