共查询到20条相似文献，搜索用时 350 毫秒
1.
This paper deals about pure hydrodynamic and radiation hydrodynamic codes developed at LUTH, dedicated to astrophysical simulations.
The studied phenomena in this area are often encountered at high Mach number and in a radiation regime where no a priori assumption can be made on the radiation transfer. The radiative hydrodynamic code HADES has to can perform simulations as
well as any optical depths, from smallest to highest. Validation of numerical schemes or physical assumptions will be made
by laboratory astrophysical experiments. Therefore a very wide domain of initial conditions has to be accepted for computing.
A succinct presentation of three codes is done, accompanied with some astrophysical applications. 相似文献
2.
A. Dizi��re C. Michaut M. Koenig C. D. Gregory A. Ravasio Y. Sakawa Y. Kuramitsu T. Morita T. Ide H. Tanji H. Takabe P. Barroso J.-M. Boudenne 《Astrophysics and Space Science》2011,336(1):213-218
In this paper, recent results obtained on highly radiative shocks generated in a xenon filled gas cell using the GEKKO XII laser facility are presented. Data show extremely high shock velocity (??150 km/s) never achieved before in gas. Preliminary analyses based on theoretical dimensionless numbers and numerical simulations suggest that these radiative shocks reach a new radiative regime where the radiative pressure plays a role in the dynamics and structure of the shock. A major effect observed is a strong anisotropic emission in the downstream gas. This unexpected feature is discussed and compared to available 2D radiation hydrodynamic simulations. 相似文献
3.
R. Paul Drake 《Astrophysics and Space Science》2005,298(1-2):49-59
This paper explores the variations in radiative shock behavior originating from the properties of the system containing the
shock. Specifically, the optical depth of the upstream region and the downstream region both affect the behavior of radiative
shocks. Optically thick systems such as stellar interiors or supernovae permit only limited shock-induced increases in density.
At the other limit, the radiation and shock dynamics in optically thin systems permits the post-shock density to reach arbitrarily
large values. The theory of the shock structure is summarized for systems in which the upstream region is optically thin,
common to some astrophysical systems and a number of experiments. 相似文献
4.
Abstract— The localized appearance of specific shock features in target rocks and meteorites such as melt veins and high pressure polymorphs suggests that regions with a local increase in pressure and temperature exist as a shock wave propagates through an inhomogeneous rock. In this paper, we investigate the effect of planar fissures on the local temperature distribution using numerical simulations. Time‐dependent parameters such as temperature, pressure, and displacement are evaluated. The simulation model is based on a shock equation of state for the involved materials, dunite and quartzite, and simulates geometries that were also used in shock‐loading experiments. An artificial gap between the materials simulates an open fissure at the interface. A strong temperature increase occurs at a gap size of 0.1 mm, which potentially can cause melting in a thin layer at the interfaces. The temperature decreases with decreasing gap size. Temperature and pressure excursions at the interface are induced by the closure of the gap, which causes a second shock wave to superpose the primary wave. Open fissures and fractures, which occur ubiquitously in shallow‐buried target rocks and projectiles, thus, act as local pressure and temperature amplyfiers and may be responsible for thin melt vein formation in shocked rocks. 相似文献
5.
The Vishniac instability is supposed to explain the fragmentation of the thin shell of shocked matter in the radiative phase
of supernova remnants. However its implication and its consequence on the morphological evolution of stellar systems is not
fully demonstrated. The present paper tackles this subject by numerical simulations and focus on the role of the adiabatic
index in the instability growth. The HYDRO-MUSCL 2D hydrodynamics code has been used to simulate the evolution of a supernova
remnant thin shell and the triggering of the Vishniac instability in this thin shell. We have studied the temporal behavior
of the perturbation. The first result of the numerical study is the existence of the Vishniac instability in the simulations.
This result is proved by the overstability process observed in the simulations as predicted by the theoretical analysis. The
second important result is the damping of the perturbation at late evolution and for all the set of parameters. Indeed the
accretion of matter onto the shock damps the instability when theoretical analysis predicts its occurrence. 相似文献
6.
