To standardize and simplify the design process, the designer wave and current loads are developed. The loads enables to calculate the extreme response of offshore structures under the given wave and current conditions by static analysis. Moreover, the intensity of loads can be adjusted based on the probability of exceedence of a barrier level predefined by regulatory bodies/owners such as according to the structural importance.
The demand for the efficient design method requires the development of design wave loads. Taniguchi and Kawano (1998 and 2002) presented the designer wave loads based on the general theory of structural response of offshore structures (Malhotra and Penzien, 1970). The loads enables to calculate the extreme response of offshore structures by static analyses without any information from dynamic and probability analysis. Since the intensity of loads can be adjusted based on the probability of first passage of a barrier level predefined by regulatory bodies/owners such as according to the structural importance, the structural safety is probabilistically secured. Moreover, since the loads statically calculate the extreme response, the superposition of responses (i.e. load combination) becomes much easier. Because other design loads, such as dead loads, live loads, etc, may be statically given. Generally, offshore structures are exposed to not only wave forces but also current forces. The subject of combined effects of current and wave on objects immersed in deep water has attracted attention, and the effects of wave-current interactions on statistical properties of fluid force on objects have been precisely investigated (Tung and Hang, 1973). Taniguchi and Kawano (2000a and 2001) published a general theory for evaluating the response of offshore structures in deep water when simultaneously subjected to random wave forces and steady current force with the nonlinearities arising from hydrodynamic drag forces and wave-current-structure interaction.