共查询到20条相似文献,搜索用时 15 毫秒
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Runnemalm A Molin NE Jansson E 《The Journal of the Acoustical Society of America》2000,107(6):3452-3459
Earlier investigations have assumed only "out-of-plane" vibrations of the plates of the violin. The violin body can, however, be described as a thin-walled, double-arched shell structure and as such it may very well elongate in one direction as it contracts in another. Therefore, at least two orthogonal vibration components have to be included to describe the vibrations. The operating deflection shapes (ODSs) of a good, professionally made and carefully selected violin were therefore measured in several directions by TV holography to determine both "in-plane" and out-of-plane vibration components of the ODSs. The observations were limited to the frequency range 400-600 Hz, as this interval includes two most-prominent resonance peaks of bridge mobility and sound radiation as well as a third poorly radiating resonance. These three peaks clearly showed orthogonal vibration components in the ODSs. The vibration behavior of the violin body, sectioned in the bridge plane, was interpreted as the vibrations of an "elliptical tube" with nodal diameters. The number of nodal diameters increases from two to three in the selected frequency range. The TV holography measurements were supported by electrodynamical point measurements of bridge mobility, of air volume resonances, and by reciprocity, of radiation properties. Furthermore, a fourth mode, the air mode, A1, is involved indirectly in the sound radiation via influence on the body vibrations. 相似文献
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Measurements of transient response are described for a system composed of multiple beams of atomic sodium passing through a high-finesse optical cavity. For switching from zero to incident laser intensities above the upper turning point of the steady-state hysteresis cycle, a delay in excess of the empty cavity filling time is observed for the time taken to reach steady state. For switching of the incident laser intensity from zero to above the upper turning point, this delay increases to up to 12 times the empty cavity filling time. The results are in qualitative agreement with earlier theoretical work based upon the mean-field theory for plane waves in absorptive bistability. 相似文献
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E.A. Johnson 《Applied Acoustics》1981,14(2):157-161
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《Comptes Rendus Physique》2005,6(6):585-594
Electromagnetic modelling plays a more and more important role in the study of complex systems involving Maxwell phenomena, such as the interactions of radiowaves with the human body. Simulation then becomes a credible means in decision making, related to the engineering of complex electromagnetic systems. To increase confidence in the models with respect to reality, validation and uncertainty estimation methods are needed. The different dimensions of model validation are illustrated through dosimetry, i.e., quantification of human exposure to electromagnetic waves. To cite this article: M.-F. Wong, J. Wiart, C. R. Physique 6 (2005). 相似文献
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Daniel M. Heffernan 《Physics letters. A》1984,103(5):286-288
The transient behaviour of degenerate four wave mixing (DFWM) in a three-level saturable absorber is analysed. We discuss two cases which are relevant to present day experiments. We obtain the transient reflectivity in the cases where the pump beams consist of (a) a single pulse and (b) a train of pulses. 相似文献
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Summary The initial-value problem of surface waves generated by a harmonically oscillating porous wave maker immersed in an incompressible
fluid of infinite horizontal extent but finite constant depth is prescribed. By the use of generalized functions and asymptotic
analyses, it was possible to get both the steady-state solution and the transient solution without the need of imposing a
radiation condition. Two limiting cases are also investigated: in the first the fluid is of infinite depth, while in the other
the fluid is shallow. 相似文献
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Linear and non-linear transient responses of a typical hydraulic engine mount are analytically and experimentally studied in this paper. First, a lumped parameter linear model is used to approximate the typical step response and to suggest parameters that must be experimentally determined. Various configurations as related to inertia track and decoupler are analyzed. Two bench experiments are constructed for the identification of non-linear compliances and resistances. One of the main non-linear characteristics, however, comes from the decoupler mechanism. To accurately predict the time events of the decoupler opening and closing, an equivalent viscous damper model is employed along with a multi-staged switching mechanism. Additionally, non-linear behavior arising due to the vacuum formation in the top chamber is studied by defining a bi-linear asymmetric stiffness curve. New transient experiments are conducted on an elastomer test system, and measured transmitted force and top chamber pressure signals are analyzed. Results of the proposed simulation model match well with measured responses when step up, step down and triangular waveforms are applied. Areas for future research are identified. 相似文献
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B.U. Felderhof 《Physica A》2010,389(24):5602-5610
The dipolar sound wave generated by a sudden impulse in an unbounded viscous compressible fluid is studied on the basis of the linearized Navier-Stokes equations. Due to viscosity the spherical wavefront is diffuse with a width which grows with the square root of time. The wavefront is followed by a spherical shell of static potential flow. The shell itself surrounds an expanding spherical region of viscous flow. At long times the energy in each of the three regions is of comparable magnitude, and decays with a t−3/2 power law. 相似文献
