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1.
A Free-Lagrange method for unsteady compressible flow: simulation of a confined cylindrical blast wave 总被引:1,自引:0,他引:1
G. J. Ball 《Shock Waves》1996,5(5):311-325
A Free-Lagrange numerical procedure for the
simulation of two-dimensional inviscid compressible flow
is described in detail. The
unsteady Euler equations are solved on an unstructured
Lagrangian grid based on a density-weighted Voronoi mesh.
The flow solver is of the Godunov type, utilising either the
HLLE (2 wave) approximate Riemann solver or the more recent HLLC
(3 wave) variant, each adapted to the Lagrangian frame.
Within each mesh cell, conserved properties are
treated as piece-wise linear, and a slope limiter of the MUSCL type
is used to
give non-oscillatory behaviour with nominal
second order accuracy in space.
The solver is first order accurate in time.
Modifications to the slope limiter to minimise
grid and coordinate dependent
effects are described.
The performances of the HLLE and HLLC solvers are compared for
two test problems; a one-dimensional
shock tube and a two-dimensional blast wave confined
within a rigid cylinder. The blast wave is initiated by impulsive
heating of a gas column whose centreline is parallel to,
and one half of the cylinder radius from,
the axis of the cylinder.
For the shock tube problem, both solvers predict shock and expansion
waves in good agreement with theory.
For the HLLE solver, contact resolution
is poor, especially in the blast wave problem. The HLLC solver achieves
near-exact contact capture in both problems.
Received May 25, 1995 / Accepted September 11, 1995 相似文献
2.
Shock wave attenuation by grids and orifice plates 总被引:2,自引:0,他引:2
The interaction of weak shock waves with porous barriers of different geometries and porosities is examined. Installing a barrier inside the shock tube test section will cause the development of the following wave pattern upon a head-on collision between the incident shock wave and the barrier: a reflected shock from the barrier and a transmitted shock propagating towards the shock tube end wall. Once the transmitted shock wave reaches the end wall it is reflected back towards the barrier. This is the beginning of multiple reflections between the barrier and the end wall. This full cycle of shock reflections/interactions resulting from the incident shock wave collision with the barrier can be studied in a single shock tube test. A one-dimensional (1D), inviscid flow model was proposed for simulating the flow resulting from the initial collision of the incident shock wave with the barrier. Fairly good agreement is found between experimental findings and simulations based on a 1D flow model. Based on obtained numerical and experimental findings an optimal design procedure for shock wave attenuator is suggested. The suggested attenuator may ensure the safety of the shelter’s ventilation systems. 相似文献
3.
A numerical study of the interaction of plane blast waves with a cylinder is presented. Computations are carried out for
various blast-wave durations and comparisons are obtained with the corresponding results of planar shock-wave. Both inviscid
and viscous results based on the solution of the Euler and Navier-Stokes equations are presented. The equations are solved
by an adaptive-grid method and a second-order Godunov scheme. The shock wave diffraction over the cylinder is investigated
by means of various contour plots, as well as, pressure and skin-friction histories. The study reveals that the blast-wave
duration significantly influences the unsteady flow over the cylinder. The differences between the viscous and inviscid results
are also discussed.
Received 2 March 1996 / Accepted 28 February 1997 相似文献
4.
A simple two-dimensional square cavity model is used to study shock attenuating effects of dust suspension in air. The GRP
scheme for compressible flows was extended to simulate the fluid dynamics of dilute dust suspensions, employing the conventional
two-phase approximation. A planar shock of constant intensity propagated in pure air over flat ground and diffracted into
a square cavity filled with a dusty quiescent suspension. Shock intensities were and , dust loading ratios were and , and particle diameters were and {\rm \mu}$m. It was found that the diffraction patterns in the cavity were decisively attenuated by the dust suspension, particularly
for the higher loading ratio. The particle size has a pronounced effect on the flow and wave pattern developed inside the
cavity. Wall pressure histories were recorded for each of the three cavity walls, showing a clear attenuating effect of the
dust suspension.
Received 15 November 1999 / Accepted 25 October 2000 相似文献
5.
B. E. Gelfand A. M. Bartenev S. P. Medvedev A. N. Polenov S. V. Khomik M. Lenartz H. Grönig 《Shock Waves》1994,4(3):137-143
On the basis of numerical modeling specific features of shock wave reflections were analyzed. It was found, that after diaphragm rupture self-modeling pressure and velocity distributions nearby the shock front establish. But in some special cases the temperature behind the shock front can rise. This peculiarity should be taken into account when performing experiments with high reactive gaseous mixtures. The temperature on the shock front and the velocity gradient behind it are uniform in the case of strong blast wave reflections. This effect is observed in the zone with an elevated temperature profile behind the incident blast wave. The reflected triangular waves conserve a quasi-self-modeling character by pressure. Typical experiments were carried out to verify the theoretical predictions. The effects of reflected wave acceleration in the case of triangular waves and the self-similar character of the pressure profiles were observed.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
6.
