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1.
H. R. Thomas 《国际地质力学数值与分析法杂志》1988,12(1):31-44
The subject of this paper is the nonlinear analysis of heat and moisture transfer in partly saturated soil. In particular, an extension of the previous work of the author to two-dimensional applications is presented. Problems of greater complexity and engineering significance can hence be solved. The theoretical basis of the problem is first outlined before the two-dimensional formulation of the numerical solution is given. The finite element method is employed to give the spatial distributions of the variables, with a finite difference scheme being used to predict the temporal variations. The method allows the nonlinear nature of the soil parameters to be modelled, predictions being given of the coupled transient simultaneous transfer of heat and volumetric moisture content. The two-dimensional nature of the work is illustrated for the case of surface evaporative soil moisture losses from sloping ground. Subsoil conditions of a uniform deposit of loam are considered with values of representative material parameters assumed after a literature search. The coupled nature of heat and mass transfer is illustrated by means of an analysis of the moisture migration patterns that occur. Two-dimensional moisture flow, out of and into the soil, is shown to take place. 相似文献
2.
非饱和介质中热能传输及水分迁移的数值积分解 总被引：1，自引：0，他引：1
在给出非饱和介质热能-水分传输的耦合质量控制方程和基于Fourier热传导定律的热能平衡方程的基础上,对热能传输及水分迁移的基本特征和机理进行了分析。其中,考虑了温度势、吸力势和重力势的耦合作用影响。给出有热源时控制方程的简化形式,并对半无限体自由表面作用平面热源条件下介质内非稳态温度场、体积含水率分布场进行数值积分求解。利用这些解答给出常热源强度和变热源强度两种情况下,温度场随时间的变化特征以及水分迁移的演化过程,并分析了重力项对计算结果的影响。 相似文献
3.
A new three-dimensional numerical model of coupled heat, moisture and air transfer in unsaturated soil is presented. In particular, the model accommodates moisture transfer in the form of liquid and vapour flow and heat transfer arising from conduction, convection and latent heat of vaporization. The bulk flow of dry air and the movement of air in a dissolved state are also included. The theoretical basis of the model, the finite element solution of the spatial terms and finite difference solution of the temporal terms are briefly presented. Attention is focused on the verification of the new numerical solution. This is achieved via comparisons with independent solutions of heat, moisture and air transfer in an unsaturated soil. The physical problem considered includes the highly non-linear hydraulic properties of sand. Thermal conductivity is also included as a function of soil moisture content. Excellent correlation of results is shown thus providing confidence in the new model. The new model is also applied to a number of test cases which illustrate the need for the development of a model which can fully include three-dimensional behaviour. In particular, three applications are presented each increasing in complexity. The first application illustrates three-dimensional heat transfer. This particular application is verified against existing commercial finite element software. Subsequent applications serve to illustrate how the coupled processes of heat moisture and air transfer combine to yield three-dimensional problems even within a simple geometric domain. Visualization of three-dimensional results is also addressed. © 1998 by John Wiley & Sons, Ltd. 相似文献
4.
H. R. Thomas 《国际地质力学数值与分析法杂志》1985,9(6):573-588
A theoretical model is presented to predict simultaneous transient coupled heat and moisture transfer in partly saturated soils. The formulation is in terms of volumetric moisture content, is two dimensional, includes gravitational flow and takes into account latent heat of vaporization effects. The numerical solution of the problem is accomplished by means of a finite element solution algorithm. Predictions from the numerical model are used to investigate the importance of gravitational flow, for the case of a soil stratum subjected to evaporation losses at the surface. The results achieved show good qualitative agreement with expected behaviour. 相似文献
5.
