Shock Waves最新文献

This study aims to contribute to the understanding of imploding detonations from a numerical perspective, focusing primarily on the detailed transient and wave structures during implosion that are challenging to capture experimentally. An inviscid perfect gas model with a single-step Arrhenius reaction is employed. Imploding detonations are initiated by collisions of multiple small hot spots, and both two-dimensional circular and polygonal implosions are examined, with attention to the effects of obstacles and varying ignition pressures. For circular implosions, a slight acceleration of detonation velocity is observed at ignition, with significant acceleration occurring only in the final stages. Near the implosion center, local wave velocities exceed twice the Chapman–Jouguet velocity, yet the wave front maintains cellular instabilities until the collapse is complete. Additionally, the merging of transverse waves is observed during the implosion. In polygonal cases, a small number of “ignition edges” allows regular reflection, preserving the initial wave front geometry, while increasing the number of ignition lines leads to Mach reflection and the formation of a circular wave front. When obstacles are introduced, the detonation reflects off the obstacle, causing localized delays in the wave front that cannot be fully compensated, as transverse waves are unable to propagate sufficiently in the circumferential direction to smooth out disturbances. Similar effects are noted for implosions with non-uniform ignition pressures. It should be noted that the findings are based on a simplified model and do not account for real gas effects or additional physical processes present in actual detonation implosions.

This note introduces a novel method for mining and tunnel blasting. The new system includes a blast tube, natural accumulation biomass powder, high pressure oxygen, and a high energy ignitor. The detonation performance of sawdust was tested, demonstrating the feasibility of such a material for blasting. Subsequently, the new method was demonstrated at a blasting site for cushion blasting. Finally, the advantages of the biomass blasting technology are discussed.

Altitude can influence the propagation of shock waves and induce various pathophysiological changes due to different air pressure and oxygen levels, resulting in distinct characteristics of blast injury. This study was performed to investigate the characteristics of biological effects of blast waves at different altitudes and explore how altitude influences the characteristics of blast injuries. In total, 126 goats were exposed to blast waves at low, medium, and high altitudes while positioned at four different distances. Injury severity was quantified according to percentage of surface area contused. Blast overpressure data were collected using blast test devices placed at locations that represented the goats’ exposure. Blood gas data were collected using a portable blood gas analyzer before injury and 1, 3, 6, and 24 h after injury. Our results showed that the shock wave attenuated significantly as the distance increased ((p< 0.05)) but did not significantly change as the altitude increased. The mortality rate, lung coefficient, and blood gas indices were significantly higher among the goats at high altitude ((p< 0.05)). The injury severity gradually increased as the altitude increased ((p< 0.05)). The goats at high altitude developed more severe and prolonged injuries than at low altitude. The main mechanism involved the low air pressure, which reduced the injury threshold of air-containing organs, and the low oxygen partial pressure, which exacerbated the injury severity and duration. These results suggested that altitudes greater than 3000 m (the medical altitude) significantly influenced the blast injury severity and duration while low air pressure and low oxygen were the primary contributing factors.

An approach to combine two different equation-of-state models is described, which expands an ideal gas model to a range that captures both cryogenic and combustion conditions for any generalized mixture. This proposed model includes a real gas Helmholtz energy semi-empirical model combined with NASA thermophysical property polynomial fits that transitions to a pure ideal gas mixture model that uses only NASA polynomial fits. Capturing cryogenic and supercritical states are important for rotating detonation rocket engines that have high pressure and cryogenic inlet conditions into the combustion chamber where downstream combustion conditions can be reasonably modeled as an ideal gas. A parahydrogen and oxygen mixture is selected and presented where chosen shock tube simulations display improvements due to higher fidelity thermophysical property calculations. Operational conditions approximating the operation of NASA’s SWORDFISH engine represents one of the test cases for the shock tube study and showed that such improvements are important to consider when capturing the entire flow regime throughout its combustion chamber in a simulation. When implemented in a CFD program, this new model shows an excellent match to all selected cases of the shock tube study.

The paper is devoted to a numerical study of a new variety of shock reflection hysteresis in axisymmetrical steady supersonic flow. A converging shock wave produced by a straight ring-wedge impinges on a cylinder placed along the axis of symmetry. The converging axisymmetrical shock gradually steepens as it approaches the surface of the cylinder. It is shown that it is possible to change the incident shock angle and Mach number and traverse the dual-solution domain by expanding and contracting the axial cylinder in a quasi-steady manner. The existence of shock reflection hysteresis induced in such a manner is demonstrated with an unstructured Euler finite-volume flow solver. The values of cylinder radius, and hence incident shock angle, at which regular-to-Mach and Mach-to-regular transitions of the hysteresis loop occur, are determined and compared with the theoretical detachment and von Neumann values.

The various nonlinear effects attributed to the propagation and the interaction of an acoustical shock with a ramp are investigated in this paper. The prevalent use of linear approximations in acoustic source localization techniques is a limitation to the accurate localization prediction required in military contexts. To address this issue, our approach seeks to identify different markers of nonlinearity within the acoustical shock wave framework, enlightening their reflective characteristics and the underlying physics. This study investigates the complex interaction between a high-amplitude acoustic pulse and a ramp, focusing on the reflection patterns of an acoustical shock. In particular, the single parameter used for the reflection pattern assessment is enhanced beyond its conventional formulation. The development of an irregular reflection detection algorithm is presented and serves as a fundamental component for a spectral analysis operating Fourier decomposition enabling a reflection-type classification solely based on time-signal measurements. This work contributes to the broader understanding of acoustic shock interactions and offers insights into improving the accuracy of source localization techniques, especially in situations where linear assumptions may prove to be limited.

