Reliability assessment of tension leg platform tethers under nonlinearly coupled loading

This paper deals with the design of TLP tethers under wind and wave induced loading using reliability analysis. Two modes of tether failure are considered, namely (1) the maximum life time tension exceeding yield stress and (2) the minimum life time tension less than zero. A dynamic response analysis is carried out considering nonlinearities due to drag, variable submergence, variable tether tension, wind induced loading and large displacements. Various degrees of freedom are considered to be coupled. Reliability assessment is carried out by Monte Carlo failure analysis using simulation techniques. A methodology is developed for finding the expected life of the platform based on the results of reliability study. Finally, a design approach is established involving the determination of optimum yield stress in tethers.