基于涡轮叶片有限元分析离散数据点的NURBS曲面重构

为解决有限元方法产生的三角网格数据不利于进行后续的曲面编辑和加工的问题，提出了一套算法将有限元网格逼近为造型和加工常用的NURBS曲面。首先对有限元网格进行预处理，提取出边界曲线并构造出初始曲面；通过基于曲率的自由曲面抽样网格规划方法，将海量离散数据点进行压缩及建立四边域网格，方法具有自组织和压缩比率用户可控等特点；采用迭代逼近的方法进行NURBS曲面拟合，在保证拟合精度的前提下提高了曲面光顺性。对真实叶片数据的处理证明了算法的实用性。     

反求工程技术在复杂曲面重构系统中的应用

论述了针对注塑零件复杂曲面的反求设计,提出运用CCD白光光栅非接触工业相机采集点云数据,将点云数据加载到Geometric软件中,利用NURBS曲面重构方法和插值算法,进行点云数据筛选,构造点云特征网格和曲面拟合,得到点云曲面的三维重构.实践证明,基于Geometric系统的NURBS曲面重构方法,在复杂曲面为原型实体重构的反求设计中具有理想的应用价值.     

反求工程自由曲面测量规划及重建技术的研究

反求工程中曲面的测量应遵循采样点密度随曲面曲率变化而疏密不断变化原则,并应根据离散采样点的分布确定自由曲面的重建工作。基于曲面Z向细化分层的测量技术和NURBS曲面方程拟合重建,能有效获取原曲面特征的最少测量点,并进行曲线数学重建,最终获得准确反映表面特征的NURBS曲面方程。     

采用截面特征点云的NURBS自由曲面构建

结合NURBS曲面的构建理论,以工程软件UG为平台,探讨了基于截面特征点云的NURBS自由曲面构建的工程实现方法.实现了由截面特征点云进行NURBS曲线拟合,再由拟合曲线进行自由曲面的构建过程,并从曲面的表面状态与误差两个方面对构建的自由曲面进行评估.实践表明:采用该方法构建的自由曲面能保证NURBS曲面拟合质量,且精度高,能有效地反映实物原型.     

离散数据环境下复杂曲面检测点布局策略研究

根据采样策略进行采样点的选择和布局,是对复杂曲面加工质量进行检测轨迹规划的重要内容之一.针对一般曲面采样点布局算法用于离散数据环境下复杂曲面测点布局存在的局限性,通过分析离散数据环境下复杂曲面数据的特点,引入局部网格曲率特性参数,构建基于三角面片微分几何特性的网格简化方法,从而提出基于网格简化的复杂曲面离散数据检测点布局策略,并建立不同层次网格之间距离值相对于简化三角形数量的拟合曲线方程,验证曲率权值优化方法在离散数据环境下对提高复杂曲面采样点布局精度的有效性.     

基于NURBS直纹面拟合敏感点的空间凸轮侧铣刀轨算法优化

基于NURBS直纹面拟合敏感点的空间凸轮侧铣刀轨算法优化原理,提出了拟合误差敏感点的选择方法,根据NURBS曲面重构的原理,将曲面曲率最值点和拟合误差最大点定义为理论加工刀轨曲面误差敏感点。利用曲率敏感点,在理论非等径刀轨曲面规划离散网格,得到初始数据点。通过最小二乘优化方法重构NURBS刀轨直纹面,再根据误差敏感点定义的等参数曲线来调整刀轨直纹面形状。构建了理论加工误差模型,并通过实例的仿真计算和数值模拟说明了该算法的有效性。     

冲压模参数化NURBS曲面造型及有限元网格划分

针对冲压模具的特点 ,提出了模具型面参数化NURBS曲面分片 ,局部网格调整的思想 ,较好地解决了板料成形有限元模拟前处理中模具型面造型及网格划分的问题。基于NURBS方法 ,在VC + +平台上开发了一个NURBS曲面造型及网格生成系统 ,对实际的盒形件拉深凹模型面进行了描述 ,获得了满意的曲面形状 ;基于参数空间法对型面进行了四边形网格剖分 ,并自动实现四边形到三角形网格的转换     

