砌体墙体积变化应力分析与伸缩缝间距

非烧结砖砌体结构房屋通常在底层窗台出现竖向裂缝,这类裂缝一般认为是由于砌体体积收缩受到地基或基础的约束引起。为了探索这类裂缝的开裂机理,采用应力函数法推导了砌体体积变化作用下墙体的平面应力问题的弹性力学解答,提出了地基或基础对墙体水平变形约束作用的基本假定,在此假定和墙体的边界条件基础上,得到了较为简便的墙体体积变化的应力分析方法。通过分析得出了在地基约束下墙体的应力分布规律,研究了影响墙体最大水平拉应力和墙体最大伸缩缝间距的主要因素,并将研究结果与我国现行规范进行了比较分析。     

均匀热流下导热裂纹Ⅱ型温度应力强度因子的解析解

研究含中心裂纹无限大板受远场均匀热流作用,热流密度方向与裂纹有一夹角的情况。当垂直于裂纹面方向有定量热流穿过裂纹时,采用复变函数理论,得出了温度、应力与位移场解析解。利用位移单值条件,确定出温度应力强度因子的解析表达式。针对铝合金LY12材料进行了数值计算,研究了裂纹导热情况与热流方向对温度场及温度应力强度因子的影响。研究表明:该文给定的温度边界条件下,只产生Ⅱ型温度应力强度因子,不产生Ⅰ型温度应力强度因子。热荷载可等效为一个远场均匀作用的剪应力。Ⅱ型温度应力场取决于热流密度沿垂直裂纹面方向的分量,平行于裂纹方向的热流分量对温度应力场没有影响。     

砌体结构裂缝的控制措施的探析

温度的变化会引起材料的热胀、冷缩,当约束条件下温度变形引起的温度应力足够大时,墙体就会产生温度裂缝在总结分析砌体裂缝的性质、控制原则和措施的基础上,提出了防止墙体开裂的具体构造措施建议为科学施工提供依据。     

墙体温度裂缝的防治方法

砖混结构墙体裂缝是影响建筑质量的重要问题之一,本文分析了砖混结构墙体温度裂缝产生的原因,如温度应力、设计方面的原因以及材料方面的原因等,并对此提出了控制和预防裂缝产生的相应措施。     

砖混结构屋顶墙体裂缝计算分析

分析了砖混结构墙体温度裂缝的成因,对常见的墙体斜裂缝进行了理论分析,推导了温度应力的计算公式,并提出了预防裂缝发生的措施。     

均匀热流作用下含裂纹板I 型温度应力强度因子的解析解

研究一种新的温度边值问题。含中心裂纹无限大板受远场均匀热流作用,热流密度方向与裂纹有一夹角。当裂纹面上维持一恒定温差时,采用复变函数理论,得出了温度场、温度应力场与位移场的解析解。利用位移单值条件,确定出温度应力强度因子的解析表达式。针对铝合金LY12 材料进行了相应数值计算,分析了热流密度大小与方向对温度分布与温度应力强度因子的影响。研究表明:该文给定的温度边界条件下,只产生Ⅰ 型温度应力强度因子,不产生Ⅱ 型温度应力强度因子。温度应力场取决于热流密度沿裂纹方向的分量,垂直于裂纹方向的分量对温度应力场没有影响。     

超急速传热过程中热弹性响应的解析分析

考虑超急速传热过程中诱发的热冲击效应,基于L-S广义热弹性理论,建立了温度突变加热条件下热弹性响应的控制方程组。借助于Laplace正逆变换,在适当简化的条件下推导了一维超急速传热问题热弹性响应的解析表达式。通过对温度场、位移场及应力场的解析求解,给出了超急速传热过程中热波和热弹性波在弹性体内的传递规律,并指出在超急速传热条件下,由于热波和热弹性波的相互叠加作用削弱了热作用产生的热冲击效应。     

混凝土裂缝施工方案及注意事项

混凝土墙体施工期间开裂主要是由于混凝土主动收缩、温度变形等引起。裂缝主要分为三大类,包括初始微裂缝,塑性收缩、沉降收缩等引起的裂缝,以及混凝土墙体由于温度、收缩应力过大引起的开裂。随着社会的不断进步,各类混凝土的高楼大厦不断拔地而起,在此对高层建筑地下室墙裂缝的施工及注意事项浅谈几点个人想法。     

