Comparison between numerical computations and measurements by LDV for fluid flow in rectangular duct systems

Fluid flows in rectangular duct systems are measured by using the laser-Doppler velocity meter and computed by commercial software of Star-CD for comparisons between flows. Three rectangular systems are investigated in this study: a rectangular duct with a 90 degree bent elbow, a rectangular duct with two branches, and a rectangular duct in the middle of which a circular cylinder is located. These investigations show that the numerical solutions satisfactorily predict design factors: for example, the K -factor for an elbowed duct, the distribution ratio of flow rates into each branch from a main duct, and the Nusselt number around the circular duct. However, there are some disagreements in the velocity profile and turbulent kinetic energy at each cross section of the duct systems.     

一种无线Mesh网络扩展改进方法研究

将ECMA-368协议应用于无线Mesh网络时,为了使其更好的适应多跳路由协议,提高网络吞吐率,减小路由中继节点接入时延,提出针对ECMA-368协议MAC层的改进方法ARTAP算法,并给出其具体实施步骤及分析过程。仿真结果表明,该方法能够提高网络吞吐率,减小中继节点接入时延,提高网络对多跳业务的服务性能。     

Spatial resolution effects on unsteady turbulent flow computations for the rectangular cylinders byκ-ε turbulence models

In predicting unsteady turbulent flows around a square cylinder usingκ-ε turbulence models, choice of right turbulence models was found to be critical. If a proper care is taken to choose a convection scheme and near-wall resolution, the conventional turbulence models may predict an unsteady turbulent flow at low Reynolds numbers with reasonable accuracy. A systematic computation is carried out to identify the effects of the aspect ratio of a rectangular cylinder and of the flow Reynold number on the spatial resolution requirement. It is found in general that the grid resolution requirement is more stringent for a cylinder with a smaller aspect ratio. By investigating high Reynolds number computations, the grid refinement in terms of viscous wall units is found unimportant in accurately predicting the unsteady aerodynamic forces on the cylinder. Instead, resolution of shear layers formed at the forward separation corners is found to be more critical.     

Time-dependent FEM simulation of dilution control of laser cladding by adaptive mesh method

Dilution is an important factor which influences the properties of clad layer. In this paper the change of dilution during laser cladding and the control of dilution are simulated by a finite element method. The adaptive mesh method is adopted for the time-dependent finite element method computation so that the shape of melt pool can be well represented. The situation of the width control of melt pool is also simulated, which indicates that the dilution can be controlled if the width of melt pool is controlled. Computational results indicate that if a line energy (input energy per unit distance) remains constant the dilution will increase with time, especially at the beginning. Simulation results show that it is possible to control dilution in a certain range if the line energy decreases with time. Experiment of Nd: YAG laser cladding with wire feeding is performed. Experiment results coincide well with the FEM results.     

基于参数化模型特征的有限元网格划分方法研究

基于开孔实体的参数化特征模型思想,本文提出了一种非自由边界分割有限元网格划分方法,可以针对开孔实体的几何特征和力学特征,对多种类型的开孔构件进行全6面体网格划分,生成的网格质量均匀、局部加密方便且疏密过渡合理.经实例应用表明,此种网格划分方法具有通用性强、简单、实用、高效等特点.     

保持形状特征的整体网格曲面变形算法

为了克服传统网格曲面变形对模型的特征只能进行近似控制的缺陷,提出一种精确的特征控制方法,使得模型特征在整体曲面变形中保持原有形状。首先提取形状特征的位置信息,将其作为变形过程中的刚性约束;再根据改进的离散拉普拉斯算子,建立反映网格曲面微分特性的柔性约束;对刚性约束条件引入拉格朗日乘子,结合柔性约束条件建立线性方程组,利用最小二乘法求出最优解,从而实现在保持形状特征的情况下网格曲面的整体变形。最后,通过实践应用证明了上述算法的合理有效性。     

有限元网格划分方法应用研究

首先探讨了有限元网格划分的一些基本原则,然后从几何模型建立方法的角度对几种不同网格划分方法进行了深入讨论,最后在ANSYS中对这些网格划分方法进行了实例比较,给出了不同网格划分方法的适用范围及其应用特点。     

CAD曲面网格建模方法

分析了CAD线框建模、表面建模、实体建模等三维几何建模方法和AutoCAD多边形网格的曲面建模方法,介绍了利用ActiveX Automation技术和VB开发工具进行二次开发实现离散点数据自动生成AutoCAD网格曲面的过程和方法.     

