The random vibration approach on gives very effective methods to the dynamic response evaluations of an offshore structure subjected to dynamic forces. While the linear response evaluation be efficiently carried out using the random vibration approach, it is hard for the random vibration approach to apply to the nonlinear dynamic analyses except for the approximate method such the equivalent linearization method. Moreover, there are some difficulties to perform the nonlinear dynamic response with the equivalent method for the offshore structure with many members. In this study, the nonlinear dynamic response evaluations of an offshore platform with uncertain parameters subjected to severe wave forces are examined. The nonlinear dynamic response analyses in the time domain are carried out using the increment method. Considering uncertain parameters included in the strength of materials of the structure and the dynamic forces such as wave forces, it is very important to clarify these uncertain parameters contributions on the responses in order to perform the reliable evaluations of the nonlinear dynamic responses. The effects are examined with the Monte Carlo Simulation. It is shown that since the nonlinear dynamic response caused by the severe wave conditions has significant roles on the maximum response evaluations, it is very important to clarify not only the nonlinear response characteristics but also the linear one.
It is indicated that since the wave force is one of the most important loads on an offshore structure, the dynamic response evaluation due to wave forces has significant roles on the reliable design of the offshore structure (Schueller, G, I(1998)). The standard design of the structure is carried out using the allowable stress method. However, it is important to clarify the effects on nonlinear responses for an offshore structure under the severe wave conditions.