脉冲风洞测力系统结构动力学特性

脉冲风洞试验过程时,试验气流引起测力系统强烈振动对测试结果产生严重干扰. 为解决测力系统振动对测力结果干扰的问题,首先根据测力系统结构特点建立了相应的动力学模型;其次,对其进行了虚拟标定和模态分析;第三,对测力系统进行了瞬态分析和惯性补偿,获得了相应的瞬态输出;最后,对测力系统进行了风洞试验,分别获得了相应的弹性输出结果和惯性输出结果. 分析和试验结果表明:惯性补偿后,测力系统均值测量精度略有提高,瞬态测量精度大幅提高;惯性补偿后瞬态测量精度最低为87.4%,出现在测力系统共振时,其他状态下,瞬态测量精度超过91%;惯性补偿后的测力系统输出结果振动基本消失,说明惯性补偿方法能够消除振动对输出结果的干扰.      

FLUENT软件对管壳式换热器壳程流体数值模拟方法可行性的验证

鉴于单弓形折流板管壳式换热器应用的广泛性,对传统单弓形折流板管壳式换热器进行了数值模拟分析,验证了FLUENT软件应用到管壳式换热器壳程流体数值模拟方法的可行性,并为换热器其它壳程支撑结构的研究提供了一定的理论依据.     

Statistical characteristics of transitional queue conditions in signalized arterials

The performance of signalized arterials is related to queuing phenomena. The paper investigates the effect of transitional traffic flow conditions imposed by the formation and dissipation of queues. A cross-recurrence quantification analysis combined with Bayesian augmented networks are implemented to reveal the prevailing statistical characteristics of the short-term traffic flow patterns under the effect of transitional queue conditions. Results indicate that transitions between free-flow conditions, critical queue conditions that exceed the detector’s length, as well as the occurrence of spillovers impose a set of prevailing traffic flow patterns with different statistical characteristics with respect to determinism, nonlinearity, non-stationarity and laminarity. The complexity in critical queue conditions is further investigated by introducing two supplementary regions in the critical area before spillover occurrence. Results indicate that the supplementary information on the transitional conditions in the critical area increases the accuracy of the predictive relations between the statistical characteristics of traffic flow evolution and the occurrence of transitions.     

基于位置反馈控制的电子节气门控制系统研究

以Infineon XC167为主芯片控制电子节气门,设计了直流电机驱动电路,开发了电子节气门控制系统的硬件电路。设计了模糊智能PID控制器,提出了电子节气门的控制策略。通过电子节气门阶跃响应试验和油门位置与节气门位置试验,验证了该控制系统可以实现节气门位置反馈的闭环控制。     

电喷汽油机燃用甲醇-汽油混合燃料的排放及催化转化特性研究

研究了多点电喷汽油机燃用不同掺混比的甲醇汽油混合燃料时的排放及催化器的转化性能。研究结果表明:在汽油机参数未做任何调整的情况下,甲醇对催化器前的CO、HC和NOx排放及其催化转化效率的影响与汽油机的转速、负荷和空燃比控制策略有关;随着甲醇汽油混合燃料中甲醇含量的增加,未燃甲醇的排放量变化不大,甲醛排放量增大,乙醇的排放量略有降低,乙醛的排放量很低并基本保持不变;醇、醛类排放经过三效催化转化器后基本接近零排放水平。     

CNG/汽油双燃料汽车燃气ECU的设计

介绍所设计的双燃料汽车燃气电控模块的组成、原理及设计过程,将该电控模块与原车的ECU和氧传感器一起构成闭环控制系统,可实现对燃气喷气量的精确控制。通过利用原车ECU的控制策略,可缩短开发周期,节约开发成本。通过试验验证了所设计的燃气ECU的控制性能。     

以截面平衡原理分析各种桥型结构体系

从材料力学中构件截面抗弯、抗剪平衡原理出发，分析桥梁的横截面、纵向桥型体系的受力特点，并以梁的受力方式来理解常用的纵向受力体系，如拱、斜拉、悬索等结构体系，称之为“等代梁”。从而将常见桥型分为两类：按正弯矩设计的体系，如简支梁、拱桥、悬索桥；按负弯矩设计的体系，如T构、连续梁、连续刚构和斜拉桥。提出了以组合体系来解决目前常见大跨径梁式桥常见病害的看法。     

Modelling route choice behaviour in multi-modal transport networks

The paper presents new findings on the influence of multi-modal trip attributes on the quality and competitiveness of inter-urban multi-modal train alternatives. The analysis covers the entire trip from origin to destination, including access and egress legs to and from the train network. The focus is on preferences for different feeder modes, railway station types and train service types as well as on the relative influence of time elements and transfer penalties. Data from dedicated surveys are used including individual objective choice sets of 235 multi-modal homebound trips in which train is the main transport mode. The observed trips have origins and destinations within the Rotterdam–Dordrecht region in The Netherlands with an average total trip time of 50 minutes. Hierarchical Nested Logit models are estimated to take account of unobserved similarities between alternatives at the home-end and the activity-end of the trip respectively, resulting in two-level nesting structures which differentiate between intercity (IC) and non-intercity railway station types at the upper level and between transit and private access modes at the lower level. In order to reflect the multi-dimensional structure of the data a more advanced so-called Multi-Nested GEV model according to the Principles of Differentiation has been estimated which significantly improves the explanatory power and stresses the importance of the home-end of the multi-modal trip.     

Rural mobility and mode choice: Evidence from the 2001 National Household Travel Survey

This article uses data from the 2001 National Household Travel Survey (NHTS) to compare travel behavior in rural and urban areas of the U.S. As expected, the car is the overwhelmingly dominant mode of travel. Over 97% of rural households own at least one car vs. 92% of urban households; 91% of trips are made by car in rural areas vs. 86% in urban areas. Regardless of age, income, and race, almost everyone in rural areas relies on the private car for most travel needs. Mobility levels in rural areas are generally higher than in urban areas. That results from the more dispersed residences and activity sites in rural areas, which increase trip distances and force reliance on the car. Somewhat surprisingly, the rural elderly and poor are considerably more mobile than their urban counterparts, and their mobility deficit compared to the rural population average is strikingly less than for the urban elderly and poor compared to the urban average. Data limitations prevented a measurement of accessibility, however, and it seems likely that rural areas, by their very nature, are less accessible than urban areas, especially for the small percentage of car-less poor and elderly households.     

Contents Volume 32 2005

Contents Volume

Contents Volume 32 2005