基于无网格一图论方法的岩体边坡稳定性分析研究

将无网格伽辽金法应用于岩体边坡稳定性分析，发展了基于无网格模型和有向加权图Bellman—Ford最短路径搜索算法相结合的无网格-图论边坡滑移面搜索方法，以搜寻节理岩体边坡失稳时的临界滑移面并得出其相应的安全系数。区别于传统的滑移面搜索算法，本文方法无需假定滑移面形状，更适用于具有复杂滑移线形状的节理岩体边坡的稳定性分析与计算，具有稳定和高效的算法特点。文中详细论述了无网格-图论最短路径算法的理论、方法和程序实现，并通过算例说明该方法在岩体边坡稳定性分析中的适用性。     

基于ICMP和图论算法的边坡稳定性分析

ICMP(Independent Cover Meshless Particle)方法利用与分析区域任意几何形状无关的离散结点及其独立矩形影响域覆盖分析物体,采用一般多项式作为结点的无网格插值函数,较好地克服了传统无网格方法面临的一些困难.本文借助ICMP方法,计算得到边坡的应力场分布,并将边坡稳定性分析转化为图论问题,利用Bellman-Ford搜索算法快速稳定地寻找出边坡的安全系数和最危险滑裂面,发展了一种新的ICMP-图论边坡稳定性分析方法.该方法计算过程和数值实施简单,无需做过多假设及迭代计算,适合于复杂地层条件、几何形状的边坡稳定性分析,具有稳定和高效的算法特点.相关典型算例验证了本文方法的适用性和正确性.     

节理岩体边坡的动力稳定性分析

阐述了动力离散元的原理及计算方法, 并将其用于一个受高烈度地震威胁的滑节理岩体边坡的动力响应分析与动力稳定性评价, 阐明了滑坡动力稳定性分析的必要性。     

大瑞铁路澜沧江大桥工程边坡岩体结构特征研究

岩体中结构面的展布及其组合特征决定了岩体的工程地质性质和力学性状,影响着岩体的破坏方式。大瑞铁路澜沧江大桥所处的澜沧江构造带,具有高地震烈度、活跃的新构造运动、活跃的外动力地质条件、活跃的岸坡浅表改造过程等地质特征。工程区两岸节理裂隙等弱面发育,岸坡浅表改造过程强烈,导致岩体结构复杂。通过野外现场调查,对两岸边坡岩体结构面数据进行统计分析,采用^x2检验与K-S检验法对结构面进行概率密度拟合,分析岩体结构特征。结果表明：(1)右岸的优势结构面有三组; (2)左岸的优势结构面有四组; (3)各组优势结构面产出状态数据均服从正态分布。在统计分析结果的基础上,建立两岸岩体结构的统计模型,并对边坡破坏模式进行定性分析,认为：(1)右岸边坡变形破坏模式为滑移 压致拉裂; (2)左岸结构面贯通性不好,主要的破坏模式是局部块体滑移。
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隧道围岩强度不均地段塌方成因及其处理方法

采用微面模型理论和损伤力学方法，建立了节理岩体的弹塑性损伤耦合微面模型. 在节理岩体的微 面上，将岩体视为由节理面与岩石组成的二元介质，以节理连通率作为岩体沿该方向的面积 损伤变量，考虑微面法向拉应力和压应力下的不同塑性变形和损伤耦合作用机制，基于塑性 理论建立了节理岩体的微面塑性损伤增量本构关系. 采用微面物理量与宏观物理量的几何约 束模型，根据微面方向积分导出了节理岩体的宏观弹塑性增量本构关系. 编制了节理岩体微 面模型的MARC有限元子程序，对节理岩体的单轴拉伸、压缩试验和泥浆压力作用下的井壁稳 定问题进行了数值模拟研究. 数值计算结果表明，该模型能很好地揭示载荷作用下节理岩体 的各向异性非弹性变形和次生节理演化过程.     

