Consequence analysis of premixed flammable gas explosion occurring in pipe using a coupled fluid-structure-fracture approach

A coupled fluid-structure-fracture approach incorporating a high-efficiency detonation modeling algorithm was proposed to study the consequences of premixed flammable gas explosion occurring in pipe. A strain-rate-dependent failure criterion which is the vital prerequisite for accurate consequences prediction was derived based on the failure mechanism of materials at high strain rates and it was applied to account for the fracture of pipe. The simulated pressure time history and fracture patterns were validated against experimental results and good agreements were acquired. The interaction between detonation wave and pipe during crack extension, dynamic fracture processes of pipes with different initial flaws, venting features of detonation products and pressure profiles out of pipe were obtained and discussed in detail. The comparison with existing semi-empirical and CFD methods was performed and it is revealed that the deformation and fracture of pipe have obvious negative influences on the peak overpressure and the rate of pressure increase out of pipe. Because the energy absorption and dissipation due to structural deformation and fracture are well taken into account, the coupled fluid-structure-fracture method is expected to provide more rational consequences prediction and analysis results.     

Propagation and intensity of blast wave from hydrogen pipe rupture due to internal detonation

The coupled fluid-structure-rupture model was developed to study the propagation and intensity of blast wave from hydrogen pipe rupture due to internal detonation. The dynamic rupture of pipe and propagation of blast wave were well coupled together in every timestep during the simulation. The numerical model was validated with experiments in terms of both typical rupture profiles and blast overpressures. Results reveal that crack branching of pipe can dramatically increase the rupture opening rate which controls the intensity and shape of the resultant blast wave. Due to the process of crack initiation and extension, the blast wave out of the pipe first forms and then is strengthened by the subsequent compression waves. This makes the maximum peak overpressure appears at a certain standoff distance above the rupture. Despite consuming some percentages of energy, the dynamic rupture of pipe generally presents positive effects (up to 2–3 times) on the blast wave intensity along the jetting direction due to the convergence effect of rupture opening on the release of internal high-pressure gas. Finally, through defining normalized overpressure and impulse based on the same hydrogen detonation in open spaces, the quantitative influences of pipe rupture on the blast wave intensity in cases of different detonation pressures and standoff distances are clarified.     

Dynamic responses and damage of storage tanks under the coupling effect of blast wave and fragment impact

Blast wave and fragment are two main types of physical damage effects representing a significant threat to storage tank structures in chemical industrial parks. Compared with the effect of only blast wave or fragment, the coupling effect of them may cause more severe consequences and is worthy of study. A numerical study of the dynamic responses and damage of a vertical storage tank subjected to the coupling effect of blast wave and fragment is conducted based on a typical accident. The simulation results reveal that stress-concentration and rapid increase of the stress exist in the impacted region of the storage tank under the coupling effect, which leads to the structural damage of the tank exhibiting different failure modes. The coupling effect is significantly apparent following a dramatic increase of the plastic strain, and the damage of the storage tank is further aggravated. From the displacement response and energy absorption, the overall damage of the storage tank subjected to the coupling effect is more severe than that caused by blast wave and fragment separately, which also indicates that the coupling effect is an enhanced damage effect. Besides, the contribution of blast wave and fragment to the coupling effect depends on scaled distance. The results of the study help reveal the coupling effect of blast wave and fragment and prevent domino accidents caused by the coupling effect.     

