建筑结构非定常绕流风场的数值模拟方法

给出了一种适用于计算建筑结构非定常绕流风场的大涡数值模拟算法．该算法基于有限差分法，采用曲线坐标结构网格，能精确描述形状复杂的物面边界，为下一步准确模拟含有因结构受风变形所致运动边界的绕流场奠定了基础．该算法采用投影法解耦纳维一斯托克斯方程中的压力和速度，对非定常流场的时间步进采用二阶Adams—Bashforth方法．采用同位网格以减少计算所需内存，为了平抑同位网格下中心差分格式导致的固有压力波动现象，计算对流速度时采用Rhie—Chow动量插值方法，利用编制的曲线坐标系下大涡模拟数值计算程序，对德州理工大学（TTU）建筑足尺模型绕流风场进行了模拟，所得结果与现场实测和风洞试验结果进行了比较，结果表明，本文算法是建筑结构非定常绕流风场数值模拟的有效方法．     

绕圆柱湍流流场及其发展的计算

为研究绕圆柱湍流流场及其发展变化,应用RNGκ-ε模型和有限体积法求解非定常雷诺平均纳维尔-斯托克斯(URANS)方程,以二阶隐式时间离散和二阶迎风空间离散格式对控制方程进行离散,采用SIMPLEC算法耦合求解平均速度场和压力场.在Re=103～107范围内对流场进行了数值模拟计算,得到了速度场、涡量场及其湍流脉动参数在下游的发展变化规律.计算与分析结果表明:在高雷诺数条件下,回流区减小,尾流区变窄,尾流在主流方向的影响区域变小,涡量向下游的衰减更慢,湍流动能和湍流耗散率在下游的影响区域也减小.     

双向流固耦合的圆柱式桥墩绕流的三维数值模拟

考虑双向流固耦合并利用软件ANSYS CFX模拟了圆柱表面涡脱的产生和变化过程,结合工程实际给出了计算实例,采用有限体积法对流体力学控制方程Navier-Stokes进行离散,用SIMPLE方法求解,分析计算了圆柱表面周向压力系数分布情况及圆柱的阻力系数、升力系数及Strouhal数,得到了流体与结构物相互作用对圆柱绕流特性的影响。结果表明:由于圆柱受到水流的作用,圆柱的升力及尾流特征显示周期性变化,并出现单一频率振动。     

时空有限元方法的高效计算

为提高时空有限元方法求解二维瞬态不可压缩的Navier-Stokes方程的计算效率并降低对计算机内存的需求,用行格式存储法存储大型稀疏矩阵,用Newton-Raphson迭代法求解非线性代数方程组,用无填充不完全分解预处理方法以及重启型GMRES方法求解子迭代步的线性方程组.为验证该方法的可行性,对Reynolds数为100的圆柱绕流问题进行数值模拟.采用行格式存储法的存储空间仅为等带宽存储法的3.68%.     

基于人工可压缩方法的后台阶绕流数值模拟

针对二维后台阶绕流采用人工可压缩方法进行数值模拟，方程的离散采用有限体积法．为了消除离散求解时可能产生的数值振荡，在离散方程的右端人为增加四阶人工耗散．在Re=45，60，90等低雷诺数下的数值试验结果表明，人工可压缩方法和有限体积离散方法联合进行数值模拟的可行性；在低Re的情况下，伪可压缩系数α取小的值会对方程求解的稳定性更有利．在其它参数取值相同的情况下，还分别针对加入和不加人人工耗散两种情况进行模拟，结果表明人工耗散的加入使迭代余量的绝对值明显减小，也就是从一定程度上消减了数值解的振荡．文中同时在数值试验的基础上提出了人工压缩系数的参考取值范围．通过采用上述方法对后台阶绕流进行模拟，模拟结果和商用软件PHOENICS3．2在相同条件下模拟结果基本吻合，表明了该方法的可行性．     

高速列车湍流绕流三维数值模拟研究

本文在般曲线坐标系下，采用Ｋ－ε双方程模型及壁面控制函数，借助于代数变换建立起以协变速度分量为独立变量的三维复杂钝体湍流绕流数值计算方法，建立了一套适合于近地大长细比复杂几何体的三维网格生成与控制方法，同时采用交错网格，成功地解决了压力－速度耦合关系。首次对高速列车三维湍流绕流场压力分布、速度分布以及气动阻力进行研究。本文的研究工作对进一步解决近地大长细比复杂几何体湍流绕流数值模拟是一个良好的开端     