节理岩体能量损伤本构模型与工程应用

本文根据Betti能量互易定理,节理岩体能量损伤演化方程,广义正交法则和塑性损伤一致性条件建立了节理岩体的能量损伤本构模型,并将该模型编制成三维非线性有限元计算程序应用于溪洛渡地下厂房洞室群施工开挖稳定性分析,获得了较为满意的计算结果。     

基于有限差分强度折减法的多级边坡破坏模式研究

总结了当前多级边坡的稳定性分析方法,引入FLAC^3D程序和强度折减理论,并运用有限差分强度折减法研究了多级边坡随台阶宽度变化的破坏模式、变形及其稳定性。分析结果表明:多级边坡的滑移面的位置、形状和破坏模式随着台阶的宽度不同而不同,且其变形也随着台阶的宽度不同表现出不同的特性。最终通过对多级边坡进行稳定性分析,发现安全系数和滑移面广义剪应变大小也随台阶宽度的变化也表现出一定的规律性。     

内排及削坡对露天矿边坡稳定性影响的实验分析

露天矿边坡稳定是煤矿工程安全生产的主要问题之一。采用内排压脚和削坡减重措施对增强边坡稳定作用较大,有利于现场开采安全。以安家岭露天矿29209工作面为研究对象,采用相似材料模型和数值模拟相结合的方法,研究内排及削坡对露天矿边坡稳定性的影响。研究结果表明,上覆岩层的垮落和变形形成的"拱式"结构使得岩体向边坡临空面方向发生水平移动,造成边坡岩体的开裂,甚至形成滑移面或潜在滑移面;随工作面的推进,地表形成W型沉陷形状,沉陷区域波及到坡面位置,累计沉降值达到2m左右;内排和削坡措施可有效减小边坡沿煤层上下面的错动;边坡的变形破坏以层间错动为主,同时伴有朝向采空区的塌陷;当工作面推进超过设计停采线50m时,垂直方向裂隙带下沉,1360平盘向边坡临空面水平推移约3m,形成典型"推移式"滑坡模式。     

龙滩水电站蠕变体B区折断面及折断错滑面成因分 析

通过对广西龙滩水电站左岸边坡蠕变体B区折断面和折断错滑面地质特征,变形特征,滑带充填物特征以及力学参数研究,结合监测,岩体风化以及构造特征、表层岩土体滑移-牵引等特征分析,认为折断面和折断错滑面的形成主要是由于边坡岩性以及河水侵蚀等作用下,岩体的风化差异所造成的,而且在目前有效的工程处理下,由监测资料可知,边坡变形波动较大,变形量值小,没有明显的滑移趋势,稳定性较可靠。     

基于非结构任意多边形网格的滑移面计算技术

基于任意多边形网格管理体系,针对流体多介质问题的数值模拟,发展了拉氏方法滑移面计算技术.文章给出了滑移线设置的数据结构,滑移线上主从点速度与位置的计算格式,及节点滑移后引起界面上点、相关网格邻域关系变化的算法.该滑移计算技术避免了传统算法中由于以模拟法(重叠或分离网格)代替直接法(拼接网格)而造成几何守恒律被破坏的缺陷.数值例子验证了该算法的可行性,体现了算法无缝连接的特点.     

A type of biased consensus-based distributed neural network for path planning

In this paper, a unified scheme is proposed for solving the classical shortest path problem and the generalized shortest path problem, which are highly nonlinear. Particularly, the generalized shortest path problem is more complex than the classical shortest path problem since it requires finding a shortest path among the paths from a vertex to all the feasible destination vertices. Different from existing results, inspired by the optimality principle of Bellman’s dynamic programming, we formulate the two types of shortest path problems as linear programs with the decision variables denoting the lengths of possible paths. Then, biased consensus neural networks are adopted to solve the corresponding linear programs in an efficient and distributed manner. Theoretical analysis guarantees the performance of the proposed scheme. In addition, two illustrative examples are presented to validate the efficacy of the proposed scheme and the theoretical results. Moreover, an application to mobile robot navigation in a maze further substantiates the efficacy of the proposed scheme.     

