Benchmarking of Analysis Tools for Thruster Assisted Mooring

While the size of new built semi-submersibles is steadily increasing, their mooring systems are not experiencing a similar change. Most of the sixth-generation drilling units rely heavily on thruster assisted mooring to increase their operability in harsh environments and shallow waters. Frequency domain programs are commonly used to calculate mooring line tensions in the design analyses. This analysis technique assumes linearity in both the mooring system and the thruster assist controller. The study presented in this paper examines the validity of these assumptions by comparing frequency and time domain analyses in two state-of-the-art analysis programs. The linear thruster assist controller in frequency domain analyses is benchmarked against the Kalman filter-based controller in time domain simulations and against a real thruster assist controller coupled with the time domain software.