Application of Duffing oscillator in ship propeller blade number recognition

Abstract

Time-frequency analysis of ship noise is often used in passive sonar target classification. DEMON spectrum analysis is a common method of obtaining propeller speed and number of blades. Obtaining propeller speed and number of blades is usually based on the amplitude characteristics between the line spectrum of the shaft rate and harmonic components in the demodulation spectrum, which calls for an evident line spectra structure. Because of the effect of modern ships' noise-reduction technology, the demodulation line spectrum is sometimes very weak. The blade rate line spectrum can only be obtained from some ship noise (it is difficult to distinguish whether it is a blade rate line spectrum or a shaft rate line spectrum in practice). Depending on the amplitude characteristics of the demodulation spectrum, it is difficult to estimate shaft frequency and harmonic components' frequency, and it is also difficult to estimate the number of blades. Actually, the line spectrum of the shaft frequency and harmonic components' frequency always exist in the ship's low noise, but the amplitude value of the line spectrum is small, so they are sometimes obscured by environmental noise. Propeller blade numbers cannot be obtained using amplitude information. Because the amplitude of some demodulation spectrums of ship radiated noise is very weak, the application of a Duffing oscillator is studied in the weak amplitude demodulation spectrum of ship radiated noise. Through simulation and experiment analysis, a Duffing oscillator can detect weak demodulation signals under strong noise compared with traditional demodulation spectrum analysis methods. a A ship demodulation signal, which only has a blade rate line spectrum, is also analysed. The number of propeller blades can be recognized quite precisely according to the frequency multiplication relationship between the shaft rate line spectrum and the blade rate line spectrum.