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1.
《岩土力学》2017,(7):2103-2112
针对非连续变形分析中开合迭代难以收敛的难题,基于块体接触约束状态和块体位移之间的关系,提出了基于逼近阶跃函数和拉格朗日插值的改进DDA方法。采用双曲正切函数来逼近阶跃函数,利用阶跃函数将块体接触约束状态用块体位移来表达,以此来替代开合迭代,避免了开合迭代难以收敛的难题。利用拉格朗日插值原理,推导得到只含有块体位移为未知量的块体系统势能函数,并利用变尺度法来求解总体势能函数的极值以得到块体位移。分别结合滑块模型和地下洞室模型,分析了改进DDA方法的计算精度和计算速度,验证了文中提出的改进DDA方法的正确性和稳定性。研究表明:基于逼近阶跃函数和拉格朗日插值的改进DDA方法具有较高的精度,且相比较传统DDA方法而言,具有更为稳定的和更为强健的计算收敛性。因此,基于逼近阶跃函数和拉格朗日插值的改进DDA方法是一种稳定有效的数值计算方法,为解决非连续变形中开合迭代难以收敛的问题提供了新思路。 相似文献
2.
《岩土力学》2017,(3):902-910
非连续变形分析(discontinuous deformation analysis,DDA)方法在处理非连续变形问题中具有显著的优越性,但由于需要处理接触并进行开闭迭代,计算量较大。为了提高DDA方法中接触查找部分的计算效率,并保持较高的精确度,通过改变距离准则下的接触查找方式,提出了改进的接触查找算法。在接触查找前增加预判,减少需要判断的角点数目,并区分两种类型的角-边接触,将对这两种角-边接触的查找分配到不同循环体中,改造了距离准则下的接触查找逻辑。通过两个计算模型来验证改进后程序的准确性和高效性,模型1用来检验程序在各种接触条件下的计算结果,计算结果表明,改进后的程序精确度可以满足;模型2采用东河口滑坡模型,计算结果表明,在保证计算结果精度的前提下,改进后程序的计算效率可提高10%左右。 相似文献
3.
非连续变形分析（DDA）是一种针对块体系统变形和位移求解的数值计算方法。引入Newmark方法于结构动力学微分方程中,考虑惯性力和阻尼力作用,改进时间步长自动调节,并实现DDA求解程序;比较研究Newmark方法中的线性加速法、常加速法和平均加速法在DDA程序中计算的收敛速度,讨论块体系统动力学计算过程中DDA方法对惯性力和阻尼力的添加和删除,并提出根据计算精度要求的误差控制实现方案。将改进的DDA方法模拟一个典型的煤与瓦斯突出过程,取得了满意的计算结果,该改进算法为DDA方法处理动力学问题提供新的途径 相似文献
4.
非连续变形分析方法(DDA) 自创立以来,已在分析不连续体的大变形、大位移的问题中显示了其优越性。但DDA方法需要人为设置一些控制参数,通过一个简单的滑块模型,分别采用不同的时步大小、不同的接触弹簧刚度、并比较相对误差,分析了人为设定的参数对DDA计算结果的影响,指出仅在合理的取值范围内,大时步和大的接触弹簧刚度才能产生较好的计算结果;同时对造成这种影响的原因做了一定的探讨,并建议了参数取值的上下限原则。 相似文献
5.
《岩土力学》2017,(6):1746-1761
由石根华提出的非连续变形分析(DDA)方法理论严密且计算较为高效,在模拟块体滑移、转动和张开等大变形、大位移问题方面具备独特优势,因而在岩土工程领域得到了广泛运用。然而DDA方法在提出初期不可避免地存在一些精度问题,对此石根华及国内外学者就问题产生原因和改进方法开展了大量研究工作。基于部分相关成果的研究学习,对改进原始DDA计算精度的各类方法进行归纳探讨,主要包括:(1)DDA块体内部应力位移场的精度控制;(2)块体接触问题处理方法的改进;(3)人为参数的合理选取;(4)能量耗散机制的考虑;(5)人工边界的改进等方面。对以上方法的改进效果和计算效率进行了简要分析和讨论,在此基础上对DDA的研究热点和发展趋势进行了概述,为该方法的进一步发展和完善提供思路。 相似文献
6.