To determine moisture movement and heat transfer through an unsaturated soil under temperature and volumetric water content gradients, it is necessary to have knowledge of phenomenological coefficients of the soil. However, in unsaturated flow, i.e. flow through unsaturated soil, these phenomenological coefficients are not constants, but vary with volumetric water content as well as temperature. In this paper, an identification technique is proposed for evaluation of the phenomenological coefficients. The phenomeno-logical coefficients are first assumed to be certain kinds of functions of volumetric water content and temperature. The choice of the functional forms is based on an understanding of the physical situation, and previous knowledge of water flow in the isothermal case. The constant parameters associated with the functional forms are evaluated through the use of the identification technique. Once these phenomenological coefficients are obtained as certain functions of the volumetric water content and the temperature for a specified soil, analysis of coupled moisture flow and heat transfer in the unsaturated soil can proceed. 相似文献
6.
Experimental study on unfrozen water content and soil matric potential of Qinghai-Tibetan silty clay 总被引：3，自引：1，他引：2
Zhi Wen Wei Ma Wenjie Feng Yousheng Deng Dayan Wang Zhaosheng Fan Chenglin Zhou 《Environmental Earth Sciences》2012,66(5):1467-1476
A new soil moisture content sensor coupled with a new matric potential sensor that can operate in the subfreezing environment was used to measure the moisture content and soil matric potential dynamics of Qinghai-Tibetan silty clay. Combined with nuclear magnetic resonance (NMR) technique and thermal resistor temperature probe, the characteristics of unfrozen water content and soil matric potential, and their relationships with temperature were analyzed. The results show that initial water content has an impact on the freezing point and unfrozen water content. The decrease in the initial water content results in a depression in the freezing point. The Qinghai-Tibetan silty clay has more similar unfrozen water content characteristic to clay than to silt. There is approximately 3% of unfrozen water content retained when the soil temperature drops to −15°C. The change of soil matric potential with temperature is similar to that of the unfrozen water content. The matric potential value of the saturated silty clay is approximately −200 kPa when the soil temperature drops to −20°C. The measured matric potentials are significantly lower than the calculated theoretical values based on the freezing point depression. Moisture migration experiment indicates that soil matric potential controls the direction of moisture movement and moisture redistribution (including ice and liquid water) during the soil freezing. 相似文献
7.
This paper presents a model for the analysis of clay liner desiccation in a landfill barrier system due to temperature effects. The model incorporates consideration of fully coupled heat‐moisture‐air flow, a non‐linear constitutive relationship, the dependence of void ratio and volumetric water content on stress, capillary pressure and temperature, and the effect of mechanical deformation on all governing equations. Mass conservative numerical schemes are proposed to improve the accuracy of the finite element solution to the governing equations. The application of the model is then demonstrated by examining three test problems, including isothermal infiltration, heat conduction and non‐isothermal water and heat transport. Comparisons are made with results from literature, and good agreement is observed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
非等温条件下道路水分迁移的数值模拟 总被引：5，自引：1，他引：5
通过分析季节冻土区的温度分布规律,建立了温度随时间的变化函数.在此基础上,基于连续介质力学和热力学理论,建立了道路水分迁移过程中的水热耦合动力学模型,并对季节性冻土地区的水分迁移现象进行数值模拟分析,初步探讨了在非等温冻结条件下,水热耦合过程中路基填料的含水量和温度随时间和深度变化的关系,计算结果表明,冻结过程中在冻结峰面附近形成一个冻结含水量峰值,且该峰值随着冻结时间的延长而向深度发展,这对于路基路面的综合设计,道路冻害的预报有着重要的理论意义和实际应用价值.但要真正体现道路路基水分迁移的机理,有待于建立水分迁移过程中水、热、动载和渗流耦合模型,这是有待于进一步解决的问题. 相似文献
9.
