In this paper the design robustness of Tension Leg Platform (TLP) tendon and tendon foundation systems of a TLP that is located in offshore Western Australia is investigated.

A case study of a TLP that is self-stable (without tendons) has been considered. The study involves the numerical simulation of progressive failure of tendons in cyclonic events. The TLP response during the transition from a restrained TLP with all tendons to the free-floating condition has been numerically simulated. The numerical results from this simulation have been verified against physical model test measurements. The numerical simulation is repeated for a TLP with an optimized hull design that does not maintain stability when all tendons fail. Cost versus benefit in these two cases is quantified and compared.

The progressive failure of the TLP Gravity Base Foundation (GBF) system has also been investigated in this paper. One of the potential failure modes for this type of foundation is the loss of suction underneath the foundation. Increasing the amount of solid ballast in the GBF increases the net downward load on the soil and reduces the reliance on the soil suction. Numerical simulations of the progressive loss of suction are performed for two cases; 1) slightly over designed foundation to include extra ballast and 2) optimized foundation design that is highly rely on the soil suction. Again, cost versus benefit in these two cases is presented.

The paper provides clear insights supported by calculations and model tests for proposed design robustness that could be built in a TLP design at a relatively small additional cost to address uncertainties associated with designing TLP in offshore Western Australian harsh environment region.

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