Interaction Of Blast Wave Research Articles

Two-dimensional numerical visualization on the interaction of blast waves with obstacles

In this study, the complex phenomena of propagation and interaction of the blast waves impacting on obstacles were visualized and investigated using a numerical method. Three different distances between an immovable wall and a bomb shelter with a square block inside were considered while a blast source is located in front of wall at the same distance from shelter. The transitional shock phenomena were simulated by means of a multi-block mesh system and a flux computational model. Spatial discretization was performed using the Roe's upwind schemes; time integration was achieved via the second-order explicit Hancock method. Proof of the numerical results indicated that those results were in close agreement with the experimental data obtained for the wedge flow. For the cases proved, the geometries of the reflected wave patterns followed by the incident blast waves crossing the immovable wall and impacting inside of bomb shelters were similar. However the height of wall has a dominating impact on the effect associated with different incident blast waves from the same blast source. Meanwhile, different reflected overpressure-time histories and streamlines were observed and analyzed for the results obtained.

Numerical simulation of blast wave interaction with structure columns

Accurate estimation of blast loads on structures is essential for reliable predictions of structural response and damage. Current practice in blast effect analysis and design estimates blast loads primarily based on empirical formulae obtained from field blast tests. Due to the limited availability of test data, those empirical formulae are usually applicable to the case that the reflection surface of the structure is big enough so that no wave diffraction around the structure exists. They will overestimate the blast loads on structure columns without infill walls around them, which are very common in the modern buildings, especially for the ground floor columns. For a standalone column, the initial reflected pressure may be quickly relieved at the edge of the column, and the column will be engulfed with the blast wave due to diffraction. Therefore, the interaction between the blast wave and structure is important for such columns. The blast loads on such columns will be different from those obtained in field blasting tests on walls. There is no method in the open literature to estimate blast loads on standalone columns. In the present study, interactions between blast waves and structure columns are simulated using AUTODYN 3D. The influence of the scaled distance of the blast, column stiffness, ratio of the supported mass to the column mass, and column dimension and geometry, on the blast wave–column interaction is investigated. Based on the numerical simulation results, some formulae are proposed to estimate the blast pressure, impulse, and the reflected pressure time history on standalone structure columns.

Impact of a shock wave on a structure on explosion at altitude

The number of explosive attacks on civilian buildings has recently increased and the pattern of damage inflicted on structures when an explosion takes place at altitude remains quite difficult to predict. The primary aim of the work reported here was to enhance the understanding of how blast waves from an explosion at altitude interact with the ground and with a structure. Small-scale experiments were conducted using a propane–oxygen stoichiometric mixture as explosive. This approach is original because it models high-explosive detonation in terms of gaseous charge explosion using TNT equivalents. Several non-dimensional laws are expressed and validated by experiments. These relationships allow determination of the propagation of a blast wave and its interaction with a structure as a function of the position of the explosive charge when the explosion occurs at altitude. Then, from knowledge of the blast loading, using Hopkinson's scaling law and TNT equivalents, we can predict the interaction of blast waves with the ground and a structure on a real scale. Simulations were performed using the Autodyn code, and good correlation with the experimental results was obtained.

A numerical study in the interaction of blast wave with a wheeled armoured vehicle

This study investigates the behaviour of blast waves by employing the finite volume method to solve the associated Euler equations for three-dimensional, time-dependent, inviscid flows. The total variation diminishing (TVD) upwind method is applied. The simulation results of a wheeled armoured vehicle identify the complex phenomena of flow structures, pressure distributions and oscillation of reflected shock waves under the chassis. It is concluded from the results that the intensity of the derived reflected waves could be greater than that of the blast wave. Inappropriate for the flow of thought, the geometry decides the phenomena of flow-field, especially the oscillation of reflected shock waves under the chassis.

