基于面固化的快速微成型控制算法设计

针对基于面固化的快速成型技术应用于成型微小器件,设计了一整套的成型控制算法,包括CAD输出STL格式文件、VC环境下对其加载和显示算法,对STL模型的切片算法以及切片后截面轮廓的填充算法。分析了基于该控制算法,利用数字微反射镜器件(DMD)作为动态掩模板来实现面固化成型的制作方法的误差,并与传统的点固化成型法的制作误差进行了比较。结果表明,面固化成型法能够减小误差并提高成型速度,是一种有效的快速成型方法。     

Minimizing staircase errors in the orthogonal layered manufacturing system

The factors that generally affect the slicing error in layered manufacturing (LM) processes are first analyzed, and issues pertaining to the current methods to deal with the slicing error are discussed in this paper. A method based on a recently developed and implemented orthogonal LM system to reduce the overall slicing error is presented. In this method, the flat region is separated from the stereolithography (STL) model and different processing methods are applied to the different areas in the part geometry. In addition, the mathematical model for calculating the slicing error is derived and an approach based on a genetic algorithm has been developed to optimize the build orientation in terms of minimizing the slicing error. Case studies are given to demonstrate the effectiveness and efficiency of the method. Note to Practitioner-The staircase effect has been the major concern for industry to widely adopt rapid prototyping technologies. It will not only worsen the surface quality but also create errors on the parts built. This paper introduces a novel approach to minimizing staircase errors based on a multidirectional deposition approach. A mathematical method combined with a generic algorithm is used to minimize the slicing errors. From the case study given, the approach has been proven to be effective in minimizing staircase errors and thus improving the rapid prototyping (RP) built part quality.     

三维有限差分计算中大规模网格生成及显示技术

针对爆炸与冲击问题并行仿真计算软件PMMIC-3D（Parallel Multi-Material in Cell 3D）的计算网格为正交六面体网格的特点,开发与PMMIC-3D接口统一的可对任意复杂三维实体模型进行大规模有限差分网格生成的三维前处理软件MESH-3D.MESH-3D采用CSG和STL模型两种建模方式进行复杂实体建模,并采用基于边的整体切片算法,借鉴计算机图形学中的扫描线填充算法完成三维有限差分网格划分.在绘制网格时,删除网格单元的公共面,大大缩短计算时间和减少存储空间,实现对网格的快速消隐显示.MESH-3D可实现百亿量级网格单元的生成和显示.三维前处理软件MESH-3D的开发有力地支持爆炸与冲击问题的仿真计算.     

A novel black-box simulation model methodology for predicting performance and energy consumption in commodity storage devices

Traditional approaches for storage devices simulation have been based on detailed and analytic models. However, analytic models are difficult to obtain and detailed models require a high computational cost which may be not affordable for large scale simulations (e.g. detailed data center simulations). In current systems like large clusters, grids, or clouds, performance and energy studies are critical, and fast simulations take an important role on them.A different approach is the black-box statistical modeling, where the storage device, its interface, and the interconnection mechanisms are modeled as a single stochastic process, defining the request response time as a random variable with an unknown distribution. A random variate generator can be built and integrated into a bigger simulation model. This approach allows to generate a simulation model for both real and synthetic complex workloads.This article describes a novel methodology that aims to build fast simulation models for storage devices. Our method uses as starting point a workload and produces a random variate generator which can be easily integrated into large scale simulation models. A comparison between our variate generator and the widely known simulation tool DiskSim, shows that our variate generator is faster, and can be as accurate as DiskSim for both performance and energy consumption predictions.     

基于分层切片原理的三维雕刻算法

分析了多种基于STL模型的快速分层算法。在综合多种算法优点的基础上,首先提出了对三角面片的顶点按其切片方向进行从小到大排序,以快速滤除冗余顶点;并在此基础上建立三角面片的顶点链表及面向量,以实现STL模型的拓扑信息重构;最后基于所重构的拓扑信息,结合几何连续性分层算法实现高效的自适应分层算法。并通过C+〖KG-*3〗+实现了这一算法,证明了快速成型技术的分层制造思想可应用于三维雕刻的CAD/CAM,在技术上是可行的。     

Semi-Unstructured Grids

We present a novel automatic grid generator for the finite element discretization of partial differential equations in 3D. The grids constructed by this grid generator are composed of a pure tensor product grid in the interior of the domain and an unstructured grid which is only contained in boundary cells. The unstructured component consists of tetrahedra, each of which satisfies a maximal interior angle condition. By suitable constructing the boundary cells, the number of types of boundary subcells is reduced to 12 types. Since this grid generator constructs large structured grids in the interior and small unstructured grids near the boundary, the resulting semi-unstructured grids have similar properties as structured tensor product grids. Some appealing properties of this method are computational efficiency and natural construction of coarse grids for multilevel algorithms. Numerical results and an analysis of the discretization error are presented. Received July 17, 2000; revised October 27, 2000     

