Weaverbird: Topological Mesh Editing for Architects

Design and computation consultant Giulio Piacentino is the developer of WeaverBird. Here he describes how the plug-in ‘gives architects more geometric control and allows them to create complex surface structures that join in orderly ways, yet in arbitrary configurations’.     

NURBS-based thermal buckling analysis of graphene platelet reinforced composite laminated skew plates

Abstract

A nonuniform rational B-spline isogeometric finite element formulation is presented in this research to analyze the thermal buckling behavior of composite laminated skew plates reinforced by graphene platelets. Formulation is based on the first-order shear deformation plate theory. It is assumed that each layer of the composite laminated plate may have different volume fraction of graphene platelets leading to a through-the-thickness piecewise functionally graded medium. The equivalent properties of the plate are obtained by means of the Halpin–Tsai rule. The developed solution method may be used for arbitrary combinations of boundary conditions. The accuracy of the developed formulation is depicted via comparison studies with respect to the available data in the open literature. Novel numerical results are also given to show the effects of volume fraction of graphene platelets, distributed patterns of graphene platelets, and geometric characteristics of the skew plate.     

NURBS曲线在服装原型中的应用

本文研究服装文化式原型中袖窿样条曲线的数字化特点，通过VBA编程，实现袖窿曲线的自动拟合。     

基于NURBS曲线的逼近研究

介绍了直线逼近和圆弧逼近2种NURBS曲线逼近算法,并在两者的基础上,提出对NURBS曲线进行混和逼近的新算法,最后,通过实例验证了该算法的正确性与可行性。     

NURBS曲线在罗茨泵转子型线设计中的应用

将NURBS曲线运用到罗茨泵转子型线的设计中,设计了叶峰曲线的合理区域。求解了NURBS曲线的包络条件,实现了由控制点和权因子决定NURBS曲线罗茨泵转子型线的方法。该方法重新设计了渐开线型转子型线,平均误差在0.1μm内,处于合理误差范围内,验证了NURBS曲线设计罗茨泵转子型线的可行性。并利用NURBS曲线局部可调的特性,对转子型线进行了改进优化,使转子型线的面积利用系数提高了1%,为罗茨泵转子型线设计提供了一种理论和方法。     

仿人研抛NURBS曲面的五坐标加工轨迹优化

从五坐标铣床的特点和人工分片研抛机理出发，提出了内圆和外圆变焦法，分别用于工件的边界子片和内部子片，可产生类似人工研抛的螺旋线工具轨迹，并模仿人工研抛的肘、腕关节姿态以产生工具轴方向矢量。该方法从减少工具轨迹的陡峭转折入手，产生了较光滑的准螺旋线工具轨迹，可降低被研抛工件的表面粗糙度，适用于五坐标研抛轨迹规划。用MATLAB验证了算法的正确性，给出了仿真的工具接触点轨迹和工具轴方向规划图。实验结果表明，该方法可行。     

Calculation of tool paths for a torus mill on free-form surfaces on five-axis machines with detection and elimination of interference

Within the framework of a study carried out in cooperation with the Sapex Company, we sought to develop an overall machining program for free-form surfaces on a 5-axis NC machine tool. This program comprises a certain number of general cases that will then have to be adapted to specific situations. In this paper, we present the algorithms allowing the following cases to be dealt with:Positioning a torus mill at a given point on the surface with automatic search for interference between the end of the tool and the surface.Angular correction or the raising of the tool to avoid interference.Calculation of trajectories for a rolling torus mill on a ruled surface resting on a free-form surface of the NURBS (Non Uniform Rational B-Splines) type.The latter can be broken down into two parts:Seeking the axis position on the adjusted surface.Determination of the tool's point of contact on the freeform surface.     

Vectorizing NURBS surface evaluation with basis functions in power basis

Several known methods for direct evaluation of NURBS curves and surfaces are described. Runtime performance and simplicity of vectorization are discussed. An evaluation method, which uses basis functions precomputed in shifted power basis, is shown to be promising. This method for surfaces is vectorized with SSE2 intrinsics, yielding 3 times performance improvement over the non-vectorized version. Branchless vectorized linear search is proposed for span search, being most efficient for small number of knots. Binary search ending with a small linear search is shown to be most efficient for large number of knots, and good for general case. Performance comparison of the evaluation method and its equivalents from available geometric kernels is included.     

螺旋定子内螺旋曲面反求建模方法研究

等壁厚橡胶衬套螺旋定子的出现,大幅提高了螺杆钻具和螺杆泵的性能.针对该种定子金属壳内螺旋曲面的复杂性和型线表达的不确定性,文章研究了采用NURBS构造螺旋定子端面型线及螺旋曲面的表达式.提出了根据测量数据点反求定子内螺旋曲面的两种方法,通过CAD软件的二次开发实现了螺旋定子内螺旋曲面的三维建模,为定子及其加工刀具廓形的设计和制造提供了技术支持.     

三次样条曲线回转面的车削加工

为了在数控车床上完成三次样条曲线回转面的车削加工,文中介绍了G1连续和G2连续的条件,讨论了通过G1连续和G2连续条件建立三次样条曲线数学表达式的方法,根据该表达式,编写了精车三次样条曲线回转面的NC程序.通过在CK6132数控车床上实际加工验证,以及与UG自动编程加工结果对比,文中通过G1连续和G2连续条件建立三次样条曲线数学表达式的方法是正确的.