增量式精确多面体可见外壳

提出一种新的增量式计算精确多面体可见外壳的算法IEPVH。首先,在新视图的图像平面,计算旧可见外壳的边被新光椎切割得到的交点。然后,恢复旧可见外壳的边上交点的局部方向信息并同时获得新光椎边上的交点。接着,恢复新光椎边上交点的局部方向信息。最后,新可见外壳的多边形面片通过一次遍历网格的边的过程被识别出来,并为了便于显示而被划分为三角面片。与EPVH等其他算法相比,IEPVH不但能够让用户更多地参与基于图像3维重建的过程,而且具有空间计算复杂度小。实验证明此算法的高效和鲁棒性。IEPVH的特点使其更易于在移动设备中得到应用。     

基于测地路径的牙齿模型交互分割算法研究

从3维牙颌模型中精确地分离出单颗牙齿是计算机辅助正畸治疗的重要步骤。由于牙齿有不同的形状并且不同个体之间有很大差异,其自动分离比较困难。为此,提出一种交互分割单颗牙齿的方法：首先,在牙颌模型上交互选定特征点,然后计算特征点间近似测地路径,待测地路径封闭后,利用区域生长方法从整个牙颌模型上精确分离出单颗牙齿。实验结果显示,该算法执行速度快,用户交互量少,且分割得到的牙齿边界线平滑,较好地满足口腔正畸的临床要求。     

基于动网格的水疗按摩喷嘴转动模拟

为克服靠经验设计水疗（SPA）按摩喷嘴成本高、周期长的缺点,利用计算流体力学（Computational Fluid Dynamics,CFD）技术对某水疗按摩喷嘴进行数值建模、仿真和计算,以优化喷嘴结构．首先求出动网格守恒方程,然后利用FLUENT的动网格模型和自定义的喷嘴转动UDF,对喷嘴的转子进行三维数值分析,实现转子的网格转动,并求出转动速度．实验和仿真结果对比表明所采用的方法是合适的．     

面向对象有限元并行计算框架PANDA

为提高我国工程数值模拟软件的开发能力,面向武器工程大规模并行计算需求,基于层次化、模块化及面向对象的现代软件设计技术,分析探讨有限元并行计算框架的设计方法,形成初步的基础开发框架PANDA 0.1版;详细描述PANDA框架的层次结构设计,并探讨该基础开发框架设计中的底层网格数据结构设计、有限元共性管理模块及并行策略等部分关键技术;简要介绍PANDA框架的扩展应用方法.研究表明：采用框架技术进行结构力学有限元程序开发,具有高效、快速和便捷等优点.     

基于有限元法的客车车架结构分析与研究

在Hypermesh软件中采用板壳单元对车架几何模型进行网格划分,建立车架的有限元模型。根据客车的承载特点和行使工况,对该车车架进行动力学分析。并对车架进行模态计算,得到车架的固有频率和固有振型。配合实验数据,对车架结构的设计提出了合理的改进方案,本文可获得较高的工程应用价值。     

A cross-layer framework for video-on-demand service in multi-hop WiMax mesh networks

In this work, we introduce a cross-layer framework to favor the video-on-demand service in multi-hop WiMax mesh networks. We first propose a joint solution of admission control and channel scheduling for video streams. The proposed approach guarantees that the required data rate is achieved for video streams, which is crucial for multimedia streaming applications. An efficient and light-weight multicast routing technique is also proposed to minimize the bandwidth cost of joining a multicast tree. Furthermore, we adopt the Patching technique in the application layer to improve the capacity of the video server. Overall, the quality of the video-on-demand service is dramatically improved with the help of the efficient cooperation between the techniques proposed in different layers of the network. Simulation study shows that with the proposed approach, true video-on-demand in WiMax mesh networks can be achieved under high video request arrival rate.     

Mesh-Mon: A multi-radio mesh monitoring and management system

Mesh networks are a potential solution for providing communication infrastructure in an emergency. They can be rapidly deployed by first responders in the wake of a major disaster to augment an existing wireless or wired network. We imagine a mesh node with multiple radios embedded in each emergency vehicle arriving at the site to form the backbone of a mobile wireless mesh. The ability of such a mesh network to monitor itself, diagnose faults and anticipate problems are essential features for its sustainable operation. Typical SNMP-based centralized solutions introduce a single point of failure and are unsuitable for managing such a network. Mesh-Mon is a decentralized monitoring and management system designed for such a mobile, rapidly deployed, unplanned mesh network and works independently of the underlying mesh routing protocol. Mesh-Mon nodes are designed to actively cooperate and use localized algorithms to predict, detect, diagnose and resolve network problems in a scalable manner. Mesh-Mon is independent of the underlying routing protocol and can operate even if the mesh routing protocol completely fails. One novel aspect of our approach is that we employ mobile users of the mesh, running software called Mesh-Mon-Ami, to ferry management packets between physically-disconnected partitions in a delay-tolerant-network manner. The main contributions of this paper are the design, implementation and evaluation of a comprehensive monitoring and management architecture that helps a network administrator proactively identify, diagnose and resolve a range of issues that can occur in a dynamic mesh network. In experiments on Dart-Mesh, our 16-node indoor mesh testbed, we found Mesh-Mon to be effective in quickly diagnosing and resolving a variety of problems with high accuracy, without adding significant management overhead.     

基于曲率流的四边形主导网格的光顺方法

网格模型是计算机图形学和数字几何处理中运用最为广泛的三维几何表达方式.四边网格(以四边形为主的网格)由于其符合人们对几何形状变化的自然感知,在表示三维几何上有其独有的优势,并且可以更为直接地应用在几何造型、细分曲面、建筑设计等方面.文中针对四边形主导网格含有噪声的情况,设计了一种基于表面微分属性的光顺方法,该方法具有易实现、计算效率高的特点.基于曲率流的几何扩散可以有效地保持原网格的几何特征,同时还针对四边形主导网格的T-顶点进行了特殊处理.     

Direct 5-axis tool-path generation from point cloud input using 3D biarc fitting

In reverse engineering, geometrical information of a product is obtained directly from a physical shape by a digitizing device. To fabricate the product, manufacturing information (usually tool-path) must be generated from a CAD model. The data digitized must be processed and in most cases, a surface model is constructed from them using some of the surface fitting technologies. However, these technologies are usually complicated and the process for constructing a surface patch from a massive digitizing data is time-consuming. To simplify the process for getting tool-path information, a simple algorithm is proposed in this paper. The algorithm is used to generate a 5-axis machining tool-path. Instead of implementing any complicated surface fitting techniques, a direct method is proposed for constructing three-dimensional (3D) triangular mesh from the digitizing data with the mesh points considered as the tool contact locations. Depending on the locations of the points digitized, a decimation procedure is applied such that some of the digitizing data will be filtered out. Then, the tool axis orientations which must be determined in 5-axis tool-path are calculated and the tool center locations are determined accordingly. A 3D biarc fitting technique is applied for all the tool center locations so that a complete 5-axis tool-path is obtained.     

An interference-aware fair scheduling for multicast in wireless mesh networks

Multicast is a fundamental routing service in wireless mesh networks (WMNs) due to its many potential applications such as video conferencing, online games, and webcast. Recently, researchers proposed using link-quality-based routing metrics for finding high-throughput paths for multicast routing. However, the performance of such link-quality-based multicast routing is still limited by severe unfairness. Two major artifacts that exist in WMNs are fading which leads to low quality links, and interference which leads to unfair channel allocation in the 802.11 MAC protocol. These artifacts cause the multicast application to behave unfairly with respect to the performance achieved by the multicast receivers.