竖向荷载作用下散体材料堆的试验研究

通过对散体材料堆竖向加载的正交试验,基于不同的堆积高度、粒径大小及加载速率,对散体材料堆抵抗竖向荷载破坏能力和竖向荷载波动进行分析.研究结果表明,抵抗力随堆积高度增大而减小,随粒径大小和加载速率增大而增大;荷载波动值与其频数有耦合关系,荷载波动值受堆积高度影响明显,且随着加载速率的增加而增加.     

不同水喷淋强度条件下医院病房火灾特性数值模拟研究

为了给医院病房火灾水喷淋灭火降温设计提供参考,本文基于北京长峰医院火灾事故案例及水喷淋系统未及时启动的现状分析,使用CFD(Computational Fluid Dynamics)数值模拟方法对不同水喷淋强度下的医院病房火灾特性开展研究。结果表明,水喷淋对病房火灾产生的火焰有一定的抑制效果,且随着水喷淋强度的增大对火焰的抑制作用越强。水喷淋对病房火灾降温效果较为明显,随着水喷淋强度提高对病房的降温效果越好。在当前火灾场景和喷淋强度范围内,水喷淋对火灾烟气的抑制效果并不明显,病房内的能见度没有改善。     

小流量煤油在变温度倾斜表面的降膜蒸发特性

在倾斜圆管内对航空煤油的降膜蒸发特性进行实验研究,其特点在于加热圆管的底部,管上的温度是不均匀分布的。分析了不同管长、煤油流量、倾斜角度、热流密度对煤油降膜蒸发特性的影响。通过实验,测出煤油的最大蒸干流量,并分析不同管长、倾斜角度和热流密度对煤油最大蒸干流量的影响。实验结果表明:在倾斜角度小于45°时,煤油最大蒸干流量会随着倾斜角度的增大而增大,在倾斜角度大于60°时,煤油最大蒸干流量会随着角度的增大而减小。煤油最大蒸干流量会随着热流密度的增大而显著提高,而过高的热流密度会造成煤油的结焦。     

并联型复合式冷却塔工作性能研究

通过对并联型复合式冷却塔模型的实验操作,研究截面风速和喷淋密度对复合式冷却塔冷却性能与阻力性能的影响规律,与此同时探究干湿区流量配比对并联型复合式冷却塔的性能影响。研究结果表明,并联型复合式冷却塔干湿区的冷却性能均随截面风速的增大,先增强后减弱。随喷淋密度的增大,先增强后减弱。对于并联型复合式冷却塔的阻力性能,干湿区皆随截面风速增大而增大,湿区随喷淋密度的增大而增大,而干区阻力随喷淋密度的增大无明显变化,且阻力系数与气水比之间呈负相关关系,截面风速和喷淋密度对其没有直接的影响。对于并联型复合式冷却塔,在干湿区流量配比为3:7时冷却性能达到最佳,冷却效率可达57.44%。     

考虑温度应力的深厚表土层井壁破裂分析

为了分析各荷载对造成深厚表土层立井井壁破裂的竖向应力的影响,对作用于井壁上的温度效应、自重、水平侧压力和竖向附加力在井壁内产生的竖向应力分量进行分析。分析表明,竖向附加应力和温度应力是造成井壁破裂的重要因素。进一步的分析表明,井壁内温度应力竖向分量随井壁内、外温度差增大而增大;随井壁厚度的增大,井壁内竖向附加应力明显减小,而温度应力则无明显变化。     

带初始角度的摩擦摆支座单层球面网壳结构受力性能研究

将带初始角度的摩擦摆支座应用到单层球面网壳结构中,通过有限元分析,研究了单层球面网壳结构的受力性能。选取El Centro波、Taft波,在水平、竖向和三维地震作用下分析带初始角度的摩擦摆支座对单层球面网壳结构抗震性能的影响。结果表明:静力荷载作用下,随着摩擦摆支座初始角度的增大,支座提供的水平支承力增加,单层球面网壳结构的内力和变形减小;当摩擦摆支座的初始角度小于15°时,在水平和三维地震作用下,网壳结构的减震效果相近,而在竖向地震作用下,随着摩擦摆支座初始角度的增大,网壳结构的减震效果增加;建议摩擦摆支座的初始角度小于15°。     

