A critical state model for sands dependent on stress and density

An elastoplastic model for sands is presented in this paper, which can describe stress–strain behaviour dependent on mean effective stress level and void ratio. The main features of the proposed model are: (a) a new state parameter, which is dependent on the initial void ratio and initial mean stress, is proposed and applied to the yield function in order to predict the plastic deformation for very loose sands; and (b) another new state parameter, which is used to determine the peak strength and describe the critical state behaviour of sands during shearing, is proposed in order to predict simply negative/positive dilatancy and the hardening/softening behaviour of medium or dense sands. In addition, the proposed model can also predict the stress–strain behaviour of sands under three-dimensional stress conditions by using a transformed stress tensor instead of ordinary stress tensor. Copyright © 2004 John Wiley & Sons, Ltd.     

Elastic solutions for stresses in a transversely isotropic half‐space subjected to three‐dimensional buried parabolic rectangular loads

In many areas of engineering practice, applied loads are not uniformly distributed but often concentrated towards the centre of a foundation. Thus, loads are more realistically depicted as distributed as linearly varying or as parabola of revolution. Solutions for stresses in a transversely isotropic half‐space caused by concave and convex parabolic loads that act on a rectangle have not been derived. This work proposes analytical solutions for stresses in a transversely isotropic half‐space, induced by three‐dimensional, buried, linearly varying/uniform/parabolic rectangular loads. Load types include an upwardly and a downwardly linearly varying load, a uniform load, a concave and a convex parabolic load, all distributed over a rectangular area. These solutions are obtained by integrating the point load solutions in a Cartesian co‐ordinate system for a transversely isotropic half‐space. The buried depth, the dimensions of the loaded area, the type and degree of material anisotropy and the loading type for transversely isotropic half‐spaces influence the proposed solutions. An illustrative example is presented to elucidate the effect of the dimensions of the loaded area, the type and degree of rock anisotropy, and the type of loading on the vertical stress in the isotropic/transversely isotropic rocks subjected to a linearly varying/uniform/parabolic rectangular load. Copyright © 2002 John Wiley & Sons, Ltd.     

Analytical solutions of one‐dimensional infiltration before and after ponding

This paper is a continuation of previous research, which obtained a convenient solution for arbitrary surface fluxes before ponding. By means of Fourier Transformation this has been extended to derive analytical solutions of a linearized Richards' equation for arbitrary input fluxes after surface saturation. Copyright © 2003 John Wiley & Sons, Ltd.     

GPS第三频载波及民用码的信号质量分析

介绍了L5载波的特点,分析了L5载波对GPS测量的影响,用实测数据分析了三频载波的信噪比及各个民用码的噪声水平。     

基于倾斜摄影测量技术的三维数字城市建模

使用较为先进的信息化手段,能够为城市的规划、建设、管理、运营以及一些应急措施的应用发挥良好作用。三维数字城市的建模,能够在很大程度上有效提高政府的实际服务和管理水平,从而有效增强城市的管理效率,为有效节约城市资源发挥重要的作用。本文主要从数字城市进行三维建模的现实状况入手,对倾斜摄影技术的内涵和技术特征进行详细分析,从而介绍基于倾斜摄影测量技术的三维数字城市建模项目的具体实施情况。     

东北三省城市扩展及植被覆盖状况

基于三期遥感影像数据( MSS、ETM、CBERS) 对城市建成区的面积进行了调查,研究30 多年来东北三省城市的扩展情况,并且结合NDVI 数据,对研究区范围内的植被覆盖情况进行了研究。结果表明: 1976-2000 年、2000-2007 年两个阶段,城市建成区的面积持续增加,年均扩展率由 5. 10%增加至6. 32%,扩展强度比较显著的区域主要分布在哈大交通经济带上; 研究区范围内东部的植被覆盖情况明显好于西部,NDVI 均值随与城市距离的增加而提高。     

The onset of chaotic motion in the restricted problem of three bodies

A full characterization of a nonintegrable dynamical system requires an investigation into the chaotic properties of that system. One such system, the restricted problem of three bodies, has been studied for over two centuries, yet few studies have examined the chaotic nature of some ot its trajectories. This paper examines and classifies the onset of chaotic motion in the restricted three-body problem through the use of Poincaré surfaces of section, Liapunov characteristic numbers, power spectral density analysis and a newly developed technique called numerical irreversibility. The chaotic motion is found to be intermittent and becomes first evident when the Jacobian constant is slightly higher thanC ₂.     

The action of chlorine on the ozone layer as given by a zonally averaged two-dimensional model

In order to study the behavior of stratospheric minor constituents related to aeronomic processes and atmospheric transport in the meridional plane, a numerical two-dimensional model is established.This model is applied to the study of chlorine compounds in the stratosphere. A special attention is devoted to the effect in the ozonosphere of an increase of CIX due to anthropogenic activities.     

Numerical modeling of three‐phase dissolution of underground cavities using a diffuse interface model

Natural evaporite dissolution in the subsurface can lead to cavities having critical dimensions in the sense of mechanical stability. Geomechanical effects may be significant for people and infrastructures because the underground dissolution may lead to subsidence or collapse (sinkholes). The knowledge of the cavity evolution in space and time is thus crucial in many cases. In this paper, we describe the use of a local nonequilibrium diffuse interface model for solving dissolution problems involving multimoving interfaces within three phases, that is, solid–liquid–gas as found in superficial aquifers and karsts. This paper generalizes developments achieved in the fluid–solid case, that is, the saturated case [1]. On one hand, a local nonequilibrium dissolution porous medium theory allows to describe the solid–liquid interface as a diffuse layer characterized by the evolution of a phase indicator (e.g., porosity). On the other hand, the liquid–gas interface evolution is computed using a classical porous medium two‐phase flow model involving a phase saturation, that is, generalized Darcy's laws. Such a diffuse interface model formulation is suitable for the implementation of a finite element or finite volume numerical model on a fixed grid without an explicit treatment of the interface movement. A numerical model has been implemented using a finite volume formulation with adaptive meshing (e.g., adaptive mesh refinement), which improves significantly the computational efficiency and accuracy because fine gridding may be attached to the dissolution front. Finally, some examples of three‐phase dissolution problems including density effects are also provided to illustrate the interest of the proposed theoretical and numerical framework. Copyright © 2014 John Wiley & Sons, Ltd.     

基于Hv方法的三轴液压振动系统频响函数估计的研究

三轴液压振动系统是实验室内模拟振动环境的主要设备,其主要功能是精确地复现给定的功率谱和时间历程。振动控制技术是实现这一目标的关键技术,它以频响函数估计为基础。频响函数估计的精度影响控制过程的快速性和稳定性。本文对几种典型的频响函数估计方法进行了分析,针对传统方法精度低且受到矩阵病态条件约束等缺点,应用特征分析与摄动理论构造了一种多入多出的Hv方法,并且应用三轴液压振动系统的实测数据对其进行了检验。结果表明该方法是适用的。