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It is more economic to compute the response of linear systems with Fourier methods using fast Fourier transform algorithms than with step-by-step numerical integration methods. However, one drawback of Fourier methods is the difficulty in computing transient responses with arbitrary initial conditions (ICs). When the system is modeled with constant-parameter ordinary differential equations, the response can be obtained in closed form but, when using spectral and boundary element methods, this is no longer possible. In this paper, a technique consisting of taking advantage of the periodic character of the discrete Fourier transform to include an ad hoc force pulse to impose the ICs is proposed. The technique is presented in detail and used to compute the responses of single and multiple degree-of-freedom lumped parameter systems. The responses are compared with step-by-step integration solutions. 相似文献
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We perform an analytical investigation of modulational interaction of an electromagnetic pump wave in a transversely magnetized weakly polar semiconductor plasma medium. Based on the hydrodynamic model, a critical examination of frequency modulational amplification is made in a moderately doped III–V semiconductor crystal (n-GaAs) duly shined by pulsed 10.6 µm CO2 laser. The effect of electron-LO phonon interaction and coupled magnetoplasma excitations on the nonlinear interaction of a laser beam adds new dimension to the analysis. Steady state and transient gain coefficients, threshold pump intensity and optimum-pulse duration for the onset of modulational instability are estimated. The paper concentrates on the study of gain characteristics mainly in transient region. Effect of doping and applied magnetic field on the threshold pump intensity and growth rate has been significantly analysed. Graphical analysis interprets strong dependence of transient amplification characteristics on these parameters. So a judicious choice of physical parameters may develop growth at much lower pump intensity improving the cost effectiveness of the system. These results may help to be important for understanding and improving the performance of modulator. 相似文献
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A. A. Vertiy S. P. Gavrilov D. S. Armaan I. ?l?er 《International Journal of Infrared and Millimeter Waves》1997,18(2):405-429
In the present paper a time response of a quasi-optical open resonator when exciting it by a pulse signal with a radiofrequency
filling has been investigated using an inverse Fourier transformation. The radiofrequency filling corresponds to millimeter
wavelengths region. Fourier image of the time response of the resonator is calculated from a product of two frequency’s functions.
One of these functions is the Fourier image of a pulse signal at the resonator input, and the second is a calculated or measured
amplitude — phase characteristic of the resonator. When calculating the amplitude- phase characteristic of the resonator (a
complex transfer coefficient) a plane — layered model of the resonator was used.
Experimental investigation has been conducted in millimeter wavelengths with Fabry-Perot type open resonator. Amplitude- phase
characteristic of the resonator were measured in “on passage“ regime in wide frequency band.
It was shown that presence of weakly absorbing layer in the resonator leads to changing of the time response of the resonator.
The obtained results can be used in the dielectric measurements, defectoscopy of stratiform materials, relaxometry, non-destructive
control of materials and structures, etc. 相似文献
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G Bissinger 《The Journal of the Acoustical Society of America》2012,132(1):465-476
A hybrid, deterministic-statistical, parametric "dynamic filter" model of the violin's radiativity profile [characterized by an averaged-over-sphere, mean-square radiativity (R(ω)(2))] is developed based on the premise that acoustic radiation depends on (1) how strongly it vibrates [characterized by the averaged-over-corpus, mean-square mobility (Y(ω)(2))] and (2) how effectively these vibrations are turned into sound, characterized by the radiation efficiency, which is proportional to (R(ω)(2))/(Y(ω)(2)). Two plate mode frequencies were used to compute 1st corpus bending mode frequencies using empirical trend lines; these corpus bending modes in turn drive cavity volume flows to excite the two lowest cavity modes A0 and A1. All widely-separated, strongly-radiating corpus and cavity modes in the low frequency deterministic region are then parameterized in a dual-Helmholtz resonator model. Mid-high frequency statistical regions are parameterized with the aid of a distributed-excitation statistical mobility function (no bridge) to help extract bridge filter effects associated with (a) bridge rocking mode frequency changes and (b) bridge-corpus interactions from 14-violin-average, excited-via-bridge (Y(ω)(2)) and (R(ω)(2)). Deterministic-statistical regions are rejoined at ~630 Hz in a mobility-radiativity "trough" where all violin quality classes had a common radiativity. Simulations indicate that typical plate tuning has a significantly weaker effect on radiativity profile trends than bridge tuning. 相似文献
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In this study the response in a transversely isotropic, semi-infinite elastic rod is found to an input on its end that is time dependent. The solution follows closely the method developed by Skalak for isotropic rods which uses integral transforms to solve the governing equations. The solution differs from that of Skalak, apart from material properties, in that in this study mixed-mixed conditions are assumed for the end of the rod. The responses are found at a “distant” station and are expressed in terms of the axial and tangential strains. 相似文献
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