内部爆炸载荷作用下容器动力响应的数值模拟

运用ANSYS/LS-DYNA非线性显式动力学有限元程序,采用流固耦合算法,对平板封头圆柱形爆炸容器(长径比1∶1)在内部爆炸载荷作用下的动力响应进行了数值模拟;研究容器壳体和平板封头典型位置的内部爆炸载荷和等效应力的历史;分别给出壳体和平板封头的应力云图;分析对比壳体和封头不同位置应力响应。数值模拟结果为爆炸容器的经验设计和防护提供了科学依据。     

爆炸冲击波在建筑群中传播规律的数值模拟研究

为了研究建筑群的布局特性对爆炸冲击波传播的干扰作用及爆炸对周围环境的影响,笔者基于任意拉格朗日多物质流固耦合算法,对空气采用ALE网格,爆轰产物采用JWL状态方程,利用LS-DYNA程序对TNT理想爆炸源的爆炸进行了数值模拟,并与经验公式的计算结果进行了对比,得出了数值模拟方法可行的结论。在该基础上,以一个建筑小区为例,对其遭受爆炸后的响应作了进一步模拟研究。结果表明,建筑物的密度和布局方式对爆炸场的数值与形态都有敏感作用,因此,在城市规划建筑布局阶段,应考虑建筑密度和布局对爆炸冲击波的影响。     

一些典型管道煤气爆炸的数值模拟研究

为了研究煤气,瓦斯之类易爆品的爆炸机理以及怎样进行类似的灾害预防,本采用气体爆炸理论,对煤气爆炸问题进行了数值模拟,在整个模拟过程中不考虑外力,外源和热交换的影响,得到了可压缩流体的偏微分守恒方程;基于多流体网格法（MMIC）,给出了该问题的计算格式;最后对得到的结果进行了分析。并且运用可视从软件进行处理后获得了煤气二维爆炸场的动画模拟结果,从动画中可以比较直观且清晰地看到煤气的爆炸过程。     

瓦斯爆炸实验研究进展及展望

瓦斯爆炸事故是煤矿的主要灾害之一,为了预防和控制煤矿井下瓦斯爆炸事故的发生,国内外研究者采用理论、实验室实验和数值模拟实验等手段对瓦斯爆炸机理、瓦斯爆炸传播规律等进行了深入研究,本文从瓦斯爆炸实验室实验和瓦斯爆炸数值模拟实验两方面入手,对瓦斯爆炸的研究进展情况进行了分析总结.对于瓦斯爆炸实验室研究,分析总结了现有瓦斯爆炸实验手段以及瓦斯爆炸传播特性研究情况;对于数值实验研究,分析总结了瓦斯爆炸数值模拟模型、现有瓦斯爆炸数值模拟商业软件以及软件应用情况.最后对瓦斯爆炸未来需要深入研究的问题提出了展望.     

泄爆静开启压力对气体内爆炸载荷的影响研究

针对约束泄爆结构静开启压力这一关键特征参数,对建筑物内气体爆炸瞬态流场展开数值模拟研究,探索不同静开启压力条件下爆炸压力载荷的分布规律。研究结果证实了爆炸压力载荷双峰结构的客观存在,阐释了双峰压力结构在时间上的分布规律,揭示了双峰时间间隔随泄爆结构静开启压力的非线性特征。研究成果为建筑物内可燃气体爆炸事故的定量风险评估及气体爆炸荷载下建筑结构动力响应与防爆抗爆安全设计奠定必要的理论基础。     

爆炸塔内爆炸流场的数值模拟

采用二维非定常流体动力学差分方法(隐式TVD格式)，以轴对称和平面问题对半球顶圆柱筒身爆炸塔内，中心和偏心爆炸的流场进行了数值模拟。本简要介绍了方法与结果。     

爆炸塔内爆炸流场的数值模拟

采用二维非定常流体动力学差分方法(隐式TVD格式),以轴对称和平面问题对半球顶圆柱筒身爆炸塔内,中心和偏心爆炸的流场进行了数值模拟。本文简要介绍了方法与结果。     

尿素合成塔爆炸事故机理的研究

尿素合成塔工艺条件复杂,体积庞大,内部物料状态复杂,需要在高温、高压下操作,国内外曾发生过几起著名的尿素合成塔爆炸事故,事故后果非常严重。工艺条件的复杂性加大了事故分析的难度,目前对事故原因众说纷纭。利用数值模拟软件,对尿素合成塔爆炸过程进行研究,对爆炸机理进行分析,对事故发生的原因进行探讨,为预防同类事故提供一定的依据。分析了顶部气相空间爆炸性混合体系的形成和爆炸过程,结合数值模拟得出关键点的压力变化和气相冲击波最终的压力,依据能量守恒推导出液相中冲击波的压力。利用数值模拟得出冲击波在液相中的传播速度和叠加的情况,综合反射、直接透射两部分冲击波进入液相的时间差,找到位于筒体底部的叠加点,冲击波在该处叠加造成筒体破裂,过热液体瞬间气化喷出,引发破坏更大的二次蒸汽大爆炸。     

