【作者】 陈曦；

【导师】 钱稼茹；

【作者基本信息】 清华大学 ， 土木工程， 2009， 硕士

【摘要】 目前,大空间火灾仿真主要侧重于模拟和研究烟流的运动规律,并以此获得一系列火灾热参量的时空分布进行探测系统的评估和设计。对于接触式感烟探测,这样做造成了火灾场景和探测系统的分离,未能考虑两者的相互作用。本文通过将探测器模型引入火灾模拟平台,在数值上实现了将火灾热参量时空分布信息与探测器模型相结合,分别在质量浓度和粒径分布这两个烟雾特征参数层面探讨了实现全探测过程仿真的策略。依托FDS火灾模拟平台,分别考虑点型和空气采样2种接触式感烟探测器的迟滞效应和稀释效应,给出了标定模型参数的方法和步骤,从而实现由环境烟雾特征参数向探测腔内烟雾特征参数的转化。对北京大学体育馆进行了早期火灾分析,模拟了3个火源13种工况下羽流形态和烟雾发展情况,得到了热障环境下大空间火灾的典型现象。基于烟雾质量浓度,针对JTY-GD-1109A点型和VESDA-LaserPLUS空气采样2款探测器产品,分别采用数值风洞实验和ASPIRE2程序模型化环境烟雾到达其各自探测腔的过程;结合北京大学体育馆火灾分析结果,给出了该2款探测器基于遮光率响应阀值的工作性能评测。结果表明:点型探测器对小功率火探测失效;空气采样探测器探测效果受管网布置影响较大,水平管结合下垂管的组合采样方式能有效克服热障环境影响,对各种火灾情况应对能力强,尤其对小功率火探测优势明显。基于烟雾粒径分布,将FDS提供的热参量信息结合Brown凝并方程的Moment解,获得了变凝并速率下烟雾凝团粒谱的演化预测。通过对不同火灾场景下烟雾凝团粒谱参数的计算及对其影响因素的讨论,提出了对于大空间火灾,可以忽略探测点位置处由于Brown凝并导致的粒谱演化,统一认为远火焰区的烟雾凝团粒谱均一,直接采用脱离近火焰区时的初值。基于此,将探测腔内烟雾凝团的质量浓度时程转换为烟雾粒径分布,通过Mie光散射模型进一步实现烟雾在探测腔内被光学感应的模拟,在更微观的层面上给出了描述全探测过程仿真的初步策略。更多还原

【Abstract】 The recent studies of simulation of large space fire are mainly emphasis on the movement of smoke flow. And according to the temporal and spatial distribution of fire thermal parameters, the performance evaluation and design of detecting systems are carried out. However, for the contact smoke detection, such operation separates the detecting system from fire scenario without considering the interactions of each other. On the basis of introducing detector models into fire simulation platform, the combination of fire analysis information and detector models is realized in this paper. A simulating strategy aiming at the whole detecting process is established respectively based on 2 smoke characteristic parameters: mass concentration and size distribution.Relying on the fire simulation platform of FDS, the parameter calibration methods for spot-type and air sampling smoke detectors were proposed with considering of their respective working characteristics: time-lag effect and diluting effect. Therefore, the conversion of smoke characteristic parameters from fire scenarios into detector’s sensing chambers is realized.Early fire analyses of Peking University’gymnasium were carried out, and some typical phenomena of large space fire was obtained with the simulation of plume shapes and smoke movements including 13 conditions subordinated to 3 fire source locations.Based on the smoke mass concentration, numerical wind tunnel experiments and ASPIRE2 program were adopted respectively to model the process of smoke entering the sensing chamber of 2 kinds of detector products: JTY-GD-1109A spot-type detector and VESDA-LaserPLUS air sampling detector. On the basis of FDS fire simulation of Peking University’gymnasium, the performance evaluation of the 2 detector products were presented based on the alarm threshold of obscuration. The analysis results show that the spot-type smoke detectors fail to detect small fires; while the effect of air sampling detection is significantly influenced by the arrangement of pipe networks. The assembled sampling, which combines ceiling and vertical pipes, can overcome the adverse effect of thermally stratified environments, and have high coping ability in various fire situations, especially for small fires.Based on the smoke size distribution, the time evolution of smoke particle spectrum with varying coagulation rate was obtained by combining numerical calculation of fire thermal parameters and the Moment solution of Brownian coagulation equation. With the predicted evolution of smoke particle spectrum parameters in different fire scenarios, the influencing factors were discussed. And furthermore, a practicable operating suggestion aiming at large space fire is proposed that the time evolution of smoke particle spectrum caused by Brownian coagulation can be neglected in detecting positions where remote from the fire origin. Thus, the initial values when the smoke particles leaving the near-zone of the fire origin can be adopted to convert the time history of smoke mass concentration into size distribution in the detector’s sensing chamber. Finally, on the basis of optical simulation by Mie model, a preliminary simulating strategy of the whole detecting process is proposed on a more microcosmic level.更多还原