Effects of currents on the stochastic response to earthquakes of multiple degree of freedom models of guyed offshore towers

The dynamic response of multiple degree of freedom (MDOF) guyed offshore towers to stochastic earthquake loads and a steady uniform current is investigated. The nonlinear cable stiffness and the fluid-structure interaction were linearized by using the stochastic linearization method. To investigate the importance of higher modes on the stochastic forces and moments of the guyed tower, numerical results for several load cases are presented and discussed. The displacement statistics from the MDOF linear analysis were compared with the statistics of an equivalent single degree of freedom (SDOF) time simulation that incorporated the nonlinearities of the structure. The increased damping of the structure with increasing current was found to significantly reduce the stochastic forces and moments of the structure.