Predicting Tortuosity for Airflow Through Porous Beds Consisting of Randomly Packed Spherical Particles

This article presents a numerical method for determining tortuosity in porous beds consisting of randomly packed spherical particles. The calculation of tortuosity is carried out in two steps. In the first step, the spacial arrangement of particles in the porous bed is determined by using the discrete element method (DEM). Specifically, a commercially available discrete element package (PFC^3D ) was used to simulate the spacial structure of the porous bed. In the second step, a numerical algorithm was developed to construct the microscopic (pore scale) flow paths within the simulated spacial structure of the porous bed to calculate the lowest geometric tortuosity (LGT), which was defined as the ratio of the shortest flow path to the total bed depth. The numerical algorithm treats a porous bed as a series of four-particle tetrahedron units. When air enters a tetrahedron unit through one face (the base triangle), it is assumed to leave from another face triangle whose centroid is the highest of the four face triangles associated with the tetrahedron, and this face triangle will then be used as the base triangle for the next tetrahedron. This process is repeated to establish a series of tetrahedrons from the bottom to the top surface of the porous bed. The shortest flow path is then constructed geometrically by connecting the centroids of base triangles of consecutive tetrahedrons. The tortuosity values calculated by the proposed numerical method compared favourably with the values obtained from a CT image published in the literature for a bed of grain (peas). The proposed model predicted a tortuosity of 1.15, while the tortuosity estimated from the CT image was 1.14.     

The Kinematic Flow Structure for the Gvirtzman–Gorelick In Situ VOC Remediation System

Potential theory and Stokes' stream function techniques are used to investigate the flow structure around the recirculation system developed by Gvirtzman and Gorelick (1992, 1993), which consists of an extraction well and a gallery (trench) for the recharge of treated water to the aquifer. Analytical formulas are derived for the drawdown, velocity, and stream function for a model in which the extraction well is modeled as a uniformly distributed line sink and the gallery is modeled as a uniformly distributed ring source. Travel times are reported for water particles traveling along the streamlines containing 50 and 90% of the flow for various degrees of well penetration and various radii of the ring source. The travel times along the streamline resulting in the shortest travel time (not necessarily the shortest path) are also reported for various degrees of well penetration and various radii of the ring source. The method completely eliminates the use of numerical finite-difference or finite-element methods and can be used for optimization of technological parameters of this remediation system.     

基于误差四元数的捷联惯导全姿态导航与控制

在舵偏控制回路中使用欧拉角姿态信息,是现有飞行器捷联惯导系统普遍采用的方法。为避免垂直状态时欧拉角姿态表示法的算法奇异问题,引入了四元数姿态表示法,但是最终形成偏差输入到舵机的仍旧是欧拉角姿态信息。对此问题,文中分析讨论了捷联惯导系统中,以欧拉角信号控制飞行器舵偏输出(推力矢量输出)的传统方法的两点不足之处:垂直状态时欧拉角姿态算法的物理奇异问题;控制路径过长问题。提出由误差四元数直接控制舵偏输出(推力矢量输出)的新的捷联导航方法。此方法控制路径最短,且克服了物理奇异问题,不局限于飞行器所处的姿态,因此,将其称之为全姿态导航方法。仿真结果表明了此方法的可行性与有效性。     

The Role of Tortuosity in Upscaling

The concept of tortuosity is an integral part of models that describe transport in multiscale systems. Traditionally, tortuosity is defined as the ratio of an effective path length to the shortest path length in the microstructure. While the shortest path length can be unambiguously specified, the same is not true for the effective path length, since it changes from one type of transport to another. Consequently, it is possible to have different values of tortuosity for different transport processes taking place in the same system. This is convenient since, under this approach, different transport processes can involve the same type of filters of the microscale information, but the nature of such information is what characterizes each type of transport process. In order to avoid running into unclear interpretations, a set of tortuosity rules are proposed, which relate this concept only to the microscale geometry. On the basis of these rules, we examine the pertinence of introducing the tortuosity concept in mass transport. In particular, we study mass diffusion with and without chemical reaction and convection in porous media. Of all these cases, our analysis indicates that the concept of tortuosity is only adequate for passive diffusion, since in the other cases there is an unavoidable coupling of the transport phenomena that determine the effective path of the solute.     

