Modulation spectrum characteristic fidelity enhancement method for ship propeller cavitation noise based on adaptive window length

Abstract

The invention discloses a modulation spectrum characteristic fidelity enhancement method for ship propeller cavitation noise based on the adaptive window length. The method comprises the steps of first, carrying out broadband square demodulation on ship propeller cavitation noise signals; second, pre-estimating a demodulation spectrum, detecting the line spectrum position of the demodulation spectrum, and giving the frequency domain signal-to-noise ratio of each line spectrum; third, determining the harmonic frequency of each line spectrum frequency relative to a pre-estimated value of the propeller shaft frequency; fourth, carrying out weighted fusion on the line spectrum frequencies, and estimating the propeller shaft frequency; and fifth, adaptively adjusting the analysis window lengthof the demodulation spectrum according to the estimated propeller shaft frequency, and carrying out secondary estimation on the demodulation spectrum. The modulation spectrum characteristic fidelity enhancement method adaptively adjusts the analysis window length of the demodulation spectrum according to the estimated propeller shaft frequency by using the inherent integer multiple relationship between each demodulation spectrum line spectrum frequency and the propeller shaft frequency, carries out secondary estimation on the demodulation spectrum, and obtains the demodulation spectrum with fidelity enhancement of modulation spectrum characteristics.

Description

technical field [0001] The invention belongs to the technical field of signal processing, and in particular relates to a method for enhancing the fidelity of modulation spectrum features of ship propeller cavitation noise based on an adaptive window length. Background technique [0002] Propeller noise includes two main components: propeller cavitation noise and propeller rotation noise. Propeller cavitation noise is caused by the collapse of a large number of air bubbles produced when the propeller rotates. Due to the unequal size and random collapse of these bubbles, cavitation noise has the nature of a smooth continuum. The propeller rotation noise is also called "singing sound", which is caused by the quasi-periodic characteristics of the generation and rupture of a large number of bubbles when the propeller rotates. Relevant literature and experiments show that the "singing sound" appears as a line spectrum component superimposed on the continuous spectrum, and its fr...

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Problems solved by technology

[0004] At present, scholars at home and abroad have proposed many methods to reduce the spectral leakage caused by non-integer period truncation of periodic signals, mainly including: (1) replace the rectangular window with Hanning window when truncation, although this method can reduce the spectral leakage to a certain extent Spectrum leakage, but adding Hanning window will make the result of discrete Fourier transform have a wider side lobe; (2) Combine wavelet transform with discrete Fourier transform, that is, wavelet transform is used for original signal sampling, and then discrete Fourier transform is used Fourier transform is used for spectral analysis. Although this method can improve the accuracy of frequency estimation, it does not fundamentally reduce the spectral leakage caused by non-integer period truncation of periodic signals; (3) adaptively estimate based on iterative correlation calculations It is used to eliminate the window length of non-integer cycle truncated discrete Fourier transform spectrum leakage of periodic signals. Although the principle of this algorithm is simple and easy to implement, it requires the signal to have a high signal-to-noise ratio. When the signal-to-noise ratio is lower than a certain threshold, the window The long estimation accuracy drops sharply as the signal-to-noise ratio decreases

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