非线性二维导热反问题的混沌-正则化混合解法

考虑热传导系数随温度变化,建立了非线性二维稳态导热反问题数值计算模型。并把混沌优化方法和梯度正则化方法相结合,构成一种混沌-正则化混合算法求该计算模型的全局解。以热传导系数随温度线性变化为例,由布置在结构边界上的观测点温度信息确定了结构材料热传导系数及其随温度变化规律。结果表明混合算法计算结果与初值无关,具有很好的全局寻优性能,而且计算量远比经典遗传算法和单纯采用混沌优化方法小。     

基于三角形区间二型模糊数的综合评价模型

为解决评价过程中分类等级的边界不确定性问题,将二型模糊集引入到模糊综合评价模型中.利用分类等级的边界限值,分别构造三角形二型区间模糊数的上、下隶属函数,在此基础上由观测数据构建相应的区间值模糊评价矩阵,结合指标权重合成得到区间值综合评价向量,最后利用区间数排序的可能度方法得到评价对象的等级隶属向量并给出评价结果.实例分析表明了该模型的有效性。     

火场-结构联合分析简化模型及其应用研究

为在建筑结构火灾反应分析中考虑实际火场特性,并简化火场分析模型与结构有限元分析模型之间的复杂对应关系,提出并建立了火场温度及对流辐射边界的热传导分析时空模型(STM)和基于时空模型的火场-结构联合分析方法。该方法根据火场模型计算出室内火场温度分布场以及对流辐射边界场离散数据,通过双向正交多项式进行拟合来得到不同时刻的构件边界连续时空模型,再通过时空模型进行热传导分析和热力耦合分析,从而实现火场-结构联合分析方法。在验证其合理性的基础上,通过ABAQUS子程序UTEMP和DFLUX实现其分析过程,并进行了北京某档案馆工程的应用分析,结果表明该方法可以较好地联合火场模拟与结构分析用于结构火灾安全评价。     

基于非傅里叶的有限空圆柱体的温度场解析解及其在谐波均匀的圆柱体上的应用

在有限空圆柱体的热冲击问题中引进非傅里叶分析,考虑了在极端热传递条件下的非稳态热传递过程中热量传播速度的有限性,建立了有限空圆柱体的轴对称非傅里叶温度场的数学模型,利用分离变量法和杜哈尔积分求得有限空圆柱体双曲型热传导问题的精确解析解.并将结果应用于外表面是谐波均匀的热通量的有限空圆柱体,得到其瞬态温度场及其径向、轴向温度分布规律.     

二维稳态热传导问题的正六边形流形元研究

发展了用于分析二维稳态热传导问题的多边形数值流形方法（numerical manifold method,NMM）.根据热传导问题的控制方程、边界条件以及多边形NMM的温度近似函数,采用修正变分原理导出了多边形NMM求解稳态热传导问题的总体方程,给出了多边形单元上的域积分策略.考虑到NMM中数学覆盖系统可不与物理域边界一致以及规则单元的精度优势,采用Wachspress正六边形数学单元对两个典型热传导问题进行了仿真,计算结果与参考解能较好地吻合,表明多边形NMM可以很好地模拟平面稳态热传导问题.     

推广的线性模型的参数估计

本文导出区间数变量和三角模糊变量的线性模型的参数公式．公式简单，形式一致，可作为经典线性回归模型参数估计最小二乘法推广。     

竖板表面温度的变化对磁流体动力学流动的影响

在横向磁场作用下,不可压缩的粘性导电流体,流经一个半无限的竖板,完成了壁面温度变化对磁流体动力学流动的分析.假定由粘性耗散和感应磁场产生的热量可以忽略不计.无量纲的控制方程为二维非稳态耦合的非线性方程.结果显示,磁场参数对空气和水的速度有着抑制作用.     

线状Mg激光等离子体热传导区特性的实验研究

基于一种新型的针孔晶体谱仪和Ly-α线翼部Stark展宽电子密度测量法,提供了一种对激光等离子体热传导区特性进行实验研究的简便方法,利用该方法对线状Mg激光等离子体的热传导区的特性进行了研究,在稳态近似下,得到Mg激光等离子体热传导区的宽度、声速及电子温度的实验值,和一维平面烧蚀稳态模型结果相比较,两者符合较好.     

粘性流体间夹有多孔介质时的非定常流动及其热传导

粘性流体间夹有多孔介质,流经壁面温度等温的水平管道时,研究其非定常振荡流动及其热传导问题.多孔介质中的流动采用Brinkman方程模型.通过集中非周期项和周期项,将偏微分的控制方程转化为常微分方程,并利用边界和界面条件,找到了每个区间的闭式解.数值计算了各种物理参数,如多孔性参数、频率参数、周期频率参数、粘度比、热传导系数比和Prandtl数,对速度和温度场的影响,并给出相应的图形.此外,导出了壁顶和壁底处的热传递率并用表格列出.     

