Blast Wave Propagation Research Articles

Experimental research of shaped charges with electrohydraulic effect with a view to improving blasting safety and efficiency

Ore mining in hard rocks generally includes drilling and blasting. Blasting technologies belong to the most hazardous industrial processes. One of the ways of increasing efficiency of mining is improvement of blasting technologies toward enhancing the rates and efficiency of growth in the mining industry at the reduced risk of injuries. The present-day stage of drilling and blasting in underground mining features the use of high-capacity drilling equipment and tools, introduction of novel drilling and blasting design and implementation methods and technologies, creation of effective mechanisms for application of innovations, and wide-scale adoption of energy- and resource-saving technologies. Higher safety of drilling and blasting ensues from upgrading of drilling equipment, firing devices, explosives and charge designs. The composition of an explosive and the design of a charge have an essential influence on the volume and composition of a gas-and-dust cloud induced in blasting, and on the range of dispersion of broken rock fragments. In this regard, shaped charges have demonstrated their efficiency but their wide introduction needs further studies into specification of the process parameters. This article focuses on the method of experimental research into the shaped charge effect using a science-based electrohydraulic laboratory model. The shaped charges have proved their exploitability. The mathematical formulation of the problem on the blast wave propagation in enclosing rock mass of structurally complex mineral deposits is discussed. The hydrodynamic theory of the shaped charge effect is substantiated and the process parameters are determined.

Progressive collapse of Murrah Federal Building: Revisited

As a typical incident of progressive collapse of RC structures caused by the terroristic vehicular bomb attack, the large-scale collapse of Murrah Federal Building (MFB) in 1995 has been attracting extensive attentions. The alternate path method and the direct simulation method are commonly adopted to evaluate the progressive collapse resistance of buildings. However, the simultaneous damage of the structural members adjacent to the removed column and the instantaneous interactions between the blast wave and the structures are neglected. This paper aims to revisit the progressive collapse of MFB through the high-fidelity numerical simulations. Firstly, the hybrid finite element model of MFB was established including both the near-range refined model and far-range simplified model. Secondly, based on the explicit dynamic finite element program LS-DYNA, the Arbitrary Lagrangian-Eulerian (ALE) method and Fluid-Structure Interaction (FSI) algorithms were adopted to simulate the ignition of explosive, propagation of air blast wave and its interactions with the building structures, which was validated based on an external explosion test on RC frame structure. Furthermore, the collapse of MFB was predicted and compared with the on-site photographs in terms of the collapse scopes of entire building and the damage of local structural members. Finally, three seismic resistant design schemes of MFB were proposed, and the corresponding progressive collapse resistance of which was further evaluated. It derives that, (i) the numerical simulation combining the hybrid modelling and ALE approaches can well reproduce the collapse process of MFB; (ii) the progressive collapse of MFB is mainly caused by the insufficiency of flexural bearing capacity of the transfer girder due to the failure of three supporting ground columns, rather than the rotation of the transfer girder; (iii) the three improved schemes can partially prevent the shear failure of the ground columns and mitigate the collapse scopes of MFB by 25%–50%, while the progressive collapse still occurs due to the shear failure of transfer girder; (iv) transfer girder is not recommended for blast-resistant buildings due to its low redundancy.

Review on quick safety assessment of building structures in complex urban environment after extreme explosion events

Extreme explosion events result in demands for emergency rescue service. From the civil engineering perspective, a quick safety assessment of building structures in the explosion’s vicinity will provide the emergency rescue committee with concrete support to make scientific decisions. In this paper, three primary issues, namely, inverse analysis of explosive characteristics, blast wave propagation in complex urban areas and blast-induced damage identification, are reviewed. These are often performed stepwise and form a multi-step whole to assist the emergency rescue service. The paper begins by introducing the inverse analysis of explosives based on craters, building damages and seismic or acoustic records. In this step, explosive characteristics, for example, charge type, original time, yield and location, could be produced and input into blast load calculation in the next step. Then, the existing literature on blast wave propagation and blast load determination is presented with close attention to complex urban environments. It shows that the current study remains in its infancy and relies on advancement in computational fluid dynamics (CFD). Besides, pressure–impulse (P-I) diagrams which predict the structural damage based on the calculated blast loads are illustrated. Onsite damage detection techniques, such as visual inspection, non-destructive testing (NDT) and vibration-based methods, are also discussed. The paper ends with a discussion of the shortcomings of previous work and the outlooks of further work.

