ISO房间火灾烟气层温度数值模拟工程方法研究

利用场模拟FDS和区域模拟CFAST软件，对ISO房间中55kW和110kW的火灾烟气层温度进行数值模拟，将不同尺寸网格划分条件和区域划分方法的计算结果与试验结果进行分析比较，在保证一定精度条件下，为减少计算所需时间而增大网格尺寸的可能性，并对区域模拟中采用多区域划分方法以提高计算精度的可行性进行了分析，为类似环境的工程应用，单区域划分和多区域划分方法的使用提出了建议。     

非均匀网格法在场模拟软件FDS中的应用

场模拟软件FDS中实现网格非均匀分布的方式包括多分区法和拉伸与收缩法。多分区法将整个计算对象划分为多个分区，每个分区内网格分布均匀，分区间网格尺寸各不相同；拉伸与收缩法通过对网格的拉伸和收缩，将均匀网格尺寸调整为非均匀的物理间隔。对5种不同网格分布情况的模拟结果进行对比，分析认为非均匀网格法能有效提高计算精度，并降低模拟时间。     

基于大涡模拟的火灾数值模拟网格划分优化方法

摘 要：网格划分是火灾数值模拟的重要环节,对模拟结果的精度以及模拟时间有很大影响。针对火灾数值模拟中的网格划分问题,提出了一种基于大涡模拟的网格划分优化方法。根据大涡模拟的原理,给出了滤波尺度的计算方法,并根据滤波尺度和网格比系数对火场中不同区域的网格尺寸进行优化处理。将优化方法应用于高层建筑火灾的数值模拟,运用FDS软件分别针对优化前网格、优化后网格以及精细网格进行数值模拟,对不同网格划分下的温度、氧气和二氧化碳体积分数进行比对。结果表明：网格优化后,模拟结果与精细网格之间相关系数的均值为0.987,保证了模拟精度;同时,模拟运行时间降低为精细网格的16%,有效提升了火灾模拟的计算效率。     

常用火灾数值模拟软件FDS的应用探讨

通过对FDS模型构建、网格划分等方面进行分析，指出了其应用中存在的局限性，并就如何初步判断FI）s软件使用的正确性进行了分析，以推广火灾数值模拟软件FDS的应用。     

浅谈FDS软件对非规则建筑边界的定义

FDS(Fire Dynamics Simulator)软件对单房间或数目较少的房间作火灾预测分析时，是一个很好的分析工具，但在对不规则建筑的边界定义粗糙时，所计算的结果将很不理想，对这些特殊建筑如弧形墙、倾斜墙及其墙上开口的边界给出了合理的定义。同时应用FDS软件对不同大小的网格进行了计算探讨，将计算结果进行了比较，发现合理的网格大小在FDS软件计算中是非常重要的。这对理解FDS软件的应用有很好的工程实用价值     

基于ISO9705房间木垛火试验的FDS模拟预测研究

为了验证FDS模拟的有效性和可靠性,在ISO 9705试验房间内进行一定荷载的木垛火试验.利用火灾动力学模拟软件FDS针对同样的火灾场景进行模拟计算,比较不同网格配置对模拟结果的影响.结果表明:Multi-block 格点配置是最佳的格点配置形式,其模拟得到的木垛火热释放速率变化、烟气温度变化、CO2 体积分数变化的结果能够很好地与实测值吻合,但对CO体积分数不能准确模拟;Multi-block能够在不降低计算精度的前提下,降低格点数目,减少计算时间,节约计算成本.     

正交异性钢桥面数值计算中网格划分 对精度的影响研究

针对有限元数值模拟计算中,网格划分尺寸影响计算精度的问题,采用不同单元尺寸对正交异性钢结构典型疲劳细节进行数值模拟。分析表明:网格划分尺寸对计算结果影响显著,铺装层、顶板、U肋、横隔板弧形切口的合理网格划分尺寸分别为8 mm、4 mm、8 mm、4 mm。     

呼吸式幕墙建筑烟气流动的网格独立性研究

对呼吸式幕墙建筑的结构特点,采用FDS数值模拟对其进行了网格独立性研究,当夹层厚度与夹层方向网格尺寸的比值不少于2.25时,认为其结果满足网格独立性要求。另外,结合了K.Overholt网格计算方法的优点,提出了一种新的解决呼吸式幕墙建筑数值计算的网格计算方法,即RK网格尺寸计算法。     

格构塔数值风洞基础研究

合理的数学模型和恰当的参数是数值风洞模拟结果可靠的前提,针对这个问题,对格构塔架进行数值模拟,比较了各种不同条件下的数值风洞平均风压模拟结果,分析了计算区域、网格划分、湍流模型和湍流强度等因素对数值模拟结果的影响程度.结果表明:湍流模型和计算区域的影响相对较大,合适的计算流域为自结构表面向外取30~50倍肢宽, 标准k-ε模型误差最大,大涡模拟(LES)模型和RNG k-ε模型最精确;格构塔的网格划分比较难,要求网格尺寸比较小,故网格划分影响不大;湍流强度对平均风压的影响比较小.     

