A modified cross-correlation algorithm for PIV image processing of particle-fluid two-phase flow

PIV (Particle Image Velocimetry) technique for flow field measurement has achieved popular self-identify through over ten years development, and its application range is becoming wider and wider. PIV post-processing techniques have a great influence on the success of particle-fluid two-phase flow field measurement and thus become a hot and difficult topic. In the present study, a Phase Respective Identification Algorithm (PRIA) is introduced to separate low-density solid particles or bubbles and high-density tracer particles from the PIV image of particle-fluid two-phase flow. PTV (Particle Tracking Velocimetry) technique is employed to calculate the velocity fields of low-density solid particles or bubbles. For the velocity fields of high-density solid particles or bubble phase and continuous phase traced by high-density smaller particles, based on the thought of wavelet transform and multi-resolution analysis and the theory of cross-correlation of image, a delaminated processing algorithm (MCCWM) is presented to conquer the limitation of conventional Fourier transform. The algorithm is firstly testified on synthetic two-phase flows, such as uniform steady flow, shearing flow and rotating flow, and the computational results from the simulated particle images are in reasonable agreement with the given simulated data. The algorithm is then applied to images of actual bubble-liquid two-phase flow and jet flow, and the results also confirmed that the algorithm proposed in the present study has good performance and reliability for post-processing PIV images of particle-fluid two-phase flow.     

一种改进的公式结构分析方法

结构分析是印刷体数学公式识别系统的关键部分,目前相关研究还很欠缺.针对结构分析的基准线方法的一些不足之处,提出一种逆向匹配方法,并结合语义规则对分析后的数学公式进行后处理.实验表明,提出的方法能够有效提高数学公式结构分析的正确率和鲁棒性.     

有限元数据场可视化的扫描母元法

介绍一种画等参单元云图及等值线的新方法,称为扫描母元法.采用自然坐标系中母元被划分为足够小的三角形子域,然后用一条水平线,依次扫描母元中子域的顶点,利用顶点的自然坐标以及等参单元的形函数计算实际坐标及场量.利用实际坐标找到像索,利用场量求出颜色,把像素设置为求出的颜色.扫描母元法适用于画二维单元及三维单元表面或剖面上的云图和等值线,由于没有对高阶场量进行线性化等近似计算,所以,保持了高阶单元的精度.实践表明,方法精度高,速度快.易于实现.     

双向特征融合的快速精确任意形状文本检测

现有的基于分割的场景文本检测方法仍较难区分相邻文本区域,同时网络得到分割图后后处理阶段步骤复杂导致模型检测效率较低.为了解决此问题,该文提出一种新颖的基于全卷积网络的场景文本检测模型.首先,该文构造特征提取器对输入图像提取多尺度特征图.其次,使用双向特征融合模块融合两个平行分支特征的语义信息并促进两个分支共同优化.之后,该文通过并行地预测缩小的文本区域图和完整的文本区域图来有效地区分相邻文本.其中前者可以保证不同的文本实例之间具有区分性,而后者能有效地指导网络优化.最后,为了提升文本检测的速度,该文提出一个快速且有效的后处理算法来生成文本边界框.实验结果表明:在相关数据集上,该文所提出的方法均实现了最好的效果,且比目前最好的方法在F-measure指标上最多提升了1.0％,并且可以实现将近实时的速度,充分证明了该方法的有效性和高效性.     

Web-based post-processing visualization system for finite element analysis

In this paper, we propose and implement a website of post-processing system for finite element analysis (WebDFEA). Finite element analysis is a computer-aided engineering tool and is popular for static/dynamic structure analysis. It includes three processing systems where post-processing system is to graphically demonstrate the analysis result of a structure model analyzed by finite element method. WebDFEA performs as a website. It is cross-platform because it can auto-detect a client computer platform and auto-download proper OpenGL API for drawing computer graphics. It can draw precise graphics on webpage which can be free controlled by the mouse as a manner in professional software. A database server is involved to store finite element model data and its analysis result. The graphic user interface (GUI) of WebDFEA is a flexible GUI comprising three parts: the switch buttons designed by HTML, the display board and the color bar both developed in Java. The three components are independent and cooperative with each other. They can be recombined without running errors for different purposes. A ship hull section with half a hatch is chosen as the study case to test WebDFEA website. Its finite element model comprises 11,442 triangle elements (shapes). The timeframe starting when WebDFEA is connected to the end when the model is demonstrated is acceptable.     

一种基于局部结构信息的指纹伪特征滤除算法

自动指纹识别系统中，灰度指纹图象经过预处理过程得到细化二值图象，其中往往含有大量的伪特征，这将对后续的分类、匹配等操作造成不良影响，导致系统识别率下降，为此首先提出一种新的快速纹线跟踪算法——8邻域编码纹线跟踪算法，然后提出一种基于局部结构信息的指纹伪特征滤除算法，该伪特征滤除算法是在纹线跟踪的基础上，提取指纹特征点的若干属性，并结合特征点的局部结构信息，对各种伪特征结构进行识别和滤除，实验结果表明，本方法可以快速、准确、彻底地滤除这些伪特征结构，效果令人满意。     

一个基于综合匹配的汉字识别后处理系统

本文实现了一个基于综合匹配法的汉字识别后处理系统，该方法既利用了帝级识别结果的信息，又利用了汉语中字的上下文制约关系，即组字成词的信息，同时用了词的使用频度。     

脱机手写体汉字识别研究综述

脱机手写体汉字识别是汉字识别领域中最难的课题。该文对目前脱机手写体汉字识别在预处理、特征提取、分类识别及后处理四个阶段主要采用的方法做了简要介绍,阐述了各种方法的优缺点,并提出了一种将支持向量机有效地用于解决多分类问题的策略。最后根据目前的研究状况,指出今后研究中需要注意的问题和研究的发展方向。     

A modified optical flow algorithm based on bilateral-filter and multi-resolution analysis for PIV image processing

Particle Image Velocimetry (PIV) technology is an efficient and powerful testing method to investigate the characteristics of flow field. The topic of PIV post-processing techniques has roused researchers׳ wide concern for its great influence on the success of flow field measurement. The traditional correlation algorithms have their innate defects. In the present study, a modified optical flow algorithm is proposed to overcome these deficiencies based on bilateral-filter and multi-resolution analysis of PIV image processing. The algorithm is designed based on the principle of multilayer segments, in which the isotropic diffusion method is employed to calculate the low-resolution layer of the image and the nonlinear filtering method is used to process the high-resolution layer. This new algorithm can reduce image noise effectively and maintain the details of the image boundary. In addition, the design of nonlinear filter makes the optical flow equation simpler, and the optimal velocity mapping factor method needs less iteration and reduces the computational load. The algorithm is first tested on synthetic time-resolved channel flow images, and the computational results from the simulated particle images are found to be in reasonable agreement with the given simulated data. The algorithm is then applied to images of actual up-channel flow, and the results also confirmed that the algorithm proposed in the present study has good performance and reliability for post-processing PIV images.     

A local extrapolation method for finite elements

In most numerical analyses using the Finite Element Method, several quantities, such as stresses, strains, fluid velocities and gradients, are computed at points in the interior of the solid elements, such as Gauss integration points for instance. Nevertheless, in many applications it is necessary to extrapolate these values to nodal points. That is the case with most visualization tools and post-processors, also in programs with auto-adaptive meshes, large deformations schemes such as Arbitrary Lagrangian–Eulerian Methods, and in programs using the Dynamic Programming Method. A generic methodology to perform this extrapolation in a precise and efficient way is proposed.