水平轴潮流能水轮机数值模拟方法对比分析

叶素动量理论和CFD方法是水平轴潮流能水轮机性能分析中运用较为广泛的数值模拟方法,文中结合小尺寸水轮机模型试验,对比分析了叶素动量理论和CFD方法在水轮机性能分析中的准确性和适用性.验证结果表明:叶素动量理论和CFD方法均能对水轮机的性能进行预报,且CFD精度高于动量叶素理论;大尖速比时,动量叶素理论偏离较高,不再适合性能预报;在小尖速比下,建议采用RNGk-ε模型的CFD方法进行分析计算;动量叶素理论适合设计初期设计方案的对比分析,而CFD方法适合对设计结果的验证校核和详细分析.     

Extended CFD–DEM for free‐surface flow with multi‐size granules

Computational fluid dynamics and discrete element method (CFD–DEM) is extended with the volume of fluid (VOF) method to model free‐surface flows. The fluid is described on coarse CFD grids by solving locally averaged Navier–Stokes equations, and particles are modelled individually in DEM. Fluid–particle interactions are achieved by exchanging information between DEM and CFD. An advection equation is applied to solve the phase fraction of liquid, in the spirit of VOF, to capture the dynamics of free fluid surface. It also allows inter‐phase volume replacements between the fluid and solid particles. Further, as the size ratio (SR) of fluid cell to particle diameter is limited (i.e. no less than 4) in coarse‐grid CFD–DEM, a porous sphere method is adopted to permit a wider range of particle size without sacrificing the resolution of fluid grids. It makes use of more fluid cells to calculate local porosities. The developed solver (cfdemSolverVOF) is validated in different cases. A dam break case validates the CFD‐component and VOF‐component. Particle sedimentation tests validate the CFD–DEM interaction at various Reynolds numbers. Water‐level rising tests validate the volume exchange among phases. The porous sphere model is validated in both static and dynamic situations. Sensitivity analyses show that the SR can be reduced to 1 using the porous sphere approach, with the accuracy of analyses maintained. This allows more details of the fluid phase to be revealed in the analyses and enhances the applicability of the proposed model to geotechnical problems, where a highly dynamic fluid velocity and a wide range of particle sizes are encountered. Copyright © 2015 John Wiley & Sons, Ltd.     

基于Voronoi图的空间信息多尺度表达

空间信息多尺度表达是地理信息系统和遥感信息科学的重要研究内容之一。Voronoi图有效的几何规则和算法,为地图目标间的复杂空间关系提供了强大的描述和分析依据。讨论了在进行空间多尺度表达时,地物要素概括和符号化带来的取舍、相交、拥挤等空间冲突问题。根据计算几何的Voronoi、Delaunay原理,探讨了点群要素选取、线要素的相交、面要素的聚合和一致性简化,使其在视觉表达上更适合于人的视觉和认知心理学特点,更有利于空间数据进行分析、处理和可视化。     

Permeability determination of porous media using large‐scale finite elements and iterative solver

The problem of finite element simulation of incompressible fluid flow in porous medium is considered. The porous medium is characterized by the X‐ray microtomography technique in three dimensions. The finite calculus‐based stabilization technique is reviewed to implement the equal order finite element interpolation functions for both velocity and pressure. A noble preconditioner, the nodal block diagonal preconditioner, is considered whose performance is thoroughly investigated. Combining this preconditioner with a standard iterative solver during the computational homogenization procedure, it is possible to carry out the large‐scale fluid flow simulation for estimating permeability of the porous medium with reasonable accuracy and reliability. Copyright © 2013 John Wiley & Sons, Ltd.     

基于朗肯土压力理论的有限土体土压力计算探究

在一般土力学及挡土墙研究中,计算土压力的方法往往是传统的朗肯土压力理论和库仑土压力理论,其都是建立在半无限土体假定基础上的.由于城市用地紧张,建筑物与支护结构的距离常常比较小,支护结构的作用越来越复杂.城市开发建设过程中,不仅要保证自身的稳定性、经济性,还要保证临近建筑物和设施的安全.对四种有限土体土压力计算方法进行推导探究,分析对比得到在同等条件下,利用极限平衡受力分析法所得到的有限土体土压力值较小,更具经济效益,而在不同的地层和墙间距情况下不同的算法有不同的特点,充分考虑特殊条件下的土压力计算方法,可以使施工设计方案更优化.     

