不同负温条件下冻土导热系数的理论模型和试验验证

基于饱和冻土的三相组成和导热系数量纲定义,将冻土简化为由土柱、液态水、冰柱组成的混合物,进而建立了冻土导热系数的几何模型。考虑实际冻土中三相组成的含量随温度变化而不断变化的事实,给出了随温度变化的水柱和冰柱体积计算与演变规律。在此基础上,利用并联体系导热效果的叠加原理,给出了随温度变化的冻土导热系数计算模型。基于热流传递过程中并联与串联同时进行的耦合特性,建立了考虑固-液界面的导热系数计算模型。将预测值与瞬态探针法的实测结果和Johansen法的计算结果对比后发现,该类计算方法能有效模拟不同负温条件下冻土的导热系数,并且具有概念清晰、方法简单等特点。     

立井冻土爆破技术的研究

建立了冻土爆破冻结管震动破坏准则,进行了冻土爆破性的分析,根据冻土掏槽参数和光面爆破参数的模型试验进行冻土爆破参数的设计,并结合冻土爆破实际,提出了冻土爆破前的准备工作,如详细分析爆破作业区内冻结管的偏斜情况,计算每根冻结管距井帮的最短距离,根据井筒断面及冻结土层的特性,选择钻眼设备等。经过实践,既保证施工安全,又提高了效率。     

铍激光热传导对接焊对接间隙的数值处理方法

提出了一种虚拟材料法,用以消除铍激光热传导对接焊热过程数值分析中钎料与母材间的对接间隙所带来的能量边界条件.假定对接间隙被一种具有不同于母材和钎料的热物性参数的虚拟材料所填充,用指数旋转抛物线体热源模型预测了铍激光热传导对接焊缝横断面轮廓,并进行了试验研究.结果表明,在考虑对接间隙的情况下计算所得的熔池轮廓更接近于试验结果.虚拟材料的导热系数对熔池形状的影响较大,而密度和比热对熔池形状的影响较小.随着导热系数的增大,熔深和熔宽均逐渐减小.当导热系数取30 W/(m.K)时,计算所得的熔池形状与试验测得的值吻合良好.     

相变效应对灌注桩与冻土回冻过程影响的研究

以传热学为基础,考虑地质条件、冻土初始地温场的影响及相变效应,在自然回冻状态下,给出冻土地区桩基温度场的二维控制微分方程及初始边界条件。结合试桩工程实例,建立二维数值模型,数值方法求解的计算值与实测值吻合较好。分析了钻孔灌注桩与冻土回冻过程,得出了灌注桩浇筑混凝土后桩体温度分布不均匀,呈非线性变化;确定了灌注桩的热扰动核心区域。     

沥青路面导热系数测试及其对路面温度场影响的模拟

沥青路面温度场是沥青路面车辙计算和沥青混合料粘弹性分析的重要参数,路面温度场的精确预估涉及到面层各层材料热物理参数的精确测试,因此沥青混合料热物理参数的准确测试变得越来越重要.基于对测试结果重现性和可比性的考虑,采用瞬态热线法进行沥青混合料导热系数的测试,选取几种有代表性的混合料进行了导热系数测试,分析了影响导热系数的因素.基于ABAQUS模拟计算路面温度场分布,通过改变路面上、中、下面层的导热系数,计算路面温度场分布变化的情形,对计算结果的分析发现,上面层导热系数对面层温度场分布的影响更显著,可以预期通过改变上面层导热系数能达到主动改善沥青路面工作温度的目的.     

电磁成形定向凝固三维非线性温度场数学模型

从基本物理模型出发,导出了电磁成形定向凝固稳态连铸过程中相变潜热在导热方程中的内热源处理形式,使之可以避免近似处理,而直接应用于数值模拟的推导过程.在此基础上,同时考虑涡电流加热、强制冷却、热辐射和热质运动等因素,建立了关于电磁成形定向凝固问题三维非线性温度场的完整导热微分方程.编程计算并与实验结果对比表明,模型正确有效.     