A novel optimal path-planning and following algorithm for wheeled robots on deformable terrains

An immense body of research has focused on path-planning and following of wheeled robots in unstructured surfaces. Nonholonomic robots traveling over deformable terrains together with complex operating conditions, however, pose further challenges in terms of a higher demand for robustness and optimality. In this paper, a Chaos-enhanced Accelerated Particle Swarm Optimization (CAPSO) algorithm is employed for planning an optimal path of a wheeled robot, so as to ensure shortest path from the starting point to the target location together with safety through guaranteed avoidance of collisions with static and dynamic obstacles. The fundamental terramechanics concepts are employed to derive essential forces and moments acting on the wheeled robot. Subsequently, a kineto-dynamic model of the robot is developed for designing a novel robust control algorithm based on an exponential-integral-sliding mode (EISMC) scheme and a RBF-NN approximator. The results revealed that the proposed algorithm is responsive and robust to withstand adverse effects of structured and unstructured uncertainties by using the designed adaptation law according to the Lyapunov stability theorem. The effectiveness of the proposed algorithm is also validated against several reported frameworks.     

Frictional passage of fluid through inhomogeneous porous system: a variational principle

A Fermat-like principle of minimum time is formulated for nonlinear steady paths of fluid flow in inhomogeneous isotropic porous media where fluid streamlines are curved by a location dependent hydraulic conductivity. The principle describes an optimal nature of nonlinear paths in steady Darcy’s flows of fluids. An expression for the total path resistance leads to a basic analytical formula for an optimal shape of a steady trajectory. In the physical space an optimal curved path ensures the maximum flux or shortest transition time of the fluid through the porous medium. A sort of “law of bending” holds for the frictional fluid flux in Lagrange coordinates. This law shows that—by minimizing the total resistance—a ray spanned between two given points takes the shape assuring that a relatively large part of it resides in the region of lower flow resistance (a ‘rarer’ region of the medium).     

Probabilistic solution of non-linear random ship roll motion by path integration

This paper investigates the probability density function (PDF) of non-linear random ship roll motion using a previously developed path integration method. The mathematical model of ship rolling motion consists of a linear-plus-cubic damping and a non-linear restoring moment in the form of odd-order polynomials up to fifth-order terms. In the path integration method, the interpolation scheme is based on the Gauss–Legendre quadrature integration rule and the short-time transition probability density function is formulated by short-time Gaussian approximation. The present work extends the path integration method to the case of non-linear random ship roll motion. Different values of non-linearity coefficient and excitation intensity are used to examine the effectiveness of the path integration method. Numerical analysis shows that the results of the path integration method agree well with the simulation results, even in the tail region. The path integration method is effective and it is simply implemented in the examined cases. Due to the presence of non-linear damping terms and non-linear restoring moment terms, the PDFs of roll angle and angular velocity exhibit highly non-Gaussian behaviors.     

砂土的应力路径本构模型

将微元应力路径线性逼近，转变成与其充分接近且易于计算应变的等平均应力微元和等应力比微元，计算任意加荷应力路径所产生的塑性应变，建立了双屈服面的砂土应力路径本构模型．模型体现了岩土塑性理论分量屈服和非关联流动法则的要求，在p，q平面内根据双线性的屈服线确定了加卸载准则．结合广义非线性强度理论采用变换应力三维化方法简单、合理地使模型实现三维化．通过试验数据的验证表明，砂土应力路径本构模型可以合理地描述各种应力路径下砂土的变形和强度特性。     

简支梁非线性响应的三维路径积分法分析

采用基于Gauss-Legendre积分公式的三维路径积分法，分析了在过滤高斯白噪声激励下的简支梁非线性随机振动响应的概率密度函数；联立一阶滤波方程与简支梁一阶模态的振动模型，得到在过滤高斯白噪声激励下的简支梁随机振动模型，基于Gauss-Legendre积分公式的积分法和短时高斯近似法求解响应的概率密度函数值。结果表明，三维路径积分法计算值与蒙特卡洛模拟值符合良好，即使在尾部区域也符合良好。三维路径积分法比等效线性化法的计算精度更高。