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Analytical coupled vibroacoustic modeling of membrane-type acoustic metamaterials: plate model  [PDF]
Yangyang Chen,Xiaoming Zhou,Gengkai Hu,Chin-Teh Sun,Guoliang Huang
Physics , 2013, DOI: 10.1121/1.4901706
Abstract: By considering the membrane's dissipation, the membrane-type acoustic metamaterial (MAM) has been demonstrated as a super absorber for low-frequency sound. In the paper, a theoretical vibroacoustic plate model is developed to reveal sound energy absorption mechanism within the MAM under a plane normal incidence. Based on the plate model in conjunction with the point matching method, the in-plane strain energy of the membrane due to the resonant and antiresonant motion of the attached masses can be accurately captured by solving the coupled vibroacoustic integrodifferential equation. Therefore, the sound absorption of the MAM is obtained and discussed, which is also in good agreement with the prediction from the finite element method. In particular, microstructure effects including eccentricity of the attached masses, the depth, thickness and loss factor of the membrane on sound absorption peak values are quantitatively investigated.
An Approximate Analytical Method of the Nonlinear Vibroacoustic Coupling System  [PDF]
Qizheng Zhou,Deshi Wang,Yongyong Zhu
Shock and Vibration , 2014, DOI: 10.1155/2014/315416
Abstract: An approximate analytical method of the nonlinear vibroacoustic coupling system is proposed for the first time. Taking the Duffing oscillator-plate-medium system as an example, the nonlinear vibroacoustic coupling equations are developed using variational principle. The two major difficulties which lie in solving the coupling equations are the uncertain motion of the oscillator and the surface acoustic pressure on the plate, a system for which the fluid-structure coupling cannot be neglected. Based on the incremental harmonic balance (IHB) method, the motion of the oscillator is expressed in the form of the Fourier series, and then the modal expression method and the incoherent assumption are employed to discretize the displacement and the surface pressure of the plate. Then the approximate analytical solution is given by the IHB method. The characteristics of acoustic radiation and surface quadratic velocity of the plate, the nonlinear characteristics of oscillator, and the influence of the excitation frequency and the nonlinear stiffness on the results are investigated by the numerical simulation. The results show that the excitation at the frequency close to the natural frequency of the oscillator can produce a significant response of the third-harmonic generation which determines the vibroacoustic characteristics of the plate. 1. Introduction The analytical solution of the nonlinear vibroacoustics coupling system is significant to the control of the vibration and acoustic radiation of structures under nonlinear excitations. The vibration isolation system as the typical supporting structure frequently encountered in many industrial applications transmits the excitation force to the radiator, and then the force excites the vibration and acoustic radiation of the radiator. The nonlinear vibration isolation mechanism is already clear, while the research on the acoustic radiation mechanism of the structure under the nonlinear vibration isolation is few. For the nonlinear vibroacoustic coupling system consisting of the nonlinear vibration isolation, plate, and acoustic medium, it is hard to obtain the exact analytical solutions due to the nonlinear factors, the vibration coupling of the oscillator and the plate, and the acoustic coupling of the plate and the acoustic medium. Although it could be solved by the numerical algorithms such as the finite element method (FEM) and the boundary element method (BEM), the results cannot represent the general rule. Therefore, this paper will propose an approximate analytical approach to the nonlinear vibroacoustic
Dynamical thickening transition in plate coating with concentrated surfactant solutions  [PDF]
Jér?me Delacotte,Lorraine Montel,Frédéric Restagno,Beno?t Scheid,Benjamin Dollet,Howard A. Stone,Dominique Langevin,Emmanuelle Rio
Physics , 2011,
Abstract: We present a large range of experimental data concerning the influence of surfactants on the well-known Landau-Levich-Derjaguin experiment where a liquid film is generated by pulling a solid plate out of a bath. The thickness h of the film was measured as a function of the pulling velocity V for different kind of surfactant and at various concentrations. Measuring the thickening factor $\alpha=h/h_{LLD}$, where hLLD is obtained for a pure liquid, in a wide range of capillary ($Ca=\eta V/\gamma$), two regimes of constant thickening can be identified: at small capillary number, $\alpha$ is large due to a confinement and surface elasticity (or Marangoni) effects and at large Ca, $\alpha$ is slightly higher than unity, due to surface viscous effects. At intermediate Ca, $\alpha$ decreases as Ca increases along a "dynamic transition". In the case of non-ionic surfactants, the dynamic transition occurs at a fixed Ca, independently of the surfactant concentration, while for ionic surfactants, the dynamic transition depends on the concentration due to the existence of an electrostatic barrier. The control of physico-chemical parameters allowed us to elucidate the nature of the dynamic transition and to relate it to surface rheology.
