Acceleration radiosity solutions through the use of hemisphere-base formfactor calculation

In this paper, we propose a novel formfactor calculation algorithm for acceleration radiosity solutions in complex environments. Our basic algorithm is an improved version of Spencer's (S.N. Spencer, ‘The hemisphere radiosity method: a tale of two algorithms’, in Photorealism in Computer Graphics, Spencer, 1992, pp. 127–135) and Van Wyk's (G.C. Van Wyk Jr., ‘A geometry-based insolution model for computer-aided design,’ Ph.D. Thesis, The University of Michigan, 1998.) methods, which fail to remove hidden surfaces for relatively large patches and cause large discretization errors in formfactors. We also demonstrate that our technique is superior to the hemi-cube method in terms of the computation time. Moreover, we parallelize our approach on a parallel computer with shared memory, and obtain a high performance with our radiosity rendering system. Our method divides a hemisphere-base into regions, and assigns a region to each processor. The approach can be applied to geometrical data generated by CAD systems, and is evaluated in terms of the computation time, the visual effects, and the parallelization performance. © 1998 John Wiley & Sons, Ltd     

锁挡多工位级进模设计

分析了锁挡零件的结构工艺性和冲压工艺,介绍了零件的排样方案、模具总体结构、工作过程、主要零部件的设计,并阐述了模具结构特点.模具结构合理、紧凑,工作平稳,生产效率高,生产的零件质量达到要求.     

一种微管单点成形有限元分析及成形机关键零部件承载分析

目的 为进一步扩展渐进成形技术在管件成形加工方面的应用,提高微管的成形复杂度、缩短加工时间,设计一款微管渐进成形机,对关键零部件承载及管件单点成形进行有限元分析.方法 通过对管件渐进成形机中关键零部件的静力学分析,根据有限元软件得到的仿真数据,对渐进成形机关键零部件进行尺寸修正和强度校核.结果 在管件的渐进成形加工中扩径20％的情况下管件壁厚平均减薄率为7.7％,管件渐进成形机的最大工作半径为83 mm.结论 管件成形机可达到设计要求,通过对管件加工工具的结构进行设计和优化,在保证零件强度的同时提高管件的扩径范围,在提高管件加工速度和可加工复杂度的同时降低减薄率.     

含双裂隙组灰岩边坡渐进失稳过程分析

利用离散元MatDEM软件二次开发功能建立了含双裂隙组的灰岩边坡数值模型,重点关注边坡位移和摩擦热的变化情况,分析了含双裂隙组灰岩边坡的渐进失稳过程,再与矿山现场位移监测数据和边坡坡顶破坏模式进行对比。结果表明,含双裂隙组灰岩边坡的破坏过程在竖向裂隙的影响下是一个由表及里逐步“剪切滑移-张拉断裂”的渐进失稳过程,依据滑移面的数量可分为裂隙贯通、初层滑动、二层滑动和三层滑动4个阶段。数值模拟结果与矿山现场监测数据一致,证实了MatDEM软件在研究裂隙边坡破坏模式上的可适用性,可为矿山未来的监测和治理提供参考。     

基于小波变换的三维网格感兴趣区域编码

在实际应用中,用户可能只对三维网格的部分区域感兴趣,希望该区域能够快速、高质量地解码,而对非感兴趣区则要求一般,以便节省网络带宽和存储.目前还未见三维网格感兴趣区编码的相关工作发表.本文提出一种基于网格小波变换的三维感兴趣区的编码方法,提出了两种感兴趣区优先编码策略和四种编码模型,以及建立感兴趣区域掩模的快速方法.实验结果表明,本文方法有效地实现了三维网格的感兴趣区域编码,较好地满足了用户浏览的交互性和个性化的要求.     

基于PTD和改进曲面拟合的高山区水电工程机载激光雷达点云滤波方法

针对高山区水电工程区域地形起伏大、植被茂密且存在部分建筑物,在提取这些区域地形时机载LiDAR点云滤波方法存在精度不高的问题,提出了一种综合点云回波特性、渐进三角网加密(PTD)算法、改进的曲面拟合算法和地面点精细化处理的山地点云滤波方法.该方法在对机载激光雷达(LiDAR)点云数据去噪的基础上,先利用植被点云的回波特...     

定位壳级进模设计

根据定位壳的工艺特点,采用单侧载体1模1件成形,增加了侧整形、侧切边、侧弯曲和精冲小孔等工序,对级进模各子模的上、下模结构进行了优化组合,使材料利用率大于25%。生产实践证明:模具结构合理,工艺性好,生产可靠,满足了企业的生产要求。     

逐步增加定数截尾下Gompertz分布的统计分析

讨论了基于逐步增加定数截尾样本Gompertz分布的参数估计,提出了模型参数的逆矩估计和一种新的联合置信区间.最后通过Monte Carlo方法进行了模拟研究,统计表明方法均有效.     

基于逆向试算法的波形片成形模具设计

以汽车离合器从动盘总成中的波形片为研究对象,基于板料回弹理论的分析提出了波形片成形高度的一种计算方法,即逆向试算法。根据逆向试算法得出波形片成形模具的型面尺寸,设计成形级进模具对波形片的成形高度进行试验验证,其试验值为1.71 mm。研究结果表明:通过逆向试算法得出的波形片成形高度为1.90 mm,逆向试算法的计算值与试验值之间的误差为11.11%,从而验证了逆向试算法的正确性。此外,波形片冲压成形级进模的应用使得单班产量由9000片提高到31000片,从而更好地指导波形片成形模具的设计,极大地提高了企业的生产效率。     

SURGEM: A solid modeling tool for planning and optimizing pediatric heart surgeries

Approximately 1% of children are born with a moderate to severe congenital heart defect, and half of them undergo one or more surgeries to fix it. SURGEM, a solid modeling environment, is used to improve surgical outcome by allowing the surgeon to design the geometry for several possible surgical options before the operation and to evaluate their relative merits using computational fluid simulation. We describe here the solid modeling and graphical user interface challenges that we have encountered while developing support for three surgeries: (1) repair of double-outlet right ventricle, which adds a graft wall within the cardiac chambers to split the solid model of the unique ventricle, (2) the Fontan procedure, which routes a graft tube to connect the inferior vena cava to the pulmonary arteries, and (3) stenosis repair, which adds a stent to expand a constricted artery. We describe several solutions that we have developed to address these challenges and to improve the performance, reliability, and usability of SURGEM for these tasks.