Study of interaction between wave-current and the horizontal cylinder located near the free surface

In this paper, the authors experimentally and numerically study the interaction between wave-current and the horizontal cylinder near the free surface. The experiments are conducted in the Circulating Water Channel with varying axis depths of cylinder. Considering the same wave height and different wave lengths, two regular waves are generated combined with current using a flap-type wave maker. Also, the numerical model based on the RANS equations is solved by the finite volume method, in which the RNG k−ε model is adopted to simulate the turbulence while the VOF method is used to capture the free surface. In this study, the free surface deformation due to wave reflection and blockage is investigated firstly. Then, the typical features of the wave-current force on the cylinder with various axis depths are studied. The peak values of the force are also discussed by comparison with those calculated by the modified Morison's equation. Besides, the vorticity field around the fully submerged cylinder is discussed in detail. It is found that the wave-current force value is affected by both wave reflection and wave blockage under lower cylinder submergence. To be detailed, the force value increases due to wave reflection while decreases because of wave blockage. With regard to the partially submerged cylinder, wave reflection plays a dominant role compared with wave blockage. Therefore, the measured force value is larger than the theoretical one by modified Morison's equation. However, for the fully submerged cylinder, its wave blockage is more notable in contrast with dramatically reduced wave reflection, resulting in a lower measured force value compared with theoretical one.