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Thermoacoustic cooling systems are insufficiently compared to compressor compression cooling systems. The reasons for this should be investigated and solved. The performance of a thermoacoustic cooling system depends on many factors. The cooling system's success is possible by precisely determining the contributions of these factors to thermoacoustic cooling. However, both numerical and experimental studies in the literature on the subject contain certain limitations. One of the most important of these is that the studies were carried out with constant frequency and only a sine wave. This study examined the effect of this approach on thermoacoustic cooling. Thus, a polypropylene stack is placed in the resonance tube, and experiments were carried out. Air is used as a refrigerant. Five different wave types (sine, square, triangle, sawtooth, and trapeze) were used as wave types; resonance tube diameters were also selected as 50, 70, and 100 mm. The study determined that the resonance tube's diameter to be selected and the wave type were related. For the highest ΔT value, it turned out that the use of a 50 mm tube diameter sine wave, 70 mm tube diameter sawtooth wave, and 100 mm tube diameter trapezoidal wave were more appropriate than the other waveforms. the use of a sawtooth wave instead of a sine wave for the 70 mm tube diameter increased the cooling capacity by 2.61%, and trapezoidal wave usage for 100 mm tube diameter increased by 5.91%. [ABSTRACT FROM AUTHOR]

Metamaterials are rationally designed composites made of building blocks which are composed of one or more constituent materials. Metamaterial properties can go beyond those of the ingredient materials, both qualitatively and quantitatively. In addition, their properties can be mapped on some generalized continuum model. We present the general procedure of designing elastic metamaterials based on masses and springs. We show that using this simple approach we can design any set of effective properties including linear elastic metamaterials,—defined by bulk modulus, shear modulus, mass density—and nonlinear metamaterials,—with instabilities or programmable parts. We present designs and corresponding numerical calculations to illustrate their constitutive behavior. Finally, we discuss the addition of a thermal stimulus to mechanical metamaterials. [ABSTRACT FROM AUTHOR]

The physics of topological insulators makes it possible to understand and predict the existence of unidirectional waves trapped along an edge or an interface. In this review, we describe how these ideas can be adapted to geophysical and astrophysical waves. We deal in particular with the case of planetary equatorial waves, which highlights the key interplay between rotation and sphericity of the planet, to explain the emergence of waves which propagate their energy only towards the East. These minimal ingredients are precisely those put forward in the geometric interpretation of the Foucault pendulum. We discuss this classic example of mechanics to introduce the concepts of holonomy and vector bundle which we then use to calculate the topological properties of equatorial shallow water waves. [ABSTRACT FROM AUTHOR]

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Abstract: The understanding of wave propagation in turbulent magnetized plasmas can be rather complex, particularly if they are inhomogeneous and time-dependent. Simulation can be a useful tool for wave propagation studies, provided that the “model” equations take into account the characteristics of the medium relevant for the studied problem and that the numerical scheme including boundary conditions is stable and accurate enough. The choices for the model equations and the corresponding schemes are analyzed and discussed as a function of various parameters, such as the order of the numerical scheme and the number of grid points per wavelength. A quick review of the up-to-date numerical developments is given on the sheath boundary conditions and on the perfect matching layer in anisotropic media. Possible developments of plasma diagnostics conclude this state-of-the-art of simulations of electromagnetic waves in plasmas. [Copyright &y& Elsevier]

Abstract: We investigate the elastic wave propagation within a non-homogeneous continuum according to W. Noll. After some preliminaries in geometry approach suggested by E. Cartan, the linear momentum equation of so-called weakly continuous medium is written. A first example illustrates the modal analysis of an axisymmetric non-homogeneous thick tube. The overall solution is the product of an attenuating exponential response with Kummerʼs functions. The second example deals with a Timoshenko beam involving transversal displacement and angular rotation of section. We observe the presence of various waves with spatial attenuation, either for the displacement or the section rotation, together with the occurring waves at different scale levels. [Copyright &y& Elsevier]

Abstract: We study the Dirichlet problem for equation in which α is a nonnegative constant, the coefficients , and the exponents of nonlinearity , are given functions. Under suitable conditions on the data, we study the finite time blow-up of the solutions. [Copyright &y& Elsevier]

