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1.
为明晰回转窑内颗粒的运动行为及偏析机理,以绿豆、黄豆和黑豆为颗粒介质,依次对3种装填顺序下的颗粒流动过程进行离散元模拟与实验研究,以颗粒质量分数和平均粒度为判据,对颗粒偏析进行评价。结果表明,回转窑内颗粒流动区可分为自由滚落区、渗流呆滞区以及窑壁携带区,自由滚落区颗粒流速最大,而渗流呆滞区流速最小。窑内颗粒沿轴向输运过程发生径向偏析,形成夹层结构,小颗粒受渗流作用在渗流呆滞区中心形成内核,大粒径和中等粒径颗粒集中在自由滚落区和窑壁携带区。窑内颗粒力链分布不均匀,强力链分布于近窑壁区,弱力链分布于自由滚落区和渗流呆滞区,且渗流呆滞区力链细而密集。当窑头附近不同粒径颗粒存在轴向速度差时,颗粒在轴向发生掺混,并产生径向偏析。  相似文献   

2.
不同尺度分布散粒材料砂堆形成过程的二维离散元模拟   总被引:5,自引:1,他引:4  
用作者开发的离散元程序,模拟不同尺寸分布的砂堆形成过程.把散体颗粒简化为圆形颗粒,模拟过程分三步:首先利用参考网格生成颗粒的松散堆积结构;为了避免颗粒下落的冲击作用对砂堆安息角的影响,先模拟颗粒在重力作用下在圆柱容器内的自由下落与堆积,直至堆积达到稳定;最后,移除容器,只保留一个底部边界,模拟颗粒体系的散落过程,直至形成一个稳定的砂堆.模拟结果表明,在其他参数保持相同的情况下,随着颗粒尺寸的减小,砂堆的安患角逐步减小并趋向于一常值.对模拟中的两组颗粒体系进行相同条件下的砂堆形成实验,结果表明,模拟与实验所得安息角大体相当.  相似文献   

3.
高召宁 《实验力学》2011,26(3):285-290
从颗粒流的一般本构方程出发,利用室内大型相对密度仪和直接剪切仪,针对粒径分形分布对孔隙率和内摩擦角的影响进行了实验研究。结果表明,在相同实体密度、弹性恢复系数和几何平均中值粒径条件下,随粒径分维数的增大,孔隙率增大,而内摩擦角、颗粒浓度、剪切应力系数与正应力系数均减小。进而分析了粒径分形特性对颗粒流动行为的影响,得出粒径分维数小的颗粒系统剪切应力大,系统的流动性能差,鲁棒性强;反之,分维数大的颗粒系统剪切应力小,系统的流动性能好,敏感性强。对系统组构的分形特征影响系统颗粒物质崩塌流动行为的机制进行了初步探索,为颗粒流系统的研究提供了新思路。  相似文献   

4.
颗粒堆积是地质工程中较为普遍的现象,而其堆积稳定后的安息角可以在一定程度上反映颗粒堆积的基本特征.用DEM方法研究不同密度分布的颗粒堆积过程及堆积结果,有助于我们在细观层面研究颗粒密度对颗粒堆积结果的影响和验证DEM方法分析颗粒堆积的合理性.本研究用圆形颗粒简化模拟散体颗粒:第一步,用EDEM软件建立相关模型,在模型内生成简化的颗粒,模拟颗粒在重力作用下自由下落和堆积稳定的过程;第二步,模型中生成颗粒下落堆积稳定后,保留模型底部边界,数值模拟研究移除模型上部边界后颗粒散落堆积稳定的过程并测定堆积体的安息角;第三步,对应数值模型,做相关的实验进行对比验证.研究结果表明:在只考虑堆积颗粒密度而忽略其他参数影响的条件下,堆积颗粒材料的密度越小,其堆积稳定后的安息角越大.  相似文献   