地铁屏蔽门的环境控制效果研究

采用一维非稳态流模型，利用连续性方程、运动方程和对流-扩散方程模拟地铁系统内气流速度场、温度场，通过对某工程不同环控方案的空调负荷和温度场进行比较，结果表明车站采用屏蔽门空调能耗降低1／3－1／2，隧道内 空气温度有所上升。通过对车站屏蔽门的分析提出了合理建议。     

具有地面效应的高速列车湍流绕流数值模拟研究

利用数值模拟方法，研究了考虑地面效应和不考虑地面效应的高速列车湍流绕流之间差别，并利用风洞试验进行了验证。应用改进的曲线网格系统和计算程序Ｔｒａｉｎ，对高速列车绕流流场进行了较为精确的数值模拟。从计算结果分析看出，考虑地面效应的阻力系数比未考虑地面效应的阻力系数增加１５％，使计算精度从７５％增加到８５％。     

小展弦比舵翼三维绕流场的数值模拟计算

采用ＲＮＡＳ方程为基本方程，应用二层ｋ－ε湍流模型封闭ＲＡＮＳ方程，采用有限体积法离散方程，对小展弦比舵翼的三维绕流场进行了数值模拟计算。不同于通常的网格划分，采用了贴体坐标与空度法相结合的方法对舵翼的几何形状及其对流场的影响进行描述，计算结果与实验结果进行了比较，结果表明，本文所采用的方法，可以对小展弦比舵翼三维流动的流体动力性能进行正确地预报，对其绕流场亦能给出合理的描述。     

模腔注射模拟显式算法中对流项作用的评估

为研究Navier-Stokes方程中对流项对粘性流注射模拟结果的影响,在基于矢量化显式算法模拟软件中加入对流作用项.应用修正后的软件模拟两个典型的注射填充过程的算例,并与相应的实验比较.对模拟和实验结果的比较表明,对流项对粘性流注射填充过程和的其中的自由表面形状的模拟结果影响可以忽略.     

A Computational Model for Pedestrian Level Wind Environment Around Tall Buildings

A computational model has been developed for the simulation of pedestrian level wind environment around tall buildings by coupling the numerical simulation of the full-scale site and meteorological station materials. In the first step, the hybrid/mixed finite element method is employed to solve the two dimensional Navier-Stokes equation for the flow field around tall buildings, in view of the influence of fluctuating wind, the flow field is revised with the effective wind velocity. The velocity ratio is defined in order to relate numerical wind velocity to oncoming reference wind velocity. In the second step, the frequency occurred discomfort wind velocity as a suitable criterion is calculated by use of the coupling between the numerical wind velocity and the wind velocity at the nearest meteorological station. The prediction accuracy of the wind environment simulation by use of the computation model will be discussed. Using the available wind data at the nearest meteorological station as well as the established criteria of wind discomfort, the frequency of wind discomfort can be predicted. A numerical example is given to illustrate the application of the proposed method.     

基于 BPF 的分布系统数字仿真方法

提出了一种应用块脉冲函数（ＢＰＦ）进行分布式系统数字仿真方法。该方法用ＢＰＦ逼近所求问题的解，将分布系统偏微分方程转换为矩阵方程，然后用Ｋｒｏｎｅｃｋｅｒ积解矩阵方程。该方法本质上是一种并行算法。与传统的差分法比较表明，该方法的仿真结果精度较高。     

Compensation of pressure enthalpy effects on temperature fields for throttling of high-pressure real gas

For the pressure enthalpy of high pressure pneumatics, the computational fluid dynamics (CFD) simulation based on ideal gas assumption fails to obtain the real temperature information. Therefore, we propose a method to compensate the pressure enthalpy of throttling for CFD simulation based on ideal gas assumption. Firstly, the pressure enthalpy is calculated for the pressure range of 0.101 to 30 MPa and the temperature range of 190 to 298 K based on Soave-Redlich-Kwong (S-R-K) equation. Then, a polynomial fitting equation is applied to practical application in the above mentioned range. The basic idea of the compensation method is to convert the pressure enthalpy difference between inlet air and nodes into the compensation temperature. In the above temperature and pressure range, the compensated temperature is close to the real one, and the relative temperature drop error is below 10%. This error is mainly caused by the velocity difference of the orifice between the real and ideal gas models. Finally, this compensation method performs an icing analysis for practical high pressure slide pilot valve.     

