饱和多孔介质中颗粒迁移和沉积特性研究

发布时间：2018-05-11 09:17

本文选题：多孔介质 + 颗粒　；参考：《北京交通大学》2013年博士论文

【摘要】：饱和多孔介质中颗粒迁移特性的研究在地下污染物扩散、核废料处置、石油开采、地下水回灌和水工结构的内部侵蚀破坏等方面有很重要的研究意义。本文通过对经典的一维颗粒过滤模型进行修正,求得了不同的注入方式以及含有源汇项的解析解。其次,建立了考虑弥散作用和沉积颗粒再释放作用影响的颗粒迁移的三维模型,将颗粒迁移问题的研究从一维向三维空间进行拓展。求得的解析解可以预测多孔介质中颗粒浓度、验证更加复杂的数值模型以及确定试验参数等。另一方面,通过室内土柱试验研究了渗流速度、渗流方向、颗粒浓度以及颗粒粒径分布等对颗粒迁移和沉积特性的影响。其次,探究了渗流速度增量和颗粒粒径对沉积颗粒再释放特性的影响。主要的研究内容包括： (1)将多孔介质视为饱和、均质和各向同性介质,通过在颗粒沉积动力方程中考虑弥散作用,建立了饱和多孔介质中颗粒迁移的一维模型,求得了三种不同的颗粒注入方式(短时注入、瞬时注入以及注入浓度衰减)和含有源汇项时的相应的解析解,并且对解析解中各种迁移参数进行了讨论。对不同情况的解析解的分析可知,随着时间、沉积系数、迁移距离或者线源宽度等参数中任意参数的增大,颗粒的浓度峰值逐渐减小。沉积动力方程中忽略弥散作用会对颗粒浓度有很大的影响,不同的情况下的影响规律大不相同。 (2)以求得的一维解析解为基础,建立三维空间的颗粒迁移模型,模型分别在沉积动力方程中考虑弥散作用和沉积颗粒再释放作用的影响,并通过Laplace变换和Fourier变换求得了相应解析解的通解形式。其次,利用推导出的解析解的通解形式求出了点源和面源形式下的瞬时注入和周期性注入的具体形式的解析解。最后,以点源瞬时注入情况下的解析解为例,对各种迁移参数进行了详细的讨论。对于考虑弥散作用的三维迁移模型的解析解来说,随着时间的增大,低浓度等高线的范围逐渐向四周扩大,高浓度等高线的范围逐渐缩小。随着沉积系数的增大,浓度等高线的范围逐渐缩小。对于考虑颗粒释放作用的三维迁移模型来说,释放系数越大,相应的浓度等高线的范围越大。 (3)通过土柱试验研究颗粒粒径、颗粒浓度和水动力对颗粒迁移和沉积特性的影响,开展了4种不同粒径和4种不同浓度的试验系列,每个系列中进行了3种不同的渗流速度的试验。结果表明：对于大小和形状一定的颗粒来说,通过测试颗粒浊度来反映其浓度的变化能取得较好的结果。其次,对于同一粒径的颗粒,渗流速度越大,流出液中颗粒的浓度峰值越大。在同一渗流速度条件下,颗粒粒径越大,流出液中其浓度峰值越小。另外,渗流速度一定时,颗粒的浓度存在一个和渗流速度相关的临界值,颗粒的临界浓度随着渗流速度增加也逐渐增大。 (4)通过试验的手段研究粒径和渗流速度对多孔介质中颗粒释放特性的影响。根据渗流速度增量的不同,试验分为两种不同的试验系列,在每一个试验系列中分别对两种不同粒径的颗粒进行试验。其次,研究了渗流速度增量和颗粒粒径对沉积颗粒释放规律的影响。最后,对试验完成后石英砂中沉积颗粒量随深度变化的特性进行了定量分析。一般来说,中位粒径小的颗粒的释放量要大于相应的中位粒径较大的颗粒。渗流速度的增量不同,沉积的颗粒的特征也大不相同。 (5)利用室内土柱试验探究了渗流速度、渗流方向以及颗粒分布对饱和多孔介质中颗粒迁移和沉积特性的影响机制。试验包括三种不同的渗流方向的试验系列(向下流,水平流和向上流)。同时,以修正后的对流弥散方程求得的解析解对试验曲线进行拟合,对3种不同粒径分布的颗粒的迁移参数进行对比分析,揭示了不同水力条件下颗粒的粒径分布对其迁移和沉积特性的影响机制。颗粒的弥散度和渗流方向有很大的关系,在渗流自上至下时弥散度的变化最明显。另外,随着渗流速度的增加,颗粒的沉积系数随之减小,相应的回收率随之增加,并且中位粒径或均一性指数对颗粒的沉积特性有一定的影响。
[Abstract]:The study of particle migration in saturated porous media has important research significance in the aspects of underground pollutant diffusion, nuclear waste disposal, petroleum exploitation, groundwater recharge and the internal erosion and destruction of the hydraulic structure. This paper has corrected the classic one-dimensional particle filtration model and obtained different injection modes and source and sink. Secondly, the three-dimensional model of particle migration, which considers the effect of diffusion and sediment release, is established, and the study of particle migration is extended from one dimension to three dimensional space. The analytical solution can predict the particle concentration in porous media, verify the more complex numerical model and determine the test parameters. On the other hand, the influence of percolation velocity, percolation direction, particle concentration and particle size distribution on the migration and deposition characteristics of particles is studied through the laboratory soil column test. Secondly, the influence of the increment of flow rate and particle size on the re release characteristics of the deposited particles is investigated.
(1) the porous medium is considered as saturated, homogeneous and isotropic medium. By considering dispersion in the dynamic equation of particle deposition, a one-dimensional model of particle migration in saturated porous media is established, and three different injection modes (short time injection, instantaneous injection and injection concentration attenuation) and corresponding source and sink terms are obtained. The analytical solution of the analytical solution is discussed and the analytical solutions of the analytical solutions show that the peak concentration of the particles gradually decreases with the increase of any parameters in the parameters such as time, sedimentation coefficient, migration distance or line source width. The influence rule is quite different under different circumstances.
