Estimation of Response Transfer Functions of Offshore Structures Using the Time-Varying ARX Model Available to Purchase

The purpose of this paper is to propose and investigate a new approach for estimating response transfer function of offshore structures with wave as excitation input. The approach is based on time-varying autoregressive with exogenous input (TVARX) model. This method is virtually unexplored in offshore engineering field, as a number of works have shown that transfer functions such as response amplitude operator are estimated based on discrete Fourier transform (DFT). Here, we outline a practical algorithm for TVARX model which uses expectation-maximization (EM) algorithm based on Kalman smoother to generate the transfer function. The method is then applied to sampled discrete wave as excitation input and the motion responses of offshore structures as output data, generated from simulated field measurements. The proposed approach outlined here has shown the tremendous potential in the estimation of transfer function. The results indicate that TVARX model produces accurate, smooth and less noise TF estimates over DFT method. TVARX model also allows for the creation of time varying transfer function (TVTF).