Basic features of plastic strains: From micro-mechanics to incrementally nonlinear models

Most rate-independent constitutive relations for granular materials are based on the existence of a regular flow rule. This assumption states that once the mechanical state of a material point belongs to the yield surface, then the direction of the plastic strains is independent of the loading direction. In this paper, the notion of a regular flow rule is shown to exist only for two-dimensional and axisymmetric loading conditions. By considering our incrementally nonlinear constitutive model, it is established that this notion disappears as soon as more general loading conditions are applied, as also predicted from discrete element simulations. Moreover, a sound micro-mechanical interpretation of the vanishing of a regular flow rule in three-dimensional loading conditions is given from a multi-scale perspective using the micro-directional model. This model highlights the great influence of the loading history on the shape of the plastic Gudehus response-envelope.     

离散时间系统Ляпунов函数的构造与稳定性判定

本文旨在以矩阵的相似变换理论为基础,以电子计算机为工具,提供一种无需求解离散?矩阵方程,而直接由系统矩阵来构造离散时间系统?函数和判定系统稳定性的方法.     

Analysis of the Mechanism of Counter-current Spray Drying

Results of experimental investigations of the effect of drying and atomization parameters on counter-current spray drying are discussed. Based on 96 experimental tests, the local and global distributions of velocity, temperature, drying air humidity and moisture content of material dried in the drying tower were determined. Analysis of the results showed that the process of agglomeration during counter-current spray drying depended mainly on air temperature in the atomization zone.     

Parametric analysis of lugged wheel performance for a lunar microrover by means of DEM

The purpose of this study was to develop a numerical tool to simulate the performance of lugged wheels designed for a lunar microrover. The performance was analyzed using a Discrete Element Method (DEM) whose accuracy was validated for interactions between lugged wheels and soil. DEM analysis indicated that, on flat horizontal lunar surfaces, wheels with 18 10-mm-high lugs would provide less net traction than would wheels with 36 5-mm-high lugs.     

Time Discrete Approximation of Weak Solutions to Stochastic Equations of Geophysical Fluid Dynamics and Applications

As a first step towards the numerical analysis of the stochastic primitive equations of the atmosphere and the oceans,the time discretization of these equations by an implicit Euler scheme is studied.From the deterministic point of view,the 3D primitive equations are studied in their full form on a general domain and with physically realistic boundary conditions.From the probabilistic viewpoint,this paper deals with a wide class of nonlinear,state dependent,white noise forcings which may be interpreted in either the It6 or the Stratonovich sense.The proof of convergence of the Euler scheme,which is carried out within an abstract framework,covers the equations for the oceans,the atmosphere,the coupled oceanic-atmospheric system as well as other related geophysical equations.The authors obtain the existence of solutions which are weak in both the PDE and probabilistic sense,a result which is new by itself to the best of our knowledge.     

A discrete model for long time sintering

A discrete model for the sintering of polydisperse, inhomogeneous arrays of cylinders is presented with empirical contact force-laws, taking into account plastic deformations, cohesion, temperature dependence (melting), and long-time effects. Samples are prepared under constant isotropic load and are sintered for different sintering times. Increasing both external load and sintering time leads to a stronger, stiffer sample after cooling down. The material behavior is interpreted from both microscopic and macroscopic points of view.Among the interesting results is the observation that the coordination number, even though it has the tendency to increase, sometimes slightly decreases, whereas the density continuously increases during sintering—this is interpreted as an indicator of reorganization effects in the packing. Another result of this study is the finding that strongly attractive contacts occur during cool-down of the sample and leave a sintered block of material with almost equally strong attractive and repulsive contact forces.     

Representation of discrete sequences with high-dimensional iterated function systems

Iterated Function System (IFS) models have been used to represent discrete sequences where the attractor of the IFS is self-affine or piece-wise self-affine in R ² or R ³ (R is the set of real numbers). In this paper, the piece-wise hidden-variable fractal model is extended from R ³ to R ⁿ (n is an integer greater than 3), which is called the high-dimensional piece-wise hidden-variable fractal model. This new model uses a “mapping partial derivative” and a constrained inverse algorithm to identify the model parameters. The model values depend continuously on all the hidden variables. Therefore, the result is very general.     

Experimental validation of distinct element simulation for dynamic wheel–soil interaction

The deformation behaviour of the soil during dynamic wheel–soil interaction was studied by using the discontinuum modelling technique, distinct or discrete element method (DEM). The simulation model was developed using DEM for two types of soil, soil-A (coarse sand) and soil-B (medium sand). A transparent sided soil bin was used to observe the soil deformation. Three CCD video camera photographic images of the validation experiments were analyzed and compared with the simulation program results.This paper presents the simulation and validation results for two types of soil at three different vertical loadings of 4.9, 9.8 and 14.7 N. Wheel sinkage, vertical and horizontal draft force acting on the rigid wheel and the soil deformation images from the validation experiments were some of the data used to compare the simulation program results with the validation experiments. The simulation program was helpful to understand the complex deformation behaviour of the soils. The simulated results for the deformation behaviour of soil-B showed better correlation with the validation experiments than soil-A. The results obtained have also been compared with the previous work on DEM to explain phenomena such as the high simulated sinkage of the rigid wheel.