火灾科学概论

 一、引言火是人类的朋友,也是人类的敌人。从远古时期,人类发现了火,并利用它取暖、熟食,在不断地学习和掌握用火的过程中,实现了人类生活由野蛮到文明的飞跃.半个多世纪来,为了给研制和设计高效、净化的燃烧装置提供科学依据、燃烧学应运而生.近20年来,人们开展了对火灾发生、发展和防治机理的研究,逐步形成了和发展了一门新的学科一火灾科学.二、发展简史失去控制的火,给人类生命财产和自然资源带来损失,则成为火灾.火灾现象遍及城市与乡村,包括森林、建筑、油类,装备设施和交通工具等火灾,以及可燃气体和粉尘的爆炸等.     

基于多传感器信息融合的火灾报警器设计

火灾是人类社会经常遇到的一个灾害,它通常给人民群众带来生命和财产的损失。针对传统火灾报警器参数单一,易出现漏报、误报的问题,本文设计了一种基于多传感器信息融合的火灾报警器;该系统以温度传感器、CO浓度传感器和烟雾浓度传感器测量的现场参数为参考,通过比较器的比较送给单片机进行信息融合,当温度高度设定值时,蜂鸣器报警;在温度高于设定值,且CO和烟雾浓度高于设定值时,蜂鸣器报警并且LED灯闪烁,提示有可能有火灾发生。最终通过对系统的调试实现了对液晶显示器的显示控制和报警器的报警。仿真结果表明了系统能够及时准确的判断是否有火灾发生,具有较强的火灾预测和报警能力。     

簡諧振动的观察

仪器的构造示于图1。1是电动机,其軸的轉速可用变阻器2調节,电动机驅动使圓盘板(用有机玻璃作成)3运动起来,圆盘的直径大約为10厘米,在圓板上固定着两个电灯泡4和5(可用手电筒小灯泡)电压通过軸、圆环和刷于6供給灯泡,連接在圆环和电刷6上。又离圆板30—50厘米的地方,放置一个多面的旋轉鏡7,如果接通一个灯     

基于嵌入式GPRS技术的大区域火灾监控系统

针对当前的大区域内火情监控以人工为主,实时性较差,报警存在延时的问题;在需求分析的基础上,设计并实现了一种基于嵌入式与GPRS技术的大区域火情监控系统,硬件平台以嵌入式 S3C2410 芯片配合温度传感器LM75A以及相关外围电路,采集处理传感温度信息,利用GPRS网络的大范围数据通信能力传递各种火情信息,软件采用了分层的设计思想,将整个系统的软件设计分为用户应用层、网络集成层、硬件驱动层3个层次结构进行设计,利用SMS的方式进行火灾报警,避免了人工检测时主观强,实时性差的弊端;系统经过大量的实际数据测试证明,误差率基本能够保持在15%以内,比传统算法,报警准确率提高了27.4%,大区域控制范围在1平方公里,报警性能良好,具有很强的实际应用价值。     

基于元胞自动机的行人疏散流仿真研究

基于元胞自动机对行人疏散流进行仿真研究.模型利用两个动态参数反映行人移动区域内的疏散情况,从而决定行人的行为选择.模型中行人可以根据自身周围的情况选择移动、等待行为.本文仿真研究了行人在正常疏散环境下,系统规模、疏散人数、安全出口宽度、多个安全出口布局对行人疏散时间的影响.研究结果表明,行人疏散时间随行人数量呈线性增加;随安全出口宽度呈负指数性减少;同时,多个安全出口布局的不平衡也会对行人的疏散过程和疏散时间产生一定的影响. 关键词： 元胞自动机 行人疏散流 动态参数 疏散时间     

火灾烟颗粒分形模型和球形模型光散射的比较研究

对烟颗粒的光散射进行模拟计算是研究火灾烟颗粒光散射特性的重要手段,目前对于火灾烟颗粒光散射的数值计算多采用球形或椭球模型.实际上,火灾烟颗粒的形貌与球形和椭球均存在着显著差异.扫描电子显微镜图像表明,烟颗粒具有近似分形的结构.本文利用离散偶极近似方法计算了随机取向的火灾烟颗粒分形凝团以及同体积的球形颗粒的光散射Muller矩阵,并对两者的归一化Muller矩阵元素随散射角的分布进行了比较.研究表明:火灾烟颗粒分形模型和球形模型的归一化矩阵元素F₁₁(θ)/     

声学消息

第十一届国际声学会议于1983年7月19日至27日在巴黎召开.参加这次会议的有42个国家和地区的1120个声学工作者,是一次规模比较大的盛会.其中人数最多的是法国声学家,约350人,美国日本各约100人,西德90多人,英国70多人.中国科学院声学所、计量科学院、环境科学院、建研院、南京大学、同济大学、陕西师范大学、哈尔滨船舶工程学院、715所等共派出了14名代表,在西欧各地的访问学者6人也参加了这次会议.     

