中庭火灾模型数值与实验研究

结合火灾相似模型实验对中庭火灾数值模型进行了比较，其中采用的燃烧子模型充分考虑了火源燃烧及蔓延过程对于烟气流动的影响。利用PHOENICS软件开发的应用程序计算表明，大空间建筑火灾数值模拟采用燃烧子模型和辐射换热模型，可以更好地反映出火源释热率的变化情况。计算结果与实验数据比较，定性合理。     

阳台对低层建筑风压作用下自然通风影响的数值研究

本文将通风量和工作平面平均风速作为衡量房间通风效果的指标,采用计算流体力学方法,分析了阳台对低层建筑风压作用下自然通风的影响.首先通过实验数据验证了数学模型的可靠性,数值模拟结果与实验结果具有良好的一致性.而后,通过模拟得到以下结论:对于单侧通风建筑,阳台能够极大地提高建筑中部及下部房间的通风性能;对于双侧通风建筑,阳台对室内通风性能的影响较小;阳台可以诱导空气进入房间更深的区域,在工作平面形成更为均匀的风环境.     

基于结构塌落的建筑火灾数值模拟方法

将流固耦合理论应用于建筑结构塌落的火灾数值计算中,建立基于结构塌落的火灾燃烧动力学模型,并将该模型嵌入火灾动力学系统FDS中,实现塌落物对火势影响的数值模拟。与原FDS进行数值模拟比对,验证该方法的可行性。将该方法应用于某居民建筑火灾案例中,进行基于结构塌落的建筑火灾数值模拟,结果表明塌落结构引起室内火灾发生轰燃现象,对室内温度、烟气浓度、CO2浓度变化产生重大影响。     

城市地震次生火灾蔓延模拟系统

地震次生火灾对人类的危害极大，在震后对火灾的发生和蔓延进行模拟，以便在最短时间内调集有限的消防力量进行救治。在ArcInfo平台上开发了城市地震次生火灾模拟系统，可以模拟地震灾变条件下城市建筑火灾危险性，模拟单个或者多个起火点可能燃烧的范围以及动态蔓延过程。介绍了火灾蔓延过程的模拟和系统的框架，并给出了实例。     

建筑火灾结构安全数值模拟框架

为了模拟建筑火灾过程中的火灾发展、结构响应及其相互作用提出了该模拟框架。该框架以现有的火灾模拟和结构分析数值模拟软件为基础,通过对其输入文件和模拟结果文件所含信息进行重新建模构成建筑火灾过程的数据环境,根据物理实验研究成果开发了材料高温强度退化和结构破坏方面的数值分析模块,与基础模拟软件一起构成覆盖灾难全过程的数值环境。该框架采用了面向对象的数据建模方法和系统集成技术,使得不同模拟模块的数据对象相互对应并协调工作,并能自动控制各模块实现对火灾过程的模拟,实现了在一个数据环境和一个软件平台上进行建筑火灾结构安全模拟。该框架为建筑火灾研究提供了数值实验方法,具有廉价和快速的特点,也是将实验室研究成果应用于具体建筑仿真的途径,对于建筑火灾性能化设计,消防救援预案的确定和火灾风险评估具有实用价值。     

某建筑火灾场景数值重建及烟气危害性评价

应用数值模拟技术重现了国内某建筑火灾发展的过程,并得到了火灾场景中烟气体积分数、温度、能见度等随时间空间变化的各种重要数据.使用生命伤害模型(LHM)和模拟得到的烟气数据分析了烟气对人造成的危害.模拟结果和分析揭示:在火灾中处在不同位置的房间,其室内的烟气体积分数变化可以分为不同的类型.在远离着火点的房间中,空气温度变化不大,但CO气体的体积分数很高,甚至比距离火源近的房间CO体积分数更高,烟气更容易在那里聚集,并且在很短的时间里,烟气对人构成致命的威胁.这与许多火灾中很多遇难者死于远离火源位置的结果是一致的.     

顶部开口腔室池火燃烧速率预测模型

为预测顶部开口腔室池火的燃烧速率,基于火灾动力学理论构建了顶部开口腔室池火燃烧速率预测半经验模型,利用实验数据的多元回归分析计算模型参数。模型燃烧速率的计算值与实际测量值的对比结果表明,燃烧速率预测模型对实际火灾场景模拟的可信度较高,研究成果可为船舶、地下建筑等顶部开口腔室的安全设计、火灾预防和火灾扑救等提供参考。     

Experimental study on fire performance of cross laminated timber structure exposed to compartment fire

