常用室内装饰材料燃烧的FDS模拟分析

为了获取室内装饰材料的火灾安全性,应用FDS火灾动力学仿真软件分别模拟了PVC(聚氯乙烯)、PMMA(聚甲基丙烯酸甲酯)、PS(聚苯乙烯)三种常用装饰材料的燃烧特性.模拟结果显示,PMMA材料初始燃烧速率最快,50s内近火源温度接近500℃,PS次之,PVC较为缓慢,但在500s内温度可达500℃以上;450s时PVC燃烧的过门热流量达到130kW,为三者最高;PVC材料初始产烟效果要弱于PMMA、PS两种材料,但70s后烟层高度下压趋势更为明显.模拟结果可以为室内消防设计及火灾现场人员的安全疏散提供参考依据.     

基于向量空间模型的中文文本层次分类方法研究

在文本分类的类别数量庞大的情况下,层次分类是一种有效的分类途径。针对层次分类的结构特点,考虑到不同的层次对特征选择和分类方法有不同的要求,提出了新的基于向量空间模型的二重特征选择方法FDS以及层次分类算法HTC。二重特征选择方法对每一层均进行一次特征选择,并逐层改变特征数量和权重计算方法;HTC算法把分别对粗分和细分更有效的类中心向量法与SVM方法相结合。实验表明,该方法相对于平面分类和一般的层次分类方法,有较高的准确率。     

热释放率对单室开口中性面影响程度的数值模拟

单室火灾的研究一直是建筑火灾研究的重点,文章运用火灾模拟软件FDS对ISO9705标准房间火灾进行了模拟研究.讨论了火源为不同液体反应物时,不同燃料的燃烧表面积与单位面积热释放率的关系,结果表明FDS模拟单位面积的热释放率受网格粗细的影响并随燃烧表面积的增加而逐渐趋于稳定;将开口处温度、速度曲线和Steckler的实验结果进行比较分析,表明模拟结果曲线与实验结果曲线符合较好;改变热释放率的大小,分析开口处的流动特点,通过对理论计算结果与模拟结果进行分析表明,开口处中性面高度随火源热释放率的增加而逐渐降低.     

Prediction of smoke back-layering length under different longitudinal ventilations in the subway tunnel with metro train

Due to the small width and the large train blockage ratio in subway tunnel, the smoke back-layering will be different from that in the wider road tunnel with small vehicle blockage ratio. In the train blockage region of tunnel, the velocity of longitudinal ventilated air-flow interacting with the back-flowed smoke gas is different from that in the upstream tunnel without train blockage. Then the back-flowed smoke gas might be prevented in the train blockage region with higher ventilation velocity, otherwise it would be stopped in the upstream tunnel without train blockage but with lower ventilation velocity. They were taken into consideration separately and an equivalent fire source was introduced by dividing the dimensionless heat release rate of fire source into two parts in the cases where the smoke back-layering length is longer than metro train length. A series of full-scale numerical simulations are carried out with FDS to investigate the smoke back-layering length in subway tunnel with different train lengths and longitudinal ventilation velocities. The simulation results indicate that the influence of metro train length on the smoke back-layering is great and cannot be ignored any more. A global correlation model is proposed based on the dimensionless analysis and simulation results.     

Numerical experiments in fire science: a study of ceiling jets

In this paper, a numerical experiment, consisting of 90 simulations in Fire Dynamics Simulator (FDS), is conducted for two different purposes. Firstly, numerical experiments are explored as a research method in fire science, and it is demonstrated that numerical experiments could be used as a complement to traditional fire experiments in fire science research. Secondly, an evaluation of previously derived correlations for ceiling jet excess temperatures and velocities is performed with the help of the results from the numerical experiment. The procedure used in this evaluation constitutes an outline for how a numerical experiment can be conducted in fire science. The evaluation indicates that the existing correlations will give a good estimate of the average temperature in a ceiling jet calculated by FDS. However, the correlations do not give a good estimate of the maximum excess temperature. A new correlation to estimate the maximum temperature has therefor been developed and is presented in the paper. Copyright © 2014 John Wiley & Sons, Ltd.     