Numerical simulation of turbulent flow in the suction chamber of a gearpump using deforming mesh and mesh replacement

The flow in the suction chamber of an external gearpump is numerically analysed. The evolution of the boundaries of the domain is very complex, and an arbitrary Lagrangian-Eulerian (ALE) formulation is used with mesh deformation and local remeshing. Nevertheless, a mesh replacement strategy is also adopted in order to avoid skewed meshes and allow for simulation of solid contact between gears. This process approximates a more realistic flow behaviour when the working pressure is larger than 10 bar, which is an important in fluid power systems where the pressure is usually greater than 100 bar.Aside from the laminar model, which fails as a result of the vortex configuration in the suction chamber, Standard k-ε, RNG k-ε, Realizable k-ε and Reynolds Stress Models (RSM) are tested. The numerical flow is compared with experimental data obtained with Time Resolved Particle Image Velocimetry. Although all of the models failed in some respect, the RSM and RNG k-ε were the best choice provided its behaviour close to the gearing zone and general shape of the vortex distribution.     

A new parametric control method for freeform mesh models

Parametric modeling technology is difficult to apply to freeform mesh models since there is no efficient way to impose geometric constraints. In this paper, we propose a novel method to control freeform mesh models parametrically. Our approach is to construct a control mesh that surrounds an object model and then impose constraints on it. The control mesh is parametrically controlled and the shape of the object model is modified by using an existing freeform deformation method. This paper is mainly concerned with automated construction of a control mesh and treatment of geometric constraints. Procedures for creating a control mesh are as follows: 1) determine the optimal orientation of the model, 2) project the model along three axes and extract contours, 3) create 2D control polygons for the contours, and 4) construct the 3D control mesh from the 2D control polygons. Geometric constraints are imposed on the edges and faces of a control mesh. Types of constraints are given by either a relative relationship between elements or an absolute displacement. A new control mesh is calculated by solving these constraints and the original model is modified accordingly. We tested our algorithms for two freeform models.     

A quadrilateral mesh generating method using mean value interpolation

Although commonly used for meshing, sub-mapping method is frequently bothered by its unstable region segmentation process. Although region segmentation can be avoided with the help of recognized models, the existing algorithms of obtaining recognized models are still flawed. In order to obtain accurate recognized models and high meshing quality, a quadrilateral mesh generation method is proposed on basis of mean value interpolation. Firstly, computational coordinates of inner loop vertices are determined by mean value interpolation according to regularization result of outer loop. Secondly, under the barycenter superposition principle, surface’s recognized model is obtained by use of regularization result of inner loops. Finally, facial mesh is generated via solving equations. Experiments are carried out to testify feasibility, advantage and stability of the proposed method. The results manifest that the proposed method is able to guarantee meshing quality and is applicable for quadrilateral mesh generation of multi-loop surfaces.     

基于动网格的齿轮箱内部流场数值模拟

基于不可压缩流体控制方程和RNGk-ε湍流模型,建立齿轮箱油浴润滑的三维流体模型。借助流体计算软件Fluent,应用动网格及UDF技术对齿轮箱油浴润滑的内部流场进行动态数值模拟,研究齿轮箱内瞬时油液分布以及油压、流速变化规律。计算表明：运用动网格技术能较好的模拟齿轮箱内部两相流场中油液分布及压力和速度的动态变化。     

高效率的三角网格模型保特征简化方法

部分三角网格模型因数据量庞大而导致其不便于存储、分析和显示,本文提出了一种结合网格精细化方法的三角形折叠网格简化算法以解决此问题。首先通过3~(1/2)网格细分法确定待折叠三角形三个顶点的修正坐标,并根据修正坐标初步确定折叠点位置,然后引入折叠点的拉普拉斯坐标和原三角形法向信息来更新折叠点位置,最后由三角形折叠后该区域的体积误差和被折叠三角形的平展度共同确定折叠代价,从而使网格优先从较为平坦和特征点较少的区域开始依次进行三角形折叠简化。对多个模型进行了实验测试和数据分析,结果表明该方法能够有效精简网格数据,与3个不同类型的简化方法相比,该方法的简化效率最高,而且能有效保持原网格模型的几何特征并控制简化三角形的质量。     

热传递法无创测量血液流速

介绍了一种利用人体皮肤和接触导体的热传递来无创测量局部皮肤组织血液流速的方法.该方法使用热量作为指示剂,利用血液是人体体内主要热传递媒介的特性,通过测量人体皮肤组织表面温度和接触导体的温度变化曲线,对获得的金属导体温度曲线进行归一化并求平均得到表征血液流速的数值.实验结果表明,该数值与血液流速具有很好的相关性,该装置实现了对人体皮肤组织的血液流速的快速测量,而且结构简单、方便实用.     

