Safety-related conclusions for the application of ultrasound in explosive atmospheres

International safety regulations such as EN 1127-1 consider ultrasound to be an ignition source. Currently, applications of ultrasound in explosive atmospheres have to comply with a threshold value of 1 mW/mm². However, it is unclear as to how this intensity has to be measured and, therefore, this threshold value is poorly defined. Moreover, it is based on theoretical estimations in analogy to other ignition sources and there are no publications or significant records on these estimations. Within a research project at PTB, it has now been investigated experimentally in relation to worst-case considerations including airborne ultrasound, focused MHz ultrasound in liquids and acoustic cavitation. On the basis of the results of the research it is now possible to revise the current regulations and to specify measures for safe operation of ultrasonic applications in explosive atmospheres. In this context, for ultrasound coupled directly to gaseous atmospheres a new threshold value of 170 dB (re. 20 μPa) can be suggested, and for ultrasonic applications in liquids, an augmentation can be made to the threshold to 400 mW/mm².     

A closer look at BLEVE overpressure

The overpressure produced by the boiling liquid expanding vapor explosion (BLEVE) is still not well understood. Various methods have been published on the overpressure modeling in the far field. They mostly differ by the modeling of the expansion energy, used to scale the distance to the source where the overpressure needs to be calculated. But these methods usually include a experimentally fitted reduction factor, and are mostly overestimating the overpressures. Today there is a growing interest in modeling the BLEVE overpressure in the near field, for studying the blast effect on critical infrastructure such as bridges and buildings. This requires a much better understanding of the BLEVE blast. This paper goes deeper in the understanding of the physical phenomenon leading to the BLEVE blast wave generation and propagation. First, mid-scale BLEVE experiments in addition to new experimental data for near field blast from a small scale supercritical BLEVE are analyzed. And second, an analysis method of the shocks observed in the experiments is presented based on fundamental gas dynamics, and allows the elaboration of a new modeling approach for BLEVE overpressure, based on the calculation of the initial overpressure and radius of the blast.     

A new leak location method based on leakage acoustic waves for oil and gas pipelines

In order to study a new leak detection and location method for oil and natural gas pipelines based on acoustic waves, the propagation model is established and modified. Firstly, the propagation law in theory is obtained by analyzing the damping impact factors which cause the attenuation. Then, the dominant-energy frequency bands of leakage acoustic waves are obtained through experiments by wavelet transform analysis. Thirdly, the actual propagation model is modified by the correction factor based on the dominant-energy frequency bands. Then a new leak detection and location method is proposed based on the propagation law which is validated by the experiments for oil pipelines. Finally, the conclusions and the method are applied to the gas pipelines in experiments. The results indicate: the modified propagation model can be established by the experimental method; the new leak location method is effective and can be applied to both oil and gas pipelines and it has advantages over the traditional location method based on the velocity and the time difference. Conclusions can be drawn that the new leak detection and location method can effectively and accurately detect and locate the leakages in oil and natural gas pipelines.     

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.     

Simplified model for the evaluation of the effects of explosions on industrial target

The evaluation of vulnerability of process equipment to explosion is a central issue in the analysis of industrial risks. In this work, we have developed a simplified model, however based on fundamental equations, which includes structural and fluid–dynamic parameters for the target (the industrial equipment) and for the impacting pressure wave (shock waves) or object (fragment, debris) produced by different type of chemical explosions.The validity of methodology has been assessed by case histories. Several insights on the dynamic of structural interaction of the explosion with the target have been obtained, with specific reference to escalation effects.The model derives from the well-known Johnson's number, often adopted in impact engineering.     

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。     

波浪与抛石潜堤相互作用的MPS法数值模型研究

为了研究波浪与抛石潜堤相互作用过程中大自由表面变形和堤内渗流等强非线性紊流运动问题，利用改进的MPS法，建立了模拟波浪与抛石潜堤相互作用的MPS法数值计算模型。模型将抛石潜堤假定为均质多孔介质，采用Drew的二相流运动方程描述多孔介质内外的流体运动；通过在动量方程中增加非线性阻力项，并引入亚粒子尺度紊流模型，模拟波浪与可渗结构物相互作用过程中的紊流运动。选取“U”型管中多孔介质内渗流过程和孤立波与可渗潜堤相互作用两个典型的渗流问题，通过将数值计算结果与理论解和实测值的对比分析，对所提出的MPS法紊流渗流模型的模拟精度进行验证。结果表明：基于改进的MPS法构建的垂向二维紊流渗流模型可以很好地再现 “U”型管中多孔介质内渗流以及波浪作用下可渗潜堤内外的复杂流场，显著缓解流-固界面处的压力震荡与粒子分布不均匀问题，实现了较高的模拟精度。     

爆炸冲击波作用下圆形通风设施的动态破坏特性

为了研究瓦斯爆炸对通风设施造成的严重破坏及其导致的通风系统紊乱与灾情迅速扩展问题，基于LS-DYNA有限元软件，模拟研究巷道中瓦斯爆炸冲击波作用下圆形通风设施的动态破坏特性，分析应力、应变、速度、位移的动态特征及其破坏过程，并对圆形通风设施动态破坏机理进行初步探索。研究结果表明:爆炸冲击波作用下，圆形通风设施正、反面出现压应力与拉应力分布圆环，且压应力与拉应力峰值处于在外部受约束边界径向圆环附近区域与圆心位置，应变、速度和位移最大值均分布在次区域；爆炸冲击波作用下，通风设施表面形成多圈的正向和反向的应变相互交替，呈现W型的褶皱变形；爆炸冲击波作用下，环向裂纹集中在受约束的边界区域附近，发生脆性破坏，其他区域会出现较多的径向裂纹，可发生韧性破坏，整个断裂过程是脆性与韧性断裂的混合型断裂。     

房地产开发地铁振动达标距离研究

已建和待建的多条地铁线路穿过某房地产开发地块,为了防治地铁运行对建筑造成振动环境影响,需要设定建筑靠近地铁的最小达标距离,包括采取减振措施后的距离。通过现场系统实验监测结合数值模型分析,从工程实践的角度提出了上述距离。对于实验中观察到随距离出现振动局部放大以及进口与国产仪器监测结果不同的现象,佐证了有关学者的理论与实验分析,提出:(1)现有地铁环境影响评价报告常用的60m评价范围偏小,推荐可扩大至80~100m;(2)迫切需要新的振动环境标准发布,避免有关项目的环境管理要求偏低。     

北京市某高层建筑高空电磁辐射环境影响分析

选取北京市某代表性高层居民楼顶平台作为高空电磁辐射环境水平监测点进行综合场强和选频监测，评价总体电磁辐射环境水平，并分析监测区域电磁辐射能量的来源。结果表明：该高空监测区域的电磁辐射环境总体水平低于国家规定的公众照射导出限值，但高于地面水平。监测区域主要受30 km 外的中波台影响，其次是9 km 外的中央电视塔。影响最大的是639 kHz频率的中波信号，占100 kHz～300 MHz总场强的95％以上，其次是1．28 MHz频率的中波信号。提出，开展敏感建筑物规划建设时，应考虑中波的传播特性和对环境的影响。