摘要
The analysis of the radiated noise of vessels given in this paper shows some strong superposed line components in low frequency spectrum below 100Hz occurring at discrete frequencies which correspond with the rotation speed of propeller shaft, or propeller blade frequency, or their harmonic frequencies. Since the line components reflect propeller's working characteristics, the propller's features can be extracted directly from low-frequency line components in addition to demodulated line component. So there are two ways to extract the features, one is direct way, the other is demodulation way. Detection performance of the line component in background-noise is discussed in this paper. The signal level is defined as the difference between the PDF's (Probability Density Function) mean of the peak of the line component and PDF's mean of the background-noise. In direct way the signal level of the line component is proportional to the signal noise ratio (S / N). In demodulation way the signal level of demodulated line component reduces with S / N descent, but the signal level reduces slowly if S / N is high and very fast if S / N is low.
The analysis of the radiated noise of vessels given in this paper shows some strong superposed line components in low frequency spectrum below 100Hz occurring at discrete frequencies which correspond with the rotation speed of propeller shaft, or propeller blade frequency, or their harmonic frequencies. Since the line components reflect propeller's working characteristics, the propller's features can be extracted directly from low-frequency line components in addition to demodulated line component. So there are two ways to extract the features, one is direct way, the other is demodulation way. Detection performance of the line component in background-noise is discussed in this paper. The signal level is defined as the difference between the PDF's (Probability Density Function) mean of the peak of the line component and PDF's mean of the background-noise. In direct way the signal level of the line component is proportional to the signal noise ratio (S / N). In demodulation way the signal level of demodulated line component reduces with S / N descent, but the signal level reduces slowly if S / N is high and very fast if S / N is low.
