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Blast deafness and balance disorders are common consequences of modern warfare and terrorist actions. A predictive evaluation system can assist commanders in quickly gathering information on the incapacitation of combat personnel. However, a critical challenge to this goal was to clarify the dose–response relationship between the blast parameters and the severity of auditory and vestibular dysfunction. This paper describes the algorithms for a prediction model. We performed blast experiments to obtain data on animal auditory/vestibular dysfunction under different overpressures. Peak overpressure and positive phase duration of the blast wave were obtained by pressure measurements. The severity of auditory and vestibular dysfunction was established by the auditory brainstem response test, behavioral rating, and vestibular-evoked myogenic potentials tests. Test data were analyzed using receiver operating characteristic (ROC) curves and logistic regression analysis to obtain the overpressure limits for auditory/vestibular function and logistic regression curves for severity separately. The ROC curve analysis showed that the overpressure limit for the auditory function was 32.635 kPa and the vestibular function was 96.275 kPa. Logistic regression fitted curves illustrated the dose–response relationship between the coefficient K, normalized by peak overpressure and positive phase duration, and the risk probability of auditory and vestibular disfunction. The prediction model for the risk of auditory and vestibular disfunction severity (mild/moderate/severe) has been established based on the overpressure limit and dose–response relationship. [ABSTRACT FROM AUTHOR]

The ongoing study of blast waves and blast wave mitigation continues to play an essential role in protecting structures and personnel. The methodology, however, for capturing far-field blast waves in large-scale tests has remained largely unchanged for three decades, relying on large arrays of pressure transducers connected by hundreds of meters of cabling and requiring a considerable amount of time to set up. This paper evaluates the use of a modern low-cost microprocessor with high computational power to capture blast waves with sufficient fidelity to provide scientists and engineers with credible data. The system utilizes an ARM Cortex M7 processor as an experimental data acquisition (DAQ) system for measuring far-field blast waves in an open-air blast arena at sampling speeds of up to 1.8 Msps (megasamples per second). The experimental system's performance was evaluated by comparing it to a traditional commercial system used for measuring blast waves. The comparison showed an average Spearman correlation coefficient r of 0.928 between the two systems, suggesting a low variance between the commercial and experimental DAQ systems. This suggests that, despite its simplicity, the experimental system is an effective and low-cost alternative for accurately measuring blast waves. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The paper presents unique blast experiments in reference to scientific literature and official standards. Experimental scenarios reflect a hypothetical realistic combat situation of a human being covered from a blast wave behind a rigid building corner. In the scenario assumed, the overpressure loads affect the lungs while the person is standing or the eardrums while the person is kneeling at the aiming position. The paper presents 27 free-field experiments measuring the overpressure loads. All the measurements were taken behind the right angle of the rigid wall. Two masses of TNT were considered: 200 g and 400 g. In the selected cases, a low test-to-test variability of the measured data was observed. Detailed plots of overpressure versus time are presented for various distances behind the building corner and TNT charge masses. Peak overpressure versus positive impulse plots are also demonstrated. Furthermore, the safety thresholds regarding different locations behind the building corner are defined for the considered explosive masses. [ABSTRACT FROM AUTHOR]

It is well established that detonation in a confined environment can lead to the formation of a Mach stem along the walls or after diffraction on an obstacle. As the formation of this kind of reflection can produce higher levels of overpressure, it is important to study and understand its formation and propagation for safety purposes in the event of an accidental or intentional detonation. This paper reports an experimental approach to the propagation of a Mach stem formed by the diffraction of a shock wave around an obstacle and compares the height of the triple point with an empirical model from Kinney and Graham. In predictive models, the Mach stem is formed by a charge detonating above the ground, which is why its evolution is different from a Mach stem formed after diffraction. The shock waves were generated by the detonation of a stoichiometric hemispherical charge of propane-oxygen. The visualization was coupled with 30 pressure sensors to record pressure history data in order to determine the influence of the Mach stem on wall overpressure inside a small-scale model, representing two rooms in a building separated by an open door. [ABSTRACT FROM AUTHOR]

The aim of this study is to characterize the interaction of a shock wave with an obstacle. The effect of the length of the obstacle on the shock wave propagation and maximum overpressure is investigated. Several previous studies investigated the use of obstacles such as porous materials, grids, pseudo-perforated walls, triangular wedges, or multi-obstacles as a way to mitigate blast intensity. Here, the focus is on the interaction of an incident shock wave on a single-plate obstacle. This obstacle can be seen as a wall or a low-rise building. The paper presents a small-scale experimental study. The blast wave is created by the detonation of a hemispherical gaseous charge. It is characterized by pressure sensors and a high-speed camera. The pressure sensors record the overpressure and arrival time. The propagation, reflection, and diffraction of the shock wave are analyzed from the pictures produced during the visualization tests. [ABSTRACT FROM AUTHOR]

The sandwich cladding is a blast mitigation technique well described in the literature. One of the key parameters for its efficiency is a good knowledge on the crushable core placed inside the cladding. This paper focuses on galvanised polyurethane foams, a new family of hybrid materials which can fill the role of a crushable core. The galvanisation process allows to add a metal layer on top of a polyurethane foam, modifying its behaviour under tension and compression. This material was subjected to quasi-static tests and then placed inside a sandwich cladding allowing its dynamic characterisation under blast load. Using the methodology recommended by previous work, the energy absorption capacity of this new material has been determined based on the measured experimental stress–strain curves. The parameters of these curves, such as the plateau stress, densification strain, and energy absorption by unit volume, are directly linked to several parameters of the galvanisation process, including the Cu/Ni composite coating as well as the coating thickness. The results of this study present galvanised polyurethane foams as a serious alternative for crushable cores, which can be tailor-made to protect different targets by changing the parameters of the galvanisation process. [ABSTRACT FROM AUTHOR]

