Reevaluation of the adhesive relationship between the tire and the soil

The author proved in an earlier article that the shear diagram is not in accord with its mechanical definition. The shear stress cannot be zero at the beginning of the initial rising portion of the curve. Shearing is not an increasing loading process, rather it is a limiting case to which a finite shear stress belongs. On the other hand the sheared surface varies under the tire. There are kinematic reasons for this. Points on the tire surface describe a looped cycloid and they slip in a backward direction (opposite to the direction of travel) while contacting the soil. Thus the driving force, which points in the direction of travel, is the product of the shear stress of finite magnitude and the sheared area. The latter increases proportionally with slip. The author describes his equation which is based on the principles discussed above. He supports his theory with a numerical example.     

Nonlinear oscillations of a pendulum cable with the effects of the friction and the radius of the support

Nonlinear Dynamics - The dynamics of a pendulum cable with a special constitutive law subjected to a time-dependent velocity is investigated. The Coulomb friction between the cable of pendulum and...     

Similarity laws of the wind wave and the coupling process of the air and water turbulent boundary layers

The statistical properties of growing wind waves are known to obey certain self-similarity laws. One of these is expressed as the -power law relation between the significant wave-height and the significant wave period in nondimensional forms. Recent experiments on turbulence above and below laboratory wind waves indicate that both the air and the water layers have a structure which is similar to that of the turbulent boundary layer over a rough solid wall. The continuity of the momentum flux through the air and water boundary layers combined with the -power law of wind waves means that all the characteristic velocities related to the air-water boundary process are proportional to one another. Our laboratory experimental data on the several characteristic variables concerned support this picture. The state of local equilibrium as expressed by the -power law is thought to be brought about by the “breaking adjustment of the wind wave” which is required by the overall continuity of the velocity and the momentum flux across a thin surface layer. The above proportionality of the characteristic velocities provides a physical basis for the observed friction velocity scaling of the ocean mixed layer.     

On the singularity index and the unfolding of the diffraction catastrophes

The caustics of high-frequency wave propagation may be classified using catastrophe theory. The wavefield in the vicinity of any caustic is described by the corresponding diffraction catastrophe. The singularity index, β, is a measure of the rate at which such a wavefield diverges as ω→∞ at the point where all control parameters and moduli are set equal to zero. It is shown that away from this point β also describes a balance between two different measures of the unfolding of the wavefield in each control direction, β = σ_nϱ_n. The indices σ_n and ϱ_n describe, respectively, the rate at which individual ray arrivals separate in time and decay as a function of control parameter.     

Diffusion and Electrical Processes in the Turbulent Boundary Layer and in the Neighborhood of the Stagnation Point

The problem of electric current (engine current) formation in aircraft jet engine ducts as a result of the development of electrical diffusion boundary layers on the surfaces of the duct and internal engine components is investigated. It is assumed that the outer flow containing electrons and positive ions is quasi-neutral and that the electrical quasi-neutrality is violated (and the electric engine current develops) in the wall flow zone as a result of the difference between the electron and ion diffusion coefficients. The problem of the development of an electrical diffusion boundary layer inside the turbulent gasdynamic boundary layer on a plane surface is formulated and solved. The engine current distribution along the duct is found for various values of a turbulent viscosity on the boundary of the gasdynamic boundary layer which affect the laminar-turbulent transition point.The electrical diffusion processes that occurs when an electrically quasi-neutral hydrodynamic stream impinges on a plane surface (simulation of the flow in the neighborhood of a stagnation point) is studied. In this case the Navier-Stokes equations have a self-similar solution. It is shown that the system of electrohydrodynamic equations also has a self-similar solution. The electrical parameter fields are determined and the engine current is found on the basis of this solution.     

