Cavitation noise modulation feature extraction method based on empirical mode

A technology of noise modulation and feature extraction, which is applied in the measurement of ultrasonic/sonic/infrasonic waves, measuring devices, instruments, etc.

Inactive Publication Date: 2011-11-23
SOUTHEAST UNIV
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  • Abstract
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  • Application Information

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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 o

Method used

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  • Cavitation noise modulation feature extraction method based on empirical mode
  • Cavitation noise modulation feature extraction method based on empirical mode
  • Cavitation noise modulation feature extraction method based on empirical mode

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Embodiment

[0066] Acquire non-stationary modulation signal sequence s(n) for 5 seconds, where n=0, 1, ..., 49999, and the sampling frequency is f s =10000Hz, its waveform is as Figure 4 shown.

[0067] According to the above step A, standardize the data s(n), E{s(n)} is the mean of s(n), and Std{s(n)} is the standard deviation of s(n). According to step B, choose a 32-order FIR band-pass filter, the pass-band frequency is 10Hz to 1000Hz, for s 1 (n) Perform band-pass filtering to obtain the band-pass signal s 2 (n), and then according to the C step for s 2 (n) perform square law detection, Such as Figure 5 shown.

[0068] According to the above step D, select a 32-order FIR low-pass filter with a cut-off frequency of 100Hz, for the envelope signal s 3 (n) Perform low-pass filtering to obtain the low-frequency envelope signal s 4 (n), according to the above E step, for the low frequency envelope signal s 4 (n) Carry out empirical mode decomposition to obtain 5th-order IMF, s...

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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...

Claims

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Application Information

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IPC IPC(8): G01H17/00
Inventor 罗昕炜方世良王晓燕
Owner SOUTHEAST UNIV
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