The present work is a numerical investigation of the influence of different microstructural characteristics on the sensitivity to shock of energetic materials. We study three energetic materials that have the same composition in terms of weight fractions of their individual constituents (RDX and wax) but markedly different microstructures and shock sensitivity. Namely, the materials are made of grains with (i) smooth grain boundaries and intra-granular defects, (ii) sharp edges and few defects, and (iii) smooth grain boundaries and very few intra-granular defects. Making use of X-ray micro-computed tomography images of the materials, we first identify and quantify morphological differences in terms of grain size distribution, grain spatial distribution, grain shape, and contact points between grains. Second, we generate representative synthetic microstructures with realistic grain shapes and controlled morphological parameters based on the segmented images. We generate virtual granular materials in two and three dimensions, with and without pores, and with different grain shapes. Third, we carry out dynamic numerical simulations of shock wave propagation on various microstructure models. In all models, points of elevated temperature (hot spots) are observed along intra-granular defects and near contact points between grains. The histograms of the computed pressure field and temperature field (albeit to a lesser extent) show differences in the tails depending on the microstructure models representing the different materials. Numerical predictions are found to be in good agreement with experimental results: the VI-RDX-based material, which is the least sensitive to shock, has the fewest hot spots, while the RS-RDX-based and RVI-RDX-based materials have similar shock sensitivities and hot spot densities. The simulations emphasize a strong influence of intra-granular defects and contact points on the sensitivity to shock for these materials.

The Chester problem (Adv. Appl. Mech. 6:119–152, 1960) introduces a quasi-one-dimensional (quasi-1D) analytical solution developed by Chester based on Chester–Chisnell–Whitham (CCW) theory (Proc. R. Soc. Lond. A 232:350–370, 1955; Lond. Edinb. Philos. Mag. 45:1293–1301, 1954; J. Fluid Mech. 2:286–298, 1957; J. Fluid Mech. 4:337–360, 1958) addressing the interaction between a steady flow within a converging–diverging duct and a shock wave entering from the converging section. Although Chester’s solution provided approximate results for both weak and strong shock waves, this study derives a solution without limitations on the shock Mach number. Additionally, experiments were conducted using a three-channel shock tube, equipped with two diaphragms with adjustable relative rupture timings, to investigate the interaction between the flow and weak shock waves (shock Mach number 1.01–1.10) in the converging section, where the lower wall is flat. The shock wave reflects off the converging upper wall; however, at particularly low shock Mach numbers, the arrival of the reflected wave at the lower wall is delayed. In such cases, the shock wave near the lower wall, which remains unaffected by duct compression, diverges from the quasi-1D solution, and the pressure behind the shock wave is reduced by the upstream co-directional flow. These findings confirm that the shock wave can be attenuated by the non-turbulent, steady upstream flow.

On the battlefield, soldiers may be injured by the detonation of explosive charges, particularly to the head. Several injury mechanisms have been proposed in the literature to explain the observed brain lesions, and numerous experiments, such as post-mortem studies, have been carried out to investigate those hypotheses. In the current study, a new skull substitute has been developed and its mechanical behaviour has been evaluated under free-field blast conditions. Instrumentation included accelerometers, strain gauges, and pressure sensors mounted in multiple positions. The substitute was embedded on a rigid mount and subjected to the detonation of 21 explosive charges. The proposed experimental campaign included seven free-field scenarios with incident pressures ranging from 75 to 200 kPa and two blast durations of 1.2 ms and 2.0 ms. The time analysis of signals revealed an “ipsi-contralateral” effect for internal pressures, i.e., an overpressure at the ipsilateral site concomitant to a depressure at the contralateral site. A slight underestimation of the first peaks versus incident pressures was also observed when compared with the literature on post-mortem human subjects. For shell strains, an overestimation of the maximum values and the first peak values versus incident pressures was attested compared to the bibliographic data. According to the current findings, the newly designed skull substitute produces results in line with post-mortem human subjects in terms of first peak strain and peak internal pressure trends. The described methodology could be applied to develop new head substitutes and, in the future, investigate injury mechanisms.

Accurate estimation of blast loads on structures is essential for reliable structural response and damage prediction. This paper introduces a novel approach to this challenge, studying the interaction between a localized blast wave and a cylindrical column. The blast wave is generated using an explosive-driven shock tube (EDST) positioned in front of the mid-span of a cylindrical column. The background-oriented schlieren technique is used to visualize the diffraction pattern of the blast wave around the column, and piezoelectric pressure gauges measure the loading distribution on its circumference. The experimental data indicate a reduction in reflected pressure of 51% and 93% at angular positions of (40^circ ) and (90^circ ) with respect to the front face of the column. Compared to the reflected pressure on a flat rigid plate under identical loading conditions, a reduction of 12% is found. Two different approaches are adopted in LS-DYNA to simulate the blast wave generation and progression within the EDST and around the column. The numerical results show a good agreement with the measured data and allow the selection of the most efficient finite element approach regarding CPU time.