制冷技术在冻土试验中的应用——测定冻土导热系数的恒温装置

土壤水的冻结和融化导致了反复的冻胀和融沉,我们必须进行冻土实验来防止寒冻破坏,所以制冷技术在冻土学中是很重要的,但是冻土学中有一些制冷技术和工艺的特殊要求,根据稳定纵向热流原理和使用比较法,测定了粗颗粒土和大含水量土的导热系数。详细介绍了冻土试验中恒温装置的特点、工艺和精度。我们的经验证明了制冷技术在冻土学中的应用具有广阔的前途。     

横向冲击作用下圆钢管混凝土构件挠度尺寸效应研究EI北大核心CSCD

由于圆钢管混凝土构件遭受横向冲击下的试验研究大多基于缩尺试验展开,冲击挠度相似律能否满足显得十分重要。基于相似准则,建立了钢管混凝土构件遭受横向冲击的相似模型,确定了各个参数间的放缩比例关系,同时利用LS-DYNA软件建立了钢管混凝土受横向冲击作用的有限元模型,在模型验证可行的基础上,对横向冲击下钢管混凝土构件挠度的尺寸效应进行了分析研究。结果表明:当构件未开裂时,挠度尺寸效应较小,误差在8%以内;当构件发生开裂或断裂时,挠度尺寸效应明显,误差可以达到15%以上。材料动态强度以及材料断裂应力都是不符合相似准则的因素,也是导致钢管混凝土构件冲击试验中挠度尺寸效应的重要原因。并提出了考虑尺寸效应的挠度修正系数,对于未断裂构件,通过小尺寸模型试验即可预测大尺寸原型试验中的挠度。     

地下换热器传热过程分析

初次冻结前后的导热系数与比热采用等效导热系数和当量比热。相变热计算式中未冻水的质量分数根据土壤的液限、塑限和含水率等求解,计算结果为0.3183。借助有限元软件Autodesk Simulation进行仿真分析,得到结论:流速越大,对流传热膜系数的数值越大;在相同流速的情况下,盐水溶液的对流传热膜系数的数值是乙二醇溶液的2倍。     

地下换热器传热过程分析

初次冻结前后的导热系数与比热采用等效导热系数和当量比热。相变热计算式中未冻水的质量分数根据土壤的液限、塑限和含水率等求解,计算结果为0.3183。借助有限元软件Autodesk Simulation进行仿真分析,得到结论:流速越大,对流传热膜系数的数值越大;在相同流速的情况下,盐水溶液的对流传热膜系数的数值是乙二醇溶液的2倍。     

Thermoelastic analysis of a partially insulated crack in a strip under thermal impact loading using the hyperbolic heat conduction theory

In this paper, the transient temperature and thermal stresses around a partially insulated crack in a thermoelastic strip under a temperature impact are obtained using the hyperbolic heat conduction theory. Fourier and Laplace transforms are applied and the thermal and mechanical problems are reduced to solving singular integral equations. Numerical results show that the hyperbolic heat conduction parameters, the thermal conductivity of crack faces, and the geometric size of the strip have significant influence on the dynamic temperature and stress field. The results based on hyperbolic heat conduction show much higher temperature and much more dynamic thermal stress concentrations in the very early stage of impact loading comparing to the Fourier heat conduction model. It is suggested that to design materials and structures against fracture under transient thermal loading, the hyperbolic model is more appropriate than the Fourier heat conduction model.     

Solution of an Inverse Problem of Heat Conduction of 45 Steel with Martensite Phase Transformation in High Pressure during Gas Quenching

In order to simulate thermal strains,thermal stresses,residual stresses and microstructure of the steel during gas quenching by means of the numerical method,it is necessary to obtain an accurate boundary condition of temperature field.The surface heat transfer coefficient is a key parameter.The explicit finite difference method,nonlinear estimation method and the experimental relation between temperature and time during gas quenching have been used to solve the inverse problem of heat conduction.The relationship between surface temperature and surface heat transfer coefficient of a cylinder has been given.The nonlinear surface heat transfer coefficients include the coupled effects between martensitic phase transformation and temperature.     

The importance of water migration in the measurement of the thermal conductivity of unsaturated frozen soils

The transport of heat in frozen soil may occur by conduction and by the convective transport of sensible and latent heat arising from the flow of water in the vapor, liquid and solid states. Theory describing the coupled flow of heat and of water in the liquid and vapor states is used to derive a definition of apparent thermal conductivity (the convective transport of heat in the movement of ice in unstaturated soils is assumed to be negligible). Calculations suggest that, at temperatures close to 0°C, the transport of latent heat may exceed the contribution of heat flow by conduction. Under these conditions, the apparent thermal conductivity will be much greater than the thermal conductivity calculated from the thermal conductivities and volume fractions of the components.Insufficient published data prevent a rigorous evaluation of the theory. However the functional dependence on temperature of both thermal conductivity and the apparent thermal conductivity are calculated for a Tomakomai soil at different subzero temperatures. These values are compared to the apparent thermal conductivities of this soil which were measured at a water content in the unfrozen state of 0.48 cm³ cm^?3 and at temperatures ranging from ?0.7°C to ?10°C using the line heat source technique. The dependence of apparent thermal conductivity on subzero temperature, as calculated from theory, compares favourably to the dependence which was observed for this soil.     

