突变阵风对列车动力响应及行车安全性的影响

突变阵风因风速在短时内发生瞬时变化容易对高速列车的行车安全性造成威胁。根据一维多变量非平稳随机过程理论，模拟了空间相关的时变阵风脉动风速场。采用多体动力学软件SIMPACK和有限元分析软件ANSYS，建立了42自由度的刚性列车与柔性轨道-桥梁相互作用的刚柔耦合模型，考虑横风向时变阵风的影响，基于刚柔耦合法形成了较为完善的风-列车-轨道-桥梁耦合动力学分析系统。以大跨度拱桥为工程背景，分析了时变阵风在不同车速和风速下对列车和桥梁动力响应特性及行车安全性的影响。结果表明：阵风对桥梁和车辆的动力响应具有重要的影响；在相同条件下考虑阵风影响时，主跨跨中横向位移增幅达到了200%，车辆的轮重减载率、脱轨系数相比于不考虑阵风时增大近30%；在风速大于25 m/s，车速大于80 km/h，轮重减载率将超过安全限值，表明车辆可能发生脱轨。     

大跨度公轨两用悬索桥风-车-桥耦合振动及抗风行车准则研究

将风、车、桥三者作为一个交互作用、协调工作的耦合动力系统,基于风-车-桥系统空间耦合分析模型,以一大跨度公轨两用悬索桥为例,采用自主研发的桥梁结构分析软件BANSYS(Bridge Analysis System)分析了风荷载作用下桥梁和车辆的动力响应,讨论了风速、车速及轨道交通布置方式等因素的影响;同时,基于合理的列车运行安全性和舒适性评价指标,对列车通过该桥时的走行安全性与舒适性进行了分析,得出了该悬索桥的抗风行车准则:当风速小于20m/s时,车速可达设计车速80km/h;当风速介于20m/s和25m/s之间时,车速不能大于60km/h;当风速大于25m/s时,应封闭轨道交通。     

露点蒸发冷却装置性能评价指标的研究

本文通过搭建逆流式露点蒸发冷却装置,实验研究了空气入口温度、湿度和风速对露点效率、湿球效率、火用效比等各性能评价指标的影响,提出了能够反映湿通道潜热交换的强弱和装置性能的适用于露点蒸发冷却的评价指标——换热放大系数。研究结果表明:进口温度为33℃、相对湿度为22%时,当风速从1 m/s增至3 m/s,制冷量从29.5 kW增至69.0 kW,换热放大系数呈先增后减的趋势,在风速为1.8 m/s时达到最大值;当入口空气的温、湿度不同,湿球、露点效率的变化规律与温降趋势及制冷效果不一致,不宜作为装置性能的评价指标;当相对湿度为43%、风速为1.3 m/s,进口温度由25℃升至40℃时,换热放大系数由11增至54,变化规律与降温效果一致,能够反映装置冷却性能。在高温低湿工况下,火用效比大、装置节能性能好。     

CO_2冷风机性能测试实验研究

本文搭建了测试CO_2冷风机性能的实验台,在直接膨胀供液系统和泵供液系统下,通过改变传热温差、库温、循环倍率、迎面风速等参数来研究CO_2冷风机的性能。结果表明:在直接膨胀供液系统中,随着蒸发温度的降低,传热系数和制冷量均呈减小的趋势,蒸发温度从-22℃降低到-47℃时,传热系数从20.2 W/(m2·K)降低到16.6 W/(m2·K),制冷量从7.5 k W降低到6 k W;在泵供液系统中,随着循环倍率的增加,传热系数呈现先增大,达到最大值后缓慢减小的趋势,当循环倍率为3时,传热系数达到最大值,以库温为-20℃时为例,当循环倍率从1增大到3,传热系数增大约13.2%,循环倍率继续增大时,传热系数开始下降,增大到5时,换热系数下降至2%左右。当迎面风速从2.2 m/s变化至2.5 m/s时,传热系数仅增加了2.12%;但迎面风速从2.5m/s变化至3.2 m/s时,增幅为11.4%;当迎面风速从3.2 m/s变化至3.5 m/s时,传热系数增长幅度又变缓,仅增加了0.88%。     

波纹翅片管换热器表面粉尘沉积特性的实验研究

空调器室外换热器大多采用波纹翅片管,因使用过程中表面积灰而导致性能下降。本文通过搭建积灰可视化实验台来观测粉尘的分布特征并测定沉积量,研究波纹翅片管换热器表面的粉尘沉积特性。其中测试样件的翅片间距范围为1.6~3.2mm,喷粉浓度范围为80~280 kg/m~3,风速范围为1~3 m/s,喷粉时间为15~90 s。研究表明,粉尘主要沉积在换热器迎风面的翅片前缘处以及换热管的迎风面上;翅片间距小时易于粉尘沉积,翅片间距为1.6 mm样件上的单位面积粉尘沉积量较3.2 mm样件最多增加了52%;提高喷粉浓度会增加粉尘沉积,喷粉浓度为280 kg/m~3下的单位面积粉尘沉积量较80 kg/m~3最多增加了88.2%;高风速能够抑制粉尘沉积,风速为3 m/s下的单位面积粉尘沉积量较1 m/s最多下降了6.3%。     

