复合材料弯管曲面的整体造型设计

利用隐式几何造型方法的优点,建立了弯管过渡曲面的方程,改进了弯管现有的过渡方法,且保持其几何造型的特征,由于控制参数的调节作用,增加了过渡曲面造型的自由度。通过对弯管的应力分析得出：在圆环面与小圆柱面接合处、小圆柱面与过渡曲面的接合处、过渡曲面与大圆柱面的接合处这三处的应力突变都很小,表明该弯管的弯曲效应好,验证所建立的弯管过渡曲面是可行的。     

三维图像中连续隐边界曲面的逼近计算

三维图像中感兴趣目标的边界曲面的检测与重构是三维图像分析中的一个重要问题.本文提出了从三维图像中计算连续隐边界曲面离散采样点的新方法.基于这些计算得到的离散采样点及其灰度值,可以推导出更合适的等值面或者自适应曲面去近似表示三维图像中的连续隐边界曲面.     

水电站蜗壳曲面造型与展开误差分析

蜗壳是水电站的重要部件之一，本文以包络理论推导了蜗壳曲面方程；并采用分段圆弧构造椭圆的方法构造了变径椭球包络曲面，为蜗壳曲面的几何造型提出了一种新的简便方法。同时，采用内外环面法设计了蜗壳曲面展开的计算机绘图程序，并与常用的直纹面法作了误差比较。     

同坡曲面的数学模型及计算机辅助几何设计

同坡曲面是水建及土建工程中最常见的一种坡面，本文从同坡曲面的特性入手，提出了一种建立这类坡面数学模型的方法，并建立了其上等高线，坡度线的参数方程，为计算机辅助几何设计奠定了理论基础。     

一种直线与隐式曲面求交的方法

绘制隐式曲面的光线跟踪算法,其本质问题就是直线与隐式曲面的求交,区间算术求根方法是计算直线与隐式曲面的一个很好方法。本文介绍了区间算术原理,研究了区间算术在直线与隐式曲面求交的应用,给出了相应的算法。应用区间算术,不仅可以求出直线与隐式曲面的最近交点,而且能求出所有交点。     

支持模型重用的三维参数化特征造型

本文提出了三维参数化特征造型的一种新的思路和方法。特征分为广义几何特征和应用特征，应用特征的几何信息可用广义几何特征表示；三维参数化特征建立在浮动基准体系上，在勾画平面上勾画二维参数化轮廓，勾画时可以引用三维模型在勾画平面上的投影，勾画轮廓经过广义扫描生成三维参数化特征，特征的定义过程用过程语义描述；隐式基准和虚索引对象为特征“剪贴”的实现提供了必要的保证，同时特征“剪贴”支持模型的重用、应用特征库的定义和用这些应用特征进行设计。     

多变量问题等值线形成的数学方法及物理意义

本文应用广义逆解法,将多变量散乱数据曲面(超曲面)拟合,把拟合后的曲面(超曲面)作为多变量问题等值线形成的数学模型,从而把超曲面、等值面、等值线这些几何概念,与等值线形成的物理意义结合起来,使人们能够从离散数据中揭示出所蕴含的物理规律。     

等值面的生成原理与算法

本文从工程实际中引出,由四变量离散数据图示等值曲面的问题,提出了构造等值曲面的四维画法几何生成方法,在用计算机实现此生成方法的过程中,从理论上证明了1982年Nguyen-Van-Phai提出的四面体网格化算法,这种算法的性质,即四面体球面过剩为最大的情况下是最佳的,可以有效地应用于计算机绘图和有限元分析的网格自动生成等方面。本文用此算法求出四变量离散数据的等值点,从而实现等值曲面的拟合。     

网格细分技术在汽车外形设计中的应用

细分造型技术因其计算规则简单、可以表示任意拓扑特性和几何特征的曲面等性质,受到造型技术领域中众多学者的关注,为复杂的汽车外形设计提供了工具.该文阐释了网格细分方法的基本思想以及两类典型的细分模式,提出了在相关几何造型、有限元分析和动态仿真软件配合下,设计复杂汽车外形曲面的细分技术方案;对车体曲面的控制网格生成、边界限定等关键技术进行了讨论.利用文中方法可以有效地缩短复杂汽车外形曲面的造型、计算和分析时间,为汽车外形设计的逆向工程应用提供方法和工具.     

