堆石体三轴剪切试验的三维细观数值模拟

从细观角度出发,采用随机模拟技术建立堆石体的三维随机颗粒模型,基于修正的增广Lagrangian算法的非线性接触算法模拟颗粒间的相互接触,采用损伤软化模型描述细观单元的应力应变关系,当细观单元的损伤度超过损伤阀值时删除该单元,采用Weibull概率分布描述堆石体材料物理力学性质的非均匀性。以水布垭面板堆石坝茅口组堆石为研究对象,进行其三轴剪切试验的变形体离散元细观数值模拟,采用应变控制加载,再现了堆石体的颗粒变形和运动规律。数值计算结果表明,数值模拟能够较好地反映堆石体三轴试验的变形规律,得到的轴向应变–偏应力曲线和轴向应变–体积应变曲线接近试验曲线。从能量角度分析了颗粒变形、颗粒间的摩擦、颗粒的损伤破碎、颗粒运动在加载过程中对系统的贡献。     

Analytical modeling of complex contact behavior between rock mass and lining structure

Based on the nondestructive test data of operating railway tunnels in China, this paper summarizes the basic characteristics of the complex contact behavior between the rock mass and lining structure. The contact modes are classified into dense contact, local non-contact, and loose contact. Subsequently, the corresponding mechanical model for each contact mode is developed according to its mechanical characteristics using the complex variable method. In the proposed mechanical model, a special algorithm is introduced to detect whether the local non-contact zone is re-contacted. Besides, a novel conformal mapping method is also proposed to accurately calculate the mechanical response of the concrete lining. Finally, the accuracy of the proposed method is verified by comparing it with the finite element method (FEM). Several parameter investigations are conducted to analyze the effects of different contact modes on the rock–lining interaction. The results show that: (i) the height of the local non-contact area does not have a significant effect on the contact stress distribution if no re-contact occurs; (ii) backfill grouting can reduce the local stress concentration caused by poor contact modes; and (iii) reducing the friction coefficient of the interface can lead to a more uniform distribution of internal forces in the concrete lining.     

盾构管片接头interface模型与罚函数接触算法比较

以一类采用斜直螺栓、不设传力衬垫的盾构管片接头作为分析案例,就interface单元模型与罚函数接触算法以及相关参数对应关系等进行了比较,研究表明:(1)管片接头interface单元模型是罚函数接触算法的一种特殊形式;(2)罚函数接触算法中的接触面法向刚度对应interface单元压缩刚度,而“穿透深度”对应Interface单元法向位移;(3)在线性转动阶段,管片接头的转动弹簧模型(弹性铰)、Interface模型、接触算法等3种模型的转动刚度是等效的;(4)采用罚函数接触算法时,接触面法向刚度的选择必须满足转动刚度等效的条件。     

化工园区人员疏散路径模型及算法研究

针对化工园区突发事件中人员疏散问题,基于网络流控制理论,借助时间窗的概念研究了人员疏散过程中路径冲突和通道受阻问题,在Dijkstra算法基础上建立了多源点人员疏散最短路径模型,提出了模型算法和步骤,结合某化工园区的实例进行验证,结果表明：该疏散模型及算法可行,能有效地缩短人员疏散所需时间。     

顾及激光反射率的点云数据分割算法研究

点云数据分割是三维模型重建的关键环节,传统的基于模糊C均值聚类（FCM）的点云数据分割算法在规则物体细节的分割上具有一定的局限性。针对此问题,在传统算法的基础上,增加了激光反射率信息,提出了顾及激光反射率的分割算法。通过实例验证,该算法具有较高的可行性和普遍适用性,分类结果较为可靠。     

改进遗传神经网络的大坝渗流监测模型

在对遗传算法的适应度函数改进并修改选择方法的基础上,用改进的遗传算法优化BP神经网络权值,提出一种改进遗传神经网络的大坝渗流监测模型。结合实例分析表明:预测模型合理,训练精度与检测性能得到提高。     

Invisible elastic bolt model concept for finite element analysis of bolted connections

In accurate numerical modeling of bolted connections challenges are introduced due to the complexities encountered in meshing and providing non-conforming mesh for the exact modeling of bolt assemblages which may undermine the monotonic convergence in the solution algorithms. Thus, an elastic invisible bolt model is introduced to represent the bolt’s effect in the finite element modeling of bolted connections. The proposed algorithm assigns three degrees-of-freedoms (DOF) to each bolt’s end that include; one translational, in the bolt axial direction, and two rotational. Constraints are introduced for the DOF of the nodes in contact with the bolt head (or nut) such that they are permitted to move in the normal direction of the bolt based on the bolt elongation and end rotations. This introduces a variable-sized element stiffness matrix for the elements in contact with bolt ends. This bolt model is implemented in a general purpose cyclic plasticity-based finite element computer program, capable of predicting energy dissipation of bolted surfaces. Finally, the proposed algorithm is validated using a benchmark case and a sensitivity study on a hypothetical connection to ensure that the expected trend in energy dissipation is observed when geometric variables are varied.     

