A STUDY ON SHIP-RADIATED NOISE RHYTHMS （Ⅱ）——ATUOCORRELATION FUNCTION AND EXTRACTION OF RHYTHM INFORMATION

On the basis of the previous paper¹, power spectrum density functions for superposition type modulation envelopes and autocorrelation functions for various types of modulation envelopes are calculated in this paper. The theoretical results are in good agreement with experimental results. According to the theoretical analyses and experimental results given in the two papers, it is found that very rich rhythm information is contained in modulation envelope of ship noise. The pieces of information are directly or indirectly related to physical att ributes of ship itself. The effective extraction of different kinds of rhythm information is very valuable to deducing the work conditions of ship and its own properties from its radiated noise.
It is pointed that a lot of information relating to ship, for example, rotative speed of propeller, number of propeller blades, nonuni formity between blades, processed and installed condition of propeller shaft, kind of propulsion machinery and factors of ship shape, can be extracted from power spectrum density and autocorrelation functions of ship-radiated noise modulation envelopes, the methods of extracting them are also investigated.