Strong Explosion Research Articles

Study of a large arched structure of interstellar H i in the southern Milky Way

We have revisited the sky region delimited by 290° < l < 320° and 3° < b < 17°, which includes a large arc of neutral hydrogen (H i), and extended the study region using the Leiden–Argentine–Bonn H i survey. The H i arc is almost an open downward semi-circumference of ≈10° of radius, with the symmetry axis perpendicular to the Galactic plane and the vertex at (l, b) ≈ (308°, 11°). The velocity component in the spectra of the 21 cm H i line that reveals the H i arc has a mean radial velocity (local standard of rest) of − 19 ± 2 km s − 1. Analysing H i maps covering the region lying below the arc (b < 0), we have investigated whether the arc could be interpreted as the cap of an expanding shell originated by a strong explosion occurred below the Galactic plane. The lower cap of the shell would have been blown out into the Galactic halo. In these conditions, the evolution of the shock wave and the associated shell was calculated by means of the Kompaneets approximation. By comparing the model’s predictions with the observations, we obtained that the distance, age and H i mass of the shell would be 640 pc, 9.3 × 106 yr and 3.4 × 105 M⊙, respectively. The shell’s sizes along and perpendicular to the Galactic plane would be 295 pc and ≈ 540 pc, respectively. By means of the model, we obtained that the energy of the explosion that gave origin to the shell would be around 5 × 1050 erg. Data from future surveys and from Gaia are expected to help confirming the proposed model. Other interstellar complexes of the region are also considered in relation to the H i shell.

Numerical study of the effect of reinforcing elements in the pole field on the strength of non-spherical shells under a pulse load

This paper describes the study of the stress-strain state in the elements of a non-spherical shell of variable thickness arising during the pulse action. The effect of the radii of inserts used as reinforcing elements on the magnitude of stresses in the non-spherical bottoms is investigated. The relationship between the stress-strain state in the shell pole and the radius of the inserts is studied. It is shown that the use of an insert with the optimal radius allows creating an equally strong explosion chamber.

Publisher’s Note: “Breakup process of cylindrical viscous liquid specimens after a strong explosion in the core” [Phys. Fluids 28, 094105 (2016)

Publisher’s Note: “Breakup process of cylindrical viscous liquid specimens after a strong explosion in the core” [Phys. Fluids 28, 094105 (2016)

Ultra-relativistic double explosions

We consider fluid dynamics of relativistic double explosion—when a point explosion with energy E1 is followed by a second explosion with energy E2 after time td (the second explosion could be in a form of a long lasting wind). The primary explosion creates a self-similar relativistic blast wave propagating with Lorentz factor Γ1(t). A sufficiently strong second explosion, with total energy E2≥10−2E1, creates a fast second shock in the external fluid previously shocked by the primary shock. At times longer than the interval between the explosions td, yet short compared with the time when the second shock catches up the primary shock at ∼tdΓ12, the structure of the second shock is approximately self-similar. The self-similar structure of the second shock exists for the case of constant external density (in this case Γ2∝t−7/3), but not for the wind environment. At early times, the Lorentz factor of the second shock may exceed that of the primary shock and may boost the synchrotron emission of locally accelerated electrons into the Fermi Large Area Telescope range.

Thermal radiation induced ignition of multipoint turbulent explosions

Abstract The severity of vapour cloud explosions is typically correlated with the peak over-pressure or, more accurately, with the total impulse caused by the pressure waves. The flame speed arising from strong (e.g. quasi-stable) turbulent deflagrations is frequently used to provide an indication of potential damage. However, conventional flame propagation mechanisms can present difficulties in terms of explaining the resulting damage. For example, the over-pressure in the Buncefield vapour cloud explosion was much higher than that predicted by conventional models. Alternative propagation mechanisms include intermittent localised strong explosions or detonations potentially supported by forward thermal radiation causing multi-point ignition of dust particles ahead of the advancing flame front. Such mechanisms are here explored using particles coated with acetylene black as the radiation target due to their relationship with soot emissions. A continuous wave laser operating in the near infrared was used as the radiation source with experiments performed in a flame tube using fuel lean CH4/H2/Air mixtures. It is shown that ignition kernels caused by irradiated particles can successfully be entrained into the main flow and/or recirculation zones formed around obstacles and cause multipoint explosions. The resulting relationship between fuel consumption ahead of the advancing flame and the evolution of the strength of the explosion is shown to be complex and typically lead to increased explosion durations with reduced peak pressures. It is also shown that chaotic pressure wave interactions can substantially increase both the explosion duration and the peak pressure depending on the timing of the radiation induced ignition.