This paper explores the ability of the Kurganov, Noelle, and Petrova numerical scheme included in the rhoCentralFoam solver of the OpenFOAM™software to model strong explosion processes, using typical gas dynamics concepts. The main objective of this study was to obtain a numerical tool to simulate strong explosions. Once the generated blast waves and their propagation were simulated, the numerical results were compared with those of Sedov's analytical solutions. Both numerical and analytical results were obtained from applications to geometrically cylindrical and spherical explosions. All comparisons were focused on the shock position as time elapsed and on the evolution of flow properties after the shock wave. [ABSTRACT FROM AUTHOR]

In this paper, a series of experiments were performed to study the energy output characteristics of CL-20-based aluminized explosives in an explosion vessel. The influences of different aluminum mass contents on the shock wave pressure and the explosion power were systematically investigated. The results showed that the peak overpressure and the positive impulse of the initial shock wave decreased with the aluminum content increased from 10 to 30%. On the contrary, the quasi-static pressure increased. The deformation and damage degree of sealing steel plates of the explosion vessel decreased as the aluminum content increased. The analysis indicated that the maximum residual deflection of the steel plates mainly represented the energy of the initial shock wave. The explosion power of the CL-20-based aluminized explosives decreased with the increase in aluminum content, and this trend was more remarkable at a large charge mass. The contrast test with LiF showed that the energy released from the combustion of aluminum can improve the positive impulse of the initial shock wave and play a role in the deformation of steel plates. [ABSTRACT FROM AUTHOR]

In this paper, blast mitigation using water mist was evaluated to assess the operational capability of the use of firefighting systems implemented in ships or infrastructures to reduce blast effects. In particular, we tried to determine the mitigation that could be obtained in specific situations. A tunnel equipped with a water mist system enabled us to assess the mitigation impact of water mist on a blast. Blast effects were evaluated using four pressure gauges on the tunnel walls and one pressure gauge at the end of the tunnel. As a first step, we evaluated the mitigation efficiency based on water mist characteristics (the droplet size and the water load) when the charge was detonated inside the mist, the tunnel being either open or closed. Then, we assessed the mitigation efficiency when the charge was detonated outside the mist with only the blast wave propagated in the mist. The reduction in the initial overpressure and the maximum impulse were higher when the charge exploded inside the water mist, and this is most likely due to the quenching of secondary reactions by the water mist. To obtain a better understanding of mitigation mechanisms, shock tube experiments were conducted. The break-up of water drops in the high-speed airstream behind the shock wave was observed, but the presence of mist had no significant effect on the shock wave profile. This is in line with the importance of fireball extinguishment in the mitigation process. [ABSTRACT FROM AUTHOR]

In this paper, computations of gaseous detonations in several configurations are performed and discussed. The objective is to investigate the detonation characteristics, specially the influence of losses, through a quantitative analysis of the mean hydrodynamic structure. The results are divided into two parts: The first one relates to the propagation of ideal detonations without losses and to their characterization for a specific set of thermodynamic parameters, and the second part investigates the influence of losses on the averaged hydrodynamic structure of detonations. This is achieved by means of a specific and canonical configuration, in which a detonation wave propagates in a reactive layer bounded by an inert gas. This topology is investigated through a comparison of the instantaneous flow-field, cellular structure, and averaged quantities such as the mean curvature and the hydrodynamic thickness. This configuration may be regarded as non-ideal, as the detonation experiences losses due to the expansion of the detonation products toward the inert layer. The prediction of the detonation characteristics, as well as the conditions at which quenching occurs, remains a challenge when losses are involved. The main objective is to assess to what extent the hydrodynamic thickness can be used as a relevant length scale in the analysis of the resulting database. The results also highlight the key features of this configuration, which isolates a specific issue related to the rotating detonation engines. The temperature of the inert layer strongly affects the structure of the detonation–shock combined wave. For a high-temperature inert gas confinement, a detached shock appears in the upper layer and a jet of fresh mixture develops downstream of the front. For this condition, we observed a reduction in the critical dimensions by a factor of two. The degree of regularity of the detonation structure, from weakly unstable to mildly unstable cases, through the variation of the reduced activation energy, was investigated. The hydrodynamic thickness appears to be a useful characteristic length scale for the detonation, as it allows a better analysis of the results and a scaling of data. Moreover, the detonation velocity deficit can be globally expressed as a function of the ratio of the hydrodynamic thickness to the mean radius of curvature at the bottom of the wall. [ABSTRACT FROM AUTHOR]

High-speed imaging and digital signal processing are used to measure temperatures and pressures produced by explosions of solid chemical energetic materials. These measurements are used to enhance understanding of hazards faced by personnel working or training near explosions. The techniques described provide a complement to point measurements. Peak incident pressures studied are between 21 and 138 kPa, a region important for injury studies of personnel exposed to airborne shock. [ABSTRACT FROM AUTHOR]

The paper by J.M. Dewey (Shock Waves 29(4):583–587, 2019) described the development of an Excel-based interface that provides the physical properties of blast waves generated by propane/oxygen explosions. The interface was developed using the data from a nominal 20 ton explosion of an assumed stoichiometric propane/oxygen mixture. Comparisons of data from the interface with measurements of small-scale stoichiometric propane/oxygen explosions show discrepancies. Further studies revealed that the 20 ton explosion was not stoichiometric and had a 43% oxygen deficiency. The interface has been redeveloped assuming that only 57% of the available propane had been detonated. The revised interface produces results which agree with measurements from both the 20 ton explosion and the small-scale (< 1 g) detonations. The revised interface and updated users' guide are available for downloading. [ABSTRACT FROM AUTHOR]

The Beirut port explosion on August 4, 2020, caused extensive destruction and significant casualties, prompting inquiries into its scale and impact on neighboring structures. Speculation arose regarding the role of the nearby port silos in shielding western Beirut from the blast. This study leverages insights from previous research and uses a tailored blast wave propagation model to settle the debate on the silos' effectiveness in mitigating blast impacts. The analysis challenges prevailing notions: firstly, that the silos offered substantial protection, and secondly, the assumption linking the transient "window" phenomenon in the Wilson cloud to a similar opening in the preceding pressure front. Contrary to expectation, the pressure at the shock front remains continuous, albeit lower on the leeward side behind the silos. Downstream lateral regions experience pressure amplification due to the constructive interference of waves diffracted around the silos, with significant attenuation observed close (10 m) behind them—approximately 12%, 58%, and 2% of free-air values for overpressure, specific impulse, and specific energy, respectively. However, this shielding effect diminishes with distance, with the blast wave intensity largely restored at 450 m. Consequently, the silos' shadowing effect was limited to nearby port structures and part of the Lebanese navy base, which still incurred severe damage. The lesser impact on western Beirut is attributed to its greater distance from the explosion rather than the silos' protective influence. These findings suggest a reevaluation of urban disaster mitigation strategies, emphasizing geographical positioning over structural barriers and advocating for a holistic approach to urban resilience. [ABSTRACT FROM AUTHOR]

