大空间温度场预测模型与实验分析

介绍国内三个大空间温度场预测模型。通过在某高大钢结构厂房内进行大空间小功率油池火实验,得到火焰正上方4.0m和7.5m处的温度变化情况。将实验结果与三个预测模型的预测结果进行对比,结果表明:三个模型都能较好地预测出火源正上方4.0m处温度变化的趋势;只有张国维公式给出了火灾全过程预测;薛素铎公式能够很好地展现增长阶段到稳定阶段的过渡过程;对7.5m处的预测结果偏差较大;三个公式都对最大温度值有较强的依赖性。     

基于复杂热解模型的CLT房间火灾温度场数值模拟及iBMB参数化火灾升温曲线修正

为研究正交胶合木(cross laminated timber, CLT)自身可燃性对CLT房间火灾温度场的影响，在FDS(fire dynamics simulator)软件中采用复杂热解模型对CLT构件和可移动火灾荷载(木垛)进行精细化实体建模，建立CLT房间火灾试验模型，结果表明，复杂热解模型能够合理反映CLT房间火灾衰减前的温度发展趋势，较准确地预测轰燃温度、峰值温度和火灾充分发展时长，与已有试验结果的误差范围分别为-3.4%～-27.8%、-1.1%～-12.5%和0.3%～34.0%。在上述研究的基础上，基于iBMB参数化火灾升温曲线将可移动火灾荷载简化为一个自定义热释放速率的燃烧器，在FDS中对可移动火灾荷载简化建模，该方法能够提高计算速度，得到的温度-时间曲线在火灾增长和充分发展阶段与试验结果较一致，但会高估火灾充分发展时间，延长15～20 min。最后，通过考虑木材可燃性修正iBMB参数化火灾升温曲线中的火灾荷载密度和峰值热释放速率，得到适用于通风控制型CLT房间火灾升温曲线的理论计算方法，计算结果与试验值吻合较好，峰值温度与试验值的误差范围都在10%以内，与其他学者...     

浅析基于BIM的图像型火灾探测器设计方法

图像型火灾探测器给人以丰富和直观的信息,清晰的图像以及其自身的特点较好地解决了高大空间如何进行早期火灾探测及报警这一难题,但在工程设计中,多组探测器的空间定位与实际保护区域的关系很难量化表达。因此本文阐述了一种基于BIM模型的高大空间火灾探测参数化设计方法,可为高大空间的电气消防设计提供有力的数据支撑。     

自然火灾中钢结构构件温度场模拟

在既有一榀框架受火实验的基础上,建立了该实验框架的精确有限元模型。通过与试验结果对比,获得了较好的温度场模拟结果。从结构抗火设计实际需要的角度出发,探究不同火灾发展因素对构件升温的影响,使用ABAQUS模拟多种参数化火灾模型下构件温度场分布。研究表明:有限元软件ABAQUS能够获得较精确的温度场分布;考虑多种随机性参数更有利于钢结构抗火工程。     

用火灾模型确定航站楼大空间自然排烟面积

利用流体力学计算软件建立火灾模型,对重庆机场T2A航站楼进行自然排烟的数值模拟,根据火灾可能发生的烟气运动规律,计算模拟大空间内温度场和烟浓度场随时间变化的分布情况,分析排烟方案的有效性。结果表明:高大空间的建筑可适当减小排烟口面积。     

超高混凝土梁水化热温度场仿真分析

笔者以厦门医学院屋顶层超大跨径超高混凝土梁浇筑施工为例,利用MIDAS/CIVIL有限元软件建立了该梁的3维实体有限元模型,对其浇筑64 h内的温度场进行了模拟分析,得到温度-时间曲线,并与现场实测数据进行了对比,结果表明有限元模型能够较好地模拟大体积混凝土实际的温度场。同时对环境温度参与对流和不同形状散热面对浇筑梁体温度的影响进行了分析总结。     

高大空间池火羽流中心线轴向温度试验研究

开展高大空间640kW及1 080kW的小功率油池火灾试验,试验测量火源上方4.0～7.5m处羽流中心线的轴向温度。采用经典McCaffrey模型、Zukoski模型以及Heskes-tad模型预测羽流中心线轴向温度,并将理论预测值与试验值进行对比。对比结果表明:三种羽流模型预测的羽流中心线轴向温度与真实火场温度基本相吻合。McCaffrey模型预测的羽流中心线轴向温度最高,Heskestad模型次之,Zukoski模型预测温度最低。Heskestad羽流模型较适合于高大空间的小功率油池火灾火场温度的精确预测。火源功率较大时,Zukoshi模型预测结果可能较真实火场温度小。     

基于CCD的大空间建筑中智能消防炮定位技术

以立体视觉原理为基础,采用垂直交汇CCD视觉测量方法对火灾进行定位,并对定位数据进行概率滤波,使定位数据的精确性更好地适用于高大空间建筑消防安全的需要。通过实验仿真并与传统的消防炮定位方式进行比较,表明该方法具备较好的精确性与可靠性,在火灾定位上有着良好的应用前景。     

