Use of Quadratic Transfer Functions to Predict Response of Tension Leg Platforms

Abstract

Higher-order nonlinear transfer functions are applied to model the computed nonlinear responses obtained from the dynamic analysis of a tension leg platform (TLP). Under the nonlinear wave-loading condition considered in the present study, the horizontal motion of TLP exhibits a significant amount of response components at frequencies that are outside the range of the excitation frequencies, but which are near the natural frequency of the TLP. Higher-order nonlinear transfer functions based on a Volterra series representation are used to model these nonlinear responses that cannot be properly represented with a linear transfer function only. The transfer function model clearly shows the degrees of nonlinearity of these responses as strongly quadratic. To examine the applicability of the nonlinear transfer functions, both the quadratic transfer functions obtained from a wave spectrum and the corresponding responses were applied to other wave spectra with different magnitude of wave power, and the results are discussed.