Propagation of sound waves in a moving medium

Summary The propagation of sound waves radiated by a two-dimensional source in a fluid moving with subsonic velocity between two perfectly reflecting parallel walls is considered. The steady state problem appears to have a non-unique solution, for which Sommerfeld's radiation condition does not apply. Two methods are used for obtaining the unique solution. First the corresponding problem for a fluid with non-zero bulk viscosity is solved, which has a unique solution and then the limit for zero bulk viscosity is taken. Secondly, the initial value problem for a source being switched on at timet=0 is solved and it is shown that its solution tends to the same steady state solution in the limit fort . In the last section the results for the corresponding axisymmetric case are given. In the appendix some properties of the twodimensional steady state solution are explained qualitatively.     

Magnetic wave propagation in a periodic medium

The propagation of magnetic waves in an infinite medium with a periodic dielectric constant is studied as a simplified example to evaluate the applications of periodic structures. Specifically, the use of those structures for filtering and distributed feedback is investigated, and a new scheme for the generation of magnetic waves using drifting charges and a distributed feedback configuration similar to DFB lasers is studied in some detail.     

The propagation of Love waves in water-saturated soil underlain by a heterogeneous elastic medium

Summary The propagation of Love waves in water-saturated soil overlying a non-homogeneous elastic medium has been investigated in the present paper. The solution of the problem is evaluated with the help of Fourier transform technique. It has been found that the velocity of body wave depends on the direction of propagation, and the velocity of Love wave depends on the porosity of the layer and the non-homogeneity character of the medium as well. Further, the effect of porosity and heterogeneity has been shown graphically.With 2 Figures     

On the open sea propagation of water waves generated by a moving bed

Within the framework of linear theory, applicable far from the shore, we investigate the two-dimensional propagation of waves generated in the ocean by a sudden seabed deformation.     

Plane defect-field wave propagation in a viscoelastic medium

The wave solutions of the system of equations describing the defect field in a viscoelastic medium are studied within the framework of the defect field theory. The refraction and absorption coefficients and the velocities of propagation of the elastic continuum and the defect continuum waves are determined. Features of the correlation between various waves are analyzed.     

Transient waves propagation in the Mindlin microelastic medium

Abstract

Different types of plane transient waves (surfaces of strong or weak discontinuities) are studied in the Mindlin micropolar medium. The theory of discontinuities is used as the method of investigation. The velocities of all types of waves have been obtained with the help of the Hadamard-Thomas conditions of compatibility, and on the each wave front it has been established which from the desired values experience discontinuities and which are continuous ones.     

Surface wave propagation in a fluid-saturated incompressible porous medium

A study of surface wave propagation in a fluid-saturated incompressible porous half-space lying under a uniform layer of liquid is presented. The dispersion relation connecting the phase velocity with wave number is derived. The variation of phase velocity and attenuation coefficients with wave number is presented graphically and discussed. As a particular case, the propagation of Rayleigh type surface waves at the free surface of an incompressible porous half-space is also deduced and discussed.     

The effect of thermal radiation on the propagation of temperature waves in a semitransparent medium

The propagation of temperature waves arising as a result of periodic external thermal stimulation is investigated in a plane layer of semitransparent absorbing and radiating medium without scattering. The classification of temperature waves on the basis of two dimensionless parameters is suggested. It is rigorously demonstrated that not more than two temperature waves may simultaneously exist in a gray semi-infinite medium. The relative contribution of radiation to complex heat transfer is estimated. The system of equations of radiative-conductive heat transfer is reduced to a single integral equation on the boundary. The effect of reflection on the boundary is discussed.     

Temperature shock waves in a moving medium with allowance for the relaxation of the heat flux

The solution of the gasdynamic equation with allowance for the heat transfer in the relaxation of the heat flux is analyzed. The relations expressing the laws of conservation on the front of strong discontinuity of the quantities sought, including the discontinuity of the temperature and the heat-flux density, are discussed. The possibility of existence of two shock waves with fixed initial data is shown using the self-similar solution of the problem on gas motion ahead of the piston. The occurrence of two strong discontinuities is due to the presence of different velocities of propagation of gasdynamic and thermal disturbances — the velocity of sound and the finite rate of heat transfer at a nonzero time of relaxation of the heat flux. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 57–68, July–August, 2006.     

粘性联结的层状固体媒质中兰姆波的传播

在复合材料中 ,当有粘弹体存在时 ,粘弹体的粘性会对波的传播造成一定影响。早期的 Thomson-Haskell矩阵以面波描述板层中的场 ,而面波的幅值在各个方向都是常数 ,因此它们不能描述在一衰减媒质中反射或透射波的衰减。本文中引入体波衰减的模型 ,即 Kelvin- Voigt的粘弹性描述 [1] ,该方法导致了一个复数波数。其实部描述了波的传播 ,而虚部则描述波的衰减。1　基本理论传递矩阵可以描述弹性波在包含任意多层的层状媒质中的传播特性 [2 ] 。1.1　无限弹性固体中的波对图 1所示的计算模型 ,其运动位移方程用矢量形式可表示为 :　　 ρ 2 U …     

在含气孔粘弹媒质中非线性声传播特性

1引言: 共振型消声是实现水下吸声的一种基本形式.结构共振消声是通过在基底粘弹(通常为橡胶类粘弹材料)材料中嵌入声学结构--各种类型和大小的空腔,利用空腔的共振吸收增加损耗.本文运用等效媒质法,着重对含气孔粘弹材料的二阶非线性声场做了研究.     