高大空间建筑中火灾探测器的选用

现代建筑中，高大空间建筑越来越多。本文详细阐述了目前能够较好解决高大空间火灾探测问题的几种感烟探测器的工作原理、主要性能特点、适用场所和设置要求，为不同空间构造、空间高度、使用功能、环境条件、火灾成因、火灾发展特征的高大空间建筑，火灾探测器的选用提供一定的技术依据。     

火灾下H型钢梁温度场的模拟

采用有限元法，对钢梁在火灾标准温升温曲线作用下的温度场进行了分析，并用VisualC＋＋进行编程，将计算结果与试验结果进行比较，得出所设计的温度场程序合理，基本可以对火灾温度下梁截面温度场进行温度计算的结论。     

Temperature fields for fire resistance analysis of structures exposed to natural fires in large space buildings

Temperature fields analysis is an essential work to evaluate the behavior of structures in fires. Large space buildings are mostly highly populated or high‐fire load places with high fire risks. So it is a research focus to predict the temperature fields of large space fires accurately. In this study, a full‐scale physical experiment on fires in large spaces has been conducted. The results show that the temperature distribution of natural fires in large spaces is nonuniform. With regard to the evolution laws of the temperature fields of natural fires in large spaces, the author developed a new temperature field prediction model for large spaces. The new model has been compared with the well‐known Li G Q model and the Xue S D model. Based on the comparative analysis, the new model can predict the change laws of the temperature fields with time in the whole fire process and reflect the gradual attenuation of temperature fields in the fire during the decay phase better. In the meantime, this new model developed by the authors can be used to structural analysis exposed to fires in large space buildings.     

A simple method to predict temperature development in a protected steel member exposed to localized fire in large spaces

Temperature development is a key issue for fire protection of steel structures. However, until now, there has been little systematic approach to predict the steel temperature development during the whole process of a localized fire in large spaces. The smoke temperature development in large spaces is different from that in normal enclosure fires as they have lower maximum temperatures and non‐uniform temperature distributions. In the present study, a whole process prediction method for the development of smoke temperatures in a large space localized fire is proposed. The prediction method accurately reflects the temperature curves (in the growing, fully developed and decay phases) and the uniform temperature distribution in large space localized fires. Based on basic heat transfer principles and the proposed smoke temperature development model, a new relationship is proposed to predict the temperature development in a protected steel member exposed to localized fire in large spaces. There is only one variable, t (time), in the proposed relationship, and thus, it is very simple to implement in evaluating temperatures, and it accurately reflects the development of the whole fire process (growing, fully developed and decay phases). Copyright © 2016 John Wiley & Sons, Ltd.     

Transport Time Lag Effect on Smoke Flow Characteristics in Long-Narrow Spaces

This paper focuses on the smoke transport lag time at the early stage of fires in long-narrow spaces, which is defined as the time from fire onset to the time when smoke reaches a given position on the ceiling. For a heat detector at a specific location on the ceiling, the smoke transport lag time is a part of the response time of the heat detector. Especially when the heat release rate is relatively small at the early stage of fires, the smoke transport lag time will be very long, which will hence lead to the increase of heat detector response time. It is clear that the prediction of smoke transport lag time is critical to the activation time of the heat detector. However, previous studies have much focused on fire characteristics in long-narrow spaces, leaving very few on the transport time lag. Therefore, in this study, a theoretical model regarding smoke transport time lag was developed for both steady and time-dependent fires based on the weak-plume theory. This model was validated by a series of reduced-scale experiments. It can be concluded from comparison that the predictions of this model agree reasonably well with the corresponding experimental results. Using the proposed method, the dimensionless equations of smoke transport time lag, velocity and temperature considering the smoke lag effect in a long-narrow space for time-squared fires were also theoretically deduced. Additionally, to further determine the applicability of ‘Quasi-steady’ state assumption for time-squared fires, a calculation method regarding the critical time was also developed. The outcomes from this study will be beneficial to the development of fire detection model in long-narrow spaces.     

双区域模拟大空间火灾烟气下降和升温规律的分析

利用以双区域模拟为基础的修正计算方法，对大空间建筑火灾进行计算，对得出的室内烟气下降和温度与时间的关系进行分析比较。通过比较得出：烟气下降的速度随着失火空间的增大而减小，随火源功率的增大而增大；平稳段烟气平均温度随着失火空间的增大而减小，随平稳段火源功率的增大而增大，但并不受火源增长速度影响。     

对运用双区域模型计算大空间建筑火灾温度方法的修正

以较为精确的场模拟为参照，对于运用双区域模拟计算出的大空间建筑火灾室内烟气温度与时间的关系曲线进行修正。通过比较计算结果得出，此修正方法提高了计算精度，并在一定程度上扩大了双区域模型计算方法的适用范围和可计算时间。     

