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.     

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.     

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.     

Generalized RayleighWave Dispersion Analysis in a Pre-stressed Elastic Stratified Half-space with Imperfectly Bonded Interfaces

Within the framework of the piecewise homogeneous body model the influence of the shear-spring type imperfect contact conditions on the dispersion relation of the generalized Rayleigh waves in the system consisting of the initially stressed covering layer and initially stressed half plane is investigated. The second version of the small initial deformation theory of the three-dimensional linearized theory of elastic waves in initially stressed bodies is applied and the elasticity relations of the materials of the constituents are described by the Murnaghan potential. The magnitude of the imperfectness of the contact conditions is estimated through the shear-spring type parameter. Consequently, the influence of the imperfectness of the contact conditions on the generalized Rayleigh wave propagation velocity is studied through the influence of the values of this parameter. Numerical results on the action of the imperfectness of the contact conditions and the influence of the initial stresses in the constituents on the wave dispersion curves are presented and discussed. In particular, it is established that the magnitude of action of the imperfectness of the contact conditions under the influence of the initial stresses on the wave propagation velocity cannot be limited with corresponding ones obtained in the case where the contact between the constituents is complete and in the case where this contact is full slipping one. The possible application of the obtained results on the geophysical and geotechnical engineering is also discussed.     

有界窄带激励下的电磁开关系统主共振分析

以电磁开关系统为研究对象,研究电路与磁路耦合系统在有界窄带激励下的强非线性振动问题。建立电磁开关强非线性系统在有界窄带激励下的随机微分方程。应用改进的多尺度法得到系统的幅频响应方程,对窄带激励下系统主共振的稳定性进行计算,并分析系统各参数对系统主共振均方值的影响。结果表明,增大阻尼系数可以减小系统主共振的均方值;增大激励电压可以增大系统主共振的均方值;增大电阻可以减小系统主共振的均方值;增大随机扰动强度,极限环变化不大。     

Calculation of the number of cracks and their dimensional distribution in pulsed ductile fracture of a ring

The basic parameters of the shear fracture process of cylindrical shells under intense pulsed (particularly explosive) loads were evaluated on the basis of the proposal of a critical intensity of deformations based on the amount of the work of plastic deformation. The position of the front of fracture, the radius of fracture, the number of cracks in the ring and the number of divisions on the axis of the cylinder, and the size distribution of the number of cracks with and without taking into consideration their mutual intersection and also of the number of fragments of the cylindrical shell by weight were determined. As a first approximation the yield strength, the reduction in area, and the impact strength were used as the parameters characterizing the shell material. A comparison is given of the calculated data and the experimental for the number of through cracks in the ring and the weight distribution of the number of fragments of cylindrical shells.Translated from Problemy Prochnosti, No. 9, pp. 73–79, September, 1989.     

变参数下角接触球轴承保持架的稳定性与振动特性分析

保持架是角接触球轴承的重要元件之一,其引导间隙和兜孔间隙设计不合理会导致轴承运动失稳与共振。针对上述问题,在理论分析的基础上,结合滚珠、保持架和滚道之间的动态接触与变形关系,在ABAQUS软件中建立了7005型角接触球轴承的显式动力学模型,并提取了特定工况下该轴承内圈、保持架与滚珠的动态响应曲线;同时,研究了不同引导间隙和兜孔间隙下保持架的打滑率、质心涡动速度偏差比和各阶振动模态的固有频率。为了验证所建立的角接触球轴承显式动力学模型的准确性,对高速角接触球轴承各元件线速度的仿真值与理论值进行了对比。结果表明：随着引导间隙的增大,保持架的打滑率、质心涡动速度偏差比和各阶振动模态的固有频率均减小,保持架的稳定性增强,但共振风险增大;随着兜孔间隙的增大,保持架的打滑率增大,质心涡动速度偏差比变化不明显,各阶振动模态的固有频率减小,保持架的稳定性减弱,共振风险增大。高速角接触球轴承各元件线速度的仿真值与理论值的最大误差仅为0.099 6%,验证了所建立的显式动力学模型的准确性。研究结果可为高速角接触球轴承保持架的优化设计提供理论依据。     

侧滑角对超空泡航行体转弯运动沾湿区域的影响

为了提高通气超空泡航行体在转弯运动过程中空泡和航行体的运动一致性,基于有限体积法和VOF多相流模型,采用动态网格技术对航行体转弯运动的空泡形态特性进行了非定常数值模拟研究。通过对航行体沾湿区域的分析,揭示了沾湿区域形成的原因,利用空化器对空泡轴线的定向效应,提出了合理改变侧滑角减缓沾湿区域出现的具体方法。通过分析侧滑角和侧滑角速度对航行体沾湿区域的影响,提出了超空泡航行体转弯运动过程中,在给定偏航角条件下避免出现沾湿区域的侧滑角和侧滑角速度的适用范围,为进一步研究超空泡航行体机动运动问题提供参考。     

Thermoelastic contact of a retaining ring with a cylinder under the conditions of frictional heat generation

We give the mathematical statement and construct the solution of the static thermoelastic problem of contact interaction of an elastic retaining ring with a circular hollow cylinder inserted in it. The bodies are compressed by a load varying along the axis of the system under the conditions of load-free contact on the surface of the ring or along an arc of the circle. In the case where radial displacements of the contact surface of the retaining ring are approximated by displacements of the surface of a long circular hollow cylinder and the process of stationary frictional heat generation is taken into account, we reduce the posed problem to systems of integral equations whose structure is determined by the type of conditions of thermal contact. We propose a numerical algorithm for the solution of these systems and study the influence of the input parameters of the problem on the distributions of contact pressure and temperature. On the basis of these results, we make a conclusion that the influence of the character of variation of the compressive load along the axis on the distribution of contact pressure is significant in the case where the kinematic conditions of interaction of the bodies are described by the Hertz theory. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36. No. 3. pp. 42–52, May-June, 2000.     

