Hydrodynamic interaction forces on multi-moduled structures

The size, complexity and critical operations of many offshore structures, including the mobile offshore bases (MOBs) of current interest, require careful determination of wave forces on the neighboring structures, including their interactions. This paper describes an analytical/numerical approach that determines the wave forces on multiple structures in the vicinity of one another. The method involves the consideration of multiple vessel interaction and scattering in waves. The analysis is an extension of the semi-analytical multiple vertical cylinder analysis published by the author. The analysis is similar to the one proposed by Kagemoto and Yue for axisymmetric bodies.The direct method of linear diffraction, while quite accurate and efficient in solving the hydrodynamic problem, demands a large amount of memory and requires considerable execution time. The present analysis is very efficient in these respects. It is accomplished by marrying the direct method with a semi-closed analytical method of multiple scattering developed for an array composed of vertical cylindrical structures. It is recognized that this analytical method has a limitation owing to the geometry of many offshore structures including MOBs. Therefore, the analysis is extended to an arbitrary geometry. In this method, the direct matrix method of diffraction problem is applied to an isolated module and then extended to structures with the multiple scattering technique to account for the interaction of multiple structures.Comparisons are made of the results from the analytical and conventional numerical diffraction theory with those of the semi-analytical tool using the above-mentioned analysis.