The results of a numerical simulation of the observed field-drying behaviour of an unsaturated clay are described. In particular, the simulation of soil drying during the summer of 1983 is addressed. Richards' pressure-based unsaturated flow formulation is adopted. Transient numerical solutions are achieved by making use of the finite element method coupled with a finite difference timestepping scheme. The application of the algorithm to the simulation of the problem in hand is described. The initial moisture content distribution represents saturated conditions as indicated by field-measured data. Boundary conditions are determined from an interpretation of meteorological data. A simple method of representing plant root extraction of soil moisture is proposed. Comparisons of numerical results with field-measured data collected by British Gas are presented. Good correlation is obtained. The numerical simulation is shown to be capable of representing the observed field-drying behaviour. The complexity of modelling soil drying, as opposed to infiltration, is clearly illustrated by the work presented. 相似文献
10.
Several series of one-dimensional heat and moisture flow tests were performed to examine the moisture and temperature distributions in the buffer material compacted to a dry density of 1.67 Mg m−3 and water content of 17.7%. In all tests, water was allowed to infiltrate into a horizontal soil column from one end under a constant hydrostatic head of 276 kPa. Also the specimens were heated from the other end by the heater to a constant temperature.
It is experimentally demonstrated that the moisture moves from both ends toward the mid part of the soil column due to both thermal gradient from one end and hydraulic gradient from the other end. It was observed that, in spite of no overall volume change, local volume change occurs in the system. The measured temperatures along the length of the specimen indicate that temperature distributions stabilize within a short period of time. The time required for the temperature to stabilize decreases as the heater skin temperature increases.
The diffusivity parameters are calculated using the measured moisture and temperature profiles combined with the finite difference method. Powell's optimization algorithm was used to determine the material parameters. Good agreements between experimentally measured and calibrated volumetric water content shows that the diffusion parameters can be expressed in a linear function of the volumetric water content and temperature. 相似文献
11.
An alternative method of solution for the linearized ‘theta‐based’ form of the Richards equation of unsaturated flow is developed in two spatial dimensions. The Laplace and Fourier transformations are employed to reduce the Richards equation to an ordinary differential equation in terms of a transformed moisture content and the transform variables, s and ξ. Separate analytic solutions to the transformed equation are developed for initial states which are either in equilibrium or dis‐equilibrium. The solutions are assembled into a finite layer formulation satisfying continuity of soil suction, thereby facilitating the analysis of horizontally stratified soil profiles. Solution techniques are outlined for various boundary conditions including prescribed constant moisture content, prescribed constant flux and flux as a function of moisture change. Example solutions are compared with linearized finite element solutions. The agreement is found to be good. An adaptation of the method for treating the quasilinearized Richards equation with variable diffusivity is also described. Comparisons of quasilinear solutions with some earlier semi‐analytical, finite element and finite difference results are also favourable. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
12.
This paper presents the results of the application of a numerical model of flow of water in unsaturated soil to simulate real field behaviour. Numerical predictions are compared with field-monitored results as part of an assessment of the approach adopted. The numerical approach is based on a finite element solution of Richards' theoretical formulation, adopting a finite difference recurrence relationship to model the transient nature of the problem. The field results have been collected by British Gas in Kimmeridge clay at a site in Swindon. The simulation addressed the autumn wetting of the soil during 1983. Comparisons of volumetric moisture content readings from the field and numerical predictions give good correlation. It is concluded that the numerical model has adequately represented field behaviour over the depth of interest. Taken in conjunction with previous results, it is claimed that the model should now be capable of use in a predictive mode. 相似文献
13.
为了研究影响地埋管周围土壤冻结的因素,文章建立了模拟严寒地区热失衡状态下地源热泵冬季运行情况的实验装置。实验研究了进口流体温度、土壤体积含水率和土壤初始温度对地埋管周围土壤冻结的影响。结果表明:进口流体温度变化改善了埋管周围的温度场,有利于埋管换热器换热;随着土壤初始温度升高,减小了土壤物性参数的变化,增加了地埋管换热器的换热量;土壤体积含水率的增加,强化了周围土壤与地埋管换热器的换热作用,有利于提高地埋管的出口流体温度和取热值。 相似文献
14.
