级配颗粒堆积体密度估算方法研究

发布时间：2018-06-27 05:45

本文选题：堆积密度 + 颗粒离散元　；参考：《华南理工大学》2013年博士论文

【摘要】：颗粒堆积密度是反映颗粒介质内部构造的一个基本指标,是土木工程中的一项必不可少的设计参数,也是研究许多颗粒力学问题的切入点。鉴于颗粒堆积密度的重要性,本文结合水利围堰中密度参数确定问题,基于PFC3D数值平台,开展了颗粒材料堆积密度的数值试验,研究影响颗粒堆积密度的相关因素,建立了堆积密度计算公式。同时进行了物理模型试验和离心机模型试验验证计算结果的可靠性。研究内容与研究成果如下： 1.建立了颗粒堆积密度的计算公式。基于颗粒的“填隙”和“替换”机制,从单粒径颗粒、二元颗粒的堆积密度,推广到级配颗粒的密度计算模式。通过数值试验研究计算公式中参数的影响,针对容器中颗粒堆积以及无侧向边界限制的颗粒堆积,分别建立了一整套估算级配颗粒堆积体密度的方法及计算公式。 2.基于Matlab的图像处理功能,进行颗粒形状信息提取和颗粒形状重建。从颗粒的三视图图像中提取圆度信息并对其进行加权平均,得到加权圆度作为反映颗粒三维形状特征的指标。在Matlab中创建具有指定加权圆度的三维凸包,对凸包进行体素化和骨架化处理,提取颗粒的三维空间信息,从而在PFC3D中重建具有特定形状的clump块体,为形状颗粒的堆积试验提供基础。 3.研究了颗粒材料特性对颗粒堆积密度的影响。针对颗粒的摩擦系数、颗粒形状、颗粒级配等颗粒材料特性,设计了相关的数值试验,得到各因素与颗粒堆积密度的影响关系。讨论了颗粒试样宏观摩擦角与颗粒间摩擦系数之间的联系,提出了反映颗粒级配情况的粒度分布宽度的计算方法。 4.研究了静水条件下颗粒堆积密度的变化规律。颗粒在水中的堆积受到重力、浮力、阻力等作用,也受到颗粒与颗粒之间相互干扰的影响,这些外力作用和影响最终反映在堆积密度的变化上。本文设计了级配颗粒在流体中的堆积试验,得出了在静水中颗粒堆积密度与级配之间的关系。 5.研究了颗粒堆积深度与密度的关系。基于数值试验结果,根据Janssen压力公式拟合得到随深度变化的孔隙比计算公式。在PFC3D中进行了不同摩擦系数的颗粒侧限压缩试验,将试验成果作为上覆荷载作用下颗粒孔隙比变化的依据,对建立的孔隙比随深度变化的公式进行扩充和完善。 6.进行了物理模型试验以及离心机模型试验,对建立的估算公式的有效性进行判断。在不同高度的圆柱筒容器中进行玻璃球和风化砂的抛填试验,对级配风化砂进行不同加速度的离心机试验,模拟不同深度的风化砂自重压密效果。将估算值与模型试验值进行对比,两者具有较好的一致性。
[Abstract]:Particle packing density is a basic index to reflect the internal structure of granular medium, is an indispensable design parameter in civil engineering, and is also a breakthrough point to study many particle mechanics problems. In view of the importance of particle packing density, based on the PFC3D numerical platform, a numerical experiment of particle packing density is carried out in this paper, and the relevant factors affecting the particle packing density are studied, in combination with the problem of determining the density parameters of water conservancy cofferdam, based on the PFC3D numerical platform. The formula of packing density is established. At the same time, physical model test and centrifuge model test were carried out to verify the reliability of the calculation results. The research contents and results are as follows: 1. The formula of particle packing density is established. Based on the mechanism of "filling" and "substitution" of particles, this paper extends the packing density of single and binary particles to the density calculation model of grained particles. By studying the influence of the parameters in the calculation formula, a set of methods and calculating formulas for estimating the bulk density of gradation particle accumulation are established for the particle accumulation in the vessel and the particle accumulation without lateral boundary restrictions, respectively. 2. Based on the image processing function of Matlab, the particle shape information extraction and particle shape reconstruction are carried out. The roundness information is extracted from the three-view image of particles and weighted average, and the weighted roundness is obtained as the index to reflect the three-dimensional shape characteristics of particles. The three-dimensional convex hull with specified weighted roundness is created in Matlab. The convex hull is voxelized and skeleton processed, and the three-dimensional spatial information of the particle is extracted, so that the clump block with a specific shape can be reconstructed in the PFC3D. Provides the foundation for the piling test of shape particles. 3. The effect of particle material properties on particle packing density was studied. According to the characteristics of particle material such as friction coefficient, particle shape and particle gradation, the relevant numerical tests are designed, and the relationship between each factor and particle packing density is obtained. The relationship between the macroscopic friction angle and the friction coefficient between the particles is discussed, and the calculation method of the particle size distribution width reflecting the particle gradation is put forward. 4. The variation law of particle packing density under hydrostatic condition was studied. The accumulation of particles in water is affected by gravity, buoyancy and resistance, and also by the interaction between particles and particles. These external forces and effects are reflected in the change of packing density. In this paper, the stacking test of grained particles in fluid is designed, and the relationship between particle packing density and gradation in hydrostatic water is obtained. The relationship between particle accumulation depth and density was studied. Based on the results of numerical experiments, a formula for calculating porosity with depth is obtained by fitting the Janssen pressure formula. The particle lateral compression tests with different friction coefficients were carried out in PFC3D. The experimental results were taken as the basis for the variation of particle void ratio under overlying load. The formula of the variation of void ratio with depth was expanded and improved. 6. Physical model test and centrifuge model test are carried out to judge the validity of the established estimation formula. The experiments of glass ball and weathered sand were carried out in cylindrical container with different heights, and centrifuge tests of different accelerations of graded weathered sand were carried out to simulate the self-compaction effect of weathered sand with different depth. The comparison between the estimated value and the model test value shows that the two values are in good agreement.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU43

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