Numerical investigation on the modulation mechanism of sediment–water vortex in stingray self-burial by pectoral fin kinematic parameters

The self-burial behavior of benthic fishes, such as stingrays, is achieved by actively manipulating seabed sediments and provides a natural paradigm for long-term concealment and stability in energetic benthic flows. This study develops a two-dimensional numerical model of flexible fins interacting with water and sediment to systematically elucidate how key flapping kinematic parameters—curvature velocity (ω), curvature amplitude (r), and number of cycles (N)—synergistically regulate vortex dynamics within the water–sediment mixture during stingray self-burial. Curvature velocity (ω) is identified as the dominant factor controlling both the total suspended sediment load and the power consumption. Curvature amplitude (r) determines the initial settling location of sediment-laden vortices, while multiple flapping cycles (N) promote inter-cycle merging of turbulence-induced vortices, progressively strengthening the mixed vortex field. In the two-dimensional trade-off space between peak power (Ppeak) and sediment transport efficiency (η), the parameter combination ω = 1.1, r = 7, N = 2 lies at the knee region of the Pareto front, representing a robust high-efficiency, low-peak-power strategy (η = 3.66 mm/J; Ppeak = 25 W). This optimal strategy is consistent with biological observations of stingrays performing 2–5 flapping cycles at frequencies of 2.5–5 Hz, and its required power remains within the measured limits of pectoral fin white muscle (approximately 50–100 W/kg). Overall, this work advances the mechanistic understanding of stingray–fluid–sediment coupling and provides a theoretical and parametric foundation for the development of efficient, low-power self-burying underwater robots.