Far-field blast loading has been studied extensively for decades. Close-in, confined, and semi-confined detonations less so, partly because it is difficult to obtain good experimental data. The increase in computational power in recent years has made it possible to conduct studies of this kind numerically, but the results of such simulations ultimately depend on experimental validation and verification. This work thus aims at using reliable experiments to validate and verify numerical models developed to represent blast loading in general. Test rigs consisting of massive steel cylinders with pressure sensors were used to measure the pressure profiles of semi-confined detonations with different charge sizes. The experimental data set was then used to assess numerical models appropriate for simulating blast loading. In general, the numerical results were in excellent agreement with the experimental data, in both qualitative and quantitative terms. These results may in turn be used to analyse structures exposed to internal blast loads, which constitutes the next phase of this research project. [ABSTRACT FROM AUTHOR]

Interaction of multiple blast waves can be used to direct energy toward a target while simultaneously reducing collateral damage away from the target area. In this paper, simulations of multiple point source explosives were performed and the resulting shock interaction and coalescence behavior were explored. Three to ten munitions were placed concentrically around the target, and conditions at the target area were monitored and compared to those obtained using a single munition. For each simulation, the energy summed over all munitions was kept constant, while the radial distances between target and munitions and the munition initiation times were varied. Each munition was modeled as a point source explosion. The resulting blast wave propagation and shock front coalescence were solved using the inviscid Euler equations of gas dynamics on overlapping grids employing a finite difference scheme. Results show that multiple munitions can be beneficial for creating extreme conditions at the intended target area; over 20 times higher peak pressure is obtained for ten simultaneous munitions compared to a single munition. Moreover, peak pressure at a point away from the target area is reduced by more than a factor of three. [ABSTRACT FROM AUTHOR]

The failure mechanism of a concrete slab-soil double-layer structure subjected to an underground explosion was investigated by experimental and numerical methods in this paper. Two underground explosion depths of 150 and 350 mm were tested. The typical failure modes such as the conoid spall of concrete, the bulge of the concrete slab and the cavity in the soil were obtained experimentally. Numerical simulations of the experiments were performed using a hydrodynamic code to analyze the effects of both the stress wave and the expansion of the blast products. Based on the experimental and numerical results, the effects of explosive depth, blast wave front and expansion of the blast products on the failure modes and failure mechanisms were discussed. The underground explosion process at different explosion depths was also analyzed. The results show that attenuation of the stress wave in the soil is significant. The blast wave front and the expansion of the blast products play different roles at different explosion depths. At the explosion depth of 150 mm, the failure mode is mainly caused by a point load induced by the blast wave front, whereas at the depth of 350 mm a sphere-shaped load resulting from the expansion of the blast products is a key factor for failure. [ABSTRACT FROM AUTHOR]

We present results of an experimental study of blast wave propagation and particle dispersion induced by a free-field detonation of spherical charges made of a 125 g C-4 explosive surrounded by inert or reactive particles. Visualization of the flow was performed with a high-frame-rate video camera. Background oriented Schlieren (BOS) methods were adapted to process the images that allowed the detection of the shock waves. BOS analysis also revealed that particles form agglomerates, which may generate precursor perturbations on the recorded pressure signals. While inert glass particles notably delay the shock, the combustion of aluminium particles can accelerate it, especially if they are small atomized or flaked particles. When a mixture of inert glass particles with reactive particles is dispersed, the agglomerates are formed by coalescence of both materials. [ABSTRACT FROM AUTHOR]

Comparisons of explosives are often carried out using TNT equivalency which is based on data for spherical charges, despite the fact that many explosive charges are not spherical in shape, but cylindrical. Previous work has shown that it is possible to predict the over pressure and impulse from the curved surface of cylindrical charges using simple empirical formulae for the case when the length-to-diameter ( L/ D) ratio is greater or equal to 2/1. In this paper, by examining data for all length-to-diameter ratios, it is shown that it is possible to predict the peak over pressure, P, for any length-to-diameter ratio from the curved side of a bare cylindrical charge of explosive using the equation $$P=K_PM(L/D)^{1/3}/R^3$$, where M is the mass of explosive, R the distance from the charge and $$ K_P$$ is an explosive-dependent constant. Further out where the cylindrical blast wave 'heals' into a spherical one, the more complex equation $$P=C_1(Z^{\prime \prime })^{-3}+C_2(Z^{\prime \prime })^{-2}+C_3(Z^{\prime \prime })^{-1}$$ gives a better fit to experimental data, where $$ Z^{\prime \prime } = M^{1/3}(L/D)^{1/9}/D$$ and $$C_1,\, C_2 $$ and $$ C_3$$ are explosive-dependent constants. The impulse is found to be independent of the L/ D ratio. [ABSTRACT FROM AUTHOR]

A two-dimensional numerical simulation is carried out to determine the optimum location of the concentrated laser energy deposition region for maximum wave drag reduction of a blunt body. A 25.4-mm-diameter semicircle, Mach 3.45, and 50 mJ pulse energy are chosen as the representative blunt body, free-stream Mach number, and magnitude of the deposited laser energy, respectively. The location of the energy deposition region is varied discretely from 21 to 50 mm upstream of the center of the semicircle along its axis of symmetry. The lower limit of the distance is just upstream of the blunt body bow shock along the axis of symmetry. It is found that for the assumed conditions, the maximum wave drag reduction happens at the lower limit of the distances. A time-resolved analysis of the interaction between the laser-induced blast wave and the bow shock is carried out to arrive at the conclusions. It is observed that the blast wave reflects as an expansion wave from the bow shock for the 21 mm case, whereas the reflected wave is a shock wave for all other cases. The time history of the static pressure at the blunt body nose and wave drag per unit depth on the blunt body are also provided for the above locations of the energy deposition region to justify the inferences. [ABSTRACT FROM AUTHOR]

