The inclusion of the effect of the evaporation coefficient on the rate of variation of droplet radius

The paper deals with the investigation of the effect of the evaporation (condensation) coefficient of droplet substance on the rate of unsteady variation of the radius of a spherical aerosol droplet in the cases of direct and indirect inclusion of this coefficient. It is found in both cases that the effect of evaporation coefficient is most significant at the initial instant of unsteady-state process of evaporation and of condensation growth of the droplet. At this instant, the size of spherical droplet has hardly any impact on the rate of variation of its radius. As the unsteady-state process continues, the effect of the evaporation coefficient on the rate of variation of the droplet radius depends significantly on the droplet size. The larger the droplet under consideration, the lower the effect of the evaporation coefficient on the rate of variation of its radius. The rates of variation, calculated for the same values of the evaporation coefficient but for different ways of inclusion of this coefficient, differ less for larger aerosol droplets. These methods of inclusion of the evaporation coefficient are considered for the process of slow evaporation of a droplet.     

一种用射影线束族生成曲线的方法

以两射影对应线束对应真线交点的轨迹是二阶曲线为基础，研究了射影线束族的形成原理，讨论了射影线束与线束族，射影线束族与线束族对应直线交点所构成的平面曲线及其性质，同时利用计算机绘制了部分曲线。     

红木文化创意产品及其开发设计原则

目的探究红木文化创意产品相关理论及开发设计原则。方法从文化创意产品的概念和红木的属性分析,提出红木文化创意产品的定义;通过对传统红木文化产品和现代红木文化创意产品的分类比对,分析出现代红木文化创意产品的新增产品种类。在红木文化创意产品定义和分类的基础上,提出红木文化创意产品的特征和红木文化创意产品开发设计原则。结论红木文化创意产品开发设计原则是对文化创意产品设计理论体系的补充,并将促进红木文化的继承和红木产品的创新。     

Special Features in the Realization of Film Boiling on Wire Heaters. Distilled Water

The existence of a region of self-oscillatory instability of heat transfer is revealed under conditions of film boiling of water subcooled to the saturation temperature. In the case of short heaters, whose length is commensurable with the Taylor instability wavelength, the process is regular. For heaters of the same length, the form of oscillations and their characteristics are fully reproducible. An increase in the heater length results in the emergence of spatially distributed oscillations. It is found that an increase in subcooling on the interface between the modes of boiling is accompanied by the formation of a structure consisting of a system of single domains of continuously decreasing size. The formation of this structure causes a significant change in the temperature distribution in the zone adjoining that of nucleate boiling, which considerably reduces the film stability. A single domain of the film mode of boiling was stable at any temperature of the liquid. The singularities of realization of minimal-size domains of the film mode of boiling under conditions of stabilization of the integral mean temperature of the heater are investigated. It is found that the minimal zone of the film mode of boiling is a system of three elementary domains.     

On the Problem of Improvement of the Damping Ability of Rotor Blades of Contemporary Gas-Turbine Engines

We present the results of experimental investigations of the influence of structural and technological factors on the damping ability of lock joints of compressor blades carried out at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine, study the possibility of using dampers mounted in shroud joints of turbine blades, and formulate some recommendations concerning the possibility of im proving the damping ability of rotor blades of contemporary gas-turbine engines.     

The shock-wave mechanism of spontaneous ignition of hydrogen under conditions of sudden efflux from reservoir at high pressure

Analysis is made of the conditions of spontaneous ignition of hydrogen as a result of emergence of a starting shock wave in air before an expanding cold flow of gas. The rise of temperature behind the shock wave causes ignition of the mixture of combustible gas with air, which forms on the contact surface. The condition for spontaneous ignition is the sufficient time of residence of mixture at high temperature for mixing and ignition. The calculations of spontaneous ignition of hydrogen jet are based on a model which takes into account the gasdynamic transport of viscous gas, the kinetics of oxidation of hydrogen, multicomponent diffusion, and thermal conductivity. The range of pressures is determined in a reservoir, during whose depressurization the shock wave forming in air exhibits intensity sufficient for igniting the hydrogen-air mixture behind the front of propagating jet of compressed hydrogen. Results of analysis are given of the dependence of conditions of ignition on the pressure of hydrogen in the reservoir, on the size of the outlet opening, and on the initial temperature of hydrogen and air.     

