Reducing numerical dissipation in smoke simulation

Numerical dissipation acts as artificial viscosity to make smoke viscous. Reducing numerical dissipation is able to recover visual details smeared out by the numerical dissipation. Great efforts have been devoted to suppress the numerical dissipation in smoke simulation in the past few years. In this paper we investigate methods of combating the numerical dissipation. We describe visual consequences of the numerical dissipation and explore sources that introduce the numerical dissipation into course of smoke simulation. Methods are investigated from various aspects including grid variation, high-order advection, sub-grid compensation, invariant conservation, and particle-based improvement, followed by discussion and comparison in terms of visual quality, computational overhead, ease of implementation, adaptivity, and scalability, which leads to their different applicability to various application scenarios.     

一种基于MI-Simba算法的香烟烟雾识别方法*

香烟烟雾对环境条件敏感以及多特征间存在冗余,都导致无法在视频监控中准确进行烟雾识别,因此提出一种高维互信息与Simba特征加权相结合的算法(MI-Simba).首先采用视频特征提取方法获取烟雾统计度量特征、颜色布局特征和动态特征,构建初始特征向量;然后利用MI-Simba算法进行自动更新,构建该环境下最优特征组合;最后采用直推式支持向量机进行分类识别.针对室内和楼宇内场景,自建封闭空间吸烟视频数据集,采用5倍交叉策略进行比较验证,实验结果验证该算法在识别率和灵敏度两方面的有效性和优越性.     

Flame interactions and smoke containment by downward displacement ventilation

Smoke contamination even from small fires of sensitive components in telephone central offices (TCO) and semiconductor clean rooms has caused disastrous disruptions in services and excessive financial repercussions. Containment and removal of smoke can be achieved by downward displacement ventilation, also used for other purposes in large floor area semiconductor facilities. Downward ventilation reverses the upward flow from the fire and removes the smoke and other combustion products through the floor. Small-scale model experiments under turbulent fire plume conditions investigate the physical parameters such as downward velocity, ceiling clearance, and size of the fire that control the extent of the smoke containment around the fire. The extent of smoke contamination is mapped by measuring the temperatures in several locations on the vertical axis and in the space around the fire. The downward velocities cause oscillation of the fire plume and the flames around the vertical axis. By combining the experimental data with similarity analysis, a characteristic length scale and nondimensional relations are deduced for the extent of the smoke containment and the onset of plume oscillations. These relations allow design of displacement ventilation effective to contain the smoke but not cause fire spread owing to the leaning of the flames. Previously reported discrepancies in the apparent width and behavior of the plume are resolved by examining the experimental data and assessing the suitability of steady state computational fluid dynamics to model the present flow.     

Verification of the accuracy of CFD simulations in small-scale tunnel and atrium fire configurations

In preparation for the use of computational fluid dynamics (CFD) simulation results as ‘numerical experiments’ in fire research, the agreement with experimental data for two different small-scale set-ups is discussed. The first configuration concerns the position of smoke-free height in case of fire with vertical ventilation in an atrium. The second set-up deals with the critical velocity for smoke backlayering in case of fire in a horizontally ventilated tunnel. An N-percent rule is introduced for the determination of the presence of smoke in the simulation results, based on the local temperature rise. The CFD package FDS is used for the numerical simulations. The paper does not scrutinize the detailed accuracy of the results, as this is hardly possible with any state-of-the-art experimental data at hand. Rather, the global accuracy is discussed with current numerical implementation and models in FDS, considering continuous evolution over different version releases with time. The agreement between the experiments and numerical simulations is very promising. Even when quantitative agreement with experimental data is not perfect, the trends are very well reproduced in the simulations. While much additional work is required, both in CFD as in ‘real’ experiments, the results are encouraging for the potential of state-of-the-art CFD to be used as numerical experiments.     

车用柴油机扭矩和烟度的神经网络分析研究

在内燃机工程中人工神经网络技术是一种较新颖的方法。本文介绍以扭矩和烟度为输出参数的车用柴油机稳态神经网络模型、根据所建立的模型对东风汽车公司6BTA柴油机的扭矩和烟度进行的神经网络计算分析,以及利用神经网络对某一工况的稳态烟度作的优化计算。     

国内外卷烟危害性评价方法现状和发展趋势

综述了国内外烟草公司、CORESTA和非烟的科研机构采用的低危害卷烟的评价方法,预测了低危害卷烟评价方法的发展趋势,并指出了存在的问题。     

Enhanced ammonia synthesis activity of Ru/Ba5Ta4O15 catalyst by reduction of Ba5Ta4O15 with CaH2

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锅炉烟尘污染及噪声污染的改进

对一例烟尘污染及噪音污染比较严重的小型锅炉进行技术改造，经过2年的运行效果良好，证明了改进旧式燃煤锅炉的烟尘污染及噪声污染是可行的。     

Results of an European inter-laboratory comparison study on the determination of the 15 + 1 EU priority polycyclic aromatic hydrocarbons (PAHs) in liquid smoke condensates

A collaborative study on the determination of the 15 + 1 EU priority PAHs in Primary Smoke Condensate (PSC) investigating the performance profile of EU Member States’ laboratories and supporting the work carried out by the European Food Safety Authority on smoke flavourings was organised. Two spiked liquid smoke condensate materials were employed in this study. The results of 25 laboratories from across the European Union, using either high performance liquid chromatography with fluorescence detection or gas chromatography with mass selective detection, were evaluated by application of robust statistics. The assessment of the data indicated broadened Gaussian distributions for all analytes. For benzo[a]pyrene (BaP), benzo[a]anthracene (BaA), chrysene and 5-methylchrysene more than 80% of the respective reported values gave rise to a satisfactory score of |z| ? 2. For benzo[b]fluoranthene, benzo[k]fluoranthene, and dibenzo[a,l]pyrene 70–80%, for the remaining analytes less than 70%, and for dibenzo[a,i]pyrene 52% of the scores were satisfactory. No systematic differences could be detected between values reported by laboratories using methods based on HPLC and the values related to methods based on GC for most of the analytes, except for benzo[k]fluoranthene and benzo[c]fluorene. In both cases laboratories using GC based methods reported about 50% higher values than laboratories using HPLC based methods. The overview on all z-scores sorted by laboratory revealed broad distributions and/or laboratory biases for several laboratories. An assessment of the reported method performance parameters revealed that for the two regulated compounds, BaP and BaA, only two thirds of the reported data were in compliance with Regulation (EC) 627/2006. Overall the methods used in the participating laboratories were – with ample room for improvement – well on the way to comply with European legislation.