The interaction of oblique blast waves with buildings

Assessment of the net load imparted to a building that is oriented at some angle to an incident blast wave is complicated by the difficulty of establishing the impulse delivered to each part of the building’s surfaces. Expansion waves originating from the edges and top of the building—where regions of different pressures meet—tend to reduce the (oblique) reflected impulses that would develop on an infinitely large surface. This process is referred to as oblique clearing. An investigation which considered a single, tall building aligned obliquely to an effectively uniform blast wave has been undertaken with the aim of demonstrating and describing the path of these expansion waves as the blast wave passes over the building. The investigation comprised a series of small-scale experiments supported by numerical simulations using the code ftt_air3d. The loads arising at two scaled stand-off distances were considered. It is shown that depending on the angle of the building to the blast and the length of the blast wave with respect to the size of the building, the effect of the expansion waves may vary considerably, hence altering the load experienced by the building.

SN 1987A after 18 Years: Mid‐Infrared Gemini andSpitzerObservations of the Remnant

Using the Gemini South 8 m telescope, we obtained high-resolution 11.7 and 18.3 μm mid-IR images of SN 1987A on day 6526 since the explosion. All the emission arises from the equatorial ring. Nearly contemporaneous spectra obtained at 5-38 μm with the Spitzer Space Telescope show that this is thermal emission from silicate dust that condensed out in the red giant wind of the progenitor star. The dust temperature is 166 K, and the emitting dust mass is 2.6 × 10-6 M☉. Comparison of the Gemini 11.7 μm image with Chandra X-ray images, HST UV-optical images, and ATCA radio synchrotron images shows generally good correlation across all wavelengths. If the dust resides in the diffuse X-ray-emitting gas then it is collisionally heated. The IR emission can then be used to derive the plasma temperature and density, which were found to be in good agreement with those inferred from the X-rays. Alternatively, the dust could reside in the dense UV-optical knots and be heated by the radiative shocks that are propagating through the knots. In either case the dust-to-gas mass ratio in the CSM around the supernova is significantly lower than that in the general interstellar medium of the LMC, suggesting either a low condensation efficiency in the wind of the progenitor star or the efficient destruction of the dust by the SN blast wave. Overall, we are witnessing the interaction of the SN blast wave with its surrounding medium, creating an environment that is rapidly evolving at all wavelengths.

Simulated X‐Ray Emission for a Runaway Model of Kepler's Supernova Remnant

We present two-dimensional numerical simulations of a model for Kepler's supernova remnant (SNR) carried out with the YGUAZU-A code. Following previous studies, we have assumed that the peculiar shape of this young remnant arises as a consequence of the interaction of the SNR blast wave with the bow shock formed by the wind of its high velocity progenitor. Furthermore, from our numerical results we have obtained synthetic X-ray emission maps, which can be directly compared with recent and previous observations of this SNR. Our models show that a nice fit with respect to the X-ray morphology and luminosity is obtained for a SN progenitor with mass-loss rate of 5 x 10(-5) M-circle dot yr(-1), an ambient medium density of 10(-2) cm(-3), an initial explosion energy of 8 x 10(50) ergs, and a total ejected mass within 1.4-2.5 M-circle dot. In our simulations, parameters typical of a young population progenitor have not been considered. This model also predicts a similar to 0.3% yearly decrease in the total X-ray luminosity, which is consistent with observed values. The parameters employed in our runs correspond to a Type Ia supernova. Based on our simulations, we find that the expansion rate increases after the SNR blast wave overruns the bow shock, and we discuss whether this can explain the observed difference between the expansion rates measured from sequences of radio and X-ray images. (Less)

A study of combined particle and blast wave loading of structures

In structural dynamics there are many instances where an appreciation of the combined effect of particulate and air blast loading are essential if an accurate prediction of structural response is to be attained. Examples include: the loading of structures via the detonation of cased munitions; the interaction of blast waves and secondary fragmentation with internal building components after an external contact explosion and the loading of vehicle bellies via the detonation of mines buried in soil. As an analytical simplification, engineers often incorporate the effect of particulate loading by applying a load factor to calculations of the blast component alone. In some cases the fragmentation, can indeed be considered as merely incidental but in others, analysis and experiments have indicated that the presence of inert matter within or in close proximity to a detonated explosive can alter the magnitude, spatial distribution and duration of loading applied to a structure. This paper describes a series of numerical simulations, conducted using the AUTODYN hydrocode, in which the effect of detonating an explosive within a matrix of particles, and the subsequent blast and particulate interaction with a target, was simulated. The total momentum transferred to a target and the spatial momentum distribution is evaluated for both mines buried under soil and confined air blasts. The momentum transferred is investigated as a function of the technique used to model particulation and detonation proximity. These comparisons offer an insight into the mechanisms by which buried blast mines load structures and lead to explanations of differences observed in thin plates deforming under simulated mine blast attacks.

