Scallop locomotion was investigated based on an analysis of fluid forces
acting on the body and the balance of the forces during swimming. A
hydrodynamic model for unsteady jet propulsion was developed, in which the
propulsion performance is characterized by three non-dimensional
parameters: the storage-discharge volume ratio, reduced clapping frequency
and reduced discharge frequency. Pulsed jet propulsion is designed to achieve
high thrust, although not necessarily with low hydrodynamic propulsive
efficiency, as previously widely considered. Swimming in scallops is realized
by orientating the body at a certain angle of attack and maintaining a
minimum swimming speed to prevent sinking. The working frequency of the
locomotor system is determined and adjusted by the swimming strategy (angle
of attack, swimming speed and trajectory angle). For Placopecten
magellanicus, the optimum angle of attack is about 6-12 degrees, at
which swimming requires the lowest energy input (lowest frequency) and has
ideal hydrodynamic behaviour (without severe separation and stall). To
maintain level swimming, Placopecten magellanicus, during almost all
their life, must swim at 5 to 7 body length per second if postured at a
6-12 degrees of angle of attack. The estimated Froude efficiency decreases
during growth from about 0.5 to 0.3 for level swimming, and from about
0.4 to 0.2 for climbing at an angle of 25 degrees. It is suggested that the
heavy body weight and inferior hydrodynamic characteristics (low aspect ratio
and imperfect planform shape) have limited scallop from becoming good
swimmers. These problems are enhanced as the animals grow.
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