Abstract. This paper presents the results obtained by a generalized cut cells strategy on 3-D blast waves problems. The mesh is cartesian except when it is intersected by the surface of the solids inserted in the computational domain. The improvement, relatively to a classical cut-cells method, is the treatment of the cut which preserves the real geometry of the surface instead of approximating it by a plane. This approach avoids a loss of precision of the numerical scheme at the boundaries and allows future extension to higher order schemes ( $>2$ ). Moreover it is useful for any kind of geometry with a high efficiency in computation time. The drawback is the complexity of the geometrical problems which can rise because of the diversity of situations in the treatment of the cuts. The performance of the approach is tested on a few examples allowing comparisons with experiments or other techniques and physical discussions. [ABSTRACT FROM AUTHOR]

A study of shock and detonation waves propagating in gaseous two-fuel CH 4 / H 2 /air mixtures and heterogeneous three-fuel CH 4 / H 2 /air/coal mixtures with the mean bulk density of the coal dust suspension equal to 95 - 560 g/m 3 and with a particle size of 0 - 200 μ m is performed. The experiments are conducted in a vertical shock tube with a length of 6.75 m and a diameter of 70 mm. The detonation parameters measured in the experiments are compared with the calculated equilibrium thermodynamic values. It is found that the detonation wave parameters are mainly affected by methane and hydrogen rather than by the coal dust suspension. Decaying shock waves are as dangerous as detonation waves because blast wave reflections can initiate detonation. An increase in the hydrogen fraction in the mixture decreases the energy of initiation of CH 4 / H 2 /air and CH 4 / H 2 /air/coal mixtures, resulting in a greater hazard for the generation of shock and detonation waves in these mixtures. [ABSTRACT FROM AUTHOR]

This paper discusses gas-dynamic aspects of intense explosions in uniform environments. In experiments, the energy of a laser is almost instantaneously released in a volume of air shaped as either a flattened or stretched cylinder generating a blast wave. Its shape evolves in time and ultimately becomes spherical. But momentum transferred to the air when the blast wave is strongly nonspherical is anisotropic. As a result, a subsonic jet and a vortex are induced and propagate along the symmetry axis or along the perpendicular plane, depending on the initial configuration of the blast wave. Simulations based on a free-Lagrangian method for a nonviscous gas are in good agreement with the experiments. Velocities, circulation, and positions of fluid particles found in computations give an insight into the causes and details of the flow. Two simultaneous and contrary processes take place – vorticity production by the anisotropic shock wave and baroclinical generation of vorticity at the boundary of the heated gas – which give rise to net circulation. [ABSTRACT FROM AUTHOR]

This paper reports the results of experiments and computations on the interaction of a pair of cylindrical blast waves in air. The waves were generated by exploding wires, and both symmetrical and unsymmetrical interactions were observed. The experimental data includes schlieren photographs of the wave interactions, their radii, shock Mach number and pressure versus time, as well as various cross plots and data on the shock regular/irregular interaction transition condition. The flow fields were computed with the help of the 'Total Variation Diminishing' (TVD) method, and appear to represent the experimental results reasonably well. Some attention is also given to the blast scaling laws of the type discussed by Sakurai (1965) and Oshima (1960). [ABSTRACT FROM AUTHOR]

The dispersion of particles by blast or shock waves induces the formation of coherent structures taking the shape of particle jets. In the present study, a blast wave, issued from an open shock tube, is generated at the center of a granular ring initially confined in a Hele-Shaw cell. With the present experimental setup, solid particle jet formation is clearly observed in a quasi-two-dimensional configuration. In all instances, the jets are initially generated inside the particle ring and thereafter expelled outward. Furthermore, thanks to the two-dimensional experimental configuration, a general study of the main parameters involved in these types of flows can be performed. Among them, the particle diameter, the density of the particles, the initial size of the ring, the shape of the overpressure generated and the surface friction of the Hele-Shaw cell are investigated. Empirical relationships are deduced from experimental results. [ABSTRACT FROM AUTHOR]

The blast loading from a detonation of a high explosive charge at high altitude is quite different from that at sea level. Due to diminished ambient pressure, the damage caused by the blast load may be more minor at high altitude. However, the shock wave parameters at diminished ambient pressure have not yet been thoroughly studied. In this research, experiments were carried out to study the relation between ambient air pressure and shock wave parameters. The explosion experiments were carried out in a sealed explosion chamber with an initial pressure of 95 kPa, 74 kPa, and 57 kPa. For these three atmospheric conditions, the history profiles of incident shock wave pressure generated by TNT charges of 106 g and 292 g were recorded. The influence of ambient pressure and temperature on the shock wave parameters was analyzed through numerical simulations. By analyzing the experimental and numerical data, it was found that ambient pressure is the main factor affecting the shock wave parameters, while the effect of temperature is not so obvious. Furthermore, based on the analysis of experimental data, formulas for evaluating shock wave overpressure, specific impulse, and arrival time using the Sachs variables are given, and the shock wave parameters at an altitude of 5000 m are calculated using these formulas. The observed maximum reduction in the shock wave overpressure was 23%, in specific impulse 27%, and in arrival time 12%, compared to the results calculated at sea level. The results can be applied to blast-resistant analyses of buildings in low-pressure environment. [ABSTRACT FROM AUTHOR]

