Time-varying spectrum estimation of offshore structure response based on a time-varying autoregressive model

Yazid, E. and Liew, M.S. and Parman, S. (2012) Time-varying spectrum estimation of offshore structure response based on a time-varying autoregressive model. Journal of Applied Sciences, 12 (23). pp. 2383-2389. ISSN 18125654

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Abstract

The purpose of this study is to propose and investigate a new approach for extracting spectral information of motion response of offshore structures. The approach is based on applying Time-varying Autoregressive (TVAR) model. This study is virtually unexplored in offshore engineering field. In the literatures, a number of works have shown that spectral content are extracted using Discrete Fourier Transform (DFT) for the frequency-domain analysis. Here, we outline a practical algorithm for TVAR model which uses Expectation-maximization (EM) algorithm based Kalman smoother. Short time Fourier transformation and Hilbert transformation are used as benchmark. The method is then applied to sampled discrete displacements of a fixed platform as a time series generated from field measurements. All the methods reveal that the spectrum characteristics of sampled platform displacement are time- varying frequency and time- varying gain distribution. The results indicate that TVAR model using KS with EM algorithm is superior to other methods in tackling frequency or amplitude modulation and systems that have low frequency dynamics. It is also found out that the mean frequency derived from the Hilbert transform is lower 8.2, around 4.8 for short time Fourier transformation and 6.2 for TVAR model than the FFT spectrum. © 2012 Asian Network for Scientific Information.

Item Type: Article
Additional Information: cited By 5
Uncontrolled Keywords: EM algorithms; Expectation-maximization algorithms; FFT spectrum; Field measurement; Gain distribution; Hilbert transform; Hilbert transformations; Kalman smoother; Low frequency dynamics; Mean frequency; Motion response; Offshore engineering; Platform displacement; Short time fourier transformations; Spectral content; Spectral information; Spectrum characteristic; Spectrum estimation; Time varying; Time varying autoregressive model; Time-varying autoregressive, Discrete Fourier transforms; Frequency domain analysis; Hilbert spaces; Offshore structures; Spectrum analysis, Algorithms
Depositing User: Mr Ahmad Suhairi UTP
Date Deposited: 09 Nov 2023 15:50
Last Modified: 09 Nov 2023 15:50
URI: https://khub.utp.edu.my/scholars/id/eprint/2662

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