粗糙热传导表面下激光介质温度场的计算分析

提出了一种计算温度场的面热源自适应调整算法,该方法通过在研究对象的封闭边界上引入虚拟面热源来求解稳态热传导方程的边值问题。建立了导热联结的具有粗糙表面介质的接触模型,在此基础上建立了随机分布的表面散热边界条件,并用面热源自适应调整算法计算了激光介质的温度场。结果表明,由于实际激光介质散热表面不能完全紧密接触,其温度场呈现一定程度的随机起伏,越靠近边界,随机起伏越明显,介质中心区域随机起伏则不明显;有效热接触面积越小,这种随机起伏越强烈。计算表明热接触面积占50%时,比接触面积占75%时温度场的随机性更明显。     

脉冲序列控制电流断续模式Buck变换器的动力学建模与边界碰撞分岔

通过建立一个开关周期内输出电容电荷变化量对应的输出电压变化量, 建立了工作于电感电流断续模式(discontinuous conduction mode, DCM)的脉冲序列(pulse train, PT)控制Buck变换器的近似离散时间模型, 研究了负载电阻及输入电压变化时PT控制DCM Buck变换器的边界碰撞分岔行为. 通过构造相应的迭代映射曲线, 分别分析了不同负载电阻时PT控制DCM Buck变换器的周期1、周期2和周期3运行轨迹的不动点稳定性, 揭示了PT控制DCM Buck变换器在不同周期态时的边界碰撞分岔的形成机理. 研究结果表明, 随参数变化, PT控制DCM Buck变换器始终运行在不同的周期态, 各周期态的切换由边界碰撞分岔引起, 李雅谱诺夫指数始终小于零. 利用PSIM电路仿真软件, 给出了不同负载电阻时的时域波形和相轨图. 实验结果验证了理论分析和仿真结果的正确性, 同时说明了本文动力学建模的可行性.     

大平板瞬态热传导问题的一种新的近似解法

１引言大平板瞬态热传导问题有着广泛的工程应用背景。对于复杂的初边值条件或含内热源问题,以及工程上常见的多层复合平壁对象,分析求解难度很大甚至无法求解。在此类情况下往往采用数值方法。但是单纯的数值解不便于理解影响该问题的各种参数的物理意义。因此,各种近似分析方法得到了发展［１,２］。但在近似精度上,往往难以对整个时间坐标范围都达到较高的精度,这就使得近似解更多地局限于定性分析。此外,对于不同的初边值条件或含内热源问题,近似解的形式相异,降低了解的通用性。增加了求解的工作量。本文提出一种基于矩阵理论…     

异质结碳纳米管的热整流效率

采用非平衡分子动力学方法, 通过分别控制异质结碳纳米管管径、手性和平均温度的方式研究了异质结碳纳米管的热整流效应. 研究表明, 随着异质结碳纳米管两端几何不对称性的增强, 其热整流效率会随之上升, 而异质结碳纳米管两端的手性的改变和夹角的大小都会对热整流效率产生一定的影响. 热整流效率会随着碳纳米管平均温度的上升而下降. 研究异质结碳纳米管热整流效率对于热二极管、碳纳米散热元器件等潜在应用价值有理论指导作用.     

准等熵压缩实验中金属铝的热力学耗散分析

为获取高压下材料的纯热力学压力-比容参考线和完全物态方程,减去应力-应变曲线中的其它信息,对准等熵压缩实验中由加载应变率引起的黏性耗散和热传导引起的热耗散做了分析讨论。基于反积分计算和流体动力学积分计算相结合的方法,根据激光加载(约108 s-1)和磁驱动准等熵压缩(约105 s-1)的实验数据,对材料声速、应力-应变曲线、温度和熵增等物理量进行计算,分析了不同应变率与该物理量的关系;还对热传导和SCG本构模型进行了计算,分析了热传导引起的温度变化对材料屈服强度、剪切模量和拉格朗日声速的影响。结果表明:激光加载实验中,应变率引起的温升差异约为180K,熵增差异约为250J/(kg·K),热传导导致温度下降40K;磁驱动准等熵压缩应变率较低,引起的熵增变化小于8J/(kg·K)。     

非线性热传导方程MLPG/RBF-FD无网格数值模拟

结合无网格局部彼得洛夫-伽辽金(MLPG)方法和径向基函数有限差分(RBF-FD)无网格方法求解非线性热传导问题.MLPG方法属于弱式无网格方法,具有处理边界条件方便的优点,然而因其要做大量的插值、积分运算而计算效率偏低;RBF-FD无网格方法属于强式无网格方法,直接对微分算子进行数值离散,计算效率高,然而其边界条件的...     

Short-range order and F ion diffusion inside the Pb1 − xAlxF2 + x solid solution Part II: Al NMR investigation and proposal of clustering process

A ²⁷Al nuclear magnetic resonance (NMR) investigation at room temperature of the Pb_{1 − x}Al_xF_{2 + x} (0 ≤ x ≤ 0.12) solid solution and of the ordered Pb₉Al₂F₂₄ phase is carried out. Two different types of aluminium ions are identified and their ratio is determined as a function of x. A clustering process based on the formation of column clusters, more and more extended when x increases, is proposed on the basis of results issued from the ¹⁹F (Part I) and ²⁷Al NMR investigations.     

一维热传导方程热源反问题基于最小二乘法的正则化方法

研究一维热传导方程热源反问题.给出基于最小二乘支持向量机（LS-SVM）求解的半解析表达式,此外还给出一种参数调节方法以及算法稳定性的证明.数值实验表明该方法具有较高的数值精度和稳定性.     

Evaporation of an emulsion trapped in a yield stress fluid

The present work deals with emulsions of volatile alkanes in an aqueous clay suspension, Laponite, which forms a yield stress fluid. For a large enough yield stress (i.e. Laponite concentration), the oil droplets are prevented from creaming and the emulsions are thus mechanically stabilized. We have studied the evaporation kinetics of the oil phase of those emulsions in contact with the atmosphere. We show that the evaporation process is characterized by the formation of a sharp front separating the emulsion from a droplet-free Laponite phase, and that the displacement of the front vs. time follows a diffusion law. Experimental data are confronted to a diffusion-controlled model, in the case where the limiting step is the diffusion of the dissolved oil through the aqueous phase. The nature of the alkane, as well as its volume fraction in the emulsion, has been varied. Quantitative agreement with the model is achieved without any adjustable parameter and we describe the mechanism leading to the formation of a front.     

Numerical investigations on the current conduction in bilayer organic light—emitting devices with ohmic injection of charge carriers

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trappedcharge limited conduction. The dependences of the current density on the operation voltage, the thickness andtrap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure an-ode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trapdepth, total trap density, and carrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL tothe sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance,can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentiallywith the mean reduced trap depth.