Flow-induced vibration of plate and cylinder under unilateral spring constraint

Flow-induced vibration (FIV) of an elastically mounted plate or cylinder under a unilateral constraint is investigated using two-dimensional numerical simulations to explore the hydrodynamic force experienced by a body with spring-loaded legs resting on the seabed. For the unilateral constraint, the spring exerts force on the body only when it is compressed. Compared with bilateral-constraint cases, distinct force features are observed. The plate exhibits an increased average lift, which is attributed to the increased vortex lift in the spring-compression phase. For the circular cylinder, an earlier transition from the initial branch to the lower branch is observed. The drag experienced by the cylinder first increases for U^*<4.2 and then decreases for 4.2<U^*\leqslant 5. By applying the modified force element theory, the mechanism for the different hydrodynamic behaviors under a unilateral constraint has been identified, i.e., the changes in the vortex-shedding patterns and the Q-induced force. The findings may provide insights into the control strategies of underwater-legged robots, potentially leading to enhancements in their design and operational efficiency.