Application of Mixed Differential Quadrature Method for Solving the Coupled Two-Dimensional Incompressible Navier-Stokes Equation and Heat Equation

The traditional differential quadrature method was improved by using theupwind difference scheme for the convective terms to solve the coupled two-dimensionalincompressible Navier-stokes equations and heat equation. The new method was compared with theconventional differential quadrature method in the aspects of convergence and accuracy. The resultsshow that the new method is more accurate, and has better convergence than the conventionaldifferential quadrature method for numerically computing the steady-state solution.

Development of experimental study on coupled heat and moisture transfer in porous building envelope

A new facility was presented which can expediently and cheaply measure the transient moisture content profile in multi-layer porous building envelope.Then,a common multi-layer porous building envelope was provided,which was constructed by cement mortar-red brick-cement plaster.With this kind of building envelope installed in the south wall,a well-controlled air-conditioning room was set up in Changsha,which is one of typical zones of hot and humid climate in China.And experiments were carried out to investigate the temperature and moisture distribution in multi-layer building envelope in summer,both in sunny day and rainy day.The results show that,the temperature and humidity at the interface between the brick and cement mortar are seriously affected by the changes of outdoor temperature and humidity,and the relative humidity at this interface keeps more than 80% for a long-term,which can easily trigger the growth of mould.The temperature and humidity at the interface between the brick and cement plaster change a little,and they are affected by the changes of indoor temperature and humidity.The temperature and humidity at the interface of the wall whose interior surface is affixed with a foam plastic wallpaper are generally higher than those of the wall without wallpaper.The heat transfer and moisture transfer in the envelope are coupled strongly.

Coupled Effects of Heat and Moisture of Early-Age Concrete

In order to analyze the coupled influence of temperature and humidity on early-age concrete(including cement and copper tailings),a mathematical model is introduced on the basis of the Krstulovic-Dabic hydration reaction kinetic equations.In such a framework,the influence of hydration-released heat and water consumption are also taken into account.The results provided by such a model are verified by means of experiments and related sensor measurements.The research results show that this model can adequately predict the internal temperature and the humidity temporal evolution laws.

Numerical simulation and experimental validation of moisture-heat coupling for saturated frozen soils

In seasonally frozen regions,freezing-and-thawing action is the main cause responsible for the destruction of canals,which is closely linked to the temperature gradient and water transport.To investigate the behaviour of soils under freezing-and-thawing actions,many numerical models have been established that consider the important coupling of moisture transport and temperature evolution;but they contain excessive parameters,some of which are rather difficult to determine.Based on the well-known Harlan's theory,a simple moisture-heat coupling model was recently proposed to quantify the coupled moisture-heat transport performance of soils in terms of the central temperature and porosity.The mathematical module of COMSOL Multiphysics was further employed to solve the governing equations numerically.To validate our model,a thorough experimental scheme was carried out in our lab.The measured temperature distribution was found to be consistent with the predicted results.

Water and heat transport in hilly red soil of southern China:I. Experiment and analysis

Studies on coupled transfer of soil moisture and heat have been widely carried out for decades. However, little work has been done on red soils, widespread in southern China. The simultaneous transfer of soil moisture and heat depends on soil physical properties and the climate conditions. Red soil is heavy clay and high content of free iron and aluminum oxide. The climate conditions are characterized by the clear four seasons and the serious seasonal drought. The great annual and diurnal air temperature differences result in significant fluctuation in soil temperature in top layer. The closed and evaporating columns experiments with red soil were conducted to simulate the coupled transfer of soil water and heat under the overlaying and opening fields’ conditions, and to analyze the effects of soil temperature gradient on the water transfer and the effects of initial soil water contents on the transfer of soil water and heat. The closed and evaporating columns were designed similarly with about 18 °C temperatures differences between the top and bottom boundary, except of the upper end closed or exposed to the air, respectively. Results showed that in the closed column, water moved towards the cold end driven by temperature gradient, while the transported water decreased with the increasing initial soil water content until the initial soil water content reached to field capacity equivalent, when almost no changes for the soil moisture profile. In the evaporating column, the net transport of soil water was simultaneously driven by evaporation and temperature gradients, and the drier soil was more influenced by temperature gradient than by evapo- ration. In drier soil, it took a longer time for the temperature to reach equilibrium, because of more net amount of transported water.