5.
离散颗粒流动堆积行为离散元模拟及实验研究   总被引:2,自引:0,他引:2  
工程应用中存在许多颗粒流动堆积问题.首先设计了一系列测量方法,通过大量的实验和统计分析,得到了颗粒的多种物理参数.并以工程中高炉炉顶称量料罐为背景,采用离散元方法模拟不同物理条件下离散颗粒的流动堆积行为,得出料罐内颗粒系统中颗粒之间力的分布不均匀,而且强力链分布主要与料罐的左下壁方向平行.同时,设计并制作了具有多参数调节的离散颗粒料罐实验模型,进行了相应的物理实验,实测结果与数值模拟吻合良好.  相似文献   

6.
本文发展了一种实施简便的颗粒介质弹性参数测量方法,设计并加工了基于该方法的实验装置。利用加载设备对该实验装置在一个方向上加卸载,在加载方向和与之垂直的另一方向上测量载荷和位移后即可获得颗粒介质的等效弹性模量和泊松比。该实验装置的容器还可方便地调节尺寸,适用于测量不同粒径颗粒堆积在不同大小容器时的弹性参数。本文还研究了尺寸效应的影响,分析了容器尺寸和颗粒粒径分别对介质弹性参数的影响规律。  相似文献   

7.
张炜  萧伟健  袁传牛  张宁  刘焜 《力学学报》2022,54(9):2489-2500
为阐明粒径分布对铁粉压制中体系内部细观力学行为的影响, 基于离散元理论, 通过改变铁粉颗粒粒径分布建立压制模型, 结合力链提取方法, 通过对力链空间分布、力链数目、力链长度和力链方向性的分析, 探究粒径分布对力链演化的影响机理. 研究结果表明: 不同粒径分布的粉体压制时形成的力链空间分布具有差异, 粒径分布范围越小, 形成的力链分布越集中, 反之, 粒径分布范围越大, 形成的力链分布越松散且均匀; 在粉末压制时, 粒径分布对力链数目也有影响, 具体表现为随着粉体的粒径分布范围变大, 力链总数逐渐减少; 粉体的粒径分布对颗粒形成短力链的数目起着显著影响, 而对力链长度的影响较为有限; 随着粒径分布范围的增大, 力链的方向由均匀分布逐渐集中在特定角度方向, 表现出一定各向异性, 形成的交叉力链网络结构有利于提高粉体致密化程度. 本文为从粉体粒径分布影响层面拓展粉末压制细观力学理论提供基础, 亦为进一步结合粉体粒径分布及体系内力链演变过程改善粉末致密化行为提供指导.   相似文献   

8.
细观结构是认知土石体力学行为本质的关键科学问题。本文通过引入物理学和数学等方法,借助颗粒物质力学理论,从几何排列与接触力的空间分布来定量刻画水平固结与山前坡地堆积两种典型环境下土石体的细观结构特征,并建立其与抗剪强度指标的关联。研究表明,(1)两种环境的土石体在细观结构上存在较大差异。在几何排列上,水平固结环境下的土石体具有长程无序和短程有序的特点,坡地堆沉积环境下的土石体表现出了无序的无定形结构;在接触力与单位接触向量的空间分布上,两者较为相似,绝大多数接触力以小于均值接触力的形式存在,其概率密度曲线P(f)呈幂函数衰减;90%以上接触方位角集中在40°~160°和220°~340°范围内。(2)基于径向分布函数、接触力概率密度和单位接触向量分别定义细观结构的特征量K_a,K_s和K_o,发现三个特征量的增大对内摩擦角呈线性促进作用,对黏聚力呈非线性削弱作用。  相似文献   

