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Boundary setting method for the seismic dynamic response analysis of engineering rock mass structures using the discontinuous deformation analysis method 
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下载免费PDF全文 Large deformations and discontinuous problems can be calculated using the discontinuous deformation analysis (DDA) method by solving time steps, and this method is suitable for simulating the seismic dynamic response of engineering rock mass structures. However, the boundary setting must be carefully analyzed. In this paper, four boundary settings for the DDA method are investigated. First, the contributions to the DDA equations for nonreflecting boundaries (including the viscous boundary and the viscoelastic boundary) are deduced based on the Newmark method. Second, a free‐field boundary is introduced in the DDA method with boundary grid generation and coupling calculation algorithms to accurately simulate external source wave motion, such as earthquakes. Third, seismic input boundary treatments are intensively examined, and the force input method is introduced based on nonreflecting boundaries. Finally, the static‐dynamic unified boundary is implemented to ensure consistent boundary transformation. The boundary setting method in the DDA method is discussed, and the suggested treatments are used to analyze the seismic dynamic response of underground caverns. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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In rock engineering, the damage criteria of the rock mass under dynamic loads are generally governed by the threshold values of wave amplitudes, such as the peak particle velocity and the peak particle acceleration. Therefore, the prediction of wave attenuation across fractured rock mass is important on assessing the stability and damage of rock mass under dynamic loads. This paper aims to investigate the applications of the discontinuous deformation analysis (DDA) for modeling wave propagation problems in rock mass. Parametric studies are carried out to obtain an insight into the influencing factors on the accuracy of wave propagations, in terms of the block size, the boundary condition and the incident wave frequency. The reflected and transmitted waves from the interface between two materials are also numerically simulated. To study the tensile failure induced by the reflected wave, the spalling phenomena are modeled under various loading frequencies. The numerical results show that the DDA is capable of modeling the wave propagation in jointed rock mass with a good accuracy. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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采用颗粒离散单元法进行动力计算时,人工截断边界上需设置吸收边界条件,以防止波的反射。鉴于颗粒离散单元数值计算模型的人工边界上颗粒单元半径大小不一、边界面凸凹不平,在连续介质的黏性、黏弹性、自由场边界条件方程基础之上,推导出适用于离散介质的等效方程。在离散介质的黏性边界条件等效方程中引入微调系数,提出比值迭代法以快速确定其最优值,以实现对波的最佳吸收。采用二维颗粒离散单元计算软件PFC2D,分别建立黏性、黏弹性、自由场边界条件相关数值分析模型,探讨颗粒分布模式对黏性边界上颗粒单元半径、速度分布及比值迭代过程的影响;采用外源波动算例及经典Lamb问题算例验证黏弹性边界设置方法的正确性;通过隧洞算例检验提出的自由场边界条件设置方法的正确性。 相似文献
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A general viscous‐spring transmitting boundary for dynamic analysis of saturated poroelastic media 下载免费PDF全文
下载免费PDF全文 A time‐domain viscous‐spring transmitting boundary is presented for transient dynamic analysis of saturated poroelastic media with linear elastic and isotropic properties. The u–U formulation of Biot equation in cylindrical coordinate is adopted in the derivation. By this general viscous‐spring boundary, the effective stress and pore fluid pressure on the truncated boundary of the computational area are replaced by a set of continuously distributed spring and dashpot elements, of which the parameters are defined assuming an infinite permeability and considering the two dilatational waves. Numerical examples demonstrate good absorption of both the two cylindrical dilatational waves by the proposed ‘drained’ boundary. For general two‐dimensional wave propagation problems, acceptable accuracy can still be achieved by setting the proposed boundary relatively far away from the scatter. Numerical comparison shows that the results obtained by using this boundary are more accurate for all permeability values than those by the traditional viscous‐spring or viscous boundaries established for u–U formulation. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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A new finite element scheme is proposed, in this paper, for solving two-dimensional wave propagation problems in multilayered soils resting on a rigid base. The multilayered soils are treated as multiple horizontal layers of lateral infinite extension in geometry. Since these horizontal layers can be truncated by two artificially truncated vertical boundaries, two high-order artificial boundary conditions are applied for propagating the incoming waves from the interior domain into the far field of the system. Both the semi-analytical method and the truncated boundary migration procedure are used to derive the high-order artificial boundary conditions, which are comprised of a physically meaningful dashpot and a generalized energy absorber. The main advantage of using the proposed finite element scheme is that the derived artificial boundary condition can be straightforwardly implemented in the finite element analysis, without violating the band/sparse structure of the conventional finite element equation. The related numerical examples have demonstrated that the proposed finite element scheme is of high accuracy in dealing with wave propagation problems in multiple horizontal layers. 相似文献
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Boundary settings for the seismic dynamic response analysis of rock masses using the numerical manifold method 下载免费PDF全文
下载免费PDF全文 Aiming to accurately simulate seismic dynamic response of rock masses using the numerical manifold method (NMM), boundary settings must be treated carefully. In this paper, 4 issues in boundary settings are investigated to improve the performance of NMM: (1) Nonreflecting boundaries including the viscous boundary and viscoelastic boundary are considered; (2) A free‐field boundary is incorporated into NMM to accurately simulate external source wave motion; (3) A seismic input boundary is considered, and the force input method is introduced; and (4) A static‐dynamic unified boundary is incorporated for the convenience of transforming displacement boundary into other types of boundaries, such as nonreflecting boundaries and seismic input boundary. Several benchmark problems are solved to validate the improved NMM. Simulation results agree well with analytical ones, indicating that the improved NMM is able to simulate seismic dynamic response of rock masses reliably and correctly. 相似文献
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《Geomechanics and Geoengineering》2013,8(4):283-292
We present validations and applications of the numerical Discontinuous Deformation Analysis method (DDA) for different cases of dynamic loading in the context of rock mass deformation. Following a review of 2D and 3D-DDA validations against analytical solutions for single and double face sliding, we present dynamic DDA applications in natural rock slopes and underground openings. Modelling dynamic rock slope deformation is demonstrated using the case of Masada rock slopes, with some new findings on the dynamic deformation of overhanging cliffs in general. Modelling underground deformation is demonstrated using the case of an active open pit mine in Israel developed in a rock mass containing multiple karstic caverns. The DDA method is shown here to be a powerful numerical tool for modelling dynamic rock mass deformation when the interaction between multiple discrete elements dictates the expected global deformation. 相似文献
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岩体裂隙网络非稳定渗流分析与数值模拟 总被引：1，自引：0，他引：1
针对裂隙岩体的非稳定渗流问题,通过将Darcy定理扩展到包含干区的整个裂隙网络区域,并令潜在溢出边界条件为Signorini型互补边界条件,将湿区上的非稳定渗流问题转化为全域上的一个新的初边值问题。为降低试探函数选取的难度,建立与定义在整个裂隙网络区域上的偏微分方程（PDE）提法等价的抛物型变分不等式（PVI）提法,并给出裂隙网络非稳定渗流分析的有限元数值分析格式和迭代算法,与砂槽模型试验数据的对比分析,验证其有效性。最后,将文中发展的计算方法应用到含复杂裂隙网络的边坡非稳定渗流分析,计算结果很好地反映出边坡内部自由面随库水降落的变化规律,并能准确地描述裂隙网络内部渗流运动特征及流量分布的不均匀性。 相似文献
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针对深埋地下结构的荷载环境特点,提出了深埋地下结构静动力耦合计算过程中边界条件的合理设置方法。该方法通过构建边界上的力系来平衡计算区域的初始地应力,然后将该力系设置成阶跃函数形式的动荷载作用于边界,并与后续的动荷载共同作用。研究表明,一次完整的地下结构静动力耦合分析过程,边界条件必须经过变换设置才能得到合理的计算结果。另外,只要计算软件具有黏性边界条件设置功能就能准确地完成地下结构静动力耦合响应分析。算例分析显示,该边界条件设置方法精度和效率高,简单适用。 相似文献
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The propagation of elastic P-wave in unfavorable geologic structures is a complex process which contains reflex, transmission, and refraction. In this paper, the discontinuous deformation analysis (DDA) method is introduced, and the viscous boundary condition and stress wave input way are applied to enable the DDA method to simulate the seismic dynamic response of underground rock mass. The improved DDA program is used to analyze the propagation laws of elastic P-wave in joints and weak interlayer. The results show that (1) for a range of joint stiffness, the difference of transmission coefficient of joint surface between DDA calculation and theoretical solution is small; (2) the lower the joint stiffness, the more obvious the attenuation of the elastic P-wave is; (3) varied joint spacing and joint number play different roles on the attenuation of elastic P-wave; (4) the DDA calculation result is consistent with the theoretical solution for the transmission coefficient of interface; (5) the thickness and elastic modulus of weak interlayer will affect the interference effect of multiple transmission waves; (6) with the increasing weak interlayer thickness H (or a), the attenuation of the elastic P-wave is more obvious; and (7) the lower the wave impedance ratio of weak interlayer, the more obvious the attenuation of the elastic P-wave is. 相似文献
