热传导的微极固体和流体介质界面上波的传播

研究微极广义热弹性固体半空间和热传导微极流体半空间界面上波的传播.讨论微极广义热弹性固体半空间和热传导微极流体半空间之间平面界面上,斜向入射平面波的反射和透射现象.假设入射波穿过微极广义热弹性固体,射向平面界面后传播.得到了封闭形式的、不同反射和透射波的波幅比,它们是入射角、频率的函数,并为介质的弹性性质所影响.对一些特定的类型,显示出微极和热松弛对波幅比的影响.还从本文的研究中推演出一些早期工作的结果.     

一维六方准晶非周期平面内中心开口裂纹的平面热弹性问题

考虑裂纹内部介质的热传导率,研究了一维六方准晶非周期平面内含中心开口裂纹的平面热弹性问题.利用Fourier积分变换技术,得到了热应力、裂纹尖端处的热应力强度因子和应变能密度因子的封闭解.数值结果讨论了裂纹内部介质的热传导率、外载荷及声子场-相位子场耦合系数对热应力强度因子和应变能密度因子的影响.结果表明,声子场-相位子场耦合系数对裂纹扩展影响较大.当声子场载荷较小或热流密度较大时,裂纹不易扩展,热流密度在裂纹尖端处会出现集中热效应.随着裂纹内部介质热传导率的增大,热流密度逐渐增加而热应力强度因子逐渐减小.该文所得结果为准晶热力学性质的实际应用提供了理论依据,进而可用于优化准晶元器件的设计和制备.     

阻尼波动方程有限元法的渐近展开和外推

经验表明,有限元外推法是一个行之有效的、借简单处理而提高计算精度的好方法。目前关于有限元法的渐近展开和外推,尤其是稳态问题(椭圆型方程和本征问题)方面,已得到许多结果,推进了有限元法的研究。但在实践中,必须考虑时间维的问题的范围很广,诸如瞬态热传导、流体中波的传播以及结构的动态性态就是典型的例子。基于这个背景,本文讨论形如     

热泳和Brown运动对太阳能辐射下热分层纳米流体边界层流动的影响

在太阳辐射下的纳米流体中,数值地研究竖向延伸壁面具有可变流条件时的层流运动.使用的纳米流体模型为,在热分层中综合考虑了Brown运动和热泳的影响.应用一个特殊形式的Lie群变换,即缩放群变换,得到相应边值问题的对称群.对平移对称群得到一个精确解,对缩放对称群得到数值解.数值解依赖于Lewis数、Brown运动参数、热分层参数和热泳参数.得到结论:上述参数明显地影响着流场、温度和纳米粒子体积率的分布.显示出纳米流体提高了基流体热传导率和对流的热交换性能,基流体中的纳米粒子还具有改善液体辐射性能的作用,直接提高了太阳能集热器的吸热效率.     

基于浸入边界-有限元法的流固耦合碰撞数值模拟方法

针对流固耦合碰撞问题,建立了流体中固体与固体碰撞界面解析直接模拟方法,采用清晰界面浸入边界法模拟流体中的动边界问题,避免了传统贴体网格方法在求解流体中存在固体间碰撞问题时网格出现负体积的问题,采用基于罚函数的有限元方法对固体的运动和碰撞进行求解,以分域耦合方式实现流体域和固体域的耦合求解.通过与静止流体中球形颗粒与壁面正碰撞和斜碰撞的实验数据对比,验证了建立的数值模拟方法对流体中固体与固体碰撞数值模拟的正确性,获得了流体域流场在碰撞前后随时间的变化,同时通过该文建立的数值模拟方法也获得了固体域中固体的碰撞力和应力.未来,将把该数值模拟方法应用到流体流动环境中,如固体颗粒对管道的冲蚀、流体诱导海洋立管之间的碰撞、坠物对海底管道的撞击等.     

多物理场中不同结构特征FCI的力学行为分析

流道插件（FCI）是ITER中包层模块的重要部件,起到电绝缘和热绝缘的作用,FCI的力学行为是对复杂的磁-热-流-固多物理场共同作用的响应.将有限体积法和有限元方法相结合,对包层流道中的流场、温度场以及FCI的应力应变场进行求解,分析了磁场效应对结构的影响,以及不同FCI壁厚和间隙流宽度等结构特征对包层的影响.计算结果表明,强磁场虽然会产生较强的MHD效应,但可以降低第一壁温度和FCI结构热应力;较厚的FCI可以降低第一壁上的最高温度,但也会增加FCI上的温度梯度和热应力;而较宽的间隙有利于降低第一壁上的最高温度,但会增加FCI的最大Mises应力.     

