Vol.21, Special Issue, 2021, pp. S29–S37
UDC:

Increase in energy demand has led to an increase in hydrocarbon exploration and production in deep water environments. Tension Leg Platform (TLP) are taut moored floating type structures operational in deep-water environments. The restraining system, a taut moored tether, forms a critical component of the TLP. Tethers are held at a high pretension and subjected to continuous variation in stress due to the dynamic loads in the ocean environment. The dynamic loads due to continuous stress reversals cause fatigue. It is essential to analyse the fatigue life of such structures during the design phase. Tether pull-out can occur in the case of any undesirable loads acting on the restraining system. The study focuses on determining the fatigue life of the tether under normal operating conditions by employing rain-flow counting and Miner’s rule. Also, fatigue life analysis is accomplished by considering the postulated failure condition in the restraining system, wherein one tether fails in each of the four legs. It is observed that there is a substantial reduction in fatigue life for the postulated failure condition. In the phenomenal sea-state condition, the fatigue life of tether reduces by 97% as compared to the normal operating condition.

Keywords: offshore engineering, Tension Leg Platform (TLP), tether, Miner`s rule, rain-flow counting