Establishing the Fundamentals of the Theory of Stability of Mine Workings

The fundamentals of the theory of stability of mine workings are analyzed. The theory is based on the linearized three-dimensional theory of stability of deformable bodies. Some results on horizontal and vertical mine workings and on underground closed cavities are analyzed     

Modeling of particle layer detachment-Role of transient kinetic effects

Particle layers tend to build up on walls in many filtration and separation processes, calling for periodic removal in order to keep the apparatus running. Important factors are the adhesion of the layer on the substrate and the cohesion of the particles in the layer. Models describing such layer detachment generally assume constant and homogeneous conditions for the forces acting on the layer. But in reality detachment is extremely non-stationary concerning place and time, primarily due to changing conditions of the detaching forces on the one hand and changes in the particle layer morphology on the other. This paper describes a model and a simulation based on this model considering such transient kinetic effects, for which some computing results are presented and discussed.     

Modelling of particle layer detachment-Role of transient kinetic effects

Particle layers tend to build up on wails in many filtration and separation processes, calling for periodic removal in order to keep the apparatus running. Important factors are the adhesion of the layer on the substrate and the cohesion of the particles in the layer. Models describing such layer detachment generally assume constant and homogeneous conditions for the forces acting on the layer. But in reality detachment is extremely non-stationary concerning place and time, primarily due to changing conditions of the detaching forces on the one hand and changes in the particle layer morphology on the other. This paper describes a model and a simulation based on this model considering such transient kinetic effects, for which some computing results are presented and discussed.     

Further study of the method of approach to testing the performance of extraterrestrial rovers/rover wheels on earth

The current practice for experimentally evaluating the performance of extraterrestrial rovers/rover wheels is to conduct tests on earth on a soil simulant, appropriate to the regolith on the extraterrestrial body of interest. In the tests, the normal load (force) applied by the rover/rover wheel to the soil simulant is set identical to that expected on the extraterrestrial surface, taking into account its acceleration due to gravity. It should be pointed out, however, that the soil simulant used in the tests is subject to earth gravity, while the regolith on the extraterrestrial surface is subject to a different gravity. Thus, it is uncertain whether the performance of the rover/rover wheel obtained from tests on earth represents that on the extraterrestrial surface. This issue has been explored previously. A method has been proposed for conducting tests of the rover/rover wheel on earth with identical mass to that on the extraterrestrial surface, instead of with identical normal load used in the current practice [1]. This paper provides further evidence to substantiate the merits of the proposed method, based on a detailed analysis of the test data obtained under various gravity conditions, produced in an aircraft undergoing parabolic flight manoeuvres [8]. In the study, the effect of slip on wheel sinkage has been evaluated. It is found that gravity has little effect on the slip and sinkage relationship of the rover wheel under self-propelled conditions.     

摩擦学白层的研究现状

综述了摩擦学领域的白层研究现旨出了当层（特别是微动白层）研究中存在的分歧和急论,分析归纳不同摩擦磨损条件下白层的形成条件和基本特征,重点讨论了白层的形成机制,提出了今后研究的方向。     

Gravitational-Tidal Model of Oscillations of Earth’s Poles

Based on the analysis of solar and lunar gravitational momentum, a viscoelastic Euler- Liouville model of the Earth’s pole oscillations is constructed. The model is based on taking into account the data on Earth’s shape and physical processes and does not involve the use of mathematical fitting methods, for example, based on polynomials. Within the framework of the model, the chandler frequency has themeaning of the fundamental frequency of the oscillations of the mechanical system, and the annual frequency is interpreted as the frequency of the compelling force. A delicate mechanism of oscillation excitation is found, based on a combination of eigenfrequencies and forced frequencies. The model has only six parameters, found from the experimental data of the least-squares method. The received forecast has high accuracy on an interval of several years.     

Slowing down of the growth of a crack of variable width under the influence of a temperature field

This paper touches upon changes in the temperature field near the ends of a crack of variable width under the action of an inhomogeneous stress field. The solution of the boundaryvalue problem on the equilibrium of the crack with partially contacting edges (there is adhesion of the edges on a certain part of the contact zone and slippage on another one) under the action of the outer inhomogeneous stress field, temperature field, and efforts on the contacting surfaces of the crack of variable width comparable with displacements in an elastic state is reduced to the problem of linear conjugation of analytic functions.     

