自由曲面结构形态创建的NURBS-GM方法

自由曲面结构以其卓越的建筑表现力成为当今空间结构发展的趋势之一,并在越来越多的实际工程中得到应用。与传统的空间结构相比,自由曲面空间结构设计的难点在于如何处理好新颖建筑造型与结构合理受力性能之间的关系。近年来,结构形态学的发展,特别是结构形态创构理论的提出,为解决自由曲面结构的形态设计问题提供了有效途径。借鉴结构形态创构的思想,将非均匀有理B样条(NURBS)曲面造型技术与寻求结构应变能最小的梯度算法相结合,提出一种适合于NURBS自由曲面结构特点的形态创构方法——NURBS-GM法。该方法的特点是,通过调整NURBS曲面的控制点坐标和权因子来获得整体应变能最小的曲面形状,从而改进了以往以直角坐标为调整变量的结构形态创构方法的计算效率。最后,通过若干算例证明本文方法的有效性。     

基于B样条的自由曲面结构形态创构方法研究

在B样条曲面上设定关键点并引入参考平面,利用所设定的关键点形成B样条曲面与参考平面上参数化B样条曲线确定的内外边界,采用Delaunay网格划分技术进行三角划分,生成能够适应复杂边界的自由曲面初始结构。利用关键点坐标的变化与自由曲面应变能的关系,推导了应变能对关键点的敏感度,建立了结构应变能最小化的自由曲面结构形态创构的方法,解决了以节点为优化变量计算效率低且优化后曲面不光滑需要二次加工的问题。研究结果表明,所提出的方法可以解决在实际工程应用中具有复杂边界的自由曲面形态创构问题,可以创构出自由、灵活的多种合理自由曲面结构,由此获得的曲面结构具有刚度大、承载力高,同时最大限度地抑制了弯矩的产生,且具有初始缺陷对结构受力性能影响减小的特点。     

自由曲面空间结构形态创建的若干关键问题探讨

如何建立具有合理受力性能的自由曲面空间结构是设计过程中需要重点考虑的关键问题。以结构形态学观点为指导,将曲面几何形状的建立与寻找曲面合理受力性能的方法相结合,这一过程称为曲面的形态创建。本文对结构形态学所涉及的若干概念进行了阐述,并对自由曲面空间结构形态创建过程中所存在的关键技术问题进行了探讨。这些关键问题包括:(1)自由曲面结构的生成方法; (2)结构合理受力性能的评价指标及指标之间的相互关系; (3)合理曲面的创建方法等。通过对这些问题的探讨试图为自由曲面的研究与应用提供若干建议。     

自由形态B样条曲面网格生成的参数化方法研究(英文)

研究了自由曲面上网格的参数化生成方法.该方法利用了张量积曲面的特性,通过在曲面上提取等参线并等分等参线来生成网格.阐述了在B样条曲面上提取等参线(实质是B样条曲线)的原理,并给出了等参线等分以及由等参数生成网格的算法步骤.列举三个不同类型曲面上网格生成的例子,通过这些算例进一步介绍该方法的使用范围和使用策略.最后通过在实际工程中的应用案例表明该法的实用性及有效性.这一新网格生成技术能够划分出既均匀又美观的网格,可以广泛应用于自由曲面空间网格结构.     

空间结构的自由曲面插值技术

空间结构中的自由曲面不具有解析函数表达式,因此建模较为困难。本文在借鉴计算机辅助几何设计(简称CAGD)理论的基础上,研究了一种基于三角B-B曲面的自由曲面插值技术,编制了相应的曲面插值程序,并进行了算例验证与分析。研究表明,CAGD理论中的曲面插值技术适用于空间结构的自由曲面,且生成的自由曲面具有良好的光川页性。     

复杂曲面空间结构设计的发展

本文通过描述建筑形态的形成和发展、建筑复杂曲面的产生和发展、复杂曲面结构形态学的发展、自由曲面结构的发展与改进等四个方面，论述了复杂曲面建筑的发展历程，再结合现状，进一步论述了复杂曲面空间结构设计的发展。     

自由曲面网格结构的力学性能研究

首先介绍了自由曲面网格结构网格划分方法的研究现状。其次,基于浙江大学空间结构研究中心自主研发的自由曲面网格划分专用软件ZD-Mesher,选取曲面展开和引导线法结合的网格划分方法,对同一曲面划分不同走向的网格。最后,根据自由曲面的网格,建立有限元分析模型,分析并比较同一曲面不同走向网格的力学性能。结果表明,由此得到的自由曲面网格,基本实现了美学与力学的兼顾统一。     