9.
张祺  乔婷  季顺迎  厚美瑛 《力学学报》2022,54(2):336-346
宏观颗粒体系的有序堆积研究可以为热系统中微观粒子的自组装提供研究模型, 也有助于工业生产中提高颗粒材料的填充率. 实验发现圆筒中的圆角立方体颗粒受容器往复旋转剪切作用会实现有序堆积. 为探究旋转圆筒中立方体颗粒有序堆积过程的内部结构演化过程和动力学机理, 采用超二次曲面方程构造了圆角立方体颗粒, 基于离散元方法对旋转剪切作用下圆角立方体颗粒有序堆积过程开展数值模拟研究. 模拟复现了实验中立方体颗粒从随机堆积状态向有序致密堆积状态转变的过程, 给出了体积分数和有序度参数在容器不同运动条件下随旋转次数增加的变化规律. 结果表明, 立方体颗粒的体积分数和有序度表现为随着容器旋转次数增加而逐渐增大直至稳定的变化趋势. 体系的有序堆积过程由外层颗粒开始逐渐向内部颗粒扩展. 通过调控容器旋转角位移发现颗粒完成有序堆积过程所需的特征旋转次数与容器旋转角位移呈现反比例关系. 旋转角位移过低, 体系只会形成两种颗粒团簇共存的结构, 即某一面平行容器底面的颗粒团簇与面对角线平行重力方向的颗粒团簇共存. 研究也发现在亚重力环境下立方体颗粒同样可以通过容器的旋转实现有序堆积. 重力加速度的减少会抑制立方体颗粒从无序堆积向有序堆积的转变.   相似文献   

10.
为考察脆性空心颗粒材料冲击载荷下的力学特性,以具有不同粒径分布的粉煤灰漂珠为研究对象,对其静动态力学性能进行实验研究。通过限制颗粒材料压缩应变为50%,分析颗粒破碎率和破碎机理与材料宏观应变率效应的关系。结果表明:(1)不同粒径的漂珠颗粒材料在动态压缩下较准静态压缩下颗粒材料的强度均有明显的增强,在0.001和150 s?1大小颗粒的强度分别提高200%和195%,在150和300 s?1大小颗粒的强度分别提高39%和51.5%,在300和800 s?1大小颗粒的强度并未发生明显的变化;(2)在相同加载速度下粒径较小的颗粒比大粒径颗粒的强度和吸能效果分别提高35%~40%和35%~48%;(3)对破碎后颗粒粒径分布曲线分析可知,随着加载速度的增加,大小颗粒的破碎率和破碎程度都会增大,且在相同加载速度下大颗粒的破碎率较小颗粒的破碎率高;(4)Hardin破碎势分析表明,单位输入能量下颗粒的相对破碎势随冲击速度增大而减小,动态冲击下用于颗粒破碎的能量利用率降低,从而导致材料在相同压缩量下产生更高的能量耗散和应力水平,即表现为宏观的应变率效应。  相似文献   

11.
Based on the principle of ultrasonic resonance scattering, sound-scattering characteristics of double-layer spherical particles in water were numerically studied in this paper. By solving the equations of the scattering matrix, the scattering coefficient determined by the boundary conditions can be obtained, thus the expression for the sound-scattering function of a single double-layer spherical particle can be derived. To describe the resonance scattering characteristics of a single particle, the reduced scattering cross section and reduced extinction cross section curves were found through numerical calculation. Similarly, the numerically calculated sound attenuation coefficient curves were used to depict the resonance scattering characteristics of monodisperse and polydisperse particles. The results of numerical calculation showed that, for monodisperse particles, the strength of the resonance was mainly related to the particle size and the total number of particles; while for polydisperse particles, it was primarily affected by the particle size, the coverage of the particle size distribution and the particle concentration.  相似文献   

12.
A new type of displacement pile, the X-section cast-in-place concrete(XCC)pile, has recently been developed in China. Extensive field tests and laboratory experiments are undertaken to evaluate its performance and quantify the non-uniform deformation effect(NUDE) of the X-shaped cross section during installation. This paper develops a simplified theoretical model that attempts to capture the NUDE. Based on the theory of complex variable plane elasticity, closed-form solutions of the stress and displacement for the X-shaped cavity boundary value problem are given. Subsequently, the analytical solution is used to evaluate the NUDE, the concrete filling index(CFI), and the perimeter reduction coefficient of the XCC pile cross section. The computed results are compared with field test results, showing reasonable agreement. The present simplified theoretical model reveals the deformation mechanism of the X-shaped cavity and facilitates application of the newly developed XCC pile technique in geotechnical engineering.  相似文献   