Applications and verification of a computational energy dynamics model for mine climate simulations

A complete thermodynamic model is described for temperature and heat flow distribution simulation for ventilation networks in underground mines.The method is called the Computational Energy Dynamics(CED)model of the heat,mass,and energy transport.The Thermal and Humidity(TH)transport elements of the full model are described for advection,convection,and accumulation,encompassing heat capacity,radiation,latent heat for evaporation,and condensation in the airways,as well as variable heat conduction and accumulation in the rock strata.The thermal flywheel effect for time-dependent temperature field applications is included in the model solution.A CED model validation exercise is described,directly evaluating the iterated,minimized energy balance errors for the mechanical and thermal energy components for each network branch after a converged solution is determined.A simulation example relevant to mine safety and health is shown with the CED-TH model,demonstrating its capabilities in efficiency and accuracy in comparison with measurement results.

AN INTEGRATION BY PARTS FORMULA FOR STOCHASTIC HEAT EQUATIONS WITH FRACTIONAL NOISE

In this paper,we establish the integration by parts formula for the solution of fractional noise driven stochastic heat equations using the method of coupling.As an application,we also obtain the shift Harnack inequalities.

Analysis and FDTD Modeling of the Influences of Microwave Electromagnetic Waves on Human Biological Systems

The interactions of electromagnetic waves with the human body are complex and depend on several factors related to the characteristics of the incident wave, including its frequency, its intensity, the polarization of the tissue encountered, the geometry of the tissue and its electromagnetic properties. That’s to say, the dielectric permittivity, the conductivity and the type of coupling between the field and the exposed body. A biological system irradiated by an electromagnetic wave is traversed by induced currents of non-negligible density;the water molecules present in the biological tissues exposed to the electromagnetic field will begin to oscillate at the frequency of the incident wave, thus creating internal friction responsible for the heating of the irradiated tissues. This heating will be all the more important as the tissues are rich in water. This article presents the establishment from a mathematical and numerical analysis explaining the phenomena of interaction and consequences between electromagnetic waves and health. Since the total electric field in the biological system is unknown, that is why it can be determined by the Finite Difference Time Domain FDTD method to assess the electromagnetic power distribution in the biological system under study. For this purpose, the detailed on the mechanisms of interaction of microwave electromagnetic waves with the human body have been presented. Mathematical analysis using Maxwell’s equations as well as bio-heat equations is the basis of this study for a consistent result. Therefore, a thermal model of biological tissues based on an electrical analogy has been developed. By the principle of duality, an electrical model in the dielectric form of a multilayered human tissue was used in order to obtain a corresponding thermal model. This thermal model made it possible to evaluate the temperature profile of biological tissues during exposure to electromagnetic waves. The simulation results obtained from computer tools show that the temperature in the biological tissue is a linear function of the duration of exposure to microwave electromagnetic waves.

Amplification effect of intra-seasonal variability of soil moisture on heat extremes over Eurasia

Drying soil has been conducive to a high frequency of extreme high-temperature events over many regions worldwide in recent decades.However,changes in the intraseasonal variability of soil moisture can also influence the likelihood of extremely high temperatures.Although previous investigators have examined the association between extremely high temperatures and large-scale atmospheric circulation variability,the role of land-atmosphere coupling dominated by soil moisture variability in extremely high temperatures,particularly over the Eurasian continent,is not well understood.In this study,on the basis of the Land Surface,Snow,and Soil Moisture Model Intercomparison Project,we found that land-atmosphere feedback amplified the variability of soil moisture in most regions of Eurasia during summer from 1980 to 2014.This amplification of soil moisture variability is closely correlated with more intensive intraseasonal variability of surface air temperature and more frequent occurrences of extreme high-temperature events,particularly in Europe,Siberia,Northeast Asia,and the Indochina Peninsula.This correlation implies that increasing the intraseasonal variability of soil moisture results in a high likelihood of heat extremes during summer in most parts of Eurasia except Asian desert areas.On the intraseasonal timescale,the land-atmosphere coupling increases the variability of surface sensible heat flux and net long-wave radiation heating the atmosphere by intensifying the soil moisture variability,thus amplifying the variability of surface air temperature and enhancing the extreme high-temperature days.This finding demonstrates the importance of changes in intraseasonal soil moisture variability for the increasing likelihood of heat extremes in summer.

