摘要
火灾是重大灾害之一,常造成大量的财产损失和人员伤亡。随着火灾理论研究的不断深入和数值计算方法的不断完善,用数值模拟手段来进行火灾科学研究成为了潮流。火灾调查是消防工作的重要组成部分,但在现阶段,起火部位的认定很大程度上依靠调查人员的经验,缺少相应的技术验证;专业的理论知识、抽象的认定结论不容易被受灾群众理解和接受。在进行全尺度火灾实验成本高、周期长,进行小尺度火灾实验难以满足所有无量纲相似要求的情况下,进行计算机数值模拟火灾实验,时间周期短、经济成本低、可以方便的进行对比实验,是一种新兴的、有效的火灾调查手段。
本文以火灾数值模拟为基础,对火灾事故数值再现技术及其在火灾调查领域的应用展开了以下研究:
1)提出了火灾事故数值再现正交优化方法。由于火灾现场的破坏性及复杂性,火场中具有许多不确定因素。文中对火灾中常见的因素进行了分析,并分析了几种模拟结果的评价方法。在火灾再现数值模拟过程中,引入正交方法进行实验优化设计,提高了数值再现的效率。
2)提出了针对薄壁结构的等效参数法。火场中经常有薄壁结构,比如吊顶和分隔墙等,它们烧穿的时候对火灾发展影响很大。由于它们的壁厚远小于常用的网格尺度,若对这些结构进行直接建模,计算量非常大。文中提出了等效参数法:通过放缩壁厚的几何尺寸以适应常用网格尺度,由此减少计算量;同时改变壁面材料的参数,以保证等效变换前后的模拟结果的一致。固体热解过程的分析验证和数值实验验证的结果都表明了等效参数法是可行的。
3)对三个典型的火灾事故进行了模拟实验研究,并应用上述两方法,进行了数值再现研究。火灾数值再现得到的数据和火灾现场勘查报告、现场照片或模拟实验的比对,表明了模拟结果是可信的,从而验证了这两个方法的有效性和调查结论中起火位置判断的合理性。基于火灾再现基础上的不同工况下的比对研究,量化了消防设施对火灾的抑制作用和对人员逃生的作用。
火灾事故数值模拟可以还原火灾事故的过程,还可以对初始状态作不同假设,比较其结果的区别,对于责任认定,起火部位、起火点的确定有很好的辅助作用。将数值模拟技术引入火灾调查,可以协助解决火灾调查中难题,应用前景广阔。
Fire is one of the most serious disasters, which often causes some of the greatest losses to property and human life around the world. It had been a trend that numerical simulation method is used in fire science research because fire theory and numerical method was deepened. Fire investigation is a very important work in fire bureau. At present, the cognizance of ignition source, to a great extent, depend on the experience of fire investigator because it lacks of corresponding technical verification. And the abstract conclusion based on professional theory is not easy to be understood and accepted by common people. Full scale fire test costs much and takes long time and small scale fire test is hard to meet all the dimensionless similar requirements. Computer fire numerical test can take less time and cost less. Furthermore, it can easily make contrast tests. So it is a new-emerging and effective method for fire investigation.
Based on fire numerical simulation, the fire numerical reconstruction technique and its application on fire investigation were studied here as follows:
1) Proposed fire numerical reconstruction orthogonal optimum method. Because the fire scene is often destroyed and complicated, there are many uncertain factors. The common factors in fire were analyzed and several evaluation methods were introduced. Then, the orthogonal optimum method was introduced in experiment design in order to improve the numerical reconstruction efficiency.
2) Proposed equivalent parameter method for thin wall modeling. There are thin walls in fire scene, such as ceiling and partition, which change the fire process when they are burning though. The thickness of thin walls is much thinner than grid length used in building fire field simulation. So calculation burden is heavy when the thin wall is modeled directly. An equivalent parameter method was proposed in the paper. In this method while the wall thickness was magnified to fit the normally used grid length in order to reduce the calculation amount, the material properties were changed to make the simulation results unchanged. The analysis on solid phase model and numerical test validated that the method was correct and practical.
3) Three typical fire cases, one of which was a real fire test, were numerically reconstructed using the two methods above. The simulation results were compared with site investigation report and photos. The comparing results showed that the simulations were reliable, and so the two methods and the cognizance of ignition source. The intercomparison of fire numerical simulations on different conditions quantified the effects of fire facilities on fire control and people escape.
Fire numerical simulation can reconstruction fire development and compare the influences of different settings. It has auxiliary function when cognizing the legal liability, the ignition location and the ignition point. Numerical simulation technique on fire investigation can help to solve many problems and has a broad prospect.
引文
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