Comparative study of mathematical models for mooring systems coupled with CFD

A numerical method that coupled a Reynolds-averaged Navier-Stokes solver with a quasi-static and a dynamic mooring model was employed and compared. Decay tests of the freely floating and the moored buoy in calm water determined the system's linear and quadratic damping characteristics. In regular waves, predicted heave and pitch amplitudes and high-frequency surge amplitudes based on the quasi-static mooring model were similar to those based on the dynamic mooring model and similar to comparable measurements. However, the low-frequency surge and pitch motions based on the quasi-static model deviated significantly from the corresponding motions based on the dynamic model and from measurements. In irregular waves, buoy motion amplitudes, especially in surge, based on the quasi-static model were overpredicted. The accurate evaluation of the moored buoy in irregular waves, especially when the moored buoy underwent large translations, was possible only by accounting also for the dynamic loads acting on the mooring lines.