Blast Propagation Research Articles

Flow field distribution and overpressure characteristics inside the crew compartment of a truck-mounted howitzer under the effect of muzzle blast

The muzzle blast overpressure induces disturbances in the flow field inside the crew compartment (FFICC) of a truck-mounted howitzer during the artillery firing. This overpressure is the primary factor preventing personnel from firing artillery within the cab. To investigate the overpressure characteristics of the FFICC, a foreign trade equipment model was used as the research object, and a numerical model was established to analyze the propagation of muzzle blast from the muzzle to the interior of the crew compartment under extreme firing condition. For comparative verification, the muzzle blast experiment included overpressure data from both the flow field outside the crew compartment (FFOCC) and the FFICC, as well as the acceleration data of the crew compartment structure (Str-CC). The research findings demonstrate that the overpressure–time curves of the FFICC exhibit multi-peak characteristics, while the pressure wave shows no significant discontinuity. The enclosed nature of the cab hinders the dissipation of pressure wave energy within the FFICC, leading to sustained high-amplitude overpressure. The frame-skin structure helps attenuate the impact of muzzle blast on the FFICC. Conversely, local high overpressure caused by the convex or concave features of the cab's exterior significantly amplifies the overpressure amplitude within the FFICC.

Development of a fast-running method for prediction of blast propagation in partially confined spaces

In this contribution, a series of findings from Computational Fluid Dynamics (CFD) simulations of blast propagation within fully confined spaces are presented. These numerical works have been carried out as part of an ongoing in-house development towards a fast-running method to predict overpressures and impulses arising from detonations within the various configurations of carparks in Singapore. In land-scarce cities like Singapore, carparks are typically located within the same structural footprints and are integrated with other functions of the building to facilitate convenient access. Design of carparks are required to meet statutory provisions with regards to the layout, headroom clearance and safety. To this end, the present research study has adopted a three-stage approach. First, different representative configurations of carparks are determined by making reference to and rationalising based on the prevailing statutory provisions in Singapore. This is then followed by a series of parametric CFD simulations to obtain essential numerical data in order to characterise the blast propagation within the respective partially confined spaces. Finally, several regression models are employed to derive relationships between the critical parameters and the blast data, with the aim of achieving a fast-running predictive method. This paper seeks to provide detailed descriptions of the first and the second stages, as well as to present the comparisons of numerically converged solutions, which are obtained from preliminary CFD simulations using two mesh sizes, against semi-analytical solutions which are calculated based on guidance from UFC 3-340-02 for fully confined detonation as initial reference cases.

Blast injury risks to humans within a military trench

In land warfare, trenches serve as vital defensive fortifications, offering protection to soldiers while engaging in combat. However, despite their protective function, soldiers often sustain injuries within these trenches. The lack of corresponding blast data alongside empirical injury reports presents a significant knowledge gap, particularly concerning the blast pressures propagating within trench spaces following nearby explosions. This absence hinders the correlation between blast parameters, trench geometry, and reported injury cases, limiting our understanding of blast-related risks within trenches.This paper addresses the critical aspect of blast propagation within trench systems, essential for evaluating potential blast injury risks to individuals within these structures. Through advanced computational fluid dynamics (CFD) simulations, the study comprehensively investigates blast injury risks resulting from explosions near military trenches. Employing a sophisticated computational model, the research analyzes the dynamic blast effects within trenches, considering both geometrical parameters and blast characteristics influenced by explosive weight and scaled distance.The numerical simulations yield valuable insights into the impact of these parameters on blast injury risks, particularly focusing on eardrum rupture, lung injury, and traumatic brain injury levels within the trench. The findings elucidate distinct patterns of high-risk zones, highlighting unique characteristics of internal explosions due to confinement and venting dynamics along the trench. This study underscores the significance of detailed numerical modeling in assessing blast injury risks and provides a novel knowledge base for understanding risks associated with explosives detonating near military trenches. The insights gained contribute to enhancing safety measures in both military and civilian contexts exposed to blast events near trench structures.