External blast flow field evolution and response mechanism of single-layer reticulated dome structure

Single-layer reticulated dome structure are commonly high-profile building in the public and can be attractive targets for terrorist bombings, so the public can benefit from enhanced safety with a stronger understanding of the behavior of single-layer reticulated dome structure under explosion. This paper investigates the fluid-structure interaction process and the dynamic response performance of the single-layer reticulated dome under external blast load. Both experimental and numerical results shown that structural deformation is remarkably delayed compared with the velocity of blast wave, which advises the dynamic response of large-span reticulated dome structure has a negligible effect on the blast wave propagation under explosion. Four failure modes are identified by comparing the plastic development of each ring and the residual spatial geometric of the structure, i.e., minor vibration, local depression, severe damage, and overall collapse. The plastic deformation energy and the displacement potential energy of the structure are the main consumers of the blast energy. In addition, the stress performance of the vertex member and the deep plastic ratio of the whole structure can serve as qualitative indicators to distinguish different failure modes.

Peak sound pressure level decay from large C-4 detonations: Establishing a 140 dB threshold

Far-field acoustical characterization of blast wave propagation from explosives is often carried out using relatively small shot sizes (less than 1 kg). This paper describes a series of eleven C-4 detonations, with shot sizes varying from 13.6 kg to 54.4 kg (30 to 120 lbs) that were recently measured at the Big Explosives Experimental Facility (BEEF) at the Nevada National Security Site. Pressure waveform data were recorded at up to nine different stations, ranging from 23 m to 2.7 km from the blast origin, with some angular variation. As part of examining blast overpressure decay with distance and comparing with literature, the data were analyzed from the context of human safety regulations. To provide improved guidance for BEEF personnel working distances, an empirical model equation was developed for the distance, as a function of shot size, at which the peak pressure level drops below 140 dB. A preliminary investigation into peak level variability due to wind was also conducted. [Work supported by Los Alamos National Laboratory.]

A Numerical Study on the Blast Wave Distribution and Propagation Characteristics of Cylindrical Explosive in Motion

In order to study the overpressure distribution law of a shock wave under the dynamic explosion of a cylindrical charge and the influence of the charge speed on the overpressure distribution law, a trinitrotoluene (TNT) cylindrical bare charge was selected. Additionally, a numerical simulation of a cylindrical charge explosion under different motion speeds was carried out using the AUTODYN finite element software. The results showed that during the static explosion of a cylindrical charge, the shock wave propagates outward in the form of an ellipsoid, whereas under the dynamic explosion, the shock wave overpressure field is an irregular ellipsoid, and the shock wave overpressure zone shifts to the velocity direction. With an increase in the charge velocity, the peak value of the shock wave overpressure increases gradually in the moving direction. The simulation data were analyzed, revealing that the calculation model of the dynamic explosion shock wave overpressure field of a cylindrical charge with a scaled distance of 1 m·kg−1/3 ≤ R ¯ ≤ 1.5 m kg−1/3 can provide a reference basis for the study of dynamic explosion shock waves.

The calculation of loads on buildings and structures caused by outdoor explosions of the fuel-air mixture

Introduction. An important engineering task, to be solved in the process of designing buildings and structures for hazardous industrial facilities, is to determine values of loads caused by outdoor explosions of the fuel-air mixture. Nowadays software packages, that use the computational fluid dynamics (CFD) approach, are widely applied in the design practice to assess various effects on building structures. In this regard, it is necessary to develop a load calculation method, that employs numerical simulation, and verify it in comparison with the experimental data.Goals and objectives. The purpose of this work is to use the method of computational fluid dynamics to analyze external sympathetic detonation loads on various types of buildings and structures.The body of the article. The article addresses the “compressed balloon” method used to analyze loads, caused by outdoor explosions of gas. Dependencies, proposed in the article, are needed to set the input data and make numerical calculations using the computational fluid dynamics (CFD) technique. The numerical modeling of various experiments in the ANSYS Fluent software package was conducted. The authors compared the results of numerical modeling and standard engineering methods with various experiments to assess the accuracy of the “compressed balloon” method used to analyze an outdoor detonation explosion.Conclusions. The authors have proven the qualitative and quantitative convergence of the numerical model of blast wave propagation and the experimental data. This calculation method allows to accurately apply the pressure profile to any surface of a building or structure in the course of an outdoor detonation explosion and estimate the bearing capacity of building structures. The proposed method can be used in the design of buildings or structures that feature various configurations.