穿层爆破中控制孔对裂隙扩展作用机理试验研究

为研究控制孔在穿层爆破中对裂隙扩展的作用机理,在实验室内进行穿层爆破相似模拟试验。研究表明:煤岩体试块上表面产生了贯穿炮孔和控制孔的裂隙,侧面生成了多条不规则的裂隙,试块内部出现了包括沿控制孔方向发展的多个断裂面;炮孔和控制孔连线上产生了较高拉应力,炮孔和控制孔连线方向上拉应变峰值是炮孔45°方向上的拉应变峰值的1.12倍;爆破产生的压缩应力波P和在控制孔处反射生成的反射横波Sr、反射纵波Pr在控制孔附近的煤岩体上产生应力叠加,造成煤岩体损伤,最终形成贯穿裂隙。穿层爆破中控制孔对爆生裂隙的扩展起到导向作用,但由于穿层爆破中煤岩交界面的存在,使得应力波出现复杂的反射、透射、叠加效应,造成煤层内裂隙无序发育,工程现场应予以重视。     

爆炸冲击波作用下靶板的塑性大变形响应研究

对四边约束方形靶板 ,在爆炸冲击波作用下的塑性大变形响应情况 ,进行了理论分析与试验研究。运用能量守恒的方法 ,同时考虑试验过程中靶板的边界约束条件 ,得到了四边约束方形靶板在爆炸冲击波作用下发生塑性大变形时挠度的半经验公式。理论计算与试验结果吻合性较好 ,这种方法可应用于板结构在爆炸冲击波作用下的毁伤或防护方面的工程预测     

Numerical study of dynamic response and failure analysis of spherical storage tanks under external blast loading

The performance of energy infrastructures under extreme loading conditions, especially for blast and impact conditions, is of great importance despite the low probability for such events to occur. Due to catastrophic consequences of structural failure, it is crucial to improve the resistance of energy infrastructures against the impact of blasts. A TNT equivalent method is used to simulate a petroleum gas vapor cloud explosion when analyzing the dynamic responses of a spherical tank under external blast loads. The pressure distribution on the surface of a 1000 m³ spherical storage tank is investigated. The dynamic responses of the tank, such as the distribution of effective stress, structural displacement, failure mode and energy distribution under the blast loads are studied and the simulation results reveal that the reflected pressure on the spherical tank decreases gradually from the equator to the poles of the sphere. However, the effects of the shock wave reflection are not so evident on the pillars. The structural damage of the tank subjected to blast loads included partial pillar failure from bending deformation and significant stress concentration, which can be observed in the joint between the pillar and the bottom of the spherical shell. The main reason for the remarkable deformation and structural damage is because of the initial internal energy that the tank obtained from the blast shock wave. The liquid in the tank absorbs the energy of impact loads and reduces the response at the initial stage of damage after the impact of the blast.     

Effect of bifurcation on premixed methane-air explosion overpressure in pipes

It is well known that bifurcation structures have a significant influence on gas explosions in pipelines or roadways. In this work, three different types of bifurcation, namely, bifurcation with two right angles (BTRAs), bifurcation with two obtuse angles (BTOAs), and bifurcation with an obtuse angle and an acute angle (BOAA), were used to study the effect of bifurcation on premixed methane–air explosion overpressure in pipes. The effect of the position of bifurcation on gas explosions was also discussed. Our results suggest that the peak overpressure evolution in pipes exhibits a downtrend before the bifurcation, a sharp increase after the bifurcation until reaching the maximum, and a downward trend when propagating into the pipe end. It was also found that gas-explosion propagation was affected by the joint action of turbulence induced by obstacles and the abrupt increase of the cross-sectional area. In addition, the bifurcation’s position had only a small effect on the maximum peak overpressure in pipes.     

三通管不同开口状态下爆炸气流湍流变化规律

为研究三通管不同开口状态下爆炸参数变化规律,基于数值模拟分析管内爆炸湍流动能大小、形态变化特征.研究结果表明:不同开口状态下三通管道内湍流动能峰值最大值均出现在垂直岔管内,垂直管道开口情况下管道内的最大湍动能峰值增大29.86％,水平管道开口情况下该数值降低10.12％,而两端均开口情况下,增大178.45％;管内与湍...     

