定常吸气改善叶型气动性能的数值研究

提高叶型升力,扩大其稳定工作范围一直是叶轮机械领域关心的问题。本文针对采用定常吸气方法减缓低马赫数流动分离,改善叶型气动特性的问题,在NACA0015叶型上进行了多种工况的数值模拟。结果表明:在叶型头部吸力面分离点附近施加定常吸气,可以提高叶型升力,降低阻力,推迟失速2°左右。存在着最佳的定常吸气动量范围和吸气位置,使得其改善叶型性能的效果最大。文中还给出了定常吸气动量和施加位置等参数对叶型气动性能的一些影响规律。     

应用分离涡模型计算斜圆柱孔气膜冷却

分离涡模型(DES,Detached eddy simulation)兼有雷诺时均湍流模型计算量较小和大涡模拟计算精度高的优点。本文利用DES对平板单斜圆柱孔的气膜冷却进行了数值模拟,并将结果同RANS湍流模型的计算结果以及实验数据相比较,表明DES能有效弥补RANS湍流模型在计算三维不均匀非定常湍流场的不足,更接近实际地反映了气膜冷却中的流动和换热的本质规律。     

器件效应数值模拟中漂移扩散模型的误差分析

为了确定数值模拟过程中的误差来源,并针对误差来源改进软件,减小计算误差,对半导体器件数值模拟中的采用的漂移扩散模型进行了研究。结合自主开发的半导体器件效应软件GSRES,分析了软件中漂移扩散模型的理论近似,对计算模型中由于温度分布、载流子复合/产生率、载流子迁移率等项采取近似而导致的误差进行了分析。根据误差分析和数值模拟算例,认为误差主要来自于器件内部温度场分布和迁移率模型的近似,给出了软件的适用范围。结合半导体器件的研究热点和发展趋势,对该模型中需要进行改进的近似项进行了分析。     

物理学史显化科学方法教育的可行性研究——以伽利略斜面实验为例

通过教育实验和有效的数据分析,以研究物理学史在科学方法教育中的作用,探究显化科学方法教育的有效途径.     

旋转体系中湍流的LBM模拟

采用基于多松弛时间因子的格子Boltzmann方法对旋转体系中的湍流进行数值研究,考察Rossby数和Ekman数对湍流的影响,包括湍流能量及其耗散率、速度、涡结构及湍流的耗散尺度即Kolmorogov尺度和积分尺度等.研究表明,系统的旋转延缓了湍流能量的衰减速率,逐步破坏初始涡结构的均匀性,与旋转方向相反的涡逐步被抑制,并最终形成若干与旋转同向的涡柱.结果还表明,系统旋转越快,湍流的耗散尺度越小而积分尺度越大.     

A velocity-difference-separation model for car-following theory

We introduce a velocity-difference-separation model that modifies the previous models in the literature. The improvement of this new model over the previous ones lies in that it not only theoretically retains many strong points of the previous ones, but also performs more realistically than others in the dynamical evolution of congestion. Furthermore, the proposed model is investigated with analytic and numerical methods, with the finding that it can demonstrate some complex physical features observed in real traffic such as the existence of three phases: free flow, synchronized flow, and wide moving jam; sudden flow drop in flow-density plane; and traffic hysteresis in transition between the free and the synchronized flow.     

基于模拟退火算法的递归自动阈值分割方法

针对目标图像灰度对比度差的现象,以及对目标对象检测实时性的要求,并考虑到传统的Otsu分割方法在分割图像质量较差以及目标区域小时准确性差的缺点,提出了一种基于模拟退火算法的递归Otsu分割方法。在图像直方图呈双峰的情况下能够准确地找到分割阈值。在成像模糊、光照度较差的情况下此方法仍然可以获得较高的准确度。该方法在保证了检测质量的同时并没有导致运算时间的大幅度提升,有效地保证了处理的实时性。实际应用表明该方法切实可行。     

电控液晶光阀中的指向矢分布特性

液晶分子具有介电和光学各向异性,在外电场作用下,液晶指向矢将会重新分布,具有高效的光学相位调制能力.本文从实验和理论角度对电控液晶光阀的光学调制特性进行了研究,结果表明:光阀阈值电压约为4V,且当外加电压高于阈值电压时,液晶光阀的透射强度随外加电压表现出非周期性特性.根据液晶连续体弹性理论,对电场作用下液晶光阀的指向矢分布特性进行数值分析,分析结果表明液晶光阀对透射光强的非周期调制特性取决于液晶体系的偏转状态,为研究液晶的偏振光调制特性提供理论依据及实验基础.     

Image reconstruction tomography with only a method for laminar optical single Monte-Carlo simulation

Laminar optical tomography （LOT） is a new mesoscopic functional optical imaging technique. Currently, the forward problem of LOT image reconstruction is generally solved on the basis of Monte-Carlo （MC） methods. However, considering the nonlinear nature of the image reconstruction in LOT with the increasing number of source positions, methods based on MC take too much computation time. This letter develops a fast image reconstruction algorithm based on perturbation MC （pMC） for reconstructing the absorption or scattering image of a slab medium, which is suitable for LOT or other functional optical tomography system with narrow source-detector separation and dense sampling. To calculate the pMC parameters, i.e., the path length passed by a photon and the collision numbers experienced in each voxel with only one baseline MC simulation, we propose a scheme named as the trajectory translation and target voxel regression （TT＆TVR） based on the reciprocity principle. To further speed up the image reconstruction procedure, the weighted average of the pMC parameters for all survival photons is adopted and the region of interest （ROI） is extracted from the raw data to save as the prior information of the image reconstruction. The method is applied to the absorption reconstruction of the layered inhomogeneous media. Results demonstrate that the reconstructing time is less than 20 s with the X - Y section of the sample subdivided into 50 × 50 voxels, and the target size quantitativeness ratio can be obtained in a satisfying accuracy in the source-detector separations of 0.4 and 1.25 mm, respectively.