Blast wave propagation characteristics in FPSO: Effect of cubical obstacles

Gas explosion accidents may result in catastrophic damage to structures and humans. Generally, the gas explosion pressures on Floating, Production, Storage, and Off-loading unit (FPSO) are affected by the obstacles. In this paper, the numerical simulation method is applied to study the blast wave propagation in the modules of FPSO. The types of the blast wave, dimensions of the obstacle, and combinations of multiple obstacles are regarded as the variables to study the change of explosion pressure fields. An effect coefficient η is defined to represent the effect of the obstacles on explosion pressures. Results show the obstacles can only affect the finite areas in the surrounding. The explosion pressures on the front or side of the obstacle only depend on the intensities of incident waves. However, the pressures at the back of the obstacle are determined by the path difference of the diffraction waves, which is sensitive to obstacle dimensions. Extending the width and height significantly reduces the explosion pressures behind the obstacle. Analyzing the effect coefficients in the multi-obstacle combinations, reveals the medium spacing distance can reduce the explosion pressure. Based on the analysis results, some suggestions are recommended for escape and refuge.

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

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

Supersonic jet by blast wave focusing

A supersonic jet of Mach number M = 4.5 in air is produced experimentally at the apex of a miniature 150 × 50 × 5 mm converging section with a 2 × 5 mm opening by the principle of blast wave amplification through focusing. An initial plane blast wave of M = 2.4 in the convergence section is generated by the exploding wire technique. The profile of the convergence section is specially tailored to smoothly transform a plane blast wave into a perfectly cylindrical arc, imploding at the apex of the section. The cylindrical form of the imploding shock delivers maximum shock amplification in the two-dimensional test section and maximum subsequent jet flow velocity behind the shock front. Blast wave propagation in the convergence chamber as well as jet generation through a 2 mm opening at the apex into the adjacent exhaust chamber is optically captured by a high-speed camera using the shadowgraph method. Visualizing the flow provided a distinct advantage not only for obtaining detailed information on the flow characteristics but also for validating the numerical scheme which further enhanced the analysis. Experimental images together with the numerical analysis deliver detailed information on the blast wave propagation and focusing as well as subsequent jet initiation and development. One of the main advantages of the described method apart from being simple and robust is the effective focusing of low initial input energy levels of just around 500 Joules, resulting in production of supersonic jets in a small confined chamber.

Experimental and numerical studies on dynamic behaviors of RC slabs under long-duration near-planar explosion loadings

Concerning the blast-resistant analyses and design of protective structures under potential far-range large-yield chemical explosions and the industrial gas/fuel explosions, the dynamic behaviors of RC slab under long-duration near-planar blast loadings are studied both experimentally and numerically. Firstly, unlike the conventional short-duration explosion with spherical waves, aiming to generate the long-duration near-planar blast loadings on the structural members, a specified apparatus including a confined shot cavity, a cubic-like steel frame and the plane charge explosion technique (PCET) is developed. Secondly, the field explosion test on five one-way simply-supported RC slabs with the dimensions of 2400×1000×100 mm3 is conducted, in which the magnitudes and durations of the near-planar blast loadings are varied within 0.1–0.4 MPa and 85–135 ms, respectively. Then, by adopting the Structured-Arbitrary-Lagrange-Eulerian (SALE) solver and Fluid-Structure Interaction (FSI) algorithm implemented in the commercial finite element program LS-DYNA, the above field test is simulated numerically. By comparing with the test data including the overpressure-, rebar strain- and displacement-time histories as well as structural post-blast damage, the validity of the adopted finite element analysis (FEA) approach for the long-duration explosion scenarios with multi-point detonations is verified comprehensively, and the propagation of blast waves, dynamic responses and damage patterns of RC slab are assessed. Finally, the applicability of single degree of freedom (SDOF) approach recommended in the specification UFC 3–340–02 to predict the maximal mid-span deflections is further verified. The present work can provide helpful references for the long-duration explosion loadings test technique and the blast-resistant design of protective structures.