A methodology to predict shock overpressure decay in a tunnel produced by a premixed methane/air explosion

A methodology for estimating the blast wave overpressure decay in air produced by a gas explosion in a closed-ended tunnel is proposed based on numerical simulations. The influence of the tunnel wall roughness is taken into account in studying a methane/air mixture explosion and the subsequent propagation of the resulting shock wave in air. The pressure time-history is obtained at different axial locations in the tunnel outside the methane/air mixture. If the shock overpressure at two, or more locations, is known, the value at other locations can be determined according to a simple power law. The study demonstrates the accuracy of the proposed methodology to estimate the overpressure change with distance for shock waves in air produced by methane/air mixture explosions. The methodology is applied to experimental data in order to validate the approach.     

管道结构对氢/空预混气体爆炸特性影响研究

为研究管道结构对氢-空预混气体爆炸特性影响,采用实验与数值模拟相结合的方法,分析不同管道结构内氢-空预混气体燃爆时火焰传播进程、爆炸压力、湍流动能变化及流场分布.结果表明:90°弯管对氢-空预混气体爆炸强度增强作用明显高于T型分岔管和直管.火焰阵面在结构突变处褶皱变形较明显,并出现大尺度强湍流和涡团,气团脉动速度与湍流...     

Premixed methane-air deflagrations in a completely adiabatic pipe and the effect of the condition of the pipe wall

A completely adiabatic pipe that is similar to a coal-mine coal or rock roadway was simulated using the computational software AutoReaGas. A partially adiabatic pipe was established using an experimental steel pipe with heat-insulating material installed in the inner wall, and a non-adiabatic pipe was also established using the experimental steel pipe without the heat-insulating material. Premixed methane/air deflagrations were studied in the three types of pipe to reveal the influence of the condition of the pipe wall on gas explosions. The results showed that in the completely adiabatic pipe, the maximum explosion overpressure was dynamic and decreased and increased with increasing distance; however, the flame-propagation speed increased gradually. In the partially adiabatic pipe and the non-adiabatic pipe, the maximum explosion overpressure and flame-propagation speed increased initially and then gradually decreased with increasing distance. The majority of explosion overpressure and flame-propagation speed values at each gauge in the completely adiabatic pipe were larger than those of the partially adiabatic pipe. Both measurements at each gauge in the partially adiabatic pipe were much greater than those of the non-adiabatic pipe. The condition of the pipe wall has a large influence on the maximum explosion overpressure and the flame-propagation speed. In future explosion experiments, heat insulating materials should be installed in the inner wall of steel pipes to obtain data for application to the prevention and control of gas explosions in underground coal mines.     

Self-ignition and explosion during discharge of high-pressure hydrogen

The phenomenon of self-ignition and explosion during discharge of high-pressure hydrogen was investigated. To clarify the ignition conditions of high-pressure hydrogen jets, rapid discharge of the high-pressure hydrogen was examined experimentally. A diaphragm was used to allow rapid discharge of the high-pressure hydrogen. The burst pressure was varied from 4 to 30 MPa. The downstream geometry of the diaphragm was a flange and extension pipes, with the pipe length varying from 3 to 300 mm. The diameter of the nozzle was 5 or 10 mm. When short pipes were used, the hydrogen jet did not ignite. However, the hydrogen jet showed an increasing tendency to ignite in the pipe as the length of the pipe became longer. At higher burst pressures, a diffusion jet flame was formed from the pipe. The blast wave from the fireball formed on self-ignition of the hydrogen jet resulted in an extremely rapid pressure rise.     