基于MODIS数据的森林火险时空分异规律研究

森林火灾严重危害生态环境,引起了全球的高度重视。将从MODIS(MODerate-resolution imaging spectroradiometer)中提取的活动火点与历史火烧痕迹进行比较研究,发现MOD14A1(火掩膜数据产品a daily Level 3 1-km fire hot spot product)中提取的8+9波段适合消防监测,与现场勘察数据相比较吻合度高达0.83。使用MOD14A1中8+9波段结合相关数据对这个区域的长达11年(2000—2010年)的森林火灾发生的时间和空间分析,结果表明：火灾发生频率最多的是春季,秋季次之,夏天概率最低,除非干旱。通过对研究区域黑龙江省分析,针叶林和温带针阔混交林过火面积所占比例分别为53.68%,44%,草原区过火面积较小为2.32%。大兴安岭是主要的燃烧区域,面积达到64.74%,小兴安岭约为23.49%,而其他区域面积不超过5%。且火灾发生的较大部分森林有个平缓的斜坡(≤5°),大部分处于中海拔(200 m≤H≤500 m)。因此,通过卫星遥感对森林火区区域的时间序列分析,阐明火灾活动规律和气候、地形、植被类型的相互关系,有助于预测火灾区域危险性等级。     

BiFeO3光伏效应研究进展

BiFeO3是一个典型的多铁性材料,是凝聚态物理研究领域的热点之一,在信息存储、自旋电子学以及传感器等方面具有诱人的应用前景.近两年来,多铁材料的光电特性引起了人们的广泛关注,许多问题有待于深入研究和探索.本文综述了近年来多铁材料BiFeO3在光伏领域的研究进展,讨论了铁电极化场、电极界面肖特基势垒以及铁电畴结构对BiFeO3光伏特性的影响规律.     

关于原子核的电四极矩

 一、原子核的电四极矩原子核的内禀电四极矩,来源于核电荷的非球形分布,一般可用并矢或(3×3)二秩不可约张量表示。如果选择核自旋轴I(沿z轴)为核电四极矩主轴,由于核对自旋轴的旋转对称性,电四极矩仅有一个独立分量,称为标量电四极矩.     

Experiment and modeling of exit-selecting behaviors during a building evacuation

The evacuation process in a teaching building with two neighboring exits is investigated by means of experiment and modeling. The basic parameters such as flow, density and velocity of pedestrians in the exit area are measured. The exit-selecting phenomenon in the experiment is analyzed, and it is found that pedestrians prefer selecting the closer exit even though the other exit is only a little far. In order to understand the phenomenon, we reproduce the experiment process with a modified biased random walk model, in which the preference of closer exit is achieved using the drift direction and the drift force. Our simulation results afford a calibrated value of the drift force, especially when it is 0.56, there is good agreement between the simulation results and the experimental results on the number of pedestrians selecting the closer exit, the average velocity through the exits, the cumulative distribution of the instantaneous velocity and the fundamental diagram of the flow through exits. According to the further simulation results, it is found that pedestrians tend to select the exit with shorter distance to them, especially when the people density is small or medium. But if the density is large enough, the flow rates of the two exits will become comparable because of the detour behaviors. It reflects the fact that a crowd of people may not be rational to optimize the usage of multi-exits, especially in an emergency.     

The escape of pedestrians with view radius

In this brief letter, we modify the classic social force model of Helbing which is applied to simulate how a pedestrian gets outside a hall full of smoke. As the Vicsek model does, the view radius is introduced to describe the range the pedestrian can see. The relation between the evacuation time and the view radius is studied with different numbers of pedestrians. The results show that the shorter the view radius is, the more time walkers will spend escaping, and even fail to escape. And the relation between the number of remaining walkers and the view radius shows non-monotonicity, if the number of pedestrians is larger than 600. And lastly, we propose to enlarge the width of the exit or to add two small exits in the corners, which may decrease the evacuation time greatly and obviously reduce the number of remaining walkers.     

Simulation of pedestrian evacuation based on an improved dynamic parameter model

An improved dynamic parameter model is presented based on cellular automata. The dynamic parameters, including direction parameter, empty parameter, and cognition parameter, are formulated to simplify tactically the process of making decisions for pedestrians. The improved model reflects the judgement of pedestrians on surrounding conditions and the action of choosing or decision. According to the two-dimensional cellular automaton Moore neighborhood we establish the pedestrian moving rule, and carry out corresponding simulations of pedestrian evacuation. The improved model considers the impact of pedestrian density near exits on the evacuation process. Simulated and experimental results demonstrate that the improvement makes sense due to the fact that except for the spatial distance to exits, people also choose an exit according to the pedestrian density around exits. The impact factors α, β, and γ are introduced to describe transition payoff, and their optimal values are determined through simulation. Moreover, the effects of pedestrian distribution, pedestrian density, and the width of exits on the evacuation time are discussed. The optimal exit layout, i.e., the optimal position and width, is offered. The comparison between the simulated results obtained with the improved model and that from a previous model and experiments indicates that the improved model can reproduce experimental results well. Thus, it has great significance for further study, and important instructional meaning for pedestrian evacuation so as to reduce the number of casualties.     