非连续变形分析(DDA)方法对大规模工程问题的数值模拟耗时太长,其中线性方程组求解耗时可占总计算时间的70%以上,因此,高效的线性方程组解法是重要研究课题。首先,阐述了适用于DDA方法的基于块的行压缩法和基于试验-误差迭代格式的非0位置记录;然后,针对DDA的子矩阵技术,将块雅可比迭代法 (BJ)、预处理的块共轭梯度法 (PCG,包括Jacobi-PCG、SSOR-PCG) 引入DDA方法,重点研究了线性方程组求解过程中的关键运算;最后,通过两个洞室开挖算例,分析了各线性方程组求解算法在DDA中的计算效率。研究表明：与迭代法相比,直解法无法满足大规模工程计算需要;BJ迭代法与块超松弛迭代法(BSOR)的效率差别不大,但明显不如PCG迭代法。因此,建议采用PCG迭代法求解DDA线性方程组,特别是SSOR-PCG值得推广;如果开展并行计算研究,Jacobi-PCG是较好的选择,当刚度矩阵惯性优势明显时,BJ迭代法同样有效。 相似文献
7.
基于DDA方法一种流-固耦合模型的建立及裂隙体渗流场分析和应用 总被引：1，自引：0，他引：1
以非连续变形分析方法（DDA）为基础并采用稳态流体计算方法将二者结合进行裂隙岩体流-固耦合分析。利用DDA方法生成裂隙岩体模型,在此基础上采用矩阵搜索等方法形成新的裂隙水通网络模型。采用稳态迭代算法和立方定律求得裂隙水压力,并把裂隙水压力作为线载荷施加到块体边界,在DDA算法中每个迭代步完成后更新裂隙开度和水压值,与DDA算法结合研究裂隙水与块体之间相互作用关系。利用以上裂隙岩体流-固耦合计算方法研究了某水封油库开挖和运行过程洞室围岩流量和密封性,为该工程预测水封效果提供了有益的主要依据,也是国内首次采用DDA方法做大型工程的流-固耦合模型分析。 相似文献
8.
传统的非连续变形分析法（DDA）法采用简单的线性位移模式计算效率高,描述大块体的高阶多项式位移模式在一定程度保留了该特点,并提高了计算精度。近年来流行的耦合有限元、自然单元的DDA法实质上是引入相应的插值形函数构成块体位移函数,计算相对低效,但具有计算更精细、更容易施加边界条件等优点。为结合传统DDA法与DDA耦合法各自的优点,建立了一种同时利用传统DDA法线性位移模式与耦合型DDA法非线性位移模式的混合法。该方法非线性模式主要针对大块体,采用了自然单元插值,缘于其具有一定无网格特征,且效率比有限元高。建立了混合模式下的整体矩阵并推导出接触等因素刚度子矩阵和荷载子向量的具体表达式。该方法建模更加方便合理,计算精度、效率介于线性模式的传统DDA法和非线性位移模式的耦合法之间。通过基本算例验证了混合法的有效性,并给出了节理围岩-隧道衬砌整体分析模型的计算结果,体现了新方法的优越性。 相似文献
9.
非连续变形分析（DDA）方法严格满足平衡要求和能量守恒,具有完全的运动学及数值可靠性,但对大规模岩土工程问题的数值模拟耗时太长,尤其是线性方程组求解,并行计算可以很好地解决该问题。首先基于DDA方法的基本理论,阐述了适用于DDA方法中的基于块的行压缩法和基于“试验-误差”迭代格式的非零位置记录;其次,引入块雅可比迭代法并行求解DDA方法的线性方程组,并改进了相应的非零存储方法;最后,基于OpenMP实现了DDA线性方程组求解并行计算,并将其应用于地下洞室群的破坏过程分析,以加速比为并行效率的指标评价,结果表明,该并行计算策略可以极大提高DDA的计算效率,而且适合各种规模的问题。 相似文献
10.