热传导方程解的稳定性以及Matlab数值模拟

应用能量估计方法,分析一类热传导方程的解对初始数据的连续依赖性,再应用Matlab中的偏微分方程工具箱PDE Toolbox对一类特殊的热传导方程进行建模求解．通过数值模拟观察温度场的分布和梯度方向的变化,结果显示,靠近热源一侧的分子最先被加热,温度由高温的一侧向低温一侧变化,在经过一段时间后,整个温度场将逐渐趋于稳态．     

Random generalized solutions to the heat equation

A solution for the heat conduction problem with random source term and random initial and boundary conditions is defined. Existence, uniqueness, properties, and asymptotic behavior of such a solution are investigated. Applications to one-dimensional problems are presented.     

Stabilization of a thermoelastic Mindlin–Timoshenko plate model revisited

This paper is a continuation of our work in Grobbelaar-Van Dalsen (Appl Anal 90:1419–1449, 2011) where we showed the strong stability of models involving the thermoelastic Mindlin–Timoshenko plate equations with second sound. For the case of a plate configuration consisting of a single plate, this was accomplished in radially symmetric domains without applying any mechanical damping mechanism. Further to this result, we establish in this paper the non-exponential stability of the model for a particular configuration under mixed boundary conditions on the shear angle variables and Dirichlet boundary conditions on the displacement and thermal variables when the heat flux is described by Fourier’s law of heat conduction. We also determine the rate of polynomial decay of weak solutions of the model in a radially symmetric region under Dirichlet boundary conditions on the displacement and thermal variables and free boundary conditions on the shear angle variables.     

An Algorithm of Linear Combinations: Thermal Conduction

This paper presents computational algorithms that make it possible to overcome some difficulties in the numerical solving boundary value problems of thermal conduction when the solution domain has a complex form or the boundary conditions differ from the standard ones. The boundary contours are assumed to be broken lines (the 2D case) or triangles (the 3D case). The boundary conditions and calculation results are presented as discrete functions whose values or averaged values are given at the geometric centers of the boundary elements. The boundary conditions can be imposed on the heat flows through the boundary elements as well as on the temperature, a linear combination of the temperature and the heat flow intensity both at the boundary of the solution domain and inside it. The solution to the boundary value problem is presented in the form of a linear combination of fundamental solutions of the Laplace equation and their partial derivatives, as well as any solutions of these equations that are regular in the solution domain, and the values of functions which can be calculated at the points of the boundary of the solution domain and at its internal points. If a solution included in the linear combination has a singularity at a boundary element, its average value over this boundary element is considered.     

Determination of three-dimensional temperature fields in multiply connected orthotropic bodies under heating with heat sources and flows

We present an algorithm for calculating temperature fields in orthotropic bodies of complex shape, which is based on the method of integral equations. To develop the algorithm, the heat conduction boundary-value problem for orthotropic bodies is preliminarily reduced to the corresponding heat conduction problems for isotropic bodies with modified boundary conditions and heat sources. An investigation of the influence of anisotropy on temperature fields in a bounded and an infinite body with a cavity that are heated by heat sources and flows is performed.     

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.     

一维抛物型方程一种新的边值问题的解法

在建立目标一维热红外温度模型时,提出了热传导方程的一个新的边值问题;通过比较,选择了GE差分格式,求解方程,并进行了稳定性分析;采用虚拟网格点法处理边界条件,得出了GE格式的完整形式;计算实例表明,分组显示方法更适合此类边值问题的实际计算.     

Inverse determination of thermal conductivity using semi-discretization method

In this work a semi-discretization method is presented for the inverse determination of spatially- and temperature-dependent thermal conductivity in a one-dimensional heat conduction domain without internal temperature measurements. The temperature distribution is approximated as a polynomial function of position using boundary data. The derivatives of temperature in the differential heat conduction equation are taken derivative of the approximated temperature function, and the derivative of thermal conductivity is obtained by finite difference technique. The heat conduction equation is then converted into a system of discretized linear equations. The unknown thermal conductivity is estimated by directly solving the linear equations. The numerical procedures do not require prior information of functional form of thermal conductivity. The close agreement between estimated results and exact solutions of the illustrated examples shows the applicability of the proposed method in estimating spatially- and temperature-dependent thermal conductivity in inverse heat conduction problem.     

关于热传导方程半离散差分格式的一个注记

本文研究了热传导方程初边值问题的半离散化差分格式直接解算法.分别从Dirichlet和Neumann边界条件出发,直接由空间差分格式导出与时间相关的一阶常微分方程组,随后通过正/余弦变换获得了原方程的半解析解,并给出了相关收敛性分析.并对中心差分格式和紧差分格式的精度差异,通过矩阵特征值理论给出了相关原因分析.另外,对于二维热传导方程初边值问题,应用矩阵张量积运算,该直接解算法可直接演变成二重正(余)弦变换.该方法由于不涉及时间上的离散,从而具有较好的计算效率.     

Amplitude equation for the stochastic reaction‐diffusion equations with random Neumann boundary conditions

In this paper, we consider a quite general class of reaction‐diffusion equations with cubic nonlinearities and with random Neumann boundary conditions. We derive rigorously amplitude equations, using the natural separation of time‐scales near a change of stability and investigate whether additive degenerate noise and random boundary conditions can lead to stabilization of the solution of the stochastic partial differential equation or not. The nonlinear heat equation (Ginzburg–Landau equation) is used to illustrate our result. Copyright © 2015 John Wiley & Sons, Ltd.