Manipulating propulsive forces with mulitple fins: Understanding how the relative location, phase relationship, compliance and flapping frequency of fins affect the swimming forces and associated flows

Fish produce swimming and maneuvering forces through the coordinated motions of their body and fins. To achieve a locomotory task, fish will typically use multiple fins cooperatively with some fins interacting with the wakes shed by the body and other fins. Since the fin locations, kinematics and mechanical properties vary for different fish species, and with multi-finned robots being more frequently found in research, a better understanding of the complex hydrodynamic interactions among the fins and body that affect propulsive forces is needed. Several studies using biorobotic and numerical models were performed to understand how the relative location, phasing, compliance and flapping frequency of fins affected the produced forces and the associated fin-wake interactions. The results of these studies showed that each experimental factor had a distinct effect on the magnitude, shape and range of propulsive forces achievable by changing the fin kinematics; and the effect of each factor is coupled via the hydrodynamic interaction between fins and wakes shed by other fins. Understanding and capitalizing on the interdependency of fin phasing, spacing, compliance and flapping frequency is essential if engineers are to successfully design and operate multi-finned robotic systems.