Highly asymmetric interaction forces induced by acoustic waves in coupled plate structures  [PDF]
Xiying Fan,Chunyin Qiu,Shenwei Zhang,Manzhu Ke,Zhengyou Liu
Physics , 2015,
Abstract: Mutual forces can be induced between coupled structures when illuminated by external acoustic waves. In this Letter, we propose a concept of asymmetric interaction between two coupled plate-like structures, which is generated by oppositely incident plane waves. Besides the striking contrast in magnitude, the mutual force induced by one of the incidences can be tuned extremely strong due to the resonant excitation of the flexural plate modes. The highly asymmetric interaction with enhanced strength in single side should be potentially useful, such as in designing ultrasound instruments and sensors.
ALOAD - a code to determine the concentrated forces equivalent with a distributed pressure field for a FEM analysis  [PDF]
INCAS Bulletin , 2010, DOI: 10.13111/2066-8201.2010.2.4.9
Abstract: The main objective of this paper is to describe a code for calculating an equivalent systemof concentrate loads for a FEM analysis. The tables from the Aerodynamic Department containpressure field for a whole bearing surface, and integrated quantities both for the whole surface andfor fixed and mobile part. Usually in a FEM analysis the external loads as concentrated loadsequivalent to the distributed pressure field are introduced. These concentrated forces can also be usedin static tests. Commercial codes provide solutions for this problem, but what we intend to develop isa code adapted to the user’s specific needs.
Non-equilibrium Casimir forces: Spheres and sphere-plate  [PDF]
Matthias Krüger,Thorsten Emig,Giuseppe Bimonte,Mehran Kardar
Physics , 2011, DOI: 10.1209/0295-5075/95/21002
Abstract: We discuss non-equilibrium extensions of the Casimir force (due to electromagnetic fluctuations), where the objects as well as the environment are held at different temperatures. While the formalism we develop is quite general, we focus on a sphere in front of a plate, as well as two spheres, when the radius is small compared to separation and thermal wavelengths. In this limit the forces can be expressed analytically in terms of the lowest order multipoles, and corroborated with results obtained by diluting parallel plates of vanishing thickness. Non-equilibrium forces are generally stronger than their equilibrium counterpart, and may oscillate with separation (at a scale set by material resonances). For both geometries we obtain stable points of zero net force, while two spheres may have equal forces in magnitude and direction resulting in a self-propelling state.
Mobility Matrix of a Thin Circular Plate Carrying Concentrated Masses Based on Transverse Vibration Solution  [PDF]
Desheng Li,Junhong Zhang
Shock and Vibration , 2014, DOI: 10.1155/2014/284367
Abstract: When calculating the vibration or sound power of a vibration source, it is necessary to know the point mobility of the supporting structure. A new method is presented for the calculation of point mobility matrix of a thin circular plate with concentrated masses in this paper. Transverse vibration mode functions are worked out by utilizing the structural circumferential periodicity of the inertia excitation produced by the concentrated masses. The numerical vibratory results, taking the clamped case as an instance, are compared to the published ones to validate the method for ensuring the correctness of mobility solution. Point mobility matrix, including the driving and transfer point mobility, of the titled structure is computed based on the transverse vibration solution. After that, effect of the concentrated masses on the mechanical point mobility characteristics is analyzed. 1. Introduction Design of quiet and low vibration equipment requires quantitative data of the sound and vibration sources. Mechanical point mobility matrix is an appropriate tool to describe the dynamic characteristics and is needed for the estimation of vibration and sound power transmission from the source to the receiving structure if the energy based methods are used. In many cases, it is impossible to measure the point mobility needed for an analysis directly; therefore, it is necessary to calculate them in terms of the relative theory. Much work has been done in finding analytical formula for point mobility. Fahy [1], Fahy and Gradonio [2] and Cremer et al. [3] gave a comprehensive summary of formulas for kinds of classical structures, such as beams, plates, and shells. Many authors, among them Sarradj ?[4], Moorhouse and Gibbs ? [5], Bonhoff and Petersson [6], and Mayr and Gibbs [7], calculated various point mobility of beam/plate-like components in more or less detail. In contrast, more results of point mobility were applied in complicated and built-up structures. Petersson and Heckl [8] studied point mobility for the plate with arbitrary thickness and the deep beams. Sciulli [9] analyzed the true effects of vibrating system flexibility. Grice and Pinnington [10] estimated the mean-square flexural vibration of a thin plate box via calculating its mechanical impedances. Putra [11] modified Laulegnat’s model by applying impedance and mobility to research the sound radiation of a perforated plate. Wang [12] provided a general formula to solve the vibration problem for continuous systems. Yun and Mak [13] reported the effects of the interaction between two vibratory machines
Estimate of thermal fatigue lifetime for the INCONEL 625lCF plate while exposed to concentrated solar radiation  [cached]
Rojas-Morín, A.,Fernández-Reche, J.
