共查询到20条相似文献,搜索用时 0 毫秒
1.
G. Rosenhouse 《Journal of sound and vibration》1979,67(4):469-486
Theoretical analysis of sound wave propagation in structures indicates considerable amplitude reduction during transmission through a bent joint, while some build-up can be observed in front of the bend. Every type of transmitted wave (longitudinal and flexural in plane frames) is found to combine with other forms of sound propagation as a result of the deflection of the axis of the wave guide. The screening effect of the bend, in solids with arbitrary viscoelastic properties, is evident even under highly simplified assumptions, such as compatibility and equilibrium. By solving several practical problems, the attenuation due to folding of the structure is compared to the damping effect of the material, with the conclusion that the former contribution is the larger of the two. A pair of examples of insulation analysis of structures is worked out, and the results yield the particle velocity—the first step in determining the radiation pattern. The influence of dense columns in walls, of beams in plates, and of coupling effects in bent structures are examined. 相似文献
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Recently, substantial attention is paid to the development of methods of generation of pulsations in high-pressure systems to produce pulsating high-speed water jets. The reason is that the introduction of pulsations into the water jets enables to increase their cutting efficiency due to the fact that the impact pressure (so-called water-hammer pressure) generated by an impact of slug of water on the target material is considerably higher than the stagnation pressure generated by corresponding continuous jet. Special method of pulsating jet generation was developed and tested extensively under the laboratory conditions at the Institute of Geonics in Ostrava. The method is based on the action of acoustic transducer on the pressure liquid and transmission of generated acoustic waves via pressure system to the nozzle. The purpose of the paper is to present results obtained during the research oriented at the determination of acoustic wave propagation in high-pressure system. The final objective of the research is to solve the problem of transmission of acoustic waves through high-pressure water to generate pulsating jet effectively even at larger distances from the acoustic source. In order to be able to simulate numerically acoustic wave propagation in the system, it is necessary among others to determine dependence of the sound speed and second kinematical viscosity on operating pressure. Method of determination of the second kinematical viscosity and speed of sound in liquid using modal analysis of response of the tube filled with liquid to the impact was developed. The response was measured by pressure sensors placed at both ends of the tube. Results obtained and presented in the paper indicate good agreement between experimental data and values of speed of sound calculated from so-called "UNESCO equation". They also show that the value of the second kinematical viscosity of water depends on the pressure. 相似文献
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Acoustic wave propagation in double porosity media 总被引:1,自引:0,他引:1
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Elsewhere [1], using the framework of multipolar continuum mechanics, the authors have discussed a possible alternative to the two-fluid theories for liquid helium 11 and showed that, in the case when the fluid is assumed to be incompressible, second sound waves exist in both the stationary and rotating fluid. Here the constitutive theory presented in the paper cited is extended to include the effects of compressibility and viscosity and a study of these effects on the propagation of small-amplitude waves. 1t is found that the qualitative predictions agree with the experimental observations in helium II. 相似文献
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We present results of calculations of the equilibrium surface tension and density profiles for the liquid-vapour interface of a binary mixture of Lennard-Jones 12-6 fluids. The calculations are based on a density-functional theory for the Helmholtz free energy of the inhomogeneous mixture. This is a ‘microscopic’ generalization of the van der Waals-Cahn-Hilliard theory for the interface of a binary mixture. Our calculations cover the full range of liquid-vapour coexistence and the whole range of concentration. We find a correlation between the excess surface tension of the mixture and the surface segregation (adsorption) of the species with the lower surface tension. The ways in which segregation and excess surface tension depend on the Lennard-Jones parameters of the pure components are briefly discussed. Our results for the excess surface tension of mixtures of Ar and N2 and Ar and CH4 are compared with experiment; the agreement is reasonable. 相似文献
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The propagation of an acoustic wave through two-phase porous media with spatial variation in porosity is studied. The evolutionary wave equation is derived, and the propagation of an acoustic wave is numerically analyzed in application to marine sediments with various physical parameters. 相似文献
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Based on the three-phase theory proposed by Santos, acoustic wave propagation in a poroelastic medium saturated by two immiscible
fluids was simulated using a staggered high-order finite-difference algorithm with a time partition method, which is firstly
applied to such a three-phase medium. The partition method was used to solve the stiffness problem of the differential equations
in the three-phase theory. Considering the effects of capillary pressure, reference pressure and coupling drag of two fluids
in pores, three compressional waves and one shear wave predicted by Santos have been correctly simulated. Influences of the
parameters, porosity, permeability and gas saturation on the velocities and amplitude of three compressional waves were discussed
in detail. Also, a perfectly matched layer (PML) absorbing boundary condition was firstly implemented in the three-phase equations
with a staggered-grid high-order finite-difference. Comparisons between the proposed PML method and a commonly used damping
method were made to validate the efficiency of the proposed boundary absorption scheme. It was shown that the PML works more
efficiently than the damping method in this complex medium. Additionally, the three-phase theory is reduced to the Biot’s
theory when there is only one fluid left in the pores, which is shown in Appendix. This reduction makes clear that three-phase
equation systems are identical to the typical Biot’s equations if the fluid saturation for either of the two fluids in the
pores approaches to zero.
Supported by the Key Program of the National Natural Science Foundation of China (Grant No. 10534040) and the National Natural
Science Foundation of China (Grant No. 10674148) 相似文献
9.