Minimization of the drag of blunt edges of projecting elements of a hypersonic object

An approximate method is given for calculating the pressure on the critical line of a cylindrical edge of an element projecting above the surface of a hypersonic object. Correlations of the pressure distribution in the interference regions are proposed on the basis of the calculations and analysis of the experimental data. Variational problems of finding the form of a leading edge having minimum drag are set up and solved on the basis of the pressure calculation model obtained. The solutions are sought with the use of Pontryagin's maximum principle. The effect on the minimum drag profile of Mach numbers and blunting of the body is analyzed. The advantage of the optimal form of the edge in comparison with a corresponding rectilinear edge is shown.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 3–9, May–June, 1976.     

Equations of state of condensed media

We discuss a method for constructing the complete equation of state of a condensed medium thermodynamically, this method being based on the utilization of experimental data on shock compression and on the second law of thermodynamics. Determination of the accuracy of the solution so obtained, so far as its dependence on experimental error connected with the dynamical experiments and initial conditions was concerned, was carried out by means of statistical tests (Monte Carlo). The method is free from restricting assumptions as to the properties and nature of the medium under investigation. In the present paper, equations of state for W, Cu, and LiF are constructed. The results obtained are compared with experimental results and with equations of state based on models.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 156–166, November–December, 1972.The author thanks L. V. Al'tshuler and V. M. Ievlev for many discussions     

Effect of texture smearing on the anisotropy of cleavage-stress of metals and alloys

The effect of crystallographic texture smearing on the anisotropy of fracture stress of metals is analyzed. It is found that texture smearing leads to an appreciable decrease in the value of the coefficient of cleavage-stress anisotropy compared with that for metals with very sharp textures. The magnitude of this effect depends on the initial plastic strain (that depends on the breadth of texture component) and the level of stress triaxiality.     

涂层厚度对喷涂层疲劳磨损寿命影响的实验研究

采用等离子喷涂制备了不同厚度的铁基涂层,采用扫描电子显微镜（SEM）表征了涂层内部和结合界面处的微观结构,采用球盘式疲劳磨损试验机分别考察了不同厚度涂层的疲劳磨损行为,采用Weibull分布分析并对比了涂层的疲劳磨损寿命。结果表明：适当地增加喷涂层的厚度可以避免整层分层失效的发生,而从在整体上提升涂层的疲劳磨损寿命。采用有限元分析（FEM）研究了涂层内部的应力分布,发现厚涂层界面剪切应力值不足薄涂层界面剪切应力的二分之一,可见显著降低界面剪切应力是较厚涂层拥有更好疲劳性能的主因。     

Study of the damping characteristics of sectional flight vehicles of different length

The dependence of the damping characteristics of axisymmetric tri-sectional flight vehicles executing plane oscillations about the zero angle of attack on their geometric parameters is investigated on the supersonic range of uniform oncoming air flow Mach numbers. Systematic data are obtained using the least laborious approach, namely, by calculating the steady-state inviscid flow past equivalent bodies determined from the principle of the local similarity of force interaction. Ranges of the vehicle design parameters on which the dependence of the damping moment coefficient in pitch on the length of the conical or cylindrical-conical stabilizer of the vehicle is nonmonotonic are found. Typical viscosity effects on the characteristics under study are estimated using a method based on the assumptions of the linear theory for finite-thickness bodies. It is established that the damping coefficient increases monotonically with decreasing Reynolds number; moreover, even transition to oscillation antidumping regimes is possible when the sign of the damping coefficient changes.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 153–162. Original Russian Text Copyright © 2004 by Antonets and Shmanenkov.     

The influence of strong crosswinds on safety of different types of road vehicles

Strong crosswinds have a great influence on the safety of road vehicles. Different vehicle types may have different behavior under strong crosswinds, thereby leading to different dominant accident modes and accident risks. In order to compare the crosswind stability of road vehicles, a probabilistic method based on reliability analysis has been applied in this paper. The crosswind is simulated as a stochastic gust model with nonstationary wind turbulence. The vehicles are classified into several categories. For each vehicle type, a worst case vehicle model and the corresponding aerodynamic coefficients have been identified. Dominant accident modes and failure probabilities have been computed and are compared. The influence of road conditions (dry/wet) and wind directions on the crosswind stability has been taken investigated. The proposed model makes it possible to compare the effect of crosswind on different vehicle types based on a risk analysis.