Evolution of acoustic nonlinearity in outdoor blast propagation from firearms: On the persistence of nonlinear behavior

Acoustic events exceeding a certain threshold of intensity cannot benefit from a linearization of the governing wave equation, posing an additional burden on the numerical modelling. Weak shock theory associates nonlinearity with the generation of high frequency harmonics that compensate for atmospheric attenuation. Overlooking the persistence of this phenomenon at large distances can lead to mispredictions in gun detection procedures, noise abatement protocols, and auditory risk assessment. The state-of-the-art mostly addresses aircraft jet noise, a stationary and largely random type of signal. The extension of such conclusions to muzzle blasts requires caution in considering their peculiar impulsive and broadband nature. A methodology based on the time and frequency analysis of an experimental dataset of eight calibres intends to find quantitative metrics linked to acoustic nonlinearity in outdoor muzzle blast propagation. Propagating three waveforms (SCAR-L 7.62 mm, Browning 9 mm, and Howitzer 105 mm) up to 300 [m] with the in-house numerical solver based on the nonlinear progressive wave equation, demonstrates that the propagation does not downgrade to truly linear.

Head injuries evaluation during a pipeline explosion

In recent years, Mexico has suffereda series of explosive accidents linked to oil drilling and fuel pipeline operations. These explosions are often triggered by the rapid vapor expansion due to abrupt pressure changes, known as Boiling Liquid Expanding Vapor Explosions (BLEVEs). Tragically, in 2019, a devastating explosion occurred in Tlahuelilpan, claiming the lives of at least 100 people and injuring many others. This research aims to investigate brain injuries resulting from such explosions. Despite the potential for severe injuries, there is a significant lack of comprehensive injury data, with most research focusing on military contexts. In this study, we employed the Baker method in three configurations, utilizing a finite element model, Hybrid III 50Th Percentile Male Standing, in LS-Dyna®. Head Injury Criteria (HIC) is a measure for acceleration behavior in head. Our findings indicate that this value for acceleration, and BLAST propagation radio decrease with greater analysis distance. Brain injuries include edemas, contusions, lacerations, and skull compression, predominantly affecting individuals within a 6-meter radius of the detonation point.

Numerical study of blast wave propagation through granular materials subjected to buried blasts

Blast wave propagation in dry sand subjected to a buried charge is numerically investigated using a charge-sand stratified configuration wherein the mass ratio between sand and charge (M/C) spans over two decades. The detonation of the central charge and the sand dynamics are modeled by the FEM-DEM method. The findings reveal the pressure-profile associated with the blast wave undergoes marked shape transition as the expansion fans catch up with the incident blast wave. The blast propagation and the associated pressure-profiles depend on the coupling between the sand and the detonation products in the central gas pocket which is in turn influenced by a variety of structural parameters. Specifically, as the M/C increases from 21 to 436, the average velocity of the blast wave decreases by 22.2%. Furthermore, a blast compaction model of sand is proposed to account for the coupling effect and justify the influences arising from key-structural parameters.

Simulation of blast propagation and structural effects of accidental hydrogen-air-mixture explosion in a two-stage light-gas gun laboratory for hypervelocity impact experiments

Two-stage light-gas guns allow to accelerate projectiles up to velocities of several kilometers per second to conduct impact experiments. The projectile acceleration is obtained through a mechanism that relies on the expansion of a light gas, such as helium or hydrogen. Hydrogen allows to employ higher projectile velocities and masses than helium, together with lower wear of the launch tube. However, its use requires a thorough assessment of potential risks of explosion. In this work, we present a combined blast and structural numerical analysis to evaluate the effects of hydrogen deflagration as a consequence of accidental leakage scenarios during the operation of a two-stage light-gas gun. As a test case, we study the Large Gun operated at Fraunhofer EMI in Freiburg, Germany. The possible failure of non-structural elements, such as doors and windows, and the subsequent blast propagation into areas adjacent to the room hosting the facility are also accounted for. The simulation procedure presented in this work is scalable to similar and larger facilities for impact research as well as to other contexts involving analogous risks of gas explosions.

