三维编织复合材料预制件表面图象滤波与纹理分析研究

首先介绍了三维编织复合材料预制件表面图象的采集方式、滤波技术以及平均编织角的测试过程;然后介绍了采用基于边缘方向判决的自适应滤波器对采集的三维编织复合材料预制件表面图象进行滤波和边缘提取以及对处理后的预制件图象进行纹理分析,而得到功率谱图的方法。通过纹理分析方法对预制件的滤波图象进行平均编织角测量的结果,及通过标准图象验证了系统的可行性试验结果说明,系统具有较高的精度,是一种行之有效的测量三维编织复合材料预制件平均编织角的新方法。     

编织复合材料预制件花节长度的自动化测量系统实现

花节长度是复合材料编织体的一种重要的参数,为了进一步研究三维编织复合材料的性质,提出了一种可行的、能够自动测量三维编织复合材料预制件花节长度的技术,实现了一套自动化的测量系统;系统的实现基于一种小波变换的多分辨率分析,整个过程完全自动化并且与图像象素点的灰度值信息、象素点的小波变换的模极大值密切相关,并通过在碳纤维和玻璃纤维预制件上进行实验,得出了编织花节长度的不均衡能够影响预制件及其复合材料的机械性能的结论.     

试析三维四步法编织复合材料结构的计算机仿真

本文主要对四步法编织技术的特点进行了分析,并根据其编制的特点在计算机相关软件模拟了编制纱线的运 动轨迹,采用计算机图形技术显示出三维编织的结构,利用计算机将三维四步法编制复合材料的设计和实现过程模拟出来。 以编织工艺参数的关系为依据,在计算机软件中设置仿真参数,以便于各种尺寸和编制角的三维编织模型的生成,这种计算机 模拟方法能够让模型无限接近编织物的真实结构。     

三维编织复合材料预制件表面图象计算机分析系统

介绍了三维编织复合材料预制件表面图像检测与纹理分析的 基本原理。该系统以CCD为传感器,与微型计算机连接,进行三维编织复合材料预制件表面 编织角的检测。本系统对改善三维编织复合材料预制件的加工工艺具有指导作用,同时也为 纺织复合材料新的性能指标建立提供了有利条件,为纺织复合材料在各个领域的广泛应用提 供理论基础。     

三维编织复合材料预制表面图象计算机分析系统

介绍了三维编织复合材料预制件表面图像检测与纹理分析的基本原理。该系统以ＣＣＤ为传感器,与微型计算机连接,进行三维编织复合预制件表面编织角的检测。本系统对改善三维编织复合预制件的加工工艺具有指导作用,同时也为纺织复合材料新的性能指标建立提供了有利条件,为纺织复合材料在各个领域的广泛应用提供理论基础。     

三维GIS模型的分层表示及可视化技术研究

在分析目前三维GIS建模策略的基础上,根据矿山地质三维数据的特征,提出了三维模型的分层表示策略和基于OpenGL的可视化技术。给定原始的分层数据,结合离散网络模型自动创建控制点之间的拓扑关系,由此建立三维实体的表面模型,加载模型内部属性数据,实现到三维实体模型的转换。然后利用OpenGL造型系统对上述模型进行渲染,进行纹理、光照、消隐、阴影等计算,从而生成高真实感的三维实体模型。最后开发了一套三维GIS仿真系统,并结合实证数据进行了仿真分析。     

C/SIC复合材料结构动态特性研究

针对C/SiC轻质复合材料结构,将三维编织C/SiC复合材料看作是组分材料的空间结构物,由有序的细观结构单胞叠合而成.采用细观结构单胞作为离散单元对三维编织复合材料结构进行宏观网格剖分,利用有限元方法研究复合材料悬臂板动态特性.计算结果与理论值符合较好.     

纤维编织复合材料几何结构的生成EI北大核心CSCD

为了对编织机的运动进行验证以及对复合编织材料的性能进行预测,提出编织机运动仿真和纱线编织结构几何模型的生成方法.面向传统的五月柱编织机的运动仿真,提出一种紧密的纱线编织结构的几何建模方法.该方法借助编织基本单元的空间状态和平面展开状态的几何对应关系得到芯模表面的编织方向场,基于该方向场得到纱线的轨迹;为了改善五月柱编织机携纱率低的问题,面向双层六边形编织机的运动仿真提出具有正确的内外关系的纱线编织结构生成方法,其中交替执行割角操作和删点操作,产生纱线拉紧的效果,同时借助虚拟纱线实现纱线和芯模的碰撞检测.基于纱线的驻留比、孔隙率和平均交织比等评估策略,对多种形状芯模的编织仿真实验结果表明,所提方法是有效和鲁棒的.     

两种复合材料几何建模算法

复合材料几何模型可用于计算其物理性能和力学性能.对于随机分布的椭球颗粒复合材料和三维编织复合材料提出几何建模方法.首先针对随机分布颗粒为椭球的情况进行了阐述,对现有生成椭球颗粒分布样本的方法进行改进,消除了随机颗粒重叠的情况;为了应用多尺度有限元方法,对单胞边界之外的椭球进行处理,得到基体和增强体的边界.另外,针对三维四向编织方法,在纤维束不重叠并尽可能排列紧密的情况下给出了构建每根纤维束的运动规律.最后通过实例验证了该方法的有效性.     