非连续变形分析（DDA）是一种隐式求解的动力学计算方法,且采用在块体界面加减刚硬弹簧的方式来满足块体界面无张拉和无嵌入的接触准则,其中时间步长和弹簧刚度两个物理量的取值直接影响DDA的计算结果。基于对DDA时间步和弹簧刚度在程序运行过程中的调整策略和块体接触的简化力学概念模型,研究了惯性力在DDA收敛求解中的作用过程。采用数值模拟试验对自由落体和斜面单滑块模型在3种力学状态下的相关力学问题进行了数值模拟研究,通过对自由落体运动的模拟,研究了时间步长单一因素对计算结果的影响规律,并初步确定了时间步长的合理取值区间。在此基础上,采用斜面单滑块模型,研究了时间步长和弹簧刚度对计算结果的共同影响,确定了不同时间步长条件下弹簧刚度的合理取值区间。研究成果表明,合适的时间步长和弹簧刚度的取值组合构成一个单连通参数取值域,当时间步和弹簧刚度的取值组合位于此“域”范围内时,DDA的计算结果是合理的。 相似文献
11.
Orienting the circular and rigid particle medium, the variational inequality-based discontinuous deformation analysis (DDA) is established. In the proposed DDA, the global stiffness matrix, the penalty parameters, and the open-close iteration are successfully avoided. The contact constraint is transferred into the problem of variational or quasi-variational inequalities. And explicit variational expression on the contact force is firstly established. To speed up the rate of solving contact force, on the basis of the two-stage prediction-correction method, we design a compatibility iteration algorithm (PPC-CI). The C++ code is developed in multicore environment through the open multi-processing (OpenMP) in order to take advantage of the parallelizable features of the new DDA. Numerical tests suggest that the presented DDA is effective and promising. 相似文献
12.
《Geomechanics and Geoengineering》2013,8(3):221-236
This paper presents a new point-to-face contact algorithm for contacts between two polyhedrons with planar boundaries. A new discrete numerical method called three-dimensional discontinuous deformation analysis (3-D DDA) is used and formulations of normal contact submatrices based on the proposed algorithm are derived. The presented algorithm is a simple and efficient method and it can be easily coded into a computer program. This approach does not need to use an iterative algorithm in each time step to obtain the contact plane, unlike the ‘Common-Plane’ method applied in the existing 3-D DDA. In the present 3-D DDA method, block contact constraints are enforced using the penalty method. This approach is quite simple, but may lead to inaccuracies that may be large for small values of the penalty number. The penalty method also creates block contact overlap, which violates the physical constraints of the problem. These limitations are overcome by using the augmented Lagrangian method that is used for normal contacts in this research. This point-to-face contact model has been programmed and some illustrative examples are provided to demonstrate the new contact rule between two blocks. A comparison between results obtained by using the augmented Lagrangian method and the penalty method is presented as well. 相似文献
13.
The high computational costs associated with the implicit formulation of discontinuous deformation analysis (DDA) have been one of the major obstacles for its implementation to engineering problems involving jointed rock masses with large numbers of blocks. In this paper, the Newmark-based predictor-corrector solution (NPC) approach was modified to improve the performance of the original DDA solution module in modeling discontinuous problems. The equation of motion for a discrete block system is first established with emphasis on the consideration of contact constraints. A family of modified Newmark-based predictor-corrector integration (MNPC) scheme is then proposed and implemented into a unified analysis framework. Comparisons are made between the proposed approach and the widely used constant acceleration (CA) integration approach and central difference (CD) approach, regarding the stability and numerical damping features for a single-degree-of-freedom model, where the implications of the proposed approach on open-close iteration are also discussed. The validity of the proposed approach is verified by several benchmarking examples, and it is then applied to two typical problems with different numbers of blocks. The results show that the original CA approach in DDA is efficient for the simulation of quasi-static deformation of jointed rock masses, while the proposed MNPC approach leads to improved computational efficiency for dynamic analysis of large-scale jointed rock masses. The MNPC approach therefore provides an additional option for efficient DDA of jointed rock masses. 相似文献
14.
The discontinuous deformation analysis (DDA) is a discontinuum‐based method, which employs a penalty method to represent the contact between blocks. The penalty method is easy to be implemented in the program, but the contact constraint is only approximately satisfied. Penetrations between contacting blocks are unavoidable even if the penalty value is very large. To improve the contact precision in the DDA, an augmented Lagrangian method is introduced, which can make use of advantages of both the Lagrangian multiplier method and the penalty method. This paper provides a detailed implementation of the augmented Lagrangian method in the DDA program and compares it with the standard DDA on the computational efficiency and contact precision. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
15.