轮辐式大跨度张拉结构地震反应分析(Ⅱ)

以世纪莲体育中心轮辐式大跨度张拉索膜结构为研究对象,分析索系预应力变化时,地震作用下结构的动力反应。结果表明：索系预应力增大,结构刚度增加,地震作用下索系竖向位移减小,但其他杆件竖向位移增大,结构内力增加,地震力造成的损伤也增大;部分预应力索松弛对索系及压环轴应力影响不大,但对压环和腹杆的弯矩、索系及压环的位移影响较大...     

基于数值模拟的住宅简易喷淋灭火系统优化探讨

通过对住宅火灾规律和特点的分析,建立典型住宅模型,采用数值模拟方法,从保障初期安全疏散角度,对住宅设置简易喷淋灭火系统的影响因素进行分析,进行不同流量分配及与报警探测装置联用等工况的对比分析,寻求最佳喷头流量分配的参数工况,从而对住宅简易喷淋灭火系统的优化设置提出建议。     

连续桥梁三维隔震体系地震反应分析

基于刚性地基假定分别建立了隔震及非隔震条件下的三跨连续梁桥三维有限元模型,通过对该两种模型进行动力特性和动力时程反应分析,验证了三维隔震桥梁的水平及竖向隔震效果,研究了支座参数、多向地震作用和桥墩高度等因素对桥梁结构的地震反应及支座隔震效果的影响.结果表明,三维隔震支座对输入地震波的频率具有一定的敏感性;水平隔震效果随支座屈服前后刚度比的增大而增加;随着桥墩高度的增大,水平隔震效果逐渐增加,但增加趋势逐渐平缓;多向地震作用对水平隔震效果的影响很小,而对竖向隔震效果的影响不容忽视.     

沥青路面粘结层性能研究

通过室内试验,控制不同试验条件,如粘层材料种类、竖向荷载、温度及粘层材料洒布量,研究不同因素对沥青路面层间抗剪强度影响。试验结果表明:沥青路面层间抗剪强度随着竖向荷载增大而增大,在乳化沥青洒布量0.4、0.7kg/m2条件下两者线性相关性高达0.962、0.941;层间抗剪强度排序为:SBS乳化沥青SBR乳化沥青普通乳化沥青;随着乳化沥青洒布量的增加,层间抗剪强度先增加后减小,存在最优洒布量;通过灰色关联分析,竖向荷载、乳化沥青洒布量、沥青温度关联度较大。     

空气幕对列车车厢火灾烟气的影响规律研究

为研究防烟空气幕对列车车厢火灾烟气的影响规律,建立了CRH2A动车组一节车厢的内部模型,利用FDS模拟软件对列车车厢火灾时期的烟气流动规律进行数值模拟.依据给定火灾场景下烟气水平运动速度设置空气幕水平切向速度,通过改变空气幕安装角度,研究车厢内部火灾时,在空气幕作用下车厢空间各区域烟气层高度的变化,温度及CO浓度的分布...     

细水雾系统参数对有障碍物液体火灾灭火效果的影响

利用FDS 数值模拟软件，采取控制变量法设置4 组数值模拟，分别研究细水雾系统水滴粒径、雾化角度、喷水强度、喷头高度对火源周围存在无法燃烧或尚未开始燃烧的障碍物情况下灭火效果的影响。研究发现，当火源设置为乙醇池火时，存在障碍物条件下，细水雾系统水滴粒径设置在250~400 μm，雾化角度设为120°，喷水强度设为2.0~2.5 L/（min·m2），喷头高度距障碍物1 m 时灭火效果较为理想。     

Extinguishment of Cooking Oil Fires by Water Mist Fire Suppression Systems

A series of full-scale experiments were conducted in a mock-up commercial cooking area to study extinguishing mechanisms and effectiveness of water mist against cooking oil fires. The impact of water mist characteristics, such as spray angle, droplet size, flow rate, discharge pressure and type of nozzle, on the effectiveness of water mist against cooking oil fires was investigated. A series of oil splash experiments were also conducted to determine if the oil was splashed by water mist. In addition, the change in oil composition during heating and fire suppression was determined using Fourier Transform Infrared (FTIR) technique.The study showed that cooking oil fires were very difficult to extinguish, because they burned at high temperature and re-ignited easily due to changes in oil composition during heating and fire suppression. The water mist systems developed in the present work effectively extinguished cooking oil fires and prevented them from re-ignition. The spray angle, discharge pressure, and water flow rate were important factors to determine the effectiveness of water mist in extinguishing cooking oil fires.     

