含有广义守恒律的生长方程标度奇异性的直接标度分析

利用直接标度分析方法研究一个含有广义守恒律生长方程的标度奇异性,得到强弱耦合区域的奇异标度指数.作为其特殊情况,这个方程包含Kardar-Parisi-Zhang（KPZ）方程、 Sun-Guo-Grant（SGG）方程以及分子束外延（MBE）生长方程,并能对其进行统一的研究.研究发现, KPZ方程和SGG方程,无论在弱耦合还是在强耦合区域内都遵从自仿射Family -Vicsek正常标度规律;而MBE 方程在弱耦合区域内服从正常标度,在强耦合区域内能呈现内禀奇异标度行为.这里所得到生长方程的奇异标度性质与利用重正化群理论、数值模拟以及实验相符很好. 关键词： 标度奇异性 强耦合 弱耦合     

定热流加热管湍流入口段的耦合热流分析

对圆管内物性随温度变化的吸收-各向同性散射介质的湍流入口段,数值研究了定热流加热下辐射与湍流正在发展流耦合换热的稳态热流特征．采用低雷诺数k-ε模型与SIMPLEC算法求解湍流流动与对流换热,采用蒙特卡罗法求解辐射换热;根据耦合换热温度场,采用等权抽样的蒙特卡罗法计算辐射热流。通过模拟计算,给出了介质内的耦合换热辐射热流与导热热流分布。通过分析介质光学厚度、散射反照率、壁面黑度对热流的影响,得出一些有价值的结论．     

光纤耦合模理论及其在光纤布拉格光栅上的应用

将正确的光纤中的正交关系应用于微扰耦合模理论得到了光纤中的微扰耦合模方程；并将其应用于光纤布拉格光栅，得到了一种新耦合模方程。该方程中作为标志性特性的耦合系数与其它理论中的耦合系数都不相同。讨论了方程的解，得到了峰值反射率与布拉格波长、光栅长度之间的简单关系式。用光纤布拉格光栅进行了实验，理论和实验结果符合得很好。     

扩展齐次平衡法与Backlund变换

将求解非线性演化方程的齐次平衡法进行了扩展,使其包含一个任意函数.此改进方法可得到耦合KdV-Burgers方程、KdV-Burgers方程、Boussinesq方程和一般KdV方程等许多非线性演化方程的Backlund变换和新的精确解.     

液相工质中热声效应数值模拟研究

基于求解可压缩流体的N-S方程,分别计算水及R134a两种液相工质在二维空间内的热声波产生及传递过程,分析初始压力及左侧壁温阶跃值对两种工质热声压力波产生的幅值及波传递到右边界后与壁面的热流交换影响情况。结果表明,初始压力对两种工质热声波产生的幅值及与向右边界换热的热流影响不大;压力幅值及右边界传热热流强度随左侧壁温度阶跃值增大而增大;在相同边界条件下,R134a可以产生更大幅值的压力波,并且与右边界换热的热流较大。     

基于互易定理的双缓变光纤模耦合特性研究

直接从电磁场的普遍原理——共轭互易定理出发,针对无损折射率双缓变光纤,得到了双缓变光纤模耦合方程,推导出了互耦合系数、自耦合系数、干涉耦合系数和传播常数之间关系。在此基础上,对模耦合方程进行了求解,得到了相同双缓变光纤模耦合方程的近似解析解,讨论了耦合系数对光功率耦合的影响。     

二维流场、热结构松耦合模拟研究

本文针对轴对称型飞行器前缘部位,采用松耦合方法,开展了二维高超声速流固界面的热耦合计算。满足非稳态N-S方程的外部流场和内部非稳态热传导均采用商用软件FLUENT进行计算。通过对相同时刻,不同松耦合推进时间步长引起的壁面热流密度、壁面温度、表面传热系数的差异对比,得出了松耦合推进时间对以上参数的影响规律,这对有效实施松耦合方法进行高超声速飞行器模拟具有积极意义。     

圆管内自由固体相变材料定热流接触熔化

针对水平圆管内自由固体相变材料储能时的吸热熔化,运用接触熔化理论建立定热流圆管热源接触熔化模型.运用Nusselt液膜理论,建立熔化控制方程,并求解得到无量纲熔化方程组.分析讨论不同工况下熔化速度、液膜层厚度和压力分布等熔化参数的变化规律,探讨各影响因素对熔化的影响,并与温差熔化结果进行比较,研究第二类热边界条件下的接...     