Abstract: We examine the band spectrum, and associated Floquet–Bloch eigensolutions, arising in a class of three-phase periodic checkerboards. On a periodic cell , the refractive index, n, is defined by with for , and for where is constant. We find that for the lowest frequency branch goes through origin with linear behaviour, which leads to effective properties encountered in most periodic structures. However, the case whereby is very unusual, as the frequency λ behaves like near the origin, where k is the wavenumber. Finally, when , the lowest branch does not pass through the origin and a zero-frequency band gap opens up. In the last two cases, effective medium theory breaks down even in the quasi-static limit, while the high-frequency homogenization [R.V. Craster, J. Kaplunov, A.V. Pichugin, High-frequency homogenization for periodic media, Proc. R. Soc. Lond. Ser. A 466 (2010) 2341–2362] neatly captures the detailed features of band diagrams. [Copyright &y& Elsevier]

Abstract: In a recent article, we described a seismic inversion method for determining the crustal velocity and attenuation of basins in earthquake-prone regions. We formulated the problem as a constrained nonlinear least-squares optimization problem in which the constraints are the equations that describe the forward wave propagation. Here, we conduct a parametric study to investigate the influence of parameters such as the form of the regularization function, receiver density, preconditioning, noise level of the data, and the multilevel continuation technique on the cost and quality of the inversion. We use the same 2D Los Angeles example as in our earlier study. [Copyright &y& Elsevier]

Abstract: We present an improved adaptive remeshing strategy based on the unit remeshing concept to control the accuracy of the numerical solution of partial differential problems. Such an adaptive remeshing is applied in computing and in representing the strong variation of the physical fields in the space of solutions. We show that, the precision of the solution being controlled, this improved scheme permits to decrease drastically the computational time as well as the memory requirements by adapting the number and the position of nodes where high variations of gradients of the solution are present. [Copyright &y& Elsevier]

Abstract: The numerical analysis of elastic wave propagation in unbounded media may be difficult to handle due to spurious waves reflected at the model artificial boundaries. Several sophisticated techniques, such as nonreflecting boundary conditions, infinite elements or absorbing layers (e.g. Perfectly Matched Layers) lead to an important reduction of such spurious reflections. In this Note, a simple and efficient absorbing layer method is proposed in the framework of the Finite Element Method. This method considers Rayleigh/Caughey damping in the absorbing layer and its principle is presented first. The efficiency of the method is then shown through 1D Finite Element simulations considering homogeneous and heterogeneous damping in the absorbing layer. 2D models are considered afterwards to assess the efficiency of the absorbing layer method for various wave types (surface waves, body waves) and incidences (normal to grazing). The method is shown to be efficient for different types of elastic waves and may thus be used for various elastodynamic problems in unbounded domains. [Copyright &y& Elsevier]

Abstract: We consider periodic travelling gravity waves at the surface of an infinitely deep perfect fluid. The pattern is non-symmetric with respect to the propagation direction of the waves and we consider a general non-resonant situation. Defining a couple of amplitudes along the basis of wave vectors which satisfy the dispersion relation, following Iooss and Plotnikov (2009), travelling waves exist with an asymptotic expansion in powers of , for nearly all pair of angles made by the basic wave vectors with the critical propagation direction, and for values of the couple in a subset of the plane, with asymptotic full measure at the origin. We prove the remarkable property that on the free surface, observed in the moving frame, the propagation direction of the waves differs from the asymptotic direction taken by fluid particles, by a small angle which is computed. To cite this article: G. Iooss, P. Plotnikov, C. R. Mecanique 337 (2009). [Copyright &y& Elsevier]

Abstract: A new approach is proposed to detect trapped modes in periodic canals. The obtained sufficient condition is new even for a straight canal with a body piercing the water surface as well. To cite this article: S.A. Nazarov, C. R. Mecanique 337 (2009). [Copyright &y& Elsevier]

