Measurement of soil parameters useful in predicting tractive ability of off-road vehicles using an instrumented portable device

An instrumented portable device that measures soil sinkage, shear, and frictional parameters in situ was developed to investigate the complexity of soil-traction device interaction process. The device was tested to determine its ability to measure soil frictional and shear characteristics. Extensive laboratory tests were conducted using dry and moist Capay clay and Yolo loam soils. In addition, field tests were also conducted in a Yolo loam field located at the UC Davis Agricultural Experiment Station. The Cohron sheargraph was also tested under the same laboratory experimental conditions to determine adhesion, soil-metal friction, cohesion, and angle of internal friction of soil. The analysis of experimental data indicated that soil adhesion and soil-metal friction were found to be functions of the intercept and slope values of cone torque versus cone index plot (r² = 0.94 and 0.95, respectively). Moreover, soil cohesion was found to be related to adhesion by the constrained adhesion relationship, and soil angle of internal friction was proportional to soil-metal friction as reported by Hettiaratchi [7] and [8]. These results imply that a simpler device consisting of a rotating cone can be developed to measure soil frictional and shear characteristics. Preliminary results showed that the soil parameters determined using this device predicted the maximum net traction developed by four different radial ply tires tested by Upadhyaya et al. [18] under similar soil conditions quite well. These results indicate that the parameters obtained from the device could be useful in obtaining traction related parameters of a soil-tractive device interaction process.     

Existence and stability of bushes of vibrational modes for octahedral mechanical systems with Lennard-Jones potential

The special non-linear dynamical regimes, “bushes of normal modes”, can exist in the N-particle Hamiltonian systems with discrete symmetry (Physica D 117 (1998) 43). The dimension of the bush can be essentially less than that of the whole mechanical system. One-dimensional bushes represent the similar non-linear normal modes introduced by Rosenberg. A given bush can be excited by imposing the appropriate initial conditions, and the energy of the initial excitation turns out to be trapped in this bush.In the present paper, we consider all possible vibrational bushes in the simple octahedral mechanical system and discuss their stability under assumption that the interactions between particles are described by the Lennard-Jones potential.     

库仑土压力的变分法研究

以滑动体静力平衡的两个力平衡方程为基础,引入拉氏乘子,将土压力问题以变分学观点来描述,转化为确定含有两个函数自变量的泛函极值问题。依据泛函取极值时必须满足的欧拉方程,得出了主动土压力和被动土压力在取极值时,墙后土体的破坏是沿平面滑动。然后,将土压力的泛函极值问题进一步转化为带有约束的函数极值问题。这种函数极值可利用M atlab6.1优化工具箱提供的fm incon函数进行求解。当土体的粘聚力等于0时,土压力计算结果与库仑土压力理论解完全一致;而当土体的粘聚力不等于0时,归纳给出了相应的土压力计算公式。     

Applications of the signs of Melnikov's function

The existence and stability of peridic solutions for the two-dimensional system x′=f(x)+g(x, a), O<ε<1,a∈R whoseunperturbed system is Hamlitonan be decided by using the signs of Melnikov's function. Theresults can be applied to the comstuction of phase portralts in the bifiacation set of codimension two bifurcations of flows with double aero eignvahues.     

Creep of axisymmetrically loaded plates with allowance for damage accumulation in their material

The Rabotnov kinetic creep theory was used to calculate the stress-strain state and damage accumulation in the material of axisymmetrically loaded circular and ring plates at any time before the beginning of fracture. It is shown that the solution of the problem can be reduced to solving the same problem under the assumption of steady-state creep of the material. The unsteady creep problem is solved by multiplying the known solution of the steady-state creep problem by certain functions of the coordinates and time, which are determined from a corresponding system of equations. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 157–168, September–October, 2006.     

Nonlinear Pressure Diffusion in Flow of Compressible Liquids Through Porous Media

In the flow of liquids through porous media, nonlinear effects arise from the dependence of the fluid density, porosity, and permeability on pore pressure, which are commonly approximated by simple exponential functions. The resulting flow equation contains a squared gradient term and an exponential dependence of the hydraulic diffusivity on pressure. In the limiting case where the porosity and permeability moduli are comparable, the diffusivity is constant, and the squared gradient term can be removed by introducing a new variable y, depending exponentially on pressure. The published transformations that have been used for this purpose are shown to be special cases of the Cole–Hopf transformation, differing in the choice of integration constants. Application of Laplace transformation to the linear diffusion equation satisfied by y is considered, with particular reference to the effects of the transformation on the boundary conditions. The minimum fluid compressibilities at which nonlinear effects become significant are determined for steady flow between parallel planes and cylinders at constant pressure. Calculations show that the liquid densities obtained from the simple compressibility equation of state agree to within 1% with those obtained from the highly accurate Wagner-Pru?  equation of state at pressures to 20 MPa and temperatures approaching 600 K, suggesting possible applications to some geothermal systems.     

