基于修正CS模型的船用低碳钢动态力学性能研究

为了得到船用低碳钢的动态力学性能及本构关系,运用静态试验机及分离式Hopkinson压杆加载装置,在应变率为0.000 2~3 900 s-1范围内得到了准静态拉伸及动态压缩条件下的应力应变曲线,对Cowper-Symonds材料模型进行了修正,得到了两种形式的本构关系,并讨论了模型的适用性。结果表明:船用低碳钢具有明显的应变率强化效应和非线性应变硬化效应;两种动态本构关系可以描述材料在冲击荷载下的力学性能;模型在高应变率(2 000 s-1)下的使用应慎重。     

青藏铁路战略地位和作用探析

青藏铁路格尔木至拉萨段的建成,标志着青藏铁路全线开通运营。从政治、经济、国防、科技、战略等方面分析探讨了青藏铁路的重要地位和作用,以期增强读者对青藏铁路重要性的认识和理解。     

“速度”是高成本时代的生产运营策略

在"中国制造"的成本优势正在或已经丧失、高成本时代到来时期,通过提高加工对象通过生产和流通过程的"速度"这一生产运营策略,来应对当前企业所面对的市场多变和高成本的困境,培育企业在生产运营领域的竞争优势。     

公路隧道节能减排技术

通过宏观视野来探讨公路隧道节能减排相关问题,提出公路隧道节能减排的基本概念,然后从经济和社会效益的平衡、节能技术产品推广应用、节能减排专项资金投入等6方面分析当前我国公路隧道节能减排存在的突出问题,总结影响公路隧道节能减排的主要因素,包括土建结构、机电设施、交通特点等,在此基础上从系统工程角度提出公路隧道节能减排措施与技术,包括结构节能、技术节能和管理节能。对我国公路隧道节能减排技术发展具有一定的参考价值。     

提速道岔尖轨与基本轨不密贴解决对策

依据分动钩式外锁闭装置技术标准规定,在分析了分动钩式外锁闭提速道岔的结构的基础上,对道岔尖轨与基本轨之间存在2mm不密贴间隙问题进行了探讨,提出了解决方案,并介绍了现场实际运用情况.     

The flight perturbation problem

Airlines spend considerable time, effort and financial resources on planning. It is essential to create a competitive timetable and construct a fleet and a crew schedule that utilizes these resources to the maximum. Unfortunately, it is all too common that an airline is faced with the necessity of reconstructing their schedules due to some unforeseen event, for example an aircraft breakdown or a crew member that is indisposed. In this paper, an application that can help airlines solve the complex problem of reconstructing aircraft schedules is presented. A mixed integer multicommodity flow model with side constraints is developed and further reformulated into a set packing model using the Dantzig—Wolfe decomposition. Cancellations, delays and aircraft swaps are used to resolve the perturbation, and the model ensures that the schedule returns to normal within a certain time. Two column generation schemes for heuristically solving the model are tested on real problem data obtained from a Swedish domestic airline. The computational tests show that the application is capable of presenting high quality solutions in a few seconds and therefore can be used as a dynamic decision support tool by the airlines.     

Incompleteness and clarity in bus contracts: Identifying the nature of the ex ante and ex post perceptual divide

In the transport sector, many types of contracts exist. Some are very precise, and strive for completeness; others are very ‘light-weight’ and are incomplete. Bus and coach contracts, won through competitive tendering or negotiation, are typically incomplete in the sense of an inability to verify all the relevant obligations, as articulated through a set of deliverables. This paper draws on recent experiences in contract negotiation, and subsequent commitment in the bus sector, to identify what elements of the contracting regime have exposed ambiguity and significant gaps in what the principal expected, and what the agent believed they were obliged to deliver. We develop a series of regression models to investigate the extent of discrepancy between the principal and the agents perceived ‘understanding’ of contract obligations. The empirical evidence, from a sample of bus operators, is used to identify the extent of perceived incompleteness and clarity across a sample of bus contracts. A noteworthy finding is the important role that a trusting partnership plays in reducing the barriers to establishing greater clarity of contract specification and obligations, and in recognition of the degree of contract completeness.     

Comparison of emerging ground propulsion systems for electrified aircraft taxi operations

Aviation is a mode with high fuel consumption per passenger mile and has significant environmental impacts. It is important to seek ways to reduce fuel consumption by the aviation sector, but it is difficult to improve fuel efficiency during the en-route cruise phase of flight because of technology barriers, safety requirements, and the mode of operations of air transportation. Recent efforts have emphasized the development of innovative Aircraft Ground Propulsion Systems (AGPS) for electrified aircraft taxi operations. These new technologies are expected to significantly reduce aircraft ground-movement-related fuel burn and emissions. This study compares various emerging AGPS systems and presents a comprehensive review on the merits and demerits of each system, followed with the local environmental impacts assessment of these systems. Using operational data for the 10 busiest U.S. airports, a comparison of environmental impacts is performed for four kinds of AGPS: conventional, single engine-on, external, and on-board systems. The results show that there are tradeoffs in fuel and emissions among these emerging technologies. On-board system shows the best performance in the emission reduction, while external system shows the least fuel burn. Compared to single-engine scenario, external AGPS shows the reduction of HC and CO emissions but the increase of NO_x emission. When a general indicator is considered, on-board AGPS shows the best potential of reducing local environmental impacts. The benefit-cost analysis shows that both external and on-board systems are worth being implemented and the on-board system appeals to be more beneficial.     

节点攻击下的海上联合作战网络鲁棒性研究

海上联合作战网络的鲁棒性是影响作战效能的关键因素之一。当某一兵力遭到攻击毁伤后,可能导致其余兵力任务或信息量超过其处理能力,即产生级联毁伤。本文以水面和水下多兵力协同作战为背景,构建由2个节点数相同的作战子网络构组成的双层相依网络。通过设定不同的相依模式和负载分配方式,获得海上联合作战网络鲁棒性的变化情况。仿真结果表明,对度正相关的作战网络,按初始比例分配任务和信息量能保证其鲁棒性最强;对于度随机相关或负相关的作战网络,需通过适当调整分配的非均匀比例来提高网络的鲁棒性。