Initiation of multifuel mixtures with bifurcation structures

The theory of a strong explosion is used as a basis for the development of an experimental technique for determining the source energy that ensures initiation of the combustible mixture. The technique is tested in experiments aimed at determining the critical energies of spherical detonation initiation E*3 with the use of an electric discharge for a stoichiometric acetylene–oxygen mixture and also for two-fuel mixtures (acetylene–nitrous oxide–oxygen) possessing bifurcation properties of cellular structures. The critical energy E*3 for the stoichiometric two-fuel mixture in terms of both fuels with a bifurcation structure is several-fold lower than the value of E*3 for the monofuel mixture whose cell size at a given pressure is determined by the large scale of bifurcation cells. This result testifies that the value of E*3 decreases with increasing number of “hot points,” which are numerous regions of collisions of large-scale and small-scale transverse waves in the mixture with bifurcation properties.

Investigation of energetic materials prepared by reactions of diamines with picryl chloride

Five compounds containing picryl group(s) were synthesized from reactions of hydrazine, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane and 1,7-diaminoheptane with picryl chloride under hydrothermal conditions in methanol. Hydrazine reaction yielded N-2,4,6-trinitrophenylhydrazine which has a single picryl group, whereas the other reactants formed symmetric products with both amine groups connected to picryl groups. These compounds are N,N′-di-2,4,6-trinitrophenyl-1,2-diaminoethane, bis-N,N′-di-2,4,6-trinitrophenyl-1,3-diaminopropane, bis-N,N′-di-2,4,6-trinitrophenyl-1,4-diaminobutane and bis-N,N′-di-2,4,6-trinitrophenyl-1,7-diaminoheptane. Molecular structures of two of these compounds, N-2,4,6-trinitrophenylhydrazine and bis-N,N′-di-2,4,6-trinitrophenyl-1,3-diaminopropane, were revealed by XRD methods. All compounds were investigated by TG and DSC methods. The thermal behaviour of N-2,4,6-trinitrophenylhydrazine was explosive, undergoing a strong explosion in a very short temperature interval, 180–185 °C. In cases of the other compounds, it was found out that the carbon chain between two picryl groups reduced the explosion enthalpy. In addition, the theoretical formation enthalpy of N-2,4,6-trinitrophenylhydrazine was calculated by running CBS-4 M energy calculations under Gaussian 09 software package. From the calculated value, reaction enthalpy values for the possible explosion pathways were investigated in accordance with the experiment. The path with reaction enthalpy closest to the experimental value was proposed as the explosion mechanism.

Breakup process of cylindrical viscous liquid specimens after a strong explosion in the core

Basic understanding and theoretical description of the expansion and breakup of cylindrical specimens of Newtonian viscous liquid after an explosion of an explosive material in the core are aimed in this work along with the experimental investigation of the discovered phenomena. The unperturbed motion is considered first, and then supplemented by the perturbation growth pattern in the linear approximation. It is shown that a special non-trivial case of the Rayleigh-Taylor instability sets in being triggered by the gas pressure differential between the inner and outer surfaces of the specimens. The spectrum of the growing perturbation waves is established, as well as the growth rate found, and the debris sizes evaluated. An experimental study is undertaken and both the numerical and analytical solutions developed are compared with the experimental data. A good agreement between the theory and experiment is revealed. It is shown that the debris size λ, the parameter most important practically, scales with the explosion energy E as λ ∼ E−1/2. Another practically important parameter, the number of fingers N measured in the experiments was within 6%-9% from the values predicted numerically. Moreover, N in the experiments and numerical predictions followed the scaling law predicted theoretically, N∼me1/2, with me being the explosive mass.

Analytical and numerical assessments of local overpressure from hydrogen gas explosions in petrochemical plants

SummaryAccurate prediction of pressure rise is important for safety assessments of a petrochemical plant in the event of an explosion accident. The sudden pressures arising from gas explosions at various hydrogen concentrations in air have been predicted analytically and numerically. These solutions were compared against experimental data. The analytical solution, based on the self‐similar solution for pointwise strong explosions in an open space, which assumed no energy loss and premixed fuel‐air mixture, reasonably predicted the explosive‐ignition detonation case while the numerical solutions were more suitable to model spark‐ignition deflagration cases that accounted for the effect of turbulence arising from three‐dimensionality and presence of obstacles in the computational domain. Comparison of both analytical and numerical results against experimental data indicates that their differences are within a 30% margin. The analytical model presented herein can be useful for field engineers who want conservative estimates of the overpressure resulting from explosive‐ignition detonation. Copyright © 2016 John Wiley &amp; Sons, Ltd.

