基于STL的三维网格剖分研究

在对铸件的充型与凝固过程进行数值模拟解析时,为了对连续的计算域进行数值计算,首先必须对计算域进行离散化处理,即网格剖分处理.在对STL文件作出介绍后,重点阐述三维网格剖分的原理,接着分析了剖分中需注意的几个问题,最后总结出了网格剖分程序流程.     

An Effective Error-Tolerance Slicing Algorithm for STL Files

Although the STL (stereo lithography) file format is the de facto standard for the rapid prototyping industries, there are always some defects in STL files, many of which are difficult to correct. Instead of correcting the defects of bad STL files by a manual, interactive and complex approach with an STL file correction program, an error-tolerance slicing algorithm for STL files is proposed in this paper. With the detailed analysis of complex defects such as cracks and non-manifold facets, a complete topological structure for the facets model with defects is built and the layer is sliced effectively. The badly sliced contour is processed by crack-tracking and non-manifold facet travelling methods to obtain a correct contour in a relatively easy 2D way.     

增材制造中STL模型的自适应分层算法研究

增材制造技术是一种先进的智能加工技术,并且通过其制造原理"分层—叠加"来加工实体。为了满足增材制造成型实体阶梯误差的要求,提出一种基于STL三角形网格法向量的自适应分层算法。首先根据三维实体成型后出现正、负偏差原理,得到统一正偏差截面轮廓的选择方法;其次以阶梯效应为依据,根据三角形网格法向量以及所允许的阶梯高度,确定自适应分层的分层厚度;最后对该算法进行实例验证。结果表明该算法符合自适应分层的要求,可有效减少阶梯效应并使得后处理工序更为方便。     

STL File Generation with Data Reduction by the Delaunay Triangulation Method in Reverse Engineering

Reverse engineering has been widely used for the shape reconstruction of an object without CAD data and typical steps include the scanning of a clay or wood model and the generation of manufacturing data such as an STL file. A new approach to remove point data with Delaunay triangulation is introduced to deal with the size problems of the STL file and the difficulties in the operation of the rapid prototyping (RP) process. The selection of a group of triangles, based on the angle, is used for a robust and reliable implementation of the Delaunay triangulation method. The developed software enables the user to specify the criteria for the selection of the group of triangles by the angle between triangles, the percentage of reduced triangles, and the allowable area. This approach can be used to reduce the measuring data from the laser scanner, thus save the handling time of point data during the modelling process and is useful for verifying and slicing the STL model during the RP process.     

基于Magics的激光快速成型三维CAD模型数据处理

Magics软件是快速成型行业中数据处理的通用软件.本文介绍了激光快速成型中基于Magics的三维CAD模型的数据处理技术,包括STL文件修复、产品的位置放置和支撑生成等.从而快速地获得精确的制造数据,并快速制得所需原型.     

Development of a Stereolithography File Interface with ArtCAM™

This paper presents the technique used for converting a 3D ArtCAM™ relief file into the stereolithography (STL) format. This 3D file is obtained from a 2D picture using a 3D CNC engraving software called ArtCAM™. The problem is to convert the 3D relief files into an STL format without compromising the accuracy and details of therelief. This paper discusses the size of the files which have been converted, and steps taken to reduce the file size by reducing the number of triangles or facets in the STL file. The discussion involves the verification of the converted model by comparing it with the original relief. The problems associated with the reduction of triangles when the file has been converted to STL format are also discussed.     

快速成形中STL格式文件的分割及其连续成形

为了避免巨型ＳＴＬ格式文件的读入错误和手工粘接带来的误差,研究了沿垂直于Ｚ向将巨型ＳＴＬ格式文件分割成多个ＳＴＬ格式文件,连续依次成形的方法,提出了分割面切割的轮廓环分解为三角形的算法。     

基于夹层板理论的圆形孔蜂窝结构隔声量研究

蜂窝夹层结构广泛应用于航空航天、船舶、高速列车等交通工具领域。基于三明治等效理论建立了圆形蜂窝结构层芯的等效剪切参数,从而得到简支边界条件下的圆形孔蜂窝夹层板的声振耦合振动模型及传声损失,并在仿真中数值验证了理论模型的正确性。同时基于理论计算,分析了圆形孔蜂窝结构中的层芯胞元半径、层芯壁厚和结构材料对隔声量的影响。由分析可知:层芯半径小、壁厚薄的钢材圆形蜂窝结构具有更好的隔声性能。     

Introspective Sorting and Selection Algorithms

Quicksort is the preferred in-place sorting algorithm in many contexts, since its average computing time on uniformly distributed inputs is Θ(N log N), and it is in fact faster than most other sorting algorithms on most inputs. Its drawback is that its worst-case time bound is Θ(N²). Previous attempts to protect against the worst case by improving the way quicksort chooses pivot elements for partitioning have increased the average computing time too much – one might as well use heapsort, which has a Θ(N log N) worst-case time bound, but is on the average 2–5 times slower than quicksort. A similar dilemma exists with selection algorithms (for finding the i-th largest element) based on partitioning. This paper describes a simple solution to this dilemma: limit the depth of partitioning, and for subproblems that exceed the limit switch to another algorithm with a better worst-case bound. Using heapsort as the ‘stopper’ yields a sorting algorithm that is just as fast as quicksort in the average case, but also has an Θ(N log N) worst case time bound. For selection, a hybrid of Hoare's FIND algorithm, which is linear on average but quadratic in the worst case, and the Blum–Floyd–Pratt–Rivest–Tarjan algorithm is as fast as Hoare's algorithm in practice, yet has a linear worst-case time bound. Also discussed are issues of implementing the new algorithms as generic algorithms, and accurately measuring their performance in the framework of the C+:+ Standard Template Library. ©1997 by John Wiley & Sons, Ltd.     

一种基于ARIMA模型与3 σ准则的取水异常检测方法

为提高取水预测数据的准确性,针对现有部分取水数据异常且难以进行人工判别的问题,提出一种基于ARIMA模型与3σ 准则的取水异常检测方法.分析每个取水点每年的日取水量的时间序列数据,使用时间序列的ARIMA模型和高斯分布的3σ 准则判断日取水量是否为异常值;通过时间序列分解算法分析异常值附近取水点的趋势,判断异常值附近是...