实体造型的现状与展望

实体造型技术经过了二十多年蓬勃发展,任何对其现状和发展进行综述的试图都是困难的。本文把实体造型的发展分为两个阶段,即基于几何模型的造型(GBSM)和基于特征模型的造型(FBSM)。贯穿这两个阶段的四条线索是:增强形体表示能力、增强建模手段、增强重设计能力和CAD/CAM一体化。文章把实体造型的主要技术纳入一个统一模型,然后从设计过程的角度,就设计语言、设计约束、设计原型和语义信息四个方面分析实体造型的若干问题和研究方向。     

机械产品的特征信息处理

本文讨论了单纯采用CSG模型和单纯采用B-Rep模型来表达机械产品的特征信息时所遇到的一些实际困难,根据机械产品设计与制造一体化的特殊要求,提出了基于CSG+B-Rep数据结构的特征信息表达方案。其主要特点是以面为特征定义的基本单位,利用FSMTS中CSG与B-ReP的一致对应关系,将产品的特征信息PIT链入CSG和B-Rep组成的循环链中,其优点在于既可通过CSG摸型建立参数化的产品模型,又可通过交互方式定义和修改产品的特征信息。     

体绘制的任意曲面切割方法

为了在体绘制的过程中,响应用户的实时交互以及对体数据进行切割。论文提出了一种预计算外部轮廓,基于ConstructiveSolidGeometry(CSG)的方法来进行切割的方法。预先计算的外部轮廓在整个体绘制过程中完成界定体元绘制的边界和进行切割交互的功能,因此提高了体元绘制和切割的效率。引入外部轮廓几何体之后,采用基于CSG的方法来进行交互式切割,保证了原有外部轮廓和切割体各自内部的拓扑关系。最后,通过对纹理坐标的实时计算,实现3D纹理的映射。论文借助于现有可编程图形流水线的功能实现该方法,完成了高效率的实时交互和绘制。     

Time-varying data visualization using functional representations

In many scientific simulations, the temporal variation and analysis of features are important. Visualization and visual analysis of time series data is still a significant challenge because of the large volume of data. Irregular and scattered time series data sets are even more problematic to visualize interactively. Previous work proposed functional representation using basis functions as one solution for interactively visualizing scattered data by harnessing the power of modern PC graphics boards. In this paper, we use the functional representation approach for time-varying data sets and develop an efficient encoding technique utilizing temporal similarity between time steps. Our system utilizes a graduated approach of three methods with increasing time complexity based on the lack of similarity of the evolving data sets. Using this system, we are able to enhance the encoding performance for the time-varying data sets, reduce the data storage by saving only changed or additional basis functions over time, and interactively visualize the time-varying encoding results. Moreover, we present efficient rendering of the functional representations using binary space partitioning tree textures to increase the rendering performance.     

Topology optimization of conductive heat transfer problems using parametric L-systems

Generative encodings have the potential of improving the performance of evolutionary algorithms. In this work we apply parametric L-systems, which can be described as developmental recipes, to evolutionary topology optimization of widely studied two-dimensional steady-state heat conduction problems. We translate L-systems into geometries using the turtle interpretation, and evaluate their objective functions, i.e. average and maximum temperatures, using the Finite Volume Method (FVM). The method requires two orders of magnitude fewer function evaluations, and yields better results in 10 out of 12 tested optimization problems (the result is statistically significant), than a reference method using direct encoding. Further, our results indicate that the method yields designs with lower average temperatures than the widely used and well established SIMP (Solid Isotropic Material with Penalization) method in optimization problems where the product of volume fraction and the ratio of high and low conductive material is less or equal to 1. Finally, we demonstrate the ability of the methodology to tackle multi-objective optimization problems with relevant temperature and manufacturing related objectives.     

Improving Clinician's Coded Data Entry through the Use of an Electronic Patient Record System: 3.5 Years Experience with a Semiautomatic Browsing and Encoding Tool in Clinical Routine

This report presents data on clinicians' use of a browsing and encoding utility. Traditional and computerized discharge summaries during three phases of coding ICD-9 diagnoses were compared: phase I (no coding), phase II (manual coding), and phase III (computerized semiautomatic coding). Our data indicate that only 50% of all diagnoses in a discharge summary are encoded manually; using a computerized browsing and encoding utility this rate may increase by 64%; when forced to encode diagnoses manually users may “shift” as much as 84% of relevant diagnoses from the appropriate section to other sections, thereby “bypassing” the need to encode. This effect can be partially reversed by up to 41% with the computerized approach. Using a computerized encoding help can ensure completeness of encoding data (from 46 to 100%). We conclude that the use of a computerized browsing and encoding tool by clinicians can increase data quality and the volume of documented data. Mechanisms bypassing the need to code can be reversed.     