Non destructive characterisation of concretes by ultrasonic wave's propagation. The non destructive characterization of concretes structures with ultrasonic wave's propagation allows determining the velocities and the attenuation or frequencies spectrum. It can be possible to diagnostic a pathology or the material state. The strong concrete heterogeneity regarding induces scattering and non linear acoustic phenomena. The consequences on the ultrasonic parameters are analysed on the forward and backscattered propagation. [ABSTRACT FROM AUTHOR]

Abstract: Non-destructive evaluation of heterogeneous materials is of major great interest in industrial and in biomedical fields. In this work, the structure is made of three layers: a laterally heterogeneous anisotropic solid layer between two acoustic fluids. An original method is proposed to solve the wave equation in such structure without using a multilayered model of the plate. This method is based on an analytical solution, the matricant, explicitly expressed under the Peano expansion form. We validate this approach for the study of a fluid-loaded anisotropic plane waveguide with two different fluids on each side. This configuration corresponds to the axial transmission technique for the ultrasound characterization of cortical bone in vivo. To cite this article: C. Baron, S. Naili, C. R. Mecanique 336 (2008). [Copyright &y& Elsevier]

Abstract: A solitary wave, resembling a soliton wave, is observed when analyzing the linear problem of polarized shear (SH) surface acoustic waves propagating in elastic orthotropic two-layered traction-free plates. The analysis is performed by applying a special complex formalism and the Modified Transfer Matrix (MTM) method. Conditions for the existence of solitary SH waves are obtained. Analytical expressions for the phase speed of the solitary wave are derived. To cite this article: I. Djeran-Maigre, S. Kuznetsov, C. R. Mecanique 336 (2008). [Copyright &y& Elsevier]

Abstract: Novel exact solutions describing surface acoustic waves on general layered structures have been found by the method of variable separation. First, solutions have been constructed with plane wavefronts and involving polynomial dependence on lateral variables. Second, their inhomogeneous plane-wave analogues have been found. At last, beam-like solutions highly localized at large lateral distances in a given sector have also been considered. To cite this article: A.P. Kiselev et al., C. R. Mecanique 335 (2007). [Copyright &y& Elsevier]

Abstract: A brief overview is given of specific features that can (or cannot) appear in the dispersion spectra of traction-free elastic homogeneous plates due to anisotropy. Its effect on the overall spectral configuration and on the short and long wave trends is illuminated with a link to anisotropic traits of bulk and surface waves. Relevant classical and recent results are put together, and new points are established. To cite this article: A.L. Shuvalov, C. R. Mecanique 334 (2006). [Copyright &y& Elsevier]

Abstract: We present an analysis of an electrostatic field within a helicoidal structure with a twist, which is small compared to the characteristic size of the cross-section. The asymptotic results are checked against exact computations thanks to helicoidal coordinates, which preserve the intrinsically two-dimensional nature of the problem. The numerical studies are performed using the finite elements. To cite this article: A. Nicolet et al., C. R. Mecanique 334 (2006). [Copyright &y& Elsevier]

Abstract: A probabilistic signal processing method, with which is possible to get some methodological suggestion to the measurement method of correlative and/or accumulative effects in the compound environment of sound, light and electromagnetic (EM) waves is discussed. In order to extract various types of latent interrelation characteristics among wave environmental factors leaked from an actually operating video display terminal (VDT), an extended regression system model, hierarchically reflecting not only linear correlation information but also nonlinear correlation information, is first introduced, especially from a viewpoint of ‘relationism-first’. Then, through estimating each regression parameter of this model, some original evaluation methods for predicting a whole probability distribution form, from one another, are proposed. Finally, the effectiveness of the methods is experimentally confirmed, by applying them to the actual observed data leaked by a VDT with some television games. To cite this article: M. Ohta et al., C. R. Mecanique 333 (2005). [Copyright &y& Elsevier]

Abstract: This Note presents a probabilistic model of transient wave reflection at a fluid–solid interface. The configuration represents an ultrasonic experiment used for bone tissue evaluation. The parametric method is used to derive the probabilistic model for the mechanical parameters of the solid (bone); the associated random variables are derived according to the maximum entropy principle. A Monte Carlo simulation, associated with the Cagniard–de Hoop method to calculate the acoustic response, yields the probability density for an output ultrasonic parameter similar to the velocity of longitudinal waves in the solid. Results demonstrate the sensitivity of the probability density of this parameter to the experimental setup. To cite this article: K. Macocco et al., C. R. Mecanique 333 (2005). [Copyright &y& Elsevier]