热防护服-空气-皮肤热传导模型及其解析解

建立了高温环境下热防护服-空气-皮肤的热传导模型.利用热传导时,层合界面间温度相等和热流量连续的条件,结合微分思想,用分离变量法推导了微小时间段内模型热传导的解析解,然后通过循环得到整个时域内的解析解.利用求得的解析解分析了在80 ℃的环境温度下模型各位置温度和热流密度的变化情况,以及在不同环境温度下皮肤表面温度变化和热损伤情况.该求解方法可用来分析一般层合结构传热问题,计算结果对热防护服的设计和效果评价具有一定的参考意义.     

耦合热弹塑性问题的泛函及其变分原理*

为用有限元法求解耦合热弹塑性问题,建立适当的泛函是有必要的.本文试图在K.N.Rysinko和E.I.Blinov提出的热弹塑性本构方程和热传导方程[1]的基础上,用泛函分析理论导出耦合热弹塑性问题的泛函.     

半导体设备热传输中的隐式-显式多步有限元法

考虑热引导半导体设备中的传输行为，用一个有限元法离散电子位势所满足的Rpoisson方程；用隐式－显式多步有限元法处理电子密度和空洞密度满足的两个对流－扩散方程，热传导方程用隐式多步有限元法离散，推导了优化的L^2范误差估计。     

肾动脉变窄和流-固结构相互作用对非Newton脉动流的影响——一个真实的腹部主动脉和肾动脉模型

研究肾动脉狭窄(RAS)对血液流动和血管壁的影响.根据CT扫描图像,重建腹部主动脉和肾动脉的解剖模型,通过模型的脉动流进行了仿真计算,计算中考虑了流体-固体结构的相互作用(FSI).研究RAS对血管壁剪切应力和位移的影响,RAS使得肾动脉中流量减少,肾素-血管紧缩素系统可能被激活,从而导致严重的高血压.     

Simultaneously developing flow and heat transfer of non-Newtonian fluids in equilateral triangular duct

A numerical investigation based on the Galerkin finite element method was carried out to solve the full three-dimensional governing equations for simultaneously developing steady laminar flow and heat transfer to a purely viscous non-Newtonian fluid described by a power law model flowing in equilateral triangular ducts. Two commonly used thermal boundary conditions, constant wall temperature (T boundary condition) and constant wall heat flux both axially and peripherally (H2 boundary condition) were examined. It is shown that the Nusselt number distribution along the walls is affected appreciably by the variation of the power law index. Results are presented and discussed for a wide range of power law indices and Prandtl numbers for T and H2 boundary conditions.     

Coupled fluid-solid thermal interaction modeling for efficient transient simulation of biphasic water-steam energy systems

This paper proposes a fluid-solid coupled finite element formulation for the transient simulation of water-steam energy systems with phase change due to boiling and condensation. As it is commonly assumed in the study of thermal systems, the transient effects considered are exclusively originated by heat transfer processes. A homogeneous mixture model is adopted for the analysis of biphasic flow, resulting in a nonlinear transient advection-diffusion-reaction energy equation and an integral form for mass conservation in the fluid, coupled to the linear transient heat conduction equation for the solid. The conservation equations are approximated applying a stabilized Petrov-Galerkin FEM formulation, providing a set of coupled nonlinear equations for mass and energy conservation. This numerical model, combined with experimental heat transfer coefficients, provides a comprehensive simulation tool for the coupled analysis of boiling and condensation processes. For the treatment of enthalpy discontinuities traveling with the flow, a novel explicit-implicit time integration method based on Crank-Nicolson scheme is proposed, analyzing its accuracy and stability properties. To reduce problem size and enhance numerical efficiency, a modal superposition method with balanced truncation is applied to the solid equations. Finally, different example problems are solved to demonstrate the capabilities, flexibility and accuracy of the proposed formulation.     

非一致性界面热流固耦合作用的整体求解

提出了非一致性界面热流固耦合作用整体求解的一种方法．热流体求解基于Boussinesq假设和不可压缩的Navier-Stokes方程．流体区域的运动采用任意Lagrange-Euler（ALE）方法．拟固体元方法实现流体区域的变形．使用几何非线性的热弹性动力学描述固体运动．为了保证界面处应力和传热的平衡,采用了基于Gauss积分点的数据交换方法,对热流固耦合最终形成的强非线性方程实现整体求解．数值实例分析表明该方法的健壮性和有效性．     

Numerical simulation for natural convection of micropolar fluids flow along slender hollow circular cylinder with wall conduction effect

This paper presents a numerical analysis of the flow and heat transfer characteristics of natural convection in a micropolar fluid flowing along a vertical slender hollow circular cylinder with conduction effects. The nonlinear formulation governing equations and their associated boundary conditions are first cast into dimensionless forms by a local non-similar transformation. The resulting equations are then solved using the cubic spline collocation method and the finite difference scheme. This study investigates the effects of the conjugate heat transfer parameter, the micropolar parameter, and the Prandtl number on the flow and the thermal fields. The conjugate heat transfer parameter reduces the solid–liquid interfacial temperature, the skin friction factor and the local heat transfer rate. The effect of wall conduction on the local heat transfer rate, interfacial temperature and skin friction factor is found to be more pronounced in a system with a greater Prandtl number. Moreover, the current results are comparing with Newtonian fluid to obtain the important results of the heat transfer and flow characteristics on micropolar fluids. It shows that an increase in the interfacial temperature, a reduction in the skin friction factor, and a reduction in the local heat transfer rate are identified in the current micropolar fluid case.     