大面积混凝土在变形荷载作用下的应力控制

大面积混凝土构筑物容易在施工水化热，外界热源（大气温差，生产热源等）和砼自身收缩等变形荷载的作用下引起开裂，本文采用理论力学方法，建立三维庆力模型，根据构筑物边界条件，推导大面积混凝土在变形荷载作用下的应力近似解，并结合混凝土工程，分析各种相关参数对构筑物变形荷载应力的影响，为土建工程的裂缝控制提供计算方法。     

浅淡砌体结构顶层墙体的温度裂缝

砖混结构房屋墙体经常出现裂缝，形成裂缝的原因很多，本文仅对房屋墙体在温度应力作用下产生的裂缝现象以及原因作了扼要分析，并结合砌体结构形式以及设计中的一些问题，提出了设计中应遵循的防止裂缝的原则和施工中应采取的防治措施。     

建筑临墙开窗对室内热压通风的模拟研究

根据进风口在墙壁上开口位置的不同,建筑开窗形式分为对墙开窗、临墙开窗、单侧墙开窗.运用airpak软件针对建筑进风口形式为临墙开窗形式下的单热源室内热压通风进行了模拟研究.通过改变进出风口中心高度差及进出风口面积比来分析中和面高度、有效热量系数、通风量、速度场及温度场的变化.结果 展示了临墙开窗形式在上述两种情况下对应...     

Materials selection for thermal comfort in passive solar buildings

This paper presents the results of a combined analytical, computational, and experimental study of the key parameters for selecting affordable materials and designing for thermal comfort in passive solar buildings. The heat transfer across the walls of buildings is modeled using a simple heat diffusion model. In this way, the passive heat storage from the sun (passive solar) and the heat load from internal heat sources are stored in the walls of buildings that provide internal cooling during the day and internal heating at night. The simple analytical model of heat diffusion is used to identify the merit indices for the optimization of affordable passive solar performance. The time dependence of wall/internal temperature is then simulated using a simple finite difference model. The results from the analytical model and finite difference model are validated by conducting temperature measurements in two affordable housing complexes in Egypt. The implications of the results are then discussed for the design of thermal comfort in affordable housing.     

The impact of a thermoelastic rod against a rigid heated barrier

The impact of a thermoelastic rod with a heat-insulated lateral surface against a rigid heated barrier is considered. The heat exchange between the rod and the wall occurs at one of its ends contacting with the wall, while the other end is heat-insulated and free from external forces. The behaviour of the rod during the impact process is described by the Green-Naghdy theory which allows one to take finite speed of heat propagation into account, neglecting therewith thermal relaxation. The Laplace integral transform with the subsequent expansion of the found images in terms of the natural functions of the problem is used as a method of solution, which is found in explicit exact closed form. The analytical time-dependence of displacements, stresses, and temperature at each rod particle is obtained. The emphasis is on the analysis of the contact stress, the temperature of the colliding bodies during their contact interaction, and on the detection of the duration of contact of the rod with the rigid wall. It is shown that the contact time essentially depends on the relationship between the mechanical and thermal values.     

Natural convection of a radiating fluid in a square enclosure with perfectly conducting end walls

Combined natural convection and radiation in an asymmetrically heated square enclosure is studied numerically with both adiabatic and perfectly conducting end walls. The momentum and energy equations are solved by a control volume based finite difference algorithm which is coupled with the discrete ordinates method for radiative heat transfer calculations. The changes in the flow patterns and temperature distributions due to the presence of radiation in an enclosure with conducting end walls are compared with those for the case of an enclosure with adiabatic end walls, and significant differences are noted. The flow field is stronger, and the heat input along the hot wall and the end walls are greater for the conducting end wall case. The effects of optical thickness, scattering and wall emissivity on the flow and temperature fields and heat transfer rates are analysed.     