A launcher's engine and in particular its nozzle are subjected to several loads during the rocket launch. Most of these loads are dynamic, such as the external pressure pulse caused by the blast wave bouncing back from the floor and engulfing the nozzle. Nevertheless, they usually are considered as quasi-static in buckling computations as conservative design methods. Few studies have been investigated on dynamic buckling of thin shells subjected to external pressure pulse. Thus, a large program including experimental tests and numerical simulations have been conducted by the CNES, the French Space Agency. The main objectives are a better understanding of dynamic buckling and establishing a robust design methodology. In this context, two experimental means used for producing dynamic pulses are here considered and investigated, to explore the dynamic buckling of such structures. In one case, the shock wave is produced using a solid explosive, in the shape of a stick in which a nitrate ammonium/sodium nitrate mix is encapsulated. In another setup, the shock wave is produced using a commercial apparatus named DaisyBell. A hydrogen/oxygen mixture is detonated within a conical shock tube, producing a directional free-air-like blast. Both apparatuses are designed to be hanged above snowpack for avalanche preventive release, thus can be held at the desired height using a crane. The pulse intensity measured at the tested sample level can be tuned by moving the explosive up or down. A simplified model of the nozzle, in the form of a cylindrical shell, is proposed for the analysis. This study aims at showing how both apparatuses can be used to simulate free-air-like blasts and can cause the dynamical buckling of a steel cylindrical shell structure. [ABSTRACT FROM AUTHOR]

Results of numerical research into the desensitization of high explosive charges in water gap test-based experimental assemblies are presented. The experimental data are discussed, and the analysis using ANSYS AUTODYN 14.5 is provided. The desensitization phenomenon is well reproduced in numerical simulation using the JWL EOS and the Lee-Tarver kinetic equation for modeling of the initiation of heterogeneous high explosives with as well as without shock front waves. The analysis of the wave processes occurring during the initiation of the acceptor HE charge has been carried out. Peculiarities of the wave processes in the water gap test assemblies, which can influence the results of sensitivity measurement, have been studied. In particular, it has been established that precursor waves in the walls of the gap test assemblies can influence the detonation transmission distance. [ABSTRACT FROM AUTHOR]

Measurements of the time of arrival of shock waves from explosions can serve as powerful markers of the evolution of the shock front for determining crucial parameters driving the blast. Using standard theoretical tools and a simple ansatz for solving the hydrodynamics equations, a general expression for the Mach number of the shock front is derived. Dimensionless coordinates are introduced allowing a straightforward visualization and direct comparison of blast waves produced by a variety of explosions, including chemical, nuclear, and laser-induced plasmas. The results are validated by determining the yield of a wide range of explosions, using data from gram-size charges to thermonuclear tests. [ABSTRACT FROM AUTHOR]

Geometrical blast dynamics is a simplified model for blast wave propagation, based on geometrical shock dynamics (GSD). This new model, first developed in a Lagrangian framework, has proven useful to obtain quite accurate results at a moderate CPU cost, but is currently limited to two-dimensional configurations. In this work, we demonstrate the ability of an Eulerian fast-marching-like algorithm to deal with complex geometrical configurations. The level-set formalism avoids most of the numerical difficulties encountered with Lagrangian methods in 3D. The algorithm is described in detail, mainly for the integration of the recent extension of GSD to low Mach numbers, which includes a transverse term. The behavior of the resulting method is illustrated on various situations and compared to experimental data when available. This Eulerian approach makes accessible 3D simulations of blast waves in a complex environment at a reduced cost. [ABSTRACT FROM AUTHOR]

The measurement of peak overpressure from the near-earth air blast is usually ineffective in the near field of special environments. It is of great significance to explore a method to obtain the distribution of the near-field peak overpressure by measuring the far-field shock data. The relationship between the near-field shock peak overpressure and the far-field shock peak overpressure in near-earth air blast is studied to predict the near-field peak overpressure. AUTODYN-2D is used to establish the numerical simulation near-earth air blast model of TNT with the cylindrical charge of different equivalent mass and length–diameter ratios (LDRs), the various scaled heights of burst (SHOBs), and the wide range scaled distance (SD). The numerical results are validated with the calculation of empirical equations and the real explosion data. The far-field peak overpressure is calculated by the polynomial fitting equation of near-field data. The relationship between the far-field numerical peak overpressure and the above calculation results is studied first. Then, the spatial distribution of near-field peak overpressure is analyzed. At last, the near-field prediction model based on the far-field data is established. The results show that the far-field-to-near-field conversion equations based on the converted far-field peak overpressure predict the near-field data well. The spatial equivalent conversion equations give a clear numerical relationship to the peak overpressure in the near field. The peak overpressure at different spatial locations in the near field is obtained by using the above two sets of equations and at least four sets of far-field peak overpressure data. The predicted peak overpressure is reliable when the LDR is from 0.5 to 7, the SHOB is from 0.496 to 2.977, the SD is from 4 to 15, and the angle is below 45 ∘ . The prediction of other positions is available for reference. Using the prediction model based on the far-field data provides a novel method for obtaining the near-field shock peak overpressure under special working conditions. [ABSTRACT FROM AUTHOR]

We conducted a series of numerical simulations to understand the effect of the initiation process of cylindrical high explosives on the blast-wave behavior and peak overpressure distribution. The first case involved the explosion of a cylindrical high explosive whose length-to-diameter ratio was equal to 2 and that was vertically placed above the ground surface. The initiation point was at the top of the high explosive. The initiation process induced the detonation momentum directed from top to bottom, and the detonation products forcefully hit the ground surface, resulting in a higher peak overpressure on the ground surface in comparison with the case using an isothermal constant-pressure volume. After the blast wave expanded far from the initiation point, the computed peak overpressures of the two approaches showed good agreement with those from experiments. The second case involved the explosion of a cylindrical high explosive whose length-to-diameter ratio was unity and that was placed in air. The initiation point was the one end side of the high explosive. The blast wave was divided into three regions that originated from the detonation in the high explosive, an oblique shock wave in air, and a bridge wave connected with them, thus causing an azimuthal distribution of peak overpressure. The highest peak overpressure values were computed in the bridge wave region. To understand the propagation behavior of the blast wave, we should thoroughly observe how and when all the waves affecting the blast-wave behavior are generated and how they propagate and interact with each other. [ABSTRACT FROM AUTHOR]