Two-dimensional adaptive mesh generation algorithm and its application with higher-order compressible flow solver

A combined procedure for two-dimensional Delaunay mesh generation algorithm and an adaptive remeshing technique with higher-order compressible flow solver is presented. A pseudo-code procedure is described for the adaptive remeshing technique. The flux-difference splitting scheme with a modified multidimensional dissipation for high-speed compressible flow analysis on unstructured meshes is proposed. The scheme eliminates nonphysical flow solutions such as the spurious bump of the carbuncle phenomenon observed from the bow shock of the flow over a blunt body and the oscillation in the odd-even grid perturbation in a straight duct for the Quirk’s odd-even decoupling test. The proposed scheme is further extended to achieve higher-order spatial and temporal solution accuracy. The performance of the combined procedure is evaluated on unstructured triangular meshes by solving several steady-state and transient high-speed compressible flow problems.     

An improved mesh simplification method using additional attributes with optimal positioning

The use of highly detailed models is continuously increasing in computer-aided design (CAD) design and computer graphics field as the technology of range scanners advances. Real-time rendering and manipulating applications are also increasing to support applications in various areas such as collaborative design and scientific visualization. Although graphics hardware technology has been improved rapidly, more attributes such as color, material property, texture coordinate, and curvature are added to CAD models, and it becomes a challenge to handle and render such heavy models. Consequently, the models with complex mesh need to be approximated to improve the efficiency of rendering and manipulation and to reduce computation time. A considerable amount of work has been done regarding geometry preservation, but relatively little research has been performed to preserve both geometry and additional attributes. We present a feature sensitive simplification method using curvature color as an additional attribute. We also use curvature color filtering and optimal positioning methods after edge collapse to preserve feature more sensitively. Our method is applied to several models, and the performance is demonstrated by comparing it with other methods.     

基于结构光辅助的网格候选点三维测量方法

光学三维测量技术是计算机视觉领域中最为活跃的研究主题之一.针对双目立体视觉三维测量方法中无纹理物体表面测量误差较大的问题,提出一种基于结构光投影辅助的网格候选点三维测量方法.设计灰度单调变化的锯齿波图案投射在被测场景中,有助于使三维网格候选点投影像点间的灰度差异最大化,依此提高系统的测量精度,实现了主动测量方法和被动测量方法的有效结合.通过3DS MAX和MATLAB软件平台下的仿真实验,验证了结构光辅助的网格候选点测量方法在计算精度上具有明显优势,且不会增加系统的复杂度,扩展了网格候选点三维测量方法的适用范围.     

一种简单高效的有限元网格优化算法及应用

针对三维有限元实体模型中网格形状优化的问题,提出了一种新的网格优化算法,并编制了基于这种算法的网格优化程序。该算法的优点是计算简单、节省机时,且网格优化效率较高,性能较为可靠。     

权重系数自适应光流法运动目标检测

为了实现Horn-Schunck光流法权重系数的自适应设定与更新,研究了权重系数对Horn-Schunck光流法的影响规律,提出一种融合模糊C均值(FCM)聚类的权重系数自适应Horn-Schunck光流法。首先,统计不同权重系数下运动目标检测的光流总值变化曲线。然后,以光流总值的最优化为依据,结合两层模糊C均值(FCM)聚类寻找最优权重和基于固定迭代次数Horn-Schunck光流法的收敛点,从而自适应地获取最优权重系数,并将收敛阈值的人工设定转化为光流值的自动寻优。最后,通过标准视频序列进行测试以验证算法的有效性。实验结果表明:相比于其他权重系数值,最优权重估计的光流图像不但运动目标明显而且噪声较少。对运动目标检测的运行时间为0.106 0s,有用比为0.596 9,幅度误差为0.801 1,满足光流法运动目标检测的最优或次优性能。     

一种PLC简单流量控制的方法

介绍一种用PLC（可编程控制器）控制流量的简单方法,该方法用简单器件完成流量控制,特别适用于对流速要求不太高,而对总量具有一定精度要求的工艺过程。