Mechanics and physics of quasibrittle fracture of polycrystalline metals under the conditions of stress concentration. Part I. Experimental results

In the present work, which consists of three parts, we make an attempt to formulate the fundamental ideas of the theory of quasibrittle fracture of polycrystalline metals and structural alloys on the macroscopic and microscopic levels. Within the framework of the usual approach, we consider physical aspects of the problem of analysis of the elementary acts of fracture of the crystal lattice and regularities of macroscopic fracture under conditions of stress concentration in connection with the problem of structural integrity. We propose simple and convenient practical criteria of quasibrittle fracture under conditions of stress concentration and formulate physically substantiated concepts of the ductility of metals. In the first part of the work, we present the results of the experimental investigation of the fracture of specimens with stress concentrators of various geometries and fatigue cracks, establish the regularities of changes in the local characteristics of fracture, and analyze the principal factors affecting the value of the critical cleavage stress σ_f. Institute of Physics of Metals, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 5–16, July–August, 1997.     

CONVERSION OF SHORT FATIGUE CRACKS INTO A LONG CRACK

This paper presents a method for the statistical processing of results of initiation and propagation of short fatigue cracks. The distribution of the lengths of these cracks followed a Weibull distribution function. The value of the size parameter of this distribution grows with the number of cycles, but the value of the shape parameter declines as the number of cycles increases. A study of the modal value of fatigue crack lengths as a function of the number of cycles yielded a statistical criterion defining the conversion of the short fatigue crack initiation and propagation stage into the long fatigue crack propagation stage. One condition for this conversion is a zero magnitude of the first derivative of the modal value of fatigue crack lengths by the number of cycles. When the dependence of the Weibull distribution shape parameter and size parameter upon the number of cycles was inserted in this condition, solution of the resultant expression revealed the critical number of cycles that is necessary for the formation of a long fatigue crack.     

Potentials and Equations of State for Two Special Reference Configurations

On the basis of the mathematical formulation of the principle of reference invariance of the functions of state of deformed bodies, we consider two special representations of the potential of state in which the reference configuration is variable and related to the current state of the body. The first of these representations (natural) follows from the general representation of the potential of state if a current state of the basis is regarded as the reference state and the corresponding stress-free configuration is taken as the reference configuration. The second (strain-free) representation is obtained if the role of the reference configuration is played by the current configuration. For both representations, we deduce the equations of state in the form of expressions for stresses and the parameters of state connected with the basis parameters. As a constructive proof of the unconditional existence of the elastic potential, we deduce the expression for the elastic potential via the potential of state by using the natural potential of state. It is proved that the general system of equations of state consists of four independent systems of equations, namely, of the equations of elasticity, piezoeffects, stress-free distortion, and stress-free state.     

Two methods of investigation of the influence of hydrogen on the propagation rate of a crack and behavior of fracture of high-strength steels

We present two methods for the investigation of the influence of hydrogen on the propagation rate of a crack and behavior of fracture of high-strength steels. The method for investigation of the influence of electrolytic hydrogenation on a subcritical growth of a crack in high-strength steels is based on the use of simple beam specimens of a certain geometry and on the application of lateral loading in such a way that the stress intensity factor can be constant at the tip of a preliminary induced crack. The method is of great importance for the performance of comparative experiments in evaluating the influence of active media and structural anisotropy of specimens made of high-strength steels with limited sizes on their corrosion crack resistance. Typical examples of the application of the method to investigation of the role of electrolytic hydrogenation in subcritical propagation of cracks and their branching in highstrength steels are given. The method for investigation of heat release under strain and fracture of hydrogenated specimens involves the use of microcalorimetric devices, which allow one to study the influence of hydrogenation on peculiarities of the kinetics of elastic and plastic strains of high-strength steels. We illustrate the efficiency of the method proposed by plotting the “load-elongation” curves and corresponding (in time) characteristics of heat release power in the process of strain and fracture of specimens made of a high-strength steel. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 4, pp. 113–120, July–August, 1998     

computer simulation of the processes of mechanical shaping of three-dimensional shells under the conditions of creep. Part 2

On the basis of the moment scheme, we obtain the resolving relations of the method of finite elements in the actual configuration used for the computer simulation of the processes of shaping of spatial shells by using a single finite element across the thickness. The reliability of numerical results is checked by the solution of a test example of shaping of a long narrow rectangular membrane. As an illustration of the possibilities of the developed approach to the analysis of the processes of shaping of thin-walled products with complicated shape, we present the results of numerical simulation of strains in a blank made of D16 alloy in a discrete press tood.     

