Hydrodynamic interaction between two elastic microswimmers

We investigate the hydrodynamic interaction between two elastic swimmers composed of three spheres and two harmonic springs. In this model, the natural length of each spring is assumed to undergo a prescribed cyclic change, representing the internal states of the swimmer [K. Yasuda et al., J. Phys. Soc. Jpn. 86, 093801 (2017)]. We obtain the average velocities of two identical elastic swimmers as a function of the distance between them for both structurally asymmetric and symmetric swimmers. We show that the mean velocity of the two swimmers is always smaller than that of a single elastic swimmer. The swimming state of two elastic swimmers can be either bound or unbound depending on the relative phase difference between them.