Hybrid encoding for test data compression

Main disputes of digital integrated circuits testing are increasing test data volume and test power. The proposed encoding schemes are a combination of nine coded and selective pattern compression, Alternate Variable Run length code to reduce test data volume. The test cubes are divided into multiples of 8, 16, 32, and 64 blocks to upsurge the relationship among the successive test patterns which offers enriched test data reduction. The test data blocks are encoded with two methods in order to reduce test data volume. In the first method, the test sets are encoded using nine coded with selective pattern coding to expand the test data density. In the second method, the test sets are encoded using nine coded with Alternate variable run length laterally with selective pattern coding to improve the test data compression. Investigational results show that the proposed first and second approaches offer a maximum of 76% and 83% of compression ratio respectively for ISCAS’89 benchmark circuits.     

基于分块混合八叉树编码的海量体视化研究

在介绍当前体数据的数据模型与绘制方法的基础上,使用混合八叉树进行体数据的描述,实现了对其自适应分块存储。并用体元投射和三维纹理映射方法分别实现了混合八叉树的体绘制与多分辨率绘制。实验结果表明,该文的算法较好地实现了基于混合八叉树结构的海量体数据的组织、存储和绘制。     

浅谈Solid Edge与ANSYS的数据传递

提出使用Solid Edge的三维建模功能进行实体建模,将模型保存成ANSYS可识别的文件格式,导入ANSYS进行有限元分析,使建模过程简化;并详细介绍了模型数据传递及之后的处理步骤,对传递转换的各种文件格式的特点进行了比较。     

浅谈SolidEdge与ANSYS的数据传递

提出使用SolidEdge的三维建模功能进行实体建模,将模型保存成ANSYS可识别的文件格式,导入ANSYS进行有限元分析,使建模过程简化;并详细介绍了模型数据传递及之后的处理步骤,对传递转换的各种文件格式的特点进行了比较．     

Power transition X filling based selective Huffman encoding technique for test-data compression and Scan Power Reduction for SOCs

Due to the excessive utilization of memory, data compression is an evergreen research topic. Realizing the constant demand of compression algorithms, this article presents a compression algorithm to analyse the digital VLSI circuits for constraint optimization, such as test data volume, switching power, chip area overhead and processing speed of testing. This article proposes a new power transition X filling based selective Huffman encoding technique, which achieves better data compression, switching power reduction, chip area overhead reduction and speed of testing. The performance of the proposed work is examined with the help of ISCAS benchmark circuits. Initially, the test set is occupied by using the power transition X filling technique to replace the don't care bits and the filled test set is further encoded by selective Huffman encoding technique. The experimental results show that the proposed power transition X filling based selective Huffman encoding gives effective results compared to the related data compression techniques with minimal time and memory consumption.     

A dual-scale lattice gas automata model for gas–solid two-phase flow in bubbling fluidized beds

Modelling the hydrodynamics of gas/solid flow is important for the design and scale-up of fluidized bed reactors. A novel gas/solid dual-scale model based on lattice gas cellular automata (LGCA) is proposed to describe the macroscopic behaviour through microscopic gas–solid interactions. Solid particles and gas pseudo-particles are aligned in lattices with different scales for solid and gas. In addition to basic LGCA rules, additional rules for collision and propagation are specifically designed for gas–solid systems. The solid’s evolution is then motivated by the temporal and spatial average momentum gained through solid–solid and gas–solid interactions. A statistical method, based on the similarity principle, is derived for the conversion between model parameters and hydrodynamic properties. Simulations for bubbles generated from a vertical jet in a bubbling fluidized bed based on this model agree well with experimental results, as well as with the results of two-fluid approaches and discrete particle simulations.     

CST: constructive solid trimming for rendering BReps and CSG

Abstract-To eliminate the need to evaluate the intersection curves in explicit representations of surface cutouts or of trimmed faces in BReps of CSG solids, we advocate using Constructive Solid Trimming (CST). A CST face is the intersection of a surface with a Blist representation of a trimming CSG volume. We propose a new GPU-based CSG rendering algorithm that trims the boundary of each primitive using a Blist of its active zone. This approach is faster than the previously reported Blister approach, eliminates occasional speckles of wrongly colored pixels, and provides additional capabilities: painting on surfaces, rendering semitransparent CSG models, and highlighting selected features in the BReps of CSG models.     