泄爆容器中粉尘爆炸的试验研究与数值模拟

为了解泄爆容器中粉尘爆炸的发展过程,采用试验和数值模拟相结合的方法对玉米淀粉在圆柱形容器内的泄爆过程进行研究。数值模型采用欧拉–拉格朗日方法模拟粉尘爆炸的两相流问题,通过求解非稳态的湍流两相反应流守恒方程对试验进行二维仿真。试验和模拟结果表明,点火位置对爆炸发展过程有明显影响,点火位置离泄爆口越远,容器中的最大泄爆压力Pred,max越高。在粉尘爆炸的安全防护设计中,应把点火位置作为重要影响因素之一加以考虑。     

钢结构危险品储柜内不同气体对爆炸超压影响的数值模拟研究

随着社会经济发展,钢结构危险品储柜越来越多地运用于危险品运输、储存过程。危险品储柜发生火灾爆炸事故主要是由于其内部存在达到爆炸极限的可燃气体并遇到点火源而引发。运用FLACS数值模拟软件对危险品储柜内不同种类可燃气体爆炸进行数值模拟研究。研究表明：不同化学性质的活泼气体在钢结构储柜内部爆炸的荷载呈现升压时间短、峰值大的现象,气体的活泼性质显著影响着荷载的大小。     

Influence of vacuum degree on the effect of gas explosion suppression by vacuum chamber

In order to study the influence of vacuum degree on gas explosion suppression by vacuum chamber, this study used the 0.2 mm thick polytetrafluoroethylene film as the diaphragm of vacuum chamber to carry out a series of experiments of gas explosion suppression by vacuum chamber with the vacuum degree from −0.01 MPa to −0.08 MPa. The experimental results show that: under the condition of any vacuum degree, vacuum chamber can effectively suppress the explosion flame and overpressure; as vacuum degree changes, the effect of gas explosion suppression using vacuum chamber is slightly different. Vacuum chamber has obvious influence on propagation characteristics of the explosion flame. After explosion flame passes by vacuum chamber, the flame signal weakens, the flame thickness becomes thicker, and the flame speed slows down. With the increase of the vacuum degree of vacuum chamber, the flame speed can be prevented from rising early by vacuum chamber. The higher the vacuum degree is, the more obviously the vacuum chamber attenuates the explosion overpressure, the smaller the average overpressure is, and the better effect of the gas explosion suppression is. Vacuum chamber can effectively weaken the explosion impulse under each vacuum degree. From the beginning of −0.01 MPa, the vacuum chamber can gradually weaken explosion impulse as the vacuum degree increases, and the effect of gas explosion suppression gradually becomes better. When the vacuum degree is greater than −0.04 MPa, the increase of vacuum degree can make the explosion overpressure decrease but have little influence on the explosion impulse. Therefore, the vacuum chamber has the preferable suppression effect with equal to or greater than −0.04 MPa vacuum degree.     

Application and effect of negative pressure chambers on pipeline explosion venting

Explosion venting is a frequently-used way to lower explosion pressure and accident loss. Recently, studies of vessel explosion venting have received much attention, while little attention has been paid to pipe explosion venting. This study researched the characteristics of explosion venting for Coal Bed Methane (CBM) transfer pipe, and proposed the way of explosion venting to chamber in order to avoid the influence of explosion venting on external environment, and investigated the effects of explosion venting to atmosphere and chamber. When explosion venting to atmosphere, the average explosion impulse 4.89 kPa s; when explosion venting to 0 MPa (atmospheric pressure) chamber, average explosion impulse is 7.52 kPa s; when explosion venting to −0.01 MPa chamber, explosion flame and pressure obviously drop, and average explosion impulse decreases to 4.08 kPa s; when explosion venting to −0.09 MPa chamber, explosion flame goes out and average explosion impulse is 1.45 kPa s. Thus, the effect of explosion venting to negative chamber is far better than that to atmospheric chamber. Negative chamber can absorb more explosion gas and energy, increase stretch of explosion flame, and eliminate free radical of gas explosion. All these can promote the effect of explosion venting to negative chamber.     

