Numerical investigation of the vortex-induced vibration of a circular cylinder wrapped by a porous layer with time-dependent permeability

This numerical study uses a two-dimensional finite volume method (FVM) to simulate the vortex-induced vibrations (VIVs) of an elastically mounted cylinder wrapped by a porous layer. The flow is incompressible, and the effects of mass ratio ( 2≤m^*≤ 10 ), damping ratio ( 0.01≤ξ≤ 0.1 ), and aspect ratio (0.75≤A_r≤ 1.5) on the lift force, pressure coefficients, and vibration response of a cylinder with constant Darcy number are investigated at Re = 150. Afterward, the dynamic response of the porous-coated cylinder with successive Darcy reduction is studied over a range of reduced velocities (4≤U_r≤ 14) for the first time to investigate the influence of gradual migration of suspended marine particles on the streamlines, flow wake, pressure contours, pressure coefficients, hydrodynamic forces, and vibration response of a vertically oscillating cylinder. According to the results, the influence of gradual Darcy reduction on C_L_rms is significant at U_r = 4 and 5 and reaches its maximum at U_r = 6, where C_L_rms increases by more than 100 U_r = 4, the effect of successive Darcy reduction on A^* becomes more significant at some critical values of reduced velocity and shows a 70 U_r = 6. Moreover, f^* slightly increases for all reduced velocities when the Darcy number decreases over successive periods. In this study, this successive Darcy reduction has an impact similar to that of the lock-in region. The normalized response frequency approaches one at 6≤ U_r≤ 8 and creates a desynchronization regime to fully suppress the vibration amplitude at reduced velocities higher than those of the lock-in area. Moreover, when the cylinder undergoes high-amplitude oscillations, the effect of successive Darcy reduction on the flow wake increases the width of the lock-in region, where galloping (2P) occurs during the transition from the initial branch to the upper regime.