火源高度对小室烟气温度场的影响研究

通过不同高度小功率火源的6组试验,结合同工况的FDS模拟,将试验、数值模拟和Heskestad理论模型计算结果对比发现:理论模型的轴线温度计算结果远高于实际值,但在顶棚发生射流处,能够准确预测温度;FDS得到的火焰高度有一定误差,且受辐射影响较大;顶棚射流烟气可以根据温度的衰减梯度划分为3个区域:稳定区、骤变区和渐变区。     

Fire Dynamics Simulator (Version 4.0) Simulation for Tunnel Fire Scenarios with Forced,Transient, Longitudinal Ventilation Flows

In this study, a series of sensitivity analyses were conducted to evaluate a computational fluid dynamic (CFD) model, Fire Dynamics Simulator (FDS) version 4.0, for tunnel fire simulations. A tunnel fire test with a fire size on the order of a 100 MW with forced, time-varying longitudinal ventilation was chosen from the Memorial Tunnel Ventilation Test Program (MTVTP) after considering recent tunnel fire accidents and the use of CFD models in practice. A careful study of grid size and parameters used in the Large Eddy Simulation (LES) turbulence model—turbulent Prandtl number, turbulent Schmidt number, and Smagorinsky constant—was conducted. More detailed analyses were performed to refine the smoke layer prediction of FDS, especially on backflow (i.e., a reversed smoke flow near the ceiling). Also, energy conservation was checked for this scenario in FDS. A simple guideline is given for smoke layer simulations using FDS for similar tunnel fire scenarios.     

基于网格变换的火灾中塌落固体建模及应用

基于网格变换的思想,提出了一种在网格中建立塌落固体并与流场进行耦合的建模方法。根据此方法对FDS 软件进行功能扩展,使其能够对塌落固体建模并模拟。利用改进后的FDS 软件对无结构塌落和有结构塌落情形的相同火灾场景的进行模拟。对于有塌落情形的模拟结果,其温度和CO2 曲线在塌落时刻之前与无塌落情形一致,而在塌落时刻之后与实际火灾中塌落造成的轰燃现象一致,证明此方法可以较好地模拟固体的塌落及其对火灾场景的影响。     

Numerical studies on heat release rate in a room fire burning wood and liquid fuel

Heat release rates of burning gasoline and wood fires in a room were studied by computational fluid dynamics (CFD). Version 5.5.3 of the software Fire Dynamics Simulator (FDS), which is the latest one available, was selected as the CFD simulation tool. Predicted results were compared with two sets of reported data from full-scale burning tests. In the two sets of experiments, the scenarios were set at gasoline pool fire and wood chipboard fire with gasoline respectively. The input heating rate of gasoline pool fire based on experimental measurements was used in the first set of experiments. Three scenarios G1, G2 and G3 with different grid systems were simulated by CFD. The grid system of scenario G2 gave more accurate prediction, which was then used to study the second set of experiments on wood chipboard with gasoline. The combustion model in FDS was used in wood chipboard fire induced by gasoline pool. The wood chipboard was allowed to burn by itself using the pyrolysis model in FDS. The effects of the boundary conditions on free openings for the same set of experiments were studied by three scenarios SOB1, SOB2 and SOB3. Boundary condition SOB2 gave more reliable prediction among the three boundary conditions. Two other scenarios on the effect of moisture content of wood were also studied. The predicted HRR curve was found to agree better with experiment in using SOB2.     

Analysis of the effect of an external fire on the safety operation of a power plant

The basic aim of this paper is to examine the relevant features of an outdoor fire event and its influence on the surrounding area. The work is based on the analytical study of fire origin, its development and spread. The computer program fire dynamic simulator (FDS) is used to simulate fire behaviour. This program uses large Eddie simulation (LES) to calculate fire development and the spread of combustion products in the environment. The fire source is located in the vicinity of a hazardous plant; e.g., power, chemical, etc. The article presents the brief background of the FDS computer program and the initial and boundary conditions used in the mathematical model. In this analysis, it is often necessary to carry out many repeat simulations of a hazardous event and the computer run time becomes an important factor. Ideally, results should be obtained with a dense computational grid but hardware resources and excessive computational time can preclude this option. The response is to reduce a grid density but to ensure that results are only acceptable if comparable to those obtained with a dense grid. The work presents some corrections of the physical model used and its validation by experimental data, which influence the quality of results.     

