Application of the Global Optimization Method to the Preliminary Design of Tension Leg Platforms

Abstract

The TLP requires a complicated and time-consuming design process. Principal dimension of hull form and tendons should be carefully determined with the consideration of many design requirements which dominantly affect the safety of the platform. In this paper, a global optimization system for both the hull-form and tendon system is developed. The maximum heave response and total weight of hull and tendons are formulated as an objective function with the several constraints related to the safety of platform. In order to find a technically and economically feasible design, a modelling and assessment processes are fully automated, which enables the algorithm can controls the modelling and analysis process while varying a set of design parameters until it figures out an optimum design. Major design requirements related to the safety of platform is assessed by ultimate limit state (ULS) and fatigue limit state (FLS) approach to ensure the accuracy of analysis. In the ULS approaches, every safety requirement is checked on the basis of the most unfavorable environments. FLS approach is conducted for all tendons since they suffer cyclic deformation for their service life, which results in collapse of mooring system with the relatively small wave loads. In the optimization module, a better set of design parameters is investigated by using a simulated annealing (SA) algorithm. Throughout the optimization system, both the heave responses and total weight of hull and tendons are improved while satisfying the all constraints related to the design requirements.