基于颜色模型和稀疏表示的图像型火焰探测

常用的图像型火焰探测算法是提取火焰在图像上表现出的单个特征信息或其有效组合作为识别的依据,需要大量的训练样本进行学习与参量优化,且识别率对特征选择的要求也很高.本文从火焰的整体特征考虑,提出了基于颜色模型和稀疏表示模型相结合的图像型火灾探测方法.首先在HIS空间建立颜色模型对火灾图像进行预处理提取出疑似区域,建立稀疏表示模型,并利用主成分分析方法构造火焰和疑似火焰物体的特征字典,最后利用l1-minimization计算测试样本与训练样本的最小逼近残差实现火焰和干扰物体的分类识别.实验结果表明,该方法提高了火灾图像的分类准确度和识别速度,同时具有较高的准确率.     

ISG-FHEV等效燃油消耗最小控制策略

针对室内复杂环境下火灾识别准确率会降低的问题,提出了一种改进的粒子群算法优化支持向量机参数进行火灾火焰识别的方法。首先在 颜色空间进行火焰图像分割,对获得的火焰图像进行预处理并提取相关特征量;其次采用PSO算法搜索SVM的最优核参数和惩罚因子,并在PSO算法中加入变异操作和非线性动态调整惯性权值的方法,加快了搜索SVM最优参数的精度和速度;然后将提取的火焰各个特征量作为训练样本输入SVM模型进行训练,并建立参数优化后的SVM分类器模型;最后将待测试样本输入SVM模型进行分类识别。算法的火灾识别准确率达到94.09%,分类效果明显优于其他分类算法。仿真结果表明,改进的PSO优化SVM算法提高了火焰识别的准确率和实时性,算法的自适应性更强,误判率更低。     

基于改进的PSO优化SVM火灾火焰识别算法研究

针对室内复杂环境下火灾识别准确率会降低的问题,提出了一种改进的粒子群算法优化支持向量机参数进行火灾火焰识别的方法;首先在YCrCb颜色空间进行火焰图像分割,对获得的火焰图像进行预处理并提取相关特征量;其次采用PSO算法搜索SVM的最优核参数和惩罚因子,并在PSO算法中加入变异操作和非线性动态调整惯性权值的方法,加快了搜索SVM最优参数的精度和速度;然后将提取的火焰各个特征量作为训练样本输入SVM模型进行训练,并建立参数优化后的SVM分类器模型;最后将待测试样本输入SVM模型进行分类识别;算法的火灾识别准确率达到94.09%,分类效果明显优于其他分类算法;仿真结果表明,改进的PSO优化SVM算法提高了火焰识别的准确率和实时性,算法的自适应性更强,误判率更低。     

CO和CO2气体红外光谱技术在火灾早期探测中的应用研究

通过对现有各种火灾探测方法进行归纳分析,提出以CO和CO2作为探测特征参量的傅里叶红外-光谱技术早期火灾探测新方法,并在此基础上建立了完善的早期火灾实验系统.通过大量真假火灾实验得出常见材料在火灾发生过程中产生气体浓度的变化特征:真实火灾产生出大量的CO和CO2,浓度变化非常有规律;假火灾只产生极少量的CO,且浓度变化杂乱无章.从浓度数据中提取出火灾发生的特征信息制定探测算法就可以有效地提高早期报警的分辨率,降低火灾探测的误报率.     

基于傅里叶变换红外光谱探测的火灾早期过程特征信息研究

通过对火灾过程中各种特征参量进行分析,提出采用CO作为早期火灾探测的探测对象,并在此基础上建立起基于傅里叶变换红外光谱仪的完善试验系统。通过该实验系统进行了大量早期火灾加热阴燃及燃烧试验,经过光谱定量分析得到其各自CO浓度变化数据。在数据分析的基础上通过时间序列分析建模建立起CO浓度数据的二阶自回归模型,提取出表征火灾整体特性的过程特征信息参数1和2。通过相平面分析表明:真假火灾的过程特征信息参数具有明显的区域分布差异性,利用这种特性可以快速将真假火灾分辨出来。大量试验结果证实该探测方法能够在火灾发生早期及时对真假火灾进行有效辨别。     