A numerical study of the interaction of water spray with a fire plume

Water spray-based fire extinguishing equipment such as sprinklers has been widely used in fire suppression and control. However, the fire extinguishing mechanism in such devices is not well understood due to the complexity of the physical and chemical interactions between water spray and fire plume. Currently, quantitative approaches (e.g. numerical modeling) to estimate the performance and effectiveness of water spray systems have not been developed to a stage where they can be used to optimize the design for different operating environments and types of fire. In the present work, a numerical simulation approach is introduced to provide a quantitative analysis of the complex interactions occurring between water spray and fire plume. The effects of several important factors (namely water spray pattern, water droplet size and water spray flow rate) on the fire suppression mechanism are investigated. The simulations show that the water spray with solid cone pattern and finer water droplet size is more effective in extinguishing fires than the one with hollow cone pattern and coarse water droplet size. To suppress a fire, the water spray flow rate has to be more than a certain critical value. However, using too high water spray flow rate does not increase fire suppression efficiency but only leads to increased operational cost because of the excess water flow rate. In the current paper, the principles of fire suppression with water spray are also discussed, which are useful in designing more effective water spray fire suppression systems.     

Experimental study on the extinction of liquid pool fire by water droplet streams and sprays

This paper provides evidence about the interaction between the water droplet stream and the flame, and explains how the interaction affects the suppression effectiveness. Two purpose-built gasoline pools were used to generate different open fires. The mono-disperse water droplet streams and water sprays were used as the flame suppressant. The first pool with a circular shape was equipped with a concentric pipe to allow the droplet stream to pass through the flame without impinging the gasoline. The second pool with a long narrow shape was equipped with expandable sides and allowed to extend the fire size. The passing ways of the droplet stream were systematically varied. The results clearly show two modes of flame inhibition; one is by blocking or interfering with the mixing of gasoline vapor and fresh air, and the other by cooling down the flames. For the stream case, the direction of the stream passing through the flame can affect the effectiveness of the suppression which increases as the angle is changed from vertical to horizontal. Also, there is an optimum distance between the stream axis and gasoline surface for flame inhibition. Moreover, the ability can be affected by the droplet size. On the same volume flow rate, the larger the droplet size, the more effective the flame suppression. For the water spray passing through the flame in the long groove pool, whenever the quantity of water vaporization reaches a critical value, the effectiveness of flame suppression by combining the obstructing and cooling effects becomes better.     

Description and application of an analytical model to quantify downward smoke displacement caused by a water spray

An analytical model is developed from basic principles to quantify the downward smoke displacement as caused by a water spray from e.g., a sprinkler head. The underlying assumptions are identified and the global balance is described between downward drag force, potentially downward buoyancy due to a cooling effect within the water spray envelope in the smoke layer, and the upward buoyant force in the ambient air below the smoke layer. From this balance, the downward smoke displacement is quantified. It is explained that the classical Bullen theory to define a criterion for smoke layer stability is in general not valid. There is always downward smoke displacement, although potentially small, depending on the circumstances. The tracking of individual water droplets leads to the evolution of the spray envelope radius and provides the total downward drag force on the smoke. An extensive sensitivity study is presented, varying the water spray angle at the nozzle, the water droplet diameter, the smoke layer temperature, and inclusion or not of the cooling effect by water and air entrainment in the downward smoke displacement. It is highlighted that the downward smoke displacement is more pronounced for smaller droplets (for fixed water mass flow rate), and for lower smoke layer temperatures. For larger water spray angle at the nozzle, the downward displacement also increases monotonically with initial smoke layer thickness. A smaller spray angle at the nozzle leads to stronger downward smoke displacement and the variation of downward smoke displacement with initial smoke layer thickness is non-monotonic: stronger descent of smoke for thinner smoke layer, but beyond a critical smoke layer thickness also again a stronger descent with increasing smoke layer thickness. The accuracy of the model as presented is illustrated by means of an experimental data set.     