多孔介质中的流动问题,与孔隙介质的特性,含水量状态以及含水量的变化历史密切相关。基于毛细循环滞回理论模型,考虑含水量变化历史对土水特征关系的影响,在开发的U-DYSAC2有限元程序中进行了相应的数值实施。在试验给定的初边值条件下进行了非饱和渗流模拟分析,并将模拟结果与实测数据比较,表明在压力边界条件反复变化下,考虑滞回效应能获得更接近实测的结果,证实该模型在模拟各种循环变化条件下非饱和土渗流初边值问题的适用性与必要性。对入渗重分布反复变化条件下非饱和土柱流动的数值模拟表明,考虑滞回与不考虑滞回条件下,含水量、孔隙水压力和湿峰的迁移的预测在入渗后的重分布过程差异较大。考虑滞回效应时,土柱上部的脱湿速率、下部的吸湿速率比不考虑滞回时要低。从而证实了非饱和多孔介质中的土水状态依赖于含水量变化,而且强烈依赖于土体的水力路径变化。因此,循环边界条件变化下,毛细滞回效应在非饱和渗流模拟中的影响显著,必须加以考虑。 相似文献
15.
渠道抗冻胀垫层设计方法研究与数值模拟 总被引：2，自引：0，他引：2
基土换填是常用的抗冻胀措施。目前非冻胀性土缺乏科学标准的定义,换填厚度基本按照经验公式和工程类比确定,不尽科学合理。在对垫层抗冻胀机制的分析基础之上,根据层状土毛管水土水势理论给出了垫层材料的选择依据,结合热阻等效原理在考虑了衬砌结构允许位移的基础上给出了渠道垫层厚度的计算公式,并根据传统算法与该方法对山东打渔张北干渠弧形坡脚梯形渠道进行抗冻胀垫层设计;同时采用ANSYS有限元软件对渠道铺设垫层前后进行热力耦合数值模拟。研究表明,垫层通过改善水分场、温度场削弱了冻胀发生的因素;该垫层算法比传统算法合理、工程造价较低。数值分析表明,渠道冻胀量、冻胀力明显被削减,其中对阴坡的削减可达90%以上。 相似文献
16.
Soil moisture potential and water content in the unsaturated zone within the arid Ejina Oasis in Northwest China 总被引：2，自引：0，他引：2
X. Zhou L. Wan B. Fang W. B. Cao S. J. Wu F. S. Hu W. D. Feng 《Environmental Geology》2004,46(6-7):831-839
Three soil profiles were selected in the Ejina Oasis, northwest China, to determine water content profiles and evolution of soil moisture potentials in the unsaturated zone within the arid area. The total soil moisture potentials have been monitored for about 3 months in 2001 at different depths in the soil profiles. The occurrence and movement of water in the unsaturated zone was analyzed using the zero flux plane (ZFP) method. It is shown that convergent ZFPs and divergent ZFPs may occur at depths between 0.5 and 3.0 m, and that the depth of the ZFPs was controlled by the root zone of plants growing on the land surface. Profiles of the total soil moisture potentials were observed to be coincident with those of the water contents at the three experimental sites. The total soil moisture potential showed a slight increasing trend and the ZFPs tend to vanish from summer to winter as the water extraction by roots decreased. Evapotranspiration through vegetation has an important bearing on the water content and the total potential in the unsaturated zone. 相似文献
17.
In this study, a capillary barrier system was designed and tested for an arid land environment. To simulate arid land conditions
of high temperature and sub-irrigation systems, the barrier was subjected to thermal and hydraulic gradients in opposite directions;
to test the barrier system under these severe conditions, an experimental apparatus was designed and fabricated. The multilayer
capillary barrier consisted of three layers made of silica sand, a mixture of sand and bentonite in equal portions, and a
mixture of clay (25%) and aggregate (75%). Several one dimensional coupled heat and moisture tests were performed. Temperature
variations along the thickness of the barrier were recorded as a function of time, and at the end of each test, the barrier
was sliced into small sections, for the determination of volumetric water content as a function of distance from the heat
source. The experimental results were discussed in view of the barrier's intended purpose of its ability to store moisture
for long time durations.
