Modeling stress wave propagation in rocks by distinct lattice spring model

In this paper, the ability of the distinct lattice spring model （DLSM） for modeling stress wave propagation in rocks was fully investigated. The influence of particle size on simulation of different types of stress waves （e.g. one-dimensional （1D） P-wave, 1D S-wave and two-dimensional （2D） cylindrical wave） was studied through comparing results predicted by the DLSM with different mesh ratios （It） and those obtained from the corresponding analytical solutions. Suggested values of lr were obtained for modeling these stress waves accurately. Moreover, the weak material layer method and virtual joint plane method were used to model P-wave and S-wave propagating through a single discontinuity. The results were compared with the classical analytical solutions, indicating that the virtual joint plane method can give better results and is recommended. Finally, some remarks of the DLSM on modeling of stress wave propagation in rocks were provided.

On the four-dimensional lattice spring model for geomechanics

Recently, a four-dimensional lattice spring model(4D-LSM) was developed to overcome the Poisson’s ratio limitation of the classical LSM by introducing the fourth-dimensional spatial interaction. In this work, some aspects of the 4D-LSM on solving problems in geomechanics are investigated, such as the ability to reproduce elastic properties of geomaterials, the capability of solving heterogeneous problems,the accuracy on modelling stress wave propagation, the ability to solve dynamic fracturing and the parallel computational efficiency. Our results indicate that the 4D-LSM is promising to deal with problems in geomechanics.

龙马溪组页岩数字岩心LSM-RVM数值建模方法研究及TOC含量影响分析

页岩气储层中含有大量有机碳(TOC),其丰度与成熟度对页岩力学特性有重要影响.建立包含TOC的精细数值模型,将有助于探索页岩微结构与矿物组分含量对等效弹性模量的作用程度,是"甜点区"预测的重要理论基础.本文提出了一种离散数值建模方法,基于高精度成像技术,采用晶格弹簧-随机孔隙耦合模型(LSM-RVM)模拟包含多种矿物组分及不同成熟度干酪根的数字岩心,分析TOC成熟度及含量对弹性参数的影响.在该模型中,参数设置(数值阻尼与加载应变速率)至关重要,选取不当会对计算精度造成一定影响.研究结果表明,LSM-RVM能够生成符合TOC及多种矿物实际分布特征的数值模型,是一种精细数值建模方法.

High-performance computing of 3D blasting wave propagation in underground rock cavern by using 4D-LSM on TianHe-3 prototype E class supercomputer

Parallel computing assigns the computing model to different processors on different devices and implements it simultaneously.Accordingly,it has broad applications in the numerical simulation of geotechnical engineering and underground engineering,of which models are always large-scale.With parallel computing,the computing time or the memory requirements will be reduced by splitting the original domain of the numerical model into many subdomains,which is thus named as the domain decomposition method.In this study,a cubic and equal volume domain decomposition strategy was utilized to realize the parallel computing on the distributed memory system of four-dimensional lattice spring model(4D-LSM)based on the message passing interface.With a more efficient communication strategy introduced,this study aimed at operating an one-billion-particle model on a supercomputer platform.The preprocessing procedure of the parallelized 4D-LSM was restructured and the particle generation strategy suitable for the supercomputer platform was employed to minimize the time consumption in preprocessing and calculation.On this basis,numerical calculations were performed on TianHe-3 prototype E class supercomputer at the National Supercomputer Center in Tianjin.Two fieldscale three-dimensional blasting wave propagation models were carried out,of which the numerical results verify the computing power and the advantage of the parallelized 4D-LSM in the simulation of large-scale three-dimension models.Subsequently,the time complexity and spatial complexity of 4D-LSM and other particle discrete element methods were analyzed.

基于数值仿真的复杂岩体TBM掘进性能评估模型

为了评估全断面隧道掘进机(TBM)在复杂岩体环境中的掘进性能,本文提出了基于数值仿真的全断面TBM掘进预测模型。首先,采用4D-LSM和DDA耦合模型数值重现工程尺度完整岩体和节理岩体的TBM掘进测试过程,分析全断面TBM掘进过程中刀盘的力学响应和岩体的破坏特征;其次,研究节理间距、节理方向、岩体单轴抗压强度以及脆性指数对可钻性指数的影响;最后,引入单神经元对数值仿真预测模型进行修正,并与岩体特征模型进行对比分析,验证基于数值仿真的全断面TBM掘进性能预测模型的适用性。研究结果表明:TBM在低强度、高脆性以及节理发育的岩体中掘进效率更高,当节理面与TBM掘进方向之间的夹角为60°~75°时,最有利于TBM的运行。基于数值仿真的TBM掘进性能预测模型提供了一种经济、灵活的可用于评估复杂环境中TBM施工性能的方法。