基于ViBe与机器学习的早期火灾检测算法

针对现有视频图像火灾检测算法前景信息丢失严重、误报率高、泛化能力弱等问题,提出一种新的火灾检测算法。其主要由前景提取和分类决策两大模块组成。在前景提取模块中改进ViBe算法,实现对运动区域的选择性更新;同时使用随机森林和支持向量机组成的两级分类器对运动区域颜色进行分类,以获取精确的前景区域。在分类决策模块中,提出两种新的早期火焰特征用于描述帧间火焰区域重叠率和火焰区域不同部分运动剧烈程度比率,再结合Hu矩特征训练出决策分类器。实验结果表明,该算法具有准确率高、误报率低、泛化能力强、响应时间短等优点,并能很好地应用于实际环境中。     

基于图像探测的早期火灾烟气模式研究

烟气是火灾过程中的重要物理现象。为改进早期火灾探测和预警,需要对基于图像探测的火灾烟气模式加以研究。以不同应用背景为依据,对烟气模式提出分类研究的思想。并以提高图像探测的可靠性和灵敏度为目的,对烟气的图像信息特征进行分析,提出了建立早期火灾烟气模式的设想。     

预混火焰前锋的观测及提取

介绍了用激光层析探测燃烧场的原理及其装置和图像处理工具的开发过程.利用预混V形火焰进行了激光层析探测火焰前锋的实验,结果显示该方法能够在入射光平面内清晰地分辨火焰皱褶在任一瞬间的几何形状.利用主动轮廓算法(ACM)从数字化图像中准确提取了火焰前锋的轮廓线形,为对火焰皱褶及其传播特性的量化分析打下了基础.     

高光谱技术融合图像信息的牛肉品种识别方法研究

高光谱图像包含了大量的光谱信息和图像信息,采用高光谱成像技术对牛肉品种进行识别。获取可见-近红外(400~1000 nm)光谱范围内的安格斯牛、利木赞牛、秦川牛、西门塔尔牛、荷斯坦奶牛五个品种共252个牛肉样本的高光谱图像。在ENVI软件中对高光谱图像进行阈值分割并构建掩膜图像,获取样本的感兴趣区域(ROI),并结合伪彩色图对牛肉样本的反射率指数进行可视化表达;采用Kennard-Stone(KS)法对样本集进行划分以提高模型的预测性能;对原始光谱采用卷积平滑(SG)、区域归一化(Area normalize)、基线校正(Baseline)、一阶导数(FD)、标准正态变量变换(SNV)及多元散射校正(MSC)等6种方法进行预处理;采用竞争性自适应重加权算法(CARS)提取特征波长。然后利用颜色矩对不同牛肉样本的颜色特征进行提取;对原始光谱图像进行主成分分析,结合灰度共生矩阵(GLCM)算法,提取主要纹理特征。最后结合偏最小二乘判别(PLS-DA)算法建立牛肉样本基于特征波长、颜色特征以及纹理特征的识别模型。KS法将牛肉样本划分为校正集190个,预测集62个;将未经预处理的光谱数据与经过6种不用预处理的光谱数据进行建模分析,结果发现经FD法处理后的光谱数据所建模型的识别率最高;结合CARS法对经FD法预处理后的光谱数据进行特征波长提取,共提取出22个波长;利用颜色矩和GLCM算法分别提取出每个牛肉样本的9个颜色特征、48个纹理特征。将特征波长数据与颜色、纹理特征信息进行融合建模,结果表明,基于特征光谱+纹理特征的模型识别效果最佳,其校正集与预测集识别率分别为98.42%和93.55%,均高于特征光谱数据模型识别率,说明融合纹理特征后使样本分类信息的表达更加全面;融合颜色特征后模型的校正集识别率均有所增加,但预测集识别率稍逊,颜色特征虽携带了部分有效信息,但这些信息与牛肉样本的相关性不大。因此,寻找与牛肉样本相关性更大的颜色特征是提高模型识别率的重要途径之一。该研究结果为牛肉品种的快速无损识别提供了一定的参考。     

火灾烟颗粒的分形结构形状模拟与光散射计算

针对火灾烟颗粒的形状特点，提出并建立火灾烟颗粒分形结构凝团的形状模型，并对烟颗粒扫描电镜(SEM)图像进行分析，获取分形结构模型中的单个凝团中基本颗粒个数、凝团分形维数、基本颗粒半径等参数.利用该模型对火灾烟颗粒的形状进行模拟的结果表明，该模型能够较好反映出烟颗粒的形貌特征.利用形状模型对火灾烟颗粒散射进行初步计算表明，在其他参数相同的情况下，相对于同体积的球形颗粒，分形凝团具有前向散射较弱，后向散射较强的特征.     