The ongoing dome emplacement and destruction cyclic process at Popocatépetl volcano, Central Mexico

The ongoing eruptive activity of Popocatepetl volcano has been characterized by emplacement and subsequent destruction of a succession of lava domes. Between the onset of the current eruption in 1994 and the time of this submission, 38 episodes of lava dome formation and removal have been identified. Each dome has showed particular features related to the magma extrusion process. Among other manifestations, dome-emplacement events have been usually accompanied by relatively low-intensity, protracted explosions referred to as exhalations. After variable times of residence, emplacements have ended in partial or total destruction of the domes by strong vulcanian explosions that produced sizeable ash plumes, with most of them also ejecting incandescent debris onto the volcano flanks. Here, we present a detailed account for the observed activity related to the domes’ growth and destruction, related seismic monitoring signals, and morphological features of the domes based on 19 years of visual observations and image analysis. We then discuss a model for the process of dome growth and destruction and its hazard implications.

Vibrations of soil and foundation due to railway, blast and impact loading

The vibrations of soil and foundations are demonstrated for different types of loading. Train-induced ground vibrations are studied in a measurement cam­paign where a test train has run with regularly varied speeds. The measured train-induced soil vibration at 2 to 100 m distance from the track is compared with the wave propagation due to hammer excitation and with the theoretical wave field. The strong influence of the soil and the train speed on the amplitudes and frequencies of the vibration has been analysed for passages of the locomotive and the carriages. - The generation of ground vibration by strong explosions has been studied on a large testing area with sandy soil. The propagating waves were measured in a regular grid of measuring points in 10 to 1000 m. Therefore, the dominance of certain waves at certain distances and the changes of compressio­nal waves and Rayleigh waves could clearly be observed. The results are compa­red with impulse hammer measurements in the range of 5 to 50 m. - A drop test facility has been built on the testing area of the Federal Institute of Materials Research and Testing (BAM). Heavy masses (containers) of up to 200 t can be dropped from 10 m height on a big reinforced concrete foundation. The founda­tion was instrumented by accelerometers, strain gauges and pressure cells to give information about the loading condition and by geophones to measure the vibra­tion of the surrounding soil and building. Both excitation processes, the release of the mass and the impact, produce high vibration amplitudes. On a smaller drop foundation, the influence of the drop height and the target stiffness has been studied more systematically.

SYSTEMATIC STUDIES OF SHOCK REVIVAL AND THE SUBSEQUENT EVOLUTIONS IN CORE-COLLAPSE SUPERNOVAE WITH PARAMETRIC PROGENITOR MODELS

ABSTRACT We conducted one-dimensional and two-dimensional hydrodynamic simulations of post-shock revival evolutions in core-collapse supernovae, employing the simple neutrino light bulb approximation to produce explosions rather easily. In order to estimate the explosion energy, we took into proper account nuclear recombinations and fusions consistently with the equation of state for matter not in statistical equilibrium in general. The methodology is similar to our previous work, but is somehow improved. In this paper, we studied the influence of the progenitor structure on the dynamics systematically. In order to expedite our understanding of the systematics, we constructed six parametric progenitor models, which are different in masses of Fe iron core and Si+S layer, instead of employing realistic models provided by stellar evolution calculations, which are sometimes of stochastic nature as a function of stellar mass on the main sequence. We found that the explosion energy is tightly correlated with the mass accretion rate at shock revival irrespective of dimension and the progenitors with light iron cores but with rather high entropies, which have yet to be produced by realistic stellar evolution calculations, may reproduce the canonical values of explosion energy and nickel mass. The mass of the Si+S layer is also important in the mass accretion history after bounce, on the other hand; the higher mass accretion rates and resultant heavier cores tend to hamper strong explosions.

Arrested diatreme development: Standing Rocks East, Hopi Buttes, Navajo Nation, USA

