Search Results (57)

A methane-air premixed gas explosion is one of the most destructive disasters in the process of coal mining, and the dynamic coupling between the shock wave triggered by the explosion and the surrounding rock of the roadway can lead to the destabilization of the surrounding rock structure, the destruction of equipment, and casualties. The aim of this study is to systematically reveal the propagation characteristics of the blast wave, the spatial and temporal evolution of the wall load, and the damage mechanism of the surrounding rock by establishing a two-way fluid-solid coupling numerical model. Based on the Ansys Fluent fluid solver and Transient Structure module, a framework for the co-simulation of the fluid and solid domains has been constructed by adopting the standard $k-\epsilon$ turbulence model, finite-rate/eddy-dissipation (FR/ED) reaction model, and nonlinear finite-element theory, and by introducing a dynamic damage threshold criterion based on the Drucker–Prager and Mohr–Coulomb criteria. It is shown that methane concentration significantly affects the kinetic behavior of explosive shock wave propagation. Under chemical equivalence ratio conditions (9.5% methane), an ideal Chapman–Jouguet blast wave structure was formed, exhibiting the highest energy release efficiency. In contrast, lean ignition (7%) and rich ignition (12%) conditions resulted in lower efficiencies due to incomplete combustion or complex combustion patterns. In addition, the pressure time-history evolution of the tunnel enclosure wall after ignition triggering exhibits significant nonlinear dynamics, which can be divided into three phases: the initiation and turbulence development phase, the quasi-steady propagation phase, and the expansion and dissipation phase. Further analysis reveals that the closed end produces significant stress aggregation due to the interference of multiple reflected waves, while the open end increases the stress fluctuation due to turbulence effects. The spatial and temporal evolution of the strain field also follows a three-stage dynamic pattern: an initial strain-induced stage, a strain accumulation propagation stage, and a residual strain stabilization stage and the displacement is characterized by an initial phase of concentration followed by gradual expansion. This study not only deepens the understanding of methane-air premixed gas explosion and its interaction with the roadway’s surrounding rock, but also provides an important scientific basis and technical support for coal mine safety production. Full article

In order to correctly measure the shock wave pressure generated by a near-field explosion, and while considering the limitations of the measurement and calibration method of the current bar pressure sensor, an improved shock wave pressure measurement method was designed based on a bar pressure sensor combined with photon Doppler velocimetry (PDV) and strain measurement. By measuring the strain on the pressure bar and the particle velocity on the rear-end face, the shock wave pressure applied on the front-end face of the pressure bar was calculated based on one-dimensional stress wave theory. On the other hand, a calibration method was designed to validate the reliability of the test system. Based on the split-Hopkinson pressure bar (SHPB) loading experiment, the transmission characteristics of stress wave in the bar and the accuracy of the system test results were verified. The results indicated that the stress wave measurement results were consistent with the one-dimensional elementary theoretical calculation results of stress wave propagation in different wave-impedance materials, and the peak deviation measured by PDV and strain measurement method was less than 1.5%, which proved the accuracy of the test method and the feasibility of the calibration method. Full article

The roof slab, as a critical component for partitioning the vertical space within RC frame structures, can effectively mitigate the propagation of shock waves and reduce damage levels in adjacent rooms. This study employed finite element (FE) modeling to investigate the vertical propagation of blast waves and roof ejection velocity in RC frames. The model’s reliability was verified by reconstructing internal explosion tests on RC frames and close-in explosion tests on masonry walls. On this basis, two typical single-room RC frame structures that are vertically adjacent were designed, and numerical simulations of the internal explosion were conducted under four explosive equivalents and four venting coefficients. The propagation of shock waves, load characteristics in the vertically adjacent room, and the dynamic response of roof slabs were examined. The results show that shock waves propagated to the vertically adjacent room decreased by approximately two orders of magnitude for peak overpressure and one order of magnitude for impulse due to the obstruction of shock waves by roof slabs, respectively, compared to the source explosion room. For larger venting coefficients, abundant energy was released through the venting openings, making it difficult to form a quasi-static pressure with a long duration inside the source explosion room. In addition to the shock wave, the explosive ejection of roof slabs in the explosion source room will further exacerbate the damage to the vertically adjacent room. Peak overpressure and impulse propagated to the vertically adjacent room were reduced significantly by the increase in the venting coefficient, resulting in an attenuation of structural damage. Finally, empirical models incorporating the venting coefficient were established to characterize the attenuation coefficients of power parameters, demonstrating the predictive capability for peak overpressure, impulse, and roof ejection velocity in both the explosion source room and the vertically adjacent room. Full article

