Hydrodynamics study of standing-and-hovering behavior of dolphins on the water surface

This paper aims to explore the standing-and-hovering (SAH) behavior of dolphins on the water surface and to reveal its hydrodynamic mechanism through numerical simulations. A virtual dolphin-like swimmer is constructed to perform the three-stage locomotion for the SAH procedure. Volume of fluid method is adopted to deal with the free surface of multiphase flow, and the fluid-structure interaction is realized by using user-defined function and dynamic grid technology. The maximum water-exit height, hover height, energy change, efficiency, and stability are chosen to evaluate the SAH performance. The results show that with the increase of swing frequency and swing amplitude, the hover height increases linearly, and the energy obtained and consumed increases exponentially. Especially, as the swing amplitude increases, the efficiency shows a trend of first increasing and then decreasing. Closer inspection reveals that different kinematic parameters of the swimmer may achieve the same hover height, but their energy consumption, efficiency, and hover stability are different. Therefore, according to the predetermined hover height, the optimal kinematic parameters could be obtained to achieve different hover goals. The findings provide an important hydrodynamic basis for the development of novel bionic robots with SAH capabilities that can perform both underwater and surface tasks.