I. V. Lisenkov R. S. Popov S. A. Nikitov 《Applied Physics A: Materials Science & Processing》2011,103(3):921-925
Acoustic wave propagation in a composite of water with embedded double-layered silicone resin/silver rods is considered. Approximate
values of effective dynamical constitutive parameters are obtained. Frequency ranges of simultaneous negative constitutive
parameters are found. Localized surface states on the interface between metamaterial and “normal” material are found. The
Doppler effect in metamaterial is considered. The presence of anomalous modes is shown. 相似文献
10.
A spiral wave front source generates a pressure field that has a phase that depends linearly on the azimuthal angle at which it is measured. This differs from a point source that has a phase that is constant with direction. The spiral wave front source has been developed for use in navigation; however, very little work has been done to model this source in an ocean environment. To this end, the spiral wave front analogue of the acoustic point source is developed and is shown to be related to the point source through a simple transformation. This makes it possible to transform the point source solution in a particular ocean environment into the solution for a spiral source in the same environment. Applications of this transformation are presented for a spiral source near the ocean surface and seafloor as well as for the more general case of propagation in a horizontally stratified waveguide. 相似文献
11.
Recently developed continuum mixture theories are extended to study the propagation of horizontally polarized shear waves in a trilaminated wave guide. A specific composite model is considered which resembles the case in which one of the materials acts as a bonding agent for the other two materials. Dispersion relations are derived and compared with exact predictions. Good correlation is shown for significant frequency ranges, especially for the lowest two modes. 相似文献
12.
In this paper wave propagation in the direction of the layering of a bi-laminated medium with the presence of imperfect bonding at the interfaces is investigated. The debonding mechanism is represented by a model which allows imperfect bonding both in the normal and tangential directions. A mixture theory is formulated in which every constituent has its own motion but is allowed to interact with the others. The resulting theory is applied to transient wave propagation in the laminated composite. It is shown that debonding in the tangential direction is significant in modifying the shape and amplitude of the propagating wave. 相似文献
13.
S. P. Bautin 《Doklady Physics》2006,51(3):148-153
14.
Pressure gain combustion in the form of continuous detonations can provide a significant increase in the efficiency of a variety of propulsion and energy conversion devices. In this regard, rotating detonation engines (RDEs) that utilize an azimuthally-moving detonation wave in annular systems are increasingly seen as a viable approach to realizing pressure gain combustion. However, practical RDEs that employ non-premixed fuel and oxidizer injection need to minimize losses through a number of mechanisms, including turbulence-induced shock-front variations, incomplete fuel-air mixing, and premature deflagration. In this study, a canonical stratified detonation configuration is used to understand the impact of preburning on detonation efficiency. It was found that heat release ahead of the detonation wave leads to weaker shock fronts, delayed combustion of partially-oxidized fuel-air mixture, and non-compact heat release. Furthermore, large variations in wave speeds were observed, which is consistent with wave behavior in full-scale RDEs. Peak pressures in the compression region or near triple points were considerably lower than the theoretically-predicted values for ideal detonations. Analysis of the detonation structure indicates that this deflagration process is parasitic in nature, reducing the detonation efficiency but also leading to heat release far behind the wave that cannot directly strengthen the shock wave. This parasitic combustion leads to commensal combustion (heat release far downstream of the wave), indicating that it is the root cause of combustion efficiency losses. 相似文献
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Temperature dependence of ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss have been studied
in (NaCl-type) barium monochalcogenides [BaX, X = S, Se, Te], in the temperature range 50–500 K; for longitudinal and shear
modes of propagation along 〈100〉, 〈110〉, 〈111〉 directions. Second and third order elastic constants have been evaluated using
electrostatic and Born repulsive potentials and taking interactions up to next nearest neighbours. Gruneisen parameters, nonlinearity
constants, nonlinearity constants ratios and viscous drag due to screw and edge dislocations have also been evaluated for
longitudinal and shear waves at 300 K. In the present investigation, it has been found that phonon-phonon interaction is the
dominant cause for ultrasonic attenuation. The possible implications of results have been discussed.
The text was submitted by the authors in English. 相似文献
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Acoustic shock wave propagation in a heterogeneous medium: a numerical simulation beyond the parabolic approximation 总被引:1,自引:0,他引:1
Dagrau F Rénier M Marchiano R Coulouvrat F 《The Journal of the Acoustical Society of America》2011,130(1):20-32
Numerical simulation of nonlinear acoustics and shock waves in a weakly heterogeneous and lossless medium is considered. The wave equation is formulated so as to separate homogeneous diffraction, heterogeneous effects, and nonlinearities. A numerical method called heterogeneous one-way approximation for resolution of diffraction (HOWARD) is developed, that solves the homogeneous part of the equation in the spectral domain (both in time and space) through a one-way approximation neglecting backscattering. A second-order parabolic approximation is performed but only on the small, heterogeneous part. So the resulting equation is more precise than the usual standard or wide-angle parabolic approximation. It has the same dispersion equation as the exact wave equation for all forward propagating waves, including evanescent waves. Finally, nonlinear terms are treated through an analytical, shock-fitting method. Several validation tests are performed through comparisons with analytical solutions in the linear case and outputs of the standard or wide-angle parabolic approximation in the nonlinear case. Numerical convergence tests and physical analysis are finally performed in the fully heterogeneous and nonlinear case of shock wave focusing through an acoustical lens. 相似文献