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定量研究了非连续变形分析(DDA)方法中的黏性阻尼与数值阻尼。首先,基于Newmark直接积分法,推导了块体系统的运动方程。其次,通过动力学中的黏性阻尼理论建立了DDA中动力系数、时间步长与黏性阻尼比的关系式,探讨了DDA中的常加速度积分方案的数值阻尼分区及阻尼比计算方法,进而得到两种阻尼共同作用时的阻尼比表达式,并分析了频域内阻尼比的分布情况。最后,以谐振激励下的块体振动为例,通过对比不同阻尼作用下块体位移的DDA计算值与理论解,验证了本文提出的阻尼比计算公式的正确性。研究表明：黏性阻尼对低频的衰减作用明显,数值阻尼则可以很快地消除高频干扰,而二者共同作用下可降低阻尼的频率相关性。该研究成果为DDA的振动、波动等动力计算的阻尼取值提供了理论依据。 相似文献
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We simulate the propagation of ultrasonic waves in heterogeneous poroviscoelastic media saturated by immiscible fluids. Our model takes into account capillary forces and viscous and mass coupling effects between the fluid phases under variable saturation and pore fluid pressure. The numerical problem is solved in the space–frequency domain using a finite element procedure and the time–domain solution is obtained by a numerical Fourier transform. Heterogeneities due to fluid distribution and rock porosity–permeability are modeled as stochastic fractals, whose spectral densities reproduce saturation an petrophysical variations similar to those observed in reservoir rocks. The numerical experiments are performed at a central frequency of 500 kHz, and show clearly the effects of the different heterogeneities on the amplitudes of shear and compressional waves and the importance of wave mode conversions at the different interfaces. 相似文献
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为研究综合管廊动力边界条件对地震动力响应的影响,以厦门地区的代表性土层为例,建立动力有限元数值模型,土体本构采用小应变硬化模型,分别设定固定边界、黏性边界和自由场3种人工边界条件,进行Rayleigh波和地震底部剪切波作用下的场地响应研究;并根据变形特征及拟绝对加速度反应谱（PSA）评价3种边界的有效性,提出综合管廊地震动力分析的优化动力边界组合方法。研究表明：在地震波（底部水平加速度时程）及Rayleigh波的作用下,由于考虑了黏性边界对外行波的吸收,但未考虑地震动的输入问题及边界外半无限介质的弹性恢复性能,边界会对模型内部土体的水平位移产生限制作用,使得场地内水平位移响应偏小,而采用自由场边界则基本不存在这种限制作用,表现出强烈的振荡;采用激励侧固定边界、远离激励侧黏性边界、其余侧自由场边界的优化组合动力边界,在Rayleigh波和底部加速度时程共同作用下,二者引起的动力响应交叉干扰较少,可按线性叠加处理;同时,黏性边界对地震波引起的动力响应有一定范围的吸收,自由场边界对Rayleigh波引起的动力响应也有一定范围的变形限制影响。研究成果可供地下综合管廊结构地震响应精细化数值模拟及抗震设计参考。 相似文献
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《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
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A Boundary Element based Discontinuous Deformation Analysis (BE‐DDA) method is developed by implementing the improved dual reciprocity boundary element method into the open close iterations based DDA. This newly developed BE‐DDA is capable of simulating both the deformation and movement of blocks in a blocky system. Based on geometry updating, it adopts an incremental dynamic formulation taking into consideration initial stresses and dealing with external concentrated and contact forces conveniently. The boundaries of each block in the discrete blocky system are discretized with boundary elements while the domain of each block is divided into internal cells only for the integration of the domain integral of the initial stress term. The contact forces among blocks are treated as concentrated forces and the open–close iterations are applied to ensure the computational accuracy of block interactions. In the current method, an implicit time integration scheme is adopted for numerical stability. Three examples are used to show the effectiveness of the algorithm in simulating block movement, sliding, deformation and interaction of blocks. At last, block toppling and tunnel stability examples are conducted to demonstrate that the BE‐DDA is applicable for simulation of blocky systems. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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模型范围是影响数值分析计算精度与效率的重要因素,针对深埋隧洞开挖数值模拟分析问题,采用有限差分软件FLAC3D和复合失稳准则,对计算模型的纵向范围取值问题展开研究。首先分析了深埋隧洞开挖过程中围岩纵向变形以及未开挖岩塞对围岩变形的约束作用,然后研究了近端边界和远端边界对监测断面位置处围岩变形的影响,最后采用最小二乘法对多组计算结果进行了位移误差分析,并给出了纵向模型范围的取值建议。研究结果表明,当监测断面距掌子面大于10倍洞径时,未开挖岩塞的约束作用基本消失;远端边界以及近端边界与监测断面的最大位移误差值之间均基本满足幂函数关系,且远端边界对监测点位移误差的影响要大于近端边界;深埋隧洞开挖数值模拟中,纵向模型范围取7.5倍洞径即可满足一般数值分析的精度要求。 相似文献
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土层场地对地震动的影响明显,研究成层场地局部复杂地形的波动场特性,对于抗震设防具有重要意义。基于土-结构相互作用理论,含有局部复杂地形的成层场地,可分解成广义结构（即近场复杂地形及其周围土体）和具有规则开挖边界的成层无限地基（即远场）。远场的格林函数可通过精细积分求解频域-波数域内的对偶波动方程获得,利用傅里叶逆变换得到频域-空间域内的柔度矩阵。近场可采用比例边界有限元进行模拟,通过高性能连分式的传递边界求解动刚度。自由场波动可通过传递矩阵法求得,将动刚度和自由场波动位移代入控制方程即可得到散射场的动力响应。数值算例验证了方法的准确性,并利用提出的方法讨论含有软夹层场地局部复杂场地的波动场特性。 相似文献