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.     

某车型车轮定位参数异常问题的分析和解决

车轮定位参数直接影响汽车操稳性和轮胎磨损情况。设计正确的定位参数,生产上更好地控制各个参数,对提高汽车行驶的安全性,获得良好的操控型和乘坐的舒适性有着极为重要的意义。文章从力学角度阐述了车轮定位的基本理论,深入分析了悬架高度,前束,外倾,主销后倾等之间的关系,强调了良好的定位参数设计和生产上精确地控制对于悬架以及整车的重要性。以某车型悬架高度测量值超差为实例,通过对悬架高度定义,悬架高度对四轮定位参数判定的影响,分析了定位参数对整车判定的影响。从测量,装配,零件质量三个大方面分别对影响悬架高度的的因素进行了逐一分析和排查,找到引起车高测量超差的原因。理论计算出了补偿值作为短期措施;在图纸无要求的情况下,通过反向测量进口零件的方法分析对修改零件做出了正确的推断,并通过试验验证了推断的正确性,通过修改弹簧连杆使得车高测量值超差问题最终得到了解决。此外,通过对潜在因素进行了逐一分析,从整车角度比较全面地分析了车高超差的原因,对于今后此类问题的解决提供了一个系统的参考方案。     

基于协同环境下城市客车自顶向下设计

针对传统自底向上设计模式效率低的问题，研究基于三维CAD协同设计环境，借助公理设计理论（AD理论）的评审准则，构建模型数据层次构架；采用发明问题解决理论（TRIZ理论）的矛盾解决原理，协调模型构建过程冲突问题，从而建立协同环境下城市客车自顶向下设计的运行模式。为企业缩短产品开发时间，提升零部件通用性提供理论及实践参考。     

浅谈基于“理实一体化”的汽车专业实训基地建设研究

在中国"十二五"规划当中,汽车工业被明确列为中国的支柱产业,中国汽车销售量已经连续四年位居世界第一,已经变成了汽车生产与消费的成果。为此,汽车未来的发展市场十分巨大。将汽车的维修与营销当作基础,才能为汽车后续的市场提供更多的商机。面对这样的市场,高职学院在培养汽车后市场人才方面发挥着十分重要的作用。文章应该将重点放在研究汽车专业人才培养的实训教育中,从而推动"理实一体化"实训基地建设的发展。     

道路路阻函数模型及适用性研究

交通诱导系统中两节点间最优路径的选择是目前的一个难点问题,其中路阻函数的确定是路径优化的核心内容.针对交通流由畅通状态到拥挤状态再到堵塞状态的过程,应用经典交通流理论和实际调查数据,构建交通流诱导系统分段路阻函数模型,以q=10veh/h为一个单位,对函数进行分段拟合,构建高速公路和城市快速路下的分段路阻函数,并对其适应性进行拟合分析.应用结果表明:在不同的流量范围内,高速公路和城市快速路分段路阻函数在自由流状态、高密度状态和低密度条件下适合不同的分段函数.     

课程设计在汽车理论教学改革中的探讨

针对现阶段汽车理论实践教学,结合课程特点,提出应当将汽车理论课程设计引入常规教学活动。然后探讨了课程设计中技术要求、任务书的合理性、课程监督以及教师教学反思的有效途径,从而提高教学质量,改善教学效果,激发学生学习迁移。     

共享停车泊位的分配-定价-收益分配机制

为科学管理共享停车资源,构建一种共享停车泊位的分配-定价-收益分配机制。首先,以存在多个地块的区域为对象,根据出行者对不同地块及停车时间模式的选择偏好构建停车许可证的最优分配-定价模型,其中,最优分配模型为组合拍卖竞胜标确定问题(NP困难问题)。其次,利用Benders分解原理、对偶理论及新型升价拍卖代理系统构建调优法对停车许可证进行拍卖。最后,为调动共享泊位提供者的积极性,利用沙普利值法构建基于对社会福利贡献程度的停车收益分配模型。由理论分析及数值试验可知,运用上述机制可精确实现社会福利最优状态,最小竞争均衡价格与公平的收益分配。结果表明:①相较VCG机制与Leonard机制,调优法不仅可精确求解停车许可证的最优分配-定价,而且在算法最坏时间复杂度方面拥有更高效率;②在调优法的每个步骤中,即使停车许可证的分配并非最优,通过机制所实现的收费定价依然具有防止策略性操作的重要性质;③调优法可在较少的步骤之内实现较高的社会福利;④新型升价拍卖代理系统拥有多项式型的最坏时间复杂度;⑤通过最优分配-定价机制可获得每位出行者的选择偏好,进而可计算不同泊位提供者组合条件下的社会福利,实现沙普利值法在现实应用中的可计算性。     

基于顾客价值的高速公路市场营销模式

以广州北环高速公路为研究对象，对其高速公路市场营销模式进行分析研究。通过分析，得出该公司成功的最大原因是基于顾客价值链，在高速公路出人口周边经济带中有意识培育关联产业，有针对性地开发高盈利能力的顾客，最大限度吸引和稳住自己的盈利顾客群体，从而培育了自己的核心竞争能力，确保了收入和效益的稳定增长。     

基于生态理论的汽车零部件产业动态演化研究

零部件产业是发展汽车工业的基础，没有强大的汽车零部件产业，就不可能有强大的汽车工业。在对我国汽车零部件产业的发展现状进行分析的前提下，应用生态理论结合汽车零部件行业发展面临的问题进行了研究．分析了我国汽车零部件产业动态演化的规律。     

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.