螺旋波纹波导研究

从耦合波方程出发，利用阻抗微扰法对螺旋波纹波导的边界不规则性进行处理，得到螺旋波纹波导的一般性耦合波传输方程，及耦合系数表达式.根据螺旋波纹波导内模式耦合的规则,得出色散方程并分析其色散特性. 关键词： 螺旋波纹波导 耦合波方程 阻抗微扰 色散特性 本征模     

感应耦合氩等离子体反应器内流场的三维数值模拟（英文）

感应耦合等离子体反应器内流场的三维数值模拟可以揭示其复杂的空间分布.利用PROE软件建立反应器的三维模型.假设等离子体是良好的导体,结合麦克斯韦方程组以及电磁学和流体力学方程,经过推导得到磁流体力学的连续、动量、能量方程.利用FLUENT软件的二次开发功能完成耦合计算.磁场的矢量方程通过复矢量技术和UDS得到解决,利用UDS定义变物性参数和添加源项.在C语言的基础上编写UDF.将划分好网格的模型和UDF导入FLUENT中,应用基于压力法的求解器进行模拟运算.通过模拟运算得到了反应器内电磁场、温度场、速度场的分布图.最后进行了二维模拟和三维模拟的对比,以验证文中所进行模拟所得结果的可行性.     

基于模拟方法生成血管树的人舌三维温度场数值模拟

采用分步模拟方法生成血管树并以此作为物理模型,进行舌体三维温度场的实验研究与数值计算。计算分为舌体组织和血液温度场数值模拟两部分,相应数学模型也包括舌体组织控制方程、血液控制方程及两者之间的耦合方程。在考虑了血液与组织间的耦合换热,舌津液蒸发的影响基础上,采用数值模拟得到的舌面对流换热系数,使计算结果与红外热像验证极为近似。以模拟方法生成的血管树替代生物体的血管铸型,在某种意义上说将生物体三维传热计算方法的研究推向了一个新的层面。     

A coupled pressure-based computational method for incompressible/compressible flows

Pressure-based flow solvers couple continuity and linearized truncated momentum equations to derive a Poisson type pressure correction equation and use the well known SIMPLE algorithm. Momentum equations and the pressure correction equation are typically solved sequentially. In many cases this method results in slow and often difficult convergence. The current paper proposes a novel computational algorithm, solving for pressure and velocity simultaneously within a pressure-correction coupled solution approach using finite volume method on structured and unstructured meshes. The method can be applied to both incompressible and subsonic compressible flows. For subsonic compressible flows, the energy equation is also coupled with flow field and the density of fluid is obtained by equation of state. The procedure eliminates the pressure correction step, the most expensive component of the SIMPLE-like algorithms. The proposed coupled continuity-momentum-energy equation method can be used to simulate steady state or transient flow problems. The method has been tested on several CFD benchmark cases with excellent results showing dramatically improved numerical convergence and significant reduction in computational time.     

RF discharge modeling considering time dependence and spatialnonlocality of the electron energy spectrum

RF discharge modeling in He is performed. New features of modeling are based on the solution of the nonstationary Boltzmann equation in the spatially nonuniform electric field, coupled with the equation for electric field and charged-particle densities. It is shown that the local equilibrium model for the electron energy spectrum in RF discharge is not valid for the pressure range ≃10 torr     

双钨极耦合电弧数值模拟

基于流体力学方程组和麦克斯韦方程组, 在合理的边界条件下, 建立了双钨极耦合电弧三维准静态数学模型. 通过对方程组的迭代求解, 获得了不同钨极间距和电弧长度下耦合电弧的温度场、流场、电弧压力和电流密度分布等重要结果, 与已有的实验研究符合良好. 模拟结果表明: 与相同条件下的钨极惰性气体保护焊电弧相比, 双钨极耦合电弧的最高温度和最大等离子流速较低, 阳极表面电弧压力和电流密度峰值明显减小; 钨极间距和弧长对耦合电弧的温度场、流场、电流密度和电弧压力等都具有显著的影响, 且耦合电弧阳极的电弧压力和电流密度分布不能用高斯近似进行描述. 关键词： 耦合电弧 三维模型 数值模拟     

射频容性耦合等离子体放电特性的光谱诊断

利用流体模型模拟和发射光谱实验诊断相结合的方法，研究了中等气压、中等功率下射频容性耦合等离子体的放电特性。理论上，采用基于流体模型的COMSOL软件仿真，建立一维等离子体放电模型，以Ar气为工作气体，研究了不同气压以及不同射频输入功率下等离子体电子温度和电子密度的分布规律。实验上，依据仿真模型设计制作了相同尺寸的密闭玻璃腔体和平板电极，采用13.56 MHz射频放电技术电离腔体内的工作气体Ar气，测量了不同气压、不同射频输入功率时放电等离子体的发射光谱。通过分析和选择适当的Ar Ⅰ和Ar Ⅱ的特征谱线，分别利用玻尔兹曼斜率法以及沙哈-玻尔兹曼方程计算了等离子体的电子温度与电子密度，并结合模拟仿真结果对光谱诊断结果进行了修正。结果表明：当气体压强为300~400 Pa、输入功率为600~800 W时，等离子体近似服从玻尔兹曼分布，此时利用光谱法得到的等离子体参数与仿真结果相符合。仿真模拟与光谱实验诊断相结合的方法可初步诊断出中等气压下等离子体的放电参数，增加了玻尔兹曼斜率法和沙哈-玻尔兹曼方程在等离子体放电中的使用范围，扩大了光谱法在低电子密度容性耦合等离子体参数诊断的应用场合，为中等气压容性耦合等离子体在工业与军事上的应用研究提供了重要物理状态的分析手段。     