为了研究室内自然火灾作用下可燃的正交胶合木(cross laminated timber, CLT)对CLT房间火灾荷载的贡献和不同层板组成的CLT对火灾的动态影响，开展4次内表面受火面积不同、板材层板组成不同的CLT房间自然火灾试验，直接受火CLT面积占CLT房间内表面积百分比分别为0%、19.8%、36.4%和87.6%；并以双区域模型为基础，建立考虑炭化层脱落的CLT结构室内自然火灾温度场计算模型，对CLT房间火灾试验进行模拟，分析双区域模型应用于CLT结构自然火灾时的有效性及局限性。试验结果表明：CLT受火面积对室内自然火灾发展过程及热量释放影响显著，随着CLT受火面积的增大燃烧速率显著提高，火灾的热释放速率增大；炭化层是否脱落对火灾发展过程影响显著，炭化层脱落时间及区域存在随机性；CLT单层层板厚度越薄，炭化层越早发生脱落；考虑CLT燃烧及炭化层脱落的双区域模型可一定程度上准确模拟CLT房间自然火灾室内空气温度，但是火灾降温阶段双区域模型预测的温度始终低于试验温度。     

多场耦合的建筑火灾数值模拟研究及应用

基于燃烧模型和结构力学模型,提出火-热耦合与热-力耦合之间的温度场转化方法。基于Python语言编写相应程序,可以实现温度场的自动转换。在此方法基础上,结合FDS与ABAQUS给出了多场耦合的建筑火灾数值模拟方法。并将此方法应用于某一农贸市场火灾,进行了火-热耦合与热-力耦合的数值模拟,得出温升、应力、形变随时间的变化,并与火灾勘验结果对比,验证该方法的可行性。     

火场通风的实验研究

本文着重研究在建筑火灾中消防救援人员所采取的通风 ,包括正压送风的作用。在消防训练楼首层的火灾模拟区中 (套间 ,含 3个房间和一个楼梯间 )以直径 0 .5 m的正庚烷油池火作为假想火源点进行了15次实验 ,其间连续记录了各房间中的温度、压力、火源质量损失速率 ,以及通过建筑外墙孔洞的空气流速等参数值。实验表明 :正压通风提高了燃烧物的燃烧速率 ,也使火场中下风方向房间 (相对于风机位置 )的室内温度升高 ,同时使上风方向房间的室内温度降低。这改善了消防队员的自身安全和工作环境 ,但却有可能会使那些困在火场中的人员遭遇火势侵袭的危险。因此 ,灭火中对于通风的应用与控制就显得十分重要了。     

Subgrid scale laminar flamelet model for partially premixed combustion and its application to backdraft simulation

Flame spread after air is suddenly introduced to a vitiated compartment in backdraft is between non-premixed and premixed flame spread under a ventilation-controlled condition. And it is necessary, but difficult to numerically simulate it. In this paper, an attempt of backdraft simulation is introduced. Numerical models including a subgrid scale laminar flamelet model and a partially premixed model are imbedded in FDS3.0 source code for backdraft simulation. Some significant fire characteristics reported in previous backdraft experiments can be seen in the numerical results. It is also indicated that these combined models can be used to predict the partially premixed combustion and fire phenomena under ventilation-controlled conditions.     

Modelling of hydrogen cyanide formation in room fires

A chemical kinetics model for calculation of the formation of hydrogen cyanide (HCN) has been made. The combustion of a mixture of methylamine and ethylene has been modelled using the stationary laminar flamelet concept. The flamelet calculations are based on several thousand elementary reaction steps including the chemical kinetics of HCN in combustion. The flamelets for both cold (293 K) and hot (1000 K) combustion product recycling have been calculated. The effect of strain is also included in the flamelet calculations. Scalar dissipation rates from 0.01 s⁻¹ to extinction values have been varied. Also the effect of radiation is included in the flamelet state relationships.

Separate flamelet sets for various levels of radiation, from adiabatic up to 30% radiation losses, incremented by 1%, have been made. In the flow field calculation, the flamelet options may be used either as adiabatic, constant radiation or an interpolation between flamelet sets of different radiation.

The chemical kinetics model, incorporated into a Reynolds-Averaging Navier–Stoke (RANS) type CFD code, has been used to simulate two laboratory fire tests of the combustion of nylon. Changing the size of the opening in the test room varied the ventilation between the two tests. Flamelet sets for a mixture of methylamine and ethylene with nitrogen content close to that of nylon were used in these simulations. The simulations were made with and without recycling the combustion products back to the fire.

The calculations show that recycling of the combustion products to the fire increases the formation of HCN and CO. Similarly, a lowered ventilation rate increases the formation of these species. The calculated temperatures and main species concentrations, including HCN, agree reasonably well with the trends in the laboratory measurements.     

Comparison of different combustion models in enclosure fire simulation

In this study, three combustion models, the volumetric heat source (VHS) model, the eddy break-up model and the presumed probability density function (prePDF) model, are examined in enclosure fire simulation. The combustion models are compared and evaluated for their performance in predicting three typical enclosure fires, a room fire, a shopping mall fire and a tunnel fire. High Reynolds number turbulence k–ε model with buoyancy modification and the discrete transfer radiation model (DTRM) are used in the simulation. Corresponding experimental data from the literature are adopted for validation. The results show satisfactory prediction in flow patterns and features in the complex enclosure fires. However, it is shown that these combustion models are not able to show consistent performance over the different locations and enclosure fires. The needs for adequate turbulent combustion models in enclosure fires are discussed.     