Post-explosion observations of experimental mine and laboratory coal dust explosions

The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) conducted joint research on dust explosions by studying post-explosion dust samples. The samples were collected after full-scale explosions at the PRL Lake Lynn Experimental Mine (LLEM), and after laboratory explosions in the PRL 20-L chamber and the Fike 1 m³ chamber. The dusts studied included both high- and low-volatile bituminous coals. Low temperature ashing for 24 h at 515 °C was used to measure the incombustible content of the dust before and after the explosions. The data showed that the post-explosion incombustible content was always as high as, or higher than the initial incombustible content. The MSHA alcohol coking test was used to determine the amount of coked dust in the post-explosion samples. The results showed that almost all coal dust that was suspended within the explosion flame produced significant amounts of coke. Measurements of floor dust concentrations after LLEM explosions were compared with the initial dust loadings to determine the transport distance of dust during an explosion. All these data will be useful in future forensic investigations of accidental dust explosions in coal mines, or elsewhere.     

氧气瓶爆炸事故性质认定及原因分析

在事故现场勘查的基础上,通过材料成分、力学性能、金相组织与断口、碎片附着物以及充装气体成分等检测和试验,结合爆炸能量的理论估算,对一起氧气瓶爆炸事故的性质和原因进行了系统分析。结果表明：瓶体存在的脱碳、微裂纹及局部腐蚀凹坑这些类裂纹缺陷在爆炸产生的巨大载荷下诱发了气瓶的开裂及扩展,其宏观断口表现为韧脆交替的快速断裂特征。依据碎片抛射距离估算的气瓶实际爆炸能量远大于其发生物理爆炸所产生的能量,气瓶爆炸属于化学爆炸。气瓶内存在的碳烃类油脂有机物以及瓶阀关闭时产生的摩擦热或静电火花是氧气瓶发生化学爆炸的直接原因。     

Theoretical pressure prediction of confined hydrogen explosion considering flame instabilities

In order to ensure the safe utilization of hydrogen energy, the explosion pressure behavior is extremely important to design chemical equipment and evaluate explosion accident consequence. This paper is aimed at establishing a theoretical method of predicting explosion pressure behavior in the confined chamber by considering flame instabilities. The tendency of flame wrinkling factor in the pressure-buildup stage is firstly evaluated using large eddy simulation and the compensation theory. The limiting value of flame wrinkling factor during entire explosion process is calculated using the fractal theory. Finally, the dynamic model of flame wrinkling factor is implemented into the smooth flame model. The results demonstrated that the flame wrinkling factor in the pressure-buildup stage almost increases linearly with time. The limiting value of flame wrinkling factor is 2.4649. The explosion pressure will be underestimated using the smooth flame model, and the calculated explosion pressure in the isothermal condition is smaller than that in the adiabatic condition. When the fully turbulent flame is considered, the explosion pressure will be overpredicted significantly. By changing the confined chamber size, the explosion pressure could be reproduced relatively satisfactorily when the flame wrinkling factor is assumed to increase exponentially. The explosion pressure prediction must consider the effect of adiabatic compression and flame instabilities on burning rate.     

Explosion temperatures and pressures of metals and other elemental dust clouds

The Pittsburgh Research Laboratory of the National Institute for Occupational Safety and Health (NIOSH) conducted a study of the explosibility of various metals and other elemental dusts, with a focus on the experimental explosion temperatures. The data are useful for understanding the basics of dust cloud combustion, as well as for evaluating explosion hazards in the minerals and metals processing industries. The dusts studied included boron, carbon, magnesium, aluminum, silicon, sulfur, titanium, chromium, iron, nickel, copper, zinc, niobium, molybdenum, tin, hafnium, tantalum, tungsten, and lead. The dusts were chosen to cover a wide range of physical properties—from the more volatile materials such as magnesium, aluminum, sulfur, and zinc to the highly “refractory” elements such as carbon, niobium, molybdenum, tantalum, and tungsten. These flammability studies were conducted in a 20-L chamber, using strong pyrotechnic ignitors. A unique multiwavelength infrared pyrometer was used to measure the temperatures. For the elemental dusts studied, all ignited and burned as air-dispersed dust clouds except for nickel, copper, molybdenum, and lead. The measured maximum explosion temperatures ranged from 1550 K for tin and tungsten powders to 2800 K for aluminum, magnesium, and titanium powders. The measured temperatures are compared to the calculated, adiabatic flame temperatures.     

