Dynamic analyses of buoyant leg storage and regasification platform: numerical studies

Abstract

Present study highlights dynamic response behaviour of a buoyant leg storage and regasification platform (BLSRP), which is one of the recent developments in the domain of offshore structural engineering. This is a hybrid platform, which has combination of flexible and stiff degrees-of-freedom by virtue of design. A large deck is supported by six buoyant leg structures (BLS), which are connected to the deck by hinged joints. Hinged joints absorb rotational response of BLS units from transferring it to the deck, while translational responses are transferred like a monolithic structure. Detailed numerical investigations are carried out on a scaled model of BLSRP. Results of the conducted studies showed that heave response of the deck is lesser in comparison with that of the buoyant legs. The presence of roll and pitch responses of the deck, despite the hinged joint at each buoyant leg is due to the differential heave response that occurred from the dynamic tether tension variations. Response of the deck is less influenced by the wave action on buoyant legs due to the presence of hinged joints. Hinged joints isolate the deck from buoyant legs and thereby improve operational comfort and safety of the platform. It is also observed that maximum variation in tether tension is within the permissible limits. Geometric design of the buoyant legs, as attempted in the present study ensures a good recentering capability of the deck in all the translational degrees-of-freedom. Phase plots of both the deck and a typical buoyant leg confirm that the motion is stable and periodic.