Modeling Hydrothermal Transfer Processes in Permafrost Regions of Qinghai-Tibet Plateau in China

Hydrothermal processes are key components in permafrost dynamics; these processes are integral to global wanning. In this study the coupled heat and mass transfer model for （CoupModel） the soil-plant-atmosphere-system is applied in high-altitude permafrost regions and to model hydrothermal transfer processes in freeze-thaw cycles. Measured meteorological forcing and soil and vegetation properties are used in the CoupModel for the period from January 1, 2009 to December 31, 2012 at the Tanggula observation site in the Qinghai-Tibet Plateau. A 24-h time step is used in the model simulation. The results show that the simulated soil temperature and water content, as well as the frozen depth compare well with the measured data. The coefficient of determination （R2） is 0.97 for the mean soil temperature and 0.73 for the mean soil water content, respectively. The simulated soil heat flux at a depth of 0-20 cm is also consistent with the monitored data. An analysis is performed on the simulated hydrothermal transfer processes from the deep soil layer to the upper one during the freezing and thawing period. At the beginning of the freezing period, the water in the deep soil layer moves upward to the freezing front and releases heat during the freezing process. When the soil layer is completely frozen, there are no vertical water ex- changes between the soil layers, and the heat exchange process is controlled by the vertical soil temperature gradient. During the thaw- ing period, the downward heat process becomes more active due to increased incoming shortwave radiation at the ground surface. The melt water is quickly dissolved in the soil, and the soil water movement only changes in the shallow soil layer. Subsequently, the model was used to provide an evaluation of the potential response of the active layer to different scenarios of initial water content and climate warming at the Tanggula site. The results reveal that the soil water content and the organic layer provide protection against active layer deepening in summer, so climate warming will cause the permafrost active layer to become deeoer and permafrost degradation.

Modeling on coupled heat and moisture transfer in freezing soil using mixture theory

A set of perfect constitutive equations including the coupling effects of heat transfer and moisture migration is constructed for freezing soil, after analyzing its thermomechanic properties, in the framework of continuum mechanics and mixture theory. By applying the theory, the influence of void ratio on frost heaving is studied after proposing a criterion for formation of layered ice; the results obtained coincide with experimental data available in the literature. The temperature distribution of freezing soil is analyzed, the controlling equation deduced appears to be a nonlinear Burgers type equation with varying boundaries, which presents a theoretic foundation for studying the nonlinear effects of heatmoisture migration in the freezing process.

水泥基材料热湿耦合传输性能

通过大气环境下水泥基材料热湿耦合传输试验,考察了温湿度梯度对湿传输、温湿度分布的影响。试验结果表明,湿传输随着温湿度梯度的增大而加快,且温度梯度比湿度梯度对湿传输的影响大;温度梯度比湿度梯度对温度分布的影响大;温湿度梯度对相对湿度分布的影响都比较大。因此,在水泥基材料热湿耦合传输过程中,水泥浆的湿传输比砂浆快,且应考虑热传输对湿传输的影响,但湿传输对热传输的影响可以忽略。计算结果表明,热湿耦合传输模型对水泥基材料具有较好的适用性。

能源连续墙对室内侧壁面热湿耦合传递行为的影响

目前国内外针对能源连续墙的研究主要集热交换性能,鲜有研究关注其对邻近地下建筑热湿环境的影响。本文通过建立热湿耦合传递三维数值模型,研究了能源连续墙对相邻地下室墙体壁面热湿状态和与室内环境热湿交互通量的影响。研究结果表明,能源连续墙的运行明显改变了室内侧壁面的热湿流方向和热湿流密度大小;与纯传热结果相比,虽然传湿过程对壁面温度的影响小于0.2℃,但是这部分差异会造成显热热流密度预测偏差超过10%;不计潜热热流会造成对地下室内热负荷的低估超过2.4%;绝缘层的隔热防潮作用能够阻碍流向室内的热量和湿汽。

