光滑质点流体动力学方法中数值断裂的防止

为解决光滑质点流体动力学方法数值模拟过程中出现的数值断裂问题,提出一种基于Delaunay三角剖分及其对偶形式最近点意义下的Voronoi图的粒子产生和消除技术,对产生数值断裂的区域重新布点。同时讨论此技术实施过程中伴随的质量、动量和能量守恒问题的解决办法。通过典型数值算例的模拟分析可以看出,粒子产生和消除技术可以有效地解决数值断裂问题。当考察程序的相对运行时间随模型粒子数目的变化时发现,只使用粒子产生技术时,由于粒子数目大量增加使程序运行时间急剧增加。而同时使用粒子产生和消除技术时,由于粒子数目基本不变,使程序运行时间只增加百分之十左右。当考察在整个程序的运行过程中模型总能量的变化时发现,使用文中提出的守恒问题解决办法,可以基本保证能量始终守恒。

一种改进的可阻止SPH数值断裂的方法

首先通过人为设定数值断裂,从数值上分析数值断裂对计算精度的影响。然后引进一种可适用于大变形的并保证系统质量守恒、动量守恒和能量基本守恒的简单加点技术,用以阻止数值断裂。并用改进的smoothed particle hydrodynamics(SPH)方法对钢弹撞击飞机蒙皮进行数值模拟以验证其阻止数值断裂的有效性。在130～250m/s的碰撞速度下,用改进的SPH方法得到的变形区直径、剩余速度以及弹坑深度与试验结果吻合较好。

钢桥面板疲劳裂纹耦合扩展机理的数值断裂力学模拟

为研究钢桥面板疲劳裂纹耦合扩展机理,建立焊接分析有限元模型,对纵肋-顶板连接细节、纵肋-横隔板连接细节的焊接全过程进行数值模拟,基于扩展有限元方法建立钢桥面板数值断裂力学模型,对疲劳敏感细节裂纹静、动态扩展行为进行分析。焊接过程分析结果表明:纵肋-顶板连接焊缝区域、纵肋-横隔板焊缝端部区域均存在较大的残余拉应力,峰值接近钢材屈服强度;横隔板挖孔边缘存在切向残余拉应力,峰值约为200 MPa。疲劳裂纹扩展行为分析结果表明:纵肋-顶板连接细节在车辆荷载单独作用下以受压为主,考虑残余应力场作用后细节处于拉-拉应力状态,疲劳裂纹为Ⅰ型主导的Ⅰ-Ⅱ-Ⅲ型复合裂纹;车辆偏载作用下纵肋产生扭转变形,计入残余应力后纵肋-横隔板连接焊缝焊趾受拉开裂,萌生于纵肋焊趾、向纵肋腹板扩展的疲劳裂纹为Ⅰ型主导的Ⅰ-Ⅱ-Ⅲ型复合裂纹,萌生于纵肋-横隔板连接焊缝横隔板侧焊趾和横隔板挖孔边缘的疲劳裂纹为Ⅰ-Ⅱ型复合裂纹;纵肋对接细节的疲劳裂纹为Ⅰ型裂纹,车辆荷载作用下以受拉为主,位于纵肋底板弧形过渡区的裂纹相较于纵肋底板中间区域具备更强的扩展能力。

一种适用于颗粒非规则分布的阻止SPH数值断裂的方法

光滑粒子流体动力学(SPH)方法已广泛应用于航空航天领域中大变形的碰撞计算。数值断裂是SPH计算中一种常见问题,可严重影响计算结果。把适用于颗粒规则分布的阻止SPH数值断裂的方法推广到颗粒非规则分布的情形,得到了一种适用于颗粒非规则分布的阻止数值断裂的加颗粒方法。然后将该方法应用于存在数值断裂的悬臂梁弯曲仿真计算,验证了其有效性。最后把该方法应用于弹丸撞击飞机蒙皮的非规则颗粒模型计算,并和规则颗粒模型得到的结果及试验结果进行比较。对比结果表明:对于非规则分布的颗粒模型,该加颗粒方法可有效地阻止数值断裂,提高计算精度,并可较为普遍使用。