Application of nonlinear resonances for the diagnostics of closing cracks in rodlike elements

The vibrations of elastic bodies with closing cracks are essentially nonlinear. As a specific feature of these vibrations, one can mention the manifestation of so-called nonlinear effects, e.g., nonlinear (i.e., sub- and superharmonic) resonances and the nonlinearity of vibrations for these resonances. The proposed method for the evaluation of the parameters of cracks (their sizes and location) is based on the analysis of the nonlinearity of vibrations in the neighborhood of a superharmonic resonance of order 2/1 and/or a subharmonic resonance of order 1/2 in the case of variation of the site of application of the driving force because, as follows from the results of numerical and experimental investigations, the level of nonlinearity of the vibrations of rods with closing cracks for nonlinear resonances depends not only on the parameters of the crack but also on the site of application of the driving forces.     

Uncertainty of Cesium-Beam Time Standards Due to Beam Asymmetry

As a consequence of the spatial phase distribution in the resonators of cesium-beam time and frequency standards, the generated frequency depends on the specific path of the atomic beam. A change of the position of the atomic beam source may result in a beam displacement normal to the beam direction. For a deflection system consisting of a combination of quadrupole and hexapole magnets for two-dimensional beam deflection, the displacement of the center of mass of the beam resulting from a misalignment of the beam source is computed. To this end, the distribution of the beam intensity on the collector is first determined. It is shown that for the cesium-beam time and frequency standard CSI of the Physikalisch-Technische Bundesanstalt (PIB), the uncertainty of the position of the center of mass of the beam entails a contribution to the uncertainty of the standard of less than 1 X 10-15. The amount of the displacement of the center of mass of the beam can be determined from the decrease of the beam flux on the collector caused by an adjustment of the beam source.     

Distortion of the sinusoidalness of the forms of vibrations of systems with a disturbed rotary symmetry and the mode localization phenomenon. Report 1

An analysis is made of data available in the literature on investigation of the distortion of the sinusoidalness of the forms of vibration and the mode localization phenomenon of systems with disturbed rotary symmetry. The results are given of a calculational experiment on determination of the influence of the amount of elastic coherence of subsystems and detuning of their frequencies to distortion of the sinusoidalness of the forms of vibrations of the systems considered.Translated from Problemy Prochnosti, No. 10, pp. 45–52, October, 1992.     

Influence of the vibrotreatment of structural elements with residual stresses on their damping ability

We investigate the influence of the vibrotreatment of annular elements made of St. 3 steel on the kinetics of residual stresses and dissipation of energy in the material. By using the characteristic features of changes in the decrement of oscillations of the material and residual stresses, we substantiated the possibility of control over the completion of vibrotreatment by the time of stabilization of the characteristic of dissipation of energy in the material. The established decrease in the decrement of oscillations shows that specimens undergo plastic deformation in the course of this process.     

Superposition states of light in a three-photon absorbing dissipative medium

We consider the process of simultaneous absorption of three photons in a medium in the presence of weak one-photon absorption. We show that in such a system stationary three-component superposition states of light may be formed in the range of small values of state amplitude (weak perturbation). This circumstance is associated with the fact that in this range of interaction the field spends more time in one of the three types of superposition states of light (constituting an ensemble of quantum trajectories of the system) than in two other types. We also show that in the range of large values of state amplitude it is possible to obtain three types of non-stationary superposition states of light. By using numerical simulation of quantum trajectories of the system we study the dynamics of the quantum entropy of the field. We calculate the Wigner functions of the field states. We also obtain analytical results for the density matrix of the steady state of the system.     

An experimental investigation of the characteristics of explosive boiling of subcooled water on a hot surface under conditions of change of boiling modes

A procedure of estimating the area of contact between cold water and a hot hemispherical surface is developed and described. Synchronous measurements of pressure pulses in liquid, the temperature of a body, and characteristics of contact between a heated body and a coolant are performed under conditions of abrupt change of boiling modes (from film to nucleate boiling). Characteristic features of the investigated processes are determined, which are largely defined by the temperature of the hemisphere, by its thermophysical properties, and by the presence of surface oxide films. It is found that the maximal value of the amplitude of pressure pulses, which may be as high as ∼1 MPa in the experiments, is observed in the region of temperatures of the hot body which are close to the temperature of limiting superheat of water. The dependences are obtained of the rate of spreading of liquid and of the time of delay of its explosive boiling from the instant of boiling on the temperature of the hemisphere.     

行李放射性测控装置对~137Cs放射源活度响应及其非线性的测量与探讨

该文介绍了行李放射性测控装置对^137Cs放射源活度响应的校;隹方法,利用点状放射源的活度与照射距离的平方成反比的核物理特性,测量行李放射性测控装置对某指定探测点的活度响应,根据一系列的活度响应值计算出行李放射性测控装置对^137Cs放射源活度响应的非线性。试验结果表明,活度响应是反映探测器对放射性辐射探测能力的重要参数,必须在规定的测量条件下进行测量。