In order to analyze the explosion risk of the engine room, this paper uses CFD software to simulate the LNG leakage process in the engine room of the ship, and uses the combustible gas cloud obtained from the leakage simulation to simulate the explosion, analyzing its combustion and explosion dynamics. On the basis of previous studies, this paper studies the coupling of leakage and explosion simulation to ensure that it conforms to the real situation. At the same time, taking explosion overpressure, explosion temperature, and the mass fraction of combustion products as the breakthrough point, this paper studies the harm of explosion to human body and the influence of ignition source location on the propagation characteristics of LNG explosion shock wave in the engine room, and discusses the influence of obstacles on gas diffusion and accumulation. The results show that the LNG leakage reaches the maximum concentration in the injection direction, and the obstacles in the cabin have a significant effect on the diffusion and accumulation of gas. In the explosion simulation based on the leakage results, it can be determined that the shape of the pressure field generated by the explosion is irregular, and the pressure field at the obstacle side has obvious accumulation. Finally, in order to reduce the explosion hazard, the collaborative strategy of modular layout, directional ventilation, and gas detection is proposed, which provides ideas for the explosion-proof design of the cabin. Full article

This work is devoted to the computational investigation of the deformation and breakup of cylindrical water bodies in the high-speed airflow behind incident shock waves. Both single-column and tandem-column configurations in various arrangements were simulated by reproducing the shock/droplet interaction process in a shock-tube device. The calculations were conducted by using a third-party solver recently developed for compressible two-phase flows in the framework of the open source finite volume toolbox OpenFOAM. The numerical approach is based on the use of the volume-of-fluid method to resolve the phase interface, where a particular discretization technique allows us to prevent unphysical instabilities. The numerical scheme makes use of more precise information of the local propagation speeds to maintain a high resolution and a small numerical viscosity. Qualitative and quantitative comparisons of the results with reference experimental and numerical data demonstrated good agreement for the main characteristics of the interaction process in terms of the morphology, dynamics, and breakup of the deforming water bodies. Full article

The evolution form of the flow field generated via the impact of a muzzle jet on a constrained moving body changes from the state of fully free-spatial development to that of constrained development, and it involves the problem of interference, owing to the spatiotemporal coupling of various kinds of shock waves and vortices. Against this backdrop, the authors use the dynamic mesh method to establish two models for simulating the flow field and exploring the mechanism of development and the characteristics of propagation of disturbances induced via the shock waves as the muzzle jet impacts a constrained moving body. The results show that the muzzle jet exhibited a circumferentially asymmetric shape under the influence of the constrained track. The shock wave leaned towards the upper part of the muzzle, and its speed of propagation above the muzzle was higher than that below the muzzle. Meanwhile, the vortex that should have been present below the muzzle disappeared, and it was replaced with a separation line. Changes in the pressure of the flow field and important parameters of the moving body also became more complex due to the influence of the constrained track. Full article

Optimizing structural resistance against blast loads critically depends on the effects of different explosive shapes, equivalents, and distances on the damage characteristics of reinforced concrete beams. This study bridges the knowledge gap in understanding how these factors influence damage mechanisms through close-range air blast experiments and LS-DYNA numerical simulations. Key damage characteristics, such as craters, overpressure, impulse, time-history displacement, and residual mid-span displacement of reinforced concrete beams, were thoroughly analyzed. Results show that cuboid-shaped explosives cause the greatest damage, with the most severe effects observed at shorter distances and higher charge weights, including an increase in mid-span displacement of up to 16.3 cm. The study highlights the pivotal role of explosive geometry, charge weight, and standoff distance in shock wave propagation and structural failure and proposes an optimized damage criterion to enhance predictive capabilities for reinforced concrete beams under blast loads. Full article

