On wave-current interaction with a horizontal cylinder: load characteristics and vortex pattern

This study performed a two-dimensional experiment to reveal the load characteristics of a submerged horizontal cylinder with the vortex pattern in the wake region under wave-current flows. Wave-current conditions were tested with both following and opposing currents. Instantaneous representations of the velocity field, streamline topology, and vorticity patterns, obtained using particle image velocimetry, provided insight into the origin of the unsteady loading of the cylinder. The spatiotemporal characteristics of the pressure distribution on the cylinder were analyzed using Fourier series expansion across the circumference of the cylinder. The results demonstrate that, unlike the action of current only, the presence of waves modifies the frequency and position of vortex shedding, resulting in three distinct modes in the frequency domain of the vertical force on the cylinder, where each mode exhibits a distinct mode of vortex shedding. The variation in frequency domain of Fourier coefficients of pressure around the cylinder is consistent with the force corresponding to different modes. Moreover, velocity rate β and the frequency relationship between the wave and current-induced vortex shedding play important roles in the frequency characteristics of the vertical force.