农田土壤表面干缩裂隙形态分析与数值模拟

发布时间：2018-07-09 23:56

本文选题：裂隙 + 闵可夫斯基函数　；参考：《宁夏大学》2017年硕士论文

【摘要】：目前,土壤干缩裂隙的发展规律以及形成机理尚不明确,为揭示农田土壤表面干缩裂隙发展规律以及形成机理,本文对农田土壤裂隙进行了试验研究。应用数字图像处理技术对农田土壤裂隙试验图像进行了二值化、去除噪点、提取裂隙边缘等处理。闵可夫斯基面积、长度、欧拉数3个可以描述裂隙空间分布以及连通性的形态参数作为裂隙定量分析指标。对裂隙试验图像进行形态学膨胀与腐蚀运算,分析了运算后裂隙试验图像的面积、长度、欧拉数密度的变化规律。同时构建了基于胡克定律的二维土壤开裂模型,模拟土壤收缩动态开裂的过程。模型假定水分蒸发是裂隙开裂的主要原因,生成裂隙的土层厚度足够小。设置均值为ε,方差为δ2的正态分布N(ε,δ2)的土壤临界应变随机场,并引入摩擦力f作为土壤静态粘合力,以及表示土壤弹塑性性能的参数网络结构连接强度nit,在由结点组成的六边形网络结构中持续减小结点间的距离模拟水分蒸发,由此引起网络结点受力改变发生断裂的过程。本文比较了模拟裂隙图像与试验图像面积、长度、欧拉数密度。结果表明:(1)应用闵可夫斯基面积、长度、欧拉数密度函数可以有效描述裂隙形态;形态学分析结果显示裂隙的闵可夫斯基面积、长度、欧拉数密度函数具有不同的变化规律,其中面积密度函数表现为0-1之间的增函数;长度密度函数表现为先增大后减小的变化规律,欧拉数密度函数表现为先增大,后减小再增大的变化规律。(2)运用基于胡克定律构建的二维土壤开裂模型,模拟由于水分蒸发而引起土壤收缩开裂过程,计算采用蒙特卡洛方法模拟获得裂隙面积、长度、欧拉数密度平均值μ以及标准差δ,试验平均密度值基本分布在模拟密度值μ± δ之间,表明模拟结果较好。(3)试验和模拟面积密度、欧拉数密度平均值相对误差较小,面积密度相对误差基本小于10%;欧拉数密度相对误差在15%左右;长度密度平均值相对误差较大,除过38-48 h之间小于10%,其余时段内均大于25%,最大相对误差达到37.38%。应用数值方法模拟土壤表面裂隙,有助于研究农田土壤裂隙的形成机理以及土壤裂隙随时间变化过程中动态演化规律。
[Abstract]:At present, the development law and formation mechanism of soil dry shrinkage fissures are not clear. In order to reveal the development law and formation mechanism of dry shrinkage fissures on farmland soil surface, this paper has carried on the experiment research to the farmland soil fissures. The digital image processing technique was applied to the field soil fissures test images to be binary, to remove the noise and to extract the fissures edge and so on. Minkowski area, length and Euler number can describe the spatial distribution of fractures and the morphological parameters of connectivity as quantitative analysis indexes of fractures. Morphological expansion and corrosion operations were performed on the fracture test images. The changes of the area, length and Euler number density of the fracture test images were analyzed. At the same time, a two-dimensional soil cracking model based on Hook's law was constructed to simulate the dynamic cracking process of soil shrinkage. The model assumes that moisture evaporation is the main cause of crack cracking, and the thickness of soil layer is small enough. The soil critical strain random field of normal distribution N (蔚, 未 2) with mean value 蔚 and variance 未 2 is set, and friction force f is introduced as the static adhesion of soil. The connection strength of the network structure, which represents the soil elastoplastic properties, decreases the distance between the nodes in the hexagonal network structure and simulates the moisture evaporation, which leads to the fracture process of the network node. In this paper, the area, length and Euler number density of simulated fracture images and experimental images are compared. The results show that: (1) Minkowski area, length and Euler number density function can be used to describe fracture morphology effectively, and morphological analysis results show that Minkowski area, length and Euler number density function of fractures have different variation laws. The area density function is an increasing function between 0 and 1, the length density function increases first and then decreases, and the Euler number density function increases first. (2) the two-dimensional soil cracking model based on Hooke's law is used to simulate the soil shrinkage cracking process caused by water evaporation, and Monte Carlo method is used to calculate the crack area and length. The average value of Euler number density 渭 and the standard deviation 未, the experimental average density value basically distributed in the simulation density value 渭卤未, which indicated that the simulation result is better. (3) the relative error of the experimental and simulated area density and the Euler number density average value is small. The relative error of area density is less than 10; the relative error of Euler number density is about 15%; the average relative error of length density is larger than 10, except that after 38-48 hours, the other period is larger than 25 and the maximum relative error is 37.38. Numerical simulation of soil surface fissures is helpful to study the formation mechanism of soil fissures and the dynamic evolution of soil fissures with time.
【学位授予单位】：宁夏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S152

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