Detailing the effects of geometry approximation and grid simplification on the capability of a CFD model to address the benchmark test case for flow around a computer simulated person

This paper details the use of a simplified CFD model to predict the flow patterns around a computer simulated person in a displacement ventilated room. The use of CFD is a valuable tool for indoor airflow analysis and the level of complexity of the model being investigated is often critical to the accuracy of predictions. The closer the computational geometry is to the real geometry of interest, the more accurate the corresponding results are expected to be. High complexity meshes enable elaborated geometries to be resolved. The drawback is, however, their increased computational cost. The Fire Dynamics Simulator (FDS) model (Version 5) enabled to investigate the effects of geometry and computational grid simplification on the accuracy of numerical predictions. The FDS model is based on a three-dimensional Cartesian coordinate system and all solid obstructions are forced to conform to the underlying numerical grid which is a potential limitation when dealing with complex geometries such as those of a human body. Nevertheless, the developed computational model was based exclusively on a three-dimensional rectangular geometry. At the same time, in order to limit the total number of grid cells, a relatively coarser grid than those used for similar simulations was adopted in the investigation. The developed model was then assessed in terms of its capability of reproducing benchmark temperature and air velocity distributions. The extent to which numerical results depend on different simulation settings was detailed and different boundary conditions are discussed in order to provide some guidance on the parameters that resulted to affect the accuracy of the predicted results. The comparison between numerical results and measurements showed that a simplified CFD model can be used to capture the airflow characteristics of the investigated scenario with predictions showing a favourable agreement with experimental data at least in the qualitative features of the flow (the detailed investigation of the local airflow field near the occupant can not be probably conducted apart from considering the real human geometry). Significant influence of simulator geometry and of boundary conditions was found.     

Quantitative comparison of FDS and parametric fire curves with post-flashover compartment fire test data

This paper presents a comparison of two parametric fire modelling techniques (Eurocode 1, and the BFD curve method) and one field model (fire dynamics simulator) against large-scale post-flashover test data. Using a method of the product moment correlation coefficient, it is shown that the BFD curve predictions are most closely representative of reality. For the computational test data, two grid resolutions are adopted in the FDS field model, the finer of which having comparable results in terms of regression analysis to the BFD method. Both the field model and the BFD curve method were found to give better predictions compared to the Eurocode method over the duration of the test. However, a direct comparison of the maximum gas temperatures shows the field model to be poorer in its predictive capability than the parametric methods, under-predicting the maximum gas temperatures. In addition, a more in-depth analysis of the FDS predictions indicates that by considering simply average compartment temperatures the more inaccurate spatially specific temperature predictions were disguised. This study provides useful quantitative data on the three techniques presented and discusses more general issues concerning fire modelling.     

Evaluation of FDS V.4: Upward Flame Spread

NIST’s Fire Dynamics Simulator (FDS) is a powerful tool for simulating the gas phase fire environment of scenarios involving realistic geometries. If the fire engineer is interested in simulating fire spread processes, FDS provides possible tools involving simulation of the decomposition of the condensed phase: gas burners and simplified pyrolysis models. Continuing to develop understanding of the capability and proper use of FDS related to fire spread will provide the practicing fire engineer with valuable information. In this work three simulations are conducted to evaluate FDS V.4’s capabilities for predicting upward flame spread. The FDS predictions are compared with empirical correlations and experimental data for upward flame spread on a 5 m PMMA panel. A simplified flame spread model is also applied to assess the FDS simulation results. Capabilities and limitations of FDS V.4 for upward flame spread predictions are addressed, and recommendations for improvements of FDS and practical use of FDS for fire spread are presented.     

常州市“数字城管”万米网格划分简介

数字城市网格化管理作为城市管理的一种新手段,已经得到了广泛的应用和发展,而科学的、合理的进行网格划分,成为数字化城市管理信息系统建设的一项基础性工作。借鉴其他城市的经验,结合常州市数字化城市管理的特点,本文简要介绍常州市＂数字城管＂万米网格划分的工作流程和划分依据,确定的划分原则,阐述在划分过程中对实际问题采取的解决办...