Development and evaluation of two new droplet evaporation schemes for fire dynamics simulations

The evaporation of sprinkler droplets is an important phenomenon in fire simulations both for heat removal from the gas and for heat removal from surfaces. In this paper, we address the problems of potential numerical instability and super-saturation that may occur in explicit time integration of the droplet equations. Two novel numerical approaches are developed and evaluated. The first is based on an analytical solution that relaxes the cell composition and temperature toward the equilibrium values. The second method is an implicit solution to the droplet equations. The two approaches are implemented in the Fire Dynamics Simulator (FDS) and verified and validated using both single droplet and practical sprinkler calculations. Ultimately, the implicit approach is deemed the most cost effective for practical fire simulations.     

Experimental and numerical study of high-pressure water-mist nozzle sprays

The performance of extinguishment of fires by water sprays is strongly influenced by the characteristics of the sprays produced by nozzles. Computational fluid dynamics (CFD) based fire models are a tool that can be used for the characterization of sprays. However, it is necessary to evaluate the capability of a CFD based fire model in predicting the behaviour of sprays before using it for such characterization. One of the basic parameters that is important in characterising the water mist spray is the distribution of flux density of water droplets impinging on the floor. This paper reports the study on the characterization of water mists, in terms of distribution of flux density of sprays, produced by a single and a multi-orifice high-pressure jet nozzle. Full-scale experiments were conducted and the distributions of volume flux density of sprays were measured. The sprays were also modelled using a CFD model, Fire Dynamic Simulator (FDS), version 6, to investigate the capability of the model in predicting the distribution behaviour of the spray. The numerical results of distribution are compared with those obtained experimentally. The predicted results of FDS has show good agreement with the experimental results.     

APPLICATION OF FDS SCHEME TO 2D DEPTH-AVERAGED FLOW-POLLUTANTS SIMULATION

1 .　INTRODUCTIONSincethe 1990’s ,severalhigh resolutionschemesadoptedintheaerodynamicsfieldhavebeenappliedtodepth averagedtwo dimensional(2D)flowsimulation (Tan 1992 ,Alcrudo 1993andZhaoetal .1994a ,1996 ) .Someofthem ,suchastheOsherandFluxVectorSplitting (FVS )schemes,havebeenimprovedtoestimatethenu mericalfluxacrosstheinterfacebetweencellsinthe 2Dcoupledflow pollutantmodel (Qietal.1998andZhaoetal.1994b ,2 0 0 0 ,2 0 0 2 ) .Thehigh resolutioncharacteristic basedupwindFulxDifferen…     

高校教学楼走廊火灾烟气风险分析研究

为了解多层教学楼建筑火灾的蔓延和烟气运动,针对火灾烟气的蔓延特性,利用计算流体力学软件（FDS）模拟了某高校教学楼走廊中火灾和烟气的蔓延传播,通过算例分析了烟气温度场、可见度和CO体积分数等火灾过程参数的变化规律．研究结果表明,在火灾发生的4～5min时间内,走廊内的烟气温度、CO体积分数均达到人员安全的承受极限,能见度也将严重影响人员安全疏散．     

大空间建筑防火分区方法研究

针对目前防火分区划分标准单一且理论依据匮乏的问题,提出了基于火灾风险评估的防火分区方法,列举了传统防火分区方法与性能化设计存在的一些问题,阐述了基于火灾风险评估的防火分区方法具体实施过程,通过对比证明了基于火灾风险评估的防火分区方法有充分理论依据同时有实践应用性.使用FDS(Fire Dynamic Simulation)软件仿真某防火分区起火后烟气蔓延情况及防火分区内人员疏散所用的时间,以仿真实验数据为依据分析了此防火分区大小的合理性,同时验证了基于火灾风险评估的防火分区方法的可行性.若在大空间建筑中使用此方法划分防火分区,其优越性将得到很好的体现,这一方法将为相关的科研人员带来新的思考.