ABSTRACT

In this paper, according to requirement of remake engineering of self-elevating platform, the natural frequency and mode of platform as well as stress state of its truss have been calculated. The platform was subjected to wind, current and wave load. Analysis results were afforded for designer as a useful basis of strength check.

INTRODUCTION

In order to explore the marginal oilfield in South China Sea, some self-elevating drilling platforms will be remade to oil producing ones. Those kind of platforms are noted for moving easily, so that they are suitable for marginal oilfield exploration. This plan will be economical and practical. In the reforming design, vibration and strength analysis of self-elevating platform is of fundamental importance. For example, the natural frequency and mode shape as well as stress state of the truss elements of the self-elevating platform Nanhai-I, under the action of wind load, wave load and current force, have been calculated. The main platform structure is composed of box ship body and three pile legs (see Fig.I), each pile leg is a truss which is formed by three vertical bars, some horizontal braces and inclined bars. In the analysis (computational) model, the box ship body is considered as a rigid body. The total weight of the ship body and equipment is averagely distributed to three pile legs. The foundation of each pile leg is a box type footing inserted into some depth below mud line. For the sake of analysis convenience, the box type footing is simplified to three intersected rigid braces, the pile legs in the mud are considered as elastic support. However, for reconstructed platform, its foundation is a caisson-type storage tank, the bottom of the pile leg is fixed to the tank. The whole calculation has been accomplished by finite element method.

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