Blast wave propagation in city streets—an overview

AbstractThis paper presents an overview of research conducted by the authors and others both experimentally and analytically in the area of blast wave interactions with buildings and structures in an urban landscape. Empirical tools for the assessment of blast wave resultants for simple‐geometry situations are first presented before the confining effects of buildings along a street are discussed. Street layouts such a T‐junctions and crossroads are then introduced and the way that blast wave characteristics are affected by street width and the height of buildings along the street is assessed. The influence of the location of the explosive charge within the street layout on the blast load experienced by buildings is also reviewed. It is likely that building façades closest to the explosion will fail and the effect on the loading experienced further from the detonation is therefore assessed. A complementary study of the loads developed inside a building whose façade has failed is also discussed. Apart from the blast loads on buildings in a street in which there is an explosion, buildings in adjacent streets will also experience blast loading. Studies concerned with the phenomena of ‘channelling’ and ‘shielding’ are presented and the extent to which both processes occur in any given situation discussed. The various studies reported throughout the paper indicate that simple tools are often inappropriate and the development of empirical rules for more complex geometries may not be reliable. This view is supported by studying blast wave propagation in a realistic cityscape comprising streets of different widths with several layout features all bounded by buildings of different size, shape and height. Such studies conclude that computational fluid dynamics analyses may sometimes be the only satisfactory approach for the engineer seeking a reliable assessment of blast loads experienced by buildings in an urban landscape.

Laboratory-scale blast wave phenomena – optical diagnostics and applications

Laboratory-scale experiments with explosive charges in the milligram range are a useful tool to investigate basic blast wave phenomena and to replicate, to some extent, large-scale explosions. This paper reviews and discusses the optical diagnostics that can be applied in these experiments and outlines how these techniques can be used to obtain new information about the propagation and interaction of blast waves. Performance criteria for the required instrumentation are established. Several examples illustrate the potential and the limitations of this approach to blast wave research.

A fuzzy set analysis to estimate loss intensity following blast wave interaction with process equipment

Blast waves are able to produce structural damage to process equipment even at great distances from the source point of an explosion. A loss of containment may follow and, if hazardous substances are released, relevant secondary scenarios may be triggered, resulting in domino effects. The present study was focused on the assessment of the expected structural damage and of the associated intensity of loss of containment of process vessels loaded by blast waves. Hence, a knowledge-based fuzzy set analysis was used to assess the expected overall probability of occurrence of different damage states defined for several categories of process equipment items. The fuzzy approach was also used to obtain specific threshold values for the escalation sequences (domino effects), taking into account the hazard due to the expected secondary scenarios caused by the loss of containment following blast wave impact.

A Three-Dimensional Numerical Investigation into the Interaction of Blast Waves with Bomb Shelters

This study investigates the behavior of blast wave by employing the finite volume method to solve the associated three-dimensional, time-dependent, inviscous flow Euler equations. The numerical results are shown to be in good agreement with the experimental results obtained from shock tube flow studies. The results also identify the complex phenomena of flow structures, pressure distributions, and different types of reflected waves for closed-ended and open-ended bomb shelters.

