本文選題：堆積密度 + 顆粒離散元��； 參考：《華南理工大學(xué)》2013年博士論文

【摘要】：顆粒堆積密度是反映顆粒介質(zhì)內(nèi)部構(gòu)造的一個基本指標(biāo),是土木工程中的一項(xiàng)必不可少的設(shè)計(jì)參數(shù),也是研究許多顆粒力學(xué)問題的切入點(diǎn)。鑒于顆粒堆積密度的重要性,本文結(jié)合水利圍堰中密度參數(shù)確定問題,基于PFC3D數(shù)值平臺,開展了顆粒材料堆積密度的數(shù)值試驗(yàn),研究影響顆粒堆積密度的相關(guān)因素,建立了堆積密度計(jì)算公式。同時進(jìn)行了物理模型試驗(yàn)和離心機(jī)模型試驗(yàn)驗(yàn)證計(jì)算結(jié)果的可靠性。研究內(nèi)容與研究成果如下： 1.建立了顆粒堆積密度的計(jì)算公式�；陬w粒的“填隙”和“替換”機(jī)制,從單粒徑顆粒、二元顆粒的堆積密度,推廣到級配顆粒的密度計(jì)算模式。通過數(shù)值試驗(yàn)研究計(jì)算公式中參數(shù)的影響,針對容器中顆粒堆積以及無側(cè)向邊界限制的顆粒堆積,分別建立了一整套估算級配顆粒堆積體密度的方法及計(jì)算公式。 2.基于Matlab的圖像處理功能,進(jìn)行顆粒形狀信息提取和顆粒形狀重建。從顆粒的三視圖圖像中提取圓度信息并對其進(jìn)行加權(quán)平均,得到加權(quán)圓度作為反映顆粒三維形狀特征的指標(biāo)。在Matlab中創(chuàng)建具有指定加權(quán)圓度的三維凸包,對凸包進(jìn)行體素化和骨架化處理,提取顆粒的三維空間信息,從而在PFC3D中重建具有特定形狀的clump塊體,為形狀顆粒的堆積試驗(yàn)提供基礎(chǔ)。 3.研究了顆粒材料特性對顆粒堆積密度的影響。針對顆粒的摩擦系數(shù)、顆粒形狀、顆粒級配等顆粒材料特性,設(shè)計(jì)了相關(guān)的數(shù)值試驗(yàn),得到各因素與顆粒堆積密度的影響關(guān)系。討論了顆粒試樣宏觀摩擦角與顆粒間摩擦系數(shù)之間的聯(lián)系,提出了反映顆粒級配情況的粒度分布寬度的計(jì)算方法。 4.研究了靜水條件下顆粒堆積密度的變化規(guī)律。顆粒在水中的堆積受到重力、浮力、阻力等作用,也受到顆粒與顆粒之間相互干擾的影響,這些外力作用和影響最終反映在堆積密度的變化上。本文設(shè)計(jì)了級配顆粒在流體中的堆積試驗(yàn),得出了在靜水中顆粒堆積密度與級配之間的關(guān)系。 5.研究了顆粒堆積深度與密度的關(guān)系�；跀�(shù)值試驗(yàn)結(jié)果,根據(jù)Janssen壓力公式擬合得到隨深度變化的孔隙比計(jì)算公式。在PFC3D中進(jìn)行了不同摩擦系數(shù)的顆粒側(cè)限壓縮試驗(yàn),將試驗(yàn)成果作為上覆荷載作用下顆�？紫侗茸兓囊罁�(jù),對建立的孔隙比隨深度變化的公式進(jìn)行擴(kuò)充和完善。 6.進(jìn)行了物理模型試驗(yàn)以及離心機(jī)模型試驗(yàn),對建立的估算公式的有效性進(jìn)行判斷。在不同高度的圓柱筒容器中進(jìn)行玻璃球和風(fēng)化砂的拋填試驗(yàn),對級配風(fēng)化砂進(jìn)行不同加速度的離心機(jī)試驗(yàn),模擬不同深度的風(fēng)化砂自重壓密效果。將估算值與模型試驗(yàn)值進(jìn)行對比,兩者具有較好的一致性。
[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.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2013
【分類號】：TU43

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