优化查询的数据库非规范化设计

数据库系统的实际应用更注重查询性能,为满足其性能要求,在简单介绍数据库设计的规范化理论及其意义的基础上,提出能满足数据库的完整性和一致性要求的非规范化设计的基本思想和技术,并在教务和资产管理系统中得到应用,取得良好效果。     

A tool to aid redesign of flexible transport services to increase efficiency in rural transport service provision

Rural areas generally have lower and more dispersed demands for travel which cannot sustain conventional public transport services and consequently have a greater number of flexible and demand responsive transport services operating. These services usually operate on a stand-alone basis, are often subsidized and are typically only accessible by certain passenger types or for specific trip purposes. This generally results in uncoordinated and inefficient transport provision overall. The Flexible integrated transport services (FITS) system featured in this paper has been designed to address this problem. FITS can be used as a planning tool to assess potential benefits from relaxing operating constraints (e.g., a service's operating boundaries), which can potentially suggest service redesign. It also includes the capacity to assign subsidy payments on a trip by trip basis to increase cost efficiency whilst meeting a greater proportion of transport needs. The case study in the paper focusses on transport to health in the Aberdeenshire and Morayshire areas of Scotland in the UK. Despite flexible transport operators receiving public funds to meet passenger needs, this is currently being supplemented by public bodies paying large amounts in taxi fares in instances where there is a statutory obligation to provide travel but where no other suitable transport service exists. The results demonstrate the potential substantial savings which could be realized by allowing transport operators to redesign their services by relaxing constraints and by the reassignment of subsidies: resulting in more passenger demands being met and a reduction in public spending on taxi fares.     

Signal coordination model for local arterial with heavy bus flows

Conventional Transit Signal Priority (TSP) controls often reach the limitation for arterials accommodating heavy bus flows since the priority function can significantly increase delay at minor streets. Under such conditions, a proper signal progression plan that accounts for the benefits of buses may offer the potential to improve the reliability of bus operations and increase the bus ridership. This study proposes a bus-based progression model to reduce the delay of buses on local arterials. Given the cycle length and green splits at each intersection, the bus-based progression model, grounded on the same notion as conventional signal progression methods, considers the operational characteristics of transit vehicles, such as the impact of bus dwell time and the capacity constraints at bus stops. Also, to deal with the stochastic nature of dwell time, this study introduces additional constraints to maximize the percentage of buses which can stay within the green band after leaving bus stops. Taking an arterial with five intersections and three two-way bus stops as an example, this study applies VISSIM as an unbiased tool for model evaluation. The simulation results demonstrate that the proposed model can significantly reduce bus passenger delays and the average person delays for the entire arterial, compared with the conventional progression models.     

基于Adams/Car的汽车操纵稳定性仿真分析

操纵稳定性优劣对评价一款车型性能好坏具有重要影响,而稳态回转试验在评价操纵稳定性方面具有作用。本文针对市场上较热门的某款车型进行操纵稳定性验证分析,首先运用MSC.ADAMS/Car软件建立了该车型多体动力学模型,并进行稳态回转仿真试验分析,得到了车辆的稳态响应性能,最后验证该车的操纵稳定性。     

隧道控制爆破深大减振孔减振效果对比

浅埋暗挖车站下穿岩石地层大多采用钻爆法施工,不可避免地对周边建(构)筑物产生振动效应。以青岛地铁某浅埋暗挖车站为例,为避免爆破施工对周边加油站等高爆炸隐患工程影响过大,施工中采取布设减振孔措施,现场开展减振孔减振效果测试试验,在受保护区打286个减振孔,对受保护区监测点和与爆心相同距离的非保护区监测点同时进行连续15 d爆破振速监测,对监测数据进行对比分析。研究结果表明:减振孔措施有效降低了爆破振动对周边环境的影响,振速平均衰减比例达到35.4%,较好地保证了周边高风险建(构)筑物的安全。     

连接片阻值对电动汽车用动力电池性能的影响

鉴于单体电池间连接片的阻值和极柱的位置影响单节电池的性能,基于Matlab/Simscape开发了单体电池模型,并利用此模型和以电阻模拟的连接片构建了单节电池模型,仿真分析了连接片阻值对单节电池性能的影响。结果表明,连接片的存在使与极柱相连的单体电池最先达到电池管理系统设定的放电截止电压,以致影响电池的性能;与极柱相连的单体电池的率先老化导致与其相邻的单体电池出现过放电的现象,影响单节电池的安全性。最后,设定各单体电池SOC间最大偏差为0.05,对不同并联电池数目的单节电池进行仿真,得出连接片与电池欧姆内阻阻值的合理比例。     

地震作用下考虑土-桥台-上部结构相互作用的大跨桥梁伸缩缝处碰撞效应研究

为了给大跨桥梁抗震设计提供参考,针对西部山区强地震带常见的高墩大跨桥梁,考虑土-桥台-上部结构相互作用以及支座的滑动效应,采用非线性时程法对地震作用下大跨桥梁伸缩缝处碰撞效应进行了研究。采用非线性弹簧模拟桩基-土体相互作用以及台背填土的弹塑性变形,采用双线性滞回模型模拟支座的滑动效应,并采用接触单元法模拟主、引桥梁体间以及引桥梁体-桥台背墙间的碰撞反应。研究结果表明:主、引桥梁体间以及引桥梁体-桥台背墙间若发生连锁碰撞效应,桥台背墙将会遭受较大的撞击力作用,过大撞击力使得台背纵向位移、台后填土塑性变形以及桥台桩基的地震响应显著增大,易引起引桥桥台破损、桩基断裂以及引桥梁体落梁等震害。     

公路桥梁随机车流的平稳性和各态历经性检验

根据6条公路桥梁28条车道上的WIM系统实测车辆信息,分别生成了各车道上的随机车流类型过程.用随机过程理论分别计算得到各随机车流类型过程的集合均值、集合相关函数、时间均值、时间相关函数等随机特性参数.进一步对比分析,验证了所建立的随机车流类型过程的平稳性和各态历经性.结果表明:从实际公路上调查一定数量的车辆,其统计特性能够代表总体样本的车流信息,对车辆各种特征的统计结果具有代表性,可为公路桥梁随机车辆荷载模型的建立提供参考.     

插电式四驱混合动力轿车控制策略研究

根据插电式四驱混合动力轿车在各种工况下的工作模式,确定了各个动力部件的转矩分配,以此为依据制定了此混合动力轿车基于逻辑门限值的控制策略,并在有限状态机Statefl ow中搭建了控制策略的核心状态流图,然后使用Cruise进行了仿真并对仿真结果进行了评价。仿真结果表明,汽车的动力性以及经济性都达到了设计指标要求,在NEDC下验证时,不论是在高电量区还是在低电量区,各动力部件均按照控制策略来工作,并且实现了各种工作模式的转换,控制策略有效而可行。     

“观察者模式”与售后诊断系统实时显示开发

根据售后诊断软件系统分层结构,结合业务数据链路采集,分析了车辆ECU实时显示数据在诊断系统用户显示层功能开发中出现的数据遗漏问题。结合C#编程中的"观察者模式",解决了实时显示功能设计中的一对多耦合关系问题,并通过数据采集试验验证了设计的可行性。