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随着全球气候变暖、城市化进程加快,世界各地大城市的“热岛”效应及其带来的各种环境和生态问题越来越严重。本文从地质环境保护的角度,分析了城市“热岛”效应的成因、特点及其对地质环境的影响,重点讨论了城市“热岛”效应环境中土体工程性质的变化及其带来的各种灾害效应,在此基础上,凝练出了4个关键科学问题,即城市“热岛”效应环境中土体温度场变化规律、土体中水分迁移规律、土体工程性质变化规律以及土体地质灾害效应,并对它们的具体研究内容进行了详细的分析。论文的分析成果对于掌握城市“热岛”效应对土体工程性质的影响,保护城市地质环境和防灾减灾,实现城市的可持续发展具有重要的理论和现实意义。
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根据Philip与Vries提出的土壤中水热交换的耦合理论,建立了植物固沙区土壤水热运移的耦合模型,考虑了液态水和汽态水运移对温度的变化,分析了植物根系吸水对土壤水热交换的影响,给出了植物蒸腾量、土壤蒸发量、根系汲水率及土壤表面热通量等有关变量的计算公式.利用本模式并采用具有二阶精度的Crank-Nicolson格式对非线性扩散方程进行离散,对沙坡头植物固沙区土壤水热交换过程进行了数值模拟,模拟结果和实测值进行了比较,总体上符合较好,证明本模型具有实用价值,可为改造沙漠提供科学依据 相似文献
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冻土力学的研究进展与思考 总被引:29,自引:0,他引:29
从冻结土的宏观力学性质,正冻土中的水、热迁移理论,正
冻土的水热力耦合模型四个方面分析综述了国内外冻土力学的发展
历史、研究现状与我国冻土力学研究中存在的问题,指出:(1)当
前冻土力学的研究内容应该从对冻结土的宏观强度与变形性质向更
切合实际工程需要的正冻土、正融土微、细观热、力学耦合性质方
面深化;(2)冻土力学的研究思路应该从对土样纯力学量的试验研
究向土样组构、级配、含水量、饱和度等土性指标在不同负温下对
土样颗粒排列与胶结特性的强度、变形影响机理方面转移;(3)冻
土力学的研究对象也应该从室内冻结试验的研究向具有各种不同水
热交换边界条件与水热迁移内在规律的冻土体发展。 相似文献
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N. K. Talukder 《Heat and Mass Transfer》2000,36(2):143-146
Due to radioactivity of spent nuclear fuel, a repository is expected to act as a heat source of exponentially decreasing
intensity over hundreds of years. In case of underground emplacement of such a heat source, the temperature changes in the
soil layers surrounding the heat source may have important implications such as evaporation of the water contained in the
soil and its subsequent condensation. Assuming a uniformly distributed power generation over a horizontal, relatively thin,
circular zone of several thousand meters diameter located several hundred meters below the ground surface, the temperature
variations along the vertical centerline of the heating zone was estimated analytically under simplifying assumptions. Unsteady
one-dimensional heat conduction in a semi-infinite solid with an exponentially decreasing heat flux at the proximal end was
considered. The corresponding solution of the Fourier equation for heat conduction contains Error Functions of complex arguments.
The evaluation of the Error Functions for discrete space and time parameters was performed applying analytical procedures
and using standard tables. The results show temperature distributions in the soil at various time points over thousands of
years after underground emplacement of spent nuclear fuel.