Maar–diatreme volcanoes, defined by their relatively large pyroclastic debris-filled subsurface structures and craters that cut into the pre-eruptive land surface, are typically found in small-volume mafic to ultramafic monogenetic volcanic fields. Diatremes are associated with strong explosions throughout most of their development, focused along feeder dikes and generally attributed to magma–water interaction, or high magmatic volatiles. Detailed mapping of the magnificently exposed Standing Rocks East (SRE) diatreme shows evidence of additional eruptive complexity, and offers new insights into how the plumbing and vent structures of small-volume volcanoes evolve during an eruption.SRE is part of a larger, basanitic volcanic complex that includes several diatremes formed along a series of irregular, offset NW–SE trending dikes exposed 300m below the pre-eruptive land surface. Its similarly oriented elliptical-shaped diatreme structure comprises predominantly country rock lithic-rich breccia of coarse inhomogeneously mixed wall-rock blocks sourced from above and below the current surface, plus sparse juvenile material. Domains of pyroclastic deposits crosscut the country rock breccia deposits, and the best exposed is the NW massif rising 35m above the current erosional surface. It represents a cross-section of an evolving crater floor, and comprises matrix-rich lapilli tuff and spatter deposits cut by irregularly distributed dikes, some with very complex textures. The most significant deposit, in terms of volume, is an unbedded lapilli tuff that is poorly sorted and has a well-mixed population of wall-rock and juvenile clast varieties, thus resembling deposits typical of diatremes. It is overlain by and locally intercalated with spatter deposits, and this irregular contact demarcates the base of what was during eruption an uneven, evolving crater floor. The generally massive, variably welded spatter deposits constitute mostly lapilli-sized juvenile clasts with fluidal, folded-over shapes and ropy surfaces, subordinate thermally altered wall-rock and variegated domains of lapilli tuff.SRE shows a progressive transition from fissure to diatreme, and overall evolution from more explosive to weakly explosive eruption styles recorded at the conduit-crater transition. Diatreme development was initiated by deep-quarrying explosive eruptions along a fissure to form the country rock-rich breccia. Only parts of the fissure remained active as magma feeding the highly explosive eruptions along the fissure localized into discrete point sources forming the matrix-rich lapilli tuff deposits. These superimposed deposits record the passage of multiple debris-jets and subvertical fallback from shallow cratering arising from explosions triggered by magma–water interaction at numerous, discrete sites. However, instead of continuing to build a well-formed diatreme, the system switched to weak spattering with intermittent explosive activity and near-surface dike emplacement into the unconsolidated anisotropic, pyroclastic debris of the crater floor. Dominant spatter from strombolian-style bursts accumulated on the topographically varied, evolving unstable syn-eruptive crater floor, and led to local failure and remobilization. This study demonstrates how the combination of fissure behavior and sensitivity of the shallow plumbing system to local conditions during an eruption can lead to a decrease in eruptive footprint within the diatreme structure, and an overall decrease in explosivity resulting in the arrested development of an immature diatreme.

Simplified method for estimating the effect of a hydrogen explosion on a nearby pipeline

To predict the effect of hydrogen gas tank explosions on nearby pipelines, we first evaluate the increase in air pressure and velocity on a pipeline after a strong explosion. Then, we calculate the bending of an initially straight pipe. We investigate the bending amplitude for various exploded masses of hydrogen, distances measured from the explosion center to the pipeline, and thicknesses of steel pipeline walls. The proposed analytic approach provides a conservative estimate of the worst-case accident scenario involving an instantaneous explosion of a large hydrogen mass leading to the formation of a shock wave. The results may be useful for plant engineers to evaluate the risks associated with pipelines under the presumed explosion scenario of not only hydrogen, but also any other fuel types.

Simulation of steam explosion in stratified melt-coolant configuration

A steam explosion is an energetic fuel coolant interaction process, which may occur during a severe reactor accident when the molten core comes into contact with the coolant water. In nuclear reactor safety analyses steam explosions are primarily considered in melt jet-coolant pool configurations where sufficiently deep coolant pool conditions provide complete jet breakup and efficient premixture formation. Stratified melt-coolant configurations, i.e. a molten melt layer below a coolant layer, were up to now believed as being unable to generate strong explosive interactions. Based on the hypothesis that there are no interfacial instabilities in a stratified configuration it was assumed that the amount of melt in the premixture is insufficient to produce strong explosions. However, the recently performed experiments in the PULiMS and SES (KTH, Sweden) facilities with oxidic corium simulants revealed that strong steam explosions may develop spontaneously also in stratified melt-coolant configurations, where with high temperature melts and subcooled water conditions a considerable melt-coolant premixed layer is formed.In the article, the performed study of steam explosions in a stratified melt-coolant configuration in PULiMS like conditions is presented. The goal of this analytical work is to supplement the experimental activities within the PULiMS research program by addressing the key questions, especially regarding the explosivity of the formed premixed layer and the mechanisms responsible for the melt-water mixing. To better understand these phenomena a comprehensive parametric analysis was performed with the MC3D code, varying the premixed layer melt fraction, void fraction, and thickness, the melt spreading area, the melt droplet size, the water height, the water subcooling and the trigger strength. The results are discussed and compared to available experimental data. It seems that both identified melt-water mixing processes contribute to the steam explosion, i.e. the premixture formation before the explosion and the melt-water layer mixing during the explosion propagation itself. Suggestions for further analytical and experimental work are also given.

