Emulating the Fast-Start Swimming Performance of the Chain Pickerel (Esox niger) Using a Mechanical Fish Design

摘要

Mean maximum start-up accelerations and velocities achieved by the fast-start specialist, northern pike, are reported at 120 m/s sq and 4 m/s, 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 m/s sq. Peak and averaged maximum velocity was calculated at 0.96 m/s and 0.8 m/s, 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 doublevortex pattern are described.