There is a need to minimize the cost of mooring systems, which can take up a large number of investments in offshore operations as human activities move into deeper waters. A methodology for cost optimisation of the mooring system of floating structures in deep water is presented. A techno-economic model was developed based on the quasi-static taut leg multicomponent equations and simple cost relations in Engineering Equation Solver (EES), used with MS Excel for the analysis. Manufacturing and pre-installation costs were combined as the cost driver. Two mooring line configurations, chain-wire-chain and chain-polyester-chain were analysed, and the genetic algorithm incorporated in EES was used to obtain optimal costs. The results showed that depending on the pre-installation cost; optimal cost resulted from a trade-off between sizes of components and number of lines. It was also revealed that components of multicomponent lines should have Minimum Breaking Strength (MBS) as close as possible to eliminate cost wastage. The chain-polyester-chain (C-P-C) system, for the selected water depth of 1473m and angle at TDP of 250 for a load of 44MN, produced a 35% cost reduction over the chain-wire-chain (C-W-C) system.
Keywords: cost optimisation, floating structure, mooring system, techno-economic model