(2) on the basis of one dimensional analytical solution, the model of particle migration in three-dimensional space is established. The effects of dispersion and sediment release are considered in the kinetic equation respectively. The general solution form of the corresponding analytical solution is obtained by Laplace transformation and Fourier transformation. Secondly, the general solution of the analytical solution is obtained. The analytical solutions of instantaneous injection and periodic injection in the form of point source and surface source are obtained. Finally, with the analytical solution of the instantaneous injection of point source as an example, the various migration parameters are discussed in detail. For the solution analysis of the three-dimensional migration model considering the dispersion effect, with the increase of time, low concentration and so on The range of high line is gradually expanded to four sides, and the range of high concentration contour is gradually reduced. As the deposition coefficient increases, the range of the concentration contour is gradually reduced. For the three-dimensional migration model considering the release of particles, the greater the release coefficient, the greater the range of the corresponding concentration contour.
(3) through the soil column test, the effects of particle size, particle concentration and hydrodynamic force on the particle migration and deposition characteristics were studied. 4 different particle sizes and 4 different concentrations were carried out. 3 different percolation velocities were tested in each series. The results showed that the particles were tested by the particles for the size and shape of the particles. The higher the velocity of the percolation, the greater the peak concentration of the particles in the effluent. The greater the particle size, the smaller the peak concentration in the effluent at the same percolation velocity. In addition, the concentration of the particles is one and the other when the seepage velocity is certain. The critical value of flow velocity also increases with the increase of seepage velocity.
(4) the effect of particle size and percolation velocity on the release characteristics of particles in porous media is studied by means of experimental methods. According to the difference of the increment of seepage velocity, the experiment is divided into two different test series. In each test series, the particles of two different particle sizes are tested. Secondly, the increment of the seepage velocity and the particle size are studied. In the end, the quantitative analysis of the characteristics of the sediment particles in the quartz sand with depth changes after the test is completed. In general, the release of the particles with small medium size is larger than that of the corresponding particles with larger medium size. The increment of the velocity of the seepage is different, and the characteristics of the deposited particles are very different.
(5) the influence mechanism of percolation velocity, seepage direction and particle distribution on the particle migration and deposition in saturated porous media is investigated by the laboratory soil column test. The test series including three different seepage directions (downward flow, horizontal flow and upward flow). At the same time, the analytical solution obtained by the modified convection diffusion equation is tested. The test curves are fitted and the migration parameters of 3 particles with different particle sizes are compared and analyzed. The influence mechanism of particle size distribution on the migration and deposition characteristics under different hydraulic conditions is revealed. The dispersion degree of particles is closely related to the direction of seepage, and the variation of the dispersion is most obvious when the seepage is from the upper to the bottom. In addition, the particle size distribution is the most obvious. With the increase of the seepage velocity, the deposition coefficient of the particles decreases and the corresponding recovery rate increases, and the grain size or homogenization index has a certain influence on the deposition characteristics of the particles.

【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU46

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