改进的曲面拼接技术在变曲率后视镜设计中的应用

介绍了传统Bézier曲面拼接方法。基于变曲率后视镜曲面光顺度高的特点,提出了改进型Bézier曲面拼接方法。根据实际测得的某型后视镜数据,进行了2种不同拼接方法的数值实验,分析了2种拼接曲面边界点的偏差量。结果表明:改进型拼接方法(improved splicing method,ISM)使得拼接曲面边界具有G2连续插值性,拼接效果更加直观有效。     

逆向工程在工程机械领域的应用与研究

将逆向工程引入工程机械行业,能够有效提高企业的市场竞争力和工业设计创新力.在研究逆向工程定义及其主要应用模式的基础上,以某发动机缸盖为研究对象,采用非接触式测量方法获取其点云数据,利用点云去噪、多视拼合、孔洞修补等数据预处理技术,以及数据分块技术、STL文件生成及优化技术获取质量较高的三角面片模型,采用以NURBS(非均匀有理B样条曲线)曲面为基础的矩形参数曲面拟合方法获得产品的NURBS曲面模型.研究表明逆向工程技术在工程机械领域中的应用是必要的和可行的.     

从尺规到NURBS——用于辅助设计曲面型建筑的几何工具的沿革

复杂曲面被认为是一种"高技术"和"后现代"的设计手法,近年来在建筑设计中得到了日益广泛的应用。本文从技术史的角度出发,讨论了这些手法所依靠的几何定义工具的沿革。从尺规曲面、解析曲面、索引离散点曲面、等值线曲面直到样条曲面和NURBS,追本溯源,帮助建筑师更确切地把握这类特殊的建筑设计。     

Novel decoupled framework for reliability-based design optimization of structures using a robust shifting technique

In a reliability-based design optimization (RBDO), computation of the failure probability (P_f) at all design points through the process may suitably be avoided at the early stages. Thus, to reduce extensive computations of RBDO, one could decouple the optimization and reliability analysis. The present work proposes a new methodology for such a decoupled approach that separates optimization and reliability analysis into two procedures which significantly improve the computational efficiency of the RBDO. This technique is based on the probabilistic sensitivity approach (PSA) on the shifted probability density function. Stochastic variables are separated into two groups of desired and non-desired variables. The three-phase procedure may be summarized as: Phase 1, apply deterministic design optimization based on mean values of random variables; Phase 2, move designs toward a reliable space using PSA and finding a primary reliable optimum point; Phase 3, applying an intelligent self-adaptive procedure based on cubic B-spline interpolation functions until the targeted failure probability is reached. An improved response surface method is used for computation of failure probability. The proposed RBDO approach could significantly reduce the number of analyses required to less than 10% of conventional methods. The computational efficacy of this approach is demonstrated by solving four benchmark truss design problems published in the structural optimization literature.     

有自由面非稳定渗流分析的改进截止负压法

截止负压法是求解有自由面渗流问题较为有效的算法之一。针对其算法特点,结合渗流本质,指出该算法的不足之处在于只引用了单参数的罚函数,从而造成自由面附近区域的渗流计算不够精确。为此,提出了引用双参数罚函数的改进截止负压法,改进后的算法更能准确地考虑单元的部分饱和非饱和作用,精确地计算单元结点外力或者结点不平衡力,进而提高计算精度和收敛速度。最后,将改进算法用于求解有自由面非稳定渗流问题,编制了相应的有限元分析程序,并通过算例进行验证。     

An improvement of the response surface method

The coupling of the Monte Carlo method and the finite element method for the reliability analysis of structures leads often to a prohibitive computational cost. The response surface method is a powerful reliability method that approximates the limit state function with a polynomial expression using the values of the function at specific points. This type of analytical function replaces the exact limit state function in the Monte Carlo simulation. Therefore, the computational effort required for the assessment of the reliability of structural systems can be reduced significantly. The position of the sample points and the type of polynomial response surface have been investigated by several authors and the performance of the response surface method is still under discussion. In this paper an improvement of the response surface method is proposed. An iterative strategy is used to determine a response surface that is able to fit the limit state function in the neighbourhood of the design point. The locations of the sample points used to evaluate the free parameters of the response surface are chosen according to the importance sensitivity of each random variable. Several analytical and structural examples are considered to demonstrate the advantages of the proposed improvement.     