Screw-matrix method in dynamics of multibody systems

In the present paper the concept of screw in classical mechanics is expressed in matrix form, in order to formulate the dynamical equations of the multibody systems. The mentioned method can retain the advantages of the screw theory and avoid the shortcomings of the dual number notation. Combining the screw-matrix method with the tool of graph theory in Roberson/Wittenberg formalism. We can expand the application of the screw theory to the general case of multibody systems. For a tree system, the dynamical equations for eachj-th subsystem, composed of all the outboard bodies connected byj-th joint can be formulated without the constraint reaction forces in the joints. For a nontree system, the dynamical equations of subsystems and the kinematical consistency conditions of the joints can be derived using the loop matrix. The whole process of calculation is unified in matrix form. A three-segment manipulator is discussed as an example. This work is supported by the National Natural Science Fund.     

Mesoscale measurement of strains by analyzing optical images of the surface of loaded solids

An algorithm for estimating the strains in solids at the mesoscale level, which is based on constructing fields of displacement vectors and calculating strain components, is studied and tested. Verification of the method is performed by comparing the analytically calculated strain components with experimental data obtained on the basis of model images and images recorded by a TOMSC optical TV measurement system during tension of polymer samples. The estimates of the strain components obtained by a correlation analysis of images are shown to be in good agreement with the results of analytical calculations for known loading parameters and sizes of the images under analysis. The results of the study confirm that the TOMSC system can be used to estimate local strains by processing images of the surface of loaded samples of materials. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 6, pp. 158–164, November–December, 2006.     

Interaction of a gasdynamic shock with small disturbances

The stability of shock wave based on the definition of Landau and Lifschitz^[1] is treated in this paper. This is tantamount to solving the problem of interaction of small disturbances with a shock wave. Small disturbances are introduced on both sides of a steady, non-dissipative, plane shock wave. Landau et al.^[1] obtained the stability criterionM ₁>1,M ₂<1 for small disturbances which are travelling in the direction perpendicular to the shock wave. In the present paper, we assume that the small disturbances may be two dimensional, i.e. they may be propagating in the direction inclined to the shock wave. The conclusions obtained are: regardless of whether the incident wave and diverging wave are defined according to the direction of the phase velocity or the group velocity, the shock wave is unstable for some frequencies and longitudinal wave lengths of the disturbances, even if the conditionsM ₁>1,M ₂<1 are fulfilled. Then several experiments are proposed, and the problem of ways to define the incident wave and diverging wave is discussed. The meaning of this problem is illustrated. The same results can be obtained for the steady shock wave in a tube.     

Numerical simulation of the flow field in a reactor for titanium dioxide production

A physicochemical and fluid dynamic model is formulated for the numerical simulation of the flow field in a reactor for titanium dioxide production, the turbulence motion is described by theKε equation, the governing equations are solved by the SIMPLER algorithm devised by Partankar and Spalding. The velocity, tmperature and concentration fields are obtained for three cases: A) with chemical reaction and thermal insulation on the walls; B) with chemical reaction and wall temperature is 450K; C) without chemical reaction and thermal insulation on the walls, and the physicochemical numerical simulation for the titanium dioxide production has been done. The results of the paper can be used as a theoretical guide for the engineers in the design of such reactors.     

A critical re-appraisal of the jet-thrust technique for normal stresses,with particular reference to axial velocity and stress rearrangement at the exit plane

It is shown that the thrust, T, exerted by a jet on the tube from which it flows, and the corresponding die-swell ratio, D, are closely related and dependent on the axial velocity and stress profiles at the exit plane. Velocity-profile data, calculated by Tanner using a finite element method, have been used to demonstrate that for a Newtonian liquid the reduction in measured thrust from the expected value arises from a re-arranged, non-parabolic axial velocity profile and the related re-arranged non-zero axial stress profile at the exit plane. The axial stress re-arrangement is the major effect.Using the correction-curve thus derived to determine the normal stresses, ν₁ + $\text{1}\text{2}$ν₂ aqueous and non-aqueous polymer solutions gives values that are higher than the “correct” results by a significant, substantial amount. The difference is not due to neglect of the second normal stress difference, ν₂, nor to the neglect of the wall pressure at the exit plane, which is shown experimentally to be very small. It is suggested that the difference, which is a function only of the shear stress (or rate of shear) at the wall, may arise from a difference in the stress profile associated with the velocity re-arrangement at the exit between Newtonian liquids and elasticoviscous liquids for which the extensional viscosity may be high.     

The Slope of Roofs

We consider a dome, modeled as a thin membrane of revolution, closed at the vertex and of unit height as shown in Figure 1. The membrane is loaded at the vertex by a force P, perpendicular to the axis of symmetry, and constrained at the base so that only membrane forces are transmitted to the ground. On assuming that the shape of the meridian is unknown, but the total volume, product of the surface area for the thickness, is given, we try to find the profile of the meridian which minimizes the highest stress at the base. It cannot yet be shown that the full problem admits a solution. However, comparison between some particular cases may give an idea of what the best shape of the dome must be.     