The supernova remnant G 6.4-0.1 and its environment

Flux calibrated CCD images, in the Hα + (N ), (S ), and (O ) emission lines, of a wide field around the supernova remnant G 6.4-0.1 are presented. The low ionization images identify a front of enhanced (S )/Hα + (N ) ratio along the east- west direction. This front is very well correlated with the filamentary radio emission of the remnant as well as with molecular CO emission and may indicate the interaction of the primary blast wave with molecular clouds present in the vicinity of the remnant. We estimate a total Hα flux, corrected for interstellar extinction, of 2 × 10 −8 erg s −1 cm −2 , and a total (S ) flux of 1.1 × 10 −8 erg s −1 cm −2 .T he Hα + (N  )a nd (S) images provide evidence for the presence of emission from shock heated gas to the south-west and to the east of the bulk of the known optical emission, implying that the primary shock wave is able to drive radiative shocks into the interstellar clouds. The image in the medium ionization line of (O )5007 A does not reveal any filamentary structures. On the contrary, the emission is diffuse and very weak, close to our detection limit of 5 × 10 −17 erg s −1 cm −2 arcsec −2 (3σ), and appears to be mainly present in the south-east to north-west areas of the remnant. The long-slit spectra indicate significant extinction in all positions observed, while the measured variations are within the 3σ error. The (O ) emission in the spectra, whenever present, is weaker than the Hβ flux suggesting shock velocities around 70 km s −1 or less all around the remnant in accordance with the (O ) imagery. Thus, the low shock velocities are a common characteristic of G 6.4-0.1 and not just of the areas where the spectra were acquired. The average sulfur line ratio suggests postshock electron densities below 120 cm −3 at the 3σ limit.

Threshold values for domino effects caused by blast wave interaction with process equipment

Abstract The present study focuses on the definition and assessment of overpressure threshold values for the damage to equipment caused by blast waves originated by primary accidental scenarios. A revision of literature data and of the available damage probability models was carried out. Threshold values were proposed for different categories of process equipment, taking into account either damage levels or release intensities following the loss of containment. Specific threshold values for domino effect were also proposed.

Optical supernova remnant observations from Skinakas Observatory

High energy studies of supernova remnants provide direct insight into major properties of these objects. Morphological and spectral studies of remnants in X-rays allow us to estimate parameters like the age of the remnant, the explosion energy and the ambient interstellar density. Optical studies of supernova remnants focus on the interaction of the primary blast wave with dense “clouds” found in the interstellar medium. Optical observations of individual remnants performed at Skinakas Observatory in Crete, Greece consist of flux calibrated wide field CCD images taken with the 0.3 m telescope and absolute flux calibrated long-slit spectra obtained with the 1.3 m telescope. The site conditions and the unique capabilities of a small telescope equipped with a CCD camera allowed us to perform high quality deep observations leading to the discovery of optical emission from several remnants for the first time. We present results on the known supernova remnants G73.9+0.9, G82.2+5.3 as well as current results on previously unknown filamentary structures. Typical densities of the interstellar “clouds” are of the order of a few atoms per cm 3, and the shock velocities are found in the range of 90–140 km s −1. The optical spectra further suggest the presence of moderate magnetic fields.

An Isolated, Recently Shocked ISM Cloud in the Cygnus Loop Supernova Remnant

Spatially resolved ROSAT X-ray and ground-based optical data for the southwestern region of the Cygnus Loop supernova remnant (SNR) reveal in unprecedented detail the very early stages of a blast-wave interaction with an isolated interstellar cloud. Numerous internal cloud shock fronts near the upstream flow and along the cloud edges are visible optically as sharp filaments of enhanced Hα emission. Faint X-ray emission is seen along a line of Balmer-dominated shock filaments north and south of the cloud with an estimated X-ray gas temperature of 1.2 × 106 K (0.11 keV), corresponding to a shock velocity of 290 km s-1. The main cloud body itself exhibits little or no X-ray flux. Instead, X-ray emission is confined along the northern and southernmost cloud edges, with the emission brightest in the downstream regions farthest from the shock front's current position. We estimate an interaction age of ∼1200 yr, based on the observed shock-cloud morphology. Overall, the optical and X-ray properties of this shocked interstellar medium (ISM) cloud show many of the principal features predicted for a young SNR shock–ISM cloud interaction. In particular, one sees shocklet formation and diffraction inside the inhomogenous cloud, along with partial main blast-wave engulfment. However, several significant differences from model predictions are also present, including no evidence for turbulence along cloud edges, diffuse rather than filamentary [O III] emission within the main body of the cloud, unusually strong downstream [S II] emission in the postshock cloud regions, and confinement of X-ray emission to the cloud's outer boundaries.