Dispersion of particles by a strong explosion.

The dynamics of particle transport under the influence of localized high energy anomalies (explosions) is a complicated phenomenon dependent on many physical parameters of both the particle and the medium it resides in. Here we present a conceptual model that establishes simple scaling laws for particle dispersion in relation to the energy released in a blast, properties of the medium, physical properties of particles, and their initial position away from a blast epicenter. These dependencies are validated against numerical simulations and we discuss predictions of the model which can be validated experimentally. Other applications and extensions to the framework are also considered.

Gamma-Ray Bursts as Sources of Strong Magnetic Fields

Gamma-Ray Bursts (GRBs) are the strongest explosions in the Universe, which due to their extreme character likely involve some of the strongest magnetic fields in nature. This review discusses the possible roles of magnetic fields in GRBs, from their central engines, through the launching, acceleration and collimation of their ultra-relativistic jets, to the dissipation and particle acceleration that power their $\gamma$-ray emission, and the powerful blast wave they drive into the surrounding medium that generates their long-lived afterglow emission. An emphasis is put on particular areas in which there have been interesting developments in recent years.

Interaction Between Arc Spot Plasma and Steel Surface in Descaling

Cathode spots of low-pressure arc discharge have been used for cleaning oxides on the steel surface. A phenomenon of two-step plasma scanning on the oxidized steel surfaces is observed, where arc spots first move on the entire surface of the sample with strong evaporation and explosion of oxides. Afterward, there is a brief scanning, and a remaining thin oxide layer is removed while a clean surface of the bulk metal appears. It is believed that the two-step plasma scanning is due to the layered structure of oxides, which results in the self-adjusting of cathode spots on the oxidized surface. The corresponding spot plasmas are investigated by a high-speed camera and an oscilloscope. The voltage waveform and plasma spot images exhibit various characteristics during the two-step scanning process. Compared with the case of Ar arc discharge cleaning, the surface hardness of the sample cleaned with N2 arc spot plasma is obviously enhanced, which should be attributed to the formation of Fe4N during descaling.

Seismotectonic study of the Fergana Region (Southern Kyrgyzstan): distribution and kinematics of local seismicity

We present new seismicity and focal-mechanism data for the Fergana basin and surrounding mountain belts in western Kyrgyzstan from a temporary local seismic network. A total of 210 crustal earthquakes with hypocentral depths shallower than 25 km were observed during a 12-month period in 2009/2010. The hypocenter distribution indicates a complex net of seismically active structures. The seismicity derived in this study is mainly concentrated at the edges of the Fergana basin, whereas the observed rate of seismicity within the basin is low. The seismicity at the dominant tectonic feature of the region, the Talas-Fergana fault, is likewise low, so the fault seems to be inactive or locked. To estimate the uncertainties of earthquake locations derived in this study, a strong explosion with known origin time and location is used as a ground truth calibration event which suggests a horizontal and vertical accuracy of about 1 km for our relocations. We derived 35 focal mechanisms using first motion polarities and retrieved a set of nine moment tensor solutions for earthquakes with moment magnitude (Mw) ranging from 3.3 to 4.9 by waveform inversion. The solutions reveal both thrust and strike-slip mechanisms compatible with a NW-SE direction of compression for the Fergana region. Two previously unknown tectonic structures in the Fergana region could be identified, both featuring strike-slip kinematics. The combined analysis of the results derived in this study allowed a detailed insight into the currently active tectonic structures and their kinematics where little information had previously been available.

Giant and Tunable Mechanical Impulse of Energetic Nanocrystalline Porous Silicon

In this paper, a nanocrystalline porous silicon-based propulsion system is designed, and its explosion impulse is tuned by varying the propulsion design parameters and etching duration. The porous silicon is ignited by an electrical current passed through 100-nm-thick aluminum film deposited on the unpolished side of the wafer and the ignited porous silicon caused strong explosion, which destroys the chip into tiny fragments. The explosion impulse in the system can reach about at optimal conditions, which is two orders stronger than the impulse produced by conventional propellants (ZakarE., “Technology Challenges in Solid Energetic Materials for Micro Propulsion Applications” U.S. Army Research Lab. Rept. ARL-TR-5035, Nov. 2009). It is also shown that, by varying the etching time, which is an important factor that determines the porous layer thickness and the volume of nanocrystallite, the strength of the impulse can be tuned. Furthermore, a linear increasing trend of the explosion impulse with etching time is observed, which can be explained as the results of heat trapping, materials confinement, and the increasing number of reaction centers.