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1.
For damped acoustic metamaterials, a discrete model is proposed in the form of a periodic structure with cells of the simplest type. The effective parameters of the model are determined by criteria based on the equality of dispersion of waves. The general properties of the model are studied. An example of one negative type of metamaterials is presented. The model is useful for analyzing wave properties and creating metamaterials with given acoustic properties. 相似文献
2.
A computer simulation of an acoustic medium characterized by a complex density and synthesized on the basis of a rubberlike material with massive spherical inclusions is performed. The properties of such media are studied for continuous and discrete distributions of the inclusions in size (the resonance frequencies), and the parameters of the medium are optimized to obtain the given properties, in particular, to provide efficient sound absorption over a wide frequency range. Numerical results are presented. 相似文献
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Based on fuzzy logic (FL) and genetic algorithm (GA), we present an optimization method to obtain the optimal acoustic attenuation of a longitudinal acoustic wave propagating in a weakly compressible medium permeated with air bubbles. In the optimization, the parameters of the size distribution of bubbles in the medium are optimized for providing uniformly high acoustic attenuation in the frequency band of interest. Compared with other traditional optimization methods, the unique advantage of the present method is that it can locate the global optimum quickly and effectively in need of knowing the mathematical model precisely. As illustrated by a numerical simulation, the method is effective and essential in enhancing the acoustic attenuation of such a medium in an optimal manner. The bubbly medium with optimized structural parameters can effectively attenuate longitudinal waves at intermediate frequencies with an acoustic attenuation approximating a constant value of lO(dB/cm). Such bubbly media with optimal acoustic attenuations may be applied to design acoustic absorbent by controlling broader attenuation band and higher efficiency. 相似文献
5.
低密度水泥在油气井中的广泛应用使得常规的声阻抗类测井方法难以准确、有效地评价固井质量,而声波倾斜入射在套管中激发的弯曲型Lamb波对水泥的性质及胶结情况具有很高的分辨能力,能够很好地解决低密度水泥的固井质量评价问题。弯曲型Lamb波对套管后介质声学信息的响应反映在声波衰减中,因此该文通过实验研究了激发弯曲型Lamb波的有效方式,分析了声波入射和接收角度对Lamb波衰减的影响。实验结果表明,入射和接收角度在一定范围内变化时,虽然激发出的Lamb波模式均为弯曲型Lamb波,但在同一套管模型下测量的声波衰减值会有差异,选择激发弯曲型Lamb波的最有效方式,计算得到的Lamb波衰减对套管后介质的灵敏度才会最高。 相似文献
6.
The nonlinear propagation of an initially harmonic acoustic wave in a microinhomogeneous medium containing defects with quadratic hysteretic nonlinearity and relaxation is studied by the perturbation method. The frequency dependences of the effective nonlinearity parameters are determined for the self-action of the quasi-harmonic acoustic wave and the higher harmonic generation processes. 相似文献
7.
Wei-Wei Kan 《中国物理 B》2022,31(8):84302-084302
The scattering behavior of an anisotropic acoustic medium is analyzed to reveal the possibility of routing acoustic signals through the anisotropic layers with no backscattering loss. The sound-transparent effect of such a medium is achieved by independently modulating the anisotropic effective acoustic parameters in a specific order, and is experimentally observed in a bending waveguide by arranging the subwavelength structures in the bending part according to transformation acoustics. With the properly designed filling structures, the original distorted acoustic field in the bending waveguide is restored as if the wave travels along a straight path. The transmitted acoustic signal is maintained nearly the same as the incident modulated Gaussian pulse. The proposed schemes and the supporting results could be instructive for further acoustic manipulations such as wave steering, cloaking and beam splitting. 相似文献
8.