井震结合复杂断裂分级识别技术及应用——以魏岗油田①号断裂带为例

南阳凹陷中部魏岗鼻状构造带主体已整体实现井网覆盖,滚动勘探范围由鼻状构造主体转向相对勘探程度较低的周缘,目标由简单的整装构造油藏向断块破碎、储层非均质强的复杂构造油藏、断层-岩性油藏转变,因此,复杂断裂系统的精细刻画是增储挖潜的关键。利用断裂模型正演、构造导向滤波、反褶积提频、RGB属性融合等技术,井震协同建立复杂断裂分级识别技术,将测井资料垂向上与地震资料空间上对低级序断裂的高分辨率优势结合起来,实现高效快速地识别低序级小断裂,建立了魏岗油田小断裂的识别模式,降低了构造解释的多解性,有效指导了魏岗油田Ⅱ断块地堑构造带复杂断块油藏的高效增储建产。

光滑质点流体动力学方法中断裂准则的引入

基于Delaunay三角剖分及其对偶形式最近点意义下的Voronoi图,提出一种粒子产生和消除技术解决光滑质点流体动力学方法中的数值断裂问题。以此技术为基础,利用光滑质点流体动力学方法的"核函数归一化特性"对粒子携带的应力重新进行分配,进而引入断裂准则最终解决数值模拟中材料出现断裂破坏的理论依据问题。通过典型数值算例的模拟分析并与实验进行对比,结果表明,提出的粒子产生和消除技术对解决数值断裂问题是有效的;引入断裂准则使材料断裂破坏受到理论的约束与指导;与加入断裂准则前相比,程序计算结果在靶板变形区直径、深度和弹丸剩余速度三个重要指标上与实验结果具有更好的一致性。

地基变形诱发大面积混凝土结构断裂损伤的数值模拟研究

针对软土地层地基变形可能引发大面积混凝土结构附加应力场及导致混凝土结构断裂损伤的问题,通过建立符合工程特性的数值模型,模拟典型地基变形形态,系统研究混凝土结构全寿命周期中地基差异沉降变形引起结构应力状态变化、裂缝形成与演化的基本规律。结果表明:地基变形将导致混凝土结构形成显著的附加应力场,其分布与地基变形特征参数密切相关且受变形曲率支配,曲率越大应力集中程度越高;结构损伤风险因素主要是拉应力超限引起的局部断裂损伤;混凝土结构断裂损伤的风险区域主要位于截面高度大、刚度突变区域;张拉应力与地基变形曲率半径呈负指数型关系,当地基变形曲率半径小于某一量值,结构局部张拉断裂损伤风险将急剧上升。结果对软土地层大面积混凝土结构工程抗渗设计具有借鉴意义。

基于SPH的射流成形机理研究

光滑粒子流体动力学是一种纯Lagrangian的无网格数值计算方法,可以很好地处理动态载荷下材料大变形问题。采用SPH方法对射流成形和拉伸进行初步研究,给出求解爆炸和射流成形的力学模型和离散格式,针对一定锥角药型罩射流成形进行数值研究。结果表明,对爆炸、射流成形等瞬态动力学问题,SPH方法是行之有效的,但在计算过程中也存在数值断裂和应力不稳定等问题。

基于增强的物质点法的非均质弹性材料仿真方法研究

在基于物理的仿真领域,近几年流行的物质点法已经成为一种越来越重要的仿真方法.物质点法已经可以仿真雪、物质状态变化、颗粒状的沙子以及粘弹性的泡沫等物理现象.现有的各种复杂物理现象的模拟已经展示了物质点法作为一种通用的求解方法的潜质,然而对于仿真形变体尤其是自然界普遍存在的非均质材质还存在一些不足.当同一网格内部包含多种材质的粒子时,由于背景网格与粒子之间的插值只考虑粒子的几何位置而不包含物质属性信息,导致不同属性的粒子在网格内部表现为"平均化"的运动趋势.为了改进传统物质点法模拟多种材质的缺陷,该文提出了一种模拟非均质弹性材料的仿真方法.首先,在预处理过程中将仿真物体离散表示成粒子,针对物质的不同属性粒子的分布,建立物质边界并确定边界粒子,仿真过程中动态更新边界粒子的位置;其次,引入粒子影响域,区分网格内部具有不同属性的粒子,增加网格内部计算自由度;最后,提出一个判断准则,根据物质边界粒子的位置判定仿真粒子是在背景计算网格上求解还是粒子区域上求解.实验结果表明,利用改进的物质点法能够有效地模拟非均质材质弹性体的形变.与有限元法相比,该文方法在模拟非均质弹性体时可以获得相似的效果,并且在模拟拓扑结构变化的问题以及碰撞处理上更有优势.

