Experimental and numerical study of wave current interactions with a dumbbell shaped bridge cofferdam

Recently, a new structure type of a vertical truncated dumbbell-shaped cylinder has been widely used in bridge cofferdams in many sea-crossing bridges in China. Wave-only and wave-current interactions with this new structure type are studied experimentally and numerically. The modified Morison equation is applied to derive the drag coefficients CD and inertia coefficients CM. The influence of the incident flow directions, current velocity, static wave height and wave periods on the hydrodynamic coefficients is explored. The study shows that the hydrodynamic coefficients are strongly correlated with the sine values of the incident flow directions. In addition, a 3D numerical model using a multilayer σ-coordinate model and an immersed boundary method based on the Navier-Stokes equations (Kang et al., 2015) is established. Based on the validated numerical model, flow patterns around the structure, including the free surface and 3D vorticity distributions, are analyzed numerically. The results presented herein provide important guidance to better understand the hydrodynamic performance of this new structure type.