Hydrodynamics of a bionic dolphin robot walking on the water surface in an inclined posture

To enhance the surface operation capabilities of bionic underwater vehicles and address challenges in surface information docking and energy replenishment, this study draws inspiration from a dolphin's surface inclined walking technique, focusing on inclined postures between horizontal and vertical orientations. The hydrodynamic performance of the bionic dolphin robot's inclined walking behavior at different inclined angles (e.g., 15°, 30°, 45°, 60°, and 75°) was investigated with single-caudal-fin and multi-fin propulsion modes. The quantitative models between kinematic parameters and hydrodynamic performance have been established. The transient evolution characteristics of the surrounding flow field were revealed, and key differences between the two modes were highlighted. The results demonstrate that kinematic parameters significantly influence the hydrodynamic performance of inclined walking behavior. Notably, the dolphin robot achieves optimal inclined walking efficiency (up to 69.8%) at inclined angles between 45° and 60°. The single-caudal-fin mode exhibits superior walking velocity and efficiency under high swing frequency and amplitude conditions but with greater variability. In contrast, the multi-fin mode demonstrates more stable hydrodynamic performance with smaller fluctuations. This study addresses the issue of traditional underwater robots being limited to a single underwater application scenario, providing a hydrodynamic basis for the design of underwater robots capable of surface operations.