In this study, the effects of pressure anisotropy and viscosity on the propagation of shock waves in spin-polarized degenerate quantum magnetoplasma are studied under the influence of the streaming energy of ion beams. The effects of different suitable plasma parameters on the shock wave’s potential profile are studied using the steady state solution of the Zakharov–Kuznetsov–Burgers (Z–K–B) equation, as well as the numerical simulation of the governing non-linear Z–K–B equation. First-order analysis of the non-linear wave propagation depicted a new beam-induced stable mode whose Mach number may be subsonic or supersonic depending on the anisotropic pressure combination in the presence of different spin density polarization ratios. This is the first observation of this new beam-induced stable mode in ion beam plasma, apart from the other existing modes of ion beam plasma systems, namely, the fast beam mode, the slow beam mode, the inherent ion acoustic mode, and the coupled mode, which also has unique propagation characteristics compared to the other modes. The spin density polarization ratio of spin-up and spin-down electrons have an unprecedented effect on the polarity and the direction of propagation of different shock wave modes in such plasma systems. Apart from the spin effect, anisotropic pressure combinations, as well as the viscosity of ions and ion beams, also play an outstanding role in controlling the nature of propagation of shock waves, especially in the newly detected beam-induced stable mode, and depending on the viscosity parameters of ions and ion beams, both oscillatory and monotonic shock waves can propagate in such plasma. Full article

The specifics of a shock wave propagation down a positive column of a DC discharge in molecular chemically inert gases has been investigated. It was shown that axial gradients caused by the imbalance in the charged particle momentum transfer to the gas molecules can be a reason for the shock velocity dependence on the electric field direction. In pure nitrogen gas, the calculated shock velocity difference of up to 13.5% is in good agreement with the 12% value obtained in the experiment. A returning gas flow organizing in the discharge as a possible mechanism for an extended shock structure and a number of kinetical factors capable of affecting the shock motion are discussed. Full article

The fourth-order nonlinear Boussinesq water wave equation, which describes the propagation of long waves in the intertidal zone, is investigated in this study. The exact wave patterns of the equation were computed using the $tanh$ method. As stability decreased, soliton wave structures were derived using similarity transformations. Numerical simulations supported these findings. The $tanh$ method introduced a Galilean modification, leading to the discovery of several new exact solutions. Subsequently, the fourth-order nonlinear Boussinesq wave equation was transformed into a planar dynamical system using the travelling wave transformation. The quasi-periodic, cyclical, and nonlinear behaviors of the analyzed equation were particularly examined. Numerical simulations revealed that varying the physical parameters impacts the system’s nonlinear behavior. Graphs represent all possible examples of phase portraits in terms of these parameters. Furthermore, the study was proven to be highly beneficial for addressing issues such as shock waves and highly active travelling wave processes. Sensitivity analysis theory and the Lyapunov exponent were employed, offering a wide variety of linear periodic and first-frequency periodic characteristics. Sensitivity analysis and multistability analysis of the Boussinesq water wave equation were thoroughly investigated. Full article

During the process of mining underground coal, the coal emits a large amount of methane into the mining space, which may lead to methane accumulation and exceed explosion safety limits When the methane encounters a fire source, a methane explosion may occur. The forceful impact caused by a methane explosion in an underground roadway can cause serious damage to the roadway structures and even lead to the collapse of the ventilation system. At the same time, the explosion impact may result in the death of workers and cause physical injury to the surviving workers. Therefore, it is necessary to study the damage effect and injury range of methane explosions. On the basis of the damage criteria and damage characteristics of methane explosions, according to the overpressure distribution of shock waves in the propagation process of a methane explosion, the explosion hazard range is divided into four ranges (from inside to outside): death range, serious injury range, minor injury range, and safety range. Four injury degrees of shock wave overpressure to personal body (slight, medium, serious injury, death), and seven damage degrees of overpressure to structures are also analyzed. The thresholds of their damage (destruction) are determined. On this basis, an experimental system and numerical simulation are constructed to measure damage characteristics, the overpressure value, and the range distance of a methane explosion with different initial explosion intensities. According to the experimental and numerical results, the attenuation formula of a methane explosion shock wave in the propagation process is derived. The research results show that the overpressure and impulse of shock waves are selected as the damage criteria for comprehensive evaluation, and the overpressure criterion is suitable of determining the injury (failure) range over long distances. The four injury ranges are in line with the actual situation and are reasonable. The injury degree also conforms to the medical results, which can be used to guide the injury degree of mine methane explosions. The injury range caused by methane explosions with different initial explosion intensities is reasonable and is basically consistent with the on-site situation. The derived attenuation formula and calculated safety distance are in good agreement with the experimental and numerical results. The research results can provide guidance and help in the escape, rescue, and protection of coal mine underground person. Full article

