控制两相邻结构地震动响应的Maxwell模型流体阻尼器优化参数研究

运用被动连接单元减小相邻结构的振动被证明是一种行之有效的手段。将两相邻结构简化为两单自由度体系,用Maxwell模型模拟连接两相邻结构的流体阻尼器,分别导出了在地面白噪声激励下主结构平均振动能量最小或两相邻结构总平均振动能量最小这两个控制目标下流体阻尼器优化参数的一般表达式,该优化参数仅与两相邻结构的相对自振频率和相对质量有关,也讨论了两相邻结构的相对自振频率和相对质量对控制效果的影响。最后,运用具有不同相对参数的三类相邻结构在El Centro 1940 NS地震波作用下时域响应的数值结果说明了这种被动优化流体阻尼器能够非常有效地减小在地震作用下两相邻结构的振动响应。     

Equation for the number of quanta and the dissociation rate in a diatomic gas

We examine vibrational relaxation in a one-component diatomic gas, the molecules of which are described by a Morse potential. An expression is obtained for the mean number of quanta of a molecule assuming there exists a sharp boundary which separates vibrational levels into two groups. In each group there dominates either vibrational-quantum exchange processes or energy-exchange processes between the vibrational and translational degrees of freedom. By solving numerically the system of equations for the number of quanta and for the dissociation rate for times larger than the vibrational relaxation time, the dependence of the dissociation constant on the number of quanta is obtained.     

地震作用下主-从结构的被动优化控制研究

提出了一种利用主－从结构间的相互作用来减少在地震作用下结构响应的控制方法。该方法通过优化设计主－从结构间的被动耗能单元,最大限度地耗散结构的相对振动能量能减小主、从结构的整体振动水平,或最大限度地吸收主结构的相对振动能量以减小主结构的振动。文章首先导出了在平稳白噪声激励下被动耗能单元优化刚度和阻尼的一般表达式,并分析了不同结构参数对控制效果的影响,比较了在不同的平稳过滤白噪声激励下主－从结构相对位     

Effect of the Boundary Conditions and Influence of the Rotational Inertia on the Vibrational Modes of an Elastic Ring

We present the small-amplitude vibrations of a circular elastic ring with periodic and clamped boundary conditions. We model the rod as an inextensible, isotropic, naturally straight Kirchhoff elastic rod and obtain the vibrational modes of the ring analytically for periodic boundary conditions and numerically for clamped boundary conditions. Of particular interest are the dependence of the vibrational modes on the torsional stress in the ring and the influence of the rotational inertia of the rod on the mode frequencies and amplitudes. In rescaling the Kirchhoff equations, we introduce a parameter inversely proportional to the aspect ratio of the rod. This parameter makes it possible to capture the influence of the rotational inertia of the rod. We find that the rotational inertia has a minor influence on the vibrational modes with the exception of a specific category of modes corresponding to high-frequency twisting deformations in the ring. Moreover, some of the vibrational modes over or undertwist the elastic rod depending on the imposed torsional stress in the ring.     

Comparison of different approaches to the calculation of chemically nonequilibrium flow with allowance for vibrational relaxation

Chemically nonequilibrium flows with allowance for vibrational relaxation are investigated numerically within the framework of the hypersonic viscous shock layer equations with reference to the example of the flow in the neighborhood of the critical line of the “Buran” orbital vehicle in its motion along a re-entry trajectory. It is found that the vibrational temperatures of the molecular components differ markedly. The distinctive feature of the model in question, as compared with a model with one average vibrational temperature, is the stronger effect on the flow characteristics over the thermally stressed part of the trajectory. The models proposed in the literature for dissociation from an effective vibrational level are compared with the model for dissociation with a certain probability from all the vibrational levels. It is shown that the use of an approximation of the total dissociation constant as a function of translational temperature only may lead to a considerable variation from the results of calculations with allowance for vibrational relaxation on the basis of the equilibrium dissociation rate constant. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 138–146, March–April, 1994.     