Coupled heat and moisture flow equations were developed and solved numerically via a finite difference method. Diffusivity
parameters were calculated by using experimental results, a numerical model, and Powell's conjugate directions method of nonlinear
optimization. The model was calibrated and the results were discussed. Good agreement between calculated and experimental
results was obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
冻土温度场分析对于冻土特性研究及冻土地区工程建设具有重要的作用,而冰水相变所产生的相变潜热大大增加了冻土温度场分析的复杂性。针对该问题,基于线热源模型和冻土传热基本理论,在考虑未冻水和相变潜热的情况下计算了冻土导热系数、体积热容和相变热容,分析其与测量初始温度的关系;在分析结果的基础上,对冻土含冰量的光纤测量技术进行了理论修正。基于主动加热光纤（AHFO）法,开展了一系列室内验证试验:在恒定的加热功率和时间下,采用自主研发的光纤光栅（FBG）刚玉管传感器,对同一初始含水量的冻土试样进行温度监测。结果表明:在本文试验条件下,FBG刚玉管传感器的影响半径小于5 cm,可以忽略边界效应;传感器所测温度增量与时间对数线性关系良好,主动加热对于冻土导热系数影响较小,线源模型适用于冻土导热系数测量;冻土导热系数与试验初始温度呈线性增长关系;在初始温度低于-6 ℃时,相变热容趋于稳定;在-6~0 ℃时,相变热容随温度升高逐渐增大,且变化趋势愈渐强烈;当初始温度高于-5 ℃时,相变热容甚至大于冻土自身的体积热容。相关结论为进一步提高冻土含冰量测试技术的精度提供了参考。 相似文献
19.
针对现有分布式单位线汇流理论未考虑土壤含水量变化引起的时变汇流路径问题,提出动态汇流路径新概念,推求同时考虑降雨强度和土壤含水量时空分布的坡面流速计算公式,引入地形指数刻画流域蓄水能力空间分布,从而获得栅格尺度流域流速分布场,进一步建立不同蓄满状态下流域动态汇流路径集合,最终实现考虑动态汇流路径的时变分布式单位线推求。以龙虎圩和东石流域为实例,通过SCS模型计算产流量,采用本文所提方法进行汇流计算,引入涵盖低流量误差、高流量误差及洪量误差的多目标优化方法率定参数,2个典型流域28场洪水预报结果表明,洪峰流量相对误差在±15%内,峰现时间误差在±6 h之间,纳什效率系数平均值超过0.8,与现有方法相比,所提方法能更加准确地反映汇流时间分布场,提高了洪水预报精度。 相似文献
20.
为了研究多年冻土表层的水热分布情况,在非饱和冻土的能量守恒方程和水分迁移的质量控制方程的基础上考虑冰水相变和水汽相变过程,并考虑水汽运移传热及温度势对水汽迁移的影响,建立了非饱和冻土的水-热-汽耦合模型。采用光滑粒子流体动力学(smoothed particle hydrodynamics,简称SPH)方法可方便地计算它们的演化过程。为此,在计算中先求解能量守恒方程的含冰量及气态水含量,再对未冻水含量和温度场进行求解,从而实现了温度场与水汽场的耦合。在此基础上,模拟计算了第1类热边界条件下半无限空间介质内非稳态温度场、体积含水率及水汽通量的分布情况,并将计算结果与未考虑耦合的解析解进行比较,结果显示水汽耦合的作用不容忽略。最后,针对处于季节性周期温度边界下路基的水热场的分布情况进行计算。研究表明,相比于水-热耦合模型,所建立的水-热-汽耦合模型得到的计算结果更为接近实际监测结果,可很好地揭示非饱和冻土中的水热汽迁移特征及其相变过程。 相似文献