One-dimensional flow model for coal-gas outbursts and initiation criterion

This paper discribes a one-dimensional flow model to explain the basic mechanism of coal-gas outbursts. A break-start criterion of coal, as the elementary outburst criterion, is given approximately. In this ideal model, the tectonic pressure before excavation, as a load on coal body, affects the break-start and then the flow field. The flow field is decoupled with the stress field, so that the gas seepage through unbroken coal body, break-start and consequent two-phase flow, and pure gas flow can be analysed independently of the stress field. The tunnelling, an external disturbance that makes the seepage intensify relatively, is an essential factor for initiating outburst. Under steady tunnelling, seepage ought to tend to be steadily progressive. From its asymptotic solution initiation criterion is obtained. This is described by three conditions, possibility condition —tectonic pressure condition, incubation condition—tunnelling or gas condition and triggering condition —seepage velocity condition. The project supported by the National Natural Science Foundation of China     

ONSET CONDITION OF STRAIN LOCALIZATION IN MATRIX OF SATURATED POROUS MEDIA

Introduction Strainlocalizationofgeomaterialsisoneofmostpopularfailuretypesinnature,which canbeshowedaslandslidesandmudflowsinmountainousareasunderincessantorheavy raining,especiallythevegetationisseverelydamagedbywoodsharvest;pipingeffect,a typeoflocalfa…     

A model for extreme plasticity

We present a mathematical model for elastoplasticity in the regime where the applied stress greatly exceeds the yield stress. This scenario is typically found in violent impact testing, where millimetre thick metal samples are subjected to pressures on the order of 10–10² GPa, while the yield stress can be as low as 10⁻² GPa. In such regimes the metal can be treated as a barotropic compressible fluid in which the strength, measured by the ratio of the yield stress to the applied stress, is negligible to lowest order. Our approach is to exploit the smallness of this ratio by treating the effects of strength as a small perturbation to a leading order barotropic model. We find that for uniaxial deformations, these additional effects give rise to features in the response of the material which differ significantly from the predictions of barotropic flow.     

BASIC EQUATIONS, THEORY AND PRINCIPLE OF COMPUTATIONAL STOCK MARKET (Ⅲ)-BASIC THEORIES

By basic equations, two basic theories are presented: 1. Theory of stock’s value v^*(t)=v^*(0) exp (ar₂^*t);2. Theory of conservation of stock’s energy. Let stock’s energy Φbe defined as a quadratic function of stock’s price v and its derivative v, Φ=Av²+Bv+Cv²+Dv, under the constraint of basic equation, the problem was reduced to a problem of constrained optimization along optimal path. Using Lagrange multiplier and Euler equation of variation method, it can be proved that Φkeeps conservation for any v,v. The application of these equations and theories on judgement and analysis of tendency of stock market are given, and the judgement is checked to be correct by the recorded tendency of Shenzhen and Shanghai stock markets.     

The application of graph theory to the limit analysis for torsion of thin-walled bars with complex cross-sections

Graph theory is employed in this paper as a means to establish the topological model of complex thin-walled cross-sections. On this basis, the upper and lower bound theorems of the plastic limit analysis are applied to the analysis of the plastic limit shear flows on the cross-section of thin-walled bars under St. Venant torsion. Corresponding mathematical programming problems are formulated and their duality is shown. After solving the linear programming problem corresponding to the lower bound theorem, the limit torsional moment of a thin-walled cross-section can be calculated according to the shear stress distribution in the limit state. The formula for calculating the limit torsional moment is given. Furthermore, the limit state of thin-walled cross-sections under St. Venant torsion is also discussed and the concept of the limit tree is introduced. A computer program has been developed by the author. Results calculated by the program for typical complex cross-sections are given.     

Analysis of the Time Behaviour of a Diffusive Transport in a Stratified Medium

The paper presents a study of the diffusive transport of passive solute plumes in a two-dimensional non-homogeneous depth stratified flow domain. All the properties of the process are expressed by depth dependent deterministic functions. The method of moments, combined with the method of Green functions are chosen to determine the relevant characteristics of the flow (mass, center of mass, variance, etc.) used to describe the behaviour of the transient motion. General relationships for the n-order concentration moments are proved. Further, it is derived that the transient motion defined by time-dependent parameters tends asymptotically at large time to a stable regime whose characteristics are determined. Consequently, under certain hypotheses, an equivalence between the mean original process and a Fickian diffusive transport at large time may be established. The time required by the process to reach its asymptotic behaviour is also calculated.     

A meshfree-based local Galerkin method with condensation of degree of freedom for elastic dynamic analysis简

Condensation technique of degree of freedom is first proposed to improve the computational efficiency of meshfree method with Galerkin weak form for elastic dy- namic analysis. In the present method, scattered nodes with- out connectivity are divided into several subsets by cells with arbitrary shape. Local discrete equation is established over each cell by using moving Kriging interpolation, in which the nodes that located in the cell are used for approxima- tion. Then local discrete equations can be simplified by con- densation of degree of freedom, which transfers equations of inner nodes to equations of boundary nodes based on cells. The global dynamic system equations are obtained by as- sembling all local discrete equations and are solved by using the standard implicit Newmark＇s time integration scheme. In the scheme of present method, the calculation of each cell is carried out by meshfree method, and local search is imple- mented in interpolation. Numerical examples show that the present method has high computational efficiency and good accuracy in solving elastic dynamic problems.