水力压裂裂缝空间转向特征三维数值模拟研究

水力压裂技术广泛应用于煤矿坚硬顶板控制、冲击地压防治和低渗煤层增透等领域,而岩体水力压裂裂缝空间转向规律尚未完全厘清。为探究岩体水力裂缝空间转向扩展特征,采用三维数值模拟手段研究地应力、排量、流体黏度、天然裂缝、缝间诱导应力的影响效应。结果表明:裂缝转向主要发生在最大主应力法平面,随着中间主应力与最小主应力之差增加,裂缝朝中间主应力方向转向,且偏转程度逐渐加剧;提高排量或流体黏度将促使裂缝沿初始方向扩展;水力裂缝穿越天然裂缝呈绕道穿越和直接穿越两种典型模式,天然裂缝仅在局部范围内阻碍水力裂缝扩展,相交后水力裂缝仍沿最大主应力方向继续扩展。多条裂缝同时压裂时,裂缝易受诱导应力的干扰发生空间扭转,中间裂缝偏转程度最为剧烈;多条裂缝分段压裂时流体返排,诱导应力干扰效应显著降低。地应力场主导水力裂缝三维扩展方位,其他因素仅在局部范围内产生次级效应。研究结论可为煤矿井下水力压裂工程提供借鉴。

Stability analysis on tunnels with karst caves using the distinct lattice spring model

The effects of karst caves on tunnel stability were numerically investigated using the distinct lattice spring model(DLSM).The DLSM was validated by investigating the mechanical behavior of Brazilian discs with various sizes of central circular holes.Then,the effects of karst cave on U-shaped tunnel were investigated under various karst caves positions(top,bottom,and right side of the tunnel),tunnelcave distances(0.5-4 times the radius of the tunnel arc),and cave shapes(circular,rectangular flat,and rectangular vertical caves).The failure processes of the tunnel under those various conditions were analyzed and both the failure process and the final failure patterns of the tunnel were discussed.Numerical simulation demonstrated that karst caves around the tunnel could weaken the stability of the tunnel,indicating tunnel-cave distance effects.The closer the cave to the tunnel,the weaker the tunnel under loading.This effect was not significant when the tunnel-cave distance(d)was larger than three times the tunnel arc radius(R).In addition,the final failure pattern of the tunnel and its surrounding rock mass were dependent on both the position and the size of the cave.The larger the cave,the weaker the tunnel and its surrounding rock mass.Furthermore,compared with those cases with top and bottom caves,the tunnel with a right side cave had more impacts on tunnel stability.The main research finding could help engineers carry out stability analysis on tunnels in karst areas and take effective measures to enhance tunnel stability.

Elastic Characteristics of Digital Cores from Longmaxi Shale Using Lattice Spring Models

Effective medium methods for the attribution of micro-structures to macro elastic properties of shales are important for the prediction of sweet spots in the shale-gas production.With X-ray micro-computed tomography(XMCT),the micro-structures of shale core samples from Longmaxi Formation are visualized and characterized by 3D digital images.As an efficient alternative to conventional effective medium methods for estimating elastic properties,we propose a consistent workflow of lattice spring modeling(LSM)to emulate the digital cores using three types of lattices.Particular attention is paid to investigate the effective Young’s moduli,Poisson’s ratios,and preferred orientations,by uniaxial compression tests along two directions.Within elastic deformation,the impact of lattice arrangements on the anisotropy is even more than those of stress disturbances and micro-structural features.Compared with analytical approximations and theoretical predictions,the LSM numerical scheme shows general applicability for heterogeneous porous rocks.