电话话筒盖曲面重构设计的方法研究

介绍基于NURBS曲面造型的电话话筒盖面反求设计方法。通过分析电话话筒盖面形状特征 ,提出采用等间距扫描采样方法进行数据采集 ,并将曲面简化成截面曲线模型 ,进行特征线NURBS曲线拟合 ,为NURBS曲面造型提供了合理化数据     

NURBS曲面的参数化离散及其在数控加工干涉避免中的应用

复杂曲面加工中，如何快速、有效地筛选出特殊曲面点以进行刀具干涉判断是实现无干涉刀具路径生成的关键。通过推导有理Bezier曲面的参数离散算法并结合NURBS曲面可转化为有理Bezier曲面的性质，实现了NURBS曲面基于参数的离散。该离散结果保留了离散曲面点与曲面参数域的一一对应关系，通过切削点的参数信息可快速筛选出少量需进行干涉校验的离散曲面点，从而有效简化了刀具干涉检测计算。实例分析表明，该算法能在保证曲面离散精度的前提下提高无干涉刀具路径规划的效率。     

散乱点曲面拟合及在车身曲面中的应用

提出了一种基于NURBS 曲面的散乱点参数曲面拟合方法,可以对散乱点云数据进行插值或基于最小二乘意义下的光顺拟合。完成了软件开发并在汽车车身外形曲面设计中得到了应用。NURBS曲面的优良品质保证了这种方法计算稳定,生成的曲面满足光顺要求。     

Reverse engineering of turbine blades based on design intent

The purpose of this paper is to describe a new approach to process the data points measured from turbine blade airfoils in order to make a valid shape via reverse engineering method. Currently, preliminary B-rep models can be created by fitting surfaces to point clouds using a 3D laser scanner. In case of a turbine blade, due to high shape complexity, the resulting model is often unsuitable in practice. A small change in blade geometry can lead to a large change in turbine performance. Therefore, control of the blade shape is critical to the design process. Authors believe that the only way to capture the valid shape of a blade airfoil out of the many manufacturing deviations is to incorporate design key-points during reverse engineering. Implementation of the new method using segmentation and constrained fitting algorithm (SCFA) on a heavy-duty industrial gas turbine blade has been reported and discussed.     

精铸涡轮叶片的误差分析技术

针对精铸涡轮叶片的检测和模具型腔设计中存在的精度控制问题,运用配准技术来进行误差分析,分别以形心、收缩中心、中心轴线点为特征点,运用CAD模型引导的最临近点迭代ICP(iterative closet point)配准方法,将叶片实际测量数据和CAD模型进行配准。对比配准结果,得到了精铸过程中误差分布,并通过分析叶片的变形情况,得出以形心为特征点时,型面重合度最大,配准效果最好,为叶片精铸模具的型腔设计提供了量化的参考依据。     

Rigid-plastic finite element analysis of sheet metal forming processes using continuous contact treatment and membrane elements incorporating bending effects

An improved method of contact treatment is developed in which both the FEM (finite element method) mesh and the tool surfaces are described with parametric patches which have C¹ continuity or more. The FEM mesh at the current configuration is globally converted into smooth surface patches of net form. A continuous sheet surface normal scheme is devised by using the globally smoothed mesh surface. A robust and efficient contact search algorithm is also developed in connection with the proposed continuous contact treatment. As an improved version of conventional membrane element, the BEAM (abbreviated from Bending Energy Augmented Membrane) element is newly developed based on node spring. In order to verify the effectiveness of the proposed continuous contact treatment and BEAM element, deep drawing processes of complicated parts including actual auto-body panel are analysed. Comparisons with the available experiment and analysis show that the proposed continuous contact treatment in connection with BEAM elements can be effectively applied to the analysis of sheet metal forming processes for arbitrarily curved parts with deformation regions in which the bending effect must be taken into account.     

