Characterization and prediction of air traffic delays

This paper presents a new class of models for predicting air traffic delays. The proposed models consider both temporal and spatial (that is, network) delay states as explanatory variables, and use Random Forest algorithms to predict departure delays 2–24 h in the future. In addition to local delay variables that describe the arrival or departure delay states of the most influential airports and links (origin–destination pairs) in the network, new network delay variables that characterize the global delay state of the entire National Airspace System at the time of prediction are proposed. The paper analyzes the performance of the proposed prediction models in both classifying delays as above or below a certain threshold, as well as predicting delay values. The models are trained and validated on operational data from 2007 and 2008, and are evaluated using the 100 most-delayed links in the system. The results show that for a 2-h forecast horizon, the average test error over these 100 links is 19% when classifying delays as above or below 60 min. Similarly, the average over these 100 links of the median test error is found to be 21 min when predicting departure delays for a 2-h forecast horizon. The effects of changes in the classification threshold and forecast horizon on prediction performance are studied.     

Simulating pedestrian movements at signalized crosswalks in Hong Kong

This paper presents a new pedestrian simulation (PS) model for signalized crosswalks in Hong Kong. This PS model is capable of estimating the variations of walking speed particularly on the effects of bi-directional pedestrian flows so as to determine the minimum required duration of pedestrian crossing time. Video records taken from the observational surveys at the selected crosswalk in urban area were used to extract the required data for model calibration. It was found that the design walking speed for signalized crosswalks should be varied by the effects of the bi-directional pedestrian flows. It was also interesting to note that the negative impact of the bi-directional flow effects (ranging from uni-directional to bi-directional pedestrian flows) on the chance of pedestrian crossing the crosswalk is increasing from free-flow to at-capacity flow conditions. The new PS model is also validated using an independent data set so as to examine the reliability of the simulation results. The validation results show that the new PS model can provide an accurate evaluation on the changes of walking speed and its standard deviation under different scenarios with particular emphasis on the effects of the bi-directional pedestrian flows. The advancement of this PS model can be applied to assess the effects of each improvement measure and to evaluate the benefits of each scenario in practice.     

基于空间计量模型的机场网络溢出效应研究

机场对区域经济发展具有重要支撑作用,但从航线网络视角进行研究的文献还比较少.本文建立了空间面板计量模型,以中国大陆 45个主要枢纽机场为例定量研究了机场对区域经济的直接效应、网络溢出效应和总体效应.研究表明：机场客运量对区域经济具有显著正向网络溢出效应,客运量每提高 10%,其网络溢出效应达到 8.25%;货运量仅对本地城市 GDP具有正向影响,其溢出效应未能通过显著性检验.同时发现,机场客货量对航线网络中相连城市的溢出效应均大于其对本地经济的直接效应,忽视网络溢出效应会低估机场区域经济的总体贡献.研究成果对科学评价机场对经济发展的作用具有参考价值.     

不规则波在斜坡地形破碎区波高分布的数值试验研究

在近岸浅水波浪分布的研究中,格鲁霍夫斯基给出适用于深水波至破碎波的整个浅水域(相对水深η>2)的波高经验分布公式,但该式在波浪发生破碎后的适用性研究欠缺。基于FLOW-3D软件对深水不规则波传播到斜坡地形上波浪发生破碎进行模拟,验证波高沿程分布与试验值的一致性,并模拟在130斜坡地形条件下波浪从有限水深传播到近岸破碎区的沿程波高分布变化。结果表明,在该坡度相对水深η<2.75情况下,格鲁霍夫斯基经验分布公式出现较大误差,不再适用;破碎区各累积率波高与平均波高的比值随相对水深变小呈递减趋势,经验公式值与之相比,总体上呈现出大波偏大、小波偏小的情况。     

复合地层大直径盾构掘进管线保护及地层加固方案分析与评价

为了确定大直径盾构隧道地层改良和管线加固最优方案;采用数字地震仪微动检测技术对加固区地层分布和密实度进行了综合分析;同时引入单位掘进能耗技术指标对各加固方案的施工效率进行评价;并通过数值模拟研究了不同加固方案下;盾构掘进时地层孔隙应力的扰动情况和不同加固方法对控制渗流扰动的控制效果;研究结果表明:工法桩加固由于未加固浅层土体;对管线沉降的控制效果最差;袖阀管次之;组合注浆加固则能显著提升对管线沉降的控制效果;通过微动探测可知;袖阀管注浆对浅层黏土地层填充效果较好;MJS工法桩则能有效弥补袖阀管注浆加固的不足;对碎石夹黏性土层与下部粉砂岩层的适应性较好;能有效加强地层密实度;减少渗透系数;分析加固前后的盾构施工效率变化可知;袖阀管加固段的地层均匀性较差;单位能耗、地层实际损失值波动较大;MJS注浆加固后的地层密实度较高、均匀性较好;该加固区工作面也较为稳定;有利于控制地表沉降与隧道轴线偏差。     

基于等效声辐射功率和形貌优化的变速箱噪声控制

针对变速箱 3 挡啸叫问题,文章首先对变速箱进行了等效声辐射功率计算分析,结合模态分析精准定位找出不满足设计要求的零件薄弱区域;然后对其进行形貌优化以提高其刚度,从而得到优化结构设计;最后经过对比分析,发现优化后的设计显著降低了等效声辐射功率,从而有效降低了变速箱噪声。该分析方法可以为变速箱壳体优化设计提供有效的指导,有助于降低变速箱的噪声水平。     

统一理论计算船舶水动力的实用性研究

目的针对切片理论计算细长船舶水动力时存在的低频限制问题,使用一种简易的方法高效计算更广频率范围内的细长船舶水动力。方法基于综合了切片理论和普通细长体理论的统一理论,编程计算椭球、修改的Wigley船模和S60船的附加质量与阻尼系数,并与实验值、切片理论、三维移动脉动源格林函数法等的计算结果进行对比,分析统一理论的计算特点及优势。结果结果显示,基于二维剖面的统一理论在零航速工况下的计算结果与三维面元法的计算结果基本一致,在有航速工况下的计算结果与三维移动脉动源格林函数法的计算值展现出相近的变化规律。结论研究表明统一理论能够反映低频区域的三维效应,相比三维方法更高效、更简易,有较高的实用价值。     

滇西北地区冰碛层分布特征及工程效应

依托铁路、公路工程建设,在野外勘察、室内和现场原位试验基础上,重点研究滇西北地区冰碛层的分布特征、岩土类型、物质组成及颗粒成分、胶结程度和物理力学性质,对冰碛层的地基强度和边坡稳定性进行综合评价。冰碛层根据分布特征分为洼地型、阶地型、谷肩型;根据物质组成等可分为角砾岩和碎石类混合土,承载力和地基稳定性均较好;角砾岩单轴抗压强度较高;碎石类混合土抗剪强度较高,但水稳定性和地基均匀性较差。冰碛层边坡局部自稳性较好,但底部和层间可能存在软弱夹层。