Shock Waves最新文献

The 2020 Beirut port’s ammonium nitrate explosion led to the most severe damage, in terms of human lives and property loss, ever seen in the history of Beirut, the capital of Lebanon. The current study focuses on the blast damage of tall buildings near the explosion site and analyses the overpressure/distance relationship based on the comparison between theoretical calculations, the blast damage scale from the SFPE Handbook of Fire Protection Engineering, and real post-explosion images. The estimated trinitrotoluene equivalent blast size for the research is assumed to be 713 tons. Six tall buildings at different distances were included in the research and divided into categories. Theoretical overpressure models of Baker’s, Sadovski’s, and Alonso’s methods and Blast Operational Overpressure Model were used in combination with the Kingery–Bulmash Blast Parameter online calculator. A wide range of overpressure values were observed. The calculated values from the theoretical overpressure models were incorporated into the blast damage scale and compared with the real images, with the better match being mainly demonstrated for buildings at closer distances.

The imperfection of shock-reloading experiments has become the main obstacle to measuring the dynamic yield strength of materials under shock compression within the framework of the self-consistent strength-measuring method. In this work, we report an improved shock-reloading technique, in which additional layers of high-hardness materials are used as the backing of the two-layer impactor to eliminate the impactor’s distortion and thus overcome the long-standing debonding issue during launching. This technique has the merits of easy accessibility, no modification of material properties, and being applicable to any materials, therefore providing a practicable and reliable way to obtain high-quality reloading data. As a demonstration, we adopt this technique to shock-reloading experiments in aluminum up to 71 GPa and record high-quality particle-velocity profiles with the details of the quasi-elastic reloading from the initial shocked state. The dynamic yield strengths are then determined using the self-consistent method and found to be consistent with data available in the literature.

In recent years, several studies have been dedicated to modeling of detonations including assumptions of thermal non-equilibrium. Modeling using two-temperature models has shown that non-equilibrium affects detonation dynamics. However, the deployment of state-to-state models, one of the foremost non-equilibrium modeling tools, in detonation modeling remains under-explored. In this work, we detail the implementation of a STS model of ({hbox {N}_{2}}) and ({hbox {O}_{2}}) in a Zel’dovich–von Neumann–Döring reactor for a mixture of ({hbox {H}_{2}})–air. Certain modifications to the usual theory and models must be performed before the deployment of aforementioned model, namely in the thermodynamics formulation. Additionally, since most codes are not compatible with STS models, a validation of an in-house code is carried out against CHEMKIN. Results indicate that the multi-temperature approach adopted in earlier works is likely not appropriate to model the internal distribution function of ({hbox {O}_{2}}) and therefore should be used with caution. A comparison of an estimated cell width with experimental values confirms the potential of the STS framework for a more accurate detonation modeling.

In this paper, we present results from spontaneous ignition of aluminium particle clouds in a series of shock tube experiments. For all experiments, the shock propagates along a narrow pile of 40-(upmu )m aluminium particles. The study includes shock Mach numbers in the range from 1.51 to 2.38. The results are visualised using photographic techniques and pressure gauges. The combination of two Phantom high-speed video cameras and a beamsplitter allows a compact schlieren setup mounted together with a dark-film high-speed camera. While the schlieren technique allows the shock features to be identified, the dark-film camera is used to capture the ignition and burning of the aluminium particle clouds. Based on extensive image processing and shock tube relations for reflected shocks, spontaneous ignition of the aluminium particle cloud is found to take place for reflected shock gas temperatures above 635 K. For increasing Mach numbers, we find a decreasing trend for the ignition delay. Additionally, the burning time is observed to decrease with increasing Mach number, indicating that the burning process is more efficient with increasing gas temperature.

We describe the implementation of several thermo-chemical analyses in Cantera and the Shock and Detonation Toolbox (SDT), that can be employed to investigate the chemical dynamics of planar steady detonation. A MATLAB graphical user interface has also been developed to post-process the data provided by the detonation codes. These utilities will be made available on request and in the future releases of the SDT.

In this paper, we provide the experimental evidence of a free-standing conical shock and the compressive confocal characteristics region in the Busemann intake flow. The experiments are carried out in the DRDC Trisonic Wind Tunnel at freestream Mach number 3.0 with a Busemann ring model. The Taylor-McColl equations are integrated to obtain the Busemann streamline and hence the inner surface of the Busemann ring. The CFD analysis of the flow using a locally adaptive unstructured Euler finite-volume code is in agreement with the experiments.

An experimental investigation of the shock wave structure, Hugoniot states, and spall strength of a shock-compressed porous carbon fiber–epoxy composite was conducted. To generate high dynamic pressures in the material, the impact of flat-plate aluminum projectiles accelerated by explosive planar shock wave generators to velocities ranging from 0.65 to 5.05 km/s was used. Particle velocity profiles were recorded on the composite surface–water window interface with a multichannel VISAR laser interferometer. On the velocity profiles for the composite with a transverse fiber orientation, a single shock wave was recorded, while for the parallel orientation, a two-wave structure was observed. It was found that the shock wave compressibility of the porous composite did not depend on the fiber orientation relative to the direction of shock wave propagation. A kink on the Hugoniot curve was observed at the pressure of 19 GPa. The results obtained for the porous composite were compared with data for a non-porous carbon–epoxy composite and epoxy resin used as a matrix in the composites. When analyzing dynamic fracture of the porous composite under shock compression, it was found that the spall strength of the material was significantly lower than that of epoxy resin.

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.

The differences of flow characterization at the different stages of flame acceleration and transition to detonation in tubes with smooth walls, solid obstacles, and fluid jets are studied, especially the effects of flow instabilities on the process. The two-dimensional viscous unsteady reactive Navier–Stokes equations with a detailed chemistry model are solved numerically based on the structured adaptive mesh refinement technique in Adaptive Mesh Refinement Object-oriented C(++). During the ignition to a low-speed flame stage, it is found that initial pressure wave interactions with the wall and Rayleigh–Taylor instabilities, induced by the density and pressure gradient misalignment between the ignition region and unburned gas, accelerate the wrinkling and deformation of the flame surface. Consequentially, the flame wrinkles trigger Darrieus–Landau instabilities and as a result the flame accelerates. At the main acceleration stage, the Kelvin–Helmholtz instability formed in the wake of solid obstacles and the strong Kelvin–Helmholtz instability caused by the jets lead to the formation of strong turbulent structures in the flowfield and accelerate the flame propagation. Richtmyer–Meshkov instabilities caused by the interactions of reflected shock waves and the flame surface lead to flame acceleration in the case with solid obstacles. Compared to the tube with fluid jets, although the solid obstacles induce stronger Richtmyer–Meshkov instabilities, the effect of Kelvin–Helmholtz instabilities is not obvious. In general, Darrieus–Landau instabilities and Rayleigh–Taylor instabilities dominate at the initial flame-developing stage, and Kelvin–Helmholtz instabilities and Richtmyer–Meshkov instabilities play a more critical role in the flame acceleration due to interactions of the flame, the shock, solid obstacles, and vortices during the deflagration propagation stage.