  The current study presents a systematic investigation of the locomotion
performance of a swimmer with a wide range of parameter settings.
Two-dimensional simulations with the immersed boundary method are employed for
the fluid-structure interaction analysis. Unlike most previous studies where
the kinematics of the swimmer is predetermined, the locomotion of the current
swimmer is the response of a single periodic torque applied on the anterior
part. The effect of the distribution of body stiffness on swimming performance
and propulsion generation is discussed with different pitch frequencies and
amplitudes. An analysis of the phase-averaged vorticity field and thrust
sequence is given to clarify the change of performance due to the variation of
flexibility. This study demonstrates that body stiffness is a key factor that
influences the performance of undulatory swimming when the pitch angle is low
or moderate. The simple torque input of the current simulations provides a more
direct and engineering-related insight for the future design of microrobotic
swimmers.
