The focus of this paper is on the application of a time domain hybrid method to the calculation of the motions and wave loads on a semi-submersible, which has been investigated extensively in ITTC benchmark studies in the past. Numerical results include hydrodynamic coefficients, motion responses and drift forces. Good agreement has been observed between the results of the present method, other numerical codes and experimental data, which confirm the capability of the developed numerical approach to deliver meaningful predictions for practical applications to offshore structures.
Accurate prediction of the seakeeping behavior of ships in heavy seas is of great importance both for ship design and operation. Quasi 2D strip theory approaches were the first to deliver satisfactory results for the prediction of ship motions in practical applications and they are widely used even today. With the rapid advance of computer technology in the 70ties, various frequency domain 3D approaches were successfully developed. But due to some inherent limitations related to the nonlinearities of the seakeeping problem, their successful application is sometimes limited to a certain extent. On the other hand, in recent years, time domain simulation methods became more and more popular as they enable the address of large amplitude ship motion problems, which is very important for the design and the assessment of safe operation of modern ships and offshore structures operating in a variety of adverse environmental conditions. Following the pioneering work of Finkelstein (1957) and Cummins (1960), many researchers (e.g., Beck and Magee, 1990) investigated seakeeping problems by different time domain approaches and showed promising results for both the linear nonlinear problem of different level. Lin & Yue (1990) showed the applicability of a time domain Green function method to large amplitude ship motions. Following this formulation, Singh et al. (2003) appeared to have obtained good results in some applications.