In this paper, a new disk-based DDA formulation is presented. In the original disk-based DDA, disks are considered to be rigid and the penalty method is used to enforce disk contact constraints. In order to improve the accuracy of the disk-based DDA, new formulations of stiffness and force matrices for non-rigid disks using a new efficient contact model are presented in this paper. Blocks are considered deformable without need to do more computations for contact detection. In the proposed contact model, disk–disk and disk–boundary contacts are transformed into the form of point-to-line contacts and normal spring, shear spring and frictional force sub-matrices are derived by vector analysis. The penalty method is quite simple to implement, but has some major disadvantages. In the presented contact model, not only the simplicity of the penalty method is retained but also the limitations are overcome by using the augmented Lagrangian method. Moreover, unlike the contact model used in the original disk-based DDA, reference line can be obtained directly by using only coordinates of disk centers and their radii, and no more computations are needed. The validity and capability of the new disk-based DDA formulation are demonstrated by several illustrative examples. 相似文献
16.
G.H. Shi 《Geomechanics and Geoengineering》2014,9(2):80-96
Continuous computation and limit equilibrium computation are the two independent computations for practical rock engineering. For global stability analysis, limit equilibrium is still the fundamental method. For any numerical method, reaching limit equilibrium requires large displacements, discontinuous contacts, precise friction law, multistep computation and stabilised time-step dynamic computation. Therefore three convergences are unavoidable: convergence of equilibrium equations, convergence of open-close iterations for contacts and convergence of the contact forces of dynamic computations. This paper utilises mainly two dimensional discontinuous deformation analysis (DDA) and an available simple version of three dimensional DDA. The applications show DDA has the ability to reach the limit equilibrium of block systems. 相似文献
17.
A Model of Point-to-Face Contact for Three-Dimensional Discontinuous Deformation Analysis 总被引：15，自引：0，他引：15
Summary The key to three-dimensional discontinuous deformation analysis (3D DDA) is a rigorous contact theory that governs the interaction of many three-dimensional blocks. This theory must provide algorithms to judge contact types and locations and the appropriate state of each contact, which can be open, sliding or locked. This paper presents a point-to-face contact model, which forms a part of the contact theory, to be used in 3D DDA. Normal spring, shear spring and frictional force submatrices are derived by vector analysis and the penalty method. Also given are the open-close iteration criteria and operations performed for different changes in contact state. Sliding at a contact can occur in any direction parallel to the contact face, as opposed to one of two directions in two-dimensional DDA. This point-to-face contact model has been implemented into a 3D DDA computer program, and numerical results from several test cases demonstrate the validity of the model and the capability of the program. 相似文献
18.
Generalized contact model for polyhedra in three‐dimensional discontinuous deformation analysis 
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下载免费PDF全文 We present a generalized contact computation model for arbitrarily shaped polyhedra to simplify the contact analysis in discontinuous deformation analysis. A list of generalized contact constraints can be established for contacting polyhedra during contact detection. Each contact constraint contains information for 2 contact points, unique contact plane, and related contact modes (open, locked, or sliding). Computational aspects of the generalized contact model include identification of contact positions and contact modes, uniform penalty formulation of generalized contact constraint, and uniform updating of contact modes and contact planes in the open‐close iteration. Compared with previous strategies, the generalized contact computation model has a simpler data structure and fewer memory requirements. Meanwhile, it simplifies the penalty formulation and facilitates the open‐close iteration check while producing enough accuracy. Illustrative examples show the ability of the method to handle the full range of polyhedral shapes. 相似文献
19.
David M. Doolin 《国际地质力学数值与分析法杂志》2005,29(12):1199-1207
Displacement boundary constraints in discontinuous deformation analysis (DDA) are applied using stiff penalty springs. A co‐ordinate‐free formulation for displacement boundary constraints is presented here for DDA, which unifies previous derivations for points of fixity, and for points constrained to induce or prohibit block motion in specified directions as a function of location or time. Examples for each type of constraint are used to illustrate the behaviour of the algorithm and provide a link with previous formulations for each case. The new, unified formulation has five benefits: (1) simple to express algorithmically; (2) easy to program and verify; (3) penalty values in different directions may be chosen to allow fixed points, lines, curves or planes; (4) formulation works for 2D and 3D; (5) displacement constraint may be a function of time or location or both. Feedback in the algorithm may induce internal resonance in homogeneously deformable discrete elements used in DDA, and resonance in block‐to‐block contact interactions. Consequently, high mass problems with insufficient damping may suffer from excessive ‘vibrational hammering’, inducing physically implausible behaviour such as elastic rebound. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献