Spherical weak blast propagation above a rough periodic surface is investigated by performing numerical simulations of the Euler equations. The study of the reflection pattern shows that waves diffracted by the surface asperities merge to form an effective reflected shock. It is initially detached from the incident shock but gradually catches up with it. If the source energy is sufficient, the reflected shock interacts with the incident one and Mach reflection occurs. Thus, the triple point has a similar trajectory to that over a smooth surface. In addition, the maximal overpressure is shown to be greater for small roughness scales in a layer near the surface. Far from the surface, it is close to that of a smooth surface for small roughness scales and to the free field for the highest ones. The increase in the maximal overpressure is related to oscillations on the waveforms that appear behind the shock. These properties are associated with the existence of a surface wave that propagates along the surface. Comparison of results in the linear regime with an analytic solution confirms this explanation. [ABSTRACT FROM AUTHOR]

The evolution of a particle cloud following its interactions with a blast wave and contact interface resulting from a detonating high-energy explosive is a difficult problem for both numerical simulations and physical experiments. In experiments, it is challenging to accurately characterize both the initial states of the explosive and the surrounding particle bed. There are also limitations in the available diagnostic tools and measurable data which can be extracted from the experiments. Thus, simulations are a cheaper alternative where the physics governing the interactions between the expanding particle cloud and the highly compressible, post-detonation fluid flow can be analyzed. Using multiphase, compressible flow simulations in an Eulerian–Lagrangian frame, the impact of introducing perturbations to a particle bed surrounding an explosive charge is studied. The analysis focuses on the multiphase instabilities and late-time behavior displayed by the particle cloud and discusses the associated underlying physical phenomena. The effects of these instabilities on the behavior of the mixing between the detonation products and the surrounding air are also discussed. The perturbations are varied to reveal the effects of the initial particle distribution and its persistence in the later-time particle cloud and the background fluid flow. [ABSTRACT FROM AUTHOR]

Current methods for testing blast pressures produced by fireworks are ad hoc and differ substantially from established methods for assessing injury risks from explosives. In this experimental study, pressure-versus-time waveforms were measured as a function of distance from the source for four consumer firecrackers and one consumer bottle rocket. Pressure-versus-time data were collected at 10 MHz using a piezoelectric blast pressure sensor at distances 75 mm, 150 mm, 225 mm, and 300 mm from the source. While large variations in peak pressure were observed, in some trials, peak blast pressures over 100 kPa were observed, which suggests a risk of primary blast injury. The results support analysis of pressure waves produced by consumer firecrackers using established methods to quantify blast waves and to evaluate the risk of primary blast injury by comparing peak pressure and positive pulse duration to injury thresholds for specific body systems. Similar methods can be applied to result in comparable measurements for other firework devices. [ABSTRACT FROM AUTHOR]

A new scaling is developed for both air and underwater blast waves based on dimensional analysis. The new length, time, velocity, and pressure scales are based on three control parameters: the energy release of the explosive E HE , the density of the undisturbed ambient medium ρ 0 , and the speed of sound in the undisturbed ambient medium C 0 . The shock wave propagation is divided into two regimes based on its decay characteristics, and the resulting control parameters are different in each regime. For strong shocks with Mach numbers M SW ≳ 5 , the increase in the shock wave radius R with time t is approximated by a power law with an exponent of 2/5 as previously described by G. I. Taylor. Shock propagation in this regime is shown to not be a function of the ambient medium sound speed, but only the ambient medium density, explosive energy release, and time. For weak shock waves with Mach numbers M SW ≲ 5 , the shock wave radius increase with time can be approximated by a linear function plus a logarithmic-type correction which decays to a sound wave at sufficiently long time. Shock propagation in this regime is scaled according to the medium's ambient density, sound speed, explosive energy release, and time. The new scaling is compared to, and agrees well with, published experimental data for air and underwater blasts, from milligram explosions to nuclear blasts. The new scaling improves upon traditional Hopkinson and Sachs scaling by relating shock propagation in liquid and gas environments, allowing them to be scaled to a single functional relationship. The functional scaling relationships developed here are dimensionless. [ABSTRACT FROM AUTHOR]

The blast waves from a series of explosions of stoichiometric, rich, and lean propane/oxygen mixtures have been analysed. The explosive mixtures were contained in hemispherical soap bubbles, 0.05 m in radius, with total masses in the order of 1 g. The blast waves were measured with a series of piezoelectric transducers, flush mounted in the horizontal surface supporting the charges, at various distances from the centres of the explosions. The measured time history of hydrostatic overpressure from each transducer was least-squares-fitted to the modified Friedlander equation to provide the best estimates of the peak hydrostatic overpressure immediately behind the primary shock and the positive phase duration. The times-of-arrival (TOA) of the primary shocks at each gauge location were used to determine the shock Mach numbers as functions of distance, and these values were used in a Rankine–Hugoniot relationship to calculate the peak hydrostatic overpressures, also as functions of distance. For all explosive mixtures, there was excellent agreement between the direct gauge measurements and the values from the TOA analyses. In order to compare the relative strengths of the blast waves from the three mixtures, the measured results were scaled to those for a 1-kg charge using the masses of propane and applying Hopkinson's cube root scaling. This analysis showed that the blast wave from the lean mixture, for which there was an excess of oxygen, was stronger than that from a stoichiometric mixture, indicating a more efficient detonation. The blast wave from the rich mixture, for which there was a deficiency of oxygen, was weaker than that from the stoichiometric mixture, but gradually strengthened relatively, probably due to the afterburning of the undetonated propane in the presence of atmospheric oxygen. The peak overpressures as functions of distance and the overpressure time histories from the three types of explosive were compared with predictions by a Propane Blast interface and in all cases showed excellent agreement. The interface predictions were based on measurements from a nominal 20-ton propane/oxygen explosion, and the agreement with results from charges with masses of less than 1 g indicates the validity of Hopkinson's cube root scaling applied to propane/oxygen explosions over a range of charge masses in excess of six orders of magnitude. [ABSTRACT FROM AUTHOR]