A two-scale approach to widen a predictive blast propagation model around a hemicylindrical obstacle

The aim of the present paper was to report on an experimental study of the characterization of a blast wave initiated by a solid explosive and its interaction with a rigid obstacle in the form of a hemicylinder. Pressure transducers located along the path of the blast wave and high-speed imaging allow (1) the measurement of the overpressure at different locations and (2) the characterization of the blast wave inception, propagation, and reflection off the hemicylinder. The scaling effect has been investigated by performing experiments in two different facilities, where one is at twice the scale of the other.

A Lagrangian DG-Method for Wave Propagation in a Cracked Solid with Frictional Contact Interfaces

We developed a discontinuous Galerkin (DG) numerical scheme for wave propagation in elastic solids with frictional contact interfaces. This type of numerical scheme is useful in investigations of wave propagation in elastic solids with micro-cracks (cracked solid) that involve modeling the damage in brittle materials or architected meta-materials. Only processes with mild loading that do not trigger crack fracture extension or the nucleation of new fractures are considered. The main focus lies on the contact conditions at crack surfaces, including provisions for crack opening and closure and stick-and-slip with Coulomb friction. The proposed numerical algorithm uses the leapfrog scheme for the time discretization and an augmented Lagrangian algorithm to solve the associated non-linear problems. For efficient parallelization, a Galerkin discontinuous method was chosen for the space discretization. The frictional interfaces (micro-cracks), where the numerical flux is obtained by solving non-linear and non-smooth variational problems, concerns only a limited number the degrees of freedom, implying a small additional computational cost compared to classical bulk DG schemes. The numerical method was tested through two model problems with analytical solutions. The proposed Lagrangian approach of the nonlinear interfaces had excellent results (stability and high accuracy) and only required a reasonable additional amount of computational effort. To illustrate the method, we conclude with some numerical simulations on the blast propagation in a cracked material and in a meta-material designed for shock dissipation.

Towards a model to predict blast propagation around a hemicylindrical barrier

Towards a model to predict blast propagation around a hemicylindrical barrier

Blast and Fragmentation Studies of a Scaled Down Artillery Shell-Simulation and Experimental Approaches

Blast and fragmentation of a scaled down model of standard artillery shell is investigated experimentally and numerically. Simple experimental techniques are employed in this study to measure the fragments’ velocity, mass and spatial distribution. Fragments of mass ranging from tens of milligram(s) to 6.4 grams are produced with velocities ranging from 960 to 1555 m/s. The cylindrical part of the shell has larger contribution among high velocity fragments ~1369-1555m/s than the conical and rear parts due to higher charge to mass (C/M) ratio. Overpressure of 44.2psi (304.7kPa) is measured at stand-off distance of 0.550m. The numerical simulation of fragmentation is carried out using Smoothed Particle Hydrodynamics (SPH) solver available in ANSYS AUTODYN. A coupled Euler-ALE (Arbitrary Lagrangian-Eulerian) approach is used to simulate the shell blast propagation in the surrounding air. A good agreement is achieved between the simulation and experimental results. The investigation can help in the development of protective configurations against the damaging effects of blast and fragmentation.

Blast wave modification by detonator placement

The blast wave generated by a high explosive detonation is dependent not only on the shape of the charge but on the location of the detonator or detonators. Even for a spherical charge, the blast wave can be very asymmetric if the initiation is not at the center of the charge. The asymmetry is even greater for cylindrical charges. High-resolution, high-fidelity calculations of the blast wave generated by several spherical and cylindrical charges have been used to quantify these differences for free-field blast propagation. Except for the center-detonated spherical charge, the blast wave never becomes spherical. Several examples are shown to demonstrate and quantify the asymmetries and to illustrate that the blast wave, once asymmetric, can never regain spherical symmetry. At distances of over 40 charge radii, the asymmetries are clearly defined. As the overpressure at the shock front decays below half a bar, the propagation velocity approaches ambient sound speed. At half a bar (50 kPa), the Mach number of the shock is 1.19 and at a tenth of a bar (10 kPa) the shock velocity is only Mach 1.04. If the shock front is asymmetric at low overpressures, all parts of the shock front are moving at very nearly the same velocity and can therefore never “catch up” to other parts of the front: once asymmetric, always asymmetric. Results of several calculations have been analyzed to determine the quantitative differences in shock properties resulting from detonator placement and charge shape. Properties are significantly different behind the shock fronts, especially in the density distribution.

