Explosion Center Research Articles

Compression response and shock-wave behavior of liquid nitrogen caused by energy injection in an enclosed pipeline

In a cryogenic liquid medium, shock waves will be formed by the expansion of compressed gas that has been vaporized due to the injection of a large amount of energy. This may severely threaten the reliability of high-Tc superconducting (HTS) apparatus. Several studies have documented the destructive forces of evaporating nitrogen produced by arc energy. However, the properties of and propagation mechanisms relating to pressure waves in liquid nitrogen have yet to be understood. The aim of this study was to clarify the evolution of pressure waves within an enclosed pipeline and reveal the effects of several factors such as the pipe size and the injected energy on the shock-wave impact using explosion dynamics simulations. The results provide evidence for the strengthening of shock waves due to multiple reflection and superposition. In addition, analysis of the pressure impulse and effective strain reveals that, in the case of moderate injected energy, the overall shape of the inside wall of the pipe will remain unchanged except at the points closest to the explosion center; in contrast, the ends of the pipeline may suffer from more severe deformation. Finally, the calculations suggest that the shock-wave impact increases almost linearly with the injected energy, and in logarithmic coordinates, the pressure is inversely proportional to the explosion distance. These findings provide a better understanding of the characteristics and propagation patterns of shock waves in liquid nitrogen, and they lay a foundation for evaluating the safety of HTS cables and energy pipelines.

Study on influencing factors and prediction of peak particle velocity induced by roof pre-split blasting in underground

Blasting technology is widely used to prevent coal bursts by presplitting the overburden in underground coal mines. The control of blasting intensity is important in achieving the optimal pre-split effectiveness and reducing the damage to roadway structures that are subjected to blasting vibrations. As a critical parameter to measure the blasting intensity, the peak particle velocity (PPV) of vibration induced by blasting, should be accurately predicted, and can provide a useful guideline for the design of blasting parameters and the evaluation of the damage. In this paper, various factors that influence PPV, induced by roof pre-split blasting, were analyzed using engineering blasting experiments and numerical simulations. The results showed that PPV was affected by many factors, including charge distribution design (total charge and maximum charge per hole), spacing of explosive centers, as well as propagation distance and path. Two parameters, average charge coefficient and spatial discretization coefficient were used to quantitatively characterize the influences of charge distribution and spacing of explosive centers on the PPV induced by roof pre-split blasting. Then, a model consisting of the combination of artificial neural network (ANN) and genetic algorithm (GA) was adopted to predict the PPV that was induced by roof pre-split blasting. A total of 24 rounds of roof pre-split blasting experiments were carried out in a coal mine, and vibration signals were collected using a microseismic (MS) monitoring system to construct the neural network datasets. To verify the efficiency of the proposed GA-ANN model, empirical correlations were applied to predict PPV for the same datasets. The results showed that the GA-ANN model had superiority in predicting PPV compared to empirical correlations. Finally, sensitivity analysis was performed to evaluate the impacts of input parameters on PPV. The research results are of great significance to improve the prediction accuracy of PPV induced by roof pre-splitting blasting.

Experimental Study on the Propagation Law of Explosive Stress Wave in Cement Mortar with Weak Layers

The weak layer has good attenuation performance when it comes to the explosive stress wave, which can be used in protective structures. In this paper, a cement mortar specimen was designed, cast, and tested. Under inner explosion, due to the expansion of air in the explosive hole, the tensile cracks formed around the explosive hole are mainly in a damage pattern. In ordinary cement mortar, the transmittance is decreasing as the distance increases. At a distance of 8 cm to 14 cm from the explosive center, the average transmittance is 50.16%, 12 cm to 18 cm, while the average transmittance is 62.89%, increasing by 12.73%. Adding one weak layer into the cement mortar, the transmittance of one weak layer is 43.37%. The effect of increasing weak layers in short spacing is not obvious, and the transmittance of the second and third weak layer is about 80%, much less than the first layer. The softer the weak layer and the larger the wave impedance, the smaller the transmission coefficient is. The research proves that the weak layer has excellent attenuation performance when it comes to the explosive stress wave.