DEPLETION POTENTIAL OF COLLOIDS: A DIRECT SIMULATION STUDY

IntroductionWhen two big hard spheres suspended in a flu-id of small hard colloidal sphere systems,the bigspheres will attracteach other when the separationbetween the big spheres is about or less than thesmall sphere diameter.The physical picture of thisattractive interaction is clear,when small particlesare depleted from the space between big spheresthe pressure of other small particles will push thebig spheres together and an attraction arise.Thiscan also be understood by the entropy argume…     

公路长隧道纵向通风的数值模拟

采用有限元法求妥二维定常不可压缩Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程的方法，进行隧道射流通风和具有射流调压的竖井吸出式通风系统的空气动力学特性数值研究，给出在不同工况条件下，实际隧道中风速的分布特征。数值解和试验结果进行比较，证明数值解是有效和可靠的。     

A new algorithm for non-newtonian flow and its application in mould filling process

The simulation of injection molding process requires a stable algorithm to model the molten polymer with non-isothermal non-Newtonian property. In this paper, a staggered and iterative scheme is particularly designed to solve the velocity-pressure-temperature variables. In consideration of the polymer characteristic of high viscosity and low thermal conductivity, the non-Newtonian momentum-mass conservation equations are solved by the Crank-Nicolson method based split (CNBS) scheme, and the energy conservation equation with convective character is discretized by the characteristic Galerkin (CG) method. In addition, an arbitrary Lagrangian Eulerian (ALE) free surface tracking and mesh generation method is introduced to catch the front of the fluid flow. The efficiency of the proposed scheme is demonstrated by numerical experiments including a lid-driven cavity flow problem and an injection molding problem.     

Fluctuation velocity correlation closure model for dense gas-particle turbulent flow

Turbulence model of kg-εg-kp-εp-kpg-θ is proposed.In the model,the two-phase velocity correlation turbulent kinetic energy k pg is modeled by transport equation.To close this turbulence model,algebraic expressions of two-phase Reynolds stresses and two-phase velocity correlation variable are established by considering both gas-particle interaction and anisotropy.This turbulence model is used to simulate dense gas-particle flow in a riser and in a downer.The predicted results show the core-annulus flow structure observed in the riser and the skin effect of particle concentration in the downer.The present model gives simulation results in much better agreement with the experimental results than those obtained by kg-εg-kp-εp-θmodel which is simply closed using a semi-empirical dimensional analysis.     

基于数值分析的大跨隧道不同工序下地层特性研究

利用有限差分软件FLAG3D,建立了浅埋大跨地铁隧道开挖模型.通过分析浅埋大跨隧道分别采用台阶法和双侧壁导坑法不同施工工序下的地层应力位移特性,得出了针对浅埋大跨隧道开挖,采用双侧壁导坑法优于台阶法,并说明了双侧壁导坑法能有效控制变形的理论依据.将数值模拟与现场测试试验结果对比,提出了优化的施工方案,对大跨浅埋隧道类似工程施工具有一定的指导借鉴作用.     

既有隧道扩建工程及衬砌稳定性研究

以当风凹隧道为工程研究背景，采用二维弹塑性有限差分分析方法，研究既有隧道扩建过程中的力学特征及其支护强度；分析并得出既有隧道扩挖与假设新建一座隧道在力学上的主要差异：采用同种施工方法时，因为已有衬砌的作用，在旧洞基础上扩挖将避免对围岩的大面积扰动，且能充分发挥围岩承载力；结合公路隧道设计规范给定的极限状态方程，计算出隧道衬砌的强度安全系数；从位移、应力和安全系数等方面分析并证明了隧道的稳定性，研究成果为类似的隧道设计施工提供参考．