ABSTRACT

The Inverted Quadrangular Frustum Pyramid shaped FPSO (IQFP) is an innovative non-ship-shaped FPSO concept that combines the advantages of the conventional ship-shaped FPSO and the cylindrical FPSO, while overcoming their disadvantages. In order to promote its practical technical application in the near future, the hull structure design and the global strength evaluation are achieved in accordance with the development requirements of the offshore marginal oilfields in the shallow water of China seas. First of all, the initial hull structure of longitudinal and transverse combined frame is designed in the light of the unique symmetrical hull shape and tank division characteristics. Then, the finite element model of the hull structure is established, and the hazardous cases are determined by the stochastic design wave method according to the marine environment and loading conditions. And then, the weak parts of the hull structure are located by the quasi-static global strength finite element analysis. Furthermore, the structural scheme is optimized until the global hull strength meets the given class rule. The results will provide both theoretical and empirical support for the follow-up research of the IQFP, and will also provide a reference for the structural design of other new floating platforms.

INTRODUCTION

FPSO is currently the most widely used floating platform in offshore oil and gas resource development, as it has outstanding advantages of large storage capacity and the widest range of applicable water depths compared to other floating platforms such as SEMI, SPAR and TLP. Since 1976, when the first FPSO was installed, more than 220 FPSOs have operated globally, representing over 60% of all the floating production platforms in service (Du et al., 2017). They have been deployed in most of the major offshore oilfields in the world, such as Brazil, West Africa, Southeast Asia, the North Sea, China Seas and the Gulf of Mexico. The FPSO is adaptable to almost all water depths, from a minimum of 20 m to 3,000 m, making it the only floating platform that can be used to develop oilfields in shallow water. FPSOs can be classified into two categories (Wang TY and Feng YX, 2011), ship-shaped and non-ship-shaped in terms of hull shape, among which ship-shaped FPSOs are currently the most commonly chosen in practice.

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