Research on Electromagnetic Radiation Characteristics of Energetic Materials

During the explosion of energetic materials, electromagnetic interference is generated, which can affect the normal operation of surrounding electronic equipment. Therefore, an electromagnetic radiation measurement device based on a short-wave omnidirectional antenna and ultra-wideband omnidirectional antenna was designed to measure the electromagnetic radiation generated by the explosion of energetic materials of different masses, and the electromagnetic radiation characteristics were obtained through data processing. The results showed that the electromagnetic signal can still be collected hundreds of milliseconds after the explosive is detonated, and the electromagnetic radiation generated by the explosion is continuous and intermittent, which is a phenomenon that has not been found in this field at present. The mass of the energetic material had a significant effect on the time-domain characteristics of the electromagnetic radiation generated by the explosion: the higher the mass of the energetic material was, the shorter the delay response of the electromagnetic signal was, the longer the duration was, and the earlier the peak appeared. The frequency of electromagnetic radiation signals generated by the explosion of energetic materials was mainly concentrated below 100 MHz, and the energy was most concentrated in the frequency band of 0~50 MHz. The composition of energetic materials had the greatest influence on the spectral distribution, and the spectral distribution of electromagnetic radiation produced by the explosion of explosives with different compositions had obvious specificity. The electromagnetic radiation intensity generated by the explosion of energetic materials had a strong correlation with the distance from the explosion center, and it significantly decreased as the distance increased. The structure and detonation method of energetic materials changed the geometrical motion pattern during the explosion, resulting in the non-uniformity of electromagnetic radiation propagation.

Numerical simulations of trajectories of shock wave triple points in near-ground explosions of TNT charges

To accurately predict the locations and trajectories of shock wave triple points in near-ground explosions, this study determined the propagation law of shock waves after the initiation of a detonator using a schlieren system. Moreover, it established a numerical simulation model using the Autodyn software and verified the accuracy of the model through a detonator explosion experiment. The propagation law of shock waves of TNT charges (1, 10 ​kg and 100 ​kg) at different heights of burst(0.5, 1.0, 1.5, 2.0 ​m,and 2.5 ​m) was studied through numerical simulations, and the triple point trajectories were fitted to an empirical formula. The results show that the maximum simulation error relative to the schlieren images of detonator explosions did not exceed 4 ​mm. As the scaled height of burst decreased, the positions of generated triple points were closer to the vertical projection of the explosion center and rose faster. As the scaled distance increased, the scaled height of triple points rose exponentially. The average error of triple point trajectories between the values predicted in this study and the experimental values was 4.1%, indicating that the accuracy of the fitted formula is acceptable. This study revealed the overpressure distribution law of shock waves and will provide a reference for shock wave overpressure measurements and explosion protection.

Dynamic Multiprojectile Attack and Killing Effects of Detonation Warheads

Dynamic spatial distribution and killing characteristics of warhead fragments are important topics in the field of weapon effectiveness and protection. However, there is little research on the fragment distribution formed by continuous dynamic attacks of multiple projectiles that explode above the ground. This study analyzes spatial distributions of warhead fragments using witness boards in a rectangular target test. The results show that the fragment distribution of multiple projectiles in continuous dynamic attacks demonstrates a spatial superposition characteristic. The superimposed distribution is the sum of the distributions of two independent fragment distributions. The distribution characteristics are consistent with fragment scattering behavior. Therefore, they can be used to analyze the killing effects of multiple projectiles conveniently. The effects of falling speed, falling angle, and explosion height on the damage range of fragments were explored by a fragment spatial distribution model obtained from experiments. Analysis indicates that the prefabricated fragment distribution conformed to a spatial superposition relationship under dynamic multiprojectile continuous attacks, and the superposition obeyed fragment scattering characteristics. As the projectile falling angle increased at the explosion center, or as the falling height decreased, the positive pressure duration increased gradually. The falling speed had the greatest impact on the specific impulse of overpressure. The falling angle had the greatest impact on the peak value of overpressure. Both the falling angle and the explosion height had the greatest impact on the positive pressure acting time.