The investigation of transient wave propagation in a dipping layered medium overlaying a half space

Abstract

The responses of transient wave propagation in a single dipping layered medium overlaying a half space was investigated in this study. To obtain the responses, a point source located in the dipping layered medium was assumed, and in order to make the results more consistent with real situations, the time functions for source mechanism, such as parabolic ramp function and triangular time function, were considered in this research. Finally, the famous mathematical tool with physical significance, the generalized ray theory [4], was employed to solve the foregoing problem, and the ray paths and responses for the distinct locations on the surface were then obtained and shown in sketches. It was found from the obtained results that the responses decay with the distance from the focus just as expected.     

On the transport of energy in water waves

Theory is developed and utilized for the calculation of the separate transport of kinetic, gravity potential, and surface-tension energies within sinusoidal surface waves in water of arbitrary depth. In Sect. 2 it is shown that each of these three types of energy constituting the wave travel at different speeds, and that the group velocity, c _g , is the energy-weighted average of these speeds, depth- and time-averaged in the case of the kinetic energy. It is shown that the time-averaged kinetic energy travels at every depth horizontally either with (deep water), or faster than the wave itself, and that the propagation of a sinusoidal wave is made possible by the vertical transport of kinetic energy to the free surface, where it provides the oscillating balance in surface energy just necessary to allow the propagation of the wave.The propagation speed along the surface of the gravity potential energy is null, while the surface-tension energy travels forward along the wave surface everywhere at twice the wave velocity, c. The flux of kinetic energy, when viewed traveling with a wave, provides a pattern of steady flux lines which originate and end on the free surface after making vertical excursions into the wave, even to the bottom, and these are calculated. The pictures produced in this way provide immediate insight into the basic mechanisms of wave motion. In Sect. 3 the modulated gravity wave is considered in deep water and the balance of terms involved in the propagation of the energy in the wave group is determined; it is shown again that vertical transport of kinetic energy to the surface is fundamental in allowing the propagation of the modulation, and in determining the well-known speed of the modulation envelope, c _g . Dedicated to Professor J.N. Newman in recollection of his many significant contributions to the theory and computation of waves and floating bodies and to the founding of the IWWWFB.     

Simulation of chemical transformation wave propagation through a flow reactor with a microbubble medium

A numerical simulation is carried out of the exothermal heterogeneous reaction of cumene oxidation on the basis of a homogeneous model of bubble liquid. The thermal properties of the bubble medium are determined according to the proposed model. The influence of different factors is investigated on an oxidation level with a volume gas content value of more than 0.5.     

Thermoelastic wave propagation in a random medium and some related problems

The mean waves in a medium with random inhomogeneities are studied within the theory of linear thermoelasticity. Under the assumption of small random fluctuations approximate integro-differential equations governing the mean displacement and temperature fields are derived. For the elastic case the material behaves effectively as a viscoelastic body with memory. The dispersion equation is obtained for the thermoelastic case. This equation is analyzed for some special cases. The random effects introduce attenuation and change of phase speeds for the compressional and shear waves. For weak thermoelastic coupling, the shear wave is not affected by the random thermal properties. Explicit results are obtained for general and special cases. In general the mean fields are coupled in a complicated way. Therefore an uncoupled theory is presented. Then the problems with random boundary conditions or a randomly varying boundary are discussed. Different perturbation methods are given. Two examples are provided respectively by the heat conduction across a rough surface and the hydrodynamic theory of lubrication under a random loading.     

The wave propagation and vibrational energy flow characteristics of a plate with a part-through surface crack

In the view of structure-borne sound, vibrational wave and energy flow characteristics of infinite thin plate of finite width with a part-through surface crack are investigated. The case of an all-over part-through crack parallel to the finite side of the plate is considered. The crack is modeled as a line spring and the flexibility of the spring is deduced from the relationship between the strain energy and stress intensity factor in fracture mechanics. The responses of both intact plate and cracked plate under the excitation of harmonic force are reduced with wave propagation approach, then the input energy flow and transmitted energy flow of intact and cracked plates are calculated. The results show that the vibrational energy flow of cracked plate is highly related to the depth and location of the part-through crack. The location and the depth of the crack can be identified by the contour lines of normalized input energy flow with different driving frequencies. The research provides theoretical basis for the crack detection by measuring the vibrational energy flow in cracked plate structures.     

Determining the energy of charged particles moving in a waveguide filled with an anisotropic dispersive medium

Generation of the Vavilov-Cherenkov radiation (VCR) by a charged particle moving in a waveguide filled with an anisotropic dispersive medium whose principal axis is parallel to the waveguide axis is considered. It is established that, for a certain character of dispersion, which can be realized using artificial metamaterials, it is possible to obtain a pronounced dependence of the frequencies of excited modes on the Lorentz factor even in the region of large values of this factor. This circumstance can be used for determining the energies of ultrarelativistic particles and beams.