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

Flow-induced vibration (FIV) of an elastically mounted plate or cylinder under 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 is first increased for U^*<4.2 and then reduced for 4.2<U^*\leqslant 5. By applying the modified force element theory, the mechanism for the different hydrodynamic behaviors under unilateral constraints has been identified, i.e., the changes in the vortex-shedding patterns and the vortex force. The findings may provide insights into the control strategies of underwater-legged robots, potentially leading to enhancements in their design and operational efficiency.