某多用途货车传动系扭振试验分析与优化

某多用途货车加速行驶时,在发动机转速1200 r/min～1500 r/min范围内,传动系出现明显振动,影响整车NVH品质.针对此问题在传动系关键节点处加装传感器,对车辆6个前进挡在加速工况下进行扭振测试,由数据处理获得传动系各部位的角加速度振幅随发动机转速变化的关系.分析获得各部位振动的主要阶次,确定发动机2阶激励...     

求解混凝土等效断裂韧度的小波基无单元方法

考虑混凝土主裂缝亚临界扩展长度及虚拟裂缝区粘聚力,利用,积分与应力强度因子的解析关系,建立基于小波基无单元方法求解混凝土等效断裂韧度的数值方法,研究不同基底小波分辨率对混凝土等效断裂韧度计算值的影响。对8个带裂缝试件的混凝土等效断裂韧度的计算结果表明:在相同小波基分辨率下,4根体积系列试件的计算值的均方差和变异系数分别小于0.0244和0.0231,4根高度系列试件的计算值的均方差和变异系数分别小于0.0384和0.0362,计算结果的一致性好;与解析解相比,8个试件的计算值的最大相对误差均在5%左右,计算结果的精度高;且不同小波基分辨率对计算结果影响不大。由此得出结论,小波基无单元方法是求解混凝土等效断裂韧度的一种可靠的高精度数值方法,可以作为混凝土断裂力学的一种有力的计算工具。     

The Conditions for the Existence of the Optimal Thickness of a Cooled Anisotropic Wall Subjected to Local Heat Exposure

The problem of the determination of sufficient conditions for the existence of the optimal thickness of an anisotropic wall, one of whose surfaces of is exposed to axisymmetric stationary heat flux with the intensity of the Gaussian type, while the other is cooled by the external medium with a constant temperature, was formulated and solved using the two-dimensional exponential integral Fourier transform. The requirement for minimization of the temperature of the most heated point of object of study was used as an optimality criterion. The sufficient condition that was obtained is an inequality that establishes the link between the thermophysical characteristics of the anisotropic material of a wall, the intensity of heat transfer on its cooled surface, and the factor of the concentration of the outer heat flux. These results confirm the well-known effect of the “drift” of the temperature field in an anisotropic material with the common type of anisotropy of its properties.     

(火用)消耗及节能潜力的研究

分析了     

Diffraction of a one-dimensional phase grating in the deep Fresnel field

We analyze theoretically the diffraction of phase gratings in the deep Fresnel field on the basis of the theory of scalar diffraction and Green's theorem and present the general formula for the diffraction intensity of a one-dimensional sinusoidal phase grating. The numerical calculations show that in the deep Fresnel region the diffraction distribution can be described by designating three characteristic regions that are influenced by the parameters of the grating. The microlensing effect of the interface of the phase grating provides the corresponding explanation. Moreover, according to the viewpoint that the diffraction intensity distribution is the result of the interference of the diffraction orders of the grating, we find that the diffraction patterns, depending on the carved depth of the phase grating, are determined by the contributing diffraction orders, their relative power, and the quasi-Talbot effect of the phase grating, which results from the second meeting of the diffraction orders carrying most of the power of the total field, as in the case of the amplitude grating.     

The initial section of a plane nonisothermal jet developing under asymmetric conditions with and without combustion

A solution of the problem obtained with the method of integral relations is given here. It is obtained in the form of simple algebraic formulas for the boundaries of the mixing zones on both sides of the jet, the position of the flame front, and the axis of the jet at the end of the initial section. It is found that asymmetry of the boundary conditions has a substantial effect on the characteristics of the jet: the position of the axis of the jet at the end of the initial section can change its sign, depending on the temperature ratio at the boundaries of the jet and for given ratios of the velocity at the boundaries of the jet to the velocity of the jet outflow, the length of the initial section can change several fold.Moscow State Aviation Institute, Moscow, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 372–379, May–June, 1995.     

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.     

Fracture of Laser-Hardened Cylindrical Rods Caused by Torsion and Tension

We study the influence of the direction of motion of a laser beam over the surface of a cylindrical rod in the process of hardening on its strength and character of fracture caused by torsion. The process of hardening of specimens made of 45 steel performed in the tangential direction along a spiral and in the longitudinal direction along the generatrix with different degrees of overlapping of laser tracks results in the formation of an anisotropic structure, which strongly affects the investigated characteristics. The best results are obtained in the case where the direction of deformation of the rods coincides with the direction of screwing of a nut on a right-hand screw and the material of hardened tracks works in compression. In the case of torsion in the opposite direction, the material of hardened tracks works in tension and the strength of the specimens slightly increases. At the same time, their plasticity abruptly decreases.     

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.     

均布人群对简支欧拉梁动力特性的影响

研究了作用在梁上的均匀分布人群对梁的动力特性的影响.将人群简化为均匀分布的弹性质量模型,考察了无阻尼的弹性质量和有阻尼的弹性质量两种模型对简支欧拉梁的动力特性的影响,得到了人群和梁耦合系统的频率和阻尼的解析表达式.并以此研究了分布质量与梁的质量之比对梁的频率和阻尼比的影响,得到了人群对结构动力特性影响的定性规律.结果表明:耦合系统在人体振动基频处分支出一系列的振动频率,并且当分布人群质量与结构质量之比达到一定程度时,均布的人群会对梁的振动特性产生显著的影响,明显改变梁的自振频率,显著提高梁振动的阻尼比.最后研究了梁的振动频率对人群-梁耦合系统阻尼比的影响.