Abstract: The influence of higher-order nonlinear terms on the shape of solitary waves is studied for mechanical systems governed by a generalization of the 5th order Korteweg–de Vries equation. New localized travelling wave with intrinsic oscillations (not breathers) is shown to arise from arbitrary initial pulse thanks only to the higher-order quadratic nonlinearity, while cubic nonlinearity is responsible for the formation of so-called ‘fat’ solitary wave. To cite this article: A.V. Porubov et al., C. R. Mecanique 333 (2005). [Copyright &y& Elsevier]

This Note presents an original approach to include diffraction in the radiative transfer method when applied to acoustics. This approach leads to a better spatial description of the acoustical energy. An energetic diffraction coefficient and some diffraction sources are introduced to model the diffraction phenomena. The amplitudes of these sources are determined by solving a linear sytem of equations resulting from the power balance between all acoustical sources. The approach is applied on bidimensional examples and gives good results except at geometrical boundaries. To cite this article: E. Reboul et al., C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

The antiplane motion of a transversely isotropic piezoelectric half-space is considered. An explicit asymptotic model is derived for the far field of the surface wave. It involves, in particular, a 1D hyperbolic equation for surface shear deformation propagating with the finite wave speed predicted for the first time by J.L. Bleustein and Yu.V. Gulyaev. Neumann and Dirichlet problems are formulated to restore interior mechanical and electric fields. The derivation utilizes asymptotic arguments combined with Lourier symbolic integration. Comparison with the exact solution is presented for surface impact loading. To cite this article: J. Kaplunov et al., C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

The instability of position of a growing spherical crystal in an acoustic field is studied. Due to the Bjerknes force, a spherical crystal, whose position is shifted from an antinode of pressure, moves in the acoustic field. This displacement, stable in the case of bubbles in a cavitation experiment, turns out to be unstable in the case of crystallization. This effect is studied for an arbitrary Atwood number. To cite this article: M. Ben Amar, C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

Near the critical point, isothermal interfacial zones are investigated starting from a non-local density of energy. From the equations of motion of thermocapillary fluids, we point out a new kind of adiabatic waves propagating along the interfacial layers. The waves are associated with the second derivatives of densities and propagate with a celerity depending on the proximity of the critical point. To cite this article: H. Gouin, C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

We consider the dynamical stability of horizontal fluid layer, performing harmonic oscillations in vertical direction. The continued fractions approach allowed us to avoid the conventional restriction to the case of small viscosity and almost-resonant frequencies. Our numerical results cover a wide range of the parameters (viscosity, amplitude and frequency of the oscillation, and depth of the layer). To cite this article: V.I. Yudovich et al., C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

A model developed for the description of finite-amplitude wave regimes in a film flowing over a spinning disc is used to explain the stabilizing role of the Coriolis forces. As in the case of waves on a falling film, a linear relationship between the wave velocity and the maximum of the film thickness has been determined for axisymmetric waves in a film flowing over a spinning disc. To cite this article: G.M. Sisoev et al., C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

In this Note, we return to the theory of characteristic modes which was introduced 30 years ago for electromagnetic scattering problems. A simple mathematical framework is proposed and complete definitions are given. The potential interest of this theory in terms of Radar Cross Section (RCS) analysis is then discussed, especially in the low frequency case. Finally, a 3-D example is presented to illustrate the efficiency of this decomposition. To cite this article: Y. Morel et al., C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

The existence and propagation of the surface waves at a vacuum/porous medium interface are investigated in the low frequency range. Two types of surface waves are shown to be possible: the generalized Rayleigh wave, which always exists, and the Stoneley wave, which exists for a limited range of wave numbers. Moreover, within the k-domain of existence the Stoneley wave cannot appear for certain values of elastic parameters of the solid phase. The bifurcation behavior of both the Stoneley wave and the Biot (P2) bulk wave, depending on the wave number, is revealed. The asymptotic formulas for the phase velocities of the surface waves are derived. To cite this article: I. Edelman, C. R. Mecanique 332 (2004). [Copyright &y& Elsevier]