     

钻井液流体特性对井下涡轮性能的影响

涡轮结构广泛应用于钻井工具,在对其进行仿真分析研究过程中通常采用清水作为介质,但该方法并不能比较确切地反映涡轮结构在井下实际的工作特征。针对该问题,本文建立了某型涡轮三维模型,采用Turbo Grid软件确定合理的网格参数,并进行了网格划分。采用Herschel-Bulkley钻井液流变模型研究了钻井液流体参数对涡轮结构的输出扭矩和效率的影响。基于响应面法,采用Box-Behnken设计方法得到了钻井液流体参数与涡轮性能指标的关系。结果表明,相较于稠度指数和流变指数而言,钻井液的密度和动切力对涡轮结构的输出扭矩和效率影响显著。因此,在探讨钻井液流变参数对涡轮性能影响时,应该优先考虑钻井液的密度和动切力特性。     

Analysis of the fluid-bed stability of FCC catalysts at high temperature in terms of bed elasticity

The effect of temperature on the fluid-bed stability of three FCC catalysts has been analyzed through considerations on fluid-bed elasticity. Experimental findings on the effect of temperature on the elasticity modulus at minimum bubbling conditions, （E）mb, were analyzed using the hydrodynamic fluid-bed stability model developed by Foscolo and Gibilaro （1984） and adopting the interparticle-forces-based stability criterion developed by Mutsers and Rietema （1977）. For both models, the parameters which control changes in （E）mb with temperature are discussed, in order to establish the origin of the fluid-bed elasticity and analyze the ability of these models to discriminate between the relative importance of the hydrodynamic and interoarticle forces on the stability of the fluidized catalysts.     

Effect of frequency of air flow on the performance of the Wells turbine

Experimental investigations on the effect of Strouhal number and rotor solidity on the performance of 0.2m diameter Wells self rectifying air turbine with NACA 0021 profile blades are presented. The results show an increase in starting torque with the Strouhal number of airflow and rotor solidity. The effect of Strouhal number on the running performance of the turbine is solidity dependent     

Motion of Solid Particles in a Liquid under the Action of an Acoustic Field: the Mechanism of Radiation Pressure

This paper is a review of studies on the motion of solid particles in perfect and viscous liquids under the action of time-average forces caused by an acoustic field. Emphasis is on studies that employed a method based on solving the hydromechanic equations for a compressible liquid and evaluating and averaging the forces acting on particles     

A study of directionality of latent hardening behavior in aluminium single crystals

By defining the yield stress in a latent hardening test as the first deviation from the elastic straight line, the yielding and hardening behavior on a latent system in the positive and negative slip direction was studied in aluminium single crystals. It is shown that the yield stresses on both the positive and negative latent systems are about equal to or a little lower than the maximum resolved shear stress in the primary test, but much higher than that of the active system. The influence of relative orientation and prestrain on latent hardening and initial work-hardening in the secondary test was also investigated, and it was found that there is a considerable effect on initial work-hardening, but none on latent hardening. With reasonable approximation, a hardening rule for single crystal could be proposed from the experimental results, that is, except for the yield stress on the system negative to the active system that is very low, hardening on the other systems is nearly the same as self-hardening.     

Mesoscopic numerical computation model of air-diffusion electrode of metal/air batteries

This work creates a droplet battery model based on the electrolyte performance in the porous electrode, studies the current density on the mesoscopic scale, and explains how the mesoscopic structure of the porous electrode influences the current density on the air-diffusion electrode. Near the three-phase line, there is a strong band containing nearly 80% current. For porous electrodes, the total current is proportional to the length of the strong band. Thus, it can be inferred that on the macroscopic scale, the longer the total length of the strong band on unit area is, the larger the current density is.     

Design of a two-element airfoil in a range of angles of attack

A numerical-analytical solution of an inverse boundary-value problem of aerohydrodynamics is obtained for a two-element airfoil in the full formulation, based on the velocity distribution defined on the sought airfoil contours in a range of angles of attack. It is demonstrated that flow separation does not occur in the entire range considered for a specified non-separated velocity distribution on the upper surfaces at the maximum angle of attack and on the lower surface at the minimum angle of attack. An example of constructing a sectional airfoil is given; verification of the results obtained is performed with the use of the Fluent software package. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 107–114, November–December, 2008.