一种改进的STL文件快速分层算法

高效的STL模型切片算法是快速成型制造的前提和基础,在有向加权图切片算法的基础上提出了一种快速STL模型切片分层算法,去除了耗时的有向加权图建立,对切片后的数据进行后处理,除去数据中的冗余点,从而提供了一种快速的STL模型切片算法。大量实验及数据表明,新算法具有较高的效率。     

激光直接制造和再制造中的三维CAD模型直接分层技术

在分析SolidWorks软件平台下CAD模型数据的内部表达方法以及拓扑信息和几何信息提取方法的基础上,研究三维CAD模型直接分层技术.对SolidWorks进行二次开发,调用SolidWorks应用程序接口函数中的曲面一曲面求交函数对CAD模型曲面与分层平面求交,得到的交线首尾相连形成轮廓轨迹;同时研究了光栅填充扫描算法及程序实现.为实现切片数据的通用化,设计了记录切片数据的文件格式,用直线、圆弧或圆描述分层轮廓.对上述的直接分层不仅进行了软件模拟,还用于直接制造.制作的试件与STL间接分层试件比较结果表明,采用直接分层的试件的精度和表面质量优于STL间接分层.     

基于虚拟格网的建筑物点云轮廓线自动提取

在分析现有轮廓线提取方法不足的基础上，提出基于虚拟格网的建筑物轮廓线自动提取方法。该方法利用建筑物点云生成虚拟格网并进行二值填充；采用邻域分析方法进行边界格网的标记与追踪；为了避免边界追踪错误，设计了基于方向的单边缘格网抑制方法及基于距离的连接关系调整方法以改善提取结果质量；根据格网追踪结果，从原始建筑物点云中提取真实轮廓点以保持原始建筑物轮廓形态；采用随机抽样一致性估计及最小二乘拟合方法进行轮廓线规则化处理，实现建筑物轮廓线的自动提取。实验结果表明，该方法能快速从建筑物点云中提取轮廓线，可为建筑物轮廓线的自动提取提供一种可行的解决方案。     

快速成型中的自适应切片方法研究

分层切片是快速成型软件系统中核心部分之一，完成将CAD实体模型离散化为层面信息的功能，提出了一种基于面积变化的自适应切片方法，并对该方法进行了实现，同时与定层厚切片方法进行了比较，表明该6算法可以有效地降低切片过程中的阶梯效应。     

OpenFoam中多面体网格生成的MPI+OpenMP混合并行方法

网格生成是计算流体力学中非常重要的一环,大规模数值模拟过程中对网格精度要求的提高会导致网格生成所耗的时间增加.文中基于OpenFoam开源软件中的网格生成算法,主要研究多面体网格的并行生成,并提出OpenMP和MPI混合并行的多面体网格生成方法.通过理论分析得到,使用混合并行方法生成相同质量的网格时,混合并行方法生成网...     

工业CT断层图像自动生成STL文件的方法

为了使工业CT（computed tomography）扫描获得的工件断层图像格式转换为快速原型设备所接受的数据格式，研究了工业CT断层图像数据格式自动生成STL（Stereolithography）文件格式的方法，并用VC^＋＋开发了软件，实验结果表明，效果较好。     

Efficient computation of volume fractions for multi-material cell complexes in a grid by slicing

The paper presents a novel slicing based method for computation of volume fractions in multi-material solids given as a B-rep whose faces are triangulated and shared by either one or two materials. Such objects occur naturally in geoscience applications and the said computation is necessary for property estimation problems and iterative forward modeling. Each facet in the model is cut by the planes delineating the given grid structure or grid cells. The method, instead of classifying the points or cells with respect to the solid, exploits the convexity of triangles and the simple axis-oriented disposition of the cutting surfaces to construct a novel intermediate space enumeration representation called slice-representation, from which both the cell containment test and the volume-fraction computation are done easily. Cartesian and cylindrical grids with uniform and non-uniform spacings have been dealt with in this paper. After slicing, each triangle contributes polygonal facets, with potential elliptical edges, to the grid cells through which it passes. The volume fractions of different materials in a grid cell that is in interaction with the material interfaces are obtained by accumulating the volume contributions computed from each facet in the grid cell. The method is fast, accurate, robust and memory efficient. Examples illustrating the method and performance are included in the paper.     

