Comparison of wave characteristic due to hybrid substructures for offshore wind turbines

For the reliable design of substructures supporting offshore wind turbines, it is very important to reduce the wave forces acting on substructures. In the present study, two hybrid substructures for offshore wind turbines are newly suggested to reduce the wave forces. The hybrid substructure (HSPG) is composed of a single pile and a gravity substructure with porous areas near free surface. The other hybrid substructure (HMPG) consists of a multi-pile near free surface and a gravity substructure at the bottom of the multi-pile. In order to calculate the wave forces acting on hybrid substructures, the fluid domain is divided into two regions and the scattering waves in each fluid region are expressed by an Eigen-function expansion method. In order to simplify the effect of porosity, Darcy´s law is also applied to the porous boundary condition. The comparison of wave forces between HSPG and HMPG is made to examine the wave characteristic according to the variation of depth of interior region and pile size.