基于弹簧模型的重要节点排序算法

重要节点排序是复杂网络研究的重要问题。用网络的鲁棒性和脆弱性指标评价基于引力模型的重要节点排序算法GM(gravity model)和其局部算法LGM(local gravity model)时,当度大的节点从网络中移除后,其引力较大的近邻节点的后续移除通常并不能在很大程度上影响网络的结构与功能,说明算法在重要节点排序精度方面仍然存在提升之处。基于此,在弹簧模型的启发下,进一步考虑网络节点近邻和路径信息,并结合网络直径,提出了重要节点排序算法SM(spring model)和其局部算法LSM(local spring model)。基于合成网络和真实网络数据集针对网络的鲁棒性和脆弱性与经典算法进行对比实验,结果表明SM算法和LSM算法对于网络中重要节点排序具有更高的准确性。特别地,在Power网络上的SIR传播实验进一步证明了SM算法相较于其他算法,具有更高的合理性和有效性。

一维周期结构中弹性波的色散关系研究

分别采用3种方法,即分别基于连续统力学、晶格动力学(单弹簧振子)和多弹簧振子模型,对一维层合结构中的弹性波传播问题进行了研究,分析了一维声子晶体中SH波的色散关系与带隙结构.作为算例,计算了钨/天然橡胶声子晶体的剪切波传播特性,得到了一、二带隙起始、截止频率,对比了3种方法的计算结果.

嵌段共聚物相容剂对聚合物共混体系力学性能影响的连续介观模拟

结合介观动力学方法和三维弹簧格子模型,研究了嵌段共聚物相容剂对相容性较差的聚合物二元共混体系力学性能的影响.在适当范围内不断增加嵌段共聚物相容剂的用量,研究了相容剂含量对体系杨氏模数及拉伸强度的影响,同时也对不同体系材料的破碎位点进行了分析.结果表明,未加入相容剂的二元共混体系在拉伸模拟中表现出较低的拉伸强度,而适量添加相容剂可以显著提升材料的拉伸强度,随着相容剂含量的增加,共混体系的破碎位点会发生转移并最终改善材料的整体性能.而相容剂的加入对体系杨氏模数的影响较小.该连续模拟方法为关联聚合物复合体系的微观结构和宏观力学性能提供了一条高效的途径.

高分子共混薄膜的分相结构与力学性能

结合蒙特卡罗(MC)方法和三维弹簧格子模型,发展了一种从非均相高分子材料的组成出发,预测材料的微观结构及力学性能的连续介观模拟方法。计算结果显示:A-B高分子共混薄膜的形貌与共混比例密切相关,改变薄膜中两种聚合物的共混比例对薄膜整体的力学性能有较大的影响。

应用弹性振子点阵模型数值模拟表面带裂痕材料中的激光激发声表面波

本文将激光等效为垂直力源,建立弹性振子点阵模型,并采用数值模拟的方法对线源激光在金属材料中所产生超声及其传播进行了研究,着重针对有无裂痕材料表面上接收到的波形进行了对比和分析。该方法特别适合处理边界问题,因此也易于处理有缺陷材料中的激光超声问题。

三元聚合物共混体系的微观结构与力学性能模拟

建立一种构型模拟与力学性能模拟相结合的连续模拟方法研究了三元共混物(两种均聚物与一种共聚物)中交替共聚结构与嵌段共聚结构对力学性能的影响。通过蒙特卡罗模拟获得其构型,然后将该构型作为弹簧格子模型的数据输入,模拟三元共混体系的微观结构与力学性能。模拟结果表明:交替共聚物在体系中更倾向于在两种均聚物的界面处自我缠绕,而嵌段共聚物的两端分别渗透进与之相容的均聚物体相中;三元共混物的力学性能与其内部的两相界面结构相关;应变在交替共聚物体系中均匀分布,导致更多的断裂发生在体相中,交替共聚物体系比嵌段共聚物体系力学性能更强且更具韧性。这种连续模拟方法为研究材料组成与力学性能之间的关系提供了一种新方案。

基于格点-弹簧模型模拟含缺陷陶瓷材料的压缩破坏过程

采用基于有限元参数映射的格点-弹簧模型(lattice spring model)对多晶三氧化二铝(Al2O3)陶瓷的压缩破坏过程进行了数值模拟.采用弹脆性模型模拟材料,用弱界面模拟材料晶界,基于Griffith能量准则判断断裂.模拟了特定孔隙率下的Al2O3陶瓷的冲击破坏过程,所得到压缩强度与实验测试结果基本吻合.考察了孔隙对材料压缩力学性能的影响,结果显示:有孔隙陶瓷表现出一定的应变率敏感性并且其裂纹密度时程曲线具有明显的"台阶",而无孔隙陶瓷没有此现象;含孔隙陶瓷的裂纹密度发展过程中的"台阶"对应了内部裂纹的发展和止裂机制,是有孔隙陶瓷和无孔隙陶瓷的重要区别.

