青藏铁路填土路基热-力耦合离散元研究

多年冻土是含有冰的特殊土体,在自然环境变化及工程扰动下易发生冻胀融沉变形,严重威胁着青藏高原工程建筑物的安全稳定,特别对青藏铁路的畅通运营提出了严峻挑战.以青藏铁路五道梁地区路基断面为研究对象,采用颗粒离散单元法,通过建立热-力离散元计算模型,对路基的温度场和变形进行了计算和预测.结果表明:离散单元法克服了有限元方法无...     

天体运行轨道的背景介质理论导引与自相似分形测度计算的分维微积分基础

通过讨论天体运行背景介质理论的连续轨道及离散轨道这二个研究方向的基础假设,介绍了天体运行轨道的具体方程形式及理论框架概要;进一步地通过讨论天体运行轨道Binet方程的一般形式及其行星近日点进动角的解,给出了连续轨道理论与Newton理论及Einstein广义相对论的联系与区别;通过讨论天体运行轨道的分维扩展方程,给出了包括太阳系行星、天王星卫星、地球卫星、绕月航天器等在内的离散轨道（稳定性轨道）方程及其预言数据.特别地,作为对天体在较为广泛区域作用曲线的初步探讨推论,指出仅由天体引力难以形成质量密度趋于无穷大的理想黑洞.通过讨论一般函数的分维导数的位置假设及幂函数的分维导数的形式假设,进一步明晰了幂函数的分维导数、分维微分及分维积分的具体方程形式,给出分维导数与分数阶导数的区别,随后讨论了基于一般分形测度的分维微积分形式定义导出的自相似分形的测度计算方程具体形式,给出了其与目前Hausdorff测度方法（覆盖方法）的区别,并对包括三分Cantor集合、Koch曲线、Sierpinski垫片及正交十字星形等自相似分形在内的测度进行了计算分析.     

球面退化四叉树格网的剖分及变形分析

为有效解决经纬度格网与四元三角网(QTM)在全球空间数据管理与操作中存在的不足,提出一种新的全球离散格网剖分方法——球面退化四叉树格网(DQG),给出该格网的剖分原理与编码规则,并对其进行几何变形计算与分析。结果表明:DQG既具有经纬度格网结构简单的特征,又具有QTM几何变形稳定等优点。     

A coupled discrete element model for the simulation of soil and water flow through an orifice

Soil erosion around defective underground pipes can cause ground collapses and sinkholes in urban areas. Most of these soil erosion events are caused by fluidization of the surrounding soil with subsequent washing into defective sewer pipes. In this study, this soil erosion process is simplified as the gradual washout of sand particles mixed with water through an orifice. The discrete element method is used to simulate the large deformation behavior of the sand particles, and the Darcy fluid model is coupled with this approach to simulate fluid flow through porous sand media. A coupled 3D discrete element model is developed and implemented based on this scheme. To simulate previous experiments using this coupled model considering the current computing capacity, we incorporated a ‘supply layer’ to study the continuous erosion process. The coupled model can predict the erosion flow rates of sand and water and the shape of erosion void. Thus, the model can be used as an effective and efficient tool to investigate the soil erosion process around defective pipes. Copyright © 2017 John Wiley & Sons, Ltd.     

The Fourier Integral Method: An efficient spectral method for simulation of random fields

The Fourier Integral Method (FIM) of spectral simulation, adapted to generate realizations of a random function in one, two, or three dimensions, is shown to be an efficient technique of non-conditional geostatistical simulation. The main contribution is the use of the fast Fourier transform for both numerical calculus of the density spectral function and as generator of random finite multidimensional sequences with imposed covariance. Results obtained with the FIM are compared with those obtained by other classic methods: Shinozuka and Jan Method in 1D and Turning Bands Method in 2D and 3D, the points for and against different methodologies are discussed. Moreover, with the FIM the simulation of nested structures, one of which can be a nugget effect and the simulation of both zonal and geometric anisotropy is straightforward. All steps taken to implement the FIM methodology are discussed.     

Sampling and Discrete Choice Analysis

Samples used to estimate discrete choice models in geography and regional science are typically assumed to be simple random samples. This assumption is not always met with existing samples. Furthermore, data collection is usually less costly if a stratified sampling strategy is adopted. Existing sampling theory suggests that stratified sampling can affect the consistency of parameter estimates. This paper reviews the salient points of this theory and relates theory to practice by means of a simple example on housing choice by elderly.     

Appreciation of Contributions by Georges Matheron and John Tukey to a Mineral-Resources Research Project

Georges Matheron (1930–2000) and John Tukey (1915–2000) were among the most prominent mathematical statisticians of the 20th century. Both men produced numerous important new theoretical and practical results. This personal appreciation of their work concentrates on contributions to mineral-resources research and describes their influence on my work in mineral-resource evaluation studies at the Geological Survey of Canada (1966–1983).     

正压模式中慢波的离散谱及其特征函数

本文对正压模式中慢波的离散谱及其特征函数作了数值计算。结果发现，在低速线性缓变切变基流的情形下，正压原始方程中慢波可有离散谱存在。本文还给出了在该基流下算得的谱点和特征函数，并与准地转模式的计算结果进行了比较。     

金江滑坡成因离散元模拟

在对金江巨型滑坡的工程环境条件及现今坡体物质组成、自身结构及变形破坏特征等方面调查研究的基础上,宏观判断滑坡为整体式滑移-弯曲破坏模式。为直观反映滑坡变形破坏的过程,根据对滑坡区基岩结构特征的分析,采用离散元软件2D_Block对滑坡成因机制进行模拟。根据滑坡普遍发育的地形地貌特征,恢复滑坡区原始斜坡地形,根据岩体结构划分模型计算单元,将地震效应考虑进2D_Block模型参数中。通过计算,展现了滑坡的发展演化过程,并将其分为三个阶段,即轻微隆起阶段、强烈隆起阶段、滑面贯通剪出阶段。