Kriging response surface reliability analysis of a ship-stiffened plate with initial imperfections

The use of structural reliability methods with implicit limit state functions (LSFs) shows the increasing demand for efficient stochastic analysis tools, because the structural behaviour predictions are often obtained by finite element analysis. All stochastic mechanics problems can be solved by Monte Carlo simulation method, nevertheless, in most cases, at a prohibitively high computational cost. Several approximations can be achieved using first-order reliability method (FORM) and second-order reliability method and response surface methods. In this paper, a method that combines the FORM and Kriging interpolation models, as response surface, is proposed. The prediction accuracy of the Kriging response surface obtained from different sampling techniques is assessed, and the failure probability estimates calculated by the FORM using the classical second-order polynomial regression models and the Kriging interpolation models as surrogates of nonlinear LSFs are compared. The usefulness and efficiency of the reliability analysis using the Kriging response surface are demonstrated on the basis of existing results available in the literature and with an application problem of a stiffened plate structure with initial imperfections.     

Nonlinear free vibration of skew nanoplates with surface and small scale effects

The nonlinear free flexural vibration of skew nanoplates is studied by considering the influences of free surface energy and size effect (small scale) simultaneously. The formulations are derived based on classical plate theory (CPT) in conjunction with nonlocal and surface elasticity theories using Hamilton's principle. Green's strain tensor together with von Kármán assumptions is employed to model the geometrical nonlinearity. The free surfaces are modeled as two-dimensional membranes adhering to the underlying bulk material without slipping. The solution algorithm is based on the transformation of the governing differential equation from the physical domain to a rectangular computational one, and discretization of the spatial derivatives by employing the differential quadrature method (DQM) as an efficient and accurate numerical tool. The effect of small scale parameter and surface effect together with the geometrical parameters and boundary conditions on the nonlinear frequency parameters of the skew nanoplates are studied.     

Fast computer graphics techniques for calculating direct solar radiation on complex building surfaces

Direct solar radiation has a major influence on a building's thermal behaviour. Current simulation engines are not up to the challenge of accurately modelling solar gains for buildings with complex or curved geometry and buildings sited in dense urban areas. Accurate thermal performance prediction for buildings in early stages of design is hindered by excessive computation time and incompatibility between architectural models and building energy simulation software. This paper proposes using a combination of modern computer graphics rendering techniques and parametric B-spline interpolation methods to quickly and accurately calculate solar gains over a full year based on sparse data with a continuous interpolation method. These new procedures accommodate complex building geometries and intricate shadow patterns and can accelerate shading calculations by several orders of magnitude. Faster calculations allow studies to be made at the early stages of design when modifications can have the greatest impact on a building's thermal behaviour.     

基于地表移动矢量的概率积分法参数反演方法

为解决概率积分法参数反演时计算不稳定、初值依赖、优化指标难以选取、非矩形工作面,多工作面影响下难以反演的问题,提出采用地表空间移动矢量反演概率积分法参数的遗传算法模型。该模型采用地表移动矢量的误差平方和最小作为计算指标,以遗传算法作为参数优化的核心算法进行概率积分法参数反演。用空间移动矢量指标可以解决分别采用下沉、水平移动监测值反演结果不相同、精度难以估算的难题。矢量反演模型对观测站设置没有特别严格的要求,降低了设站不当引起的计算误差。为解决遗传算法多次计算结果不同的问题,建立了组合预测计算方法,依据中误差加权均值得到唯一的计算结果。基于矢量移动值的反演模型,避免了传统计算方法的多个缺陷,计算效率高、易于与已有开采沉陷预计程序结合,为解决非矩形、多工作面地表移动观测站参数反演的工程应用问题提供了新的解决思路和计算方法。     

适于岩体结构三维建模的非连续地层界面整体重构

在岩体结构三维建模中,利用分区块方法重构被复杂断层系统切割的非连续地层界面时,插值与裁剪计算量巨大、过程烦琐,且无法反映断层两侧地层的相关性。针对该问题,提出了一种非连续地层界面整体重构方法。首先在不考虑断层影响的条件下进行整体插值形成初始地层界面,并根据断层信息形成断层面;然后求出所有断层面与初始地层界面的交线,并以这些交线作为约束,重新进行剖分与插值形成原始地层界面;再利用局部迭代求交计算实际断层交线;最后通过比较法确定断层影响范围,利用离散光滑插值方法(DSI)进行局部调值,实现非连续地层界面的整体重构。     

应力水平影响下的软土边界面模型研究

针对饱和软粘土在固结不排水条件下受到循环荷载作用时的应力应变响应,采用剑桥模型屈服面,可移动的映射中心,参数意义明确的塑性模量插值函数,建立了一个简单有效的弹塑性边界面本构模型。特别是针对一般边界面模型中参数难以确定的问题,通过将模型参数与应力水平建立函数关系,较好地得到了参数的确定方法。最后通过预测不同应力水平作用下的三轴压缩和拉伸试验,验证了模型的合理性。