Model of the physico-chemical kinetics behind the front of a very intense shock wave in air

A model of the physico-chemical kinetics of the reactions taking place behind the front of an intense shock wave propagating in air with a speed of 9–14 km/s is proposed. The problem of describing the chemical reactions, namely, molecular dissociation and exchange reactions involving vibrationally excited molecules in the absence of vibrational equilibrium, is solved. The vital role of the vibrational excitation delay in the dissociation of oxygen and nitrogen is established. The rate of the exchange reaction between nitrogen molecules and oxygen atoms in the shock wave depends only slightly on the vibrational excitation level. It is demonstrated that the rate constants for thermally nonequilibrium dissociation reactions can be represented within the framework of the one-temperature approximation at constant vibrational temperatures of the dissociating species satisfying quasi-stationary conditions.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 169–182, March–April, 1995.     

管道及管路系统流固耦合振动问题的研究动态

对管道及管路系统流固耦合振动问题在近二十年来的进展作了综述。根据问题特点，将本课题分为三个分支，即从紊流到振动噪声源的研究，流－弹耦合振动的研究和声－弹耦合振动的研究。在分别总结这三个分支的研究成果的同时指出了尚需进一步研究的某些问题。     

The three-dimensional analysis of the self-vibrational characteri-stics of the 2050mm hot-strip mill housing by means of laser holographic interferometry and finite element method

According to the theory of similarity,a three-dimensional simulation study on the self-vibrational characteristics of the2050mm hot-strip finishing mill housing at Baoshan Ironand Steel Complex has been carried out.The analysis of the main vibrational modes of thefirst three orders has also been done by means of holographic interferometry.In addition,the authors have carried out the numerical analysis of finite elements in three dimensions.The comparison of the results of both analyses(simulation analysis and numerical analysisof finite element)shows that they are consistent.     

On the problem of the stability of convective two-phase medium flows under high-frequency vibration

The principles and methods of constructing a model of vibrational convection in a medium consisting of a liquid (gas) and a solid admixture are discussed. A closed system of averaged equations is first obtained. The system admits passage to the limits of the equations of both vibrational convection in a homogeneous fluid and convection in a dusty medium in the static case. As a measure of the difference with respect to the homogeneous fluid, in addition to the sedimentation parameter, which also manifests itself in the absence of vibrational accelerations, it is possible to take the inhomogeneity parameter introduced in this study and responsible for the pulsatory transport of the average fields. The problem of the stability of plane parallel flow in a vertical layer of a two-phase medium under horizontal longitudinal vibration with respect to infinitesimal perturbations is considered. It is shown that the introduction of particles into the flow leads to qualitatively novel effects which cannot be predicted within the framework of the homogeneous fluid model.     

Effect of laser radiation on the vibrational distribution of CO2

In connection with progress in the field of CO₂ lasers, questions of the vibrational kinetics of molecules of CO₂ have been discussed in many communications. In a majority of cases of practical importance, the distribution of CO₂ is due to processes of vibrational exchange (V-V) on which is based the well-known thermodynamic model [1]. In other cases, the V-V exchange does not determine the vibrational distribution, since the perturbation is small; therefore, it is found sufficient to consider a small number of levels of CO₂ (usually three), whose populations satisfy the linear equations of the balance [2]. There is the possibility of conditions where the vibrations are strongly excited and, at the same time, V-V processes are insignificant (a very small CO₂ impurity in the inert gas, with a high degree of ionization). Then the number of equations becomes large. The present article discusses one such case: the excitation of a steady-state vibrational distribution in a glow discharge by laser radiation, whose solution is rather graphic.     

On the size-dependent flexural vibration characteristics of unbalanced couple stress-based micro-spinning beams

On the basis of the modified couple stress theory, some analytical results are obtained for vibrational parameters of micro-spinning Rayleigh beams with an axial mass-eccentricity distribution. The modified couple stress theory is a nonclassical continuum theory capable to capture the size effects in small-scale structures. After writing the governing equations of motion, they are transformed to the complex form. Then by utilizing the Galerkin method, analytical expressions for natural frequencies of the micro-spinning beam in forward and backward whirl motions are obtained. Critical speeds are also analytically presented in the two whirl motions for different modes. Moreover, the vibrational amplitude of the micro-spinning beam with axial mass eccentricity distribution is determined. Some numerical results are presented to study the effect of the length scale parameter on the vibrational characteristics.     