体内预应力钢屋架成形过程研究

具有几何大变形的体内预应力钢结构在成形过程中索与结构的接触摩擦将会耗散大量能量,为了准确确定索力和结构内力,本文采用接触有限元法(简称接触算法)对体内预应力钢屋架结构进行成形过程研究。与模型试验结果相比,用接触算法计算的索力和结构内力与试验结果吻合较好。本文还对比了结构成形过程采用接触算法和施加温度载荷算法(简称温度算法)的结构内力,结果表明温度算法可能存在安全隐患,文中提出安全设计建议,并指出引入接触算法的必要性。     

颗粒离散元方法中接触模型的开发

 在对颗粒离散元方法的理论基础进行深入研究的基础上,推导了广义Kelvin模型颗粒间接触力的理论解和数值解;采用面向对象的程序技术,通过颗粒离散元程序的接口,研制了广义Kelvin接触模型颗粒离散元计算程序;通过算例,验证了程序编制的正确性。在此基础上,以某深埋隧洞为例,计算不同接触本构模型条件下岩体的开裂破坏情况。结果表明,相对于弹性接触关系,采用广义Kelvin接触模型得出的结果与由Hoek-Brown强度准则得出的计算图更为接近。     

耗能支撑危险截面的有限元分析

应用ANSYS分析软件对T型截面防屈曲支撑进行单调荷载作用下三维有限元模拟,在模型中钢芯和混凝土之间采用接触单元,混凝土与钢套筒之间完全粘结。通过有限元模拟分析可知:当T型截面防屈曲支撑一端施加的面荷载增加到一定值时,构件应力最大值位于防屈曲支撑钢芯反面截面削弱处,此处是该构件的薄弱位置;构件应力最小值位于防屈曲支撑钢芯连接段反面处,此处是构件最安全位置。模拟分析与试验结果表明:T型截面防屈曲支撑最危险截面出现在加载端过渡段与工作段的连接处,该处可作为设计防屈曲支撑的控制截面。     

北京国际饭店蝶形箱基地基反力实验研究

荣获北京８０年代十大建筑之一的北京国际饭店，其天然地基蝶形箱基的设计超出了箱基设计与施工规程（ＪＧＪ６－８０）的范围，为了获得设计依据进行了室内模型试验，随后又进行了工程现场实测。本文重点介绍基础工程和土力学主要课题之一的地基反力分布性状实验结果，供设计和研究人员参考。     

考虑三维形貌特征的粗糙节理渗流空腔模型研究

 为研究粗糙节理中的渗流,建立节理渗流空腔模型。将节理平面离散成1 mm×1 mm的单元格,单元格节点处的隙宽值由节理三维空腔组合形貌确定,假设单元格内渗流服从立方定理,逐一对单元格进行分析,用连续性方程求解整个节理面渗流,编制MATLAB程序进行计算。用大理岩人工节理试件沿节理长度方向将同一节理上表面相对下表面分别错开1,2,3,4,5和6 mm,形成节理不同的接触状态,计算这6种情况下的节理三维空腔组合形貌,得到不同接触状态下节理的隙宽分布和平均隙宽值。将节理渗流空腔模型和立方定理在不同接触状态下的渗流计算结果与节理试件在不同接触状态下的室内试验结果进行比较。分析结果表明：节理渗流空腔模型计算结果比立方定理更接近室内渗流试验结果,但是空腔模型计算结果和试验结果还有一定的差距,并对其误差存在的原因进行分析。     

Numerical investigations on the thermo-mechanical behavior of steel-to-timber joints exposed to fire

A three-dimensional finite element model is developed to predict the thermo-mechanical behavior of steel-to-timber doweled joints in tension parallel to grain exposed to fire. To manage the plastic yielding of the materials, the mechanical model is based on the von Mises criterion for steel and the Hill criterion for timber. In fire, the material characteristics depend on the temperature. Two different meshes are used for the thermal and the thermo-mechanical models. The thermal model is continuous, to take account of the thermal continuity between the joint components. The thermo-mechanical model is discontinuous, to consider the contact evolution between the joint components. The thermal model is used to predict the evolution of the temperature field inside the joint which depend on the gas temperature. It is validated on the basis of measured temperatures during fire tests. The complex transformations in wood during fire are represented by apparent values of thermo-physical characteristics proposed in the bibliography and calibrated on the basis of the experimental measurements. The mechanical model is validated by comparison with the experimental results of joints in normal conditions. The thermo-mechanical model is validated by considering the experimental failure times of some joints. The numerical models showed a good capacity to simulate the behavior of the timber joints in cold and in fire situations. These developed and tested models can be used as a general tool to analyze the behavior of a large variety of joint configurations to constitute a data base that can be used in safe and economic practice of fire engineering of wood joints.     