Attenuation model of tunnel blast vibration velocity based on the influence of free surface

In tunnel blasting excavation, it is important to clarify the attenuation law of blast wave propagation and predict the blast vibration velocity effectively to ensure safe tunnel construction and protection design. The effects of the free surface area its quantity on the blast vibration velocity are considered, and free surface parameters are introduced to improve the existing blast vibration velocity prediction formula. Based on the Tianhuan railway Daqianshiling tunnel project, field blast vibration monitoring tests are performed to determine changes in the peak blasting vibration velocity based on the blast distance and free surface area. LS-DYNA is used to establish tunnel blasting excavation models under three operating conditions; subsequently, the attenuation law of blast vibration velocity and changes in the vibration response spectrum are analysed. Results show that the free surface area and number of free surfaces enable the blast vibration velocity to be predicted under various operating conditions: a smaller free surface area results in a narrower frequency band range, whereas more free surfaces result in a narrower frequency band range. The improved blast vibration velocity prediction formula is validated using field and numerical test data. It is indicated that the improved formula is applicable to various tunnelling conditions.

Numerical investigation on free air blast loads generated from center-initiated cylindrical charges with varied aspect ratio in arbitrary orientation

In current guidelines, the free air blast loads (overpressure and impulse) are determined by spherical charges, although most of ordnance devices are more nearly cylindrical than spherical in geometry. This may result in a great underestimation of blast loads in the near field and lead to an unsafe design. However, there is still a lack of systematic quantitative analysis of the blast loads generated from cylindrical charges. In this study, a numerical model is developed by using the hydrocode AUTODYN to investigate the influences of aspect ratio and orientation on the free air blast loads generated from center-initiated cylindrical charges. This is done by examining the pressure contours, the peak overpressures and impulses for various aspect ratios ranged from 1 to 8 and arbitrary orientation monitored along every azimuth angle with an interval of 5°. To characterize the distribution patterns of blast loads, three regions, i.e., the axial region, the vertex region and the radial region are identified, and the propagation of blast waves in each region is analyzed in detail. The complexity of blast loads of cylindrical charges is found to result from the bridge wave and its interaction with primary waves. Several empirical formulas are presented based on curve-fitting the numerical data, including the orientation where the maximum peak overpressure emerges, the critical scaled distance beyond which the charge shape effect could be neglected and blast loads with varied aspect ratio in arbitrary orientation, all of which are useful for blast-resistant design.

Investigating the Effect of the Geometry of RC Barrier Walls on the Blast Wave Propagation

Evaluating the performance of several types of reinforced concrete barrier walls subjected to blast loads is the target of this research paper. A parametric study is carried out for nine RC barrier wall systems with different geometries modelled in the three dimensions with different configurations and variable parameters. ANSYS Autodyn software version 18.2 is used to model and analyse these systems using three-dimensional explicit dynamics analysis. The nine systems are studied under the effect of several parameters, such as explosive charge weight (W) and the stand-off distance from the explosion source to the wall (R). Their effect on the wall damage and its deformations and the pressure-induced at different locations are analysed. Eighteen reinforced concrete barrier wall models are studied to achieve this research goal. Comparisons between the results showed the deformation performance of the 60° concave face with planar back walls and the walls with the constant base of 1.0-meter-thick up to 0.5-meter-high with a face hunch up to 2.0-meter-high are better than all other studied walls. However, the concave face-convex back wall that has 70° curvature mitigate the pressure behind the wall by 10% regardless of its deformation.

Propagation of spherical weak blast waves over rough periodic surfaces

Propagation of spherical weak blast waves over rough periodic surfaces

Features of seismic wave travel along a coal pit wall

Triple gain of the maximum amplitudes or massif vibrations in a final phase of the consecutive blasting of groups of borehole charges during the propagation of a seismic blast wave outside the mined block in the Quarternary deposits of a coal mine slope has been experimentally established. The effect of “rocking” the massif occurs stepwise, and it is synchronized according to the selected delay intervals at detonation.

Investigation of the confinement effects on the blast wave propagated from gas mixture detonation utilizing the CESE method with finite rate chemistry model

ABSTRACT In this paper, we investigate the effect of confinement on the explosion characteristic of a certain volume of a gas mixture in an environment. Instead of using the equivalent weight of TNT, we use a computational fluid dynamics method with a reduced chemical kinetic mechanism to simulate the gas mixture detonation. In this method, reacting flow equations including realistic finite-rate chemistry models are solved by employing the space-time conservation element and solution element (CESE). To evaluate the accuracy of the kinetic mechanism and the validity of the simulation of the volumetric explosions, including the blast wave propagation and its interaction with the walls, the explosion of a certain volume of stoichiometric propane/oxygen mixture in a semi-confined volume is investigated and the numerical results are compared with an experimental data. The excellent agreement between the numerical results and the experimental data indicates that it is possible to predict the behavior of the blast wave generated by the detonation of a gas mixture in a relatively complex environment accurately by using appropriate chemical kinetics. Therefore, we have used this method to investigate the effects of confinement on the blast wave propagation caused by gas detonation in more detail.

