Design of biomimetic compliant devices for locomotion in liquid environments

Abstract

Presently, there is a need for devices capable of autonomous locomotion in liquid environments. Humanitarian, industrial and defense applications are numerous and include examples such as search and rescue missions, ocean exploration, and de-mining operations. Due to the nature of the environments involved, the required devices must overcome several challenges. The main challenges are related to hardware performance in terms of propulsion efficiency, mechanical robustness, maneuverability, adaptability, stealth and autonomy. Current traditional approaches that use propeller driven devices have limited success in addressing these challenges. As a result devices that mimic fish-like swimming techniques have emerged as a promising alternative that can provide additional maneuvering features and the promise of improved performance. However, the inherent problems of current biomimetic devices have been identified as: (i) mechanical complexity due to the use of discrete and rigid components, and (ii) lack of a systematic design approach. These problems limit the practical implementation of biomimetic techniques in real mission environments. This thesis presents an alternative approach for implementing biomimetic fish-like swimming techniques by exploiting natural dynamics of compliant bodies.

(cont.) The resultant devices are simpler and more mechanically robust than traditional biomimetic devices. Models are developed to express both the swimming kinematics and the corresponding swimming performance of the proposed devices, in terms of material, actuation and geometry design parameters. Design methodologies that identify the required prototype design parameters for a given target performance are proposed. The designs for caranguiform and thunniform type swimming devices are presented and their performance is characterized experimentally. Predictions based on an elongated body theory model that uses a second order approximation for the body kinematics display good agreement with prototype performance. Finally, the performance limits and the sensitivity to changes in design parameters are shown to be related to the second order system approximation of the body kinematics.