Research on the distribution characteristics of explosive shock waves at different altitudes

There are great differences in the distribution characteristics of shock waves produced by ammunition explosions at different altitudes. At present, there are many studies on plain explosion shock waves, but there are few studies on the distribution characteristics of plateau explosion shock waves, and there is still a lack of complete analysis and evaluation methods. This paper compares and analyzes shock wave overpressure data at different altitudes, obtains the attenuation effect of different altitudes on the shock wave propagation process and proposes a calculation formula for shock wave overpressure considering the effect of altitude. The data analysis results show that at the same TNT equivalent and the same distance from the measuring point, the shock wave overpressure at high altitude is lower than that at low altitude. With the increase in the explosion center distance of the measuring point, the peak attenuation rate of the shock wave overpressure at high altitudes is smaller than that at low altitudes, and the peak attenuation rate of the shock wave overpressure at high altitudes gradually intensifies with increasing proportional distance. The average error between the shock wave overpressure and measured shock wave overpressure in a high-altitude environment obtained by using the above calculation formula is 11.1389%. Therefore, this method can effectively predict explosion shock wave overpressure in plateau environments and provides an effective calculation method for practical engineering tests.

Chain destruction of methane–hydrogen explosion in utility tunnel to adjacent space

Abstract Hydrogen is clean energy possible be transported in pipelines under utility tunnels in the future. Current research about gas explosions in the utility tunnel ignored the damage in the adjacent zones, the fire-proof wall, the above ventilated mezzanine and the escape room. The numerical simulation of methane–hydrogen explosion considering the chain destruction is conducted. The results show that the maximum overpressure peak is 6 MPa under 100% H2, and the fire-proof wall will increase the explosive intensity, so the length of one gas compartment should increase to 400 m or 600 m. The maximum overpressure sometimes presents in the adjacent zone rather than the explosive center, and the shock wave will not influence the ventilated mezzanine much. However, the flame will influence ventilated mezzanine, even the ground, so the adjacent zones, ventilated mezzanine and escape room are also dangerous. Therefore, a novel emergency system should be discussed for high-proportion-hydrogen transportation in utility tunnels.

Supernova Fallback as Origin of Neutron Star Spins and Spin-kick Alignment

Abstract Natal kicks and spins are characteristic properties of neutron stars (NSs) and black holes (BHs). Both offer valuable clues to dynamical processes during stellar core collapse and explosion. Moreover, they influence the evolution of stellar multiple systems and the gravitational-wave signals from their inspiral and merger. Observational evidence of a possibly generic spin-kick alignment has been interpreted as an indication that NS spins are either induced with the NS kicks or inherited from the progenitor rotation, which thus might play a dynamically important role during stellar collapse. Current three-dimensional supernova simulations suggest that NS kicks are transferred in the first seconds of the explosion, mainly by anisotropic mass ejection and, on a secondary level, anisotropic neutrino emission. By contrast, the NS spins are only determined minutes to hours later by the angular momentum associated with the fallback of matter that does not become gravitationally unbound in the supernova. Here, we propose a novel scenario to explain spin-kick alignment as a consequence of tangential vortex flows in the fallback matter that is accreted mostly from the direction of the NS’s motion. For this effect the initial NS kick is crucial, because it produces a growing offset of the NS away from the explosion center, thus promoting one-sided accretion. In this new scenario conclusions based on traditional concepts are reversed. For example, pre-kick NS spins are not required, and rapid progenitor core rotation can hamper spin-kick alignment. We also discuss implications for natal BH kicks and the possibility of tossing the BH’s spin axis during its formation.

