Effect of morphology and flexibility on directional stability of fish and bio-inspired robots

Aquatic animals have long been a source for inspiration to improve our man-made vehicles. Even so, there still exists a gap between the maneuvering performance of even bio-inspired robots and fish. In this paper, the influence of body morphology and flexibility on maneuverability through stability analyses is explored, as a preliminary step towards advancing bio-inspired robot design. A theoretical approach based on slender-body theory and Euler-Bernoulli beam theory was used with numerically found mode shapes. Non-dimensional parameters representing body morphology and fin lift were defined to learn general lessons. The findings highlight that both stable and unstable fin configurations, along with body shape, must be considered concurrently during the design process to ensure that the desired maneuverability characteristics are achieved. The role of flexibility and body morphology for tuna, sailfish and barracuda body profiles were examined. From these investigations it was found that for a soft robot, its stiffness distribution and body morphology can be used to change stability characteristics.