Effect of vibrational relaxation of molecules on dissociating air characteristics behind a strong shock front

Molecular vibrational relaxation has a considerable effect on the dissociation rate in a gas consisting of molecules of a single type [1]. In gas mixtures such as air, vibrational relaxation also affects the other reaction rates, which may be important in solving several problems of hypersonic aerodynamics. This is due to the fact that in air at temperatures above 5000° the vibrational excitation of nitrogen molecules and the dissociation of oxygen molecules proceed almost simultaneously. We study the effect of vibrational relaxation on the conditions behind a strong shock front.     

Estimation of the effect of vibrational excitation of diatomic molecules on their diffusional transport and dissociation in a boundary layer

Relations for the diffusion fluxes of vibrationally highly excited diatomic molecules are found by means of the Chapman-Enskog method. On the basis of these relations a quantitative estimate of the changes in the diffusion coefficients under vibrational excitation and the corresponding changes in the macroscopic dissociation rate is obtained under conditions of disequilibrium of the upper vibrational levels of the dissociating molecules caused by the diffusion processes. The diffusion relations obtained are used in deriving the boundary conditions for the equations of level vibrational kinetics. A simplified version of this derivation is presented for noncatalytic and catalytic surfaces.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 169–182, January–February, 1996.     

Measurement of the vibrational temperature of oxygen behind a shock wave front under thermal and chemical nonequilibrium conditions

In shock tube experiments the profiles of light absorption in oxygen are obtained for the wavelength interval 200–260 nm over the temperature range 4000–10800 K. Using these data, the vibrational temperature profiles are measured for oxygen molecules behind the shock front. The method of determination of the vibrational temperature of oxygen is based on comparing absorption measurements and detailed absorption spectrum calculations for oxygen in the Schumann-Runge system.     

Analysis of Nonequilibrium Dissociation Kinetics in a Boundary Layer Using Various Reaction Models

Values of the nonequilibrium macroscopic reaction rate for a nonisothermal boundary layer of a monatomic diluent gas are calculated using a number of models for thermal dissociation of diatomic molecules — anharmonic Morse oscillators. Analysis is performed for conditions where the diffusive transfer of excited molecules has a significant effect on the population of their upper vibrational levels, which does not only amount to change in vibrational temperature. Under the joint influence of diffusive transfer of molecules, vibrational exchanges, and reactions involving vibrationally excited particles, the local vibrational distribution functions are substantially nonequilibrium. The kinetic models considered take into account the possible contribution of the energy of molecular translational and rotational degrees of freedom to the energy required to overcome the reaction threshold. The effect of multiquantum vibrational—translational exchanges on the distribution of dissociating molecules in their upper vibrational levels is taken into account approximately.     

Direct Shocks in a Vibrationally Nonequilibrium Gas

Direct shocks in flows of a high-temperature diatomic gas with rotational and vibrational degrees of freedom are considered. Gas-dynamic parameters and populations of molecular vibrational levels behind a shock are studied for the case of disturbance of vibrational equilibrium in an incident flow.     

Experimental Investigation of Vibrational Deactivation of CO Molecules in a Supersonic Gas Flow

The vibrational temperature and vibrational deactivation time of CO molecules in collisions with hydrogen atoms are measured using the broadband version of the coherent anti-Stokes Raman scattering technique (CARS). Carbon monoxide with hydrogen-containing admixtures (H₂, H₂O) heated in a reflected shock wave up to temperatures 2900–5100 K escaped through a supersonic wedge-shaped nozzle. The measurements demonstrate the high efficiency of hydrogen atoms in the vibrational deactivation of CO. A difference in the measured temperature dependences of the vibrational excitation and deactivation times of CO molecules in collisions with H atoms, which seems to be associated with a difference in the mechanisms of CO-H complex formation, is noted.     

Modeling of vibrational impact motion of mobile-based body

The paper deals with vibrational impact motion of a mobile-based body on an inclined plane, which is a characteristic for vibrational alignment of components subjected to an automated assembly. The alignment model is presented by a two-degree-of-freedom vibro-impact system in which the moving body is impacting the plane obliquely. Properties of the vibrational impact motion under kinematical excitement of the moving body and under the excitement of the plane in two perpendicular directions were investigated by numerical methods. It was determined that impact displacement occurs under transient regimes of motion from static to dynamic state of equilibrium. Dependencies of maximum displacement of the body and average displacement velocity on force of elastic resistance, amplitude of plane vibration in the direction of the displacement, and phase angle between the perpendicular members of vibration components were established. Zones of system and excitement parameter combination when the vibrational impact motion occurs were defined.