When a high explosive detonates, a large amount of energy is released within a short time, creating a high-temperature and high-pressure environment accompanied by a blast wave. When the blast wave interacts with field obstacles such as building structures and ground soil, it produces a reflected wave. The complexity of the pressure field created by blast waves depends on the spatial characteristics of the explosion domain. To understand the blast wave characteristics in various environmental constraints, this study develops a large-scale hydrodynamic solver of shock wave propagation in complex spatial domains of two kinds. First, the propagation of a blast wave in large open spaces (20 m × 10 m area) was simulated using an adaptive mesh refinement technique programmed to capture the details of moving blast waves and multiple reflections. Second, a point source explosion in a two-room concrete structure (5 m × 7 m × 3 m) was simulated which makes use of the optimal merging of two equations of state, while a spherical detonation wave is stabilized before spreading into multiple rooms. The experimental data in both tests are used to validate the computational results presented. [ABSTRACT FROM AUTHOR]

The direct numerical simulation of blast waves is a challenging task due to the wide range of spatial and temporal scales involved. Moreover, in a real environment (topography, urban area), the blast wave interacts with geometrical obstacles, resulting in reflection, diffraction, and wave recombination phenomena. The shape of the front becomes complex, which limits the efficiency of simple empirical methods. This work aims at contributing to the development of a fast running method for blast waves propagating in the presence of obstacles. This is achieved through an ad hoc extension of the simplified hyperbolic geometrical shock dynamics (GSD) model, which leads to a drastic reduction in the computational cost in comparison with the full Euler system. The new model, called geometrical blast dynamics, is able to take into account any kind of source and obstacle. It relies on a previous extension of GSD for diffraction over wedges to obtain consistent physical behavior, especially in the limit of low Mach numbers. The new model is fully described. Its numerical integration is straightforward. Results compare favorably with experiments, semiempirical models from the literature, and Eulerian simulations, over a wide range of configurations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

It is well established that the knowledge about shock wave propagation in the free field cannot be applied to confined environments, especially when it comes to predicting the reflected shock wave. With the increase in accidental or intentional detonations of explosives in confined or urban environments, it is important to study and thoroughly understand the propagation of shock waves to provide behavior prediction tools. The present research focuses on understanding the influence of a variation in the explosion center in a confined room and how this variation affects the shock wave propagation and the reflection due to the confined environment. The shock waves were generated by the detonation of a stoichiometric hemispherical charge of propane–oxygen mixture. The charge was placed in a small-scale model (Hopkinson's scaling law) which represents a typical room in a building. The model was equipped with 29 pressure sensors distributed on the walls and the floor to record pressure history data. The aim of this study was to determine experimentally the evolution of the shock wave parameters such as the maximum overpressure or the arrival time and to predict the origin of the first three reflected peaks with the help of a simple and fast tool. [ABSTRACT FROM AUTHOR]

The TNT equivalences of equal masses of propane, a stoichiometric mixture of propane and oxygen, and ammonium-nitrate–fuel-oil (ANFO) were calculated based on the peak hydrostatic and dynamic pressures, the hydrostatic and dynamic pressure positive-phase impulses, and the positive-phase integrated work flux. It was assumed that the propane had been dispersed as a vapour/droplet cloud to form a stoichiometric mixture with atmospheric oxygen before detonation. This is the objective for fuel–air weapons and the worst-case scenario for accidental propane explosions such as boiling liquid expanding vapour explosions. The TNT equivalences of propane/oxygen and ANFO, which have energy yields less than TNT, show little variation when calculated using the different blast wave physical properties. In contrast, the equivalences for propane, which has a significantly higher energy yield than TNT, show a broad range of values, with those based on the impulses being significantly larger than those based on the peak values. The equivalence based on the positive-phase integrated work flux is intermediate between the peak and impulse values. The reasons for these differences are illustrated and discussed. [ABSTRACT FROM AUTHOR]

We have investigated one-dimensional compression waves, produced by heat addition in quiescent and uniform initial conditions, in six different supercritical fluids, each taken in four states ranging from compressible pseudo-liquid fluid to ideal gas. Navier–Stokes simulations of a canonical semi-infinite domain flow problem, spanning five orders of magnitude of heating rate, are also carried out to support the theoretical analysis. Depending on the intensity of the Gaussian-shaped energy source, linear waves or shock waves due to nonlinear wave steepening are observed. A new reference heating rate parameter allows to collapse in the linear regime the whole dataset, together with the existing experimental data, thanks to its absorption of real-fluid effects. Moreover, the scaling strategy illustrates a clear separation between linear and nonlinear regimes for all fluids and conditions, offering motivation for the derivation of a unified fully predictive model for shock intensity. The latter is performed by extending the validity of previously obtained theoretical results in the nonlinear regime to supercritical fluids. Finally, thermal to mechanical power conversion efficiencies are shown to be proportional, in the linear regime, to the fluid's Grüneisen parameter, which is the highest for compressible pseudo-liquid fluids, and maximum in the nonlinear regime for ideal gases. [ABSTRACT FROM AUTHOR]

In this study, a combined experimental and numerical approach is taken to further investigate the thermomechanics of shock wave formation in combustible mixtures. This study focuses on several gas mixtures including air, methane/N2, methane/air, and biogas/air. The lean and stoichiometric combustible mixtures are studied at three different laser energy levels. The Jones blast wave theory is used to calculate the energy involved in development of the resulting shock waves and used to specify the initial conditions for the plasma in simulations. In addition, interferometry is used to gain insights into the thermodynamic conditions within the plasma kernel, for validation of the numerical model results. The energies calculated for the different mixtures studied show that shock waves generated in the combustible mixture likely gain energy early in the breakdown process from exothermic chemical reactions. Shock wave results from experiment are shown to be replicated by the model, and the variations of the density inside of the hot core region are in agreement between the simulation and experimental results. [ABSTRACT FROM AUTHOR]

With the increasing use of improvised explosive devices (IEDs), the need for better mitigation, either for building integrity or for personal security, increases in importance. Before focusing on the interaction of the shock wave with a target and the potential associated damage, knowledge must be acquired regarding the nature of the blast threat, i.e., the pressure–time history. This requirement motivates gaining further insight into the triple point (TP) path, in order to know precisely which regime the target will encounter (simple reflection or Mach reflection). Within this context, the purpose of this study is to evaluate three existing TP path empirical models, which in turn are used in other empirical models for the determination of the pressure profile. These three TP models are the empirical function of Kinney, the Unified Facilities Criteria (UFC) curves, and the model of the Natural Resources Defense Council (NRDC). As discrepancies are observed between these models, new experimental data were obtained to test their reliability and a new promising formulation is proposed for scaled heights of burst ranging from 24.6–172.9cm/kg1/3. [ABSTRACT FROM AUTHOR]