International stock market co-movements following US financial globalization

In this paper, I propose a novel hypothesis to examine whether financial globalization was the economic cause of cross-market co-movement and crisis propagation before and after the global financial crisis; this has been an unsolved puzzle until today. The hypothesis suggests that it is the global outreach of the crisis-originating country, rather than the global outreach of the crisis-infected countries, that caused cross-country co-movement and crisis spread of 2008 crisis. Using data on 59 countries from 2003 to 2013, I present evidence consistent with the blast propagation hypothesis and find that foreign direct investment and foreign portfolio investment were two important channels for cross-market co-movement and global propagation of the crisis before and after crisis. These findings can help governments create international coordination programs to limit crisis propagation in the future.

SIMULATION MODEL OF THE INFORMATION TECHNOLOGY FOR THE TECHNICAL DIAGNOSIS OF THE IMPULSE HEAT MACHINE

A simulation model of the information technology for the technical diagnosis of the impulse heat machine has been developed and studied. The model incorporates such mathematical models as barrel energy; ballistic wave parameters; pressure of powder gases blasting from the barrel face behind the shell and the shot blast and determination of its attenuation rate. The information model enables to obtain parameters of the ballistic wave that accompanies an shot. A simplified mathematical model allows of determining the oblique shock inclination angle to the stream speed depending on Mach number which is represented by the two-dimensional flow wedge. The model of powder gas pressure blasting from the barrel face behind the shell is based on the energy conservation law for the compresses powder gases and makes it possible to avoid solution of the complicated modified Lagrange problem. While the shot blast propagates, at the initial stage it is possible that this blast reaches the record point earlier than the ballistic wave. Such phenomenon can be avoided by selecting a proper angle. The adopted mathematical model determines the shot blast propagation law and allows of evaluating the shot blast speed attenuation. The barrel energy model was based on the solution of the inverse problem of pyrostatics by determining a composition of the combustion gas of the shot. The applied approach provided for use of the model that describes combustion of the fuel and oxidizer mixture. The peculiarity is a necessity to know composition of all components of the arbitrary mixture. The limitation is a necessity that all components are gaseous. The considered case needs to develop a combustion model of a single-component solid substance (nitrocellulose powder) that provides for a possibility to vary the composition of its active part because of its degradation with time.

Characterization of debris throw from masonry wall sections subjected to blast

The failure of structural components, e.g. masonry walls, due to accidental or intentional explosions exhibits a considerable risk to the health of persons, operational safety, and surrounding structures. The debris throw originating from overloaded structural elements poses a significant threat to structures and persons in the surrounding environment in distances, which may exceed the hazard-range of the blast wave itself. Insights into the break-up process during structural failure and the resultant debris throw characteristics expressed in terms of fragment mass distributions, initial velocities and launch angles, are thus essential to assess the significant potential explosion hazard. However, to date the data basis for hazard assessment and model development on debris throw of masonry structures is limited. In this article, we present the results from shock-tube experiments of single-span masonry walls subjected to dynamic blast loads characteristic for far-field explosions and free-field blast propagation. Reflected peak overpressures in the tests ranged from 100 to 150 kPa with corresponding maximum impulses of approximately 2000 kPa ms to 3000 kPa ms. A new methodology based on high-speed stereo video imaging allows to analyze the break up process and the resulting debris sizes, launch velocities and three-dimensional launch angles before the debris hit the ground. The data derived can be used for empirical predictions of debris launch characteristics as well as for the validation of numerical simulations aimed at the proper assessment of hazardous secondary blast effects from masonry failure.