Received on 19 July 1999 相似文献
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One-dimensional heat and moisture transfer in the aeration region of reclaimed land is considered for two limiting cases. In the first, the heat transfer is mainly due to the thermal conductivity of the soil; in the second, to the motion of moisture. The influence of the water-table depth on the thermal regime is investigated. A solution to the problem of unsteady heat transfer in soil is found analytically by the method of matched asymptotic expansions.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 63–71, September–October, 1981.We thank V. S. Berman for discussions and valuable comments. 相似文献
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基于应力平衡条件、渗流连续方程、能量守恒方程,考虑土颗粒和孔隙水热膨胀系数的不同,建立考虑热水力耦合的饱和土体三维热固结控制方程。利用傅里叶变换和拉普拉斯变换导出变换域上的控制方程,解得点热源在变换域和实数域上的解析解,再利用区域积分给出两平行圆柱形热源热固结土体温度、孔压、位移的解析解,并对其进行分析,发现径距比增大会导致两热源温度相互影响程度减弱,热固结系数减小会导致孔压和位移的峰值增大。 相似文献
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Heat and mass transfer in unsaturated porous media at a hot boundary: I. One-dimensional analytical model 总被引:2,自引:0,他引:2
We present a model of heat and mass transfer in an unsaturated zone of sand and silty clay soils, taking into account the effects of temperature gradients on the advective flux, and of the enhancement of thermal conduction by the process of latent heat transfer through vapor flow. The motivation for this study is to supply information for the planned storage of thermal energy in unsaturated soils and for hot waste storage. Information is required on the possibility of significant drying at a hot boundary, as this would reduce the thermal conductivity of a layer adjacent to the boundary and, thus, prevent effective heat transfer to the soil. This study indicates the possibility that the considered system may be unstable, with respect to the drying conditions, with the occurrence of drying depending on the initial and the boundary conditions. An analysis performed for certain boundary conditions of heat transfer and for given soil properties, disregarding the advective flux of energy, indicated that there are initial conditions of water content for which heating will not cause significant drying. Under these conditions, fine soils may be better suited for heat transfer at the hot boundary, due to their higher field capacity, although their heat conduction coefficients at saturation are lower than those of sandy soils. At present, these conclusions are limited to the range of 50–80°C. Potential effects of solute concentration at the hot boundary are indicated. 相似文献
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非饱和正冻土的三场耦合理论框架 总被引:11,自引:2,他引:9
在``饱和正冻土的理论构架'的基础上,假定了冻土体内的空气的流动是一
种Darcy流,进一步考虑了非饱和土中气相的影响,提议了一种综合考虑两种极端
情况:(1) 气体与外界完全相通. (2) 气体与外界完全不相通的相关水、热、力相
耦合的多孔多相介质理论构架------半连通、半封闭非饱和正冻土理论构架.
重点讨论了较简单的气体半连通半封闭的非饱和孔隙冻土体的三场耦合模型. 为
检验三场耦合分析模型及所开发的针对冻土工程三场耦合模型的软件系统3G2001
的合理性与正确性, 与214国道花石峡 试验路基实测的地温变化和路基路面变形
进行了对比验证, 对比结果显示: 路基中分析所得的温度场与实测值变化规律一
致, 量化相差大都在10\%$\sim$20\%以内; 分析所得耦合变形随时间的变化也与
实测值完全一致, 路中的分析变形与实测相差也在10%-20%以内 相似文献
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Migration of salts in the unsaturated zone caused by heating 总被引:3,自引:0,他引:3
Heat-transfer phenomena as well as moisture movement in unsaturated soils due to thermal gradients, have been extensively studied during the last four decades. Less attention has been devoted to the transport and redistribution of solutes caused by heating.Solar radiation, radioactive waste repositories, underground energy storage, buried electric cables and steam pipes, disposal of waste heat from power plants are examples of heat sources in the soil.Soil-water properties, such as surface tension, viscosity, density, as well as the equilibrium composition of phases, depend on temperature. Hence, nonuniform heating of a soil partially saturated by saline water has an effect on such processes as water flow under capillary and gravitational forces, evaporation, condensation and diffusion of vapor and transport and precipitation of salts.A mathematical model is presented for the migration of salts in the vadoze zone in the soil under nonisothermal conditions, taking into account the above-mentioned phenomena. The physical assumptions underlying the model are briefly discussed.The study of a particular case shows that under certain conditions, a heat source may attract dissolved salts, and cause their precipitation in the hot area. 相似文献
