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。     

位移多点约束法在面板堆石坝精细模拟中的应用研究

面板堆石坝数值模拟中为了兼顾计算精度和计算效率,可对混凝土面板划分精细网格,并与堆石体相对稀疏的网格进行合理的连接过渡。基于自主研发的有限元执行平台,开发实现了基于位移多点约束的疏密网格过渡方法,并应用于在建200m级面板堆石坝工程数值模拟。通过方案对比,验证了该方法的精度,且面板精细网格与堆石体稀疏网格之间变形协调。相较于传统模拟方法,面板精细模拟方法可细致表达面板内应力变化梯度,能够为跨尺度精细模拟混凝土面板性状提供技术基础。该方法简便实用、易于数值实现,具有较好的推广应用前景。     

风场大涡模拟中网格非匹配算法

计算风工程中对风场进行大涡模拟是从流体角度诠释风压产生、发展、分布的数值方法.风场需分割为多个子块,并根据风活跃程度分别指定不同的网格密度,在各块界面上网格非一一匹配.本文针对:三维子块,提出了一种搜集非匹配信息的算法,用以计算子块间的风流体通量.根据结构网格规律性,将公共界面上两个子块的网格线合并为一套网格,从而将公共界面划分为小面,形成联接信息进行全场联立求解.典型算例表明可在节省计算资源的同时保证精确性,同时实现网格密度平滑过渡,为大跨度结构风场模拟解决了一个基础问题.     

基于天气预报模式和大涡模拟的台风风场多尺度耦合数值模拟

结合2015年第1509号超强台风“灿鸿”期间在杭州九堡大桥的现场实测数据,基于WRF(weather research and forecasting)和LES(大涡模拟)的台风多尺度耦合数值模拟方法,重现了台风“灿鸿”的中小尺度发展演化过程,并对九堡大桥周边台风风场进行多尺度精细化模拟;以多项式插值的方式解决疏网格向密网格的背景风场要素降尺度耦合问题;最后通过大涡模拟获得了九堡大桥周边地区30min瞬态台风风场数据。模拟得到的瞬态风速结果与实测数据在统计意义上较为吻合,表明WRF-LES耦合系统能实现从气象中尺度到建筑小尺度的多尺度数值模拟,有效地获取一次台风过程中目标区域的瞬态台风风场。NSRFG(narrowband synthesis random flow generator)方法生成的入口脉动风速适用于局部台风风场的LES计算,模拟所得风速功率谱与实测结果在低频段基本一致。     

低雷诺数圆柱绕流数值模拟及控制措施

采用层流模型并结合合理的网格划分模拟了低雷诺数圆柱绕流,使用FLUENT软件模拟了圆柱表面涡脱的产生、发展变化过程;计算了圆柱表面周向压力系数分布情况及圆柱的阻力系数、升力系数和Strouhal数;为研究圆柱绕流的控制措施,引入不同导流板进行数值计算。分析结果表明:在圆柱尾部中轴线位置引入导流板可以很好地控制圆柱表面涡脱,减小阻力,抑制振动;各系数计算结果与文献中的结果吻合很好,该方法具有较高的精度。     

基于三维地质模型的工程岩体结构精细数值建模

针对岩体结构数值模拟分析前处理工作中存在的地质模型建立、空间单元划分等难点,提出将三维地质模型与数值模拟分析进行耦合来简化其前处理的具体思路和方法。在三维地质建模系统中,建立精细的工程地质三维统一模型,通过单元网格几何模型的自动生成和模型数据的转换输入,可快速、准确地为岩体结构数值模拟分析提供不同类别、信息丰富的精细三维网格剖分模型,不仅简化了数值计算分析的前处理工作,同时也可丰富三维地质模型的属性信息,为工程设计与优化提供更直观、便捷的信息平台。     

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。     

乌鲁木齐市“7·19”自建房火灾事故数值重构

采用大涡模拟技术对"7.19"乌鲁木齐市重大火灾事故进行数值重构。根据火灾事故的调查结果报告,建立与物理模型并进行网格划分和初始边界条件设定,在Linux系统下再现火灾发展的三个阶段以及烟气蔓延过程,分析此次火灾在短时间内造成大量人员伤亡的原因。通过对可燃物质量损失的计算模拟壁面装修材料的烧损痕迹图,推断起火点位置、火势蔓延方向,帮助火灾调查人员快速确定起火部位。     

大跨球面屋顶结构周围风场数值模拟研究

基于计算流体动力学(CFD)中的大涡模拟(LES)技术,应用经典的Smagorinsky亚格子模型对三维大跨球面屋顶结构在大气边界层风剖面环境内的风场进行了数值模拟。数值算例显示,三维球面屋顶结构周围的流向速度场(U)和竖向速度场(W)分布十分复杂,基于CFD数值计算的大涡模拟方法可以随时间精细、稳定和有效的刻画球面屋顶结构周围复杂的三维风场分布。     