Effects of viscosity and vibrational nonequilibrium on the profile of a weak, spherical N-wave in air are experimentally and numerically studied. Weak blast waves were generated, in a quiescent air dome, by spark discharges and exploding wires and observed by high frequency response microphones over 40 meters. Some similarity relationships were obtained from the blast wave experiments. For observed N-waves having less than 100 Pa peak overpressure, the peak overpressure p
f
and the duration of the positive phaset
d+
are found to vary with the radial distance from the sourcer as p
f
r
–1.38 andt
d
+ r
0.19, whilst the rise time of the blast wave t
f
linearly increases with distance. Similar trends were also found for the negative phase of the blast wave. Numerical simulations were carried out to compare with the blast wave data. The Navier-Stokes equations for spherical symmetric flows were solved by coupling with a relaxation equation for vibrational excitation of oxygen using the random choice method (RCM) adapted to supercomputing with an operator splitting technique. The resultant N-wave profiles are in good agreement with the experimental results. The numerical results clearly indicate that the wave-easing process due to the dispersive effect of vibrational relaxation plays a dominant role in determining the rise time of the N-wave.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
7.
This paper discusses gas-dynamic aspects of intense explosions in uniform environments. In experiments, the energy of a laser
is almost instantaneously released in a volume of air shaped as either a flattened or stretched cylinder generating a blast
wave. Its shape evolves in time and ultimately becomes spherical. But momentum transferred to the air when the blast wave
is strongly nonspherical is anisotropic. As a result, a subsonic jet and a vortex are induced and propagate along the symmetry
axis or along the perpendicular plane, depending on the initial configuration of the blast wave. Simulations based on a free-Lagrangian
method for a nonviscous gas are in good agreement with the experiments. Velocities, circulation, and positions of fluid particles
found in computations give an insight into the causes and details of the flow. Two simultaneous and contrary processes take
place – vorticity production by the anisotropic shock wave and baroclinical generation of vorticity at the boundary of the
heated gas – which give rise to net circulation.
Received 21 April 1997 / Accepted 27 June 1997 相似文献
8.
Saito T. Marumoto M. Yamashita H. Hosseini S.H.R. Nakagawa A. Hirano T. Takayama K. 《Shock Waves》2003,13(2):139-148
The attenuation of an underwater shock wave by a thin porous layer is studied both experimentally and numerically. The shock waves are generated by exploding 10 mg silver azide pellets and the pressures at different distances from the explosion center are measured. Measurements are also carried out with a gauze layer placed between the explosion source and the pressure gauge. The results with and without the gauze layer are compared evaluating the shock wave attenuation. Numerical simulations of the phenomenon are also carried out for a simple wave attenuation model. The results are compared with the experimental data. Despite the simple mathematical model of wave attenuation, the agreement between the experimental and numerical results is reasonable.Received: 22 October 2002, Accepted: 17 June 2003, Published online: 5 August 2003PACS:
47.11.+j, 47.40.Nm, 47.55.Mh 相似文献
9.
Numerical investigations on the launch process of a projectile in a nearly realistic situation have been performed in this
article. The Arbitrary Lagrangian–Eulerian (ALE) of Euler equations is solved by the AUSMDV scheme and the dynamic chimera
grid technique are used for describing the moving of the projectile. Based on our numerical results, the muzzle blast flow
field of the transient launch process of a projectile at a relative high Mach number of 3.0 has been visualized numerically,
and the prominent characteristics including the propagation of first and second blast waves, the generation of bow shock wave
and moving of the projectile, etc. have been discussed in detail.
相似文献
10.
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. These data are discussed with regard to the scaling laws concerning
the decay of blast overpressure. The results point out the possibility of detecting source explosions from far-field pressure
measurements.
相似文献
11.
对混凝土、岩石类脆性材料的层裂实验进行了有限元模拟,研究了应力波在此类材料中传播的衰减规律,包括两类机制:弹性波因大尺寸试样的几何弥散产生的小幅度线性衰减、与应变率相关的黏塑性波因本构关系导致的指数衰减。在此基础上,提出了包含常数项的指数型应力波峰值拟合公式。建议采用可以忽略应力波衰减影响的细长形试样进行层裂实验。混凝土类脆性材料层裂破坏模拟结果显示,有限元模拟得到的层裂片厚度与一维应力波理论得到的结果非常吻合,验证了按一维应力波理论确定层裂强度的实验方法的有效性。通过对比3种不同入射波形下层裂片的形状和净拉应力波形,发现不对称的入射波形状更有利于实验获得平直的层裂断面和较准确的层裂强度。 相似文献
12.