Numerical and Experimental Models of the Mandible

This study aimed to validate a numerical model of an intact mandible for further development of a new TMJ implant. Numerical and experimental models of the biomechanics of the mandible were elaborated to characterize the human temporomandibular joint and to approach the development of a condyle implant. The model of the mandible was obtained through the use of a polymeric replica of a human cadaveric mandible and through 3D geometry acquisition. The three-dimensional finite element model was generated as a tetrahedral finite element mesh. The level of mesh refinement was established via a convergence test and a model with more than 50,000 degrees of freedom was required to obtain analysis accuracy. The functional loading cases included muscle loading in four different load boundary conditions. The same boundary conditions were applied to the experimental model. The strains were measured with an experimental procedure using electric resistance strain gauges applied on the external surface of the mandible. The mechanical response is shown and discussed in terms of strains, principal numerical and measured strains. This study proved that FE models of the mandible can reproduce experimental strains within an overall agreement of 10%. The FE models correctly reproduced bone strains under different load configurations and therefore can be used for the design of a novel TMJ implant considering other load configurations and bone mechanical properties.     

合金元素Ta、Ag对镍基合金机械性能和摩擦学性能的影响及机理研究

利用高能球磨和真空热压烧结方法制备了添加Ta和Ag的镍基复合材料. 考察了复合材料在宽温域范围内的摩擦磨损性能和力学性能,利用SEM、XRD等表征分析其物相组成、磨损机理及断裂机制. 结果表明: 热压烧结过程中,Ta与石墨模具中的C反应生成TaC陶瓷相并在基体中弥散分布;Ta、Ag的加入降低了材料的摩擦磨损,NiCrMoAl-Ta-Ag复合材料实现了在室温~800 ℃的连续润滑,室温时Ag提供润滑作用,中温时由磨屑和Ag形成局部润滑膜,800 ℃时磨损表面形成了含氧化物、钼酸银和Ag的润滑膜. 加入Ta极大提高了材料的机械性能,NiCrMoAl-Ta合金在室温~1 000 ℃具有优异的机械性能,归因于原位生成的TaC和Al₂O₃陶瓷相的弥散强化;材料的断裂机制随温度升高由微孔聚集型断裂转变为以微孔聚集型和氧化断裂为主的断裂.      

捷联式惯性导航系统惯性元件的设置与可靠性

本文对惯性元件的最佳冗余设置及其在飞行器上的布局与可靠性之间的关系进行了研究，建立了相应的可靠性数学模型，探讨了３／６（Ｇ）冗余惯性元件出现第三个故障时故障的检测与识别的方法。所得结果可供惯性导航系统可靠性分析及工程上应用。     

线弹性幂强化材料平面杆系弹塑性分析的数值解

各杆任意铰接在一个刚体上的平面杆系是一种比较复杂的杆系结构,某些其它类型的平面杆系常常可以看作是它的特例。本文将材料的本构关系描述为线性幂强化形式,推导出了该类平面杆系结构弹塑性分析的普遍表达式,编制了通用程序,使这一类问题有了一个通用的解题方法。     

On the completeness and uniqueness of the Papkovich-Neuber and the non-axisymmetric Boussinesq,Love, and Burgatti solutions in general cylindrical coordinates

The exact conditions under which the Papkovich-Neuber, non-axisymmetric Boussinesq, non-axisymmetric Love and non-axisymmetric Burgatti solutions (to be defined below) are complete and unique for a general (not necessarily axi-symmetric) problem in general (not necessarily circular) cylindrical coordinates are investigated. They form four problems. The first one is the conjecture that any component of the curvilinear form of the Papkovich-Neuber solution can be omitted and also the general uniqueness of this solution in term of three harmonic functions. The remaining three concern the completeness and uniqueness of the non-axisymmetric Bousinesq, non-axisymmetric Love, non-axisymmetric Burgatti and a non-axisymmetric augmented Love solutions. Love's solution is shown to be incomplete for the case of a hollow sphere with the internal void pressurised.     

Connection between the characteristics of the signal of a shadow instrument and the spectrum of the turbulence

The shadow method is one of the most widely used methods for investigating turbulence [1, 2]. Using a shadow instrument with photoelectric recording, there exists, in principal, the possibility of finding the statistical characteristics of the turbulence from the statistical characteristics of the random signal taken from the instrument. In the present work, an investigation is made of the connection between the mean value and the scattering of the signal of a shadow instrument and the energy spectrum of optical inhomogeneities in the medium.     