Mitigation performance of the process protection system on the accident consequences of H2S-containing natural gas release and explosion

Toxic loads and explosion overpressure loads pose grave threats to the offshore oil and gas industry. Many safety measures are adopted to prevent and mitigate the adverse impacts caused by toxic loads and explosion overpressure loads. As a general safety barrier, the process protection system has been widely used but rarely evaluated. In order to assess the barrier ability, the mitigation performance of the process protection system is concerned in this study. Firstly, several chain accidents of H₂S-containing natural gas leakage and explosion are simulated by varying the response time of the process protection system with CFD code FLACS. Qualitative assessment is conducted based on the variation of the dangerous load profiles. Furthermore, the quantitative assessment of the mitigation performance is accomplished by considering its ability in reducing the probability of fatality. Emergency evacuation and no emergency evacuation are considered respectively in the quantitative assessment. The results prove that the process protection system takes effect on mitigating the toxic impact and explosion overpressure impact. The results also demonstrate that although the emergency evacuation may result in a severer explosion load to the operator, the process protection system can mitigate the adverse impacts regardless of whether the emergency evacuation is conducted or not.     

Effect of ignition delay on explosion parameters of corn dust/air in confined chamber

This paper presents the explosion parameters of corn dust/air mixtures in confined chamber. The measurements were conducted in a setup which comprises a 5 L explosion chamber, a dust dispersion sub-system, and a transient pressure measurement sub-system. The influences of the ignition delay on the pressure and the rate of pressure rise for the dust/air explosion have been discussed based on the experimental data. It is found that at the lower concentrations, the explosion pressure and the rate of pressure rise of corn dust/air mixtures decrease as the ignition delay increases from 60 ms; But at the higher concentrations, the explosion pressure and the rate of pressure rise increase slightly as the ignition delay increases from 60 ms to 80 ms, and decrease beyond 80 ms. The maximum explosion pressure of corn dust/air mixtures reaches its highest value equal to 0.79 MPa at the concentration of 1000 gm⁻³.     

Experimental study on the feasibility of explosion suppression by vacuum chambers

In view of the invalidity of suppression and isolation apparatus for gas explosion, a closed vacuum chamber structure for explosion suppression with a fragile plane was designed on the base of the suction of vacuum. Using methane as combustible gas, a series of experiments on gas explosion were carried out to check the feasibility of the vacuum chamber suppressing explosion by changing methane concentration and geometric structure of the vacuum chamber. When the vacuum chamber was not connected to the tunnel, detonation would happen in the tunnel at methane volume fraction from 9.3% to 11.5%, with flame propagation velocity exceeding 2000 m/s, maximum peak value overpressure reaching 0.7 MPa, and specific impulse of shock wave running up to 20 kPa s. When the vacuum chamber with 5/34 of the tunnel volume was connected to the flank of the tunnel, gas explosion of the same concentration would greatly weaken with flame propagation velocity declining to about 200 m/s, the quenching distance decreasing to 3/4 of the tunnel length, maximum peak value overpressure running down to 0.1-0.15 MPa and specific impulse of shock wave below 0.9 kPa s. The closer the position accessed to the ignition end, the greater explosion intensity weakened. There was no significant difference between larger section and smaller vacuum chambers in degree of maximum peak value overpressure and specific impulse declining, except that quenching fire effect of the former was superior to the latter. The distance of fire quenching could be improved by increasing the number of the vacuum chambers.     

Further study of the intrinsic safety of internally shorted lithium and lithium-ion cells within methane-air

National Institute for Occupational Safety and Health (NIOSH) researchers continue to study the potential for lithium and lithium-ion battery thermal runaway from an internal short circuit in equipment for use in underground coal mines. Researchers conducted cell crush tests using a plastic wedge within a 20-L explosion-containment chamber filled with 6.5% CH₄-air to simulate the mining hazard. The present work extends earlier findings to include a study of LiFePO₄ cells crushed while under charge, prismatic form factor LiCoO₂ cells, primary spiral-wound constructed LiMnO₂ cells, and crush speed influence on thermal runaway susceptibility. The plastic wedge crush was a more severe test than the flat plate crush with a prismatic format cell. Test results indicate that prismatic Saft MP 174565 LiCoO₂ and primary spiral-wound Saft FRIWO M52EX LiMnO₂ cells pose a CH₄-air ignition hazard from internal short circuit. Under specified test conditions, A123 systems ANR26650M1A LiFePO₄ cylindrical cells produced no chamber ignitions while under a charge of up to 5 A. Common spiral-wound cell separators are too thin to meet intrinsic safety standards provisions for distance through solid insulation, suggesting that a hard internal short circuit within these cells should be considered for intrinsic safety evaluation purposes, even as a non-countable fault. Observed flames from a LiMnO₂ spiral-wound cell after a chamber ignition within an inert atmosphere indicate a sustained exothermic reaction within the cell. The influence of crush speed on ignitions under specified test conditions was not statistically significant.