A kinematic wave approach to traffic statics and dynamics in a double-ring network

Recently there has been much interest in understanding macroscopic fundamental diagrams of stationary road networks. However, there lacks a systematic method to define and solve stationary states in a road network with complex junctions. In this study we propose a kinematic wave approach to defining, analyzing, and simulating static and dynamic traffic characteristics in a network of two ring roads connected by a 2 × 2 junction, which can be either an uninterrupted interchange or a signalized intersection. This study is enabled by recently developed macroscopic junction models of general junctions. With a junction model based on fair merging and first-in-first-out diverging rules, we first define and solve stationary states and then derive the macroscopic fundamental diagram (MFD) of a stationary uninterrupted network. We conclude that the flow-density relationship of the uninterrupted double-ring network is not unique for high average network densities (i.e., when one ring becomes congested) and unveil the existence of infinitely many stationary states that can arise with a zero-speed shockwave. From simulation results with a corresponding Cell Transmission Model, we verify that all stationary states in the MFD are stable and can be reached, but show that randomness in the retaining ratio of each ring drives the network to more symmetric traffic patterns and higher flow-rates. Furthermore we model a signalized intersection as two alternate diverge junctions and demonstrate that the signalized double-ring network can reach asymptotically periodic traffic patterns, which are therefore defined as “stationary” states in signalized networks. With simulations we show that the flow-density relation is well defined in such “stationary” states, and asymptotic traffic patterns can be impacted by signal cycle lengths and retaining ratios. But compared with uninterrupted interchanges, signalized intersections lead to more asymmetric traffic patterns, lower flow-rates, and even gridlocks when the average density is higher than half of the jam density. The results are consistent between this study and existing studies, but the network kinematic wave model, with appropriate junction models, is mathematically tractable and physically meaningful. It has offered a more complete picture regarding the number and type of stationary states, their stability, and MFD in freeway and signalized networks.     

基于存储论的高速公路通行卡库存管理研究

为了提高高速公路通行卡的流转效率,提出了一种基于存储论的高速公路通行卡库存管理模型。利用高速公路复合通行卡CPC历史流转数据,基于自回归移动平均模型（Autoregressive Integrated Moving Average Model, ARIMA),对CPC卡需求量及流转量进行预测。该模型结合存储论的方法与思想,提出库存管理周期以及最大库存、预警值及最佳订购/调拨量等相关参数,实现了库存管理的动态调整。最后进行实例分析,得出基于存储论的库存管理模型对通行卡需求量与流转量的预测误差分别为7.4%和11.5%,表明该模型预测精度较高且能够根据通行卡流转情况动态调整各相关变量,减少了收费站库存成本,提高了通行卡使用效率以及高速公路服务水平。     

基于X-CT技术的沥青混合料三维数值化试样重建

为了对沥青混合料内部结构进行三维重构,采用德国Compact-225型工业X-CT扫描混合料试件,实现试件的三维可视化,计算出集料、砂胶、空隙的体积组成。采用自行编写的程序,实现了由三维可视化模型向三维数值化模型的转化。提出了边界空隙率的概念,通过设置一定的边界空隙率,使模型的边界空隙分布符合实际试样的空隙分布。建立了基于实际试样真实内部微细观分布的数值化试样,弥补了传统的数值方法采用统计学原理或采用对试件损伤研磨建立三维细观模型的不足,为数值化测试奠定了重要基础。     

A fast-simplified wheel–rail contact model consistent with perfect plastic materials

A method is described which is an extension of rolling contact models with respect to plasticity. This new method, which is an extension of the STRIPES semi-Hertzian (SH) model, has been implemented in a multi-body-system (MBS) package and does not result in a longer execution time than the STRIPES SH model [J.B. Ayasse and H. Chollet, Determination of the wheel–rail contact patch in semi-Hertzian conditions, Veh. Syst. Dyn. 43(3) (2005), pp. 161–172]. High speed of computation is obtained by some hypotheses about the plastic law, the shape of stresses, the locus of the maximum stress and the slip. Plasticity does not change the vehicle behaviour but there is a need for an extension of rolling contact models with respect to plasticity as far as fatigue analysis of rail is concerned: rolling contact fatigue may be addressed via the finite element method (FEM) including material non-linearities, where loads are the contact stresses provided by the post-processing of MBS results [K. Dang Van, M.H. Maitournam, Z. Moumni, and F. Roger, A comprehensive approach for modeling fatigue and fracture of rails, Eng. Fract. Mech. 76 (2009), pp. 2626–2636]. In STRIPES, like in other MBS models, contact stresses may exceed the plastic yield criterion, leading to wrong results in the subsequent FEM analysis. With the proposed method, contact stresses are kept consistent with a perfect plastic law, avoiding these problems. The method is benchmarked versus non-linear FEM in Hertzian geometries. As a consequence of taking plasticity into account, contact patch area is bigger than the elastic one. In accordance with FEM results, a different ellipse aspect ratio than the one predicted by Hertz theory was also found and finally pressure does not exceed the threshold prescribed by the plastic law. The method also provides more exact results with non-Hertzian geometries. The new approach is finally compared with non-linear FEM in a tangent case with a unidirectional load and a complete slip: when plasticity is taken into account, and for large adhesion values, friction forces have an influence on the size of the contact patch. The proposed approach enables also to assess extensively the level of plasticity along a track through an indicator associated with a given yield stress.     