泄漏油气燃爆灾害下FPSO结构响应分析

为评估FPSO泄漏油气燃爆事故中结构损伤风险,采用等效TNT法结合AUTODYN软件分析结构在爆炸冲击波下动态响应,分析其塑性、变形及应力分布,评估不同工况下结构损伤程度。结果表明,TNT起爆后冲击波高速传播,10ms时已覆盖工艺I区,经反射叠加耦合后破坏力增强;原油热处理器和电脱盐器发生失效和变形,生产甲板边缘位置受约束较小,发生较大变形,部分区域屈曲破坏;参与反应的油气越多,相同结构等效应力及变形越大,大应力、大变形区域分布越广;d=60mm时部分结构完全失效。     

Review of the DESC project

Dust Explosion Simulation Code (DESC) was a project supported by the European Commission under the Fifth Framework Programme. The main purpose of the project was to develop a simulation tool based on computational fluid dynamics (CFD) that could predict the potential consequences of industrial dust explosions in complex geometries. Partners in the DESC consortium performed experimental work on a wide range of topics related to dust explosions, including dust lifting by flow or shock waves, flame propagation in vertical pipes, dispersion-induced turbulence and flame propagation in closed vessels, dust explosions in closed and vented interconnected vessel systems, and measurements in real process plants. The new CFD code DESC is based on the existing CFD code FLame ACceleration Simulator (FLACS) for gas explosions. The modelling approach adopted in the first version entails the extraction of combustion parameters from pressure–time histories measured in standardized 20-l explosion vessels. The present paper summarizes the main experimental results obtained during the DESC project, with a view to their relevance regarding dust explosion modelling, and describes the modelling of flow and combustion in the first version of the DESC code. Capabilities and limitations of the code are discussed, both in light of its ability to reproduce experimental results, and as a practical tool in the field of dust explosion safety.     

Dust explosions and collapsed ductwork

One of the more obvious consequences of a dust deflagration inside process equipment or a structure is the mechanical damage caused by shock (compression) waves. This overpressure damage is revealed through the displacement of equipment, the outward deformation or rupture of enclosures constructed of ductile materials, or the projection of missiles. However, a different type of damage is sometimes observed in the ductwork connecting process equipment. In particular, the ductwork is collapsed as if it were subjected to an external, rather than an internal pressure. The phenomenon that causes this collapse of thin-walled conduit is a gas dynamic process called an expansion wave. When a dust deflagration travels through a conduit, it accelerates and causes a rise in pressure. When the dust deflagration is vented (say through a deflagration vent), the discharge of the high-pressure combustion products causes the formation of an expansion wave that travels in the reverse direction of the original discharge. The expansion wave causes the pressure in the ductwork to fall below atmospheric pressure. The sub-atmospheric pressure, in turn, causes the ductwork to fail by buckling. In this study, we examine the gas dynamics of the expansion wave, demonstrate how to calculate the degree of pressure drop caused by the expansion wave, and illustrate the concept with case studies of dust explosions.     

3D Voronoi等效晶质模型在岩石破坏细观研究中的应用

基于3D Voronoi图提出一种能够反映岩石矿物晶粒结构的三维精细化建模方法,分析了晶粒排列均匀化程度及大小等微观结构的变化对模型宏观力学性质的影响程度,并进行了晶粒结构优化设计。通过模拟粉砂质板岩单轴压缩和巴西劈裂的破坏过程,以及与室内试验对比验证了其适用性,并从细观角度揭示了岩石的破坏机理。研究结果表明:通过裂纹生长速率大致可以表征室内试验中弹性变形、非弹性变形和峰值后宏观破坏阶段;岩样在单轴压缩和巴西劈裂破坏过程中以拉伸断裂为主,在宏观上表现为脆性断裂;岩样宏观断裂呈现沿晶和穿晶断裂的组合形态,弹性变形阶段裂纹的萌生和扩展以沿晶断裂为主,而穿晶断裂的扩展和贯通往往导致局部失稳,表现为非弹性变形阶段。     