The nonlinear motion (collapse/explosion) of a homogeneous, rapidly rotating, gaseous ellipsoid has been studied with the effects of an external gravitational field incorporated. The non-axisymmetric motion has been followed using an efficient numerical code based on certain properties of the potential functions. The gravitational radiation associated with the phenomenon was calculated, and the wave forms studied to extract information on the dynamics of the source. Possible implications of our results for various astrophysical processes are discussed. 相似文献
7.
Recovery of entire shocked samples in a range of pressure from ~100 GPa to Hugoniot elastic limit 
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下载免费PDF全文 Keita Nagaki Toshihiko Kadono Tatsuhiro Sakaiya Tadashi Kondo Kosuke Kurosawa Yoichiro Hironaka Keisuke Shigemori Masahiko Arakawa 《Meteoritics & planetary science》2016,51(6):1153-1162
We carried out laser shock experiments and wholly recovered shocked olivine and quartz samples. We investigated the petrographic features based on optical micrographs of sliced samples and found that each recovered sample comprises three regions, I (optically dark), II (opaque), and III (transparent). Scanning electron microscopy combined with electron backscattered diffraction shows that there are no crystal features in the region I; the materials in the region I have once melted. Moreover, numerical calculations performed with the iSALE shock physics code suggest that the boundary between regions II and III corresponds to Hugoniot elastic limit (HEL). Thus, we succeeded in the recovery of the entire shocked samples experienced over a wide range of pressures from HEL (~10 GPa) to melting pressure (~100 GPa) in a hierarchical order. 相似文献
8.
P. A. Rosen B. H. Wilde R. J. R. Williams J. M. Foster P. A. Keiter R. F. Coker T. S. Perry M. J. Taylor A. M. Khokhlov R. P. Drake G. R. Bennett D. B. Sinars R. B. Campbell 《Astrophysics and Space Science》2005,298(1-2):121-128
In recent years, we have carried out experiments at the University of Rochester’s Omega laser in which supersonic, dense-plasma
jets are formed by the interaction of strong shocks in a complex target assembly (Foster et al., Phys. Plasmas 9 (2002) 2251). We describe recent, significant extensions to this work, in which we consider scaling of the experiment, the
transition to turbulence, and astrophysical analogues. In new work at the Omega laser, we are developing an experiment in
which a jet is formed by laser ablation of a titanium foil mounted over a titanium washer with a central, cylindrical hole.
Some of the resulting shocked titanium expands, cools, and accelerates through the vacuum region (the hole in the washer)
and then enters a cylinder of low-density foam as a jet. We discuss the design of this new experiment and present preliminary
experimental data and results of simulations using AWE hydrocodes. In each case, the high Reynolds number of the jet suggests
that turbulence should develop, although this behaviour cannot be reliably modelled by present, resolution-limited simulations
(because of their low-numerical Reynolds number). 相似文献
9.
We discuss the design of jet-driven, radiative-blast-wave experiments for a 10 kJ class pulsed laser facility. The astrophysical motivation is the fact that jets from Young Stellar Objects are typically radiative and that the resulting radiative bow shocks produce complex structure that is difficult to predict. To drive a radiative bow shock, the jet velocity must exceed the threshold for strong radiative effects. Using a 10 kJ class laser, it is possible to produce such a jet that can drive a radiative bow shock in gas that is dense enough to permit diagnosis by x-ray radiography. We describe the design and simulations of such experiments. The basic approach is to shock the jet material and then accelerate it through a collimating hole and into a Xe ambient medium. We identify issues that must be addressed through experimentation or further simulations in order to field successful experiments. 相似文献
10.
C. Michaut T. Vinci L. Boireau M. Koenig S. Bouquet A. Benuzzi-Mounaix N. Osaki G. Herpe E. Falize B. Loupias S. Atzeni 《Astrophysics and Space Science》2007,307(1-3):159-164
This paper deals with the radiative shock from both theoretical and numerical points of view. It is based on the whole experimental
results obtained at Laboratoire d'Utilisation des Lasers Intenses (LULI, école Polytechnique). Radiative shocks are high-Mach
number shocks with a strong coupling between radiation and hydrodynamics which leads to a structure governed by a radiative
precursor. These shocks are involved in various astrophysical systems: stellar accretion shocks, pulsating stars, interaction
between supernovae and the interstellar medium. In laboratory, these radiative shocks are generated using high power lasers.