13.
为分析不同材料和尺寸的薄板试样在室温下拉伸破坏后均形成与横截面夹角在20°~25°之间斜断口的原因,首先用统计方法对试样内随机分布微缺陷进行讨论,提出一种在宏观尺度上材料内微缺陷分布局部非均匀简化模型的假设.应用含孔材料损伤本构模型对含有不同方向微缺陷分布局部非均匀薄带区域的16MnNb薄板试样变形至破坏全过程进行数值模拟.结果表明,斜断口形成主要是由于试样内在与横截面夹角小于45°的带形区域内微缺陷分布局部非均匀造成,且与该带形区域在试样中位置无关;由于考虑微缺陷分布局部非均匀,得到试样的斜断口形成过程与试验现象完全一致;同时结合试验断口形貌,对变形过程中颈缩截面内损伤演化和破坏过程进行研究,进一步解释薄板试样的损伤破坏机制.  相似文献   

14.
陡倾滑面滑坡推力竖向分力显著,基于滑坡推力水平假定与普通抗滑桩相互作用不充分这一问题,建立锯齿形抗滑桩结构。依据梯形分布滑坡推力的假设,推导了受荷段内力计算公式,采用Winkler弹性地基理论推导了锚固段内力计算公式,并开展锯齿形抗滑桩的力学性能研究。分析表明,(1)随着滑面倾角的增加,锯齿形抗滑桩的受荷段、锚固段的弯矩、剪力以及侧应力均减小,内力减小幅度随之增大;(2)滑面倾角在20°~40°时,随着滑面倾角的增加,锚固段的理论最小长度在逐渐增加,40°时锚固段的长度为4.2 m达到最大值,且该长度仅占整个桩长35%,远小于按现行规范取得的锚固段长度最大值(1/2总桩长),桩侧摩阻力就可以完全满足竖向力学平衡;(3)将锯齿形抗滑桩与普通抗滑桩内力对比,受荷段和锚固段的弯矩减小34%、剪力减小36%及桩侧应力减小幅度大于30%,力学性能良好。  相似文献   

15.
In industrial blast furnaces (BFs), the investigations involving the flow behaviors of particles and the resultant burden structure are essential to optimize its operation stability and energy consumption. With the advance of computing capability and mathematical model, the discrete element method (DEM) specialized in characterizing particle behavior has manifested its power in the investigation of BFs. In the framework of DEM, many particle models have been developed, but which model is more suitable for simulating the particle behaviors of BFs remains a question because real particles in BFs have large shape and size dispersity. Among these particle models, the super-ellipsoid model possesses the ability to change shape flexibly. Therefore, the focus of this study is to investigate whether the super-ellipsoid model can meet the requirement of authenticity and accuracy in simulating the behaviors of particles with large shape and size dispersity. To answer this question, a simplified BF charging system composed of a hopper and a storage bin is established. The charging process and the final packing structure are analyzed and compared between experiments and simulations with different shape indexes. The results show that super-ellipsoid particles have prominent advantages over spherical particles in terms of representing the real BF particles, and it can more reasonably reproduce the flow behaviors and packing structure of experimental particles. The computation cost of super-ellipsoid particles is also acceptable for engineering applications. Finally, the micro-scale characteristics of packing structure is analyzed and the single-ring charging process in industry-scale BF using super-ellipsoid particles is conducted.  相似文献   

