Turbulent Wind and Tension Leg Platform Surge

A procedure is presented for estimating surge response to turbulent wind in the presence of current and waves. The procedure accounts for the nonlinearity of the hydrodynamic forces with respect to surge and for the coupling of aerodynamic and hydrodynamic effects. It is shown that current wind spectra do not model correctly the wind speed fluctuations at very low frequencies and an alternative model of the wind spectrum, whose ordinate at the origin is consistent with fundamental principles, is presented. The equation of surge motion under turbulent wind in the presence of current and waves is solved for typical tension leg platforms, and it is shown that under extreme wave conditions the damping provided by the hydrodynamic forces precludes the occurrence of significant wind‐induced resonant amplification effects even if the drag coefficient in the Morison equation is very small (e.g., $C_d=0.1$). It is verified that for the platforms being investigated the use of a one‐minute wind speed to represent the effect of the mean wind and of the turbulent wind fluctuations is acceptable for the purpose of estimating peak surge response.