Laser-doppler measurement of the velocity and diameter of bubbles using the triple-peak technique

The velocity and diameter of nitrogen bubbles rising in quiescent water were simultaneously measured by a dual-beam laser-Doppler anemometer. The range of bubble diameters was 0.8–1.8 mm. The triple-peak technique was used to obtain the bubble diameter from the anemometer signal. Using a single stream of bubbles, the horizontal area of the bubble-detection region was proportional to the square of the bubble diameter. Using additional streams of bubbles to generate an optical disturbance, the probability of detecting a valid signal decreased linearly with increasing bubble flowrate of the additional streams and was independent of their location and number. The maximum void fraction was 0.01.     

Quasiconvexity at the Boundary and the Nucleation of Austenite

Motivated by experimental observations of H. Seiner et al., we study the nucleation of austenite in a single crystal of a CuAlNi shape-memory alloy stabilized as a single variant of martensite. In the experiments the nucleation process was induced by localized heating and it was observed that, regardless of where the localized heating was applied, the nucleation points were always located at one of the corners of the sample—a rectangular parallelepiped in the austenite. Using a simplified nonlinear elasticity model, we propose an explanation for the location of the nucleation points by showing that the martensite is a local minimizer of the energy with respect to localized variations in the interior, on faces and edges of the sample, but not at some corners, where a localized microstructure, involving austenite and a simple laminate of martensite, can lower the energy. The result for the interior, faces and edges is established by showing that the free-energy function satisfies a set of quasiconvexity conditions at the stabilized variant in the interior, faces and edges, respectively, provided the specimen is suitably cut.     

On the buckling and the Strouhal law of fluid columns: the case of turbulent jets and wakes

An extension of the buckling model of oscillating fluid columns is presented that considers the nonuniform velocity profiles observed in various free turbulent flows. The buckling Strouhal number, defined as the reciprocal of the dimensionless wavelength, is calculated for some flows well documented in the literature. In all cases, the buckling Strouhal number is the same, despite the difference in flow configurations. The buckling model is compared with the universal Strouhal law, showing that the two models are equivalent to each other. Finally, a relationship between the maximum entropy generation and the difference between predicted and experimental Strouhal number is presented.     

Effect of the coefficient of condensation on the flow of vapor and the condensation at sub- and supersonic speeds

A method is presented for calculating the process of one-dimensional steady condensation at an arbitrary value of the coefficient of condensation. The method is based on the use of the solutions of [1], which were obtained for the case of total absorption of incident molecules on an interphase surface, and on application of the rule of scaling proposed in [4]. An analysis is made of an experiment [3] on supersonic flow of a stream of air onto a surface cooled by liquid helium.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 189–192, March–April, 1988.     

The Acoustic Analogy and the Prediction of the Noise of Rotating Blades

The acoustic analogy was introduced into acoustics by Lighthill in 1952 to understand and predict the noise generated by the jet of an aircraft turbojet engine. The idea behind the acoustic analogy is simple but powerful. The entire noise generation process is mathematically reduced to the study of wave propagation in a quiescent medium with the effect of flow replaced by quadrupole sources. In jet noise theory, Lighthill was able to obtain significant and useful qualitative results from the acoustic analogy. The acoustic analogy has influenced the theoretical and experimental research on jet noise since the early 1950s. This paper, however, focuses on another area in which the acoustic analogy has had a significant impact, namely, the prediction of the noise of rotating machinery. The governing equation for this problem was derived by Ffowcs Williams and Hawkings in 1969. This equation is a wave equation for perturbation density with three source terms, which have become known as thickness, loading, and the quadrupole source terms, respectively. The Ffowcs Williams–Hawkings (FW–H) equation has been used for the successful prediction of the noise of helicopter rotors, propellers, and fans. Several reasons account for the success and popularity of the acoustic analogy. First, the problems of acoustics and aerodynamics are separated. Second, because the FW–H equation is linear, powerful analytical methods from linear operator theory can be used to obtain closed-form solutions. Third, advances in digital computers and computational fluid dynamics algorithms have resulted in high-resolution near-field aerodynamic calculations that are suitable for noise prediction. We present some of the mathematical results for noise prediction based on the FW–H equation, including examples for helicopter rotors. In particular, we discuss the prediction of blade-vortex interaction noise and high-speed impulsive noise of helicopter rotors. For high-speed propellers, we briefly discuss the derivation of a singularity-free solution of the FW–H equation for a supersonic panel on a blade. Received 24 January 1997 and accepted 30 May 1997     