《Comptes Rendus Physique》2016,17(5):543-554
The propagation of intense acoustic waves in a one-dimensional phononic crystal is studied. The medium consists in a structured fluid, formed by a periodic array of fluid layers with alternating linear acoustic properties and quadratic nonlinearity coefficient. The spacing between layers is of the order of the wavelength, therefore Bragg effects such as band gaps appear. We show that the interplay between strong dispersion and nonlinearity leads to new scenarios of wave propagation. The classical waveform distortion process typical of intense acoustic waves in homogeneous media can be strongly altered when nonlinearly generated harmonics lie inside or close to band gaps. This allows the possibility of engineer a medium in order to get a particular waveform. Examples of this include the design of media with effective (e.g., cubic) nonlinearities, or extremely linear media (where distortion can be canceled). The presented ideas open a way towards the control of acoustic wave propagation in nonlinear regime. 相似文献
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基于等效介质理论, 提出了具有共焦层状结构的椭圆柱形声隐身衣设计方法. 理论分析与有限元数值模拟表明, 所设计隐身衣依然具有完美隐身衣典型特征, 可使刚性圆柱体散射场明显减小, 并且在隐身衣区域表现出波阵面弯曲的特性, 同时在隐身衣外部波阵面保持不变. 增加隐身衣离散层数可以拓宽其有效工作频带, 改善隐身效果. 由于是一种线变换隐身衣, 隐身效果受到了入射波方向的影响, 只有当入射波方向与椭圆长轴平行时效果最佳. 另外当椭圆柱焦距非常小的时候, 可近似认为是圆柱形隐身衣. 仿真实验结果证明了方法的正确性. 该研究为实现复杂形状声隐身衣提供了一种有效途径. 相似文献
11.
Two phenomenological models of hysteretic equations of state for media with imperfect elasticity are described and compared. On the basis of these equations, a theoretical study of nonlinear effects caused by the acoustic wave propagation in an unbounded medium is performed. The profiles, parameters, and spectra of waves are determined. The distinctive features of nonlinear wave processes in such media are revealed, so that these features can be used to choose the appropriate hysteretic equation of state for analytically describing the experimental data. 相似文献
12.
Improving the performance of acoustic invisibility with multilayer structure based on scattering analysis
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In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoustic parameters of the isotropic cloak media are assumed to be single-negative, and the resulting cloak can reduce acoustic scattering from an acoustic sensor while allowing it to receive external information. Several factors that may influence the performance of the cloak, including the number of layers and the acoustic dissipation of the medium are fully analyzed. Furthermore, the possibility of achieving acoustic invisibility with positive acoustic parameters is proposed by searching the optimum value in the parameter space and minimizing the scattering cross-section. 相似文献
13.
The effective wave velocity, attenuation, and nonlinear properties of slightly compressible porous media permeated with air-filled
bubbles are studied numerically by employing the nonlinear Hooke’s law for different surrounding pressures. Numerical simulations
show that the acoustic properties of porous media are greatly affected by the surrounding pressure if the shear modulus of
the elastic medium is very small due to the fact that the acoustic wave propagation in porous media are strongly influenced
by the nonlinear oscillation of bubbles; moreover, the oscillation of a bubble depends on the equilibrium bubble radius, which
is affected by the surrounding pressures.
Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 4, pp. 490–496.
The text was submitted by the authors in English. 相似文献
14.
A revised formalism of SBS is given based on a new optical nonlinear wave equation which explicitly accounts for the macroscopic spatial inhomogeneity resulting from the induced acoustic wave in the medium. The new equation applies to other scattering phenomena, and more generally to optical wave propagation and interaction in nanostructured media for which characteristic spatial scale lengths of material structures (existing or optically induced) are smaller than the optical wavelength. 相似文献
15.
QIAO Wenxiao 《声学学报:英文版》1993,(1)
Based on the Boit theory of acoustic wave propagation in fluid-satu-rated porous medium we have studied in this paper the acoustic reflection andtransmission on multilayered porous media,in which the adequate boundaryconditions across the interfaces are taken into account.Numerical calculationsof the reflection and transmission coefficients at different incident angles andfrequencies of the fast compressional wave incident on porous media with threeor four layers are presented.The results indicate that the maximum or mini-mum reflection and transmission coefficients appear at certain ratios of thewavelength to the thickness.The acoustic incident angle and porous mediumproperties are shown to affect significantly these coefficients.As an example,the measured transmission coefficients in a water-saturated fused glass beadsample are in good agreement with theoretical prediction. 相似文献
16.
Wave propagation of acoustic waves in porous media is considered. The medium is assumed to have a rigid frame, so that the propagation takes place in the air which fills the material. The Euler equation and the constitutive relation are generalized to take into account the dispersive nature of these media. It is shown that the connection between the fractional calculus and the behavior of materials with memory allows time-domain wave equations, the coefficients of which are no longer frequency dependent, to be worked out. These equations are suited for direct and inverse scattering problems, and lead to the complete determination of the porous medium parameters. 相似文献
17.