Experimental research on flame revolution and precession of fire whirls

This paper presents the first experimental effort to explore the large scale 3-D flame instabilities of fire whirls, including the inclined flame revolution during the transition from a general pool fire to fire whirl, and the swirling flame precession in a quasi-steady fire whirl. The experimental medium-scale fire whirls were produced by a fixed-frame facility. Experimental observations indicate that flame revolution is an important flame instability during the formation of fire whirl, showing that the entire flame is inclined and revolves around the geometrical axis of symmetry with increasing angular velocity until the critical point, without the self-rotation of the flame. It is found that the inlet velocity fluctuates synchronously with the flame revolution. As soon as the fire whirl forms, the erect swirling flame starts to precess around the geometrical axis of symmetry. Analysis indicates that during flame precession the periodic fluctuations of inlet velocity disappear and a local annular external recirculation zone (ERZ) is produced outside the flame (vortex core), while the flow is upward inside. It is found that the inlet velocities are nearly constant within the continuous flame in order to maintain a stable generating eddy. A good linear correlation exists between the average inlet velocities and average ambient circulations for all fuel pan sizes. The precession frequency is relatively stable during one test. The frequencies of flame revolution and precession are both proportional to the average inlet velocity, and the corresponding Strouhal numbers are constants of 0.42 and 0.80, respectively. The flame revolves and precesses in the same direction as the self-rotation of the fire whirl flame in all tests. The flame revolution is related to the periodical fluctuations of inlet flow, while the flame precession is considered to be linked to the occurrence of ERZ in fire whirls.     

Effect of flow circulation on combustion dynamics of fire whirl

In this paper, the effect of flow circulation on the combustion dynamics of fire whirl is systematically investigated by experiments. New correlations for the burning rate, flame height, radial temperature and mass flow rate are established for fire whirl. It is clarified that flow circulation helps increase both the fuel-flame contact area and the actual fuel surface area, which in turn increases both the heat feedback to the fuel surface and the radial velocity in the ground boundary layer, leading to increase of burning rate. A novel idea for correlation of fire whirl flame height is proposed by assuming that the ratio of the fire whirl flame height to the flame height without circulation solely characterizes the effect of circulation. This idea is fully verified, thereby a new formulation for flame height is established, which successfully decouples the burning rate and the circulation. It is indicated that the fuel-rich core in the flame body of fire whirl significantly affects the radial temperature distribution in the continuous flame region, and the flame body can be described by the combination of a cylinder and a cone. The flow circulation significantly suppresses fire plume radius and thus decreases its increasing rate with vertical distance. It is also demonstrated that the fire whirl flame involves laminarized regions in its lower section, coexisting with turbulent regions in the upper portion. The flow circulation enhances the air entrainment in the ground layer by altering the radial velocity profile and increasing the radial velocity. In the low section of flaming region, the significant decrease of mixture between the combustion products and surrounding air dominates the pure aerodynamic effect of flow circulation on the flame height. Finally, it is clarified that fire whirls maintain higher centerline excess temperature than general pool fires due to the effect of less air entrainment.     

The burning rate’s effect on the flame length of weak fire whirls

This paper discusses why the visibly-determined flame length of a weak fire whirl increases as compared with the corresponding pool fire without spin. Here, a fire whirl is called weak when the pure aerodynamic effect of flow circulation has a negligible influence on the flame length. Split cylinders were used to apply a flow circulation to a 3-cm-diameter methane burner flame and a 3-cm-diameter ethanol pool fire. After applying the flow circulation, the flame length of the ethanol pool fire increased about three times, while little change was observed in the flame length of the methane burner flame. The difference is explained by the fact that the burning rate of the methane burner flame was fixed constant, whereas that of the ethanol pool fire increased due to the increased heat input to the fuel surface caused by a change in flame shape pushed toward the fuel surface. The experimental observations thus demonstrate that the burning-rate effect can significantly increase the flame length even under a weak circulation condition. Computational fluid dynamics (CFD) simulations were conducted to understand the detailed flow structure of a fire whirl. An analytical model was then developed based on the experimental observations and CFD calculations; the predicted relationship between the flame height and the burning rate agreed with experimental data.     