危岩主控结构面应力强度因子求解分析

危岩是迄今研究程度极其薄弱的地质灾害类型,而主控结构面受荷损伤断裂是危岩发育机理研究的核心技术。遵循应力强度因子的可叠加性假定,运用断裂力学方法及极限平衡理论,构建了倾倒式危岩主控结构面的应力强度因子计算方法,以及损伤-断裂判别式,并建立了主控结构面的断裂数值模拟方法,为深入研究危岩发育机理以及危岩灾害的有效治理奠定了理论基础。

含球形孔洞脆性材料拉伸破坏的扩展有限元法分析

应用扩展有限元法模拟了含球形孔洞脆性材料拉伸破坏机理及破坏过程。分析了含球形孔洞的脆性材料单向拉伸情况下孔洞体积百分数对结构承载力的影响。数值计算结果显示,基于扩展有限元模型的数值方法可以准确的和可视化的直观方式分析含球形孔洞脆性材料拉伸破坏过程。结果表明,含球形孔洞脆性材料结构拉伸破坏的承载力与孔洞体积百分数密切相关。

Orthogonal design and numerical simulation of room and pillar configurations in fractured stopes

Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3~. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.

Prediction of application scope of vertical fracture strike based on scattered wave fracture orientation function

Fracture system plays a very important role in the enrichment and accumulation of oil and gas in the reservoirs. Based on scattering wave information, Fracture Orientation Function （FOF） was built, which can be used to predict the fracture orientations. However, this method has only been verified by physical experiments without studies on the application scope. In this study, based on the linear sliding theory, F0F of the scattering wave was applied to the numerical simulation and the application scope was further studied according to fracture flexibility tensor. According to the fractures filled with gas and liquid, numerical simulation was conducted on the models with various fracture flexibilities. Numerical simulation results were used to inverse fracture orientation with the aid of the FOF of the scattering wave. The results show that it is workable to predict the vertical fracture orientation with the F0F of the scattering wave. Application of this method is more effective when the fractures are filled with gas than liquid. Moreover, the application scope can be predicted by the fracture flexibility.

Rupture Property of the 1927 Gulang M_s8.0 Earthquake and Numerical Simulation of Rupture Mechanism

The 1927 Gulang M_S8.0 earthquake is a severe earthquake that followed the Haiyuan M_S8.5 earthquake of 1920 in the Qilian Mt._Hexi Corridor earthquake zone. There are divergences of opinion in the previous studies about the rupture properties of the earthquake. Based on trenching and field investigation, and analysis of historical data, we hold that the earthquake resulted from the joint process of the Tianqiaogou_Huangyangchuan fault, Dongqingding segment of the Huangcheng_Shuangta fault and the Wuwei_Tianzhu buried fault, which constitute the Gulang nappe. By finite_element numerical simulation on the deformation mechanism of Gulang nappe, it is found that the stress and strain mainly concentrate in the western segment of the Tianqiaogou_Huangyangchuan fault, the Dongqingding segment of the Huangcheng_Shuangta fault, and the Gulangxia segment of the Wuwei_Tianzhu buried fault and the Gulang_Shuangta fault. The stress concentration coincides with the distribution of the earthquake surface rupture. It also proves that the earthquake is an outcome of the Gulang nappe activity as a whole.

Fault Type Analysis along the San Andreas Fault Zone: A Numerical Approach

Finite Element (FE) modeling under plane stress condition is used to analyze the fault type variation with depth along and around the San Andreas Fault (SAF) zone. In this simulation elastic rheology was used and was thought justifiable as the variation in depth from 0.5 km to 20 km was considered. Series of calculations were performed with the variation in domain properties. Three types of models were created based on simple geological map of California, namely, 1) single domain model considering whole California as one homogeneous domain, 2) three domains model including the North American plate, Pacific plate, and SAF zone as separate domains, and 3) Four domains model including the three above plus the Garlock Fault zone. Mohr-Coulomb failure criterion and Byerlee's law were used for the calculation of failure state. All the models were driven by displacement boundary condition imposing the fixed North American plate and Pacific plate motion along N34°W vector up to the northern terminus of SAF and N50°E vector motion for the subducting the Gorda and Juan de Fuca plates. Our simulated results revealed that as the depth increased, the fault types were generally normal, and at shallow depth greater strike slip and some thrust faults were formed. It is concluded that SAF may be terminated as normal fault at depth although the surface expression is clearly strike slip.

