三峡永久船闸高边坡开挖三维离散元数值模拟

采用面-面接触的三维离散元刚性块体模型，从实测节理面中取出其中的三组，按照其倾向、倾角和节理间距将三峡永久船闸未开挖的区域划分为10~5个离散单元，通过施加力边界条件，给出了与实测初始地应力场接近的数值模拟结果；然后，分4步模拟了永久船闸的开挖过程。计算结果表明：开挖过程会引起节理面出现张开趋势，个别岩体还会沿着节理面滑移。岩体位移的不对称现象较为自然地说明了由节理引起的岩体各向异性特征。

允许变形及断裂的三维离散元计算方法

在三维离散元面-面接触刚性块体单元模型基础上,提出块体单元允许变形、断裂的一种计算模型.此计算模型不仅考虑岩块之间的节理刚度,而且考虑岩块自身变形以及岩块可能发生断裂的情况.

Transient Temperature Distribution in a Sheet Metal by Low-Energy Laser Scanning

Low-energy laser-heating techniques are widely used in engineering applications such as, thinfilm deposition, surface treatment, metal forming and micro-structural pattern formation. In this paper,under the conditions of ignoring the thermo-mechanical coupling, a numerical simulation on the spatialand temporal temperature distribution in a sheet metal produced by the laser beam scanning in virtue of thefinite element method is presented. Both the three-dimensional transient temperature field and thetemperature evolution as a function of heat penetrating depth in the metal sheet are calculated. Thetemperature dependence of material properties was taken into account. It was shown that, after taking thetemperature dependence of the material absorbance effect into consideration, the temperature change ratealong the scanning direction and the temperature maximum were both increased.

EQUIVALENT MODEL OF EXPANSION OF CEMENT MORTAR UNDER SULPHATE EROSION

The expansion property of cement mortar under the attack of sulfate ions is studied by experimental and theoretical methods. First, cement mortars are fabricated with the ratio of water to cement of 0.4, 0.6, and 0.8. Secondly, the expansion of specimen immerged in sulphate solution is measured at different times. Thirdly, a theoretical model of expansion of cement mortar under sulphate erosion is suggested by virtue of represent volume element method. In this model, the damage evolution due to the interaction between delayed ettringite and cement mortar is taken into account. Finally, the numerical calculation is performed. The numerical and experimental results indicate that the model perfectly describes the expansion of the cement mortar.

Torsion fracture behavior of drawn pearlitic steel wires with different heat treatments

In this paper, torsion fracture behavior of drawn pearlitic steel wires with different heat treatments was investigated. Samples with different heat treatments was investigated. Samples with different heat treatment conditions were subjected to torsion and tensile tests. The shear strain along the torsion sample after fracture was measured. Fracture surface of wires was examined by Scanning Electron Microscopy. In addition, the method of Differential Scanning Calorimetry was used to characterize the thermodynamic process in the heat treatment. A numerical simulation via finite element method on temperature field evolution for the wire during heat treatment process was performed. The results show that both strain aging and recovery process occur in the material within the temperature range between room temperature and 435 degrees C. It was shown that the ductility measured by the number of twists drops at short heating times and recovers after further heating in the lead bath of 435 degrees C. On the other hand, the strenght of the wire increases at short heating times and decreases after further heating. The microstructure inhomogeneity due to short period of heat treatment, coupled with the gradient characteristics of shear deformation during torsion results in localized shear deformation of the wire. In this situation, shear cracks nucleate between lamella and the wire breaks with low number of twists.

线性压电材料的有限元分析

本文利用线性压电学理论，编制了线性压电材料四结点等参有限元程序，进行了校核，并对PZT-5A材料压电智能元件和压电材料标准断裂试进行了计算，计算包括：①采用实际工程应用的压电智能元件尺寸，计算了元件的压电响应；并针对元件内部电极尖端区域容易引起破坏的现象，计算了该区域的奇异应力、应变场及电场。②计算了加力和加电两种情况下压电材料标准断裂试件应力强度因子影响系数F_I和电位移强度因子影响系数F_D。裂纹面边界条件采用D-P条件，试件包括紧凑拉伸标准试件和三点弯曲标准试件。③应用Lagrange乘子法将Parton裂纹边界条件加于有限元程序中，计算了上述两种标准断裂试件的F_I和F_D，计算结果与采用D-P裂纹边界条件的计算结果有很大差异。

A surface energy model and application to mechanical behavior analysis of single crystals at sub-micron scale

Size effects of mechanical behaviors of materials are referred to the variation of the mechanical behavior due to the sample sizes changing from macroscale to micro-/nanoscales. At the micro-/nanoscale, since sample has a relatively high specific surface area (SSA) (ratio of surface area to volume), the surface although it is often neglected at the macroscale, becomes prominent in governing the energy effect, although it is often neglected at the macroscale, becomes prominent in governing the mechanical behavior. In the present research, a continuum model considering the surface energy effect is developed through introducing the surface energy to total potential energy. Simultaneously, a corresponding finite element method is developed. The model is used to analyze the axial equilibrium strain problem for a Cu nanowire at the external loading-free state. As another application of the model, from dimensional analysis, the size effects of uniform compression tests on the microscale cylinder specimens for Ni and Au single crystals are analyzed and compared with experiments in literatures. (C) 2009 Elsevier B.V. All rights reserved.