一维传热方程瞬态问题解析解及其应用

探究路基及浅层土体的温度随深度的分布规律，对冻土区域路基的合理设计有重要意义。该文根据实际浅层土体温度边界情况，建立了一维传热瞬态模型并给出其解析解，通过与数值模拟及现场测试结果的对比验证了解析解的正确性。仔细考察介质分层情况下的热传导过程发现，传热问题在一定程度上存在与波动问题类似的现象，即在分层界面处有热传导的反射与透射，结合对解析解的分析及数值模拟，对此种“温度波”现象进行了论证分析，发现此种波总是伴有明显的衰减。此外，还探讨了解析解在冻深估计、有关模型试验中几何相似关系的确定、“覆盖效应”数值模拟等方面的应用。     

水化热及入模温度对灌注桩回冻过程影响的研究

以传热学为基础,给出冻土地区桩基温度场的二维控制微分方程及初始边界条件.结合试桩工程实例,建立二维数值模型,采用数值方法求解,计算值与实测值吻合较好,研究了成桩后由于混凝土水化热作用对冻土的热扰动以及这种热扰动的消散规律,讨论了入模温度和总水化热对回冻过程的影响,分析结果表明:混凝土水化热对地温的热扰动是一个长期的过程...     

不同离散化方法在正冻土水热耦合模型中的应用

为了研究土体冻结过程中温度传导与水分迁移的变化,在不饱和土理查德斯方程的基础上考虑相变作用建立了一维土体冻结过程的水热耦合模型。分别应用有限差分与有限元方法对模型进行离散化,得到两种方法各自的数值计算程序。同时对土体室内单向冻结实验进行模拟,将两种数值方法得到的土体冻结深度、冻结速率与温度变化分别与实验结果进行对比。结果表明:对于一维冻结问题,有限差分模拟更接近实验结果,有限元模拟具有更高的计算稳定性。     

Basic Problems in Thermal-Conductivity Measurements of Soils

The thermal conductivity of pozzolanic soil (a fine sandy, unconsolidated, alluvial soil from Lazio, Italy, based on volcanic ash) and blue marlstone rocks (from Alba, Piedmont, north Italy) was measured, using a thermal probe technique, over a wide range of temperatures from ${-}20\,^\circ \mathrm{C}$ to ${+}20\,^\circ \mathrm{C}$ . Unfrozen pozzolanic soil thermal-conductivity data display surprisingly low values about 3 to 4 times smaller than water; for frozen soils, the data are just slightly higher than for the unfrozen state but they are still 2 to 3 times lower than for water and seven times lower than for ice. This outcome is probably due to a high internal porosity of individual volcanic ash particles. The influence of the bulk soil porosity on the measured thermal conductivity was found to be rather negligible; the observed slight variation of the thermal conductivity is possibly due to the diverse grain size distribution of soil samples excavated from different depths of the ground. The blue marlstone rock has a considerably higher thermal conductivity than pozzolanic soil, likely due to its very small porosity, consolidated structure, and different implicated minerals. The frozen rock has just about a 30 % higher thermal conductivity than that for the unfrozen state. A temperature-dependent thermal conductivity is observed in the freezing state only. Test results show how heat transfer between the thermal probe and surrounding soil is influenced by storage of heat in the tested material, conduction heat flow, water evaporation due to heating, and finally by vapor diffusion and circulation.     

Heat conduction in composite materials due to oscillating temperature field

A mathematical model is presented to obtain the effective thermal conductivity and the effective heat capacity in composite materials due to oscillating temperature field. An integro-differential equation for temperature field in composites is derived using the Green's function for heat conduction. The ensemble averaged temperature field is determined by a self-consistent scheme to yield algebraic equations for the effective thermal conductivity and the effective heat capacity. The obtained expression for the effective thermal conductivity is not symmetrical with the interchange of the matrix phase and the inclusion phase.     

Hyperbolic Heat Conduction in a Cracked Thermoelastic Half-Plane Bonded to a Coating

In this paper, the transient temperature field around a thermally insulated crack in a substrate bonded to a coating is obtained using the hyperbolic heat conduction model. Fourier and Laplace transforms are applied, and the thermal conduction problem is reduced to solving a singular integral equation. Numerical results show that the hyperbolic heat conduction parameters, the heat conductivity of the substrate and coating, and the geometric size of the composite have significant influence on the transient temperature field. In the case of very small time scales, the results predicted by the hyperbolic model are more conservative than that by the parabolic model.