ABSTRACT:

This paper presents a reliability analysis model for a tension leg platform (TLP) against severe store events by the domain crossing approach of the random tensile stress in the tendons. Two limit conditions are considered, i.e., the exceedance of ultimate tensile capacity and the occurrence of negative tension. In order to consider the correlation effects among the failure events of the tendons at four corners, the system limit state is defined in terms of the TLP motions in the vertical plane, i.e., heave, roll, and pitch. To investigate the validity of the present method, numerical analysis is carried out for two TLPs with different structural dimensions. Numerical experiments are also performed to investigate the sensitivity of the reliability to several parameters, such as the cross-sectional area of the tendons, the mean tension in the tendons, and the uncertainties of the severe storm data.

INTRODUCTION

A tension leg platform (TLP), schematically shown in Fig. 1, is a drilling and production platform developed for deep-sea applications. It is a floating platform vertically moored by tension legs at each comer of the hull structure. The tension legs, so-called tendons, are secured to the pile-anchored templates on the seafloor. The excessive buoyancy of the platform maintains tension in the tendons so that the tendons never become slack under any loading conditions the structure may encounter during its service lifetime. The tendon system seems to be the most critical element for the safety of the TLP. From this point of view, notable works on TLP reliability have been reported by Cornell et al. (1984), Prucz and Soong (1984), and Stahl and Geyer (1985). Those efforts are of a preliminary nature aimed at developing better design insights. In those studies, loads and resistance are treated as time invariant random variables.

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