Coupled-dynamic Response Of TLP And Research For Mooring System Wave-induced Fatigue

Tension Leg Platform (TLP) has good motion performances, and has gradually widespread application. In order to guarantee its safety performance at different sea status, it is necessary to study its hydrodynamic performance. Tendon system is the special structure of TLP, which limits its movement and ensures its safety, even if the strength meets requirements of rules. However, the tendon is fatigue injured under the alternative load, which would effect the safety. Therefore, the fatigue damage of tendon is a focus among the research of TLPs.This paper is based on three dimensional potential theory, using the time domain software HARP of totally coupling, the dynamic performance of a multifunction triangle TLP is studied in time domain, its wave-induced fatigue life of mooring systems is also calculated.Firstly, the added masses, damping,RAOs of the platform is obtained by the frequency-domain-analysis methods,on this basis coupling dynamic analysis is worked out in the time-domain-analysis methods, and make sure that it has adequate strength with requirements of rules.Then, the frequency short-term prediction of motion responses under the different wave loads should be worked; The motion response in frequency and time domain analysis methods and the tension of the tendon are compared, the tension has not large difference, the motion of the platform is different, and the reasons of different results in time domain and frequency domain are studied.Besides above, some other analysis was performed for factors in the preliminary design of TLP including tendon axial stiffness, number of tendons, pretention for the mooring system etc. All the results showed that those factors mentioned above can affect the motion of TLP and tension performance of its mooring system.Finally, the fatigue life prediction of mooring systems are worked out based on the theoretical model of cumulative damages with S-N curves, the results meet the requirements of rules, the sensitivity analysis of parameters influencing fatigue life of tendon was made in order to choose the proper parameters to provide the references to the fatigue design of tendon.