WIND-EXCITED SURGE RESPONSE OF TENSION-LEG PLATFORM - FREQUENCY-DOMAIN APPROACH

This paper presents a frequency-domain analysis procedure to evaluate wind-excited surge response of a tension-leg platform (TLP) in the presence of waves and currents. The nonlinearities of hydrodynamic origin and those resulting from tether-restoring force are included in the analysis. Unlike conventional frequency-domain analysis procedures based on an equivalent linearization approach, the present technique is based on an equivalent quadratization concept. in which terms up to second order in the expansion of nonlinear quantities are retained. Accordingly, the analysis reflects important features of nonlinear interactions and offers accuracy comparable to the time-domain approach, at a fraction of the computational effort. The wind load effects are described by the space-time description of the random wind field. The hydrodynamic loads are expressed in terms of a combination of viscous and potential effects. A stochastic decomposition technique that significantly enhances the efficiency of the frequency-domain analysis of this complex fluid-structure interaction problem is utilized. The second-moment response statistics of a TLP are evaluated using a combination of iteration-based techniques. The numerical results show good comparison with the time-domain simulation.