Theoretical And Experimental Study On The Spatiotemporal Evolution Of Acoustic Field With Nonlinear Interaction Of Acoustic Waves

Non-linear phenomenon is a phenomenon that exists universally in nature.Any physical system in nature is a non-linear system.With the continuous development of science and technology,traditional linear assumptions cannot meet the exact description of physical system models,and nonlinear factors have become increasingly important.Nonlinear acoustics is one of the branches of nonlinear science.When the amplitude of the acoustic wave is large enough or the nonlinearity of the medium is acting,the non-linear term cannot be ignored and the acoustic wave does not meet the superposition principle.The non-linear interaction of sound waves will generate sum frequency waves,difference frequency waves,and higher harmonics.Because the higher harmonics have a larger attenuation coefficient when they propagate in the water medium,the main research object is the sum frequency and difference in the sound field.Frequency waves.In this paper,the Westervelt equation is used to describe the non-linear interaction process of two columns of acoustic waves.The spatial and temporal evolution of sum and difference frequency waves in the sound field of non-linear interaction between plane waves and spherical waves is derived by successive approximation.When the two columns of waves propagate collinearly,the resulting SPL sound field pressure levels are cumulative in the axial direction,and the axial phase change meets the traveling wave phase change law.When plane waves and spherical waves are propagated non-collinearly,the sound pressure level will increase with the increase of the wave vector angle and the space period of the oscillation will increase and satisfy the law of spherical wave attenuation,and the starting point of the law of spherical wave attenuation and the wave vector clip The angle is related;within the tolerance range,the test results on the lake are basically consistent with the simulation results.The spatial-temporal evolution of the non-linear interaction sound field of two columns of sound waves can be used to design the corresponding hydrophone receiving matrix,and the array gain can be used to make up for the shortcomings of the low efficiency of the parametric receiving array.For the nonlinear three-wave interaction process of resonance,we mainly study the two cases of opposite propagation and co-propagation of two rows of spherical waves;the sourcefunction of the nonlinear interaction between plane waves and two rows of spherical waves propagating are derived.Burgers will be used An equation describing the three-wave process is transformed into an elliptic equation,and the analytical solution of the amplitude parameters and the resonance phase of the nonlinear three-wave interaction of the resonance are obtained by solving the elliptic equation.The finite element method is used to simulate the non-linear interaction of sound waves to form a sound field numerical simulation.The axial and differential sound pressure levels of the same-frequency spherical wave and plane interaction sound field propagating in the opposite direction have the lowest sound pressure level at the center position and the axial phase spatial distribution.Similar to its axial sound pressure level distribution.When the sound source levels of the two waves of spherical waves are the same,the sound pressure level of the differential frequency wave generated in the opposite direction is lower than that in the same direction;the phase propagation law is basically the same when the angle of the wave vector is small.Utilizing the spatiotemporal evolution of the three-row non-linear interaction sound field to design the amplitude and phase of the pump wave emitted by the high-frequency transmitting transducer to amplify or weaken the low-frequency weak signal.Under the condition of collinearity and optimal phase,the increase amount of low-frequency signal enhancement of each array element is about 5 ?10d B.When the incident angle of low-frequency waves changes,the optimal phase changes;within a certain error tolerance range,the test results can be obtained.The low frequency sound wave amplification or reduction effect is consistent with the simulation results.