Clinical Data Management in the United States Where We Have Been and Where We Are Going

In the United States, clinical data management (CDM) has been accelerating from a single focus on collecting and preparing clinical trial data for study analysis to a multi-pronged endeavor. This endeavor emphasizes quality data from inception or planning of study design to collection, coding, analysis, reporting, and sharing of all applicable and available data. In this article the influence of legislation and scientific expertise in the collection and analysis of valid, sound data is detailed. FDA requirements as well as academic and technical developments have led to better, more precise and reliable methods in CDM. As such, the perspectives of industry, academia, and non-profits are presented. The role of CDM, at the center of the clinical data explosion, is described, demonstrating how data managers coordinate and build on expertise from all stakeholders. The dependence of biomedical research on CDM and quality data for breakthroughs in diagnostics, drugs, biologics and vaccines is examined. The state of current educational programs is detailed and suggestions are made for new interdisciplinary programs that can provide technical support for all clinical research endeavors. In the article, CDM is viewed through the lens of providing leadership in clinical research and striving to overcome obstacles in communicating the latest technological changes to all stakeholders.  

Simulation of the Deformation and Failure Characteristics of a Cylinder Shell under Internal Explosion

Under the load of an internal explosion shock wave, the failure of a cylindrical shell is the basis of safety evaluation and failure analysis of explosion vessel design. This paper carried out the explosion loading experiment of a cylindrical shell, and used the nonlinear dynamic finite element analysis program LS-DYNA for the dynamic response of the cylindrical shell along the directions of thickness and length, and analyzed the failure law of a cylindrical shell. The results showed that the deformation of the core section of the cylindrical shell was not different in the same specific distance, the strain decreased more slowly with the increase of thickness at the end of the explosion center, and the expansion failure process and fracture mode of metal shell under explosive load were affected by the material and structure size of the shell, as well as the characteristics and mode of the load. Based on the plastic theory, this paper discussed the evolution characteristics of the stress state during the expansion process of cylindrical shells under different explosion pressures, and analyzed the explosion pressure effect on the tensile fracture and shear fracture. The expansion failure experiment of a 20# steel-made cylindrical shell and the microscopic and metallographic analysis of the recovered debris were carried out.

Modification of the cathode material around the explosive electron emission centers in the spark stage of vacuum breakdown

On the basis of numerical calculations estimates for the fields of mechanical stresses around the explosive electron emission centers of the cathode during the development of pulsed vacuum breakdown are given. Expansion of material due to conduction loss was taken into account. It is shown that the sizes of regions with broken crystalline structure is much larger than the corresponding of explosive emission centers. Keywords: vacuum breakdown, explosive electron emission, mechanical stresses.

Модификация материала катода вокруг центров взрывной электронной эмиссии в искровой стадии вакуумного пробоя

On the basis of numerical calculations estimates for the fields of mechanical stresses around the explosive electron emission centers of the cathode during the development of pulsed vacuum breakdown are given. Expansion of material due to conduction loss was taken into account. It is shown that the sizes of regions with broken crystalline structure is much larger than the corresponding of explosive emission centers.

Fire and Explosion Risks and Consequences in Electrical Substations—A Transformer Case Study

Abstract This study aims to find how fires and explosions can occur in enclosed spaces where electrical transformers are installed and to investigate the consequences of the damages to the surrounding areas caused by these accidents. This study began with the collection of a mineral oil waste sample from an indoor substation transformer in Riyadh, Saudi Arabia. This sample was analyzed to determine its composition. Results revealed that 30 components ranging from C6 to C30 were detected in the sample. The mixture flammability limits, calculated using Le Chatelier rules and found to be 0.97 and 6.56, indicated that the vapor mixture for the waste oil sample was not flammable at 25 °C and 1 atm. Consequence analysis was used to predict the outcome of fire and explosion events based on a transformer with a capacity of 1100 liters. The peak overpressure generated by an explosion was estimated to be 80.97 kPa. Moreover, the thermal radiation produced by various types of fires was estimated as a function of the distance from the accident center. The thermal flux from a boiling liquid expanding vapor explosion (BLEVE) was 99.8 kW/m2, which is greater than that from jet and pool fires. The probability of an individual suffering injury or dying as a result of exposure to fire and/or an explosion was estimated using dose-response models. The results showed that the peak overpressure produced by an explosion can cause severe damage within 20 m of the explosion center. However, the results also showed that there is a 100% probability of the thermal radiation from a BLEVE causing fatalities up to a distance of 140 m. The risk due to the fragmentation of the transformer tanks was also assessed, and a majority of fragments would land within a range of 111.2 m.