Computer modelling of liquids salts RbBr, CuCl, CuBr, CuI and AgBr

Computer models of liquid ionic systems RbBr, CuCl, CuBr, CuI and AgBr containing 498 ions in the basic cube were constructed using experimental diffraction data. Modelling was conducted using algorithm BELION with varying ionic charges. Calculated atomisation energies were close to experimental data when charges were ±1.00 for RbBr, ±1.15 for AgBr, ±1.20 for CuCl, ±1.48 for CuBr, and ±1.37 for CuI. Partial pair correlation functions of models agree well with experimental data.     

Statistical trend and change-point analysis of land-cover-change patterns in East Africa

This work presents a new four-tier hierarchical change-point algorithm designed to detect land-cover change from satellite data. We tested the algorithm using Global Inventory Modelling and Mapping Studies (GIMMS) data for eastern Africa. Using a unique sequence of four statistical change-point detection methods, we identified significant increases or decreases in normalized difference vegetation index (NDVI), estimated the approximate time of change, and characterized the likely forms of change (i.e. linear trend, abrupt mean and/or variability change, and hockey-stick shaped change). Our method allows not just the identification of the change point but also the manner of change, and it can provide considerable insights into land-cover trajectories. In that sense, our approach has a significant advantage over other types of change-detection methods commonly reported in the remote-sensing literature. Although we demonstrated our algorithm using annual averages for coarse resolution data, our method can be easily adapted to finer spatial or temporal scale data, assuming assumptions of normality and independence are met. Overall, the changes detected by the algorithm are consistent with changes observed by other authors for the East Africa study area. We have demonstrated a powerful new tool for the detection of land-cover change using multi-temporal satellite data.     

Direct volume manipulation for visualizing intraoperative liver resection process

This paper introduces a new design and application for direct volume manipulation for visualizing the intraoperative liver resection process. So far, interactive volume deformation and resection have been independently handled due to the difficulty of representing elastic behavior of volumetric objects. Our framework models global shape editing and discontinuous local deformation by merging proxy geometry encoding and displacement mapping. A local-frame-based elastic model is presented to allow stable editing of the liver shape including bending and twisting while preserving the volume. Several tests using clinical CT data have confirmed the developed software and interface can represent the intraoperative state of liver and produce local views of reference vascular structures, which provides a “road map of vessels” that are key features when approaching occluded tumors during surgery.     

Selective refinement queries for volume visualization of unstructured tetrahedral meshes

We address the problem of the efficient visualization of large irregular volume data sets by exploiting a multiresolution model based on tetrahedral meshes. Multiresolution models, also called Level-Of-Detail (LOD) models, allow encoding the whole data set at a virtually continuous range of different resolutions. We have identified a set of queries for extracting meshes at variable resolution from a multiresolution model, based on field values, domain location, or opacity of the transfer function. Such queries allow trading off between resolution and speed in visualization. We define a new compact data structure for encoding a multiresolution tetrahedral mesh built through edge collapses to support selective refinement efficiently and show that such a structure has a storage cost from 3 to 5.5 times lower than standard data structures used for tetrahedral meshes. The data structures and variable resolution queries have been implemented together with state-of-the art visualization techniques in a system for the interactive visualization of three-dimensional scalar fields defined on tetrahedral meshes. Experimental results show that selective refinement queries can support interactive visualization of large data sets.     

Analysis of a parallel volume rendering system based on theshear-warp factorization

This paper presents a parallel volume rendering algorithm that can render a 256×256×225 voxel medical data set at over 15 Hz and a 512×512×334 voxel data set at over 7 Hz on a 32-processor Silicon Graphics Challenge. The algorithm achieves these results by minimizing each of the three components of execution time: computation time, synchronization time, and data communication time. Computation time is low because the parallel algorithm is based on the recently-reported shear-warp serial volume rendering algorithm which is over five times faster than previous serial algorithms. The algorithm uses run-length encoding to exploit coherence and an efficient volume traversal to reduce overhead. Synchronization time is minimized by using dynamic load balancing and a task partition that minimizes synchronization events. Data communication costs are low because the algorithm is implemented for shared-memory multiprocessors, a class of machines with hardware support for low-latency fine-grain communication and hardware caching to hide latency. We draw two conclusions from our implementation. First, we find that on shared-memory architectures data redistribution and communication costs do not dominate rendering time. Second, we find that cache locality requirements impose a limit on parallelism in volume rendering algorithms. Specifically, our results indicate that shared-memory machines with hundreds of processors would be useful only for rendering very large data sets