点到隐式曲线曲面的最小距离

求解给定点到隐式曲线曲面的最小距离通常都是应用一般的搜索算法，但搜索算法的稳定性和有效性通常不高。文章基于隐式曲线曲面的几何特性，将这个求最小值问题转化为方程组求解的问题。对于方程组的求解，则应用了计算复杂度较低的离散牛顿法。将其迭代区间进行细分并在各个细分区间中应用离散牛顿迭代算法，增强了算法的稳定性。     

A new volume warping method for surface reconstruction

Volumetric models of 3D objects have recently been introduced into the reverse engineering process. Due to their efficiency and simplicity, grid-based methods are considered the major technique for reconstructing surfaces from these volumetric models. Yet these methods suffer from a number of inherent drawbacks, resulting from the fact that the imposed Cartesian grid is generally not well adapted to the surface in size or in orientation. To overcome the above obstacles, this paper proposes a new iso-surface extraction method for volumetric objects. The main idea is first to construct a geometrical field induced by the object's shape. This geometrical field represents the natural directions and grid cell size for each point in the domain. Then, the imposed volumetric grid is deformed by the produced geometrical field to approach the object's shape. The iso-surface meshes can be extracted from the resulting adaptive grid by any conventional grid-based contouring technique. These meshes provide a better approximation of the unknown surface and exhibit the anisotropy present in this surface. Since the produced meshes are all quad, Catmull-Clark subdivision surfaces can be directly constructed from them. Moreover, accurate physical models of the reconstructed objects can be produced using rapid prototyping (RP) technology.     

A new volume warping method for surface reconstruction

Volumetric models of 3D objects have recently been introduced into the reverse engineering process. Due to their efficiency and simplicity, grid-based methods are considered the major technique for reconstructing surfaces from these volumetric models. Yet these methods suffer from a number of inherent drawbacks, resulting from the fact that the imposed Cartesian grid is generally not well adapted to the surface in size or in orientation. To overcome the above obstacles, this paper proposes a new iso-surface extraction method for volumetric objects. The main idea is first to construct a geometrical field induced by the object's shape. This geometrical field represents the natural directions and grid cell size for each point in the domain. Then, the imposed volumetric grid is deformed by the produced geometrical field to approach the object's shape. The iso-surface meshes can be extracted from the resulting adaptive grid by any conventional grid-based contouring technique. These meshes provide a better approximation of the unknown surface and exhibit the anisotropy present in this surface. Since the produced meshes are all quad, Catmull–Clark subdivision surfaces can be directly constructed from them. Moreover, accurate physical models of the reconstructed objects can be produced using rapid prototyping (RP) technology.     

Automatic metric 3D surface mesh generation using subdivision surface geometrical model. Part 2: Mesh generation algorithm and examples

In this paper, a new metric advancing front surface mesh generation scheme is suggested. This new surface mesh generator is based on a new geometrical model employing the interpolating subdivision surface concept. The target surfaces to be meshed are represented implicitly by interpolating subdivision surfaces which allow the presence of various sharp and discontinuous features in the underlying geometrical model. While the main generation steps of the new generator are based on a robust metric surface triangulation kernel developed previously, a number of specially designed algorithms are developed in order to combine the existing metric advancing front algorithm with the new geometrical model. As a result, the application areas of the new mesh generator are largely extended and can be used to handle problems involving extensive changes in domain geometry. Numerical experience indicates that, by using the proposed mesh generation scheme, high quality surface meshes with rapid varying element size and anisotropic characteristics can be generated in a short time by using a low‐end PC. Finally, by using the pseudo‐curvature element‐size controlling metric to impose the curvature element‐size requirement in an implicit manner, the new mesh generation procedure can also generate finite element meshes with high fidelity to approximate the target surfaces accurately. Copyright © 2003 John Wiley & Sons, Ltd.     

一种改进的边界轮廓矢量化算法

左右于断层测量的反向建模中，物体断面图像序列的区域边界和实现模型重构的基础，如何从边界轮廓精确提取几何特征是实现重构的关键。本文提出一种改进的矢量化算法，该算法的基本思想是首先提取曲率极值点作为初始分段点。然后判定每两个相邻初始分段点之间轮廓线的形状，并区别直线段与曲线段分别进行拟合和矢量化。实践表明，该算法既能准确提取边界形状的特征关键点，又保证了重构后曲面的光滑规整。     

Green innovations for sustainable development of China: Analysis based on the nested spatial panel models