CFD analysis of large-scale hydrogen detonation and blast wave overpressure in partially confined spaces

The effect of confinement on the magnitude of overpressure due to a gaseous detonation of a hydrogen-air mixture was studied with the aid of numerical simulations. A simplified combustion reaction kinetic model applied along with computational fluid dynamics (CFD) allowed for the numerical simulation of large-scale detonations of hydrogen-air mixtures. The model was validated against experimental data reported in the literature for the case of a large-scale (300 m3) surface (unconfined space) detonation of a hydrogen-air mixture and the results of a hydrogen-air (confined space) detonation test performed in a 263 m3 tunnel facility. The predicted overpressure and detonation velocity was in agreement with the measurements in both unconfined and confined detonation cases. To verify the effect of confinement on the magnitude of the blast wave overpressure due to detonation of a combustible gas cloud, a series of CFD simulations of hydrogen detonations followed by propagation of a non-reactive blast wave in various geometries were carried out. The results were compared with the correlation applicable for unconfined detonations, which was also found to be applicable for partially confined detonations after the transformation of the distance from explosion centre to spherical blast wave equivalent radius.

The influence of sensor installation angle on explosive shock wave overpressure test

In the engineering measurement of explosion shock wave pressure, the installation method of shock wave pressure sensor is of great significance to accurately obtain shock wave pressure. Based on the actual shooting range explosion shock wave overpressure test program, this paper uses AUTODYN to establish a finite element numerical simulation model. The distance from the ground reflection pressure sensor to the explosion center is 3 m, 4 m, 5 m, and 6 m. The shock wave overpressure data in the range of 8° and 10° are acquired and analyzed. The analysis results show that the shock wave overpressure obtained when the sensor installation angle is absolute zero is the ideal value. When the sensor installation plate is within a certain range, the overpressure value of the explosion shock wave increases with the increase of the installation angle of the plate, and the installation angle of the sensor is positively correlated with the overpressure of the explosion shock wave.

Experimental study on TNT equivalent coefficients for two new kinds of propellants

The TNT equivalent coefficient is an important evidence to guide the blast-resistant design and safe-distance determination for dangerous goods. To find out the TNT equivalent coefficients of two new kinds of propellants (H1, H2), a series of free-field static detonation tests were performed for the two propellants (H1, H2) and flaky 2,4,6-trinitrotoluene (TNT). Five repeated tests were carried out for each explosive and the mass of the tested explosive was 10 kg in each test. And the existing method for calculating the TNT equivalent coefficients was modified. Base on the overpressure-time curves of the shock waves at different distances from the explosion centers, the TNT equivalent coefficients for overpressure and specific impulse at different scaling distances were analyzed by the modified calculation method. The results show that the propagations of shock waves induced by explosions of the propellants agree well with the similar law, and are similar with that induced by explosion of the TNT explosive. Meanwhile, the overpressures and specific impulses of shock waves induced by explosions of the two propellants are much higher than those of the TNT explosive. With the increase of scaling distance, the overpressure TNT equivalent coefficient of H1 first increases to 1.34 and then decreases, while that of H2 decrease monotonously, and the maximum value is 1.26. With the increase of the scaling distance, both the specific impulse TNT equivalent coefficients of H1 and H2 first increase and then decrease. The specific impulse TNT equivalent coefficient of H1 with the peak value 1.38 is greater than that of H2. The modified method can be used to accurately calculate the TNT equivalent coefficients of the tested samples, and the results can improve the safety design of blast-resistant structures.