宁夏衬砌渠道渠基冻胀率水热响应试验研究

衬砌渠道周围的水分与温度场分布存在明显差异,此范围内渠基土在水热两场耦合作用下冻胀有明显不同。基于这种差异,开展渠基土在不同水分、温度条件下冻胀率试验研究。结果表明:在不同温度条件下,土体冻胀率随温度的变化过程可分为2个阶段,当温度从0℃降至-5℃左右时,在此阶段产生的冻胀率约占整个冻胀过程的50%~80%,冻胀率与温度线性关系明显。随着温度继续降低,2者非线性关系明显。在无补水情况下,相同温度条件下的土体,初始含水率越大,所产生的冻胀率越大;初始含水率25%和35%的土体产生的冻胀率均为初始含水率15%土体的1倍到2倍以上。当土体在冻胀过程中有水分补充时,其冻胀率与水分变化线性关系明显,初始含水率越大的土体产生的冻胀率增量越大,初始含水率25%、35%的土体冻胀率增量均为15%土体的2倍以上。提出的水热耦合条件与渠基土冻胀率的多元非线性关系与试验数据吻合较好。建立数值模拟模型,对衬砌渠道不同位置处冻胀作用分布与变形进行计算与分析,结果表明:温度越低、水分越大,衬砌渠道所受到的切向冻胀力与法向冻胀力越大。水热变化差异越大时,土体冻胀导致的衬砌渠道冻胀变形越显著。

制冷装置柔性接触式密封机构性能提升的关键技术研究进展

柔性接触式密封机构在制冷装置中起到重要的隔热隔湿作用。针对装配状态下刚-柔多体接触对其性能提升带来的技术挑战,从柔性接触式密封机构技术特点和总体发展出发,综述了影响其性能提升的测量、建模等关键性问题的研究现状,并对未来的发展趋势进行了展望。结果表明:基于反向热平衡的热传递测量技术精度不足,引入滤波算法可降低热流信号噪声波动;现有示踪气体技术未考虑湿空气在刚柔接触界面中的流动扩散,应运用界面微观检测及接触动力学理论来明确流动型式,构建匹配的示踪源和检测回路;对柔性接触式密封机构热流固耦合建模研究尚处于空白,仅建立了传热数值模型与流动平均解析方程,可采用数值计算温度、变形场与解析计算渗流参数的迭代算法来建立耦合模型。未来,除开展测量与建模的基础研究外,还需突破“尺寸效应”技术瓶颈,实现密封组件间的良好配合,应用超低导热材料和电磁感应技术,以提升密封机构的隔热隔湿作用。

热-湿-力耦合作用对高温后方钢管混凝土短柱轴压力学性能影响试验研究

火灾发生时钢管混凝土内部会产生水蒸气,为探讨热-湿-力耦合作用对高温后方钢管混凝土轴压力学性能的影响,进行了10根高温后方形钢管混凝土短柱轴压力学性能试验,研究排气孔数量、布置位置、轴压比和升温时间等参数对其破坏形态、轴压刚度与剩余承载力等力学性能的影响。试验结果表明,试件破坏形态表现为压溃破坏;在其他参数相同的情况下,与升温前相比,随着排气孔数量从2个增加至4个和6个,轴压刚度分别降低了69.1%、73.3%、76.4%,剩余承载力分别降低了15.8%、16.2%、21.7%。轴压刚度随轴压比的增大而降低;随着升温时间的延长,剩余承载力先随轴压比的增大而增大,后随轴压比的增大而减小。研究结果可为钢管混凝土柱的抗火设计和该类结构火灾后的损伤评估与加固提供参考。

