Research On Measurement Method Of Characteristics Of Transient Underwater Sound Sources In Non-free Field

The acoustic signal from the transient sound source is short and the energy is concentrated in a short time.The radiated sound power can be expressed as a function of time.The forms of underwater transient sound source are explosion pulse sound,object entering water sound,rudder sound,torpedo emission sound,etc.Nowadays,the transient sound source has become a new acoustic characteristic of underwater vehicle exposure.How to accurately measure the characteristics of underwater transient sound source and get its specific evaluation method is of great engineering significance.The traditional method of measuring the characteristics of sound source is to use free field to measure the sound source level.However,the natural free field environment is not everywhere.The artificial anechoic pool has low-frequency limitation.The actual measurement environment often becomes non-free field due to the influence of boundary.Typical non free fields,such as reverberation pool and shallow water channel,in these measurement environments,the sound pressure signal at a single point is not only affected by the characteristics of the sound source itself,but also by the measurement environment,such as the boundary and measurement location.The acoustic characteristics of a sound source usually refer to the sound power radiated from the sound source in all directions.Compared with the sound pressure in the sound field,it is not sensitive to environmental changes.When the radiation impedance does not change significantly,the radiated sound power is basically unchanged.In this paper,the method of measuring the radiated sound power of the transient sound source in the non-free field is proposed.Through theoretical,simulation and experimental research,the effectiveness of the method in the reverberation pool and channel pool is verified,which provides technical support for the measurement and evaluation of the acoustic characteristics of the transient sound source.In this paper,time and frequency characteristics of two kinds of common transient sound source signal models,CW pulse and explosion sound source,are studied firstly.Combining the sound field characteristics of two typical non free fields,reverberation pool and channel pool,a method of measuring the radiated sound power of transient sound source under the condition of non-free field is proposed,that is,for reverberation pool,the radiated sound power of transient sound source is measured by reverberation method;for channel pool,the sound power radiated by the transient sound source is measured by the sound energy flux ofthe equivalent cylinder surrounded surface;and the autocorrelation function is used to reflect the time-domain characteristics of the radiated sound power of the transient sound source.After that,COMSOL software is used to simulate the conditions of various pools to verify the effectiveness of the proposed measurement method.Finally,the experiment of measuring the radiated sound power of the transient sound source is carried out in the reverberation pool and channel pool,and the measurement data in the anechoic pool is used as a reference to test the effect of the proposed method in practical application.The validity of the proposed method is proved by theoretical analysis,modeling simulation and pool experiment.The results show that: in the measurement of reverberation pool,the spatial average autocorrelation function of the transient sound pressure can be used to accurately measure the radiated sound power of the transient sound source;in the channel pool,according to the equivalent cylindrical surrounding surface,the measurement of sound energy flow can also accurately measure the radiated sound power of the transient sound source,which is suitable for different depth pools and different types of transient sound sources.In the non-free field,it is easier to obtain the real characteristics of the sound source by measuring the radiated sound power of the transient sound source than by measuring the signal result of the single point position in the sound field.The work in this paper provides an effective measurement method for the in-depth study of the acoustic characteristics of the transient sound source.