Impact of Stiffness On the Response of a Multimodule Mobile Offshore Base

The linear, wave-induced response of a 5-module, 1500-m-long mobile offshore base (MOB) is investigated. Each module is a 2-pontoon, 8-column semisubmersible, and the MOB is represented by the lumped-parameter rigid module-flexible connector model. An extensive parametric study is carried out to determine the impact of the stiffness on the motions and connector loads. Results show that the hydrodynamic interaction between modules is relatively small. Although the response is a complicated function of the connector stiffness, the maximum extreme connector forces for hinged modules are often a result of horizontal bending induced by oblique waves. Also, it is shown that resonance can be a significant problem, especially for lower stiffnesses. *ISOPE Member. Received July 6, 1998: revised manuscript received by the editors January 25, 1999. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 24-29, 1998.