火灾调查中某仓库特大火灾场景的数值模拟重构

将数值模拟中的大涡模拟方法应用于某汽车配件城仓库火灾场景重构,对火灾原因和过程进行分析。根据现场人员证词和燃烧现场取证,对火灾的发生进行场景重构模拟,确定火灾是由电气短路造成。将模拟结果中关键部位的温度、有毒气体和烟气浓度等数据与火灾现场专家勘察结果对比,排除了人为纵火的可能性。采用并行运算方法,较好的预测了火灾发展和有毒烟气的运动。为实际火灾场景的调查提供了数值模拟的科学方法。     

Influence of cell geometry and mesh resolution on large eddy simulation predictions of flow around a single building

A number of research studies have employed a wide variety of test conditions to numerically assess flow field around buildings. In such studies, the employed mesh system and its resolution played a crucial role in determining the ultimate degree of solution accuracy. The objective of this study is to better establish a quantitative assessment of the influence of cell geometry and mesh resolution on the numerical predictions of large eddy simulation (LES) of the flow field around a single building. In order to achieve this objective, a number of mesh styles including conventional hexahedral-based mesh, tetrahedral-based mesh, and prism-based mesh have been considered. In addition, hybrid meshes of tetrahedron and hexahedron cells are also considered. In each mesh style, four grid resolutions were investigated: coarse, medium, fine, and very fine. Accuracy of the simulation has been assessed by applying comparisons to the experimental data available in literature. Moreover, quantitative grid convergence was calculated based on the grid convergence index, which accounts for the degree of grid refinement. Future studies are needed to analytically evaluate the influence of cell geometry on the solution accuracy and to more precisely evaluate other grid system options including various forms of hybrid configuration meshes.     

浅谈大空间火灾烟气运动规律的计算机模拟

分析并讨论了当前大尺度空间火灾烟气运动规律的计算机模拟研究现状。结果表明,采用大涡模拟方法结合多单元区域模拟是研究火灾烟气运动规律的发展趋势。     

LES field model-based fire accident reconstruction with the OED method and its experimental validation

One of the objectives of fire accident reconstruction is to determine the cause of the fire and to examine the fire spread. The temperature and extent of fire damage are the two most important characteristics in a fire accident. They can be fully utilized in a fire accident simulation that is based on a Large Eddy Simulation (LES) field model, which has been widely used as a simulation model for fire analysis. However, since it needs many simulation runs using this model in fire accident reconstruction, it will increase the reconstruction time and cost. The use of an Orthogonal Experimental Design (OED) method as a tool to reduce the simulation runs in fire accident reconstruction is proposed. An orthogonal array is selected on a discrete design space and levels are chosen from candidate values. Matrix experiments with the orthogonal array are conducted and a range difference analysis is used to find out the optimum levels. The method is applied to a fire experiment as a validation. The numerical and experimental results fit very well.     

膜结构风振响应的二维数值模拟研究

结合膜结构的风振响应特点,采用流固耦合问题数值计算方法,实现了二维情况下膜结构风场的数值模拟。阐述了膜结构流固耦合计算中的结构域与流体域的网格关系和流固耦合边界的控制条件。选择大涡模拟作为湍流模型,并采用隐式时间积分TR-BDF法对流体域的Navier-Stokes方程进行时间域的离散。对耦合系统的有限元方程组采用Newton-Raphson法进行求解。计算结果表明,湍流模型选择大涡模拟可以较好模拟二维情况下膜结构在流场中的脉动反应。对于一般性的算例,瞬态流场中膜的应力增加较为明显。合理选择膜结构体型可以减小膜结构风振响应的脉动幅度。     

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.     

湍流反应流研究中的大涡模拟

针对湍流反应流分析高质量数值解所应具有的特征和准则，对比大涡模拟与N-S方程雷诺平均的能谱空间分解图，说明了大涡模拟的特点。使用FDS2程序对油池火进行模拟，以展示湍流反应流研究中的大涡模拟技术。     

建筑火灾场模拟计算中的网格独立性 --建筑防火性能化设计的若干问题探讨

建筑火灾的计算机模拟是建筑防火性能化设计的重要组成部分，场模拟是建筑火灾计算机模拟的主要方法之一。在场模拟计算中网格独立性分析直接影响计算结果的误差，甚至影响计算结果是否定性合理。通过对网格独立性问题进行研究和探讨，以求科学地认识和理解场模拟计算在性能化防火设计中的正确使用。     

Numerical simulation of flow past a square cylinder using Partially-Averaged Navier-Stokes model

In this study, we carry out a two-stage partially averaged Navier-Stokes (PANS) simulation past a square cylinder to examine the effect of a grid system on the predicted results. The important focus in PANS is how the control parameter which is the ratio of unresolved-to-total turbulent kinetic energy is determined in the flow field. In this work, the parameter is evaluated by using an equation that we propose. The model equation utilizes the turbulent length scale, the Kolmogorov length scale and the cut-off grid length. We first perform RANS simulation to approximately evaluate the turbulent length scale and the Kolmogorov length scale. Then we construct five different grid systems based on these length scales and perform PANS simulation in which the length scales to determine control parameter are also updated as the simulation proceeds. Simulation results are compared with experimental data and the other LES and DES results. The comparison suggests that PANS approach is very effective in simulating separated turbulent flows in the sense that accurate predictions can be obtained by using a much coarser grid system than is required for LES. We then suggest the grid spacing requirements for a proper PANS simulation.