鼻尖状态对高速列车气动性能的影响

基于三维定常不可压N-S方程以及k-ε两方程湍流模型,分别在无横风和有横风环境下,用有限体积法研究高速列车车头鼻尖不同开闭状态对列车明线运行时气动性能的影响.用FLUENT分析车头鼻尖全开、全闭和半开半闭等3种不同开闭状态的高速列车气动性能,发现车头鼻尖开闭状态对列车侧向力和升力几乎没有影响,但对头车的阻力影响较大,这主要是由于头车鼻尖部分阻力变化较大引起的.在无横风环境下,车头鼻尖开闭状态对头车的气动力矩影响不大,但对尾车的点头力矩有一定影响.在横风环境下,车头鼻尖开闭状态对列车气动力矩影响不大.     

普速列车与动车组交会过程的车窗安全性研究

随着既有线路上普通快速列车和动车组运行速度的提高,会车时两车之间的气动压力会明显增大;因此,会车压力波给交会的普通快速列车和动车组造成的舒适性和安全性等影响明显加剧;采用基于雷诺时均法(RANS)的RNG k-e二方程的湍流模型仿真计算普通快速列车时速140 km与动车组时速200 km时,明线和隧道两种工况下会车过程的压力波动情况,并用计算得到的车窗处压力从车窗玻璃的静强度、车窗玻璃的动态冲击强度和车窗安装强度三个方面分析了交会过程的车窗安全性;结果表明:明线会车过程两车交会侧车窗受正压和负压的影响,隧道会车过程两车交会侧车窗主要受较大的负压的影响;受压缩波和膨胀波的叠加影响,交会压力波的头波波峰和尾波波谷的波动较小,而头波波谷和尾波波峰的波动较大;在隧道会车时,动车组车窗中心处的负压极值最大值约为明线会车的3.87倍,压力波幅值最大值和最大压力平均变化率较接近;普通快速列车车窗中心处的负压极值最大值约为明线会车的4.25倍,压力波幅值最大值和最大压力平均变化率相差较大;车窗的长宽比越大,安装结构强度越大,安装结构越宽,安装强度越大。     

横风对高速列车气动性能的影响

随高速列车在横风下的气动特性急剧变化,安全问题十分突出。本文以京沪高铁CRH型动车组作为典型研究对象,建立三维模型,研究横风风速和列车车速对列车轮轨动力学的影响、单列高速列车在明线横风环境中运行的气动特性,从而得出如下结论：(1)列车在横向风中行驶时,选择列车的气动升力为例,以200 km/h和300 km/h运行的列车在风速从15.1m/s逐渐增加到30.0 m/s分别增加了340.6%和337.2%的气动升力;在风速为15.1 m/s, 22.2 m/s和30.0 m/s时,车速从200 km/h增加到300 km/h时,分别增加了18.3%、19.1%和20.1%的气动升力。由此可知,在横向风环境下列车车体所受的气动升力随着车速和风速的提高而逐渐增大。(2)在横风环境下,列车的迎风侧大部分区域受正压,背风侧大部分受负压,最大正压区域为头车鼻尖处,空气流速在列车上端拐角边缘最高。根据列车长度方向,列车两侧的压强差逐渐减少。通过对高速列车的气动特性进行研究,从而为高速列车风灾防治和运行安全管理提供参考,以及为制定具有自主知识产权的高速风灾安全预警控制系统提供了科学依据。     

高速列车隧道压力波模拟迭代遗忘因子控制

高速列车在隧道运行、隧道交会时车内、外会产生交替变化的气压差,对车体气密性及材料耐疲劳强度提出更高要求.基于Matlab和AMESim构建联合仿真平台,设计高速列车隧道压力波模拟系统.使用实测隧道压力波数据作为期望输出,研究车体气密疲劳性能.考虑到模拟系统非线性、大时滞及多扰动特点,采用一种带有时变遗忘因子的开环迭代PID控制算法.仿真结果表明,其系统更稳定、收敛速度更快.     