基于AGA-PPGE的大型公共建筑室内环境质量评价

针对大型公共建筑室内环境质量问题,基于投影寻踪（PP）和加速遗传算法（AGA）,建立大型公共建筑室内环境质量评价模型。通过对实例的分析与评价,验证模型的可行性和有效性。     

基于遗传算法给水管网优化模型的改进研究

目前基于遗传算法的给水管网优化模型存在很多缺陷,为提高其实用性,对优化模型进行了改进.在约束条件中,用流量约束代替最小管径约束,并加入了流速约束.在此基础上,采用罚函数法对目标函数进行改进,实现了给水管网多工况优化设计.通过实例计算对比了各种设计方案,验证了改进后的优化模型在供水安全性和经济性方面的优越性.     

基于简支梁模型的岩体超低摩擦效应理论分析

 考虑深部煤层开采情况,基于塑性动力学理论建立岩体超低摩擦效应简支梁模型,通过理论推导得到动载荷作用下顶板在弹性阶段和弹塑性阶段,岩层与顶板间接触界面法向应力解析表达式,分析动荷载P(t)作用下接触面法向应力与初始接触面法向应力的比值(q/p)与顶板位置参数 及时间t的关系曲线,据此得到岩体接触界面摩擦力变化规律,从塑性动力学角度解释岩体超低摩擦效应。研究结果表明：动载荷作用下,顶板在弹性和弹塑性状态,岩层与顶板间接触界面法向应力均有所降低,且降低幅度十分显著,即其接触界面摩擦力急剧下降,具有“摩擦消失”效应,这充分说明岩体超低摩擦效应的存在;比较弹性变形阶段与弹塑性变形阶段接触界面法向应力变化,前者降低幅度更大,说明顶板在弹性阶段岩层与顶板间接触界面更易发生超低摩擦效应。     

接触动力学参数对隔震结构碰撞挡土墙#br# 动力响应影响分析

结合碰撞模型,根据已有的隔震结构试验,建立基础隔震结构碰撞挡土墙计算模型,研究接触刚度、隔离缝宽度、峰值地面加速度(PGA)和接触阻尼对隔震层动力响应的影响。计算结果表明：接触刚度与隔震层最大位移呈乘幂函数关系(指数为-1.49～-0.88),与隔震层最大速度呈乘幂函数关系(指数为10-3～10-2量级),与隔震层最大加速度呈正比例函数关系。隔离缝宽度与接触位移(隔震层最大位移与隔离缝的差值)、隔震层最大速度负相关,与隔震层最大加速度正相关。PGA与接触位移、隔震层最大速度和加速度正相关。接触阻尼对隔震层动力响应的影响受其他参数的影响较大;当接触刚度较小,且PGA较大或隔离缝宽度较小时,接触阻尼对隔震层最大位移、速度以及加速度有影响;其他情况时,影响不大。     

数值流形方法接触检索算法的改进

 数值流形方法(NMM)的接触理论是其一大特色,然而也是NMM在计算中耗时最多的计算部分,有必要提高NMM接触算法的效率。首先介绍NMM的覆盖系统和接触判断方法,着重分析NMM接触检索算法的效率及其所存在的缺陷。然后,根据NMM接触判断方法特点,定义接触阈值、接触线段以及每个接触线段的接触覆盖区,并提出求接触覆盖区x轴极值和y轴极值的方法。最后基于DESS(double-ended spatial sorting)接触检索算法对所求得的接触覆盖区极值进行空间排序,建立了新的NMM接触检索算法。改进后的接触检索算法,可以直接判断出具体的接触点–边对,以及具体的接触形式(角角接触或角边接触),且提升NMM接触检索算法的效率。     

A Kriging-based hybrid optimization algorithm for slope reliability analysis

First, the artificial bee colony (ABC) algorithm was used to optimize the Kriging model. A typical example was given to validate a good function fitting performance of the ABC-optimized Kriging model. Next, a structural reliability optimization method was proposed on the basis of the Kriging surrogate model, combined with the artificial bee colony optimization method and penalty function method. A nonlinear limit-state function example was provided to validate the accuracy and efficiency of the hybrid algorithm by comparing the algorithm’s solution with the exact solution of the example. Finally, the proposed method was applied to earth slope reliability analysis using a commercial finite difference program to calculate the slope’s factor of safety. Comparison of the results between the proposed method and the other methods shows that the proposed algorithm is the most suitable for slope reliability analysis.     

基于隧道-土体体系的时域子结构损伤识别方法

城市轨道地下结构在复杂环境和自身材质劣化等多因素作用下会产生不同程度的损伤,影响城市轨道地下结构的正常服役性能。为了实现城市地下结构的损伤诊断,本文基于动力响应灵敏度模型修正算法,提出了一种时域子结构损伤识别方法,实现了无需输入力和界面力信息情况下结构的损伤识别。针对城市地下结构的超长线状特性和复杂性,以隧道-土体体系的有限元模型为基础,推导了时域子结构动力响应关于结构刚度变化参数和力的正交参数的灵敏度矩阵,同时结合动力模型缩聚技术以降低结构的自由度数量,采用提出的时域子结构损伤识别方法可准确识别出隧道衬砌结构的损伤位置和程度,并与整体结构分析对比,验证了时域子结构识别方法的高效性。