Multiresolution Representation of 2D CSG Models

Multiresolution is currently one of the main schemes used in CAD modeling for representing objects, particularly when large-scale geometric data must be transferred interactively over a network, as in the case of collaborative design. Increasingly complex products and growing competition have turned design into a collaborative team effort. Furthermore, the widespread development of Internet viewers has also necessitated the transfer and display of large-scale CAD models over networks. In order to reduce the volume of transferred data, efforts have been made to transfer CSG (Constructive Solid Geometry) models rather than those based on B_rep (Boundary Representation). This paper presents an original new method for speeding up data transfer by using multiresolution CSG models at different levels of details (LOD). The multiresolution CSG algorithm generates a hierarchy of multiresolution CSG trees; at each level, the shape is further approximated and represented by a smaller number of CSG primitives. The paper analyzes the proposed algorithm, and demonstrates its feasibility.     

胶凝堆石料动本构关系及动模量衰减模型

基于动三轴试验,研究了不同围压、不同胶凝含量下胶凝堆石料的动本构关系及动模量衰减规律。结果表明,胶凝堆石料动本构关系仍可用Kondner R L双曲线模型进行描述,围压、胶凝含量对动本构关系均有影响,但围压对其影响较大;胶凝堆石料动模量随动应变的增大而非线性减小,且具有明显的应变软化特征,同等条件下动模量随围压和胶凝含量的增大而增大。根据动模量衰减曲线,提出了动模量衰减模型,通过线性回归分析,得到了胶凝堆石料动模量衰减模型参数表达式,为胶凝堆石坝的动力分析提供了参考。     

CAD/CAM中几何模型系统和数据结构的研究

如何更好地表示三维实体的几保模型,是ＣＡＤ／ＣＡＭ中的首要问题,本文提出的混合模型结构既能完整、精确地表示几何模型,又充分了适应特征造型的发展,便于ＣＡＤ／ＣＡＭ的集成。改进的翼边结构能够完整无二义性地定义几何实体,方便快捷地访问相关数据,从根本上保证了ＣＡＤ／ＣＡＭ系统的稳定性及可扩展性。     

CSG坝的应用前景研究

以Nagashima坝上游围堰为例,论述了CSG坝的施工优势,对CSG坝筑坝材料单价进行了计算,并与混凝土的单价进行了对比,分析了CSG坝存在的问题及其应用前景。     

Advanced Geometric Modeler with Hybrid Representation

An advanced geometric modeler GEMS4.0 has been developed,in which feature representation is used at the highest level abstraction of a product model.Boundary representation is used at the bottom level,while CSG model is adopted at the median level.A BRep data structure capable of modeling non-manifold is adopted.UNRBS representation is used for all curved surfaces,Quadric surfaces have dual representations consisting of their geometric data such as radius,center point,and center axis.Boundary representation of free form surfaces is easily built by sweeping and skinning method with NURBS geometry.Set operations on curved solids with boundary representation are performed by an evaluation process consisting of four steps.A file exchange facility is provided for the conversion between product data described by STEP and product information generated by GEMS4.0.     

振动法水泥稳定砾石的力学疲劳特性与强度标准

为确保振动法水泥稳定砾石(VTM-CSG)基层在交通荷载反复作用下不出现疲劳破坏,研究了VTM-CSG的疲劳特性与不同龄期的力学强度(无侧限抗压强度、劈裂强度与抗压回弹模量);基于路面荷载响应、VTM-CSG的力学与疲劳特性,结合Miner疲劳累积损伤理论,提出了抗疲劳开裂的VTM-CSG强度标准.结果表明:VTM-CSG力学强度随水泥剂量的增加呈线性增加、随养生龄期的延长呈非线性增长,采用骨架密实级配可提高VTM-CSG的力学强度;所建立的VTMCSG强度增长方程可较为精确地表征其强度增长特性;当试验条件受限时,可利用所建立的力学指标间的关系模型来预估其他力学强度.通过回归分析建立的VTM-CSG疲劳方程表明,在高应力水平下骨架密实级配VTM-CSG的疲劳性能优于悬浮密实级配VTM-CSG;提出了控制疲劳开裂的VTM-CSG的7d无侧限抗压强度标准与7d劈裂强度标准,该标准与路面结构、VTM-CSG的材料属性以及使用寿命相关联,实现了结构与材料一体化控制VTM-CSG基层开裂的目的.     

多直流馈入系统电压支撑强度指标及其在南方电网STATCOM配置方案研究的应用

采用EMTDC和BPA仿真工具,分析了动态无功设备对交流系统故障情况下直流逆变站母线电压和直流功率的影响。配置动态无功设备情况下故障后直流逆变站电压及功率恢复的时间加快,同一时刻直流逆变站电压及功率都比无动态无功设备情况下有所提高,且直流功率的增量与电压的增量基本呈比例关系。从有效抬高各逆变站的母线电压,改善直流功率的恢复特性,提高系统稳定性的角度出发,提出各母线对多回直流逆变站电压支撑强度的指标。该指标可以用于动态无功设备配置站点对多回直流支撑作用的敏感性分析。在该指标计算和系统稳定分析的基础上,提出了南方电网STATCOM的配置方案。该方案被采纳,相关工程已在2013年投产。     

南方电网500kV串补MOV压力释放事件分析

2008年以来,南方电网的500 kV串补站发生过多起金属氧化物限压器(metal oxide varistor,MOV)压力释放动作。在对这些事件进行统计分析的基础上,针对其中三起典型事件进行了事故原因分析。仿真计算表明,MOV吸收能量远小于其允许通流能力,吸收能量不是事故的原因。故障分析及MOV的解体研究表明,当系统发生短路故障时,MOV阀片在工频暂时过电压下发生沿面闪络,从而导致MOV压力释放动作。     

数字城市建设中单体建筑物三维模型的实现

介绍了CSG/B-rep混合模型的基本情况，以太原理工大学办公楼为例，利用OpenGL在VC 下建立模型，绘制和显示了三维图形，指出该混合建模手段的采用，对数字城市的建设具有重要的意义。