Fluid-structure interaction analysis of offshore structures based on separation of transferred responses

A new partitioned fluid-structure interaction (FSI) method is proposed for dynamic analysis of offshore structures. The main idea of the developed approach is to provide the separation of different components caused by different contributions (such as transferred conditions and updated loadings). One theoretical development is that separated Laplace-domain responses can be obtained from the previous responses. The other is that the structural responses in time domain can be easily calculated by inverse Laplace transform. Once solutions to the structural responses at the time of interest are obtained, the fluid loadings can be updated to consider the impacts of the responses on the geometry of the fluid domain. More importantly, the proposed method is able to improve the estimation accuracy of the structure responses, and hence, may provide better updating results of fluid loadings when the FSI mechanism is considered. To demonstrate the correctness and accuracy of the approach, three numerical examples are used in this paper. The first example is a single degree-of-freedom (DOF) system subject to an irregular dynamic loading. The computation results show that the system responses at previous time steps can be successfully separated into typical components that correspond to different contributions such as transferred conditions and updated loadings. The system responses at current time, obtained by combining previous responses, are in a good agreement with analytical results and those obtained by the Newmark-β method. Then, the second example of a four-DOF lumped system is explored to indicate the superiority of the proposed method over the Newmark-β method in terms of accuracy. Finally, in the third example of an elastic upright cantilever beam in water, results show that the developed method has the ability to calculate dynamic responses with high precision when solving FSI problems, which implies a potential application in ocean engineering.