基于STL文件的实体分割算法研究

由于快速成型机加工尺寸的限制,难于制造尺寸较大的零件。针对这一问题本文提出一种基于STL文件格 式的实体分割算法,对STL文件分割过程中的关键问题进行了详细地论述,包括:截面轮廓的生成,截交三角面片的 处理和截面轮廓的三角化算法;通过对STL文件的分割处理,提高了快速成型系统对大尺寸零件的制造能力。     

Investigation on a new type of low-stress cropping system with variable frequency vibration

This paper presents a new type of precision cropping system with variable frequency vibration by which the high-quality cutting surface can be obtained. On the basis of D’Alembert’s principle, the approximate relationship between the exciting force and the excited frequency in the cropping is acquired through computation. Five types of excited frequency control curves are designed and applied in the cropping experiments and the influences of these control curves on the cropping cross-section and the cropping time are investigated by experiment in details. According to the special feature of the cross-section obtained in the course of variable frequency vibration cropping, a new measurement method is proposed and applied to assess the quality of the cross-section. The theoretic and experimental results show that the exciting force acted on the bar in the vertical direction is larger than that in the horizontal direction and the linear decrease control curve, by which the high quality cross-section is obtained and the cropping time is reduced, is an ideal control mode compared with other control modes mentioned in the paper. The experiment also proves that the width of the bar instantaneous fracture region is decreased by reducing the value of every step frequency change, and the cropping time is also shortened by reducing the durative time of every step variable frequency under the action of the linear decrease frequency curve.     

Vegetable tannin composition and its association with the leather tanning effect

Abstract

The increasing environmentally friendly approach of using renewable materials has led to vegetable tannins having an important role as tanning agents in the leather industry. Tannins are complex phenolic structures, and the literature shows that a considerable amount of chemical parameters measured through analytical techniques can be associated with their tanning ability. In the present study, five types of vegetable tannins highly used in the tanning industry were chosen for the evaluation of some of their relevant chemical parameters and the correlation with their cross-sectional penetration in the hide. Black wattle (Acacia mearnsii), quebracho (Schinopsis lorentzii), chestnut (Castanea sativa), tara (Caesalpinia spinosa), and myrobalan (Terminalia chebula) were tested. The chemical properties of the total tannin polyphenols, non-tannin polyphenols, insoluble solids, soluble solids, total solids, total phenols, non-tannin polyphenols:total phenols ratio, and residual tanning float concentration were measured and associated with the leather cross-sectional penetration results. The statistical Mann–Whitney-U test showed that the insoluble solids, non-tannin polyphenols, soluble solids, and total tannin polyphenol percentages distinguished the groups of tannins that crossed the hide from those that did not well. Hence, since the analysis of insoluble solids is the simplest and the most direct among them, it would be recommended to use this parameter to define a cutoff to distinguish the performance of tannins for leather application.     

Y/Δ降压启动供电动机导线截面的选择

对于绕组具有六个出线端子,且为Δ形接法的鼠笼电动机,当采用Y/Δ方式降压启动时,其六根供电动机导线截面应按电动机线电流的1/!3值为依据来选取,而不应以该电动机的线电流值为依据来选取。     

武汉市内河航道断面测量

简述了武汉市内河航道断面测量坐标系统、断面基点、断面点和断面选择的要求;断面点和水工建(构)筑物、河道沿岸重要地物、地貌的施测方法;纵、横断面图的绘制要点.     

Transport model based on three-dimensional cross-section generation for TRIGA core analysis

Three-dimensional (3-D) transport model for the Pennsylvania State University Breazeale Reactor (PSBR) core analysis has been developed based on the discrete ordinates (S_n) method. The effective fine- and broad-group structures for the TRIGA cross-section libraries were selected based on CPXSD (Contributon and Point-wise Cross-Section Driven) methodology. The study shows results of the following effective broad-group energy structures – a 12-group structure in 2-D geometry vs. a 26-group structure in 3-D geometry. Different 3-D pin/core configurations were used to verify and validate the selected effective group structures. The results agree with continuous energy cross-section Monte Carlo calculations for eigenvalues and normalized pin-power distributions, which are used as a reference in this research.     

变截面三维编织技术的研究进展

为深入了解变截面三维编织技术的研究进展情况,阐述了变截面三维编织原理,介绍了当前实现变截面三维编织成型的关键技术和研究现状,分析了现有变截面三维编织技术存在自动化程度不高、普适性不佳、工序复杂和纱线不均匀等问题,提出利用塑性金属选择性地添加纱线设计携纱器的思路。认为:变截面三维编织技术的优劣,需通过反复检验三维预制件的力学性能是否满足要求来评判。     

Cosmic ray physics with the ARGO-YBJ experiment

Cosmic ray physics in the 10¹²–10¹⁵ eV primary energy range is among the main scientific goals of the ARGO-YBJ experiment. The detector, located at the Cosmic Ray Observatory of Yangbajing (Tibet, P.R. China) at 4300 m a.s.l., is a full coverage Extensive Air Shower array consisting of a carpet of Resistive Plate Chambers of about 6000 m². The apparatus layout, performance and location offer a unique possibility to make a deep study of several characteristics of the hadronic component of the cosmic ray flux in an energy window marked by the transition from direct to indirect measurements. In this work we will focus on the experimental results concerning the measurements of the primary cosmic ray energy spectrum and of the proton-air cross-section. The all-particle spectrum has been measured, by using a bayesian unfolding technique, in the 1–100 TeV energy region. The proton-air cross-section has been measured at the same energies, by exploiting the cosmic ray flux attenuation for different atmospheric depths (i.e. zenith angles). The total proton–proton cross-section has then been estimated at center of mass energies between 70 and 500 GeV, where no accelerator data are currently available.     

三维正交机织物组织结构的几何表征和数学表征

切取三维正交机织物沿经向和纬向的连续横截面,在三维视频显微镜下拍摄和分析织物横截面中经纱、纬纱和Z纱的横截面形态、纱线空间构型,用参数方程表征理想状态下织物中经纱、纬纱和Z纱截面尺寸及屈曲形态。基于三维绘图软件Pro/E,重构三维正交机织物单胞模型及大尺寸织物模型,使其能更准确、更真实地反映三维正交机织物真实细观结构。     

不锈钢椭圆中空受压构件的结构响应

冷加工不锈钢椭圆中空截面结合了圆形中空截面和不锈钢的美感以及不同几何形状的横截面相对于两个主轴的结构功效。迄今为止,对这种横截面的构件尚没有结构设计指南,主要是产品相对较新,缺乏基础结构试验数据。对冷加工不锈钢椭圆空心截面受压构件的结构响应进行研究,提出设计建议。为获得结构性能的基础数据,进行一系列试验。首先,通过张拉试验建立基本的材料应力-应变关系。随后,通过短柱试验确定横截面的平均受压响应,通过弯曲试验获得极限承载力以确定不锈钢椭圆中空截面合理的弯曲曲线。对试件进行包括初始缺陷的几何性质测定。对试件的荷载位移响应进行记录并在文中给予介绍。与试验同步,进行了有限元模拟。如果有限元模拟的结果与试验结果不相符,将对个别关键参数进行进一步的研究,包括外形比例、横截面长细比和构件长细比。基于试验与数值分析结果,提出3组不锈钢椭圆中空截面受压限值以及椭圆中空截面柱合理弯曲曲线。