Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Research on Feature Extraction Method of Periodic Pulse Vibration Signal of Ship Shafting Based onWavelet Threshold Denoising and Variational Mode Decomposition
Fayou Liu and Weijia Li

Huazhong University of Science and Technology, School of Naval Architecture and Ocean Engineering
Wuhan, Hubei, China

ABSTRACTeffectively reflect the pros and cons of shafting assembly
quality, and then serve as an effective quality evaluation method
in non-self-propelled conditions. However, shafting vibration
signals are easily affected by factors such as strong backgroundnoise, transmission path complexity, signal attenuation, etc.
(Chen, 2020). There are currently few researches on signal
processing methods for ship shafting, and traditional methods
are difficult to obtain effective results. Long et al., 2015
proposed a fault diagnosis method based on Information
Entropy and Haar Wavelet Transform for switched current
circuits, which reduced signal redundancy; Zheng et al., 2020
proposed a fault diagnosis method based on parameter
optimization VMD for rolling bearings. Compared withtraditional signal processing methods, the proposed method caneffectively improve the sensitivity of fault feature extraction;
Liu et al., 2016 proposed a novel signal denoising method
combining Detrended Fluctuation Analysis and VMD, whichshowed better denoising performance than EMD and Discrete
Wavelet Threshold Denoising; Xie et al., 2019 proposed a signal
feature extraction method based on Optimized Variational ModeDecomposition (OVMD), Permutation Entropy (PE) andnormalized Spearman correlation coefficient (NSCC) for ship
radiated noise. Under the radiated noise samples, the recognition
rate of the proposed scheme is 94%; Hu et al., 2015 studied thepros and cons of different ship shafting fault feature extraction
methods, and compared the applicability and accuracy of three
periodic fault feature information extraction methods. However,
the method in that paper is mainly empirical but it lacks ofThe assembly quality of the ship propulsion shafting is directly
related to the reliability of the propulsion system and the safetyof the ship sailing. The assembly quality problems existing in theassembly process will be manifested by weak feature signals ofperiodic pulse vibration which are easily submerged by strong
background noise. In this paper, a method based on Wavelet
Threshold Denoising and Variational Mode Decomposition(WTD-VMD) is proposed to extract these features efficiently andaccurately. For the original signal with low frequency and weakfeature, Wavelet Threshold Denoising is used to remove themedium and high-frequency noise in the signal. Then, the filteredsignal is subjected to Variational Mode Decomposition to obtaina limited number of IMFs with different center frequencies.
Furthermore, the optimal IMF is selected by maximum kurtosis
criterion to carry out envelope demodulation analysis. The
periodic pulse feature that can evaluate the assembly quality
problems of the ship shafting is extracted. Through the analysisof simulation signals, compared with the traditional Empirical
Mode Decomposition (EMD) and Variational Mode
Decomposition (VMD), WTD-VMD can extract periodic featurefrequencies more effectively and accurately. The effectiveness ofthe method is further verified by analyzing the measured signals
on comprehensive test platform of ship propulsion shafting.
KEY WORDS: Ship Shafting; Shafting Alignment; Feature
extraction; Variational Mode Decomposition.

theoretical basis.

INTRODUCTION

Aiming at the features of the vibration signal of the ship
propulsion shafting, in this paper, a method for extracting
periodic pulse features of ship shafting vibration signals basedon Wavelet Threshold Denoising and Variational Mode
Decomposition (WTD-VMD) is proposed. Through the analysis
and comparison of simulation signals, the effectiveness andaccuracy of WTD-VMD are verified, and the effectiveness ofThe vibration signal of the ship propulsion shafting is atypical non-stationary nonlinear signal, which has the features oflow frequency and low signal-to-noise ratio. Simultaneously
some periodic pulse are contained features under actual working
conditions. These features can more comprehensively and3938