USE OF QUADRATIC TRANSFER-FUNCTIONS TO PREDICT RESPONSE OF TENSION LEG PLATFORMS

Higher-order nonlinear transfer functions are applied to model the com puted nonlinear responses obtained from the dynamic analysis of a tens ion leg platform (TLP). Under the nonlinear wave-loading condition con sidered in the present study, the horizontal motion of TLP exhibits a significant amount of response components at frequencies that are outs ide the range of the excitation frequencies, but which are near the na tural frequency of the TLP. Higher-order nonlinear transfer functions based on a Volterra series representation are used to model these nonl inear responses that cannot be properly represented with a linear tran sfer function only. The transfer function model clearly shows the degr ees of nonlinearity of these responses as strongly quadratic. To exami ne the applicability of the nonlinear transfer functions, both the qua dratic transfer functions obtained from a wave spectrum and the corres ponding responses were applied to other wave spectra with different ma gnitude of wave power, and the results are discussed.