Numerical Simulation Of Wave Forces On Small-diameter Cylinders Using Three-dimension Unsteady Reynolds Equation Model

Water wave is a key hydrodynamic factor in offshore and coastal engineering, and wave forces acting on the structures are usually the control load for design. It is necessary to study the interaction between water waves and coastal structures. In coastal and ocean engineering, the structure with the ratio of its diameter to the wavelength being less than 0.15 is regarded as small-diameter structure, and the structures of arrays of small-diameter cylinders are widely used in practice. Three dimensional numerical model based on the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations which being closed with k ?εturbulence model has been developed to simulate the interaction between water waves and coastal structures in this study. The VOF (Volume of Fluid) method is used to track the free surface. An active generating-absorbing numerical wave paddle is used to generate waves, and an active sponge layer is introduced at the open boundaries to absorb waves.Two-steps projection method is used to calculate the URANS. Firstly, the effect of pressure on velocity is ignored. Secondely, the temp velocity is projected into a none-divergent space to calculate the real veolocity. The inertia force is obtained by integrating the pressure and the drag force is calculated by using the veolocity field.In order to validate the numerical model, two examples were simulated by using the numerical model, given as follows: (1) solitary wave run-up on a vertical wall (2) wave forces on a solitary small-diameter cylinder. The numerical results of velocity fields, free surface and wave forces agree with the analytical and experimental results very well.Wave forces on solitary small-diameter cylinder in different wave fields were simulated, and the results were compared with the results obtained by using the Morison equation, the two results are similar. Finally, the interaction between water waves and arrays of small diameter cylinders were simulated. The hydrodynamic properties of the structures and the interference coefficients of every cylinder were analysed.