SAFETY EVALUATION FOR DISTRIBUTED TENSION-LEGS OF FLEXIBLE FLOATING STRUCTURES

A probabilistic approach is presented for evaluating the safety of distributed tension-legs which are arranged over the bottom surface of a flexible floating structure subjected to wind-induced waves and seaquakes at a specific site. The floating structure is idealized as an elastic circular plate with uniformly distributed tension-legs. Both wind-induced waves and seaquakes are represented in terms of long-term and short-term descriptions. The long-term description is concerned with the recurrence pattern of all possible load intensities, while the short-term description is associated with the details of load time history during each load intensity. The short-term tendon response which is conditional on each load intensity is evaluated by a stationary random vibration analysis, taking into account structural flexibility and fluid-structure interaction. Tensile stresses induced in the distributed tension-legs are compared with tendon failure criteria which are assumed in such a way that its failure occurs when the tension in the legs exceeds its tensile limit or drops to zero. Numerical examples are presented to illustrate the proposed method and to discuss the safety of the mooring system against both waves and seaquakes at different sites.