Using computational fluid dynamics (CFD) for blast wave predictions

Explosions will, in most cases, generate blast waves. While simple models (e.g., Multi Energy Method) are useful for simple explosion geometries, most practical explosions are far from trivial and require detailed analyses. For a reliable estimate of the blast from a gas explosion it is necessary to know the explosion strength. The source explosion may not be symmetric; the pressure waves will be reflected or deflected when hitting objects, or even worse, the blast waves may propagate inside buildings or tunnels with a very low rate of decay. The use of computational fluid dynamics (CFD) explosion models for near and far field blast wave predictions has many advantages. These include more precise estimates of the energy and resulting pressure of the blast wave, as well as the ability to evaluate non-symmetrical effects caused by realistic geometries, gas cloud variations and ignition locations. This is essential when evaluating the likelihood of a given leak source as cause of an explosion or equally when evaluating the potential risk associated with a given leak source for a consequence analysis.In addition, unlike simple methods, CFD explosion models can also evaluate detailed dynamic effects in the near and far field, which include time dependent pressure loads as well as reflection and focusing of the blast waves. This is particularly valuable when assessing actual near-field blast damage during an explosion investigation or potential near-field damage during a risk analysis for a facility. One main challenge in applying CFD, however, is that these models require more information about the actual facility, including geometry details and process information. Collecting the necessary geometry and process data may be quite time consuming. This paper will show some blast prediction validation examples for the CFD model FLACS. It will also provide examples of how directional effects or interaction with objects can significantly influence the dynamics of the blast wave. Finally, the challenge of obtaining useful predictions with insufficient details regarding the geometry will also be addressed.     

爆破和降雨作用下诱发含后缘裂缝岩质边坡失稳机制研究

为了探讨爆破和降雨对边坡失稳的影响,基于边坡实际结构,提出了将滑面分为后缘张拉裂缝段、中部锁固段、下部剪切滑动段。利用断裂力学理论,分析了爆破和降雨双重工况下的裂缝起裂扩展判据。基于格里菲斯（Griffith）能量准则,推导了边坡滑动块断裂后沿底滑面的剧动距离。通过实例验证了理论计算的可行性和适用性,研究结果表明:边坡表面裂缝起裂的根本动力为降雨、爆破以及二者的共同作用;在一定外力条件下,裂缝起裂扩展存在最小临界深度;降雨和爆破共同作用时,裂缝扩展临界深度最小;中部锁固段长度为控制边坡失稳的关键因素;降雨并不能使裂缝扩展,预知裂缝深度时,可通过控制爆破药量来控制边坡失稳。     

轴向单缝偏心药柱爆破效应模型试验研究

为了探究轴向单缝偏心药柱在掏槽爆破中爆炸应力波传播规律和裂纹扩展情况,采用水泥砂浆模型试块开展模型爆破试验,采用超动态应变测试系统对爆炸应力场进行测量。结果表明:在相同爆心距下,背对切缝侧A测点仅为正对切缝侧B测点峰值应力的73.82%;一定角度范围内,峰值应力随偏转角度的增大而减小,偏转角度为0°时峰值应力最大,偏转角度为60°处峰值应力是偏转角度为30°处的74.39%,峰值应力在0°到60°范围内最大衰减达到32.74%;正对切缝方向产生一条贯通炮孔的主裂纹,裂纹发育优于其他方向,且切缝方向没有明显的细小裂纹,这表明轴向单缝偏心药柱具有良好的定向断裂能力。     

External pressures generated by vented gas and dust explosions

Several different data correlations have been developed for the external pressures associated with vented gas explosions and dust explosions. These correlations, which are applicable to external locations in the direct line-of-sight of the enclosure vent, are reviewed here. In addition, the application of spherically symmetric and of ellipsoidal blast wave models is explored as a possible means of calculating external pressures over a wider range of conditions than is possible with the existing data correlations. Results indicate that the spherically symmetric blast wave model can obtain a comparable accuracy (8–9 kPa standard deviation) for line-of-sight locations as the more recent data correlations. In the case of the lower blast pressures at locations perpendicular to the vent line-of-sight, the ellipsoidal blast wave provides significantly better agreement with data (to within 1 kPa standard deviation for the one set of available test data) than the spherically symmetric model.