探空温度传感器受太阳辐射影响的仿真分析

随着高空温度探测精度要求的日益提高,如何减小温度传感器测量误差已成为亟需解决的问题,而太阳辐射作为影响温度传感器探测性能的重要因素已成为该领域研究的热点.利用计算机仿真技术,引入太阳高度角、引线夹角2个影响因子,根据流体动力学模型模拟分析探空温度传感器从海平面上升到32 km高空时所受太阳辐射的影响,最终得到辐射误差与海拔高度的关系曲线族,仿真结果将为开展高空温度传感器误差分析提供基础依据,从而提高传感器测量准确度.     

Construction and Validation of an Urban Area Flow and Dispersion Model on Building Scales

This paper presents a numerical model that simulates the wind fields, turbulence fields, and dispersion of gaseous substances in urban areas on building to city block scales. A Computational Fluid Dynamics（CFD） approach using the steady-state, Reynolds-Averaged Navier-Stokes（RANS） equations with the standard k-ε turbulence model within control volumes of non-uniform cuboid shapes has been employed. Dispersion field is computed by solving an unsteady transport equation of passive scalar. Another approach based on Gaussian plume model is used to correct the turbulent Schmidt number of tracer, in order to improve the dispersion simulation. The experimental data from a wind tunnel under neutral conditions are used to validate the numerical results of velocity, turbulence, and dispersion fields. The numerical results show a reasonable agreement with the wind tunnel data. The deviation of concentration between the simulation with corrected turbulent Schmidt number and the wind tunnel experiments may arise from 1） imperfect point sources, 2） heterogeneous turbulent difusivity, and 3） the constant turbulent Schmidt assumption used in the model.     

强制通风温度传感器的计算流体动力学分析

本文利用计算流体动力学(Computational Fluid Dynamics, CFD)方法对基于076B型强制通风防辐射罩的温度传感器进行流固耦合传热分析,计算不同太阳辐射强度、下垫面反射率、强制通风速度、气象站海拔高度和下垫面长波辐射强度等影响因子条件下温度传感器的辐射误差。为实现影响因子连续变化时能提供准确修正数据的目标,采用神经网络算法仿真值计算结果进行拟合,获得辐射误差订正方程。结果表明,辐射误差订正方程的修正误差在0.005℃以内。订正后的气温观测数据有望用于气候变化研究和高精度天气预报。     

一种“准拉格朗日法”和“欧拉法”统一算法时间积分方案

从欧拉算符出发,用泰勒级数展开,给出二阶时空微商余项预报方程,进而讨论一种数值分析新算法———双三次曲面拟合(插值)的准拉格朗日时间积分方案与数值模式。它是将大气运动描述成为非线性的三次运动,即是通过对原始大气运动方程中包括标量、矢量的压、温、湿、风、以及旋转地球上广义牛顿力加速度场和散度场等,做双三次曲面拟合,实现对各个大气运动变量场的二阶可导,即限定气块上游点在各个不同双三次曲面(片)、具有斜率、曲率和挠率的非线性三次变量场上活动,从而可对各个大气运动方程做时间离散积分,即为双三次曲面拟合—时间步积分—双三次曲面拟合……,实现成为一种新动力框架数值模式。由于双三次曲面具有数学定律收敛性和二阶可导最优性,故选用双三次曲面插值求算二阶余差上游点,具有充分必要的数学理由:它包含了大气运动变量场之斜率、曲率和挠率。因此,埃尔米特双三次曲面片具有对网格变量场二阶可导运算等价性、及其数学收敛性与最佳曲率最优性,并且将准拉格朗日法与欧拉法,以及柯朗-弗里德里希斯-列维判据统一起来。容易实现全球网格变量场的双三次曲面拟合,和可按双三次曲面变量场的斜率、曲率或挠率判断,作变量场局域或单点平滑,以此保持三次模式的时间积分稳定...