Constitutive modeling of aluminum foam including fracture and statistical variation of density 总被引:1,自引:0,他引:1
A. Reyes O. S. Hopperstad T. Berstad A. G. Hanssen M. Langseth 《European Journal of Mechanics - A/Solids》2003,22(6):89-835
An existing constitutive model applicable for aluminum foam was evaluated. The model was implemented in LS-DYNA, and several test cases were analyzed and compared to experimental data. The numerical analyses consisted of foam subjected to both simple and more complex loading conditions where fracture was of varying importance. Therefore, simple fracture criteria were added to the model. Additionally, the inhomogeneities in the foam were modeled by incorporating the possibility of statistical variation of the foam density. The implemented model is efficient and robust, and gives satisfactory results compared with the experimental results. 相似文献
13.
Particle dispersal by blast waves is an interesting phenomenon. A model problem, i.e., a sudden release of a compressed gas–particle mixture contained in a spherical container, is employed to investigate the fundamental physics of particle dispersal. The problem is simulated by the multiphase flow models proposed in Part 1 of this article that include unsteady contributions in momentum and energy exchange between gas and particles. At early times, when particles are accelerated in the expansion fan, unsteady force and heating contributions are much larger than the corresponding quasi-steady contributions. Consequently, neglecting unsteady contributions leads to significant errors in particle front location (the boundary of the particle cloud). The complex wave interactions in the flow have strong influence on the particle motion. As a result, the particle motion is a non-monotonic function of particle density or diameter and the evolution of particle concentration is non-uniform and unsteady. 相似文献
14.
A Free-Lagrange CFD code is used to simulate the collapse of a cylindrical air cavity in water by a 1.9 GPa incident shock.
The Lagrangian treatment allows the air/water interface to be tracked throughout the interaction. The incident shock is partially
transmitted into the cavity, within which it experiences multiple reflections. The upstream cavity wall involutes to form
a high-speed jet which, on impact with the far cavity wall, produces an intense blast wave. Heating of the gas within the
cavity is highly non-isentropic, and is dominated by shock heating. The predicted final gas temperature is of order 12000
K, although the modelling assumptions used here lead to over-prediction of temperature during the later stages of collapse.
Received 14 September 1999 / Accepted 28 June 2000 相似文献
15.
16.
借助极化偏振分析方法,针对一组现场爆破实验,分析了水平光面爆破激发地震波的成分构成及特性,比较了不同波的衰减特征及各自对爆破振动的影响,并探讨了水平光面爆破的内在力学机理。结果表明,爆破振动中不同波的相对量值及主导波的类型均会随测点位置的改变而变化,爆源特性和沿传播路径的不同衰减共同决定波的成分构成及演化,各测点的优势振动方向也与波的成分构成密切相关。对于水平光面爆破,在光爆孔平面上,P波的影响可忽略,S波主要在竖直向振动,R波对水平及竖直向的振动均有贡献,其中水平向的振动主要由R波引起,而S波的竖直向振速在近区远高于R波,但归因于S和R波的不同衰减,R波在距离爆源22.5 m/kg^1/2(58~67 m)处开始主导竖直向的振动;在光爆孔平面外,P波的影响不可忽略,且在特定位置会成为优势波型。 相似文献
17.
The objective of this study is to understand the flow structures of weak and strong spherical blast waves either propagating
in a free field or interacting with a flat plate. A 5th-order weighted essentially non-oscillatory scheme with a 4th-order
Runge-Kutta method is employed to solve the compressible Euler/Navier-Stokes equations in a finite volume approach. The real-gas
effects are taken into account when high temperature occurs. A shock-tube problem with the real-gas effect is first tested
in order to verify the solver accuracy. Moreover, unsteady shock waves moving over a stationary wedge with various wedge angles,
resulting in different types of shock wave reflections, are also tested. It is found that the computed results agreed well
with the existing data. Second, the propagation of a weak spherical blast wave, created by rupture of a high-pressure isothermal
sphere, in a free field is studied. It is found that there are three minor shock waves moving behind the main shock. Third,
the problem of a strong blast wave interacting with a flat plate is investigated. The flow structures associated with single
and double Mach reflections are reported in detail. It is found that there are at least three local high-pressure regions
near the flat plate.
Received 27 July 2000 / Accepted 25 January 2002 – Published online 17 June 2002 相似文献
18.
In the Shock Wave Journal Vol. 2, No. 4 a benchmark test for shock wave reflection over wedges was announced. International
scientists who are interested in shock wave research were invited to participate. The benchmark test aimed at comparison of
various advanced numerical schemes as well as experimental results. During the last three years more than twenty results,
including both CFD and experiments, were collected from all over the world. Efforts contributed by these scientists made the
present benchmark test reach to a standard of the state of the art of the computational fluid dynamics applied to the shock
wave research. However, it was regrettable not to publish all the results collected due to limitation on the available page
number.
Received 5 November 1994 / Accepted 9 September 1996 相似文献
19.