The forces due to wave breaking on the structures are a major concern in the design of offshore wind turbine substructures installed in shallow waters with sloping bottom. As the wave-breaking phenomenon is extremely complicated and involves strong non-linear effects, the characteristics of these forces are not fully understood by conventional numerical models. With the rapid development of computers and the computational fluid dynamics, 3D numerical models based on the Navier-Stokes equations have been widely used to study the breaking wave impact phenomenon on offshore structures. It is evident that the accuracy of the simulated results depends greatly on the solution methods used in the numerical model. There are many choices to be made on the selection of proper parameters to be used in these numerical models. However, there is not much guidance available on the selection of correct parameters to be used in these models. Incorrect selection of the parameters may lead to inaccurate solutions. In the present paper, a sensitivity study of numerical parameters used in a 3D Navier-Stokes solver is performed for a more accurate estimation of the breaking wave forces on a jacket structure. The effect of grid sizes, numerical schemes, wall boundary conditions, surface tension, turbulence model and wave theories is studied in detail for a selected wave condition and finally recommendations are made for the selection of suitable parameters.
Ocean waves in shallow water with sloping bottom are subjected to non-linear processes such as refraction, diffraction, breaking etc. Among them, wave breaking is one of the most important phenomenon for an ocean engineer as it has a strong impact on the design of offshore structures. If the offshore structures are installed in the region where wave breaking occurs, the structure should be designed against the breaking wave forces in addition to the Morison forces. According to Kaldellis and Kapsali (2013), more than 90% of existing offshore wind turbines are fixed-type and are installed in shallow water regions. The substructures of these wind turbines are predominately monopiles. However, in recent times jacket structures have gained popularity due to higher wind turbine capacity and operational feasibility in deeper waters compared to monopiles.