超高应变率下岩石的破坏机理

通过对大理石的轻气炮试验进行三维数值仿真重现,探索了岩石在超高应变率下的破坏机理。大理石试样中两个高速应力计的实测应力信号被用作数值模拟的匹配目标,结果表明,在高速冲击压缩载荷下,细观静水压破坏是大理石的主要破坏机制,而不是通常认为的细观剪切或拉伸破坏。此外,为再现不同冲击速度下大理石的物理实验观测数据,提出了新的考虑时间非局部效应的细观速率相关岩石破坏模型,并且发现对岩石轻气炮的数值模拟需采用准静态测量的弹性力学参数而不是超声测量的弹性参数。最后对具有不同孔隙度的虚拟岩石样本进行进一步的轻气炮数值试验,结果表明,岩石的孔隙度越大,在冲击压缩载荷下的动态强度和动力学率效应越小。

弹性体纳米复合材料力学行为的连续介观模拟

结合介观动力学方法和弹簧格子模型,研究了基于软-硬两种嵌段的嵌段共聚物纳米复合体系的力学行为,结果显示软、硬组分之间的应力传递与结构密切相关,而纳米颗粒的加入会改变其应力分布,并且纳米粒子的选择性分布对体系的力学响应有重要作用。在海岛结构中,纳米颗粒分布在硬组分分散相可以在提升体系硬度的同时保持体系的高延展性。该连续模拟方法为寻找具有合适力学性能的弹性体纳米复合材料提供了指导。

聚合物材料力学性能的计算机模拟

聚合物材料的宏观力学性能与其微观结构具有密切的关系,计算机模拟是研究这种结构与性能关系的重要手段之一,近年来国内外学者已经发展了多种模拟方法并从不同尺度来模拟聚合物材料的力学性能。本文综述了不同方法在聚合物材料力学性能模拟研究中的应用,重点介绍了Monte Carlo模拟、分子动力学模拟和基于弹簧格子模型的多尺度模拟这3种常见模拟方法的应用情况,如在分子动力学模拟中重点关注无定形聚合物玻璃态、结晶聚乙烯和部分非均质体系,而在多尺度模拟中则重点关注复杂的非均质聚合物体系,并讨论了各种方法的应用前景及亟待解决的问题。

Simulation of Morphologies and Mechanical Properties of A/B Polymer Blend Film

The effects of blend composition and micro-phase structure on the mechanical behavior of A/B polymer blend film are studied by coupling the Monte Carlo(MC) simulation of morphology with the lattice spring model(LSM) of micro mechanics of materials.The MC method with bond length fluctuation and cavity diffusion algorithm on cubic lattice is adopted to simulate the micro-phase structure of A/B polymer blend.The information of morphology and structure is then inputted to the LSM composed of a three-dimensional network of springs to obtain the mechanical properties of polymer blend film.Simulated results show that the mechanical response is mainly affected by the density and the composition of polymer blend film through the morphology transition.When a force is applied on the outer boundary of polymer blend film,the vicinity of the inner cavities experiences higher stresses and strains responsible for the onset of crack propagation and the premature failure of the entire system.

基于四维离散数值方法的岩石圆环试样动态破坏及耗能规律

利用最新提出的四维离散弹簧元法(4D-LSM)对岩石圆环的动态抗变形及耗能特性进行研究。首先对4D-LSM用于描述岩石圆环试样破坏的适用性进行了验证,发现4D-LSM可以较好地再现岩石试样的孔径比与破坏形态和强度间的影响规律。在此基础上,对孔隙率、非均质性、厚径比等因素与抗变形及耗能间的规律进行研究,得到了对应的数学公式。利用4D-LSM模拟大变形方面的优势,发现当岩石材料的变形抵抗能力较大时,岩石圆环将表现出与传统仅考虑小变形情况下实验和数值计算不同的破坏形态,岩石圆环的材料抗拉强度与抗变形能力也分别呈现非线性关系。通过建立圆环阵列模型,研究了由多个岩环构成的组合结构的抗变形和能量抵抗能力以及对应的破坏形态。结果表明,组合结构中的圆环单元与单圆环受力的破裂形态有所不同,但单圆环的抗变形及耗能规律仍适用于岩环阵列结构的分析。