Blast enhancement from metalized explosives

Experiments are carried out to determine the effects of particle size and mass loading on the free-field blast wave from spherical, constant volume metalized explosive charges. The charges are comprised of gelled nitromethane with uniformly embedded aluminum, magnesium, or glass particles. Particle sizes are varied over an order of magnitude with particle mass fractions up to 50%. Peak blast overpressures are directly measured within the fireball with piezoelectric pressure gauges and outside the fireball are inferred by tracking the velocity of the blast wave and using the Rankine–Hugoniot relation. With the addition of inert particles, the peak blast overpressure is initially mitigated, but then recovers in the far field. For charges with reactive particles, the particles react promptly with oxidizers in the detonation products and release energy as early as within the first few hundred microseconds in all cases. The particle energy release enhances the peak blast overpressures in the far field by up to twice the values for a constant volume charge of the baseline homogenous explosive. By plotting the peak blast overpressure decay as a function of energy-scaled distance, it is inferred that at least half of the particle energy release contributes to the blast overpressure in the far field of higher mass loadings, and nearly all of the particle energy for a particle mass fraction of 10%. For aluminum, the blast augmentation is not a systematic function of particle size. This observation implies that conventional models for particle combustion that depend on particle surface area are not appropriate for describing the rapid aluminum reaction that occurs in the extreme conditions within the detonation products, which influences the blast wave propagation.

On the Blast Wave Propagation and Structure in a Rotational Axisymmetric Perfect Gas

In this paper, the approximate analytical solution for the propagation of a blast (shock) wave in a rotating perfect gas in the case of cylindrical geometry is studied. The axial and azimuthal components of fluid velocity are taken into consideration, and these flow variables in the undisturbed medium are assumed to be varying according to the power laws with distance from the symmetry axis. The shock wave is considered to be strong one for the ratio $${\left(C/{W}_{S}\right)}^{2}$$ to be a small quantity, where $$C$$ is the sound velocity in undisturbed fluid and $${W}_{S}$$ is the shock wave velocity. The initial density in the undisturbed medium is taken to be constant to obtain the similarity solution. To obtain the approximate analytical solution, the flow variables are expanded in power series in power of $${\left(C/{W}_{S}\right)}^{2}.$$ The first- and second-order approximations to solutions are discussed with the help of power series expansion. The analytical solutions are constructed for the first-order approximation. The distribution of the flow variables for the first-order approximation in the flow-field region behind the blast wave is shown in graphs. A comparison is also made between the solutions obtained for non-rotating and rotating medium. It is shown that the constant quantity $${J}_{0}$$ in the flow field region behind the shock front increases in rotating medium in comparison with its value in non-rotating medium; but an increase in adiabatic exponent causes a decrease in it. Further, it is concluded that shock strength increases with adiabatic exponent and decreases due to the consideration of the rotating medium.

Micro-mechanical fracture dynamics and damage modelling in brittle materials.

This study explores the interplay between wave propagation and damage in brittle materials. The damage models, based on micro-mechanical fracture dynamics, capture any possible unstable growth of micro-cracks, introducing a macroscopic loss of stability. After stating the non-dimensional mathematical problem describing the wave propagation with damage, we introduce a non-dimensional number, called the microscopic evolution index, which links the micro and macro scales and discriminates the microscopic scale behaviour. For large values of microscopic evolution index, corresponding to a microscopic quasi-static process coupled with a macroscopic dynamic one, the macroscopic dynamic system could lose its hyperbolicity or become very stiff and generate shock waves. A semi-analytical solution to the one-dimensional wave propagation problem with damage, which could be very useful in the accuracy evaluation of the numerical schemes, was constructed. Concerning the asymptotic behaviour of the dynamic exact solution on the microscopic evolution index (or on the strain rate), an important strain rate sensitivity was found: the pulse loses its amplitude for decreasing strain rate and, starting with a critical value, the micro-scale model is rate independent. A possible regularization technique to smooth the shock waves at low and moderate strain rates is discussed. Finally, some numerical results analyse the role played by the the friction on the micro-cracks in the damage modelling of blast wave propagation. This article is part of the theme issue 'Fracture dynamics of solid materials: from particles to the globe'.