高速列车车体疲劳试验压力加载控制仿真研究

高速列车在隧道通过或明线交会时,列车表面会产生较大的气压波动,此压力波动通过车体传递到车内也会影响车内压力波动,加之运行速度的不断提高,可引起车体表面材料疲劳甚至断裂;为研究高速列车在复杂工况下车内、外压力波动对车体材料疲劳性能的影响,设计了一种能同时对车内及车外进行压力加载的试验系统;利用AMESIM与SIMULINK接口技术进行联合仿真平台的构建,并进行车内、外压力控制仿真;针对系统数学模型难以建立,且存在大容量、大时滞、非线性及多扰动等特点,采用基于前馈补偿的高阶非因果型迭代PI型控制算法实现车内及车外压力的精确控制;仿真结果表明该算法控制误差较PI型控制算法小,控制效果更理想。     

列车底部结构对交会高速列车气动性能的影响

用CFD法对具有复杂底部结构(带有转向架或带有转向架和裙板)的高速列车以200 km/h等速交会的情况进行数值模拟和分析,研究其压力波、气动力和气动力矩以及车体周围的流场结构的变化.结果表明:与简化模型相比,带有复杂底部结构的列车交会时的压力波的头波和尾波都有所减小且尾波减小的程度更高,带有转向架的车体的横向力、横摆力矩和侧翻力矩的峰值明显减小,但变化更复杂;带有复杂底部结构的列车在车体底部会形成涡结构,有明显的能量耗散.     

8051在光电测速中的应用

由于高速列车交会时的空气压力波与其运行速度有直接关系,所以如何准确得到动模型运行时的速度就十分重要。本文作者为解决模拟列车在高速运行时带来的一系列空气动力学问题,在其单位建成了高速列车动模型装置及其测控系统。文章介绍了利用光纤或光电传感器测量高速运动...     

高速列车车内压力波动模糊控制研究

高速列车在通过隧道或两车交会时,列车表面会产生很大的气压波动,此压力波动通过车体缝隙和换气风机、风道传入车内,引起车内空气压力较大波动,造成乘客耳鸣、耳痛等症状.影响乘坐舒适性;为了抑制高速列车车内压力波动,根据某型高速列车换气风机特性曲线与车体等效泄露关系,建立了换气风机频率可变的车内外空气压力传递数学模型;采用模糊控制策略,以车内压力、车内压力变化率为控制输入,对高速列车换气系统中的新风风机、废排风机运行频率进行调节;仿真结果表明:该控制方式能够提高现有换气系统对车内空气压力波动的抑制能力,提高乘坐舒适性。     

基于遗传算法的高速列车头型多目标优化

高速列车的气动阻力与列车的外形,特别是头部外形有着密切的关系.为了改善列车气动性能降低列车运行的气动阻力,建立高速列车的三维参数化模型,以高速列车头部所受的阻力和升力为优化目标,通过FLUENT软件与Isight软件多学科优化联合仿真分析方法,利用Sculptor软件对车头部分网格自动变形,基于计算流体力学,实现对高速列车流线型头型进行减阻的多目标自动优化设计.优化完成后,得到影响优化目标阻力和升力的关键设计变量,并对优化设计变量和优化目标之间的非线性相关性进行分析.通过对比原始流线型列车气动性能发现,列车头部的长度对阻力的影响比较大,列车头部的高度能够对列车所受到的升力产生较大的影响.     

横风下桥梁高度对高速列车交会性能的影响

为研究横风下桥梁高度对高速列车会车性能的影响,基于空气动力学和列车系统动力学,分析指数风分布下不同高度桥梁周围的流场,建立高速列车多体系统动力学模型,模拟横风下列车在不同高度桥梁上会车时的表面压力特性和气动载荷特性.将得到的气动力作为外加载荷作用于列车上,分析桥梁高度对高速列车会车安全性能的影响.结果表明:当列车在环境风下交会时,背风侧列车的气动力波动大于迎风侧列车的气动力波动;当监测点风速固定且桥梁高度小于15 m时,随着桥梁高度的增加,列车的气动载荷最大幅值和安全指标最大幅值均有所减小;当桥梁高度为15～30 m时,随着桥梁高度的增加,列车的气动性能和动力学性能基本保持不变.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).