A numerical time domain simulation model has been developed for the prediction of the hydrodynamic response of an LNG FPSO with an alongside moored LNG carrier. The model has been validated using the findings of dedicated basin model tests. The hydrodynamic response of two bodies in close proximity is a complex hydrodynamic interaction problem. Three influencing factors showed to play an important role on the quality of the results:

  • the use of a free surface lid in the multiple-body diffraction analysis for accurate calculation of the drift forces;

  • the use of accurate input data on relative viscous damping in the horizontal plane for the correct prediction of the low frequency motion response, and

  • the use of the complete matrix of retardation functions for the correct prediction of the heave and pitch motions.


Background Shell is developing a Floating LNG System to economically produce and process gas in remote offshore locations. The system can be used in remote oil developments, or in green field gas cases. In remote oil developments, the floating LNG system converts the problem of associated gas disposal into a moneymaking opportunity. In the green field gas case, the Floating LNG System is an economical means to develop remote offshore gas fields. The Floating LNG System (see Fig. 1) consists of a barge type LNG FPSO with accommodations, an external turret, a gas preconditioning and liquefaction plant, a number of LNG storage tanks and offioading facilities. It is positioned over the reservoir and replaces the offshore platform, the pipeline to shore, the onshore LNG plant and the jetty. When sufficient LNG is accumulated in the storage tanks, it is offioaded to a LNG carrier and shipped to the customer.

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