通过博弈的室内行人疏散动力学研究

在室内行人疏散过程中,行人博弈对疏散效率有着重要的影响.本文把抵制博弈策略更新的强度定义为抵制强度. 为了研究抵制强度对疏散效率的影响, 通过在行人博弈策略更新的概率中引入抵制强度,基于元胞自动机模型数值计算在不同的行人密度, 出口宽度下疏散总时间随抵制强度变化的关系.结果表明: 室内行人疏散过程中, 抵制强度小会使得争抢行为极其容易蔓延. 当行人密度小且出口宽大时, 输入以急速疏散为主的规范信息,鼓励行人模仿优胜者更新博弈策略, 当行人密度大且出口狭小时, 输入以避让为主的规范信息抑制行人争抢,都能提高疏散效率. 最后找出不同条件下与最短疏散总时间相对应的优化抵制强度, 为提高室内行人疏散效率提供一个新的视角.     

Study on evacuation behaviors at a T-shaped intersection by a force-driving cellular automata model

A force-driving cellular automata model considering the social force on cell movement, such as the desirous willing of a pedestrian to exit, the repulsive interaction among pedestrians or between pedestrians and obstacles, was set up to investigate the evacuation behaviors of pedestrians at a T-shaped intersection. And an analogical formulation, taking reference of the magnetic force, was introduced to describe the above repulsive actions. Based on the model, the evacuation behaviors of pedestrians were simulated in terms of different pedestrian density, distribution and corridor width, and then evacuation time was obtained and analyzed. Furthermore, an experiment was conducted to verify the results of the presented model. The results demonstrate that when the density of pedestrians is greater than a certain threshold, pedestrians of a certain direction would be jammed by the repulsion from pedestrians of the counter flow from another direction, and the evacuation time of the former would be longer, even though they are closer to the exit, which would possibly result in a serious casualty in an emergency circumstance. And the phenomenon has been validated by the experiments well. In addition, a corresponding critical corridor width related to different DOPs, beyond which the evacuation time could be decreased rapidly due to a strong degradation of jamming behaviors near the T-shaped intersection, was also discovered and predicted by the proposed model.     

Logit-based exit choice model of evacuation in rooms with internal obstacles and multiple exits

A logit-based discrete choice model is proposed to study the exit choice behaviour of evacuees in rooms with internal obstacles and multiple exits. Several factors influencing the exit choice behaviour, including the information obtained by evacuees, the tendency of following others, the visibility and familiarity of exits and the physical conditions of nearby exits, are considered. Evacuees are allowed to re-select their target exits for minimizing the perceived disutility during evacuation process. Numerical results from applying the model to cellular automata simulation of evacuation are presented and the effects of some model parameters on evacuation time are investigated.     

双出口房间人群疏散的实验研究和数学建模

本文设计了一个双出口房间内人群疏散的实验方案,通过不同条件下疏散过程的实况录像及视频检测,得到不同人数疏散时间的许多定量结果.提出了双出口房间吸引区间的概念,证明了较小出口吸引区间的边界总是一段圆弧,可以解释行人流出口处的圆形成拱现象.通过类比地铁候车厅内人群疏散过程,建立了双出口房间内疏散时间的二次函数模型,成功拟合不同条件下的实测数据.疏散人数较少时,疏散时间随着人数增加而线性增长;人数较多,在出口附近出现待行区域时,疏散时间则呈二次函数增长.与一些已知疏散时间数学模型相比,本文模型对出口宽度变化的反应更敏感.     

Simulation of crowd dynamics in pedestrian evacuation concerning panic contagion: A cellular automaton approach

The study of the panic evacuation process is of great significance to emergency management. Panic not only causes negative emotions such as irritability and anxiety, but also affects the pedestrians decision-making process, thereby inducing the abnormal crowd behavior. Prompted by the epidemiological SIR model, an extended floor field cellular automaton model was proposed to investigate the pedestrian dynamics under the threat of hazard resulting from the panic contagion. In the model, the conception of panic transmission status (PTS) was put forward to describe pedestrians' behavior who could transmit panic emotions to others. The model also indicated the pedestrian movement was governed by the static and hazard threat floor field. Then rules that panic could influence decision-making process were set up based on the floor field theory. The simulation results show that the stronger the pedestrian panic, the more sensitive pedestrians are to hazards, and the less able to rationally find safe exits. However, when the crowd density is high, the panic contagion has a less impact on the evacuation process of pedestrians. It is also found that when the hazard position is closer to the exit, the panic will propagate for a longer time and have a greater impact on the evacuation. The results also suggest that as the extent of pedestrian's familiarity with the environment increases, pedestrians spend less time to escape from the room and are less sensitive to the hazard. In addition, it is essential to point out that, compared with the impact of panic contagion, the pedestrian's familiarity with environment has a more significant influence on the evacuation.