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The hydrodynamics of batoid swimming motions is investigated using the three-dimensional simulation of a self-propelled body in still water.The kinematics of batoid swimming is characterized by large amplitude undulations of the pectoral fins while the middle part of the body remains straight.The majority of the thrust is generated by pectoral fins.Linear and quadratic amplitude variations are used for the pectoral fins in analyzing the locomotion of the batoid.Navier-Stokes equations are used to solve the unsteady fluid flow.A user defined function and a dynamic mesh method are applied to track the batoid locomotion.The mean swimming velocities of 1.6 BL/s and 1.3 BL/s are achieved,respectively,with thrust coefficients of 0.13 in and 0.095 in the dynamical simulation,where BL/s is the body length per second.The maximum propulsive efficiency 19％ is achieved when the frequency of the undulation is 2.2 Hz in both amplitude variations.