An Optimized Consideration for Catenary Mooring System Designs

Catenary mooring systems have been widely used in offshore industry when oil and gas exploration and production was conducted in shallow to deep water. To ensure a catenary mooring system arrives at the seabed horizontally, a very long seabed anchor chain is usually used. In actual applications, a substantial length of anchor chain could be saved if a small load angle at Touch-Down Point (TDP) can be considered in the design. This paper first reviews the chain-soil interaction analysis model from previous studies. Based on this, an excel spreadsheet tool to simulate the behavior of chain-soil interaction has been developed. Then, the chain’s configuration in soft clay is investigated using the developed tool. The influence of a small load angle at TDP on the embedded chain length in soil and the influence of a load angle at TDP on the padeye load or load components are checked. Finally, a recommendation is made to improve (or optimize) the traditional design concept of a catenary mooring system (i.e., no uplift load at TDP for any stage) by considering a small load angle at TDP (i.e., 1° – 5°) for the intact and damage conditions under the maximum design environment (i.e., extreme design loading cases).