Nearfield acoustical holography (NAH) data measured by using a microphone array attached to a high-speed aircraft or ground vehicle include significant airflow effects. For the purpose of processing the measured NAH data, an improved nearfield acoustical holography procedure is introduced that includes the effects of a fluid medium moving at a subsonic and uniform velocity. The convective wave equation along with the convective Euler's equation is used to develop the proposed NAH procedure. A mapping function between static and moving fluid medium cases is derived from the convective wave equation. Then, a conventional wave number filter designed for static fluid media is modified to be applicable to the moving fluid cases by applying the mapping function to the static wave number filter. In order to validate the proposed NAH procedure, a monopole simulation at the airflow speed of Mach=-0.6 is conducted. The reconstructed acoustic fields obtained by applying the proposed NAH procedure to the simulation data agree well with directly-calculated acoustic fields. Through an experiment with two loudspeakers performed in a wind tunnel operating at Mach=-0.12, it is shown that the proposed NAH procedure can be also used to reconstruct the sound fields radiated from the two loudspeakers. 相似文献
18.
An effective quiescent medium for sound propagating through an inhomogeneous,moving fluid 总被引:1,自引:0,他引:1
Godin OA 《The Journal of the Acoustical Society of America》2002,112(4):1269-1275
The idea of similarity between acoustic fields in a moving fluid and in a certain "effective" quiescent medium, first put forward by Lord Rayleigh, proved very helpful in understanding and modeling sound propagation in an atmosphere with winds and in an ocean with currents, as well as in other applications involving flows with small velocity compared to sound speed. Known as effective sound speed approximation, the idea is routinely utilized in the contexts of the ray theory, normal mode representation of the sound field, and the parabolic approximation. Despite the wide use of the concept of effective sound speed in acoustics of moving media, no theoretical justification of Rayleigh's idea was published that would be independent of the chosen representation of the sound field and uniformly apply to distinct propagation regimes. In this paper, we present such a justification by reducing boundary conditions and a wave equation governing sound fields in the inhomogeneous moving fluid with a slow flow to boundary conditions and a wave equation in a quiescent fluid with effective sound speed and density. The derivation provides insight into validity conditions of the concept of effective quiescent fluid. Introduction of effective density in conjunction with effective sound speed is essential to ensure accurate reproduction of acoustic pressure amplitude in the effective medium. Effective parameters depend on sound speed, flow velocity, and density of the moving fluid as well as on sound propagation direction. Conditions are discussed under which the dependence on the propagation direction can be avoided or relaxed. 相似文献
19.
A. V. Razin 《Radiophysics and Quantum Electronics》2006,49(7):520-534
We study excitation of acoustic, leaky, and surface waves by a time-harmonic force source located in a homogeneous isotropic
elastic half-space contacting a homogeneous gas. The force acts in the normal direction to the interface between the media.
We consider the case where the sound velocity in the gas is less than the velocity of the Rayleigh wave propagating along
the surface of the solid. An expression is derived for the period-averaged radiation power of the surface Stoneley wave. The
total radiation power is calculated for the acoustic wave in the gas and for the leaky pseudo-Rayleigh wave. Variations in
the radiation powers of the surface and leaky waves are analyzed as functions of the source depth. If the velocities of compressional
and shear waves in the elastic medium significantly exceed the sound velocity in the gas, then the radiation power of the
Stoneley wave turns out to be a factor of 106–108 smaller than the radiation powers of other waves. The radiation power of the Stoneley wave decreases monotonically with increasing
source depth, and the decrease becomes more pronounced with the increase in the difference between the acoustic impedances
of the contacting media. If the shear-wave velocity in the solid is close to the sound velocity in the gas, then the radiation
power of the Stoneley wave is comparable with the radiation powers of other waves and exhibits maximum at a certain source
depth. For some parameters of the gas and the solid, and for certain source depths, the Stoneley wave carries away more than
a half of the total radiation power. It is shown that, for certain relations between the parameters of the media, the radiation
power of the Stoneley wave increases due to redistribution of the radiated power from the pseudo-Rayleigh leaky wave. The
total power of these waves remains approximatly constant and, with accuracy of the order of 10−3, is equal to the radiation power of the Rayleigh wave at the vacuum-solid interface. It is shown that the acoustic-wave power
which can be transmitted to the upper layers of the atmosphere during an earthquake does not exceed 0.01% of the total power
radiated at a given frequency.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 577–592, July 2006. 相似文献