Hydrodynamic interaction forces on multi-moduled structures

The size, complexity and critical operations of many offshore structures, i ncluding the mobile offshore bases (MOBs) of current interest, require care ful determination of wave forces on the neighboring structures, including t heir interactions. This paper describes an analytical/numerical approach th at determines the wave forces on multiple structures in the vicinity of one another. The method involves the consideration of multiple vessel interact ion and scattering in waves. The analysis is an extension of the semi-analy tical multiple vertical cylinder analysis published by the author. The anal ysis is similar to the one proposed by Kagemoto and Yue for axisymmetric bo dies. 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 efficien t in these respects. It is accomplished by marrying the direct method with a semi-closed analytical method of multiple scattering developed for an arr ay composed of vertical cylindrical structures. It is recognized that this analytical method has a limitation owing to the geometry of many offshore s tructures including MOBs. Therefore, the analysis is extended to an arbitra ry geometry. In this method, the direct matrix method of diffraction proble m is applied to an isolated module and then extended to structures with the multiple scattering technique to account for the interaction of multiple s tructures. Comparisons are made of the results from the analytical and conventional nu merical diffraction theory with those of the semi-analytical tool using the above-mentioned analysis. (C) 2000 Elsevier Science Ltd. All rights reserv ed.