Numerical analysis of an offshore platform with partial porous cylinders due to wave excitation forces and seismic forces

In order to reduce the wave excitation forces on structures, the partial porous cylinder, which is composed of a porous part located near free surface and a rigid part bounded top and bottom by impermeable end caps, is newly suggested. The fluid domain is thus divided into three regions: a single exterior region, N inner regions and N beneath regions to calculate the wave force on the partial porous cylinder, and the scattering wave in each fluid region is expressed by an Eigenfunction expansion method with using 3-dimension liner potential theory. In order to simplify the effect of porosity, Darcy´s law is also applied to the porous boundary condition. Using the wave excitation forces and seismic forces on the offshore platform with partial porous cylinders, the dynamic response evaluations of the platform are carried out through the modal analysis and the substructure method based on the effect of soil-structure interaction. The displacement and bending stress at critical structure members are computed using the various input parameters, such as the shear-wave velocity of soil, the porosity rate and the wave period.