Effects of Reynolds and Prandtl number on mixed convection in a ventilated cavity with a heat-generating solid circular block

A numerical study has been executed to analyze the effects of Reynolds and Prandtl number on mixed convective flow and heat transfer characteristics inside a ventilated cavity in presence of a heat-generating solid circular obstacle placed at the center. The inlet opening is at the bottom of the left wall, while the outlet one is at the top of the right wall and all the walls of the cavity are considered to be adiabatic. Galerkin weighted residual finite element method is used to solve the governing equations of mass, momentum and energy. Results are presented in terms of streamlines, isotherms, the average Nusselt number, the Drag force and the average fluid temperature in the cavity for different combinations of controlling parameters namely, Reynolds number, Prandtl number and Richardson number. The results indicate that the flow and thermal fields as well as the heat transfer rate, the Drag force and the average fluid temperature in the cavity depend significantly on the mentioned parameters.     

流经有热辐射的无限垂直多孔平板时非稳定MHD流动的Soret和Dufour效应

不可压缩粘性导电流体,流经无限垂直多孔平板,平板存在振荡吸入速度和热辐射时,研究流动参数对自由对流和传质的非稳定磁流体动力学流动的Dufour(扩散热)和Soret(热扩散)效应.应用有限单元法,数值求解该问题的速度、温度和浓度场,还得到了表面摩擦、传热传质率的表达式.数值结果以图表方式给出,对外表致冷的平板(Gr0)和外表加热的平板(Gr0),给出了该方程中所遇参数的影响.     

Effects of variable viscosity on non-Darcy MHD free convection along a non-isothermal vertical surface in a thermally stratified porous medium

An analysis is performed for non-Darcy free convection flow of an electrically conducting fluid over an impermeable vertical plate embedded in a thermally stratified, fluid saturated porous medium for the case of power-law surface temperature. The present work examines the effects of non-Darcian flow phenomena, variable viscosity, Hartmann–Darcy number and thermal stratification on free convective transport and demonstrates the variation in heat transfer prediction based on three different flow models. The wall effect on porosity variation is approximated by an exponential function. The effects of thermal dispersion and variable stagnant thermal conductivity are taken into consideration in the energy equation. The resulting non-similar system of equations is solved using a finite difference method. Results are presented for velocity, temperature profiles and local Nusselt number for representative values of different controlling parameters.     

Mixed convection flow of a micropolar fluid from an unsteady stretching surface with viscous dissipation

An analysis is performed to study the unsteady mixed convection flow of a viscous incompressible micropolar fluid adjacent to a heated vertical surface in the presence of viscous dissipation when the buoyancy force assists or opposes the flow. The flow of the fluid and subsequent heat transfer from the stretching surface is investigated with the aid of appropriate transformation variables. The effect of the governing parameters on the flow and heat transfer characteristics as well as the local skin friction coefficient, wall couple stress and the heat transfer rate are thoroughly examined.     

Convective flows of micropolar fluids from radiate isothermal porous surfaces with viscous dissipation and Joule heating

In this study, the steady laminar free-forced convective flow and heat transfer of micropolar fluids past a vertical radiate isothermal permeable surface with viscous dissipation and Joule heating is investigated numerically. The local similarity solutions for the flow, microrotation (angular velocity) and heat transfer characteristics are illustrated graphically for various material parameters. The effects of the pertinent parameters on the local skin friction coefficient, plate couple stress and the rate of heat transfer are also calculated. It was shown that micropolar fluids presented lower viscous drag and heat transfer values than those of the Newtonian fluids. The effect of radiation on the rate of heat transfer in a weakly concentrated micropolar fluid is higher than a strongly concentrated micropolar fluid. Results also show that full radiation has significant effect on the rate of heat transfer compared to the linear radiation.     

双曲拉伸面上的流动及其热交换

研究不可压缩粘性流体,在双曲拉伸面上的边界层流动及其热传导．分别使用级数展开法和局部非相似（LNS）法,得到解析结果和数值结果,给出了表面摩擦和Nusselt数的解析结果和数值结果,并进行了互相比较．同时发现动量和热边界层厚度,随着离前缘距离的增加而减小．众所周知,线性拉伸项方程的解,可以作为双曲拉伸首次项方程的解．