16.
大跨斜拉桥结构健康监测实验室模型试验平台   总被引:1,自引:0,他引:1  
本文基于山东滨州黄河公路大桥,建立面向结构健康监测的实验室模型试验平台.基于相似理论,分析模型相关参数的相似关系,确定模型缩尺比、材料和截面尺寸,并对模型附加质量和斜拉索进行合理地简化.采用ANSYS建立物理模型的三维空间实体有限元数值分析模型,实体建模能较好的体现模型局部特征和模拟损伤.模型制作采用分段整体浇注,分段之间设计连接件连接,模拟斜拉桥施工顺序进行实验室组装,基于影响矩阵法对斜拉索进行张拉成桥.建立了包括传感器系统、静动力加载系统、数据采集系统和数据处理四大部分的完整试验体系,并对隔离出的桥塔和桥面板子结构进行了静动力试验,对全桥模型进行了动力测试.子结构和全桥模型的试验结果与有限元计算结果,以及原桥实测值都吻合较好,验证了斜拉桥模型的准确性和试验平台的有效性.试验系统的建立,为结构健康监测技术提供了一个试验研究平台.  相似文献   

17.
The role of particle size heterogeneity on micro- and macromechanical properties of assemblies of spherical particles was studied using DEM simulations. The response to an imposed load of a granular material composed of non-uniformly sized spheres subjected to uniaxial confined compression was investigated. A range of geometrical and micro-mechanical properties of granular packings (e.g., void fraction, contact force distribution, average coordination number and degree of mobilisation of friction at contacts between particles) were examined, and provided a more accurate interpretation of the macroscopic behaviour of mixtures than has previously been available. The macromechanical study included stress transmission, stiffness and angle of internal friction of the granular assemblies.The degree of polydispersity showed slight effect on both, the void fraction and the elastic properties of the system. The tendency for increase in the lateral-to-vertical pressure ratios was observed with an increasing degree of particle size heterogeneity; however, the different pressure ratios calculated for samples with various degrees of polydispersity lay within the range of data scatter.  相似文献   

18.
This paper presents a numerical model for simulating the pore-scale transport and infiltration of dilute suspensions of particles in a granular porous medium under the action of hydrodynamic and gravitational forces. The formulation solves the Stokes’ flow equations for an incompressible fluid using a fixed grid, multigrid finite difference method and an embedded boundary technique for modeling particle–fluid coupling. The analyses simulate a constant flux of the fluid suspension through a cylindrical model pore. Randomly generated particles are collected within the model pore, initially through contact and attachment at the grain surface (pore wall) and later through mounding close to the pore inlet. Simple correlations have been derived from extensive numerical simulations in order to estimate the volume of filtered particles that accumulate in the pore and the differential pressure needed to maintain a constant flux through the pore. The results show that particle collection efficiency is correlated with the Stokes’ settling velocity and indirectly through the attachment probability with the particle–grain surface roughness. The differential pressure is correlated directly with the maximum mound height and indirectly with particle size and settling velocity that affect mound packing density. Simple modification factors are introduced to account for pore length and dip angle. These parameters are used to characterize pore-scale infiltration processes within larger scale network models of particle transport in granular porous media in a companion paper. Articlenote: Currently at GZA GeoEnvironmental Inc., 1 Edgewater Drive, Norwood, MA 02062, U.S.A.  相似文献   

19.
A set of governing equations for nonlinear theory of spatially curved elastic beams of thin-walled open cross section composed of straight rectangular elements is presented explicitly in the Lagrangian form. It is shown that local deformations, i.e. in-plane distortion of the cross section may easily be taken into account by the use of the analytical model proposed by Epstein and Murray. The essential feature which distinguishes the present work from Epstein and Murray's is the use of an auxiliary element when the axial curve of beams is not located on the cross section. This enables us to select arbitrarily the axial curve of rods. For the engineering theory of rods, the simplified governing equations for the nonlinear and linear theories with and without local deformations are derived from the rigorous nonlinear theory by employing the thinness assumption. It is also shown that the reduced linear theory without local deformations agrees with the Vlasov theory.  相似文献   

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