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排序方式: 共有3505条查询结果,搜索用时 15 毫秒
991.
Xavier Amandolese Pascal Hemon Françoise Santi Jan Wojciechowski 《Comptes Rendus Mecanique》2002,330(2):101-106
We present experimental results obtained with a deep cavity, such as a Helmholtz resonator, excited by an airflow. The resonance under the action of the vortices generated in the shear layer is well described and quantified. The mounting of actuators, based on a few piezo-electric elements, allows us to generate a series of two-dimensional vortices forced at a frequency which is different than the natural resonance frequency. The sound level in the cavity is strongly decreased and only the broadband noise of the turbulence remains. To cite this article: X. Amandolese et al., C. R. Mecanique 330 (2002) 101–106. 相似文献
992.
The monotonous instability of the adsorption front formed in a two-component gas filtered vertically through a fixed bed of adsorbent is demonstrated. A threshold value of the Archimedes adsorption criterion is calculated and the corresponding critical gas flow is considered. 相似文献
994.
V. V. Vedeneev 《Fluid Dynamics》2005,40(5):805-817
The stability of an elastic plate in the form of a wide strip in a supersonic inviscid gas flow is investigated in the linear approximation. An expression for the dependence of the pressure on the plate deflection, asymptotically exact for wide plates, is used. Two qualitatively different instability types are obtained: flutter with respect to a single oscillatory mode due to negative aerodynamic damping and flutter of a related type due to the interaction of oscillatory modes. For each type the stability criterion and the frequency at which the oscillation amplitude grows most intensely are found. 相似文献
995.
In a previous work, the instability of a liquid film deposited on the inner walls of a capillary under the presence of insoluble surfactant was analyzed; for that purpose the surface tension was related to the interfacial concentration of surfactant by a linear equation. In general, that assumption is valid when just trace amounts of surfactant are present. The present work extends previous analysis by considering a non-linear surface equation of state derived from the Frumkin adsorption isotherm. This equation of state account not only for the existing quantities of surfactant but also for non-ideal interactions between adsorbed molecules. Except for the equation of state, both the model and the numerical technique employed do not differ from those used in the preceding work. The new predictions here presented show that a linear surface equation of state gives reasonable results for strong surfactants. However, the action of weaker surfactants strongly depends on other parameters: the initial concentration and the type and strength of interaction between adsorbed molecules. Thus, the use of a linear equation of state in these circumstances might give erroneous results. 相似文献
996.
To interpret the results of direct numerical simulations for the one-dimensional pulsating detonation, a nonlinear oscillator
model is proposed based on the integral conservation considerations. A gauging procedure is suggested in which the results
from the direct numerical simulation are used to compute the coefficients of the oscillator equation. Various terms of the
oscillator equation obtained are compared with those of mechanical nonlinear oscillators in order to illustrate their analogy.
Among many important features captured by this nonlinear oscillator equation, the oscillatory behavior of the detonation wave
front can be interpreted as resonant excitation of the chemical energy release.
Received 24 March 1997 / Accepted 7 May 1998 相似文献
997.
This study investigates the nonlinear dynamics of a rotating circular string subjected to a spring force fixed in space. The governing equation for out-of-plane vibration is developed using Hamilton's principle. The nonlinearities of the string deformation and the spring stiffness are considered in the governing equation. Applying Galerkin's method, the governing equation is transformed from a nonlinear partial differential equation into a set of coupled nonlinear ordinary differential equations through orthogonal trigonometric shape functions. Butenin's method is adopted to develop a closed-form analytical solution for single-mode oscillations of the system. Comparison shows that the closed-form solution is in a good agreement with the numerical results over a wide range of the nonlinearities. Multi-mode responses of the string are investigated by means of numerical integration. Based on the results, the nonlinear dynamics of the string are discussed. 相似文献
998.
The controlled free jet instability is used for elongational rheometry of polymer solutions. The instantaneous elongational viscosity represents a convenient comparative parameter. Its dependence on the operating parameters and the conditions of operation will be discussed. 相似文献
999.
Flow visualization is performed on an elastically-dominated instability in several similar Boger fluids in Taylor-Couette flow. The onset and evolution of secondary flow are observed over a range of shear rates using reflective mica platelet seeding. Sequences of ambiently and sheet-illuminated images were digitally processed. Rotation of the inner cylinder was ramped from rest to its final value over a time on the order of a polymer relaxation time. Dilute solutions of high molecular weight polyisobutylene in oligomeric polybutene manifest a flow transition at a Deborah number, De
s
=
s
1.5 with a Taylor number of 0.00022 in a cell with dimensionless gap ratio = 0.0963. At this transition, simple azimuthal shearing is replaced by steady, roughly square, axisymmetric counter-rotating vortices grossly similar to the well-known Taylor vortex flow that is observed at De
s
= 0, Ta = 3612. At De
s
= 3.75, Ta = 0.0014, an axisymmetric oscillatory secondary flow develops initially but is replaced by the steady vortices. At De
s
= 7.5, Ta = 0.0054, the oscillatory and vortex flow coexist and possess an irregular cellular cross-section. A wide span of growth rates is observed: the ratio of onset to polymer relaxation time ranges from 170000 at De
s
= 1.5 to O(10) at De
s
> 5. The role of inertia was explored through changing the solvent viscosity. A transition similar to the one that occurs at De
s
= 3.75, Ta = 0.0014, from the base azimuthal shearing flow to axisymmetric vortices, was also observed with a much lower viscosity fluid at De
s
= 3.3, Ta = 74. 相似文献
1000.
G. A. Ruev A. V. Fedorov V. M. Fomin 《Journal of Applied Mechanics and Technical Physics》2005,46(3):307-314
Based on the previously formulated mathematical model of mechanics of a two-velocity two-temperature mixture of gases, the
evolution of an initially disturbed mixing layer of two gases with different densities under the action of shock waves is
considered in a two-dimensional unsteady approximation. Problems of interaction of shock waves with a sinusoidally disturbed
diffuse layer are solved numerically. The predicted variation of the mixing-region width are in satisfactory agreement with
experimental data.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 3, pp. 3–11, May–June, 2005. 相似文献