A reduced-scale experimental investigation of facade flame behavior ejected from a top-hung window of fire compartment

In case of a room fire, facade flame ejected from a window could lead to catastrophic consequence. Top-hung window is a common feature in modern buildings. This paper investigates, for the first time, the ejected facade flame behavior from a top-hung window. Experiments are performed by a cubic scale model compartment with a top-hung window of four opening angles and four dimensions under various heat release rates (HRR). A total of 119 test conditions are involved to quantify generally the ejected facade flame behavior and morphological characteristics, characterized by its vertical height and horizontal depth (normal to facade). It is found that the position of neutral plane between the inflow and outflow at the top-hung window increases with opening angle, while being smaller as the window width is larger or the window height is smaller. The critical HRR for flame ejection is higher as the top-hung window opening angle is larger. The facade flame depth increases, while the flame height decreases, with increasing of opening angle of the top-hung window. A new characteristic length taking into account both the top-hung window dimensions and window opening angle is deduced by the mass balance analysis of the inflow and outflow as well as ventilation factor through the top-hung window. New dimensionless models are established to describe the critical HRR for flame ejection, the height of the facade flame and flame depth as a function of the newly derived top-hung window ventilation factor as well as characteristic length, showing good fitting of experimental results. The present study provides the basic data, understanding and model of facade flame characteristics from a top-hung window of a fire compartment, which is essential in estimation of its risk and adverse impact to urban environment as a new supplementary over previous knowledge limited for freely opened windows.     

Limiting conditions for flame spread in fire resistant fabrics

Fire resistant (FR) fabrics are used for astronauts, firefighter and racecar driver suits. However, their fire resistant characteristics depend on the environmental conditions and require study. Particularly important is the response of these fabrics to varied environments and radiant heat from a source such as an adjacent fire. In this work, experiments were conducted to study the effect of oxygen concentration, external radiant flux and oxidizer flow velocity on the concurrent flame spread over two FR fabrics: Nomex HT90-40 and a Nomex/Nylon/Cotton fabric blend. Results show that for a given fabric the minimum oxygen concentration for concurrent flame spread depends strongly on the magnitude of the external radiant flux. At increased oxygen concentrations the external radiant flux required for flame spread decreases. Oxidizer flow velocity influences the external radiant flux only when the convective heat flux from the flame has similar values to the external radiant flux. The results of this work provide further understanding of the flammability characteristics of fire resistant fabrics in environments similar to those of future spacecrafts.     

着火油罐辐射热传递过程实验研究

通过对直径D=1 m、 1.5 m、2.7 m全掀顶油罐着火特性实验研究,分别得出汽油、柴油的火焰形状,及距油罐1D、1.5D的火焰辐射强度和温度动态分布数据,对直径1 m的相邻油罐,得出在火灾辐射场中其壁面温度分布和罐体内部压力及温度动态变化曲线,研究内容对修订我国相关消防规范和工程设计提供参考,同时为开展数值模拟提供参照标准。     

低密度EPS不同角度及厚度情况下火蔓延特性研究

本文采用小尺寸实验的方法探究了低密度EPS火蔓延及其熄灭特性,分析了密度、厚度以及角度综合因素对EPS火蔓延及熄灭的影响。研究发现:密度为6 kg/m^3的EPS,由于密度很小,材料厚度以及放置角度受到密度影响的抑制,EPS均无法被火源点燃进而进行火蔓延;而当密度为10 kg/m^3的EPS,随着材料厚度以及放置角度的增加,试样经历了从不能点燃,到短距离不稳定火蔓延,正常蔓延,以及蔓延过程中收缩性熄灭等过程。研究发现,密度为10 kg/m^3,厚度为4 cm的EPS试样,当放置角度为0°、10°、20°和30°时,能够正常蔓延,而当角度增加至40°、50°时,EPS火蔓延过程中出现了收缩性熄灭的现象.通过分析火蔓延过程收缩性熄灭机理,发现火蔓延速度与预热区的长度之间的相互竞争机制,是导致熄灭现象产生的主要原因。实验结果表明,收缩性熄灭对火蔓延速度,池火区长度以及表面火焰区火焰形态等都产生了相应的影响。     

Large eddy simulation of fire plumes

FireFOAM, a new fire modeling code based on the OpenFOAM platform (www.openfoam.org), is developed and applied to model a series of purely buoyant fire plumes with heat release rates from 14 to 58 kW. The calculations are compared with McCaffrey’s (1979) experiments. The simulation results demonstrate good quantitative agreement with experimental measurements, and show the scaling relations of mean temperature and velocity in the continuous flame, intermittent and plume regions. The numerical simulations are shown to be strictly conservative in energy. Predicted flame heights and entrainment rates also compare well with experimental correlations. The good agreements in all aspects examined show that the current CFD model performs well for small-scale fire plumes. Turbulent fluctuation intensities and PDF of mixture fraction are presented to gain more insights into the structure of fire plumes.