Under the assumption of potential flow and linear wave theory, the diffraction in each fluid region is expressed by an eigenfunction expansion method. The dynamic response of the offshore platform with N permeable or impermeable for the wave force interaction is examined by using an eigenfunction expansion method, and the reliability evaluation on the offshore platform subjected to wave and seismic force is carried out using the MCS approach in the present study. It is suggested that the offshore platform with porous cylinders is very efficient to reduce effects of wave forces and wave run up. It is important to verify the response properties of the offshore platform with uncertainties to dynamic forces and structural properties. In order to enhance the performance based design of the offshore structure, it would be important to examine the uncertainty on the random response situation due to seismic forces.
To perform the reliable design of an offshore structure on ocean, it is very important to evaluate the wave and seismic forces acting on the offshore structure. The dynamic response evaluation due to wave and seismic forces has significant roles on the reliable design of the offshore structure. For the offshore structure subjected to dynamic forces, the dynamic response is usually carried out with the modal analysis. While the wave force should be most important dynamic force, it should be taken into accounts for the combined contribution with the seismic force for the offshore structure located in seismic active area. The wave forces on an offshore structure are usually obtained by diffraction theory and Morison equation. The wave diffraction problem about a vertical circular cylinder is proposed by MacCamy & Fuchs (1954). Under the assumptions of potential flow and linear wave theory, a semi-analytical solution for impermeable cylinders is obtained by an eigenfunction expansion approach by Spring & Monkmeyer (1974), and latter simplified by Linton & Evans (1990) for N bottom-mounted circular cylinders.
