广州地铁四号线直线电机车辆柔性转向架

直线电机地铁车辆是我国城市轨道交通领域出现的新技术,其采用的柔性转向架是最有特点的地方。文章以广州地铁四号线车辆为例,对柔性转向架的曲线通过能力和直线电机运用进行分析。     

Curving performance simulation of an EMS-type Maglev vehicle

For electromagnetic suspension (EMS) type urban Maglev vehicles using a U-shaped electromagnet, the levitation and guidance forces are generated by only one electromagnet. Although the levitation force is actively controlled by changing the voltage of the electromagnet, the guidance force is passively determined by the levitation force. In addition, the curve negotiation performance of EMS-type urban Maglev vehicles using a U-shaped electromagnet must be considered, because an urban guideway may have some curves with shorter radii. It is, therefore, necessary to predict the curving performance with the greatest accuracy possible, in order to improve electromagnetic suspension and establish guideway design specifications. The objective is to establish a new dynamic modelling technique, so as to achieve more realistic curving simulation and thus to more accurately evaluate the curving performance of an EMS-type Maglev vehicle. The use of a full vehicle multibody dynamic model is proposed, and is applied to the evaluation of curving performance. Design changes are also investigated to obtain the bogie design directions for minimising variation in the lateral air gap, which is a criterion for curving performance.     

钽薄壁管焊接成形前期开口间隙场计算的有限元模型

为了控制钽薄壁管焊接成形的质量，进行钽薄壁管开口间隙场计算模型的研究。借助有限元方法、薄壳理论以及平板弯曲理沦，得到整体单元的刚度矩阵，建立了钽薄壁管开口间隙场计算的有限元模型。该模型精确描述了钽薄壁管焊前成形开口间隙的形状．利用该模型可以系统地研究钽薄壁管焊前成形的过程，为正确地选择成形工艺参数提供了理论依据。试验表明，理论计算与实测结果吻合得较好。     

低速大推力导管桨水动力性能预报及优化设计

为研究低速大推力导管桨水动力性能,应用商业软件Fluent,采用RANS方法结合k-ω湍流模型,开展了对原型和改型导管桨敞水状态下的数值计算。采用多运动参考坐标框架(MRF)技术,通过局部网格加密,来模拟桨叶和导管间的间隙流动。重点考察了设计工况点的水动力性能,压力分布等,通过计算分析,对导管桨(包括桨叶、导管以及前后定子)进行了优化设计。研究发现,导管桨在低速高负荷状态下,桨叶吸力面叶梢附近有很大的低压区。提高导管推力占比,可较大幅度提升推进效率。优化后置定子,能使效率得到一定提升。相关结果进行了试验验证,吻合良好,表明该数值研究方法可靠,具有广阔的工程应用前景。     

作业水深对浮式半潜平台波浪砰击的影响

结合模型试验,基于数值重构和外推的计算模型,采用时域全耦合分析方法,对浮式半潜平台全尺寸锚泊系统以及风、浪、流载荷的联合作用进行模拟,针对动力辅助锚泊定位平台与锚泊定位平台在不同作业水深下的波浪砰击进行对比研究。研究结果表明：浮式半潜平台关注点处波浪砰击次数受作业水深的影响敏感。平台在同等环境工况下,关注点处负气隙以及波浪砰击次数随着作业水深的增加而加剧。动力辅助锚泊定位平台较之于锚泊定位平台的随动性更好,可有效减小平台与水质点的相对运动,作业水深变化引起的动力辅助锚泊定位平台同一关注点的砰击次数、气隙变化以及改善幅值明显优于锚泊定位平台。在平台设计过程中,作业水深对平台气隙和波浪砰击的影响应引起重视。     

晶格常数的变化对FeNCN电子结构影响的第一性原理研究

采用第一性原理计算方法研究了c/a形变下FeNCN晶体的电子结构。结果表明在c/a形变下FeNCN晶体经历了半金属性到金属性的变化,当c/a不大于2.5时,FeNCN晶体表现为半金属性;当c/a大于2.5时,FeNCN晶体表现为金属性。Fe原子是晶体分子磁矩的最主要的贡献者,其自旋磁矩受c/a变化的影响程度较小。当FeNCN晶体表现为半金属性时,其分子磁矩能维持在稳定的整数值8.00μB;随着c/a的增加,分子磁矩逐渐减小。对c/a为2.3时FeNCN晶体电子结构的研究表明:此时自旋向上的子能带表现出间接带隙的半导体特征,晶体的半金属隙为0.11 eV。     

船舶柴油机拉缸检查和预防中的一些观点

在船厂安装和修理实践过程中,对船舶柴油机运行中出现的活塞拉缸现象进行检查和系统分析,得出存在问题的一般规律性以及主要原因,提出了一些改进意见和预防措施处理方法等。     

道岔缺口报警系统在地铁车辆段信号中的应用

道岔是信号系统的重要设备。在影响行车的信号故障中,道岔故障所占的比例很大,其中道岔缺口造成道岔失表示故障又是道岔的主要故障。通过对西安地铁2号线渭河车辆段道岔缺口报警系统的原理、构成及其设计等几个方面的介绍,说明了道岔缺口报警系统的使用不仅可以提前预防由于道岔缺口造成的道岔失表示故障,而且还可以解决长期以来运营维修人员用目测的方法检查和调整道岔缺口的落后手段以及降低运营维修人员的维修难度,缩短维修时间,提高工作效率。     

Meta-frontier function approach to operational efficiency for shipping companies

ABSTRACT

This study uses a meta-frontier function approach to estimate operational efficiency and technology gaps for shipping companies. Researchers have evaluated the relative efficiency of shipping firms with the assumption that shipping firms operate under one frontier technology. However, the assumption of one frontier technology is being argued by efficiency literature. Therefore, this study estimates relative efficiency of shipping firms in different market segments (dry bulk, liquid bulk, and containerized cargo), possibly operating with different technologies and, hence, under different frontiers. This study uses a meta-frontier function approach that allows us to distinguish separate frontiers for different groups and decompose efficiency scores relative to the meta-frontier. Data used in this study is collected from Thomson One Banker from 2001-2013 in the form of unbalanced panel data. Empirical results suggest that dry bulk firms’ production technology is more advanced than others and the production frontier is the closest to that of the meta-frontier. In addition, efficiency scores are all low, but containerized cargo firms achieve higher technological efficiency than the other two groups. It is also suggested that containerized cargo and liquid bulk firms should prioritize improvements in their production technology and dry bulk firms should prioritize improving group efficiency.     

高等级公路可接受间隙控制系统分析与构模

本文针对我国机动车辆构成的实际情况，科析高等级公路立交地段车流特性、可接受间隙控制系统组成和动作情况，并对系统进行了抽象简化，构造了控制系统分析模型。利用该模型，能够得出高等级公路上不同交通需求条件下控制系统的运行状况。模型适用性强，不但适用具有合流匝道入口控制，而且能用于单入口匝道控制系统分析，文中提出的系统评价指标反映实际，给出的分析示例说明了系统的有效性、正确性和通用性。