Experimental measurements,integral modeling and smoke detection of early fire in thermally stratified environments

Building fires go through a series of stages. They start with a fire plume period during which buoyant fire smoke rises to the ceiling. A second stage is the following enclosure smoke-filling period. In this paper, the first stage is the subject, especially for the fire plume behavior in thermally stratified environments in large volume spaces. In NFPA 92B, Morton's integral equation was introduced for calculating the maximum plume rise, and beam smoke detectors were recommended for smoke detection design. In this work, experiments and CFD simulations were conducted in a small-scale enclosure and a large space to investigate early fire movements in temperature-stratified ambients. The results show that in a thermally stratified environment, the axial temperature and velocity of a fire plume decrease more quickly along the vertical axis than in uniform environment, and in some cases the fire plume ceases to rise. The previous integral equation was shown to underestimate the actual maximum height of a fire smoke plume, and also was unable to explain the differences of the maximum heights of low-density and high-density smoke plumes with the same stratification and outlet conditions. The integral equation was improved by introducing two correction factors, and extended for non-linear temperature stratified environments. A light section smoke detection method with three space-protected area was suggested and discussed.     

Vereinfachtes Naturbrandmodell für die Brandschutzbemessung von Bauteilen und Tragwerken

Simplified natural fire model for the fire safety of components and structures In this contribution a simplified natural fire model is presented, which is based on a realistic design fire and was derived on the basis of extensive simulations with heat balance models. With so‐called real fire curves the temperature‐time curves of natural fires in multi‐storey residential and office buildings can be gathered realistically with a simple hand resp. spread sheet calculation. In contrast to the design with ISO 834 standard temperature‐time curve, the fire safety design according to Eurocode can be performed with the thermal action given by the real fire curves considering the existing boundary conditions (ventilation, fire load, geometry). The application of the method is demonstrated by means of an example.     

不同火灾下膨胀型钢结构防火涂层的隔热性能

基于36个试件在标准火与大空间火下的隔热性能测试,计算膨胀型钢结构防火涂层的等效导热系数,研究升温条件对防火涂层隔热性能的影响规律及机理.结果表明,防火涂层是否反应完整取决于火场的最高温度,升温速率影响膨胀-固化阶段防火涂层的发泡程度;升温历史不同,防火涂层的膨胀倍率和炭化层泡孔结构不同,最终表现为防火涂层隔热性能的差异.防火涂层在标准火下的隔热性能优于大空间火下的隔热性能,两者的等效导热系数代表值λr最大差异为65%.升温速率越快,火场最高温度越高,防火涂层的等效导热系数值越低,隔热性能越好,因此,用标准火下防火涂层隔热性能的检测结果来指导大空间火下防火涂层的设计是不安全的.大空间火下防火涂层等效导热系数随升温条件变化的程度还要受涂层厚度的影响,随涂层厚度增加,不同工况下的防火涂层等效导热系数差异程度减小.     

大空间火灾下铝合金构件温升计算方法

性能化抗火设计过程中,火灾下结构构件的温升计算方法对设计结果具有重大影响。为研究大空间火灾下铝合金构件的温升计算方法及火焰辐射对构件温升的影响,对2种常见的铝合金构件截面试件进行了火灾温升试验。试验结果表明,由于火焰辐射的作用,构件温度与周围空气温度较为接近。基于铝合金构件的导热微分方程,提出了一般室内火灾和大空间火灾下铝合金构件的温升计算方法,并与试验结果进行了对比分析。结果表明：计算大空间火灾下铝合金构件温升时,忽略火焰辐射的作用会导致结果偏于不安全;所提出的基于点火源假定的火焰辐射热量计算方法较欧洲规范中的计算方法更为简单准确。此外,火焰辐射下烟气黑度值对构件温升的计算具有较大影响,并根据试验结果拟合了烟气黑度的实用计算式,计算结果与试验拟合结果吻合良好。     

A Simplified Mathematical Model for Predicting the Vertical Temperature Profiles in Enclosure Fires Without Vertical Opening

This paper presents a mathematical model to predict the instantaneous temperature profiles in sealed or ceiling vented compartment fires. It has been observed in the existing research that in compartments without vertical opening, smoke fills the volume very soon indicating that the so-called one-zone type distribution forms quickly, and the gas temperature inclines linearly with height above the fire source. These characteristics are different from the smoke filling properties in enclosure fires with vertical openings. An assumption of linear distribution for temperature was introduced and a modified one-zone model was subsequently proposed in order to predict the transient smoke temperature profiles after the smoke fills the enclosure. With the knowledge of the heat release rate, the prediction model was established based on unsteady energy conservation by changing the heat loss factor using the semi-empirical models for fire plume and ceiling jet. Experiments including sealed and ceiling vented conditions were conducted to validate the model and the comparisons between measurements and predictions suggested the model can give fairly satisfactory estimations for the transient temperature profiles for both tests.