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1.
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. 相似文献
2.
We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire. 相似文献
3.
在高高原实验室(61 kPa、4 290 m)和广汉实验室(96 kPa、520 m),分别开展常低压条件下FXL型航空电缆的对比燃烧实验。通过热辐射加热箱、烟密度及成分测试仪和氧指数仪等设备,测量点燃时间、烟密度、质量损失速率和CO、CO2及O2等浓度变化。实验结果表明:在96 kPa和61 kPa两种实验环境下,低压下最小点燃时间及温度的数值更大,两者的温度和时间差分别为15℃和4.8 s;烟密度曲线快速升高后趋于平衡,61 kPa条件下的发烟量小于96 kPa;O2体积浓度随着加热时间先下降后升高,而CO2的变化趋势相反。在61 kPa条件下,CO曲线会出现双峰现象且更明显;随着氧浓度增加,质量损失速率加快且呈线性关系;压力因素对燃烧影响减弱且燃烧持续时间差值变小。研究结果揭示了低压环境对航空电缆的燃烧影响,为增强航空安全提供参考。 相似文献
4.
为探究烟支规格对卷烟质量的影响,在烟丝原料、填充密度、卷烟纸透气度、接装纸规格、丝束材料以及滤棒吸阻条件相同的情况下卷制4种规格卷烟[烟支规格(烟支圆周×长度):常规(24.3 mm×84 mm)、22 mm卷烟(22 mm×84 mm)、中支(20 mm×89 mm)、细支(16.9 mm×97 mm)],检测其物理指标、烟气指标、烟气致香成分含量和感官质量。结果表明:①随着烟支规格由常规逐渐变化到细支,单支含丝量减小,烟支吸阻增加,烟支硬度下降,烟丝段通风率增加超过一倍,其中烟丝段吸阻与烟支圆周平方的倒数呈良好的线性关系。②烟支规格由常规到细支,抽吸口数下降了0.92口/支,烟气焦油、烟碱、CO释放量整体呈现减小的趋势;燃吸比率和单口抽吸耗丝量呈现先增加后减小的趋势,中支卷烟的燃吸比率和单口抽吸耗丝量最大,分别为29.37%和19.98 mg/口,中支卷烟单口烟气焦油释放量最大。③中支卷烟单支和单口烟气粒相物致香成分总量均为最高;烟支由常规到细支,主流烟气致香成分中杂环类化合物含量呈现先增加后减少的趋势,单口烟气致香成分含量中3-甲基-2-环戊烯-1-酮、3-乙烯基吡啶、苯酚含量呈现增加的趋势。④中支卷烟总体感官质量评价得分较高,细支卷烟总体感官质量评价得分最低,香气量、烟气浓度、刺激性感官评价得分均随着烟支圆周的减小呈现降低的趋势。 相似文献
5.
利用费诺德(Froude number)相似模型理论,建立1∶12的某地下高大空间(高大空间为高度大于10 m,体积大于10 000 m~3)比例模型,研究了地下高大空间火灾烟气自由填充过程及温度变化特性。1∶12模型试验结果和火灾动力学模拟(fire dynamics simulator,FDS)模拟值与McCaffrey预测值吻合度较高。1∶12火灾模型试验能较好的预测地下大空间烟气流动特点,且是验证数值结果正确性的重要手段。试验表明:高大空间"蓄烟效应"显著,火灾发生时高大空间竖向温度呈线性分布,且温升较小,温度不是影响人员逃生和排烟效果的主要因素;火源位置分别处于模型端部的烟气层下降速度慢于中心位置。该研究为制订火灾排烟和疏散方案及高大空间防排烟规范提供了初步理论依据和第一手的试验资料。 相似文献
6.
For the analysis of the adverse effects of smoke on health, it is essential to determine the amount and location of smoke particles deposited in the respiratory tract. However, the deposition characteristics of the particles are influenced by their morphology and size distribution. Moreover, the real-time particle size distribution during inhalation is important for determining smoke particle deposition in the lungs. Smoke particles generated under different fire conditions differ in their physical and chemical characteristics. Thus, there is a need to adopt international standard methods for characterizing the particles generated in fire. In the present study, the size distributions together with morphology of smoke particles were measured for each fire stage by using the steady-state tube furnace method given in ISO/TS 19700. The size distributions of smoke particles from wood and polypropylene (PP) were measured in real time by using an electric low-pressure impactor (ELPI+), and their morphologies were analyzed using transmission electron microscopy (TEM). 相似文献
7.
8.
A novel video-based method is proposed for long-distance wildfire smoke detection. Since the long-distance wildfire smoke usually moves slowly and lacks salient features in the video, the detection is still a challenging problem. Unlike many traditional video-based methods that usually rely on the smoke color or motion for initial smoke region segmentation, we use the Maximally Stable Extremal Region (MSER) detection method to extract local extremal regions of the smoke. This makes the initial segmentation of possible smoke region less dependent on the motion and color information. Potential smoke regions are then selected from all the possible regions by using some static visual features of the smoke, helping to eliminate the non-smoke regions as many as possible. Once a potential smoke region is found, we keep tracking it by searching the best-matched extremal regions in the subsequent frames. At the same time, the propagating motions of the potential smoke region are monitored based on a novel cumulated region approach, which can be effectively used to identify the distinctive expanding and rising motions of smoke. This approach can also make the final smoke motion identification insensitive to image shaking. It was proved that the proposed method is able to reliably detect the long-distance wildfire smoke and simultaneously produce very few false alarms in actual applications. 相似文献
9.
《Food Control》2014,35(2):347-355
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. 相似文献
10.
In this work, a numerical model of tunnel fire is developed and aimed to investigate the influence of cross-sectional fire locations on critical velocity and smoke flow characteristic. It is shown that the critical velocity for a fire next to the wall is obviously higher than that for a fire in the middle or on the left/right lane. The ratio is estimated to be 1.12. The predictions of critical velocity from ‘small-fire’ models show a good agreement with that for a fire in the middle or on the left/right lane from CFD. The tunnel height at the fire location is proposed to be instead of the hydraulic tunnel height in the ‘big-fire’ model of Wu and Bakar for a fire next to the wall. The smoke moves backward in a tongue like form as the ventilation velocity is lower than the critical velocity. The back-layering length of a fire in the middle is shown to be approximate twice than that on the left/right lane under the same ventilation velocity, although they share the same critical velocity. Whereas a relatively short back-layering length for a fire next to the wall under the velocity of 2.6 and 2.7 m/s. In addition, a snaky high-temperature profile on the top wall at the initial downstream is observed for a fire on the left lane and next to the wall, and finally a steady and layered smoke flow. The likely cause of this phenomenon is subsequently explained in this study. 相似文献