Validation of FDS for the prediction of medium-scale pool fires

Fire dynamics simulator (FDS) has been applied to simulate a medium-scale methanol pool fire. The simulation used predominantly the existing features in FDS except that an additional sub-grid-scale combustion model based on the laminar flamelet approach of Cook AW and Riley JJ [Combust and Flame 1998;112:593–606] was used alongside the default mixture fraction combustion model for comparison. The predictions of the two different combustion models for temperature and axial velocity distributions were found to be in reasonably good agreement with each other and the experimental data. The pulsating nature of air entrainment was demonstrated by the air entrainment velocity fluctuations and the instantaneous velocity vectors, which revealed formation and shedding of vortices and the well-known “neck-in” at a distance of approximately one diameter from the pool surface. The predicted variations of air entrainment at different heights agreed well with some published data and correlation. Although the limitation of the code in predicting the puffing frequency was noticed as the spectra of temperature fluctuations failed to demonstrate any dominant frequency, the present study has demonstrated the capability of FDS to deliver reliable predictions on most important parameters of pool fires.     

Modeling carbon black trace in building fire and its validation

The carbon black trace is an important characteristic in a building fire accident and becomes crucial evidence in fire investigation. Based on the particle deposition theory, the mathematical model is established for the carbon black trace in a building fire. The numerical model of the carbon black trace is implemented into the Fire Dynamics Simulator (FDS) software. The total mass of the carbon black particle deposited on the wall surface can be calculated quantitatively and be simulated visually. The proposed model is applied into a fire accident as a validation. A numerical model is used to simulate the fire accident. In numerical simulations, the grid size resolution is analyzed. The accident reconnaissance data, accident interview record and accident scene photo/video are compared with the results of numerical simulations. It shows that the simulation results have a good agreement with those in the fire accident, which validates the mathematical model in this study. The proposed method can provide useful data for fire reconstruction and fire investigation.     

A simple method for combining fire and structural models and its application to fire safety evaluation

To consider the actual fire characteristics in the fire response analysis of building structures and to simplify the complex relationship between the fire analysis model and the structural finite element analysis model, a spatio-temporal model of the fire temperature and heat flux boundary for heat conduction analysis is developed. The proposed model adopts a two-way orthogonal polynomial approach for fitting the discrete data from the fire simulation and obtains continuous spatial polynomial equations. It is shown to be accurate for capturing the distributions of temperature and heat flux that are required for a heat conduction analysis and a thermal mechanical coupling analysis. Finally, the model is implemented through user-subroutines UTEMP and DFLUX in ABAQUS, and it is applied to a new archive in Beijing. The results show that this method may be used to combine fire simulation and structural analysis for the safety evaluation of structures under fire.     

Real-Time Forecasting of Building Fire Growth and Smoke Transport via Ensemble Kalman Filter

Forecasting building fire growth and smoke dispersion is a challenging task but can provide early warnings to first responders and building occupants and thus significantly benefit active building fire protection. Although existent computer simulation models may provide acceptable estimations of smoke temperature and quantity, most simulations are still not able to achieve real-time forecast of building fire due to high computational requirements, and/or simulation accuracy subject to users’ inputs. This paper investigates one of the possibilities of using ensemble Kalman filter (EnKF), a statistical method utilizing the real-time sensor data from thermocouple trees in each room, to estimate the spread of an accidental building fire and further forecast smoke dispersion in real time. A general approach to forecasting building fire and smoke is outlined and demonstrated by a 1:5 scaled compartment fire experiment using a 1.0 kW to 2.8 kW propane burner as fire source. The results indicate that the EnKF method is able to forecast smoke transport in a multi-room building fire using 40 ensemble members and provide noticeable accuracy and lead time. Unlike other methods that directly use measurement data as model inputs, the developed model is able to statistically update model parameters to maintain the forecasting accuracy in real time. The results obtained from the model can be potentially applied to assist mechanical smoke removal, emergency evacuation and firefighting.     

建筑防火性能化设计中火灾场景的设定

性能化防火设计方法的应用为我国建筑防火设计领域中的有关难题提供了较为科学合理的解决方案，同时也对设计者提出了更高的要求。设计者对设计过程、方法以及工具有一个比较深入全面地认识，是保证建筑防火设计安全合理的基本前提之一。通过对建筑防火性能化设计的火灾场景问题进行探讨，以求科学地认识和理解性能化防火设计方法，促进性能化防火设计方法在在我国建筑防火设计领域的健康发展。