A model designed to predict the motion of objects translated by classical blast waves
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It will be shown that a combination of single element detectors and simple optics in an appropriate configuration is a capable solution. Blast wave mitigation by dry aqueous foams. This paper presents results of experiments and numerical modeling on the mitigation of blast waves using dry aqueous foams. The multiphase formalism is used to model the dry aqueous foam as a dense non-equilibrium two-phase medium as well as its interaction with the high explosion detonation products.
New experiments have been performed to study the mass scaling effects. The experimental as well as the numerical results, which are in good agreement, show that more than an order of magnitude reduction in the peak overpressure ratio can be achieved.
The positive impulse reduction is less marked than the overpressures. The Hopkinson scaling is also found to hold particularly at larger scales for these two blast parameters. Furthermore, momentum and heat transfers, which have the main dominant role in the mitigation process, are shown to modify significantly the classical blast wave profile and thereafter to disperse the energy from the peak overpressure due to the induced relaxation zone. In addition, the velocity of the fireball, which acts as a piston on its environment, is smaller than in air.
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Moreover, the greater inertia of the liquid phase tends to project the aqueous foam far from the fireball. The created gap tempers the amplitude of the transmitted shock wave to the aqueous foam. As a consequence, this results in a lowering of blast wave parameters of the two-phase spherical decaying shock wave.
Muzzle Blast Amplification.
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Army Ballistic Research Laboratory, Aberdeen Schmidt, E. Gion, and D. Blast waves and how they interact with structures. The paper defines and describes blast waves , their interaction with a structure and its subsequent response. Explosions generate blast waves , which need not be due to explosives.
A blast wave consists of two parts: a shock wave and a blast wind. The paper explains how shock waves are formed and their basic properties. The physics of blast waves is non-linear and therefore non-intuitive. To understand how an explosion generates a blast wave a numerical modelling computer code, called a hydrocode has to be employed.
This is briefly explained and the cAst Eulerian hydrocode is used to illustrate the formation and propagation of the blast wave generated by a 1 kg sphere of TNT explosive detonated 1 m above the ground. The paper concludes with a discussion of the response of a structure to a blast wave and shows that this response is governed by the structures natural frequency of vibration compared to the duration of the blast wave.
The basic concepts introduced are illustrated in a second simulation that introduces two structures into the blast field of the TNT charge. Computation of viscous blast wave flowfields. A method to determine unsteady solutions of the Navier-Stokes equations was developed and applied.
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The structural finite-volume, approximately factored implicit scheme uses Newton subiterations to obtain the spatially and temporally second-order accurate time history of the interaction of blast-waves with stationary targets. The inviscid flux is evaluated using MacCormack's modified Steger-Warming flux or Roe flux difference splittings with total variation diminishing limiters, while the viscous flux is computed using central differences.
The use of implicit boundary conditions in conjunction with a telescoping in time and space method permitted solutions to this strongly unsteady class of problems. Comparisons of numerical, analytical, and experimental results were made in two and three dimensions. These comparisons revealed accurate wave speed resolution with nonoscillatory discontinuity capturing. The purpose of this effort was to address the three-dimensional, viscous blast-wave problem. Test cases were undertaken to reveal these methods' weaknesses in three regimes: 1 viscous-dominated flow; 2 complex unsteady flow; and 3 three-dimensional flow.
Comparisons of these computations to analytic and experimental results provided initial validation of the resultant code. Addition details on the numerical method and on the validation can be found in the appendix. Presently, the code is capable of single zone computations with selection of any permutation of solid wall or flow-through boundaries. The scaling and similarity laws concerning the propagation of isolated spherical blast waves are briefly reviewed.
Both point source explosions and high pressure gas explosions are considered. Test data on blast overpressure from the interaction and coalescence of spherical blast waves emanating from explosives in the form of shaped charges of different strength placed in the vicinity of a solid propellant stack are presented. The results point out the possibility of detecting source explosions from far-field pressure measurements.
Reactive Blast Waves from Composite Charges. Investigated here is the performance of composite explosives - measured in terms of the blast wave they drive into the surrounding environment. Afterburning of the booster detonation products with air also enhances and promotes the Al-air combustion process. Pressure waves from such reactive blast waves have been measured in bomb calorimeter experiments.
Here we describe numerical simulations of those experiments.
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- A Model Designed To Predict The Motion Of Objects Translated By Classical Blast Waves.
A Heterogeneous Continuum Model was used to model the dispersion and combustion of the Al particle cloud. It combines the gasdynamic conservation laws for the gas phase with a dilute continuum model for the dispersed phase, as formulated by Nigmatulin.
Inter-phase mass, momentum and energy exchange are prescribed by phenomenological models of Khasainov. The model takes into account both the afterburning of the detonation products of the booster with air, and the combustion of the Al particles with air. The model equations were integrated by high-order Godunov schemes for both the gas and particle phases. Adaptive Mesh Refinement AMR was used to capture the energy-bearing scales of the turbulent flow on the computational grid, and to track. Characterising the acceleration phase of blast wave formation.
Fox, T. Intensely heated, localised regions in uniform fluids will rapidly expand and generate an outwardly propagating blast wave.
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The Sedov-Taylor self-similar solution for such blast waves has long been studied and applied to a variety of scenarios. A characteristic time for their formation has also long been identified using dimensional analysis, which by its very nature, can offer several interpretations. We propose that, rather than simply being a characteristic time, it may be interpreted as the definitive time taken for a blast wave resulting from an intense explosion in a uniform media to contain its maximum kinetic energy.
Ebook A Model Designed To Predict The Motion Of Objects Translated By Classical Blast Waves 1961
We study the close-in blast waves created by the detonation of spherical high explosives HE charges, via numerical simulations with our Arbitrary-Lagrange-Eulerian ALE3D code. The thermodynamic properties of the detonation products and air were specified by the Cheetah code. A programmed-burn model was used to detonate the charge at a rate based on measured detonation velocities.
A variety of explosives were studied. Conclusions are: i close-in R blast wave e. Scaling laws will be proposed for such close-in blast waves. Rock fragmentation by blasting is determined by the level and state of stress in the rock mass subjected to blasting. With the application of electronic detonators, some researchers stated that it is possible to achieve improved fragmentation through stress wave superposition with very short delay times.
This hypothesis was studied through theoretical analysis in the paper. First, the stress in rock mass induced by a single-hole shot was analyzed with the assumptions of infinite velocity of detonation and infinite charge length. Based on the stress analysis of a single-hole shot, the stress history and tensile stress distribution between two adjacent holes were presented for cases of simultaneous initiation and 1 ms delayed initiation via stress superposition. The results indicated that the stress wave interaction is local around the collision point.
Then, the tensile stress distribution at the extended line of two adjacent blast holes was analyzed for a case of 2 ms delay.