基于三维各向异性扩散的图像平滑及三维重构效果分析

为了实现理想的三维重构效果,在重构前需要对切片集进行预处理。主要研究各向异性扩散的平滑方法,并将二维各向异性扩散平滑技术向三维空间进行推广,并就二维和三维各向异性扩散平滑技术对三维重构效果进行了分析,结果表明三维各向异性扩散具有更好的各向协同的平滑效果。     

正六角形蜂窝芯层面内等效弹性参数研究

由于蜂窝芯层结构在外载作用下,蜂窝胞元壁板不但会产生弯曲变形,而且也会产生伸缩变形和剪切变形。过去Gibson公式在计算蜂窝芯层等效参数时只考虑了弯曲变形,虽然简便,但在导致蜂窝芯层分析时,弹性矩阵会出现不确定性;后来,宋明慧公式在Gibson公式的基础上,进一步考虑了伸缩变形的影响,但由于没有考虑剪切变形的影响,导致的蜂窝芯层结构不稳定,而且简化的弹性矩阵会出现奇异。该文新推导的面内等效弹性参数理论计算公式考虑了弯曲变形、伸缩变形和剪切变形对面内等效刚度的影响,是对Gibson和宋明慧公式的修正,克服了他们公式上的缺陷。     

基于虚拟现实技术的商品展示平台研究

虚拟现实有效地模拟人在自然环境中的各种主观感官,是一种新型的人机交互体验方式。介绍了虚拟商品展示平台实现过程中的关键技术,设计出在Web环境下进行商品虚拟展示的功能模块。此外,借助3D Max和Virtools对三维模型的构建、贴图及交互控制脚本的设计进行了重点阐述。最后,设计结果被发布成网页形式,并通过了系统测试。测试结果表明:设计方案可行且运行效果良好。     

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以北京交通大学中国综合交通研究中心的成立为契机,围绕“综合交通基础理论与基础平台建设”主题,阐述了交通发展的综合化、一体化趋势,以及交通与经济、能源、环境以及科技创新的关系。指出不仅要对交通技术进行综合,也要对行政管理进行综合。分析了系统科学对智能交通研究的启示,以及综合交通中的相关影响因素。结合铁路、水运、公路、航空、管道不同运输方式的综合,交通枢纽内部不同换乘方式的综合,城市交通中不同出行方式的综合等,探讨了复杂大系统理论在综合交通研究中的应用前景,以及建设综合交通基础平台的重要意义。     

基于大质量法的太湖隧道三维地震动响应分析

以太湖隧道为工程背景,运用大质量法建立类矩形隧道结构的三维地震动分析模型,研究在水平地震作用下隧道结构的内力变化规律及位移响应规律。研究表明:1)类矩形断面结构在水平向地震作用下的结构内力在侧墙底部最大,且弯矩是主要控制内力;2)过渡段1和过渡段2是隧道结构在地震作用下受力的薄弱点,且过渡段1产生的内力最大;3)从浅埋段至深埋段,隧道结构顶底板层间位移角逐渐增大,最大层间位移角均小于规范限值。研究成果可为太湖隧道的抗震设计提供参考。     

“互联网+”背景下“以证、赛促学”的“三维建模技术应用”课程混合式教学模式的实践与探索

本研究在分析"三维建模技术应用"课程特点的基础上,在教学中利用"互联网+"时代下的丰富网络教学资源,探索了一种"以证书、竞赛来促进教学"教学实践,并使用了"PBL+翻转课堂"的混合教学模式,提供了一种新的教学思路和途径。