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1.
确定一类二维参数化CAD模型中参数的有效范围,可减少在参数化CAD系统中重建几何实体失败的情况,为此提出了相应的代数算法。所有简单多边形中距离约束参数的有效值取值范围均可以通过此算法求出,但是求解效率不高。通过多次计算验证得出无论在有效取值范围内的任一赋值均可使重建后的几何实体的拓扑形状不变,提高参数化CAD软件的设计效率和人机交互的智能化水平,并分析出该算法的复杂度为O(n)2。  相似文献   

2.
基于拓展LIMD算法的智能动态几何软件设计   总被引:4,自引:0,他引:4  
林强  任磊  陈颖  范科峰  戴国忠 《计算机学报》2006,29(12):2163-2171
几何约束求解技术是新一代智能化参数化CAD的核心技术之一,是CAD领域的一个前沿课题.其目的是提供工程图形的自动求解,其主要特点是:自由拖动元素、动态图形生成、动态测量、动态轨迹生成.LIMD是约束求解中一个应用较广的算法,作者对该算法进行了拓宽和改进,提出了具体解决方法,并得到了较好结果.  相似文献   

3.
PADS──一个基于几何推理的参数化设计系统   总被引:5,自引:0,他引:5  
PADS是一个基于几何推理的参数化设计系统。该系统采用一面向对象的数据模型统一表示几何元素与几何约束;基于一个普通算法实现几何推理,并且推理算法采用了一个更加适合于几何推理的推理策略;系统的参数变动处理通过局部的几何推理,将尺寸变动后的重新计算限制在局部范围;为减轻用户的输入负担,系统具备几种有效的输入与建模手段。  相似文献   

4.
圆锥齿轮实体参数化逆向造型设计   总被引:14,自引:1,他引:14  
提出实体参数化逆向造型设计的方法,介绍应用该方法开发圆锥齿轮三维实体参数化造型设计系统的过程。采用小型CAD软件的基本造型功能对圆锥齿轮三维基体作造型设计,再利用其宏记录自动生成程序的功能将宏文件和齿形生成程序结合,在Visual Basic环境下实现圆锥齿轮基体与齿形三维实体参数化逆向造型设计。旨在提供一种对CAD软件二次开发的新方法,使设计者掌握运用该方法对复杂三维实体进行参数化设计,从而提高开发小型CAD软件的能力。  相似文献   

5.
STAR.CCM+从V5.02开始集成完全参数化的CAD几何建模功能3D—CAD.3D—CAD模块搭建起CAD与CAE之间沟通的桥梁,用户无须担心在仿真过程中使用到的不同软件之间的数据交换问题.3D—CAD完全集成在STAR—CCM+的界面和工作流程中,实现STAR.CCM+从参数化CAD建模到表面准备、体网格生成,再到计算求解和后处理的一体化工作流程.3D.CAD的完全参数化功能使用户可方便地修改几何模型尺寸,  相似文献   

6.
参数化设计中的物性快速计算   总被引:1,自引:0,他引:1  
本文针对参数化总体设计,提出了基于离散算法的物性快速求解算法,解决了参数化设计中常见的几何特征值快速算法问题。  相似文献   

7.
PADS—一个基于几何揄的参数化设计系统   总被引:5,自引:1,他引:4  
PADS是一个基于几何推理的参数化设计系统,该系统采用一面向对象的数据模型统一表示几何元素与几何约束;基于一个普通算法实现几何推理,并且推理算法采用了一个更加适合地几何推理的策略;系统的参数变动处理通过局部的几何推理,将尺寸变动后的重新计算限制在局部范围;为减轻用户的输负担,系统具备几种有效的输入与建模手段。  相似文献   

8.
为了提高设计效率,提出一种全参数化设计方法,系统阐述其实现机理,给出自动施加约束、约束实时显示及约束可视管理算法。并运用AutoCAD二次开发技术,将几何约束求解器CBA和CAD绘图平台有机结合,实现全参数化绘图。  相似文献   