Revista de Metalurgia , 2011,
Abstract: A system for testing the thermal cycling of materials and components has been developed and installed at the DISTAL-I parabolic dish facility located at the Plataforma Solar de Almería (PSA) in Spain. This system allows us to perform abrupt heating/cooling tests by exposing central solar receiver materials to concentrated solar radiation. These tests are performed to simulate both the normal and critical operational conditions of the central solar receiver. The thermal fatigue life for the INCONEL 625LCF plate when subjected to concentrated solar radiation has been estimated with this system. We have also developed a numerical model that evaluates the thermal behavior of the plate material; additionally, the model yields the tensile-compressive stresses on the plate, which allow the estimation of the Stress-Life (S-N) fatigue curves. These curves show that the lifetime of the plate is within the High Cycle Fatigue (HCF) region at the operational temperatures of both 650 °C and 900 °C. En el concentrador solar de disco parabólico DISTAL-I, situado en la Plataforma Solar de Almería (PSA), en Espa a, se ha instalado un sistema para pruebas de ciclado térmico de materiales. Este sistema permite realizar pruebas abruptas de calentamiento y enfriamiento, en materiales para receptores solares de torre central, al exponerlos a radiación solar concentrada. Estas pruebas se realizan para simular las condiciones de operación de un receptor solar, las condiciones críticas y las condiciones normales. Con este sistema se ha estimado el tiempo de vida bajo fatiga térmica, en una placa de INCONEL 626LCF , cuando es sometida a radiación solar concentrada. Asimismo, hemos desarrollado un modelo numérico que evalúa el desarrollo térmico en el material de la placa: adicionalmente, el modelo obtiene los esfuerzos de tensión-compresión en la placa, los cuales permiten la estimaciónde las curvas de fatiga vidaesfuerzo (S-N). Estas curvas muestran que la vida útil de la placa se encuentra dentro de la región de Fatiga de Alto Ciclado (HCF) a temperaturas de operación de 650 °C y 900 °C.
Photonic forces in the near field of statistically homogeneous fluctuating sources  [PDF]
Juan Miguel Aunon,Manuel Nieto-Vesperinas
Physics , 2012,
Abstract: Electromagnetic sources, as e.g. lasers, antennas, diffusers or thermal sources, produce a wavefield that interacts with objects to transfer them its momentum. We show that the photonic force exerted on a small particle in the near field of a planar statistically homogeneous fluctuating source uniquely depends and acts along the coordinate perpendicular to its surface. The gradient part of this force is contributed by only the evanescent components of the emitted field, its sign being opposite to that of the real part of the particle polarizability. The non-conservative force part is uniquely due to the propagating components, being repulsive and constant. Also, the source coherence length adds a degree of freedom since it largely affects these forces. The excitation of plasmons in the source surface drastically enhances the gradient force. Hence, partially coherent wavefields from fluctuating sources constitute new concepts for particle manipulation at the subwavelength scale
Stochastic Lorentz forces on a point charge moving near the conducting plate  [PDF]
Jen-Tsung Hsiang,Tai-Hung Wu,Da-Shin Lee
Physics , 2007, DOI: 10.1103/PhysRevD.77.105021
Abstract: The influence of quantized electromagnetic fields on a nonrelativistic charged particle moving near a conducting plate is studied. We give a field-theoretic derivation of the nonlinear, non-Markovian Langevin equation of the particle by the method of Feynman-Vernon influence functional. This stochastic approach incorporates not only the stochastic noise manifested from electromagnetic vacuum fluctuations, but also dissipation backreaction on a charge in the form of the retarded Lorentz forces. Since the imposition of the boundary is expected to anisotropically modify the effects of the fields on the evolution of the particle, we consider the motion of a charge undergoing small-amplitude oscillations in the direction either parallel or normal to the plane boundary. Under the dipole approximation for nonrelativistic motion, velocity fluctuations of the charge are found to grow linearly with time in the early stage of the evolution at the rather different rate, revealing strong anisotropic behavior. They are then asymptotically saturated as a result of the fluctuation-dissipation relation, and the same saturated value is found for the motion in both directions. The observational consequences are discussed. plane boundary. Velocity fluctuations of the charge are found to grow linearly with time in the early stage of the evolution at the rate given by the relaxation constant, which turns out to be smaller in the parallel case than in the perpendicular one in a similar configuration. Then, they are asymptotically saturated as a result of the fluctuation-dissipation relation. For the electron, the same saturated value is obtained for motion in both directions, and is mainly determined by its oscillatory motion. Possible observational consequences are discussed.
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