Identification of time-varying linear and nonlinear impulse response functions using parametric Volterra model from model test data with application to a moored floating structure

Abstract

Identification of the time-varying linear and nonlinear impulse response functions (LIRF and QIRF) of moored or tethering floating structures is deemed a very challenging work because of nonlinearity and nonstationarity. This paper proposes an identification method, namely a time domain parametric Volterra model based on Cuckoo search optimized Kalman smoother (CS-KS) to identify the LIRF and QIRF of 1:100 scale model test of spar platform. A conventional frequency domain Volterra model is used as a benchmark. Given the numerical and model test data in terms of measured wave height and surge motion of the platform, the proposed identification method can produce high time resolution of the time-varying LIRF and QIRF. The linear and nonlinear responses as well as natural frequency and damping ratio can be accurately extracted. Through numerical simulation supported by experimental results, this paper also highlights the practical benefits of the proposed identification method to estimate the time-varying kernel coefficients.