Numerical study on hydrodynamic effects of intermittent or sinusoidal coordination of pectoral fins to achieve spontaneous nose-up pitching behavior in dolphins

The composite fin structure of dolphins is highly coordinated and specialized, making it an important research subject in the fields of marine engineering and biomimetic mechanics. This study aims to explore the promoting effects of the sinusoidal and intermittent flapping of the dolphin's pectoral fins on its spontaneous nose-up pitching behavior from the perspective of computational fluid physics. We adopt a hybrid mesh embedding method combined with dynamic overlapping techniques to handle the local flexible deformation of the dolphin's pectoral fins and the rigid translational motion of the body. The results indicate that, following the principles of biomechanics in nature, the inclusion of pectoral fins, whether in intermittent or sinusoidal mode, can effectively correct the dolphin's original heading, resulting in a trajectory that closely resembles a nonlinear, sawtooth-shaped fan pattern. For the sinusoidal mode, the ascent force coefficient C_FPy of the pectoral fins exhibits asymmetry between the rising and falling phases within a cycle. For the intermittent mode, C_FPy displays a single peak pulse characteristic within one cycle. Through the quantitative analysis of three specific performance parameters, we conclude that the sinusoidal mode provides high stability and sustainability, while the intermittent mode excels in optimizing trajectory radius and energy conversion.