A decomposition approach to determining fleet size and structure with network flow effects and demand uncertainty

This paper presents a new methodology to determine fleet size and structure for those airlines operating on hub‐and‐spoke networks. The methodology highlights the impact of stochastic traffic network flow effects on fleet planning process and is employed to construct an enhanced revenue model by incorporating the expected revenue optimization model into fleet planning process. The objective of the model is to find a feasible allocation of aircraft fleet types to route legs using minimum fleet purchasing cost, thus ensuring that the expected fleet profit is maximized subject to several critical resource constraints. By using a linear approximation to the total network revenue function, the fleet planning model with enhanced revenue modeling is decomposed into the nonlinear aspects of expected revenue optimization and the linear aspects of determining fleet size and structure by optimal allocation of aircraft fleet types to route legs. To illustrate this methodology and its economic benefits, an example consisting of 6 chosen aircraft fleet types, 12 route legs, and 57 path‐specific origin‐destination markets is presented and compared with the results found using revenue prorated fleet planning formulation. The results show that the fleet size and structure of the methodology proposed in this paper gain 211.4% improvement in fleet profit over the use of the revenue prorated fleet planning approach. In addition, comparison with the deterministic model reveals that the fleet size and structure of this proposed methodology are more adaptable to the fluctuations of passenger demands. Copyright © 2016 John Wiley & Sons, Ltd.     

��������·��·����ά�޼ƻ��Ż�ģ��

制定铁路线路养护维修计划既要保证线路充分维修,又要兼顾经济效益.为此,以区域路网为研究对象,建立了基于整数规划的铁路线路养护维修计划优化模型.模型考虑了路网中线路之间维修资源的约束,以维修时间和股道占用状态为决策变量,以股道占用费用、维修费用及惩罚费用总和最小化为目标,通过集中安排线路中各项养护维修活动节省维修支出,减少维修活动对股道的占用时间进而达到优化目的.基于启发式算法设计了模型求解方法,仿真实验结果表明,模型具有较好的实用性,能够为编制铁路线路年度养护维修计划提供决策支持.     

直线感应电机模型分析与转差频率控制研究

介绍了考虑端部效应后直线感应电机在两相同步旋转坐标系下的数学模型,并对速度与反应板对端部效应的影响进行了分析。在此基础上讨论了直线感应电机转差频率控制方案的可行性,并给出了控制方案。采用Matlab／Simulink构建了直线感应电机数学模型并对其转差频率控制进行了仿真。仿真结果验证了控制方案的可行性。     

联锁块软体排深水沉排受力的线性有限元分析

长江南京以下12.5 m深水航道一期工程在狼山沙左缘的铺排工程中,遇到流速2 m/s及水深达30 m的沉排条件,使排体受力十分复杂。设计中通过对软体排沉排过程的受力状态进行有限元分析,提出了排体所受水流力的大小与移船距离的相对关系;通过分析深水铺排施工要点,优化排体设计方案。     

直左复线有轨电车干线可变带宽绿波模型

为降低有轨电车在交叉口的停车次数和交通延误,同时兼顾社会车辆通行效率,提出可容纳直行线路、左转线路有轨电车和社会车辆3类绿波系统的干线信号协调控制方法.设计直左轨道分叉交叉口的4种信号相位组合方案,构建社会车辆绿波系统、有轨电车直行线路和左转线路绿波系统的约束条件,以及3个绿波系统的交互性约束条件.基于可变绿波带宽优化...     

浅谈高速公路路线线形设计与行车安全

高速公路线形指标的合理选择不但有利于行车安全,也有利于路基工程稳定和环境景观,坚持“以人为本”、“安全至上”、“环保优先”的原则,更新设计理念,搞好山区高速公路的线形设计,使公路路基与地形地貌相吻合,避免高填深挖工程,为行车安全和环境保护做出贡献。     

Analysis of peak and non‐peak traffic forecasts using combined models

Accurate and timely traffic forecasting is crucial to effective management of intelligent transportation systems (ITS). To predict travel time index (TTI) data, we select six baseline individual predictors as basic combination components. Applying the one‐step‐ahead out‐of‐sample forecasts, the paper proposes several linear combined forecasting techniques. States of traffic situations are classified into peak and non‐peak periods. Based on detailed data analyses, some practical guidance and comments are given in what situation a combined model is better than an individual model or other types of combined models. Indicating which model is more appropriate in each state, persuasive comparisons demonstrate that the combined procedures can significantly reduce forecast error rates. It reveals that the approaches are practically promising in the field. To the best of our knowledge, it is the first time to systematically investigate these approaches in peak and non‐peak traffic forecasts. The studies can provide a reference for optimal forecasting model selection in each period. Copyright © 2010 John Wiley & Sons, Ltd.     

沥青混合料疲劳响应模型试验研究

首先总结分析了沥青混合料不同疲劳试验方法的特点、两种疲劳试验控制模式的适用范围,建议采用应力控制模式的间接拉伸疲劳试验方法。然后分析了不同试验因素的影响,选定了加载波型,确定了疲劳试验的应力比水平、频率及温度等试验参数的范围。采用旋转压实成型方法,对3种沥青混合料进行试件成型。分别考虑3种空隙率水平,应用均匀试验设计方法,进行了不同温度、频率、应力比水平下的间接拉伸疲劳试验,对试验结果进行了显著性分析,并应用多元线性回归方法,得到了适用于不同荷载条件下基于温度、频率、沥青饱和度、初始应变及初始劲度模量的沥青混合料疲劳模型。与国外疲劳模型进行了对比分析,表明得到的疲劳模型具有较好的比对性,可用于沥青混合料疲劳寿命的预估。     

快速整周模糊度求解技术在高精度GPS定位和导航中的应用

给出了GPS卫星测量模型，分析误差源，并推导出差分值，以便提高GPS的精度。求解GPS载波相位整周模糊度是高精度定位和导航的关键。计算效率至关重要，因为它直接影响求解模糊度的时间，而且还影响模糊度求解过程的可靠性。分析了搜索空间中的独立变量，并推导出新的传递矩阵。该矩阵将所有的测量残差直接和最小求解搜索空间相关联。该技术不仅可以改善计算效率以及缩短模糊度求解时间，还能提高可靠性。通过仅选择那些与卫星几何尺寸和测量残差一致的模糊度的组合，搜索空间被最小化，应用于高精度定位和导航。     

复杂条件下超大跨地铁车站施工仿真技术研究

研究目的：研究复杂条件下超大跨浅埋暗挖地铁车站施工时,不同施工工序下开挖引起的地层扰动对地表沉降及拱顶下沉的影响规律。研究方法：以某超大跨浅埋暗挖地铁车站作为工程背景,利用ANSYS有限元软件作为开发平台,以浅埋暗挖隧道开挖支护理论为基础,采用平面应变模式,对双层两柱暗挖结构的三跨连拱隧道开挖支护全过程进行非线性仿真研究。研究结果：仿真计算结果与现场监测数据基本吻合,可以指导该类型隧道施工的地层沉降仿真研究、施工作业及信息化施工。研究结论：地表沉降影响范围约3倍洞径,最大沉降量为20.75 mm,拱顶最大下沉量为29.93 mm;超大跨隧道分部开挖“群洞效应”明显,在“上软下硬”围岩地层中,地层变形控制的关键工序是上部软岩断面的开挖支护,下部断面要减少爆破振动对地层变形的影响;大跨隧道开挖支护中,不同分部开挖引起的沉降量及沉降槽宽度是不同的。