集中防烟模式下特长铁路隧道救援站火灾烟气控制数值模拟分析

采用三种方法对集中防烟模式下,避难室及横通道的加压送风量进行理论计算,获得对应的加压送风量分别为140m3/s、200m3/s、240m3/s,针对三种工况送风量,在集中防烟模式下,分析当安全隧道送风风机关闭和开启时救援站火灾烟气控制效果,探讨集中防烟模式下火灾烟气控制的关键参数。研究结果表明,集中防烟模式下加压送风量大于140m3/s即可,集中送风量的变化对救援站内温度、能见度及CO浓度等参数分布影响不大;安全隧道辅助送风有利于救援站避难室防烟,各横通道入口处的风速随着安全隧道送风风速的增大而增大。     

开放式立管吸嘴风速分布的模拟与实验

建立内径40 mm开放式立管吸嘴的吸气模型,在入口风速为38.5 m/s的状态下对立管周围风速的分布进行数值模拟;利用粒径2~11 mm的玻璃球作为实验散料,在内径40 mm的立管中进行了开放式吸送实验。模拟结果表明:立管周围的气流速度明显衰减,越远离管口,速度衰减的程度越大。在轴线上距入口10 mm处,气流速度降至15.7 m/s;距入口20 mm处,气流速度已衰减至6.5 m/s。在立管入口外部,等速线发生弯曲,并且随着距入口距离的增加,曲线的曲率与直径均相应增大;而且数值模拟与实验结果吻合较好。     

下击暴流作用下高速列车运行安全性能评估

建立了一套利用物理模拟器的下击暴流作用下高速列车运行安全性评估方法。结果表明:受下击暴流风速场与气压场的共同影响,列车距下击暴流中心不同相对位置,所受气动力作用机制明显不同;下击暴流作用下,侧力对轮轨横向力贡献最大,侧滚力矩对轮轨垂向力贡献最大;轮对横向力、脱轨系数、轮重减载率等列车安全运行评价指标随径向距离的增大先增大后减小,相对径向距离r/D_jet=0.83时(D_jet为喷口直径),为列车安全运行的最不利径向位置;列车安全运行指标随风速、车速的增大而增大,列车安全运行的下击暴流临界风速值随车速的增大而急剧减小。     

低温低压下工业铁粉的干燥特性及传热传质分析

本文通过搭建低温低压热泵干燥装置,研究了工业铁粉在不同低压下的干燥效果并分析了低温低压干燥过程中的传热与传质。结果表明:降低干燥环境压力会增大湿铁粉的除湿量,当环境压力从101 kPa降至10 kPa,除湿量增加2.5倍,且在10 kPa压力下铁粉含湿量能降至1%以下。当干燥空气为50℃,风速为0.5 m/s时,随着压力从101 kPa逐渐降至10 kPa,传质系数降低28.1%,传热系数降低68.4%,因此表征传热传质相对强度的刘易斯因子LF随着环境压力的降低而降低。当环境压力为10 kPa、风温为50℃时,流速从0.2 m/s增至2.0 m/s时,传质系数增加32.9%,传热系数增加67.8%,表明低压环境抑制了风速对传质系数的强化作用,因此LF随着风速的增加而增加。在10 kPa环境压力下,LF低至0.5~0.6,表明低压环境中质量扩散与热量扩散存在明显区别。     

射流风机对地铁隧道人员疏散影响的数值分析

为满足昆明市地铁6号线由大板桥至综合交通枢纽站3号隧道内射流风机设置于人员安全疏散的设计要求。利用CFDFluent软件建立一个三维区间隧道计算模型,模拟了无阻塞和列车阻塞两种工况下射流风机出流对区间隧道内空气流场分布的影响。结果表明,无阻塞工况下射流风机稳定运行时,疏散走道处所形成风速均低于4m/s;列车阻塞工况下,当停留列车距离射流风机出风口越远,容易在列车与隔墙之间的疏散走道处形成局部高速风,但人员所接受风速均低于6m/s。通过Fluent计算程序的建立,可以方便地将研究结论转化成简单易用的设计资料,为今后设计提供参考。     

Carbon Dioxide Snow Cleaning

As a powerful new tool for precision surface cleaning, CO₂ snow cleaning involves the formation and acceleration of small dry ice crystals onto a surface. The resulting physical and chemical interactions lead to particle and organic contamination removal. CO₂ snow cleaning has proved to be an effective surface cleaning process in many areas. Furthermore, it is a residue-free and nondestructive cleaning method. Particle removal has been observed for sizes ranging from visible to less than 40 nanometers; organic contamination removal matches that of commercial solvents to reagent grade solvents. In this article, CO₂ snow cleaning is reviewed with emphasis on thermodynamics, cleaning mechanisms, cleaning parameters, equipment, and applications.     