凸体、旋转体的体几何模型与内部可视化

在可视化与ＣＡＤ／ＣＡＭ的许多应用问题中,不但需要描述三维实体的外形,也要求表达实体的内部信息。传统的面壳模型只能描述实体的外形,无法表达实体的内部信息。针对这种情况,利用Ｂｌｅｎｄｉｎｇ形变技术给出了由实体的面壳模型构造其实体模型（体几何模型）的简易方法,从而把实体的面壳模型与实体模型的表示统一起来。体几何模型可应用于实体内部的可视化及ＣＡＤ／ＣＡＭ中。     

Micromechanics of braided composites via multivariable FEM

A new method for micromechanical properties of three-dimensionally braided composite materials via homogenization theory and incompatible multivariable FEM is proposed in this paper. An incompatible displacement element and a hybrid stress element are developed to model the effective mechanical properties of three-dimensional textile composites. Some illustrative applications are presented for a typical class of four-step braided composites. Results of the hybrid stress element approach compare more favorably with the experimental data than other numerical methods widely used.     

三维多元地学数据一体化显示框架设计

随着三维地质信息系统发展与应用的深入,对地学数据的可视化需求更加迫切。采用面向对象的思想设计并实现了一个可扩展的多元地学数据一体化显示框架。该框架主要划分为模型层、场景层和渲染层,使得数据与绘制流程分离。围绕此框架详细阐述了绘制管线、绘制过程的设计和多层次地学场景组织,满足地质多领域、多专题数据的统一显示与分析需要。基于此框架在OpenGL环境下开发了北京市三维城市地质信息管理与服务系统。     

Computational analysis of fatigue behavior of 3D 4-directional braided composites based on unit cell approach

The fatigue behavior of 3D 4-directional braided composites was investigated based on the unit cell approach. First, the unit cell models of 3D 4-directional braided composites with different braiding angles and fiber volume fraction were built up using ABAQUS. Then, the fatigue behavior of the 3D 4-directional braided composites was analyzed, and the effect of fatigue loading direction on the fatigue damage evolution and fatigue life was studied. Finally, the effect of braiding angles and fiber volume fraction of the unit cell on the fatigue behavior of 3D 4-directional braided composites was analyzed. These results will play an important role for evaluating the fatigue behavior of 3D 4-directional braided composites in engineering.     

Simulation of Tearing Cloth with Frayed Edges

Woven cloth can commonly be seen in daily life and also in animation. Unless prevented in some way, woven cloth usually frays at the edges. However, in computer graphics, woven cloth is typically modeled as a continuum sheet, which is not suitable for representing frays. This paper proposes a model that allows yarn movement and slippage during cloth tearing. Drawing upon techniques from textile and mechanical engineering fields, we model cloth as woven yarn crossings where each yarn can be independently torn when the strain limit is reached. To make the model practical for graphics applications, we simulate only tearing part of cloth with a yarn‐level model using a simple constrained mass‐spring system for computational efficiency. We designed conditions for switching from a standard continuum sheet model to our yarn‐level model, so that frays can be initiated and propagated along the torn lines. Results show that our method can achieve plausible tearing cloth animation with frayed edges.     

A Volumetric Approach to Predictive Rendering of Fabrics

Efficient physically accurate modeling and rendering of woven cloth at a yarn level is an inherently complicated task due to the underlying geometrical and optical complexity. In this paper, a novel and general approach to physically accurate cloth rendering is presented. By using a statistical volumetric model approximating the distribution of yarn fibers, a prohibitively costly explicit geometrical representation is avoided. As a result, accurate rendering of even large pieces of fabrics containing orders of magnitudes more fibers becomes practical without sacrifying much generality compared to fiber‐based techniques. By employing the concept of local visibility and introducing the effective fiber density, limitations of existing volumetric approaches regarding self‐shadowing and fiber density estimation are greatly reduced.     

熔丝制造的三维连续编织填充图案

为提高熔丝制造(FFF)工件的机械强度,降低各向异性,提出一种3D连续编织路径规划方法.采用连续纤维增强丝材作为打印材料,设计了1个8层循环结构,利用3D打印机喷嘴挤出丝材生成经纬纱线,控制FFF平台在z方向的运动,生成类似3D编织的连续沉积路径,不同层的纤维相互交错和嵌入以实现相邻切片平面之间的互锁,以提高层内与层间...     

A Practical and Hierarchical Yarn-based Shading Model for Cloth

Realistic cloth rendering is a longstanding challenge in computer graphics due to the intricate geometry and hierarchical structure of cloth: Fibers form plies which in turn are combined into yarns which then are woven or knitted into fabrics. Previous fiber-based models have achieved high-quality close-up rendering, but they suffer from high computational cost, which limits their practicality. In this paper, we propose a novel hierarchical model that analytically aggregates light simulation on the fiber level by building on dual-scattering theory. Based on this, we can perform an efficient simulation of ply and yarn shading. Compared to previous methods, our approach is faster and uses less memory while preserving a similar accuracy. We demonstrate both through comparison with existing fiber-based shading models. Our yarn shading model can be applied to curves or surfaces, making it highly versatile for cloth shading. This duality paired with its simplicity and flexibility makes the model particularly useful for film and games production.     

三维氨基酸描述子(SVTD)在HLA-A*0201限制性CTL表位肽QSAR中的应用

应用新型的三维氨基酸描述子-SVTD对65个HLA-A 0201 限制性CTL表位肽进行结构表征,通过多元线性回归对其结构与活性的关系建立定量构效关系 QSAR 模型,采用内外双重验证的办法分析验证模型的稳定性,建模计算值,留一法(leave-one-out,LOO)交互检验预测值和外部样本预测值的相关系数R,Rcv,...     

自由旋转链末端距及其分布矩的模拟计算

以一种模拟微观过程的模型、循环迭代的算法和快捷的程序来计算各种尺度高分子自由旋转链的方末端距，并将计算结果与按统计力学式运算的结果进行比较，实该模型特别适用于较短的碳链与任意键角的分子链。不仅与矢量运算方法相对应，而且为有内转链角限制的真实大分子链的复杂构象研究提出了一条新途径。