Three‐dimensional numerical simulation of coalescence and interactions of multiple horizontal bubbles rising in shear‐thinning fluids

The dynamics of multiple horizontal bubbles rising from different orifice arrangements in shear‐thinning fluids was simulated numerically by three‐dimensional Volume of Fluid method. The effects of bubble size, rheological properties of shear‐thinning fluids, and orifice structure arrangements on multiple bubbles interaction and coalescence were analyzed, and the mechanisms of bubble coalescence and breakup were fully discussed and elucidated. The variation of bubble rising velocity during coalescence process and freely rising processes for different orifice arrangements was also deeply investigated. The critical initial horizontal intervals for coalescence of multiple horizontal bubbles with various orifice arrangements were attained by simulation, which could serve as the critical criterion of bubble coalescence or noncoalescence. Furthermore, the critical bubble interval was predicted based on the film drainage model, the prediction accords well with the simulation result and is quite conducive for the design and optimization of perforated gas–liquid contact equipment. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3528–3546, 2015     

基于Sobel的多方向算子模板边缘检测算法

针对传统Sobel算子存在的边缘检测方向性不强及提取边缘较粗等问题,提出了一种改进的多方向算子模板的边缘检测算法。算法增加了22.5°,45°,67.5°,112.5°,135°和157.5°六个方向算子模板,能够较好地检测出图像不同的方向边缘。模板权值根据中心像素点到邻域像素的距离及方向夹角的大小进行设定,充分考虑到了邻域内像素对中心点方向梯度的贡献大小;算法对梯度图像采用了改进的非极大值抑制方法进行细化,得到了较细的图像边缘。实验结果表明,与传统Sobel算法相比,该算法提取的边缘图像具有边缘方向性强且边缘较细的优点,具有较高的应用价值。     

Characterization of extensional rheological filament stretching with a dual‐mode Giesekus model

A new, simple, formulation that describes capillary thinning as predicted by a two‐mode Giesekus model is derived, and its application in analyzing data from extensional rheometry (capillary thinning) experiments is discussed. An algorithm is presented that can be used to fit the expressions obtained from the Giesekus model to extensional rheometry data. Examples of data fitting are given for an idealized data set, for measurements obtained for aqueous solutions of 6 wt % 900,000 molecular weight polyethylene oxide, and for biological fluids obtained from pitchers of Nepenthes Rafflesiana. Good fits to the data were obtained, with coefficients of determination in excess of 0.98. For each data set, it was possible to calculate values of extensional viscosity and relaxation time for each of the two modes, allowing quantitative comparison of different fluids or of the same fluid as it ages. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2188–2199, 2016     

新型磁流变刹车装置设计与性能研究

设计了一种兼顾盘式与筒式结构优点的新型磁流变刹车装置,采用Maxwell软件结合田口算法思想对结构进行仿真优化。搭建实验测试平台,测试了磁流变液刹车装置的静态以及动态性能,验证了所设计的结构是有效的,实验结果达到预期目标,建立了制动力矩与输入电流的关系式,修正了τ-H经验公式,修正后的理论计算值与测量值基本一致,验证了磁流变液在高速剪切情况下存在剪切变稀的现象。     

EFFICIENT METHOD OF MOMENTS ESTIMATORS FOR INTEGER TIME SERIES MODELS

The parameters of integer autoregressive models with Poisson, or negative binomial innovations can be estimated by maximum likelihood where the prediction error decomposition, together with convolution methods, is used to write down the likelihood function. When a moving average component is introduced this is not the case. To address this problem an efficient method of moment estimator is proposed where the estimated standard errors for the parameters are obtained using subsampling methods. The small sample properties of the estimator are investigated using Monte Carlo methods, while the approach is demonstrated using two well‐known examples from the time series literature.     

Microstructure analyses and volume fraction model of 3D 6-directional variable cross-sectional cone-shaped tubular braided fabric

The three-dimensional 6-directional variable cross-sectional cone-shaped tubular braided fabric (6DCTBF) has been applied successfully as the components in aerospace craft. The application of cone-shaped tubular braided fabric requires the densification of a small end to ensure ablation uniformity during composite fabrication. In this paper, in order to meet the size and performance requirements for 6DCTBF, a unique yarn-thinning technique used in the braiding process has developed and explained in detail by first analyzing the fiber bundle movement and distribution in modeling. After the yarn has been thinned, different zones are divided according to the constituting method of the yarn in its unit cell. Geometric models are built for different zones to determine the geometrical dimensions and volume fraction variation range. It has been shown that the theoretical model can accurately describe the 6DCTBF and provide a theoretical basis for the design of its structure and properties.     

改进的细化算法在印刷文字检测中的技术研究

针对印刷文字缺陷检测难等问题，本文提出了一种改进的图像细化算法用于文字检测。首先根据投影法分割字符，进一步对分割的字符图像逐步细化得到文字的骨架，然后根据文字骨架的信息完成检测；     

Overview and Lessons from More Than a Decade of Feeder Life Management

This paper provides an overview of the degradation in CANDU~a （Canadian Deuterium Uranium） feeders in operating plants observed from the mid 1990s onward. The degradation has been dominated by feeder wall thinning, caused by FAC （flow accelerated corrosion） and feeder cracking. This paper summarizes the industry＇s response to the discovery of these two degradation mechanisms and the methodologies, tools and technologies developed to monitor the degradation and assess the continued fitness for service to manage the plant life. This paper identifies some of the lessons gained from more than a decade of industry effort, and discusses how these lessons are being implemented in the refurbished and new CANDU plants. CANDU~a is a registered trademark of Atomic Energy of Canada Limited.     

A simple scaling derivation of the shear thinning power-law exponent in entangled polymer melts

By suggesting that the polymer dynamics in entangled polymer melts possesses the property of dynamical self-similarity, we argue that the power-law exponent of the Carreau-Yasuda law, which empirically describes the shear thinning effect of the polymer melt viscosity, is inversely proportional to the exponent of the molecular mass dependence of the terminal relaxation time. This finding is obtained in cases where the shear rate dependence of the segmental relaxation time is negligible. If such dependence is essential, the Carreau-Yasuda law is slightly modified at high shear rates: instead of a power-law dependence with a small shear rate independent exponent, a weaker logarithmic dependence is found both for shear rate and molecular mass dependence, which resembles the approach to zero of an effective shear rate and molecular mass dependent power-law exponents at sufficiently high shear rates.     

基于退化HMM的印刷体文字识别研究

提出一种新的基于退化隐马尔柯夫模型的印刷体文字识别方法.此方法按照一定规则提取文字的一维笔段序列特征,然后将该特征输入到设计好的分类器中进行分类.在分类器的设计上摒弃传统的左右型结构模型,采用了遍历型结构模型.实验证明此方法能够更好地完成文字分类任务,识别率可以达到99%以上.