RTL数据通路模拟矢量自动生成方法研究与实现

针对已有的RTL数据通路模拟矢量自动生成方法的不足，提出一种利用约束逻辑编辑(CLP)自动生成数据通路模拟矢量的新方法．该方法首先对给定的Verilog RTL描述采用程序切片进行设计化简，然后对化简后的结果基于位向量算术原理生成CLP约束，并利用CLP求解器GProlog进行约束求解，最终生成满足输出要求的模拟矢量．该方法约束求解速度快，生成的约束是统一的，得到的模拟矢量较完备，能满足模拟验证的要求．实验结果表明，文中方法是一种高效的RTL数据通路模拟矢量自动生成方法．     

二元超声速进气道数值仿真建模过程自动化

研究高速巡航导弹动力装置优化问题,针对进气道结构严重影响速度的提高,为减少人工建模的工作量,以提高数值仿真分析工作效率和满足二元超声速进气道设计方案的快速评比和选型的需要,提出建立流场计算域通用的结构化分区几何模型,统一基于所构造的基准进气道模型,一次性人工划分进气道结构化计算网格,根据边界几何控制,运用网格映射和比例变换方法,编程自动化实现由基准进气道计算网格映射生成实际结构不同的系列化二元进气道计算网格。用建立的模型进行仿真。结果证明,减少了建模工作量和提高了工作效率。     

接地网故障诊断中的拓扑分解及其应用研究

为了对接地网进行故障诊断,通过对接地网支路拓扑结构进行分析,提出了一种以可及节点为裂点的分层拓扑分解方法,将接地网分解为元版块网、可及接地网和本征接地网。根据不同的数据结构,实现了接地网网络拓扑自动分解,明确了由拓扑结构决定的各层支路的关联性,采用结构判断和诊断后判断结合的方法对接地网支路的可测性进行了研究,可以自动识别诊断结果唯一确定的明晰支路,为科学利用诊断结果具有指导意义。对一个60支路的实验接地网采用所提出的算法进行分解和可测性判断,验证了提出的方法的正确性和实用性。     

基于CAD模型的直接快速成型软件

目前国内普遍使用的基于STL模型的快速成型软件在精确度和灵活性上都存在着很多缺陷，在一定程度上影响了快速成型技术在生产中所起的作用，以三维几何造型系统GEMS6．0为平台，实现了一个基于CAD模型的直接快速成型软件，可进行分层、填充、构造支撑体以及生成CLI文件等，针对其中的若干问题给出了相应的算法和应用实例。     

3D矢量模型切片方案评价方法

针对目前对切片方案的评价只能通过实际成品来事后检验,提出了一种3D矢量模型切片方案的预测评价方法。根据封闭轮廓环点集和工程图文件两种数据类型对3D模型进行重建,并计算扫描路径总长。通过2D逐点连线及3D逐层拉伸技术完全模拟实际的叠层制作过程,得到跟切片方案相对应的具有阶梯效应的可视化模型。实验表明,该方法可对切片数据进行快速3D重建及路长计算,其结果可用于切片方案的预测评价,有效降低了开发成本。     

Automatic multi-direction slicing algorithms for wire based additive manufacturing

One of the key challenges in Additive Manufacturing is to develop a robust algorithm to slice CAD models into a set of layers which requires minimal support structures. This paper reports the concept and implementation of a new strategy for multi-direction slicing of CAD models represented in STL format. Differing from the existing multi-direction slicing approaches that are mainly focused on finding an optimal volume decomposition strategy, this study presents a decomposition-regrouping method. The CAD model is firstly decomposed into sub-volumes using a simple curvature-based volume decomposition method. Then a depth-tree structure based on topology information is introduced to merge them into ordered groups for slicing. In addition, a model simplification step is introduced before CAD model decomposition to significantly enhance the capability of the proposed multi-direction strategy. The proposed strategy is shown to be simple and efficient on various tests parts especially for geometries with large number of holes.     

利用区域划分的多密度快速聚类算法

针对基于网格的聚类算法存在簇边缘网格中包含噪声点、利用网格相对密度差进行网格合并时不能区分密度均匀变化的网格等问题。提出一种利用区域划分的多密度快速聚类算法MFCBR。算法把数据空间划分成密度不同的网格,利用网格索引表和网格中心密度差合并网格形成簇,然后分别计算每个簇的边界网格质心、边界网格和最近簇网格中心位置,利用三者之间的关系来排除簇边界网格数据中包含的噪声点。实验表明,该算法在降低噪声数据对聚类干扰的同时,且对密度均匀变化的多密度数据集也有较优的处理效果。