Carbon Dioxide Snow Cleaning

As a powerful new tool for precision surface cleaning, CO₂ snow cleaning involves the formation and acceleration of small dry ice crystals onto a surface. The resulting physical and chemical interactions lead to particle and organic contamination removal. CO₂ snow cleaning has proved to be an effective surface cleaning process in many areas. Furthermore, it is a residue-free and nondestructive cleaning method. Particle removal has been observed for sizes ranging from visible to less than 40 nanometers; organic contamination removal matches that of commercial solvents to reagent grade solvents. In this article, CO₂ snow cleaning is reviewed with emphasis on thermodynamics, cleaning mechanisms, cleaning parameters, equipment, and applications.     

Snow Leopard terminates Eltron agreement

Canada’s Snow Leopard Resources Inc has terminated its efforts to reach a definitive agreement with US company Eltron Research Inc on licensing sulphur mitigation technology developed by Eltron.This is a short news story only. Visit www.filtsep.com for the latest filtration industry news     

Snow induced collapse of hail protection canopies

This paper addresses the snow induced collapse of hail protection canopies of a major car dealership in Istanbul, Turkey. Each of them with different plan dimensions has been built to provide an enclosed space of over 50,000 square meters for parking. The structural system of each hail protection canopy consists of successive steel frames spaced at 5.0 m intervals. Some of these canopies collapsed on January 1st, 2016. The rest has been saved thanks to the immediate intervention provided by the employees allowing accumulated snow to slide off the roof. Following the incident, a site investigation has been conducted to inspect the structural failures and a numerical 3D model to represent the whole structure was developed using OpenSEES to understand the collapse mechanism of the hail protection canopies. In addition, the scope of the structural design calculations was examined to check for potential incorrect design assumptions. Consequently, site observations and analysis results indicate that the hail protection canopies collapsed due to a combination of erroneous design assumptions on snow load and the poor design and construction of structural members and their connections.     

Pneumatic Conveying for Snow Storage Plants

In Japan, the number of snow storage plants has been increasing for the purpose of storing agricultural products and for the air-conditioning of buildings in summer. In order to gather snow into the snow storage room, a rotary snow plow is often used, but it is difficult to pile up snow within the room from inside out. To overcome this limitation, a pneumatic snow conveying system was developed in order to transport snow to the snow storage plant. The system consists of a blower, snow feeder, cyclone separator, and pipeline. The pressure type of the conveying system incorporates both negative and positive pressures, with a capacity to convey wet snow at 10 t/h a distance of 40 m. For snow with free water content below 15%, the system conveyed wet snow without sticking to the inside walls of the pipeline.     

冰雪运动主题网络游戏临时用户模型研究

目的从用户体验角度出发,总结出针对冰雪运动主题网络游戏的临时用户模型,理论上为后续冰雪运动主题网络游戏设计研究提供研究思路与方法,实践上通过建立临时用户模型快速了解用户需求,增强网络游戏产品的更新迭代、满足用户多感官体验的需求。方法根据Alan Cooper提出的临时用户模型理论,对冰雪运动主题游戏用户进行划分,通过挑选出用户研究相关因子等建立临时用户模型。结论建立3个冰雪运动主题网络游戏临时用户模型,并结合相关主题的冰雪运动游戏进行测试及访谈,验证临时冰雪运动主题网络游戏临时用户模型,提出相关应对建议。通过总结冰雪运动主题网络游戏设计中临时用户模型的研究方法提出相关对策,为后续的虚拟冰雪游戏设计提供思路。     

Snow water equivalent estimation by microwave radiometry

Snow water equivalent (SWE) is one of the most important parameters for accurate prediction of snowmelt runoff. Conventionally, SWE is monitored using observations made at widely scattered points in or around specific watersheds. Remote sensors, which provide data with better spatial and temporal coverage, can be used to improve the SWE estimates. Microwave radiation, which can penetrate through a snowpack, may be used to infer the SWE.Calculations made from a microscopic scattering model are used to simulate the effect of varying SWE on the microwave brightness temperature. Data obtained from truck mounted, airborne and spaceborne systems from various tests sites have been studied. The simulated SWE compares favorably with the measured SWE for dry snowpacks. In addition, whether or not the underlying soil is frozen or thawed may be discriminated using the polarization information obtained by spaceborne sensors.     

雪晶成核和生长机理研究

在自然界,雪晶的形成是一个非常复杂的过程,要经历成核、生长、融并等阶段.探索雪晶的成核和生长机理对人工造雪技术的发展具有重要的作用.雪晶的形态是由冰晶的晶格结构和雪晶的生长环境所决定的.通过对均相成核和异相成核过程中自由能变化的分析,确定了晶核形成所需的临界半径和成核势垒,为研究晶核的形成过程提供了理论依据.依据雪晶质量生长率与水蒸汽通量之间的关系,从理论上明确了各种雪晶形态与生长速率之间的规律.     

On Convective Instability of Air in the Snow Cover

This paper considers the system of equations describing the convective instability of air in the snow cover. We analyze the conditions under which the principle of monotony of normal perturbations is fulfilled and estimate the critical parameters of the main level of air equilibrium instability with allowance for the heat and mass exchange between the snow surface and the environment.