Hull mooring coupled dynamic analysis of a truss soar in time-domain

Nonlinear coupled dynamic analysis of a moored truss spar in waves with collinear winds and currents is numerically carried out in the time domain and the results are compared with 1:61 scale experiments and uncoupled analyses. The first- and second-order wave forces, added mass and radiation damping, and wave drift damping are calculated from the hydrodynamics program WINTCOL. The total wave force time series are then generated based on a two-term Volterra series model. The mooring dynamics are solved using the software WINPOST which is based on a generalized-coordinate-based finite element method. The mooring lines are coupled to the platform through generalized springs and dampers. A case study was conducted for the Marlin truss spar with nine taut mooring lines in 3240-ft water depth. The numerical results show that dynamic effects are very important for the present mooring design. The motion and tension spectra of uncoupled analyses with linear spring or nonlinear spring are also compared with those obtained from fully coupled analysis to assess the importance of hull/mooring coupling.