Experimental Study of Underwater Propeller Low-frequency Noise Flied

摘要

There are several sources of noise and vibration in a contemporary ship, and propeller noise is the main one of them. The sound field radiated by rotating systems such as propellers have intricate structure, displaying a wide range of complex behaviour. This complexity makes the study of such systems both scientifically challenging and technologically important. As one of the three most important noise sources in ship, especially when the ship sailing in high speed, low-frequency propeller noise becomes the main component of ship radiated noise. The low frequency noises of a propeller are composed of discrete spectrum (line-spectrum) noise and broadband noise. The line-spectrum noise is the part we are concerned with in this paper. The low-frequency discrete noise of the propeller is caused by the interaction of blades and the stern wake field. Discrete spectrum noise prediction calculation using the theory of underwater acoustic methods could obtain results with practical significance in engineering. There is similar performance between ship propeller noise and ship model propeller noise in the same degree. Ship propeller noise can be predicted by analyzing a ship model propeller. Considering the similar performance of the ship propeller noise spectrum, we could analyze the test data using similar theory. Experiments of measuring the low-frequency radiation noise field for propellers under different rotational speed - through regulating the speed governor - is studied in a Towing Tank. The frequency of line-spectrum has been found by the abovementioned experiments, and the stability of them should be realized. Time-frequency theory is used for measuring radiation noise, and the stability of line-spectra at a certain frequency is analyzed. The mechanism analysis of low-frequency line-spectrum noise of the propeller has important engineering value in area of propeller noise control.