The wave and current loads are the primary loads acting on the offshore structures. Rogue wave, a typical steep wave, is considered to occur due to wave focusing and wave-current interaction in the ocean and becomes one of the major causes of offshore structure damage. In this study, the hydrodynamic forces on horizontal cylinders exerted by the focused steep waves has been investigated considering wave-current interaction. The RANS equations solving by finite volume method are applied to evaluate the strongly nonlinear interaction between waves and current, in which the VOF method is adopted to capture the free surface. The velocity and water depth are given at the inlet boundary of the computation domain to generate deep water focused wave. In this paper, the wave forces acting on the cylinder in focused waves without current are investigated firstly. The wave forces are simulated for different horizontal distances between the cylinder and the pre-designed wave concentration point, and the maximal wave forces are analyzed. Meanwhile, the effects of the cylinder on wave deformation are also discussed. To validate the numerical model, the simulation results of wave forces on a cylinder by regular wave and the water surface elevation of a focused wave are compared with published experiment and simulated results. Then, the nonlinear interaction between the focused wave and current are investigated, the hydrodynamic forces acting on cylinder are simulated for different current velocities. Accordingly, the nonlinear effects of wave-current interaction on the hydrodynamic forces are discussed with respect to the results of wave deformation at concentration point, forces under actions of focused wave and combined wave-current conditions.

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