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

摘要

The purpose of this paper is to propose and investigate a new approachfor estimating response transfer function of offshore structures withwave as excitation input. The approach is based on time-varyingautoregressive with exogenous input (TVARX) model. This method isvirtually unexplored in offshore engineering field, as a number ofworks have shown that transfer functions such as response amplitudeoperator are estimated based on discrete Fourier transform (DFT).Here, we outline a practical algorithm for TVARX model which usesexpectation-maximization (EM) algorithm based on Kalman smootherto generate the transfer function. The method is then applied to sampleddiscrete wave as excitation input and the motion responses of offshorestructures as output data, generated from simulated field measurements.The proposed approach outlined here has shown the tremendouspotential in the estimation of transfer function. The results indicate thatTVARX model produces accurate, smooth and less noise TF estimatesover DFT method. TVARX model also allows for the creation of timevarying transfer function (TVTF).