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71.
A two-phase model based upon principles of continuum mixture theory is numerically solved to predict the evolution of detonation
in a granulated reactive material. Shock to detonation transition (SDT) is considered whereby combustion is initiated due
to compression of the material by a moving piston. In particular, this study demonstrates the existence of a SDT event which
gives rise to a steady two-phase Chapman-Jouguet (CJ) detonation structure consisting of a single lead shock in the gas and
an unshocked solid; this structure has previously been independently predicted by a steady-state theory. The unsteady model
equations, which constitute a non-strictly hyperbolic system, are numerically solved using a modern high-resolution method.
The numerical method is based on Godunov's method, and utilizes an approximate solution for the two-phase Riemann problem.
Comparisons are made between numerical predictions and known theoretical results for 1) an inert two-phase shock tube problem,
2) an inert compaction wave structure, and 3) a reactive two-phase detonation structure; in all cases, good agreement exists.
Received 4 August 1995 / Accepted 17 February 1996 相似文献
72.
James K. Knowles 《Mechanics Research Communications》2003,30(6):581-587
In uniaxial tension, the stress–strain curve for rubber changes curvature from concave to convex as the strain increases. For sudden tensile loading of a bar, a one-dimensional model that reflects this behavior leads to an under-determined problem reminiscent of that arising in materials capable of undergoing phase transitions. In the latter setting, adding the kinetic relation underlying the phase change to the conventional statement of the problem removes the indeterminacy; the same is true when such a relation is used in a formal way in the problem for rubber. This presents a physical question: What is the evolutionary process at the microscale whose kinetics are needed in the dynamics of rubber? 相似文献
73.
Dynamics of oblique detonations in ram accelerators 总被引:2,自引:0,他引:2
Time-accurate numerical simulations are used to study the dynamic development of oblique detonations on accelerating projectiles
in ram accelerators. These simulations show that the oblique detonation can be stabilized on the projectile. The high pressure
generated behind the detonation can result in accelerations up to 106G and propel the projectile to velocities higher than 4.0 km/s. The detonation structure on the projectile is sensitive to
the projectile geometry. A small change in the projectile shape is sufficient to alter the overall detonation structure and
significantly affect the pressure distribution on the projectile. In order to maximize the thrust, an appropriate projectile
shape has to be chosen to generate the detonation structure just behind the widest part of the projectile body. The projectile
acceleration also has strong effects on the flow field and the detonation structure. During the acceleration, the location
of the oblique detonation moves upstream from one reflected shock to another. However, one the detonation is stabilized behind
the upstream shock, it remains at the new location until the transition to the next upstream shock occurs. In the simulations,
the Non-Inertial-Source (NIS) technique was used to accurately represent of the projectile acceleration. Also, the Virtual-Cell-Embedding
(VCE) method was employed to efficiently treat the complex projectile geometry on cartesian grids. 相似文献
74.
Background oriented schlieren for flow visualisation in hypersonic impulse facilities 总被引:1,自引:0,他引:1
Experiments to demonstrate the use of the background-oriented schlieren (BOS) technique in hypersonic impulse facilities are
reported. BOS uses a simple optical set-up consisting of a structured background pattern, an electronic camera with a high
shutter speed and a high intensity light source. The visualization technique is demonstrated in a small reflected shock tunnel
with a Mach 4 conical nozzle, nozzle supply pressure of 2.2 MPa and nozzle supply enthalpy of 1.8 MJ/kg. A 20° sharp circular
cone and a model of the MUSES-C re-entry body were tested. Images captured were processed using PIV-style image analysis to
visualize variations in the density field. The shock angle on the cone measured from the BOS images agreed with theoretical
calculations to within 0.5°. Shock standoff distances could be measured from the BOS image for the re-entry body. Preliminary
experiments are also reported in higher enthalpy facilities where flow luminosity can interfere with imaging of the background
pattern.
A version of this paper was presented at the 25th International Symposium on Shock Waves in Bangalore in July 2005. 相似文献
75.
Two problems of heterogeneous media mechanics are investigated in the paper. The first one, concerned with the shock wave/dust layer interaction, is solved within the framework of the equilibrium model of heterogeneous media mechanics. The second problem deals with the simulation of a Riemann problem for a stratified layer of solid particles.This paper is based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive Systems, Montreal, Canada, July 31–August 5, 2005 相似文献
76.
Absolute intensity measurements of impurity emissions in a shock tunnel nozzle flow are presented. The impurity emission intensities were measured with a photomultiplier and optical multichannel analyser and calibrated against an intensity standard. The various metallic contaminants were identified and their intensities measured in the spectral regions 290 to 330 nm and 375 to 385 nm. A comparison with calculated fluorescence intensities for predissociated laser-induced fluorescence signals is made. It is found that the emission background is negligible for most fluorescence experiments.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
77.
The purpose of this paper is to report the blast loading characteristics resulting from the detonation of a stoichiometric
propane–oxygen mixture, and to validate the approach which relies on simulating TNT explosions at large scale by small-scale
experiments of gaseous explosions. Several dimensionless correlations are obtained from experimental data. These relationships
allow determination of the parameters of a blast wave interacting with a structure as a function of the positions of the explosive
charge and the structure. Simulations carried out with the Autodyn code show good correlation with experimental results. The
Hopkinson law is suggested to predict the blast wave’s parameters at large scale on the basis of small-scale experiments and
simulations.
This paper was based on work that was presented at the 20th International Colloquium on the Dynamics of Explosions and Reactive
Systems, Montreal, Canada, July 31–August 5, 2005. 相似文献
78.
A new device to prevent erroneously focused shock waves to the renal parenchyma during extracorporeal shock wave lithotripsy (ESWL) has been developed; an anti-miss-shot control device (AMCD) and experiments have been conducted to evaluate its effectiveness. For shock wave generation and stone localization, piezoceramic elements (PSE) and ultrasound localization, respectively were used. After stone localization, probing ultrasounds (PU) were emmitted from the PSE towards the focal region and the reflected sound levels (RSL) were monitored by the PSE which also functioned as a microphone. A direct hit by the PU to the stone or a miss was judged from the RSL, i.e. a high RSL indicates a direct hit and a low RSL indicates a miss. Shock waves were generated only when the RSL exceeded the level which indicated a direct hit. The experimental results showed that the injury to the renal parenchyma was decreased by using the AMCD. Clinical application of the AMCD is expected to increase the safety of ESWL.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
79.
It has been shown that pressure waves can have a large effect on the burning rate of flames. In this paper, the evolution
of convection-driven fast flame, which is acoustically linked to a shock wave via an induction zone, is examined in detail.
It is found that there is positive feedback mechanism and the asymptotic model breaks down as blow up occurs. Comparison
is made between the case of a piston driving a shock wave into a combustible atmosphere with these studies of a shock wave
passing through an existing premixed flame.
Received 4 August 1995 / Accepted 20 March 1996 相似文献
80.
A numerical parametric study of the flow field which develops when a planar shock wave impinge on a rigid porous material
is presented. This study complements an earlier study (Levy et al. 1996a) where the values of some dominating parameters were
estimated and the dependence of the resulting flow field on these values was not checked.
Received 22 April 1996 / Accepted 5 January 1997 相似文献