各向异性介质二维稳态热传导问题的分析解

本文利用双变量函数及其偏导数在闭区间上完整的双重付里叶级数表达式求得矩形区域中各向异性介质稳态热传导问题的分析解。文中例子给出各向异性介质内的温度场和热流密度的数字结果,并讨论介质的各向异性效应。     

电弧增材制造TC4钛合金宏观晶粒演化规律

由于电弧增材制造是目前众多增材制造方法中的研究热点之一,且TC4是研究最广泛的钛合金,因此本工作研究了电弧增材制造TC4直壁墙的宏观组织演变。首先通过单道单层实验修正双椭球热源模型的形状参数,应用修正后的模型模拟四组直壁墙成形过程中的温度场及温度变化速率,通过模拟结果分析组织的演变规律。直壁墙底部为等轴晶组织,上部为柱状晶组织。低焊接电流有助于等轴晶的形成,但等轴晶区的尺寸及等轴晶的大小与线能量密度无关。     

Free convection heat and mass transfer along a vertical surface in a porous medium

Summary This study deals with free convection heat and mass transfer from a vertical plate embedded in a fluid saturated porous medium with constant wall temperature and concentration. The temperature and concentration variations across the boundary layer produce a buoyancy effect which gives rise to flow field. Integral method of Von-Karman type is applied to obtain the analytical solution of this fundamental problem.     

基于场协同理论的冷藏展示柜内流体对流换热分析

目的研究冷藏柜内对流换热机理,增强冷藏柜内流体对流换热效果,提高冷气流冷却效率。方法从冷藏柜出风口角度出发,建立数学模型,通过Ansys流体分析软件对冷藏柜内流场进行模拟仿真,应用场协同理论研究冷藏柜内流体流动及传热机理。结果出风口角度在30°附近时冷藏柜内换热效率较高且温度分布较为均匀,此时商品壁面的存在改变了冷气流流动方向。在壁面增加半圆突起后,气流沿圆弧切线方向流动,改善了速度与温度梯度之间的协同程度,从速度场、温度场及其相互作用的角度增强了冷藏柜内的对流换热效果,整体换热效率提高了38.65%。结论冷藏柜内流体流动及传热强化的根本在于流体的扰动,而出风口角度的改变和壁面凸起的存在加强了商品对流体的扰动,两者共同作用改变了冷藏柜内场的分布,进而提高了冷藏柜整体的冷藏效率,该研究可为冷藏柜的工厂化生产提供参考价值。     

能源地铁车站板式热交换构件瞬态传热问题的理论解

能源地铁车站技术是一种利用地球地温能的新型建筑节能技术,对其传热计算方法进行的研究是推动该项技术前进的重点与难点。根据能源地铁车站板式热交换构件实际瞬态传热的特点,对该传热问题的理论解进行了研究与探讨。首先根据有足够埋深、有足够的换热面积两个作为热交换构件的前提条件,探讨了地铁车站中可用作热交换构件的地下结构构件,并根据其外形特点将其分为板式热交换构件和桩柱式热交换构件两大类;其次通过分析板式热交换构件实际瞬态传热特点,利用傅立叶变换对其热流边界条件进行变换,推导出能源地铁车站板式热交换构件实际瞬态传热问题的理论解;最后,分别用理论解和数值解对某具体工况进行了计算,理论解和数值解得到的两条曲线基本重合,可见,该理论解推导正确。     

Thermal Response of a Two-Phase Near-Critical Fluid in Low Gravity: Strong Gas Overheating as Due to a Particular Phase Distribution

An experimental study of the thermal response to a stepwise rise of the wall temperature of two-phase near-critical SF₆ in low gravity for an initial temperature ranging from 0.1 to 10.1 K from the critical temperature is described. The change in the vapor temperature with time considerably exceeds the change in the wall temperature (overheating by up to 23% of the wall temperature rise). This strong vapor overheating phenomenon results from the inhomogeneous adiabatic heating process occurring in the two-phase near-critical fluid while the vapor bubble is thermally isolated from the thermostated walls by the liquid. One-dimensional numerical simulations of heat transfer in near-critical two-phase ³He confirm this explanation. The influence of heat and mass transfer between gas and liquid occurring at short time scales on the thermal behavior is analyzed. A model for adiabatic heat transfer, which neglects phase change but accounts for the difference between the thermophysical properties of the vapor and those of the liquid, is presented. A new characteristic time scale of adiabatic heat transfer is derived, which is found to be larger than that in a one-phase liquid and vapor.