Numerical modeling of wave propagation in a cracked solid

In this study, we investigate the dynamics of (damaged) materials with a nonlinear microstructure (microcracks in frictional contact) using a discontinuous Galerkin method. Although the propagation of a plane wave is associated with a complex phenomenon and the stress field loses its homogeneity, the loading pulse has an overall front wave at each moment. Thus, a macroscopic behavior can be extracted and compared with reference solutions based on analytical formulas deduced from the effective (static) elasticity models of a cracked solid. The influences of the mesh and of the microcrack pattern have been tested to choose an optimal numerical setting. We analyzed the sensitivity of the damaged pulse with respect to microcrack density, wavelength, and microcrack orientation. For small values of crack density parameter, the theoretical formula and the computed speed of the damaged pulse are very close, but for larger values there is an important gap between them. For large ratios of wavelength over crack length, the wave speed depends only on the crack density parameter. However, if this ratio is of the order of unity, the wave speed, pulse duration, and pulse amplitude are very sensitive to the wavelength. For more complex phenomena, namely blast propagation in a cracked material, we discuss how the microcrack orientation affects wave propagation and scattering.

Blast wave propagation in survival shelters: experimental analysis and numerical modelling

The propagation of blast and shock waves in confined environments is a complex phenomenon; yet, being able to derive valid predictions of such phenomena is highly relevant, for example, when it comes to the assessment of protection of personnel in military environments. This study looks at the propagation of blast waves inside a compound survival shelter. Experimental analyses are performed on a small-scale model of the actual configuration of the shelter subjected to the detonation of an explosive charge at different locations close to its entrance. Pressure-time signals are recorded on a number of locations in the model. A numerical model is also developed to complement the experimental programme, based on the explicit finite element (FE) code LS-DYNA. The recorded experimental data (e.g., pressure and impulse) are compared with the numerical predictions to validate the FE model. The authors discuss two different modelling approaches (the Lagrangian and the MM-ALE formulations) and analyse the influence of using a different number of ambient layers, the advection method, the time-step size, and level of discretisation. The proposed numerical model predicts and captures the relevant stages of the propagation of the shock wave very well, with error levels on the resulting specific impulse always lower than 19% when compared to the experimental observations.

Experimental investigation of blast wave propagation in an urban environment

Experimental studies of blast propagation in urban environments are described in the literature, but only a few studies at laboratory scale were found while this scale option represents an economical and safe approach. Experimental investigations on blast wave propagation in a complex environment using gram-range explosive charges are proposed in this paper.Five experimental configurations, built with wood boxes on a 2.8 m wood table, are tested in a 1:200 reduced scale using three types of condensed phase explosives. Several characteristics of the explosives are given: the geometry of the explosion, the repeatability, and the TNT equivalent.An overview of impacts of a complex environment on the blast wave characteristics is proposed. The urban configurations investigated are the straight street, the T-junction, the cross junction, and the channeling. Investigations on reduced-scale effects on blast measurement and characteristics are detailed.

Acoustic shooter localisation using a network of asynchronous acoustic nodes

The present study focuses on the acoustical detection and localisation of shots using a network of wireless asynchronous acoustic nodes. The first sections describe the detection and classification schemes of the developed real-time acoustic nodes and the asynchronous shooter localisation principle. This localisation method is evaluated in free field and in complex propagation conditions, where obstacles affect the propagation of the muzzle blast and shock waves. More than 600 shots with calibre 5.56 to 12.7 mm weapons at distances varying from 100 to 800 m constitute the database used for the evaluation of the localisation performance. It shows that the localisation of shooters in complex environments is possible when the group of acoustic nodes is near to the shot trajectory.

Interaction of Blast Load on AASHTO Girder Bridge

Guidelines of blast resistant design for AASHTO girder bridges have not taken up much importance on researches. As the transportation infrastructure mainly bridges are highly vulnerable for bomb attack, they must be designed to resist it. The analysis and design of bridges subjected to blast load requires a detailed understanding of blast propagation and its dynamic effects on various structural elements. The response of bridge components subjected to blast load is carried out using Abaqus explicit finite element software. The bridge is modeled on the basis of AASHTO-LRFD bridge design specification for highway bridges. Blast load has been introduced on different critical location of the bridge to understand their effects on various structural elements and extent of damage. A thorough parametric study varying standoff distance and TNT mass is done to understand their importance in developing a blast resistant design for AASHTO Girder Bridge. The study concludes that the value of maximum displacement decreases with the increase in standoff distance.