周期性边界下围岩热湿耦合传递特性及影响因素研究

为研究周期性边界下围岩热湿耦合传递特性,以相对湿度和温度为驱动势,建立了围岩热湿耦合传递数学模型,并设计正交试验,探究围岩热湿耦合传递特性的影响因素,得到了围岩年平均热湿吸放量及时长的预测公式。研究结果表明:围岩温湿度呈现季节性变化,围岩内部温湿度幅值存在延迟和衰减,越远离壁面其温湿度幅值越小,峰值温度越低且峰值出现的时间越晚;围岩调温圈厚度逐月增加,从1月厚度为5m到12月扩展至11m;年温度波幅对围岩吸放热量影响最大,年平均温度对吸放热时长影响最大,年湿度波幅对围岩放湿量影响最大,年平均湿度对围岩吸湿量及吸放湿时长影响最大。

土壤湿度-地表气温耦合对长江中下游地区2022年8月复合型热浪事件的影响

2022年8月长江中下游地区的复合型热浪给社会经济、人类健康、农业生产和自然环境等方面均造成了严重影响.本文利用国家信息中心提供的1979—2022年6—8月逐日最高、最低气温和欧洲中期天气预报中心再分析数据集的土壤湿度等资料,定义了复合型热浪事件强度指数及其相应的土壤湿度-地表气温耦合指数,采用分段线性拟合等方法,探讨此次复合型热浪特征及土壤湿度-地表气温耦合的影响.结果表明:(1)2022年8月长江中下游地区的复合型热浪事件强度为1979年以来最强,伴随最强的土壤湿度-地表气温耦合.空间分布显示,强的热浪发生在四川东部、重庆西部、湖南等地,这些区域的土壤湿度严重偏干,蒸发受限,获得的净辐射主要用于地表向上的感热通量,使土壤湿度-地表气温出现强的正反馈过程,对热浪的维持起重要作用.(2)复合型热浪中土壤湿度-地表气温耦合影响日间和夜间热浪的物理强迫及过程不同:日间,地表净太阳短波向下辐射增强的强迫作用,促使发生强的土壤湿度-地表气温耦合,引起日间热浪.夜间,白天积累在土壤的热量,通过减小大气热量通量辐散,使夜间地表气温下降减慢,形成夜间热浪,这与以往研究单独夜间热浪的过程不同,后者认为夜间热浪主要与大气柱水汽增加引起的大气逆辐射增强有关.

寒冷地区热湿耦合下墙体热桥的模拟研究

在寒冷地区气候条件下,通过COMSOL Multiphysics模拟软件建立热湿耦合模型,对钢筋混凝土柱红砖砌体墙所形成柱墙角热桥进行模拟研究。结果表明,湿传递的作用比只有传热作用的墙体内表面温度低,在实际工况下不能忽略湿传递对建筑材料导热系数的影响。由于热桥的影响使围护结构的热通量增加19.6%,热桥的影响区域为距离最不利点0.4 m左右,在相同保温板厚度时,外保温比内保温墙体内表面温度高,保温效果更好。随着保温板厚度的增加,墙体内表温度升高,墙体内表面热通量降低。为了降低冬季房间供暖能耗,可以通过对热桥外保温来解决墙体结露现象。

基于HIE-FDTD方法的电磁热耦合分析快速计算方法研究

基于混合显隐式时域有限差分(hybrid implicit-explicit finite-difference time-domain,HIE-FDTD)方法,提出了一种电磁热耦合分析快速计算方法。仿真电磁场时,采用HIE-FDTD方法求解Maxwell旋度方程;计算温度场时,采用时域有限差分(finite-difference time-domain,FDTD)方法求解热传导方程。由于HIE-FDTD方法只对1维空间偏导数采用隐式差分方法进行离散,因此时间步长不受电磁目标精细结构所在方向网格大小的限制。采用电磁热耦合分析快速计算方法对十字缝隙频率选择表面的电磁热耦合效应进行分析,并将仿真结果与采用传统FDTD方法、CST软件以及COMSOL软件的仿真结果进行对比,所有结果均相互符合。十字缝隙频率选择表面算例结果表明:在保证计算精度的前提下,采用HIE-FDTD方法的仿真时间仅为传统FDTD方法仿真时间的1/6,有效提高了电磁热耦合仿真的计算效率。