Evaluating the Impact of the Covariance of the Friction and Potential Gradient on Describing the Infiltration Process

During infiltration of water in soil, menisci form at the interface of water, grains, and air in the pores, inducing suction due to surface tension. Due to the random distribution of interconnected pores of different sizes, characteristic of porous media, differences in suction and friction inside pores give a diffusing infiltration front. The process of infiltration is often simulated by solving Richards’ equation in which the water flux is calculated with Darcy’s law. Underlying Darcy’s law is the assumption that the gradients in flow potential and the flow resistance due to viscous forces are independent from each other. This paper shows that these parameters are dependent and negatively correlated. A new method for calculating flows in unsaturated porous media has been developed to evaluate the impact of the covariance on infiltration predictions. The results show that the impact is significant and leads to a reduction in infiltration rate and mean friction experienced during infiltration. The method thereby provides a physical explanation for the subdiffusion observed during water infiltration in soil and is consequently expected to provide more insights into the processes of infiltration.     

Exact Analytical Solution of the Kirsch Problem within the Framework of the Cosserat Continuum and Pseudocontinuum

The Kirsch problem of onesided tension of a plate with a circular hole is considered within the framework of the nonsymmetric theory of elasticity under the assumption that material deformation is described not only by the displacement vector but also by the rotation vector. The general analytical solution of this problem is expressed in terms of the Bessel functions. The resulting solution is compared with the corresponding solutions for a symmetric medium and Cosserat pseudomedium. A macroparameter characterizing the distortion of the boundary of the circular hole upon deformation is introduced.     

船舶水润滑尾轴承当量半径等效计算及其摩擦学性能研究

水润滑尾轴承摩擦磨损性能是影响船舶工作性能的主要因素之一,合理预测水润滑尾轴承工作过程中的摩擦系数对其性能评估具有重要意义.目前对于水润滑尾轴承摩擦系数的理论计算公式已经存在.但由于销盘试验下无法有效获取当量半径,公式在销盘试验条件下的实用性不佳.对此在总结了边界润滑条件下,水润滑尾轴承摩擦机理的基础上,通过在CBZ-1销盘试验机上进行大量试验来进行当量半径等效参数计算公式的总结与摩擦系数经验公式的验证.研究结果表明:(a)在使用理论摩擦系数计算公式的前提下,当量半径等效参数公式拟合合理,具备较高准确性;(b)试验材料的理论摩擦系数与实际摩擦系数误差较小,为同类型试验摩擦性能研究提供了理论与试验基础;(c)水润滑尾轴承材料在工作过程中的摩擦力来源主要分为滞后摩擦力、犁沟摩擦力以及黏着摩擦力.当其处于边界润滑状态下时,滞后摩擦力为主要的摩擦力来源.该研究为水润滑尾轴承的等效当量半径在销盘试验条件下的应用提供了试验基础.     

An experimental and theoretical study of the effect of the elongational history on the dynamics of isothermal melt spinning

Isothermal spinning of a low-density polyethylene (LDPE) melt has been compared with isothermal creep under a constant force. Although the same initial stress was applied in both measurements, there was a tremendous difference in the stretch ratio vs. time curves, which demonstrates the enormous effect the flow before and in the capillary has on the rheological behaviour of a polymer melt.The modelling of the upstream flow as a plug flow with velocity inversely proportional to the square of the channel radius has been the basis of the development of a computer program incorporating the effect of the prehistory on the velocity profile during spinning. The constitutive equation used was a well tested, single integral constitutive equation containing a memory function and a nonlinearity function. The calculated results have been compared with isothermal spinning data for various boundary conditions. The agreement between calculation and experiment is encouraging and indicates the importance of the elongational component in the upstream flow.