氩气微腔放电中特性参数的数值模拟研究

本文采用二维自洽完全流体模型,针对阳极为通孔的高气压微腔放电结构,研究了微腔放电的参数特性.数值计算得到了氩气压强为100 Torr,放电稳态时的电势分布、电子数密度分布和电子温度分布等重要参数.模拟结果表明放电区存在显著的阴极鞘层结构,电子数密度的峰值达到10²⁰ m^-3,电子温度的量级为几个eV至十几eV,该结论与实验结果相一致.数值模拟合理的解释了微腔放电的基本原理. 关键词： 微腔放电 等离子体模拟 流体模型     

Numerical study on the characteristics of nitrogen discharge at high pressure with induced plasma

Based on the fluid theory of plasma, a model is built to study the characteristics of nitrogen discharge at high pressure with induced argon plasma. In the model, species such as electrons, N2+, N4+, Ar+, and two metastable states (N 2(A3∑u+), N2 (a1 ∑u-)) are taken into account. The model includes the particle continuity equation, the electron energy balance equation, and Poisson抯equation. The model is solved with a finite difference method. The numerical results are obtained and used to investigate the effect of time taken to add nitrogen gas and initially-induced argon plasma pressure. It is found that lower speeds of adding the nitrogen gas and varying the gas pressure can induce higher plasma density, and inversely lower electron temperature. At high-pressure discharge, the electron density increases when the proportion of nitrogen component is below 40%, while the electron density will keep constant as the nitrogen component further increases. It is also shown that with the increase of initially-induced argon plasma pressure, the density of charged particles increases, and the electron temperature as well as the electric field decreases.     

A new pressure-dominant approximation model for acoustic–structure interaction

A high accuracy approximation modeling approach for the acoustic–structure interaction problem with a shell structure is presented in this paper. The new approximation model aims to accurately reveal the relationship between pressure and velocity in the acoustic field. The main idea of this model is to separate the velocity terms into a combination of velocity and pressure by using a weighting parameter. The modal analysis was performed to find an appropriate weighting parameter for the new model for the spherical case. The stability range of the model is limited during this process. An approximation model was coupled with the equation of motion of a spherical shell to check the performance of the model. Responses of a spherical shell excited by a plane step wave and cosine-type incident pressure from the new model were compared to the exact solution and solutions from former approximation models such as Doubly Asymptotic Approximations (DAAs). The new proposed model can approximate high accuracy responses in both early and late time.     

Elastic response of an acoustic coating on a rib-stiffened plate

This paper develops a three-dimensional analytical model of a fluid-loaded acoustic coating affixed to a rib-stiffened plate. The system is loaded by a plane wave that is harmonic both spatially and temporally. The model begins with Navier-Cauchy equations of motion for an elastic solid, which produces displacement fields that have unknown wave propagation coefficients. These are inserted into stress equations at the boundaries of the plate and the acoustic coating. These stress fields are coupled to the fluid field and the rib stiffeners with force balances. Manipulation of these equations develops an infinite number of indexed equations that are truncated and incorporated into a global matrix equation. This global matrix equation can be solved to determine the wave propagation coefficients. This produces analytical solutions to the systems’ displacements, stresses, and scattered pressure field. This model, unlike previously developed analytical models, has elastic behavior and thus incorporates higher order wave motion that makes it accurate at higher wavenumbers and frequencies. An example problem is investigated for three specific model results: (1) the dynamic response, (2) a sonar array embedded in the acoustic coating, and (3) the scattered pressure field. An expression for the high frequency limitation of the model is derived. It is shown that the ribs can have a significant impact on the structural acoustic response of the system.     

Coupled hydrodynamic-acoustic modeling of sound generated by impacting cylindrical water jets

A coupled hydrodynamic-acoustic model describing acoustic propagation in a fluid containing multiple bubbles is proposed and applied to simulate noise generated by impacting water jets. The total pressure is decomposed into a "hydrodynamic" part and an "acoustic" part and computed using different schemes. The hydrodynamic pressure field is calculated independently using a generalized hydrodynamic model, and the pressure variations serve as sources in the wave equation for the acoustic pressure. A numerical algorithm developed to calculate wave propagation in an irregular region is used to account for the existence of the cavities. Noise generated by the impact of two cylindrical water jets is predicted. The computed near-field pressure is compared with the experimental data.