It is shown that the criterion of incompressibility applicable to any medium, contradicts to the real meaning of this term. On the basis of expression of speed of sound in inhomogeneous medium and generalized equation...It is shown that the criterion of incompressibility applicable to any medium, contradicts to the real meaning of this term. On the basis of expression of speed of sound in inhomogeneous medium and generalized equation of continuity of mass obtained in papers [1,2] respectively, it is proved that so called internal gravitation waves do not exist in nature. This concept appeared as a result of incorrect interpretation of incompressibility of medium. Correct understanding of criteria of compressibility or incompressibility leads to qualitatively new understanding of homogeneity or heterogeneity of medium, in particular—only strongly inhomogeneous medium can be incompressible while weakly inhomogeneous medium is always compressible. Besides, it is shown that in inhomogeneous media additional terms are added to known hydrodynamic (gas dynamic) correlations applicable to any medium which disappear at transfer to homogeneous model of medium.展开更多
Generalized equation for linear gravity waves in moving medium has been obtained. Sound wave is considered as a particular case and it is shown that in inhomogeneous medium at rest it is propagated in full concordance...Generalized equation for linear gravity waves in moving medium has been obtained. Sound wave is considered as a particular case and it is shown that in inhomogeneous medium at rest it is propagated in full concordance with the Doppler law and principle of motion relativity, i.e. these laws are invariant with reference to properties of medium (homogeneity or inhomogeneity). In moving medium they are fair only in the case of its homogeneity. In strongly inhomogeneous moving medium, propagation of sound is absolutely impossible.展开更多
In this paper, a general model on sound reflection from a layered solid medium with rigid and slip interfaces is proposed by using matrix method. Analytical expressions for reflection coefficients of both longitudinal...In this paper, a general model on sound reflection from a layered solid medium with rigid and slip interfaces is proposed by using matrix method. Analytical expressions for reflection coefficients of both longitudinal and transverse waves from the layered solid medium with one or two slip interfaces are derived. Numerical results of sound reflection coefficients from some typical adhesive joints with slip and rigid interfaces are presented, which may be useful for correct choice of technical parameters in ultrasonic evaluation of their interface properties.展开更多
Based on the former research, the mechanism of the influence of the medium structure on the sound velocity of the three-phase seabed deposit is discussed by theoretical method. Through analysis of several structure mo...Based on the former research, the mechanism of the influence of the medium structure on the sound velocity of the three-phase seabed deposit is discussed by theoretical method. Through analysis of several structure models of three-phase seabed deposit, an equation of sound velocity is presented, which can describe the effect of structure of three-phase deposit on its acoustic velocity. Seen form the derived equation, the equations of the sound velocity of the deposits with different medium structures are different, the influence of the medium structure on the sound velocity is apparent. The equation in the paper provides the theoretical basis to understand the mechanics properties through sound velocity test, and it can be easily adopted in engineering. The influences of the parameters of deposits, void ratio, gas concentration and modulus on sound velocity through the deposit are investigated by numerical analysis of the acoustic velocity. Numerical result shows that the sound velocity of three-phase medium is affected by void ratio, gas concentration and body modulus, and the sound velocity generally increases with the gas concentration increasing. The results of the paper can be helpful to the acoustic method.展开更多
The anechoic performance and mechanism of underwater elastic spherical shell covered with coating are studied at low frequencies.The acoustic cloak is anisotropic material,which can be designed with homogeneous isotro...The anechoic performance and mechanism of underwater elastic spherical shell covered with coating are studied at low frequencies.The acoustic cloak is anisotropic material,which can be designed with homogeneous isotropic materials on the basis of effective medium approximation theory.The analytic expression of scattering acoustic field from the shell covered with multilayered medium is formulated and the scattering form function,resonance mode,acoustic field distribution are computed,the scattering characteristics and mechanism of transmission are analyzed.The results show that the direction of sound transmission inside the multilayered medium is changed,the acoustic field is deflected gradually,and the acoustic energy flux is guided around the target,which reduces the scattering intensity at low frequencies,the acoustic intensity of target＇s surface is very weak.Excepting the first resonance peak in spectrum produced by the zero order partial wave,the other resonance modes of elastic spherical shell are not excitated and the multilayered medium can suppress the resonance of the spherical shell effectively.展开更多
文摘It is shown that the criterion of incompressibility applicable to any medium, contradicts to the real meaning of this term. On the basis of expression of speed of sound in inhomogeneous medium and generalized equation of continuity of mass obtained in papers [1,2] respectively, it is proved that so called internal gravitation waves do not exist in nature. This concept appeared as a result of incorrect interpretation of incompressibility of medium. Correct understanding of criteria of compressibility or incompressibility leads to qualitatively new understanding of homogeneity or heterogeneity of medium, in particular—only strongly inhomogeneous medium can be incompressible while weakly inhomogeneous medium is always compressible. Besides, it is shown that in inhomogeneous media additional terms are added to known hydrodynamic (gas dynamic) correlations applicable to any medium which disappear at transfer to homogeneous model of medium.
文摘Generalized equation for linear gravity waves in moving medium has been obtained. Sound wave is considered as a particular case and it is shown that in inhomogeneous medium at rest it is propagated in full concordance with the Doppler law and principle of motion relativity, i.e. these laws are invariant with reference to properties of medium (homogeneity or inhomogeneity). In moving medium they are fair only in the case of its homogeneity. In strongly inhomogeneous moving medium, propagation of sound is absolutely impossible.
文摘In this paper, a general model on sound reflection from a layered solid medium with rigid and slip interfaces is proposed by using matrix method. Analytical expressions for reflection coefficients of both longitudinal and transverse waves from the layered solid medium with one or two slip interfaces are derived. Numerical results of sound reflection coefficients from some typical adhesive joints with slip and rigid interfaces are presented, which may be useful for correct choice of technical parameters in ultrasonic evaluation of their interface properties.
文摘Based on the former research, the mechanism of the influence of the medium structure on the sound velocity of the three-phase seabed deposit is discussed by theoretical method. Through analysis of several structure models of three-phase seabed deposit, an equation of sound velocity is presented, which can describe the effect of structure of three-phase deposit on its acoustic velocity. Seen form the derived equation, the equations of the sound velocity of the deposits with different medium structures are different, the influence of the medium structure on the sound velocity is apparent. The equation in the paper provides the theoretical basis to understand the mechanics properties through sound velocity test, and it can be easily adopted in engineering. The influences of the parameters of deposits, void ratio, gas concentration and modulus on sound velocity through the deposit are investigated by numerical analysis of the acoustic velocity. Numerical result shows that the sound velocity of three-phase medium is affected by void ratio, gas concentration and body modulus, and the sound velocity generally increases with the gas concentration increasing. The results of the paper can be helpful to the acoustic method.
文摘The anechoic performance and mechanism of underwater elastic spherical shell covered with coating are studied at low frequencies.The acoustic cloak is anisotropic material,which can be designed with homogeneous isotropic materials on the basis of effective medium approximation theory.The analytic expression of scattering acoustic field from the shell covered with multilayered medium is formulated and the scattering form function,resonance mode,acoustic field distribution are computed,the scattering characteristics and mechanism of transmission are analyzed.The results show that the direction of sound transmission inside the multilayered medium is changed,the acoustic field is deflected gradually,and the acoustic energy flux is guided around the target,which reduces the scattering intensity at low frequencies,the acoustic intensity of target＇s surface is very weak.Excepting the first resonance peak in spectrum produced by the zero order partial wave,the other resonance modes of elastic spherical shell are not excitated and the multilayered medium can suppress the resonance of the spherical shell effectively.