In conventional double-hulled submarines, the connecting structures that facilitate the linkage between the two hulls are crucial for load transmission. This paper aims to elucidate the effect of these connecting structures on resistance to shock waves generated by underwater explosions. Firstly, a self-developed numerical solver is built for the one-dimensional water-filled elastically connected double-layer plate model. The shock wave propagation characteristics, shock response of structure, water cavitation, and impact loads transmitted through the gap water and the connecting structures are analyzed quantitatively. The results reveal that the majority of the shock impulse is transmitted by the gap water if the equivalent stiffness of the connecting structures is much less than that of the gap water. Then, a three-dimensional model of the double-hulled, water-filled cylindrical shell is constructed in Abaqus/Explicit, utilizing the acoustic-structural coupling methodology. The analysis focuses on the influence of the thickness and density distribution of the connecting structures on the system’s shock response. The results indicate that a densely arranged connecting structure results in a wavy deformation of the outer hull and a notable reduction in both the impact response and strain energy of the inner hull. When the stiffness of the densely arranged connecting structure is comparatively low, the internal energy and plastic energy of the inner hull are decreased by 16.5% and 24.1%, respectively. The findings of this research are useful for assessing shock resistance and for the design of connecting structures within conventional double-hulled submarines. Full article

The paper describes the implementation of internal boundary conditions in the 1D ORSADEM hydraulic model to simulate the effect of a hydraulic in-line structure. The proposed model introduces a simplified representation of the bridge geometry by imposing an equivalent narrowing, computed according to the opening size and characteristics, combined with the mass and energy balance at the structure. The model is then applied to a series of experimental tests concerning the propagation of shock waves through different types of bridges, representing different flow conditions, from free surface flow to overflow. The tests are also simulated with the original 1D ORSADEM model, including the standard head losses and the cross-section narrowing due to the presence of a structure. The comparison with the experimental measurements shows that the proposed model can simulate the shock wave flow through the bridges with a higher accuracy than the standard formulation. These findings highlight the possibility of properly evaluating the backwater effect at bridges even with a simple 1D model if the physical narrowing of the cross-section is modeled. Full article

In the bench method of tunnel excavation, the blasting impact from upper bench blasting poses significant risks to personnel and equipment. This study employed dynamic analysis software, ANSYS/LS-DYNA, and field testing to examine the propagation characteristics and attenuation behavior of tunnel shock waves. The findings revealed that, near the central axis of the tunnel, shock wave overpressure was lower compared to areas near the tunnel wall due to reflections from the wall. As the shock wave traveled a distance six times the tunnel diameter, it transitioned from a spherical wave to a plane wave. The attenuation coefficient for the plane wave ranged from 1.03 to 1.17. A fitting formula for shock wave overpressure attenuation, based on field test results, was proposed, and it showed good agreement with the numerical simulation results. This provided valuable theoretical insights for predicting shock wave overpressure during bench method tunnel excavation. Full article

Oblique detonation waves (ODWs) are hypersonic combustion phenomena induced by oblique shock waves. When applied to air-breathing engines, ODWs offer high thermal cycle efficiency, adaptability to a wide range of flight Mach numbers, and the advantage of a short combustion chamber, making them highly promising for hypersonic propulsion applications. Despite numerous numerical studies on the heat release and multi-wave flow mechanisms of ODWs, practical applications of oblique detonation engines (ODEs) remain limited due to several technical challenges. These challenges include generating the required high-velocity test environments, achieving effective fuel and oxidant mixing, and measuring the flow field structure in hyper-velocity and high-temperature flows. These limitations hinder the development of ODEs, underscoring the importance of experimental research, particularly for understanding the initiation and propagation mechanisms of ODWs. One of the primary experimental techniques involves inducing oblique detonation using high-velocity models. This method is extensively used to study the initiation process, shock structure, initiation criteria, and ODW propagation. It is advantageous because the state of the experimental mixture is controllable, and the model state can be precisely measured. This paper reviews studies on oblique detonation induced by hyper-velocity projectiles, presenting advances in experimental methods, detonation wave structures, unsteady processes, and initiation characteristics. Additionally, we discuss the deficiencies in existing studies, noting that the current measurement methods fall short of the requirements for observing the ODW initiation process, propagation process, and fine structure. The application of advanced combustion diagnostic techniques and the exploration of the relationship between initiation processes and criteria are crucial for advancing our understanding of ODW initiation and stabilization mechanisms. Finally, we summarize the current state of experimental facilities and measurement techniques, providing suggestions for future research on the measurement of shock waves and chemical reaction zones. Full article