CAD/CAPP集成系统中基于三维特征模型的零件信息自动提取

在传统的CAD/CAPP集成系统中,零件的非几何信息的自动传输问题一直未能得到很好的解决。针对这一关键问题,文中面向CAD/CAPP集成系统,构建了基于三维特征模型的零件信息数据结构,实现了集成系统中零件信息(包括几何信息和非几何信息)的自动提取,并以齿轮零件为例,在UGNX3.0软件环境下,实践了该方法下的模型建立及其信息的自动提取。该方法弥补了传统集成系统的不足,解决了系统中零件特征信息的三维模型显示、自动更新、识别和储存问题。

集成三维特征模型的桥梁管理系统研究

从桥梁管理活动的角度出发,对桥梁管理系统进行了定义和业务流程分析,针对桥梁管理的信息需求在桥梁管理系统的数据库中扩展了桥梁的三维行征模型库,以此为基础研究和设计了集成三维特征模型的桥梁管理系统体系结构。

三维模型表面特征的水墨效果渲染算法

提出一种对三维模型实现水墨效果渲染的两步二维纹理映射方法.该方法首先通过模型顶点的视线向量和法线向量的点乘积计算其夹角的余弦值,作为第一步的纹理坐标进行映射;再通过欧拉公式计算径向曲率及其方向导数值,作为第二步映射的纹理坐标.为达到实时的交互浏览,在第二步映射时还可采用基于视点无关的曲率特征的映射策略(如平均曲率、高斯曲率、主曲率等).在快速生成水墨画效果的同时也显示出更多的特征细节.

基于曲率特征的三维模型对称性检测技术

针对三维模型上对称性提取效率不高的问题,在此提出了一种改进的对称性检测方法,该方法通过分析和计算三维模型上曲面的曲率特征,得到模型表面上凸起或者凹陷的褶皱线,再将褶皱线作为分析检测曲面对称性的依据,结合变换空间聚类的方法,计算得到模型整体的对称变换。实验结果表明,该方法通过以简单的褶皱线来描述和刻画模型上的复杂曲面,不但能够得到正确的对称变换,还能够大幅减少算法的计算量,加速提取过程。

三维可变形物体的特征点层次提取

针对不同姿态下的三维可变形物体特征点一致性问题,提出了一种基于样例学习的特征点层次提取方法。该方法首先提取出三维模型的外部特征点;其次,根据外部特征点在不同姿态下所具有的局部特征相似性,采用热核信号和支持向量机识别出外部特征点的语义标签;最后,根据语义标签和测地距离,层次地提取出三维模型的其它语义特征点。实验结果表明,该方法能很好地得到三维可变形物体的各种语义上的有效特征点。

评价素养的模型建构、内涵特征与实施建议要要以中学英语教师评价素养的提升为例

评价素养与教育教学质量和学生学习成效紧密关联。本文从深化课程改革和推进评价改革对教育评价的双重需求分析出发,通过对教师评价素养相关的研究述评,构建了教师评价素养三维模型并概述了其内涵特征,结合教师评价素养模型实施面临的问题进行成因分析,提出了相应的实施建议,以期能助力教师评价素养稳步发展。

采用SolidWorks的弧面分度凸轮三维造型设计及运动仿真分析

从单头弧面分度凸轮基本动作入手,根据凸轮带动转盘的运动规律,设计主要运动参数和几何参数,然后输入到Matlab软件中进行计算及曲线分析,最后通过SolidWorks软件建立凸轮的三维特征模型并进行运动仿真分析。通过仿真分析结果证明,采用该设计方法设计的凸轮曲面与理论值符合度较高,为弧面分度凸轮的快速、高效设计和动态改进提供了一种高效可行的方法。

Theoretical analysis of characteristics of acoustic emission in rock failure based on statistical damage mechanics

Based on statistical damage mechanics,the constitutive model of a rock underthree-dimensional stress was established by the law that the statistical strength of rockmicro-element obeys Weibull distribution.The acoustic emission (AE) evolution model ofrock failure was put forward according to the view that rock damage and AE were consistent.Moreover,in the failure process of rock under three-dimensional stress,the change inrelationship between stress condition parameter and the characteristic parameters of AE,such as the event number and its change rate,were studied.Also,the rock AE characteristicunder uniaxial compression was analyzed in theory and verified with examples.Theresults indicate that the cumulative event number and change rate of AE in rock failure aredetermined by stress state parameter F.Along with the gradual increase of F,first the cumulativeevent number increases gradually,then rapidly,and then slowly after the stresspeak.The form of change rate of an event by increasing F is consistent with the distributionform of rock micro-element strength.The model explained the phenomenon that a relativelyquiet period of AE appears before rock rupture that is observed by many researchersin experiments.Verification examples indicate that the AE evolution model is consistentwith the test results,so the model is reasonable and correct.

Multi-level spherical moments based 3D model retrieval

In this paper a novel 3D model retrieval method that employs multi-level spherical moment analysis and relies on voxelization and spherical mapping of the 3D models is proposed. For a given polygon-soup 3D model, first a pose normalization step is done to align the model into a canonical coordinate frame so as to define the shape representation with respect to this orientation. Afterward we rasterize its exterior surface into cubical voxel grids, then a series of homocentric spheres with their center superposing the center of the voxel grids cut the voxel grids into several spherical images. Finally moments belonging to each sphere are computed and the moments of all spheres constitute the descriptor of the model. Experiments showed that Euclidean distance based on this kind of feature vector can distinguish different 3D models well and that the 3D model retrieval system based on this arithmetic yields satisfactory performance.