A mesoscale model based on Monte-Carlo method for concrete fracture behavior study

An aggregate generation and packing algorithm based on Monte-Carlo method is developed to express the aggregate random distribution in cement concrete. A mesoscale model is proposed on the basis of the algorithm. In this model, the concrete con- sists of three parts, namely coarse aggregate, cement matrix and the interracial transition zone （ITZ） between them. To verify the proposed model, a three-point bending beam test was performed and a series of two-dimensional mesoscale concrete mod- els were generated for crack behavior investigation. The results indicate that the numerical model proposed in this study is helpful in modeling crack behavior of concrete, and that treating concrete as heterogeneous material is very important in frac- ture modeling.

Numerical simulation of the segmentation of the stress state of the Anninghe-Zemuhe-Xiaojiang faults

We established a three-dimensional finite element model of the Anninghe-Zemuhe-Xiaojiang faults region using contact surfaces of different sizes to describe the spatial segmentation characteristics of the faults. Our model is based on constraints from GPS observations, models of the crust and upper mantle, precise earthquake locations, the tectonic stress field, the slip rate of the faults, and the rheology of the lithosphere in the Sichuan-Yunnan area. Considering the influence of strong earthquakes since A.D. 1327, we analyzed the main controlling factors of the characteristics of the strong earthquakes and also studied by numerical simulation the possible areas of future earthquake risk and their relationship with tectonic stress. The numerical results showed that the gravitational potential energy of the Qinghai-Tibet Plateau and the interaction of adjacent blocks are the main kinetic factors affecting the characteristics of the tectonic stress distribution. There appears to be some correspondence between the distribution of tectonic stress and the b value; however, we also found that some low b value locations correspond to regions of lower stress. This contradiction may be the result of some comprehensive factors, such as the release of strain energy caused by strong earthquakes.

Fabrication and performance analyses of 45#steel supports using liquid forging

In this paper,45#steel supports prepared by liquid forging showed excellent performances and the effects of processing techniques on the development of microstructures and mechanical properties of these steel supports were researched.The liquid forging process was simulated and technological parameters were optimized via a Pro CAST simulation software.The solidification time,temperature distribution,first principal stress distribution of the 45#steel supports varied with time,temperatures,and position.Two principal parameters,pouring temperature and dwell time,were assessed for their effects on microstructures,mechanical properties,and wear resistance properties of 45#steel supports.Results showed that the optimal pouring temperature of the molten metal and the pressure-holding time were between 1540℃ and 1560℃ and between 35 s and 40 s,respectively.The microstructure,mechanical properties,and fracture behavior of different positions in the support were also discussed,and the central position performed better than the edge because of plastic deformation.Finally,the dynamic solidification process was also investigated and the liquid forging process of 45#steel supports was complex and contained some special metal liquid convection and several plastic deformation stages.

A combined continuous-discontinuous approach for failure process of quasi-brittle materials

Rock,concrete and other geo-materials,due to the presence of microstructural inhomogeneity,their fracture processes and damage characteristics are associated with the distribution of micro-cracks contained in the materials.In this study,by introducing a cohesive zone model based on fracture mechanics into the framework of deformable discrete element method,a continuous-discontinuous coupling analysis approach for simulating the fracture of quasi-brittle materials is proposed.The cohesive interface elements are inserted into certain engineering or research region.It is assumed that damage and fracture occur only in the interface elements,while bulk material is modeled to be elastic.The Mohr-Coulomb criterion with tension cut-off is adopted as the damage initiation criterion,and a scalar damage variable representing damage in the material is used to describe the rate at which the material stiffness is degraded.Cracks are simulated explicitly by the failure of the interface elements.Numerical simulations are performed in order to validate the suggested method.Partial applications are also listed.The results show that this method provides a simple but effective tool for the simulation of crack initiation and propagation,and it can reflect the whole process of quasi-brittle materials from small deformation to large deformation and failure.