Experimental Study On Acoustic Characteristics Of Gas Bearing Sandy Sediments

The acoustic characteristics of marine sediments have an important impact on the propagation of sound waves in water,and the gas in sediments will significantly change the acoustic parameters of sediments.In recent decades,domestic and foreign experts and scholars have proposed several acoustic models of gas bearing sediments,and the applicability of these models needs to be further tested and verified.Due to the high cost of direct measurement at sea,it is necessary to prepare gas bearing sandy sediments for experimental research in the controllable environment of the laboratory.In this paper,the effects of different bubble radius,gas volume fraction,gas type and characteristic parameters of sediment model on the dispersion and attenuation of sound velocity of sediment are simulated and analyzed for three kinds of acoustic models of gas bearing sediment – the Anderson Hampton model,the corrected Biot Stoll model and the corrected effective density fluid approximation model(EDFM).The results show that near the resonance frequency of the bubble,the peak value of sound velocity and attenuation will appear,and the frequency of the peak value of sound velocity is always lower than that of the attenuation peak value.The bubble radius is negatively correlated with the resonance frequency;The gas volume fraction is positively correlated with the peak value of sound velocity and attenuation;The larger the particle size of sediment particles,the greater the sound velocity and the smaller the attenuation;The type of gas only has an obvious influence on the Anderson & Hampton model.To test the applicability of the model,an experimental platform was designed in the water tank of the laboratory.Four kinds of sand with different particle sizes were screened.Water saturated sandy sediments were prepared by boiling,and then gas was injected into them with a needle tube to obtain sediments containing different gases(air,carbon dioxide and helium).The narrowband measurement method and broadband measurement method of sound velocity and attenuation coefficient of sandy sediments are introduced.The copy correlation method of time delay estimation and the pulse compression technology of wide-band measurement are simulated and analyzed.In order to solve the problem of the spectral peak shift of CW signal,the transmitted signal is compensated,and its effectiveness is verified by simulation and experiment.The sound velocity and attenuation coefficient of four different particle sizes of sediments containing three different gases in the frequency range of 90 k Hz to 200 k Hz are measured by narrow-band and wide-band measurement methods respectively.The measurement results of the two methods are basically consistent.The experimental results show that bubble radius,bubble volume fraction,sediment particle size and gas type have significant effects on the sound velocity and attenuation coefficient of sediment.The applicability of the model is tested.In the experiment,it is also found that the solubility and density of gas will have a great impact on the experimental measurement.The gas with high solubility is more vulnerable to the influence of ambient temperature,which changes the bubble volume fraction and radius distribution in the sediment.The gas with low density is more buoyant in the sediment and easier to escape.