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.     

Simulation of smoke from a burning vehicle and pollution levels caused by traffic jam in a road tunnel

Detailed analyses of smoke movement from a burning vehicle in a road tunnel have been carried out for the westbound Melbourne City Link tunnel. The time-averaged equations for velocity, pressure, temperature, and mass fraction of emissions were solved for transient condition using the CFD software FLUENT 6.0. For the analysis, a burning bus was assumed to release an equivalent energy of burning 500 l of diesel in 6 min, with vehicles upstream of the fire at a standstill. On the other hand, the vehicles downstream of the fire had enough time to escape from the tunnel through the exit portal. Due to the action of jet fans, most of the smoke was pushed downstream of the fire. The smoke had also dispersed about 55 m upstream of the fire, putting the passengers in this region at great risk. The emissions released from the vehicles in the jam, with their engines running, also posed a threat to human health. Within 8 min after the fire had started, the mass concentrations of O₂, CO₂ and CO were in the ranges of 0.12–0.15, 0.08–0.11 and 0.0006–0.0014, respectively. Therefore, quick evacuation of the passengers is essential in the event of a fire in the tunnel.     

建筑塑料的阻燃和抑烟

建筑塑料是化学建材的重要组成部分，人们关注建筑塑料的阻燃和抑烟问题。本文论述建筑塑料的燃烧过程、阻燃机理、成烟机理，提出了阻燃和抑烟的技术措施。     

电石生产项目的环境保护措施

密闭电石炉生产过程中产生的炉气必须经过净化除尘综合利用，针对全密闭式电石炉炉气净化问题，论述了3种环保措施。     

用两层分类算法进行视频烟雾检测

为提高视频烟雾检测的准确性,提出一种基于概率的两层最近邻自适应度量分类算法(PTLNN)来进行烟雾检测.该算法以最小化平均绝对误差为原则,结合AdaBoost和KNN算法的优势,充分考虑局部和全局的样本分布,能明显提升分类精度.采用离散余弦变换(DCT)和离散小波变换(DWT)两种方式对烟雾特征进行提取,并验证算法性能.通过与传统算法的对比实验发现,采用离散余弦变换并结合PTLNN算法在视频烟雾检测方面具有更好的效果,既满足实时性要求又提高了检测精度.     

GMRES算法求解烟雾仿真N-S方程

烟雾在大规模战场仿真和复杂环境仿真中扮演着重要角色,因此研究烟雾仿真具有重大意义。提出用广义极小残差算法(GMRES)来求解烟雾仿真中的N-S方程。首先给出GMRES算法的计算原理;其次用GMRES算法对烟雾仿真N-S方程进行求解,并对求解结果进行收敛性分析,分析结果表明GMRES算法可以对烟雾仿真N-S方程进行求解,结果收敛;最后运用GMRES算法通过计算机技术对烟雾进行可视化仿真,仿真结果表明,采用GMRES求解算法的烟雾仿真效果比较真实,基本符合现实中的烟雾。     

气相色谱法测定卷烟烟气中烟碱的影响因素

为提高气相色谱法测定卷烟烟气中烟碱含量的准确性,依据行业标准YC/T156-2001对各种影响因素进行了考察,发现标准品配置方法、纯度是主要影响因素。根据试验结果,确定了用直接称重法制作标准工作曲线,采用校正标样的气相色谱法测定卷烟烟气中的烟碱。结果表明,改进后方法的准确度高、检测结果稳定,监测卷烟的测定结果与标定值基本一致。     

叶丝风选工艺实用性评价

为评价叶丝风选工艺对卷烟综合质量的影响,在相同条件下,分别对薄板干燥和气流干燥出口叶丝进行了采用与不采用叶丝风选工艺的对比试验。结果表明:①风选能剔除叶丝中气流干燥产生的湿团和薄板干燥产生的焦片,烟丝纯净度可提高0.2百分点以上;②风选降低了高档卷烟香气的透发性,明显改善了低档卷烟的杂气、刺激性和余味,"散花(软蓝)"感官得分提高了0.8分;风选对卷烟烟气成分的影响不显著;③风选提高了叶丝填充能力,降低卷烟单箱消耗0.1kg以上。     

艾叶及其烟气粒相物挥发性成分的分析

采用同时蒸馏萃取和GC/MS法对艾叶及其卷烟烟气粒相物挥发性成分进行了分离鉴定。艾叶中鉴定出54种挥发性成分,主要有1,8-桉树脑、艾酮、艾醇、樟脑、龙脑、异龙脑、β-石竹烯、斯巴醇和γ-古芸烯。艾叶烟气粒相物中鉴定出46种挥发性成分,主要有苯甲醛、苯酚、1,8-桉树脑、龙脑、4-松油醇和绿花白千层醇。     

Influence of different smoke generation methods on the contents of polycyclic aromatic hydrocarbons (PAH) and phenolic substances in Frankfurter-type sausages

The contents of polycyclic aromatic hydrocarbons (15 + 1 EU priority PAH) and phenolic substances (guaiacol, 4-methylguaiacol, syringol, eugenol, and trans-isoeugenol) in smoked Frankfurter-type sausages were investigated depending on the smoke generation method applied in a total of 63 smoking experiments. The smoke was generated by smouldering with different air supplies (smouldering smoke), by leading overheated steam through wood chips (steam smoke), by friction of a log (friction smoke), and by heating plates (touch smoke). The type of smoke generator had a noticeable influence on the contents of PAH and phenolic compounds. The highest mean content of PAH4 (2.6 μg/kg) was observed for sausages when intensive smouldering smoke was applied, the lowest (0.3 μg/kg) in friction-smoked sausages. The highest mean sum content of the five phenolic compounds was observed for sausages smoked with steam smoke (45 mg/kg) whereas the contents in friction- (15 mg/kg) and touch- (18 mg/kg) smoked products were relatively low.