Improving green innovation efficiency (GIE) is crucial for attaining sustainability in China's stage of high-quality development. However, there is a paucity of research on the roles of and links among the government and market in GIE. This study bridges this research gap by unifying marketization, local government competition, and GIE into one empirical framework. First, we extend a super-efficiency Ray slacks-based measure model to evaluate provincial GIE in China during 1997–2018 and then analyze its evolution of spatial-temporal dynamics. Subsequently, marketization, local government competition, and GIE are incorporated into a nest of spatial panel models to address the endogeneity concerns resulting from model misspecification and omitted variables. The empirical results show that China's GIE at the national level is only 0.4813, and above 80% of provinces are far from reaching the green innovation frontier. Moreover, the observed imbalance in GIE between regions continues to worsen; notably, this coincides with the emergence of a pattern under which the gap between the north and south is widening. Furthermore, the seven spatial panel models assessed in this study reveal that local government competition not only has a direct inhibitory effect on GIE, but also indirectly impedes the corresponding promotional effect of marketization. This finding provides new evidence supporting the “grabbing hand of government” view and sheds light on the behaviors of the market and government in green innovation development.     

Simultaneous recovery of an infinite rough surface and the impedance from near-field data

In this paper, we consider an inverse rough surface scattering problem in near-field optical imaging. This problem is actually to reconstruct the scattering surface as well as its impedance coefficient from multifrequency near-field data, and can be reduced into an integral scheme by employing an integral representation. We solve this integral scheme by a non-linear integral equation method, and further develop a fast inversion algorithm for reconstructing both the rough surface and the impedance coefficient. Numerical experiments are presented to illustrate the effectiveness of the algorithm.     

基于单义域邻接图的工程图纸扫描图像的字符提取

工程图纸扫描图像的图文分割是一个重要问题。本文在构建单义域邻接图基础上来提取字符及其特征。图文分离先从单义域中筛选字符笔画域,进行初步分离。然后,以字符笔画域为起点,遍历邻接图来搜索邻接字符笔画域提取字符域,分析特性作进上步筛选。以字符域邻近与共线为判据来组合字符串域,字符域,分析特性作进上步筛选。以字符域邻近与共线为判据来组合字符串域,字符域邻近是用其外接膨胀矩形相交来判定。利用共串字符域外接矩     

Deer Body Adaptive Threshold Segmentation Algorithm Based on Color Space

In large-scale deer farming image analysis, K-means or maximum betweenclass variance (Otsu) algorithms can be used to distinguish the deer from the background. However, in an actual breeding environment, the barbed wire or chain-link fencing has a certain isolating effect on the deer which greatly interferes with the identification of the individual deer. Also, when the target and background grey values are similar, the multiple background targets cannot be completely separated. To better identify the posture and behaviour of deer in a deer shed, we used digital image processing to separate the deer from the background. To address the problems mentioned above, this paper proposes an adaptive threshold segmentation algorithm based on color space. First, the original image is pre-processed and optimized. On this basis, the data are enhanced and contrasted. Next, color space is used to extract the several backgrounds through various color channels, then the adaptive space segmentation of the extracted part of the color space is performed. Based on the segmentation effect of the traditional Otsu algorithm, we designed a comparative experiment that divided the four postures of turning, getting up, lying, and standing, and successfully separated multiple target deer from the background. Experimental results show that compared with K-means, Otsu and hue saturation value (HSV)+K-means, this method is better in performance and accuracy for adaptive segmentation of deer in artificial breeding scenes and can be used to separate artificially cultivated deer from their backgrounds. Both the subjective and objective aspects achieved good segmentation results. This article lays a foundation for the effective identification of abnormal behaviour in sika deer.     

High‐frequency response analysis via algebraic substructuring

High‐frequency response analysis (Hi‐FRA) of large‐scale dynamical systems is critical to predict the resonant behavior of modern micro‐devices and systems operated over MHz or GHz frequency range. Algebraic substructuring (AS) is a powerful technique to extract a large number of natural frequencies. In this work, we extend the AS technique for FRA between two specified cutoff frequencies ω_min and ω_max. The technique is referred to as ASFRA. ASFRA can be efficiently applied to Hi‐FRA, as demonstrated by two examples of microelectromechanical sensors operated at 1–2 and 200–250 MHz ranges. To some extent ASFRA generalizes the underlying numerical algorithm and functionality of commercially viable automated multi‐level substructuring (AMLS) technique. AMLS is designed for FRA up to a specific frequency ω_max, starting from the lowest, and is inefficient for Hi‐FRA. Copyright © 2008 John Wiley & Sons, Ltd.