Fish Propulsion

Aquatic creatures such as fish have had the luxury of optimizing their design through evolution over millions of years to achieve remarkable locomotive skills. Some of the larger swimmers that are optimized realize high swimming speeds, long ranges, and excellent propulsive efficiencies. Many fish over a broad scale of sizes have likewise developed maneuvering techniques that allow them to complete a 180 degree turn in less than half of their body length.

To be sure, the performance of fish, unparalleled in marine propulsion by human-engineered system, provides inspiration to the development of unique and exciting marine propulsion alternatives.

In an attempt to quantify the performance assertions commonly held about fish propulsion, the MIT Vortical Flow Research Laboratory (VRFL) and the MIT Testing Tank Facility have developed a suite of tools to analyze both fish straight-line swimming as well as maneuvering, both through experimental observations and measurements as well as detailed approximate analytic and numerical methods.

Since 1992, the MIT Testing Tank facility has been developing and testing the RoboTuna, a robotic mechanism in the form of a bluefin tuna. Additional work is being done towards the development of two more mechanisms, in the form of a pike, to study turning.

The VFRL has developed a three-dimensional numerical code which is capable of simulation of complex multiple-finned bodies of arbitrary flexibility, incorporating multiple nonlinear desingularized wake representation and interaction. Use of this code has supported the robotic flexible hull experimental effort and has provides unique insights into the vorticity dynamics of flexible body propulsion.

The three-dimensional code has also been used to simulate the swimming motions of live fish, discretized from images obtained by experimental DPIV techniques. For example, a Giant Danio has been examined in great detail because this species is robust in handling and has morphological features similar to the large swimmers. Simulation of the Giant Danio motions has provided a thorough understanding of wake-wake and wake-body interactions, as well as three-dimensional vorticity control to achieve large, short-duration maneuvering forces.