Basic Research on Key Techniques Related to Urban 3D Pipe Network Modeling

A new geometric modeling approach is introduced in this paper.First the principle of modeling of 3D pipe network is discussed in detail.Then the procedures of implementing pipe network visualization and system functions are presented.Last,several efficient methods for speeding up display of graphics are introduced.The new geometric modeling approach offers to people a new way to solve 3D visualization of complex urban pipe network.

3-D BAROCLINIC NUMERICAL SIMULATION OF THE SOUTH CHINA SEA I. UPPER CIRCULATION

A three dimensional baroclinic shelf sea model was employed to simulate the seasonal characteristics of the South China Sea (SCS) upper circulation. The results showed that: in summer, an anticyclonic eddy, after its formation between the Bashi Channel and Dongsha Islands in the northeastern SCS, moves southwestward until it disperses slowly. There exists a northward western boundary current along the east shore of the Indo China Peninsula in the western SCS and an anticyclonic gyre in the southern SCS. But at the end of summer and beginning of autumn, a weak local cyclonic eddy forms in the Nansha Trough, then grows slowly and moves westward till it becomes a cyclonic gyre in the southern SCS in autumn. At the beginning of winter, there exists a cyclonic gyre in the northern and southern SCS, and there is a southward western boundary current along the east shore of the Indo China Peninsula. But at the end of winter, an anticyclonic eddy grows and moves toward the western boundary after forming in the Nansha Trough. The eddy’s movement induces a new opposite sign eddy on its eastern side, while the strength of the southward western boundary current gets weakened. This phenomenon continues till spring and causes eddies in the southern SCS.

Calculation of Ground Vertical Displacements,Tilts and Their Distribution Characteristics around an Irregular Load

Based on the load model of a uniform isotropic semi-infinite elastic medium,we deduced a calculation of vertical displacement and tilt and proposed a method of calculation of vertical displacements and tilts caused by irregular load on the ground or underground at a certain point with two-dimensional and three-dimensional shapes. We compared the difference between the simplified model and the irregular model. Finally,the vertical displacements near the irregular load and the distribution of horizontal tilt are presented.The results show that,compared with the point simplified model,the irregular load model has certain advantages for describing the near field. The establishment of a twodimensional irregular load model can help with the calculation of the modal vector superposition after load scattering. The three-dimensional irregular load model can redistribute load through different weights given to the scattered points after the load scattering,and then obtain displacement with the vector calculation method. The results of vector superposition calculation from the scattered irregular load both in two-dimensions and three-dimensions are all convergent obviously as grids become denser,and it is shown that the calculation method is correct and feasible.

Numerical simulation of sandy bed erosion by 2D vertical jet

A two-dimensional numerical model of vertical jet scour was developed based on the turbulent flow theory and jet scour mechanism. In this model, drag force acts as the main reference variable and the critical Shields number acts as the incipient motion criteria of sediment. The morphological change in the bed caused by bed-load transport is simulated using the moving mesh method and the suspended-load is not considered. An experiment investigating vertical clear water jet scour was conducted in the laboratory, and some effective experimental results, such as flow pattems and distribution characteristics of scour pits, were obtained. Numerical simulation of the 2D jet scour was conducted using the same parameters as were used in the flume experiment. The evolution process of the jet scour observed in the experiment was simulated by the new model; validation of the numerical model and the algorithm was conducted. Semi-empirical formulas of the characteristic length of the equi-librium scour hole were deduced based on the results of the experiment and simulation.

A method of shadow puppet figure modeling and animation

To promote the development of the intangible cultural heritage of the world, shadow play, many studies have focused on shadow puppet modeling and interaction. Most of the shadow puppet figures are still imaginary,spread by ancients, or carved and painted by shadow puppet artists, without consideration of real dimensions or the appearance of human bodies. This study proposes an algorithm to transform 3D human models to 2D puppet figures for shadow puppets, including automatic location of feature points, automatic segmentation of 3D models, automatic extraction of 2D contours, automatic clothes matching, and animation. Experiment proves that more realistic and attractive figures and animations of the shadow puppet can be generated in real time with this algorithm.

Dynamics of saltwater intrusion in the Modaomen Waterway of the Pearl River Estuary

Observations indicate an abnormal characteristic of saltwater intrusion in the upper Modaomen Waterway of the Pearl River Estuary,i.e.,the maximum salinity occurs during the neap tide or the coming moderate tide instead of during the spring tide.To explore the associated dynamic mechanisms,a high resolution three-dimensional numerical model was set up based on the Finite Volume Coastal Ocean Model(FVCOM),which covered the entire river network,the Pearl River Estuary,and the adjacent sea.Numerical experiments illustrated that the upper Modaomen Waterway is significantly influenced by the saltwater intrusion from the Hongwan Waterway,a narrow and shallow channel connecting the Modaomen Waterway to the sea.Specific topography,spring-neap tidal variation,local wind stress,and their interaction drive an up-estuary residual current in the Hongwan Waterway,which is much stronger during the neap tide than during the spring tide.As a result,more saltwater in the Hongwan Waterway is spilled over into the Modaomen Waterway during the neap tide or the coming moderate tide.This is the inherent dynamic mechanism why the saltwater intrusion in the upper Modaomen Waterway reaches its maximum during the neap tide or the coming moderate tide.Besides,we also found that the winter prevailing wind can pronouncedly enhance the saltwater intrusion in the Modaomen Waterway.