Winds from massive stars: implications for the afterglows of -ray bursts

Recent observations suggest that long-duration γ-ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in core-collapse explosions. The pre-explosive ambient medium provides a natural test for the most likely progenitors of GRBs. Those stars that shed their envelopes most readily have short jet crossing times and are more likely to produce a GRB. We construct a simple computational scheme to explore the expected contribution of the presupernova ejecta of single Wolf–Rayet (WR) stars to the circumstellar environment. Using detailed stellar tracks for the evolution of massive stars, we discuss the effects that the initial main-sequence mass, metallicity, rotation and membership in a binary system have on the ambient medium. We extend the theory of GRB afterglows in winds to consider the effect of the relativistic fireball propagating through the WR ejecta. Specific predictions are made for the interaction of the relativistic blast wave with the density bumps that arise when the progenitor star rapidly loses a large fraction of its initial mass or when the ejected wind interacts with the external medium and decelerates. A re-brightening of the afterglow with a spectrum redder than the typical synchrotron spectrum (as seen in GRB 970508, GRB 980326 and GRB 000911) is predicted. We also calculate the luminosity of the reflected echo that arises when circumstellar material Compton-scatters the prompt radiation, and examine the spectral signatures expected from the interaction of the GRB afterglow with the ejected medium.

Numerical Study of Cylindrical Blast-Wave Propagation and Reflection

The problem of an unsteady cylindrical blast-wave interaction with a e at plate is numerically investigated. The numerical simulation aims at the understanding of blast-wave propagation, ree ection, and its transition phenomenonaswellasthee owfeaturesinducedbytheblastwave.Ae fth-orderweightedessentiallynonoscillatory scheme for spatial discretization associated with a fourth-order Runge ‐Kutta method for time integration is employed for solving the two-dimensional Euler/Navier ‐Stokes equations in a e nite volume fashion. To verify the accuracy of the numerical solver developed, several problems were tested. The computed results for the test problems are shown to be accurate in comparison with experimental data. To study the e owe eld of a blast wave, theproblemofblast-wavepropagation in a freee eld isexplorede rst.Twotypesofinitial conditionsareconsidered. A contact-surface instability that developed around a contact surface was found in the problem with the e rst kind of initial condition. Next, the problem of the blast-wave interaction with the e at plate is investigated. The e ow structure of a shock-shock interaction induced by the unsteady blast wave and its evolution are studied in detail. It was found that the lower the height of burst or the higher the shock Mach number, the earlier the occurrence of the transition from a regular ree ection to a Mach ree ection and the higher the triple points.

A Windy Gamma-Ray Burst

ASTROPHYSICS The origin of gamma-ray bursts (GRB)—energetic, short-duration flashes of bright gamma rays—is unknown. Recent observations of iron-intensified x-ray emissions in the afterglow of GRB991216 about one and one-half days after the main burst (see [Piro][1] et al. , Reports, 3 November 2000) have underscored the need for explanatory models. An existing two-stage model posits a supernova explosion followed several days later by the burst of gamma rays; this allows the stellar remnant to expand before the burst-induced blast wave interacts with the envelope and results in the iron-intensified emissions. Rees and Meszaros offer an alternative scenario, beginning with a stellar collapse of either a rapidly spinning neutron star (collapsar model) or the highly magnetized torus of a black hole (magnetar model) into the GRB progenitor. The burst would occur soon afterwards, producing the bright flash followed by the decay of the x-ray continuum in the afterglow from the GRB blast wave. The iron-intensified x-ray emissions would develop later, due to the interaction of the GRB blast wave with the magnetohydrodynamic wind emanating from the recently collapsed and possibly not quite stable neutron star or black hole. — LR Astrophys. J. 545 , L73 (2000). [1]: /lookup/doi/10.1126/science.290.5493.955

A Model of the Vela Supernova Remnant

A model of the Vela supernova remnant (SNR) based on a cavity explosion of a supernova (SN) star is proposed. It is suggested that the general structure of the remnant is determined by the interaction of the SN blast wave with a massive shell created by the SN progenitor (15-20 M⊙) star. A possible origin of the nebula of hard X-ray emission detected around the Velapulsar is discussed.