An Improved Ce/Se Scheme For Multi-Material Elastic-Plastic Flows And Its Applications

In this paper, a new definition of SE and CE, which is based on the hexahedron mesh and simpler than Chang's original CE/SE method (the space-time Conservation Element and Solution Element method), is proposed and an improved CE/SE scheme is constructed. Furthermore, the improved CE/SE scheme is extended in order to solve the elastic-plastic flow problems. The hybrid particle level set method is used for tracing the interfaces of materials. Proper boundary conditions are presented in interface tracking. Two high-velocity impact problems are simulated numerically and the computational results are carefully compared with the experimental data, as well as the results from other literature and LS-DYNA software. The comparisons show that the computational scheme developed currently is clear in physical concept, easy to be implemented and high accurate and efficient for the problems considered. (C) 2008 Elsevier Ltd. All rights reserved.

New Numerical Algorithms in SUPER CE/SE and Their Applications in Explosion Mechanics

The new numerical algorithms in SUPER/CESE and their applications in explosion mechanics are studied. The researched algorithms and models include an improved CE/SE (space-time Conservation Element and Solution Element) method, a local hybrid particle level set method, three chemical reaction models and a two-fluid model. Problems of shock wave reflection over wedges, explosive welding, cellular structure of gaseous detonations and two-phase detonations in the gas-droplet system are simulated by using the above-mentioned algorithms and models. The numerical results reveal that the adopted algorithms have many advantages such as high numerical accuracy, wide application field and good compatibility. The numerical algorithms presented in this paper may be applied to the numerical research of explosion mechanics.

Numerical Study on Critical Wedge Angle of Cellular Detonation Reflections

The critical wedge angle (CWA) for the transition from regular reflection (RR) to Mach reflection (MR) of a cellular detonation wave is studied numerically by an improved space-time conservation element and solution element method together with a two-step chemical reaction model. The accuracy of that numerical way is verified by simulating cellular detonation reflections at a 19.3∘ wedge. The planar and cellular detonation reflections over 45∘–55∘ wedges are also simulated. When the cellular detonation wave is over a 50∘ wedge, numerical results show a new phenomenon that RR and MR occur alternately. The transition process between RR and MR is investigated with the local pressure contours. Numerical analysis shows that the cellular structure is the essential reason for the new phenomenon and the CWA of detonation reflection is not a certain angle but an angle range.

对数值模拟气相爆轰中二阶段化学反应模型再研究

采用改进的高精度时-空守恒元解元算法(the space-time conservation element and solution element method,CE/SE method)和考虑组分的二阶段化学反应模型(Sichel的二步模型)对气相爆轰问题的数值模拟进行了分析.分析发现采用Sichel的二步模型得到的数值结果虽然比早期二阶段化学反应模型(旧二步模型)更接近实验值,但是仍然不能得到爆轰过程准确气体动力学参数.为此通过修改组分的质量分数分布形式对Sichel的二步模型进行了改造,然后采用新的二步模型对平面爆轰波进行了数值模拟.数值结果表明采用新的二步模型计算得到气体动力学参数更接近于实验值和基元反应模型的计算值,在计算精度上有较大提高.

A CE/SE Scheme for Flows in Porous Media and Its Applications

In this paper, a new computational scheme for solving flows in porous media was proposed. The scheme was based on an improved CE/SE method (the space-time Conservation Element and Solution Element method). We described porous flows by adopting DFB (Brinkman-Forchheimer extended Darcy) equation. The comparison between our computational results and Ghia's confirmed the high accuracy, resolution, and efficiency of our CE/SE scheme. The proposed first-order CE/SE scheme is a new reliable way for numerical simulations of flows in porous media. After investigation of effects of Darcy number on porous flow, it shows that Darcy number has dominant influence on porous flow for the Reynolds number and porosity considered.

Numerical Study On Transient Flow In The Deep Naturally Fractured Reservoir With High Pressure

According to the experimental results and the characteristics of the pressure-sensitive fractured formation, a transient flow model is developed for the deep naturally-fractured reservoirs with different outer boundary conditions. The finite element equations for the model are derived. After generating the unstructured grids in the solution regions, the finite element method is used to calculate the pressure type curves for the pressure-sensitive fractured reservoir with different outer boundaries, such as the infinite boundary, circle boundary and combined linear boundaries, and the characteristics of the type curves are comparatively analyzed. The effects on the pressure curves caused by pressure sensitivity module and the effective radius combined parameter are determined, and the method for calculating the pressure-sensitive reservoir parameters is introduced. By analyzing the real field case in the high temperature and pressure reservoir, the perfect results show that the transient flow model for the pressure-sensitive fractured reservoir in this paper is correct.

Effects of rainfall infiltration on deep slope failure

With the finite element method and the limit equilibrium method, a numerical model has been estab-lished for examining the effects of rainfall infiltration on the stability of slopes. This model is able to reflect the variations in pore water pressure field in slopes, dead weight of the soil, and soil softening caused by rainfall infiltration. As a case study, an actual landslide located at the Nongji Jixiao in Chongqing was studied to analyze the effects of rainfall infiltration on the seepage field and slope sta-bility. The simulated results showed that a deep slope failure is prone to occur when rainfall infiltration leads to a remarkable variation in the seepage field, especially when the pore water pressure in slopes increases in a large range.

扩展有限元方法计算多夹杂问题时圆形夹杂与四边形单元的几何关系

用扩展有限元法XFEM(Extended Finite Element Method)解决夹杂问题时,夹杂与基质的界面把单元分成若干部分.求单元刚度矩阵时,需要分别在这各个部分求积分.找到便于程序编制的描述各积分区域几何形状的方法是亟待解决的问题.本文把各积分区域的形成过程看成是圆对四边形的多次切割.考虑切剩区域与圆的关系时,把不完整的边仍看作完整的边,把切剩区域看成是四边形或是切去一两条边的四边形.采用排列组合的方法,把它们与圆的所有位置关系列了出来.