The modeling of human body biomechanics resulting from blast exposure poses great challenges because of the complex geometry and the substantial material heterogeneity. We developed a detailed human body finite element model representing both the geometry and the materials realistically. The model includes the detailed head (face, skull, brain and spinal cord), the neck, the skeleton, air cavities (lungs) and the tissues. Hence, it can be used to properly model the stress wave propagation in the human body subjected to blast loading. The blast loading on the human was generated from a simulated C4 explosion. We used the highly scalable solvers in the multi-physics code CoBi for both the blast simulation and the human body biomechanics. The meshes generated for these simulations are of good quality so that relatively large time-step sizes can be used without resorting to artificial time scaling treatments. The coupled gas dynamics and biomechanics solutions were validated against the shock tube test data. The human body models were used to conduct parametric simulations to find the biomechanical response and the brain injury mechanism due to blasts impacting the human body. Under the same blast loading condition, we showed the importance of inclusion of the whole body. [ABSTRACT FROM AUTHOR]

This study describes experimental work examining the critical energy for direct initiation of detonation by laser ablation in a stoichiometric acetylene-oxygen mixture. The amount of input energy, the target material, and the surface roughness of the target were varied to study their effects on shock wave generation. Aluminum and stainless steel were used as target materials. The propagating shock wave induced by laser ablation was observed using high-speed shadow imaging. The critical energy for direct initiation of detonation was calculated using the strong blast wave theory. The critical input energy for aluminum was found to be lower than that for stainless steel. Because the thermodynamic critical temperature of aluminum is lower than that of stainless steel, aluminum caused a phase explosion more easily than stainless steel, thus resulting in direct initiation of detonation with a lower amount of input energy. The effects of surface roughness on critical input energy and shock wave generation were negligibly small. The critical initiation energy was estimated to be $$10.3 \pm 0.2$$ mJ, which is in agreement with the experimental data obtained in previous work. The estimated critical initiation energy was independent of the target material. However, other predictions of the critical initiation energy by using the cell size overestimated this value because of the scatter in cell size data of an unstable cellular structure. Furthermore, interaction between plasma plumes formed by laser ablation and those formed by breakdown near the target surface might have contributed to requiring a lower amount of energy for initiating detonation. [ABSTRACT FROM AUTHOR]

Weak spherical blast waves in static air and their breakup of ethanol and Jet A-1 kerosene droplets were investigated. The blast waves were created by laser-induced air breakdowns at ambient temperature and pressure. In the first part of this study, they were visualized with schlieren imaging, and their trajectories were tracked with high temporal resolution. The laser pulse energy was varied to create blast waves of different strengths. Their initial energies were determined by the application of a numerical and a semi-empirical blast wave model. In the second part, monodisperse ethanol and kerosene droplet chains were injected. Their interaction with the blast waves was visualized by the application of shadowgraph imaging. The perpendicular distance of the breakdown origin toward the droplet chains was varied to study the effect on the fuel droplets as a function of the distance. Droplets within a few millimeters around the breakdown origin were disintegrated into two to three secondary droplets. The blast-induced flow velocities on the post-shock side and the corresponding Weber numbers were calculated from the data of a non-dimensional numerical simulation, and a close look was taken at the breakup process of the droplets. The analysis showed that the aerodynamic force of the blast-induced flow was sufficient to deform the droplets into disk-like shapes, but diminished too fast to accomplish breakup. Due to the release of strain energy, the deformed droplets relaxed, stretched into filaments and finally disintegrated by capillary pinching. [ABSTRACT FROM AUTHOR]

In this study, we numerically investigate a novel means to reduce blast overpressure to the rear of a muzzle-loaded cannon. Reduction in blast overpressure, and thus peak overpressure, leads to an increase in the number of allowed rounds that can be fired over a given period of time for the crew manning the system. New propellant leak methods are studied using numerical simulations, where the propellant gas is intentionally allowed to leak in front of the projectile into the precursor region (while the projectile is still in the bore). This is done through the addition of a bulge or leak channels in the tube. The focus of this work is on a large-caliber muzzle-loaded cannon at $$80^{\circ }$$ (1,422 angular mils) elevation and with firing done at the max zone with the round and charge conditioned to ambient. We employ a hydrocode (ALE3D) to predict the blast overpressure for three types of geometries comprising five geometric configurations in total. These include one baseline configuration (i.e., with no modification) as well as four additional configurations with bulges and channels to allow propellant leak. The leaking of propellant gas into the precursor region leads to changes in the flow field associated with the precursor. In the case of channels, propellant leak results in a significantly reduced exit pressure ratio during projectile separation, and thereby, leading to a weaker primary blast wave. This in turn attenuates the peak overpressure to the rear of the muzzle without the aid of a muzzle device. For the channel leak method, at one monitored location, with the largest peak overpressure, a reduction of about 38 % was observed in peak overpressure as compared to the baseline case. [ABSTRACT FROM AUTHOR]

Blast wave parameters including incident overpressure, impulse and duration of the positive phase of the incident blast wave and its time of arrival were experimentally determined for 50 g charges of low bulk density ( $$0.4\, \hbox {g/cm}^{3}$$ ) dry TATP (3,3,6,6,9,9-hexamethyl-1,2,4,5,7,8-hexoxonane). The results were compared with published TNT data, and TNT equivalencies were determined, resulting in the values of 70 % based on overpressure and 55 % based on impulse of the positive phase of the blast wave. Brisance by the Hess method (lead cylinder compression) was found to be about one-third of that for TNT (at density $$1.2\, \hbox {g/cm}^{3})$$ . Detonation velocities averaged around $$2,660 \,\hbox {m/s}^{1}$$ [ABSTRACT FROM AUTHOR]