Beirut explosion: TNT equivalence from the fireball evolution in the first 170 milliseconds

The evolution of the fireball resulting from the August 2020 Beirut explosion is traced using amateur videos taken during the first 400 ms after the detonation. Thirty-nine frames separated by 16.66–33.33 ms are extracted from six different videos located precisely on the map. Time evolution of the shock wave radius is traced by the fireball at consecutive time moments until about t approx 170 ms and a distance d approx 128 m. Pixel scales for the videos are calibrated by de-projecting the existing grain silos building, for which accurate as-built drawings are available, using the length, the width, and the height and by defining the line-of-sight incident angles. In the distance range d approx 60–128 m from the explosion center, the evolution of the fireball follows the Sedov–Taylor model with spherical geometry and an almost instantaneous energy release. This model is used to derive the energy available to drive the shock front at early times. Additionally, a drag model is fitted to the fireball evolution until its stopping at a time t approx 500 ms at a distance d approx 145pm 5 m. Using the derived TNT equivalent yield, the scaled stopping distance reached by the fireball and the shock wave-fireball detachment epoch within which the fireball is used to measure the shock wave are in excellent agreement with other experimental data. A total TNT equivalence of 200pm 80,mathrm{t} at a distance d approx 130 m is found. Finally, the dimensions of the crater size taken from a hydrographic survey conducted 6 days after the explosion are scaled with the known correlation equations yielding a close range of results. A recent published article by Dewey (Shock Waves 31:95–99, 2021) shows that the Beirut explosion TNT equivalence is an increasing function of distance. The results of the current paper are quantitatively in excellent agreement with this finding. These results present an argument that the actual mass of ammonium nitrate that contributed to the detonation is much less than the quantity that was officially claimed available.

Experimental and numerical investigation on fabricating multiple plates by an energy effective explosive welding technique

An innovative explosive welding method for the fabrication of multiple plates (EWMP) was proposed to further improve the energy efficiency of explosive welding explosive charges and reduce the impact on the surrounding environment. In this method, six metal plates were placed in parallel and three composite plates were obtained through one explosion in this paper. The microstructure of the joint was analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron backscattering diffraction (EBSD). Compared to traditional explosive welding (TEW), the EWMP dramatically reduced the noise and vibration and increased the energy efficiency of explosives. The results showed the vibration data of EWMP were reduced by 16.7, 16.4, 2.8, and 1.5%, respectively, and at places of 3, 4, 5, and 6 m away from the explosion center, and explosive consumption of EWMP was reduced by at least half, compared to the traditional method when obtaining the same amount of welded plates. Through numerical simulation, the collision speeds of the composite plate are 610, 516, and 471 m/s, respectively, and the waveform of the composite plate is basically in coincidence with the result of the experiment.

Basic calculation methods of investigation of circumstances and mechanism of man-made explosions

The article purpose is to analyze the danger of man-made explosions and provide calculation methods for determining the mechanism of the occurrence of an explosion during forensic examinations of the study of the circumstances and mechanism of man-made explosions.
 The relevance of the article is caused by the fact that present-day production and everyday life cannot dispense with the usage of combustible and explosive substances. The particular attention to be paid to emergency prevention related to explosives, as well as the research to determine the mechanism of man-made explosions. The research on the mechanism of man-made explosions will make it possible to determine the technical cause of their occurrence, to analyze for what reason and for whose fault the event occurred, and also what measures should be taken to minimize the likelihood of such situations occurence.
 It is noted that in order to obtain reliable conclusions about the mechanism of man-made explosions, it is necessary to use scientifically based methods and methodologies allowing us to assess the extent of destruction. The degree of destruction of surrounding building structures and harm to people depends on overpressure caused as the result of a significant expansion of the explosion products and their spread to all directions from the center of explosion. The most frequent causes of explosions in the explosive object are: destruction and damage to production tanks, equipment and pipelines; deviation from production regulations (excess pressure and temperature of equipment operating mode), low-quality control of equipment and work while conducting require work, and untimely or poor-quality maintenance of technological equipment.
 The main calculation methods for the research of the man-made explosions in open areas, indoors, and limited space are given, which will allow to systematize the research process and analyze the flow of explosions in specific situations, and to establish a mechanism for their occurrence when conducting forensic examinations of the circumstances and mechanism of man-made explosions.