Research On Sound Velocity Dispersion Characteristics Of Bubbly Media

Acoustic waves are by far the only forms of energy that can travel long distances in the ocean.For the propagation of sound waves in ocean waveguides,the seawater as the medium of transmission and the marine sediments as the lower boundary,the presence of a small amount of gas in seawater and sediment will significantly change its acoustic characteristics,mainly reflected in the dispersion and decay Frequency characteristics.Studying the acoustic characteristics of bubble-bearing media is of great significance for the prediction of ocean sound field,seabed exploration and seismic monitoring.In this paper,we first derive the acoustic velocity and attenuation model of bubble-containing liquid.By comparing the bubble's vibration with the mechanical movement of the spring,the bubble's equivalent mass and equivalent stiffness are analyzed to derive the bubble's vibrational frequency and corrected for heat conduction and surface tension.The vibration damping of bubble was obtained by analyzing the scattering sound field.According to the relationship between damping,compression coefficient and sound velocity,the velocity and attenuation of bubble containing liquid were obtained.In addition,the volumetric vibration model of bubble was obtained by analyzing the Lagrange equation,and the same result was obtained by analysis.Then from the angle of linear propagation of sound waves in the liquid,the bubble vibration equation is established with the acoustic propagation equation of bubble-containing liquid,and the expressions of sound velocity and attenuation of bubble-containing liquid are also obtained.In order to correct the sound velocity and attenuation model of bubble-containing liquid,the correction is made in two directions: the equivalent wave number and the multi-body scattering of bubbles,and the correction results of the multi-body scattering of bubble with equivalent wave number and confinement effect are obtained.Corrected the speed of sound and decay model of the bubble-containing liquid.Based on the two models of bubble-containing liquid,the model is generalized to the bubble-containing sediment,and the velocity of sound and the attenuation model of bubble-containing sediment are obtained.In the model based on bubble vibration and scattering,the sediment is approximately considered as a fluid and added to the sediment-specific shear modulus.When the model is based on linear propagation,the sediment is considered as viscoelastic medium,Vibration analysis in viscoelastic media The bubble resonance frequency and radius change.After obtaining the sound velocity and attenuation model of bubble-containing sediment,the method of retrieving the bubble distribution is given by the method of B-spline curve fitting.In studying the reflection and transmission of bubble-bearing sediments,the sediment is considered as a porous medium.By introducing the modified Biot wave equation,the three transmitted waves in bubble-containing porous media are substituted into the Biot's wave equation to obtain the ratio of potential functions and the expression of wavenumber.By analyzing the layered bubble-containing unsaturated porous media For the first time,the acoustic reflection and transmission coefficients of layered porous media were obtained with eight boundary conditions.In order to validate the model,a pool experiment was carried out to simulate the bubble-bearing seafloor sediments,and the attenuation data were obtained through experiments.Obvious resonance peaks were found,the existence of bubbles was proved and the B-spline inversion method was used Bubble distribution of the measured environment.