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在作者已建立的饱和多孔介质耦合非线性热弹性理论基础上,考虑热渗效应,建立了饱和多孔介质耦合热弹性固结方程,并推导了有限长圆柱热固结问题的解析解,进而以温控三轴试验的试样为例进行了算例分析,同时利用COMSOL软件进行了数值模拟,并将解析结果和数值结果进行对比.结果表明:在不排水条件下,影响试样最终孔压大小的参数是:土的泊松比>弹性模量>水的体膨胀系数,渗透系数对孔压变化影响不大,考虑与不考虑水土压缩性不影响孔压的计算;相对线弹性情况,考虑非线弹性膨胀系数随温度变化时的孔压有所下降,轴向应变变化很小. 相似文献
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Jin-Huek Hur Tae-Gu Lee Sun-Ae Moon Sang-Jae Lee Hoseon Yoo Seung-Jae Moon Jae-Heon Lee 《Heat and Mass Transfer》2008,44(11):1355-1369
The thermal reliability of a closed-type BLDC motor for a high-speed fan is analyzed by an accelerated-life testing and numerical
methods in this paper. Since a module and a motor part are integrated in a closed case, heat generated from a rotor in a motor
and electronic components in the PCB module cannot be effectively removed to the outside. Therefore, the module will easily
fail due to high temperature. The experiment for measuring the temperature and the surface heat flux of the electronic components
is carried out to predict their surface temperature distributions and main heat sources. The accelerated-life test is accomplished
to formulate the life equation depending on the environmental temperature. Moreover, the temperature of the PCB module is
different from the environmental temperature since the heat generated from the motor cannot be effectively dissipated owing
to the motor’s structure. Therefore a numerical method is used to predict the temperature of the PCB module, which is one
of the life equation parameter, according to the environment. By numerically obtaining the maxima of the thermal stress and
strain of the electronic components according to the operation environments with the temperature results, the fatigue cycle
can be estimated. 相似文献
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A. D. Chernyshov 《Journal of Applied Mechanics and Technical Physics》2012,53(6):940-947
A wedge-shaped mass of snow or soil on a flat mountain slope is simulated in a connected formulation by a thermoelastic medium acted upon by gravity, a uniform surface load, and a heat flux. An exact solution of the problem of equilibrium of the mass is obtained. Two criteria for the descent of an avalanche or a landslide are derived from the conditions of impossibility of equilibrium. This result can be used to predict soil landslides and the descent of avalanches in the mountains. 相似文献
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An analytic solution to the one dimensional heat diffusion equation is presented where the diffusion coefficient varies as a power of temperature. The discussion is motivated by the transmission of heat through the strongly nonlinear medium of soil. Under boundary conditions representing the daily, or seasonal, sinusoidal fluctuation in temperature it is seen that, despite the nonlinearity, the period of the oscillation is preserved on passage through the medium. The nonlinearity acts to accelerate the heating phase and retard the cooling phase within a period which itself remains stable. These effects are calculable from a second harmonic arising in the analysis. 相似文献
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土体剖面温度物理模型试验研究 总被引:1,自引:0,他引:1
利用自主开发的土体温度物理模型试验系统,研究了土体剖面温度随时间的变化规律,通过改变土体表面的覆盖层属性,对比分析了裸土和混凝土板覆盖下土体剖面的热传递特点。结果表明:在恒定热源作用下,土体剖面温度迅速上升到一定值之后逐渐趋于稳定,初始升温速率随深度的增加而呈指数递减,最终平衡温度随深度的增加而显著衰减; 温度在土体剖面上的传递存在明显的滞后效应; 混凝土板覆盖下土体的初始升温速率和最终平衡温度较裸土高; 土体剖面热通量反映了土体中热量的传递特征,其变化规律与上下土层间的温度差变化规律一致。 相似文献
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Devendra Narain Singh Konchenapalli Devid 《Experimental Thermal and Fluid Science》2000,22(3-4):133-143
Thermal properties of soils are of great importance in view of the subsurface transmission of either heated fluids or high power currents. For these situations, it is essential to estimate the resistance offered by the soil mass in dissipating the heat generated through it. Thermal resistivity of soils is a complex phenomenon that depends upon various parameters, viz., type of the soil, particle size distribution, its compaction characteristics, etc. A laboratory probe has been developed based upon the principle of transient method to measure thermal resistivity of different soils for a state of compaction. Based on these results, generalised relationships have been developed, for predicting soil thermal resistivity, and their efficiency has been established by comparing the obtained results with those available in literature. 相似文献