9.
一种基于几何推理的参数化设计方法   总被引:10,自引:2,他引:8  
高曙明  彭群生 《计算机学报》1994,17(11):816-822
本文提出一种基于几何推理的参数化设计方法,该方法引入了已知元素,已知约束等新概念;通过扩展一般的图形数据结构统一表示几何元素与几何约束;基于普通算法而不是专家系统实现几何推理,并采用一个更适合地几何推理策略;基于几何推理实现参数化设计。  相似文献   

10.
针对目前飞行器多学科设计优化(MDO)在计算机仿真应用中参数化几何建模方法在设计变量可控情况下描述能力不足、适应性差的问题,结合当前几种常见方法的建模思想,引入图形基、曲线乘法修正和加法修正的概念,提出一种适用范围更广的参数化描述方法,并将其应用到CAD几何建模中,衍生出一套基于CAD的半解析混合参数化几何建模方法,该方法结合CAD与解析方法的优势,描述能力强、实现简单。翼型和飞行器参数化建模及弹头形状优化的算例表明,基于CAD的半解析混合参数化方法能兼容传统的参数化方法,将图形基构成的设计空间与传统参数空间合并,可有效提高参数化方法的描述能力和适应能力,可用于丰富MDO几何建模的参数选择,探索新型设计。  相似文献   

11.
Gröbner bases are the computational method par excellence for studying polynomial systems. In the case of parametric polynomial systems one has to determine the reduced Gröbner basis in dependence of the values of the parameters. In this article, we present the algorithm GröbnerCover which has as inputs a finite set of parametric polynomials, and outputs a finite partition of the parameter space into locally closed subsets together with polynomial data, from which the reduced Gröbner basis for a given parameter point can immediately be determined. The partition of the parameter space is intrinsic and particularly simple if the system is homogeneous.  相似文献   

12.
RED算法是网络拥塞控制的基础算法,加载算法需要设置队列平均长度、队列丢包上下限阈值、数据包平均尺寸等多项参数,且参数设置没有明确的规则限制和理论依据,不合理的参数值会削弱算法的拥塞控制效果。在网络拥塞特征分析的基础上,挖掘数据包达到速率和数据包处理速度两个拥塞控制指标之间的关系,建立指标与RED算法参数的映射,消解多余参数并确定参数值域范围,改善算法在网络环境中的拥塞控制效果,提高算法的实用性。  相似文献   

13.
We present a parameter synthesis algorithm for planar, higher pair mechanical systems. The input is a parametric model of a mechanical system (part shapes and configurations) with nominal values and tolerance intervals for the parameters. The output is revised parameter ranges that guarantee correct kinematic function for all system variations. Nominal values are changed when possible and tolerance intervals are shrunk as a last resort. The algorithm consists of a three-step cycle that detects and eliminates system variations with incorrect kinematic function. The first step finds points in parameter space whose kinematic variation is maximal. The maximum of the higher pairs are derived by contact zone construction and are then combined into system maximums. The second step tests the points for correct kinematic function using configuration space matching and kinematic simulation. The third step adjusts the parameter ranges to exclude the points that fail the test. The cycle repeats until every point exhibits correct function. We demonstrate the algorithm on five real-world examples.  相似文献   

14.
We present a fast and accurate parameter estimation method for image segmentation using the maximum-likelihood function. The segmentation is based on a parametric model in which the probability density function of the grey levels in the image is assumed to be a mixture of two Gaussian density functions. For more accurate parameter estimation and segmentation, the algorithm is formulated as a compact iterative scheme. In order to reduce the computation time and to make convergence fast, histogram information is combined into the algorithm. Estimates of the initial values are properly selected for fast convergence. In addition, we find the optimal threshold values for several different types of mixture density which have one, two or no intersections between two component densities. The performance of the algorithm is evaluated on a set of artificial and real images and compared with those of other algorithms as well.  相似文献   

15.
A symbolic-numerical algorithm for the computation of the matrix elements in the parametric eigenvalue problem to a prescribed accuracy is presented. A procedure for calculating the oblate angular spheroidal functions that depend on a parameter is discussed. This procedure also yields the corresponding eigenvalues and the matrix elements (integrals of the eigenfunctions multiplied by their derivatives with respect to the parameter). The efficiency of the algorithm is confirmed by the computation of the eigenvalues, eigenfunctions, and the matrix elements and by the comparison with the known data and the asymptotic expansions for small and large values of the parameter. The algorithm is implemented as a package of programs in Maple-Fortran and is used for the reduction of a singular two-dimensional boundary value problem for the elliptic second-order partial differential equation to a regular boundary value problem for a system of second-order ordinary differential equations using the Kantorovich method.  相似文献   

