Emulating the fast-start swimming performance of the chain pickerel (Esox niger) using a mechanical fish design
Watts, Matthew Nicholas
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Mean maximum start-up accelerations and velocities achieved by the fast-start specialist, northern pike, are reported at 120 ms-2 and 4 ms-1, respectively (Harper and Blake, 1990). In this thesis, a simple mechanical system was created to closely mimic the startle response that produces these extreme acceleration events. The system consisted of a thin metal beam covered by a urethane rubber fish body. The mechanical fish was held in curvature by a restraining line and released by a pneumatic cutting mechanism. The potential energy in the beam was transferred into the fluid, thereby accelerating the fish. The fish motion was recorded and the kinematics analyzed while using a number of different tail shapes and materials. Performance of the mechanical fish was determined by maximum acceleration, peak and averaged maximum velocity, and hydrodynamic efficiency. Maximum start-up acceleration was calculated at 48 ms-2. Peak and averaged maximum velocity was calculated at 0.96 ms-1 and 0.8 ms-1, respectively. The hydrodynamic efficiency of the fish, calculated by the transfer of energy, was 11%. Flow visualization of the mechanical fast-start wake was also analyzed. The visualization uncovered two specific vortex-shedding patterns; a single and a double-vortex pattern are described.
Submitted in partial fulfillment of the requirements for the degree of Master of Science in Oceanographic Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2006
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