| The underwater exhaust air bubble flow will radiate acoustic signals outward during the formation process,and its acoustic signal contains lots of information about the size,number and distribution of bubbles in the bubble flow.The use and control of the acoustic characteristics of bubble flow is currently a hot spot in many fields.For example,in the process industry,by analyzing the characteristics of the bubble flow radiating acoustic signal in the bubble column,the bubble flow regime in the column can be identified,thereby providing guidance for production operations;in the field of underwater navigation,the relationship between exhaust parameters and acoustic signal characteristics can be used to optimize exhaust parameters so as to reduce the intensity of exhaust noise.In short,understanding the acoustic characteristics and its mechanism of the bubble flow produced by underwater exhaust,and knowing the quantitative relationship between acoustic characteristics and exhaust parameters,are of great significance to many engineering fields such as underwater passive acoustic detection and underwater exhaust noise reduction.This paper takes the bubble flow formed by underwater exhaust as the research object.For the sound signal radiated by the bubble flow when generated,in-depth research has been carried out to study its time-frequency characteristics and of which the generation mechanism and the changing laws with exhaust parameters through theoretical analysis and experimental research,so as to provide support for the research of underwater passive acoustic detection and underwater exhaust noise reduction methods based on bubble flow.The main work is as follows:(1)The acoustic characteristics and mechanism of the bubble flow generated by underwater exhaust is studied through bubble acoustics and a self-designed-and-built underwater synchronous experimental measurement system of acoustic field and flow field of bubble flow.By combining bubble acoustics,image processing and digital signal processing methods,the characteristics of the acoustic signal radiated by bubble flow and its formation mechanism are studied;through the simultaneous analysis of the bubble flow field and the sound field,the generation mechanism of bubble flow radiating sound signal is studied.(2)The quantitative relationship between the leading frequency of the underwater exhaust bubble flow and the exhaust parameters is established by combining bubble acoustics,bubble dynamics and experimental research.Based on signal processing and statistical analysis methods,the equivalent peak frequency that can effectively characterize the energy distribution of bubble flow acoustic signal in frequency domain is extracted;combining bubble dynamics and bubble acoustics,the quantitative relationship between bubble flow peak frequency and exhaust parameters,respectively the exhaust gas velocity,the diameter and number of the orifices,is established with bubble parameters as an bridge;by the established quantitative relationship,the influence of exhaust parameter on the bubble flow acoustic signal characteristics is analyzed.(3)An underwater exhaust noise reduction method is proposed based on the quantitative relationship between the acoustic characteristics of the bubble flow and the exhaust parameters,and its noise reduction effect is experimentally studied.Based on the law that acoustic characteristics are affected by exhaust parameters,an exhaust noise reduction method using multiple small-diameter orifices instead of one single large-diameter pipe is proposed,and noise attenuation is accelerated by the frequency increase of exhaust noise;and an effective underwater exhaust noise reduction device has been designed based on this method,and the noise reduction effect of the device has been studied through experiments.In this paper,the research on the acoustic characteristics of underwater exhaust bubble flow reveals the acoustic characteristics of bubble flow and its formation mechanisms,and establishes the quantitative relationship between acoustic characteristic parameters and underwater exhaust parameters,which provides theoretical support for underwater passive acoustic detection;the underwater multi-orifice exhaust noise reduction method proposed based on the quantitative relationship,and the effective underwater exhaust noise reduction device designed according to the noise reduction method,can provide new solutions for underwater exhaust noise reduction. |