16.
Medical parametric imaging with dynamic positron emission tomography (PET) plays an increasingly potential role in modern biomedical research and clinical diagnosis. The key issue in parametric imaging is to estimate parameters based on sampled data at the pixel-by-pixel level from certain dynamic processes described by valid mathematical models. Classic nonlinear least squares (NLS) algorithm requires a "good" initial guess and the computational time-complexity is high, which is impractical for image-wide parameter estimation. Although a variety of fast parametric imaging techniques have been developed, most of them focus on single input systems, which do not provide an optimal solution for dual-input biomedical system parameter estimation, which is the case of liver metabolism. In this study, a dual-input-generalized linear least squares (D-I-GLLS) algorithm was proposed to identify the model parameters including the parameter in the dual-input function. Monte Carlo simulation was conducted to examine this novel fast algorithm. The results of the quantitative analysis suggested that the proposed technique could provide comparable reliability of the parameter estimation with NLS fitting and accurately identify the parameter in the dual-input function. This method may be potentially applicable to other dual-input biomedical system parameter estimation as well.  相似文献   

17.
In parametric design, changing values of parameters to get different solution instances to the problem at hand is a paramount operation. One of the main issues when generating the solution instance for the actual set of parameters is that the user does not know in general which is the set of parameter values for which the parametric solution is feasible. Similarly, in constraint-based dynamic geometry, knowing the set of critical points where construction feasibility changes would allow to avoid unexpected and unwanted behaviors.We consider parametric models in the Euclidean space with one internal degree of freedom. In this scenario, in general, the set of values of the variant parameter for which the parametric model is realizable and defines a valid shape is a set of intervals on the real line.In this work we report on our experiments implementing the van der Meiden Approach to compute the set of parameter values that bound intervals for which the parametric object is realizable. The implementation is developed on top of a constructive, ruler-and-compass geometric constraint solver. We formalize the underlying concepts and prove that our implementation is correct, that is, the approach exactly computes all the feasible interval bounds.  相似文献   

18.
In order to obtain a high-resolution and well-focused image from compressively sampled echo data in the presence of wall ambiguity, a parametric sparse representation algorithm is proposed in this paper. A parametric dictionary with an unknown wall parameter is designed to represent the wall’s ambiguity. Then, imaging through unknown walls problem is converted into a joint optimization one which can be decomposed into sequential sparse imaging and wall parameter estimation. Specifically, the wall parameter estimation is performed by searching the maximum contrast. Numerical results are presented to demonstrate the validity and effectiveness of the proposed algorithm.  相似文献   

19.
Recently, pathfollowing algorithms for parametric optimization problems with piecewise linear solution paths have been developed within the field of regularized regression. This paper presents a generalization of these algorithms to a wider class of problems. It is shown that the approach can be applied to the nonparametric system identification method, Direct Weight Optimization (DWO), and be used to enhance the computational efficiency of this method. The most important design parameter in the DWO method is a parameter (λ) controlling the bias-variance trade-off, and the use of parametric optimization with piecewise linear solution paths means that the DWO estimates can be efficiently computed for all values of λ simultaneously. This allows for designing computationally attractive adaptive bandwidth selection algorithms. One such algorithm for DWO is proposed and demonstrated in two examples.  相似文献   

20.
In this paper, we introduce ByzantineCAD, a parametric CAD system for the design of pierced medieval jewellery, which is jewellery created by piercing, a traditional Byzantine technique. ByzantineCAD is an automated parametric system where the design of a piece of jewellery is expressed by a collection of parameters and constraints and the user's participation in the design process is through the definition of the parameter values. We present an approach to designing traditional pierced jewellery using a voxel-oriented feature-based Computer Aided Design paradigm: a large complex pierced design is created by appropriately placing elementary structural elements. We also present a scaling algorithm for enlarging pierced designs without altering the size of the elementary structural elements used to construct them.  相似文献   

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