We consider the problem of solving the integral form of the radiative transfer equation in an atmosphere with optical thickness τ0≫1. We propose a method transforming this problem in the same problem posed in an atmosphere with optical thickness τ1≪τ0. An error over- estimation is derived. To cite this article: A. Amosov et al., C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

The theory of generalized rays is dedicated to the investigation of the transient response of elastic layered media. It yields exact solutions, whatever the duration of the applied impulse (i.e., for any frequency content of the excitation). This Note is part of a research project on the modeling of non-penetrating impact on thorax. We investigate a simplified model of the thoracic wall – a layer welded to a semi-infinite medium – submitted to an impulse of variable duration. Among other things, it is found that the response computed for a “long” impulse is consistent with a result of the classical plate theory. To cite this article: Q. Grimal et al., C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

This Note investigates the effect of a renormalization technique on high-order shallow water approximations of gravity waves. The method is illustrated for the solitary surface wave. Applied to the solution of a generalized KdV equation, it is shown that the renormalization significantly increases the accuracy. To cite this article: D. Clamond, D. Fructus, C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

We establish a theoretical model to explain the nucleation of a crystal of helium by an acoustic over-pressure. We explain the interfacial laws for this ultra-fast cristallization, close to the sound speed. Assuming spherical symmetry and taking into account the experimental data, we recover the dynamics of the growth and melting during an over-pressure impulse. To cite this article: M. Ben Amar et al., C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

The Large Eddy Simulation of closed-loop active flow control applied to a 3D cavity excited by a compressible airflow with a Mach number of 0.6 is presented. The control actuator is an idealized synthetic jet located at the upstream cavity edge, and the control function is supplied by a feedback LMS-type algorithm whose input is a pressure signal measured inside the cavity. The radiated sound, provided directly by the LES simulation, was shown to decrease substantially when active control was applied. A simultaneous reduction of the vertical velocity fluctuations in the shear layer was observed. The intensity of vortical structures inside the cavity was also reduced, although the general aspect of the recirculation zone was not modified. The direct noise computation technique, which supplies the pressure field by solving the fluid mechanics equations, is shown to constitute a powerful tool for studying active aeroacoustic noise control. To cite this article: O. Marsden et al., C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

Estimates of convergence rates for rescaled eigenvalues of the stiff Neumann problem for the Laplacian are obtained. The bounds are expressed in terms of the stiffness ratio and properties of the limit spectrum both for low and middle frequency ranges. To cite this article: M. Lobo et al., C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

This paper presents a method to estimate reflected and transmitted wave amplitude spectra in a bounded domain such as a wave tank, when available data signals must be shortened due to interferences and wall effects. This paper extends the well known Goda and Suzuki two-probe method to three probes. The paper also suggests solutions to compute reliable transmission and reflection coefficients in spite of problems linked to higher harmonics and to the interference between different wave trains propagating in the tank. To cite this article: G. Duclos, A.H. Cle´ment, C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

The nonlinear problem for propagation of wave-packets along the interface of two semi-infinite fluids is solved on the basis of multiple scale asymptotic expansions. Unlike all previous investigations dealing only with third-order approximations, here fourth-order approximation is developed. The corresponding solvability condition is obtained and the evolution equation in the case away from the cut-off wave number is derived. As a result, the nonlinear higher-order Schro¨dinger equation is obtained which contains the nonlinear part in a compact form. This equation is valid for a wide range of wave numbers. The stability diagram shows regions of stability and instability of capillary-gravity wave-packets. To cite this article: I. Selezov et al., C. R. Mecanique 331 (2003). [Copyright &y& Elsevier]

We consider the integral form of the radiative transfer equation over a large interval. This equation describes the radiative transfer of energy in a star. The asymptotic expansion of the solution is constructed and justified. The method of asymptotic partial decomposition of domain is applied. Numerical results are discussed. To cite this article: G. Panasenko et al., C. R. Mecanique 330 (2002) 735–740. [Copyright &y& Elsevier]