Abstract: Forces on cylinder in stratified flow environment differs notably with those in uniform density flow due to the opposite velocity directions of two layers.A splitter plate deployed upstream of the cylinder in uniform density flow with its frontal face normal to the wave propagation is employed to explore the reduction of forces on an erected cylindrical pile.A 3-D numerical wave flume model is established to investigate the reduction of forces acting on cylinder through Large-Eddy Simulation (LES) approach.Results unveil that splitter plate has prominent influence on the force distribution of the pile in the upper layer,but hardly any effect on the counterpart in the lower layer.The pattern of vortex structure behind the splitter plate plays a fundamental role in reducing the drag forces on pile.Key parameters blockage ratio l/D and plate position ratio s/D characterize the feature of vortex structure around the pile.The reduction effect is quantified by forces reduction ratio B_R,and an empirical formula between B_R and s/l is fitted by regression analysis.The parameters of splitter plate should be controlled at an appropriate level to prevent from over-reduction.

Key words: internal wave, cylinder, drag reduction effect, large eddy simulation, force behaviors