风力机叶片蒙皮初始裂纹的盲信号提取

针对风力机叶片初始裂纹特征难以提取的问题,提出了一种逐步提取并消减噪声源信号从而获得微弱裂纹故障特征的盲提取方法.首先基于卷积混合模型极小化改进代价函数推导自适应学习迭代算式,在仿真实验中确定非线性激励函数和滤波器的传输函数,根据输出信号的性能参数证明了改进算法对尖峰噪声的异常点更加敏感稳健.在风力机叶片疲劳实验台上模拟叶片蒙皮的初始横向裂纹,通过声发射信号采集系统获得观测信号,分析噪声源的特性并提取了初始裂纹的声发射信号特征,为风力机叶片状态监测和预警提供了依据.     

大型混流式水轮机转轮叶片结构动力特性分析

转轮是水轮机结构中重要部件之一。比较不同单元类型对转轮叶片振动计算精度的影响，从推导的转轮叶片液固耦合运动方程出发，分别计算混流式水轮机转轮叶片在空气中和在工作流道中振动的主频与主振型。结果表明，叶片在水中的频率较空气中的频率有所降低，而且不同阶的频率降低值不同。     

基于隐函数转化的点取样模型布尔运算

提出一种基于点取样模型的布尔运算算法。该算法首先将点模型隐式化，得到点模型的隐函数表示；然后采用隐式曲面的布尔运算方法对点模型进行布尔操作。提出了隐式曲面布尔运算的简单形式。点模型的隐式化采用散乱点径向基函数（RBF）变分插值，采用该算法可由多个点模型构造复杂的点模型。所提出的点模型布尔操作算法可用于一般网格模型，实现网格模型的剪切／粘贴编辑处理。     

The development of a technique for 3D complex surface reconstruction from unorganized point cloud

In this paper, we propose a new neural network based on our two-level adaptive hierarchical clustering algorithm. The algorithm is to manage unorganized points, so that the triangular mesh models can be correctly obtained by applying the triangular mesh creation algorithm. We also develop adaptive self-flipping triangle edges to improve triangular mesh structure. Only one parameter, the maximal edge length of triangle, is needed in the neural network. The proposed two-level consists of the first level for clustering the cloud of points that has same order of the maximal edge length into a same cluster and the second level for generating triangular surface model or drape surfaces over the points of the same cluster. The normal vector for the generated triangular 3D surface model can be obtained from the second level. This helps to generate the STL file or stereolithography format. From the experimental results it can be shown that the proposed method is very effective for clustering unorganized point clouds for generating a triangular mesh of complex surfaces.     

A study on motion of machine tools’ hexapod table on freeform surfaces with circular interpolation

Accuracy is greatly affected by nonlinear motion of hexapods. This need is more obvious when these mechanisms are used in machining environments where precision and surface qualities are of critical importance. In this paper, comprehensive algorithm for hexapod tool path programming is developed. Using C#.Net, this algorithm is developed based on circular motion and rotation of the table which has the capability of checking nonlinear error and keeping it in a controlled limit as well. Improved Tustin algorithm is used for interpolating circular path. To evaluate the accuracy of the developed algorithm on a freeform surface, a turbine blade is scanned, and its CAD model is developed. Taking zigzag strategies, movement on turbine blade surface is approximated with smaller circles using the algorithm presented in this paper. The output accuracy resulted from interpolation algorithm for passing on turbine blade surface is studied in SimMechanics of MATLAB software. Using Total Station camera, motion path of two turbine blades with different radius curves on the hexapod table is experimentally obtained. Finally, it can be stated that the developed algorithm based on circular interpolation has the capabilities of motion on freeform curves.     

[刀具及切削工艺]一种基于几何调控的辊轧叶片前后缘加工曲面自适应重建方法

针对航空发动机压气机辊轧叶片前后缘溢料端数控加工问题，提出了一种基于设计曲面几何调控的前后缘加工曲面自适应重建方法。根据自由变形理论以及曲面能量控制原理，建立了具有变形约束能力的自由曲面几何调控模型；利用该模型建立了基于遗传算法求解的辊轧叶片前后缘加工曲面自适应重建策略。该策略通过微量调整叶片设计曲面几何形状，使其在逼近叶身型面测量数据的同时尽可能维持初始几何形状，最终实现了辊轧叶片前后缘加工曲面的自适应重建。实例验证结果表明：利用该方法获得的辊轧叶片前后缘加工曲面可以在保证叶片形状精度的同时实现其与实际叶身的圆滑转接。