Cavitation noise modulation feature extraction method based on empirical mode

Abstract

The invention provides a cavitation noise modulation feature extraction method based on an empirical mode. The method comprises the following steps: firstly standardizing a short cavitation noise signal; carrying out bandpass filtering on the standardized signal to obtain the bandpass signal of cavitation noise; carrying out envelope detection on the bandpass signal to obtain an envelope signal; carrying out lowpass filtering on the envelope signal to obtain a low-frequency envelope signal; decomposing the low-frequency envelope signal into a plurality of intrinsic mode functions (IMFs) by using empirical mode decomposition analysis; selecting the optimum IMF through evaluation; carrying out Hilbert transformation on the optimum IMF to obtain a Hilbert spectrum of the optimum IMF; and calculating the instantaneous frequency at every moment by using the Hilbert spectrum, so as to complete cavitation noise modulation feature extraction. According to the method provided by the invention,based on the adaptability of empirical mode decomposition and high resolution of Hilbert-Huang transformation, the disadvantage of the traditional modulation feature extraction method that modulationfeature extraction is difficultly carried out on short-time and non-stably modulated cavitation noise data can be overcome.

Description

Technical field: [0001] The invention relates to underwater acoustic noise signal processing, in particular to a cavitation noise modulation feature extraction method based on empirical modes. Background technique: [0002] Cavitation is a fluid phenomenon that occurs when the pressure of the liquid flow drops below the vaporization pressure of the liquid in this state. The collapse of the cavitation produces shock waves in the liquid, and the impact of the microjet on the solid wall produces vibration. When the propeller generates cavitation in water, the vibration caused by bubble burst and water flow impact produces high-frequency pulses as broad-spectrum signals, which are often modulated by the mechanical rotation effect of the propeller. Therefore, the modulation characteristics of cavitation noise reflect the important information of the propeller. The rotational speed of the propeller can be extracted through the demodulation analysis of the cavitation noise. The co...

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Problems solved by technology

[0005] In order to overcome the shortcomings of the traditional method for the modulation extraction of non-stationary cavitation noise, a method of cavitation noise modulation feature extraction based on empirical mode is proposed, which uses the adaptability of empirical mode decomposition and the high efficiency of Hilbert-Huang transform Resolution, for the short-term cavitation noise data, through the evaluation and selection of the mode, the Hilbert spectrum of the optimal mode is used to obtain the instantaneous modulation frequency at each moment, and the modulation feature extraction of the cavitation noise is completed

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