Numerical simulation of the penetration capability of sprinkler sprays

Computational models have been utilized to investigate the penetration capability of sprinkler sprays directly above a fire source with respect to water flow rate, spray drop size, and spray momentum. The spray models are generated by assigning a representative drop size, mass flow rate, discharge speed, and discharge angle for each of 275 trajectories in such a way that they produce computed results which match the measured water flux distribution and spray momentum in the absence of a fire. The spray/fire plume interaction models are created by combining the spray models using a Lagrangian particle tracking scheme with free-burn fire plume models. Actual delivered densities and penetration ratios are computed through the interaction simulations at six flow rates, three fire sizes, and two ceiling heights. Drop sizes and spray momentum at two flow rates are increased by 25 and 50% from the original values without changing the other spray characteristics in order to investigate the effects of each parameter on penetration capability independently. The study indicates that there is an optimal flow rate for a given sprinkler that gives the highest penetration ratio within a practical flow range. It is also shown that increasing drop size is a much more effective way for obtaining a higher penetration ratio compared to increasing spray momentum.     

模拟酸雨大气环境下Q420B高强钢角钢的腐蚀疲劳性能试验研究

目前,高强钢在建筑结构中逐渐得到广泛应用,而其耐候性和疲劳性能对结构安全影响较大。对于长期暴露在野外大气环境中的结构,如输电铁塔,因长期受风致振动和大气环境中酸雨腐蚀的耦合作用,易发生腐蚀疲劳破坏甚至倒塌,所以研究酸雨大气环境下高强钢(如输电塔常用钢Q420B)的腐蚀疲劳性能具有重要意义。为此,对43根Q420B等边角钢在模拟酸雨大气作用下的腐蚀疲劳性能进行了研究,并基于简化的单点 似然法及单点 成组法拟合了其应力-疲劳寿命(Δσ-N)曲线和不同保证率p下的p Δσ N曲面。研究结果表明：酸雨大气环境缩短了Q420B角钢在中低荷载水平下对应的中长期疲劳寿命,而对高荷载水平下对应的短期疲劳寿命影响不大;环境因素对角钢的腐蚀疲劳性能有显著的影响,在模拟试验中,腐蚀液的pH值越低,间隔喷雾时间越长,相同荷载下角钢的腐蚀疲劳寿命越短。     

挡土墙地震主动土压力的库仑解

传统的Mononobe-Okabe法在实际工程中有着广泛应用,但它仅适用于无黏性土的极限土压力计算,且不能给出土压力分布。基于极限平衡理论,视墙后填土为服从Mohr-Coulomb屈服准则的理想弹塑性材料,假定墙后塑性区的一簇滑移线为直线即平面滑裂面,考虑墙背倾角、地面倾角、土黏聚力和内摩擦角、墙土之间黏结力和外摩擦角、地面均布超载、塑性临界深度以及水平和竖向地震系数等因素的影响,建立较为完善的塑性滑楔分析模型,进而采用极限平衡法求解挡土墙地震主动土压力、滑裂面土反力及其分布,并且通过量纲一化的分析首次提出几何力学相似原理。研究结果表明,总地震主动土压力随水平地震系数代数值的增大而增大;但随竖向地震系数代数值的增大并非总是减小,当水平地震系数较大时,可能出现先减后增的情况。     

水电站电缆竖井细水雾灭火性能数值模拟研究

水电站电缆竖井是用于给水电站铺设供电电缆或通信电缆的竖直高层通道,高度可达百米。如若封堵不严或无封堵,火灾将沿着电缆竖井迅速蔓延。本文以某水电站电缆竖井为研究对象,采用FDS 数值模拟软件,研究了高压细水雾喷头纵向间距、同时启动的楼层数、喷头流量系数和喷雾角度4 种因素对灭火效果的影响。确定了各因素临界值,以有效发挥灭火作用,该结果可为水电站电缆竖井灭火系统设计提供参考。