New diagnostics have been implemented to study the geometrical shape of the shock and the front shock density. Data were obtained
varying initial conditions for different laser intensities and temperature. The modeling of these phenomena is mainly performed
through numerical simulations (1D and 2D) and analytical studies. We exhibit results obtained from several radiative hydrodynamics
codes. As a result, it is possible to discuss about the influence of the geometry and physical parameters introduced in the
1D and 2D models. 相似文献
11.
12.
I. M. Hall T. Durmaz R. C. Mancini J. E. Bailey G. A. Rochau 《Astrophysics and Space Science》2011,336(1):189-194
New, high spectral resolution X-ray observations from astrophysical photoionised plasmas have been recorded in recent years
by the Chandra and XMM-Newton orbiting telescopes. These observations provide a wealth of detailed information and have motivated
new efforts at developing a detailed understanding of the atomic kinetics and radiation physics of photoionised plasmas. The
Z facility at Sandia National Laboratories is a powerful source of X-rays that enables us to produce and study photoionised
plasmas in the laboratory under well characterised conditions. We discuss a series of radiation-hydrodynamic simulations to
help understand the X-ray environment, plasma hydrodynamics and atomic kinetics in experiments where a collapsing wire array
at Z is used as an ionising source of radiation to create a photoionised plasma. The numerical simulations are used to investigate
the role that the key experimental parameters have on the photoionised plasma characteristics. 相似文献
13.
M. Koenig T. Vinci A. Benuzzi-Mounaix S. Lepape N. Ozaki S. Bouquet L. Boireau S. Leygnac C. Michaut C. Stehle J. -P. Chièze D. Batani T. Hall K. Tanaka M. Yoshida 《Astrophysics and Space Science》2005,298(1-2):69-74
We present the set-up and the results of a supercritical radiative shock experiment performed with the LULI nanosecond laser
facility. Using specific designed targets filled with xenon gaz at low pressure, the propagation of a strong shock with a
radiative precursor is evidenced. The main measured quantities related to the shock (electronic density, propagation velocities,
temperature, radial dimension) are presented and compared with various numerical simulations. 相似文献
14.
Impacts into quartz sand: Crater formation,shock metamorphism,and ejecta distribution in laboratory experiments and numerical models 下载免费PDF全文
下载免费PDF全文 We investigated the ejection mechanics by a complementary approach of cratering experiments, including the microscopic analysis of material sampled from these experiments, and 2‐D numerical modeling of vertical impacts. The study is based on cratering experiments in quartz sand targets performed at the NASA Ames Vertical Gun Range. In these experiments, the preimpact location in the target and the final position of ejecta was determined by using color‐coded sand and a catcher system for the ejecta. The results were compared with numerical simulations of the cratering and ejection process to validate the iSALE shock physics code. In turn the models provide further details on the ejection velocities and angles. We quantify the general assumption that ejecta thickness decreases with distance according to a power‐law and that the relative proportion of shocked material in the ejecta increase with distance. We distinguish three types of shock metamorphic particles (1) melt particles, (2) shock lithified aggregates, and (3) shock‐comminuted grains. The agreement between experiment and model was excellent, which provides confidence that the models can predict ejection angles, velocities, and the degree of shock loading of material expelled from a crater accurately if impact parameters such as impact velocity, impactor size, and gravity are varied beyond the experimental limitations. This study is relevant for a quantitative assessment of impact gardening on planetary surfaces and the evolution of regolith layers on atmosphereless bodies. 相似文献
15.
V. I. Sotnikov H. Ruhl R. Presura T. Cowan J. N. Leboeuf P. Hellinger P. Travnicek 《Astrophysics and Space Science》2005,298(1-2):369-374
The problem of producing collisionless shocks in the laboratory is of great interest for space and astrophysical plasmas.
One approach is based on the idea of combining strong magnetic field (up to 100 Tesla) created during a Z-pinch discharge
with a plasma flow produced in the process of the interaction of a laser pulse with a solid target. In support of laboratory
experiments we present hybrid simulations of the interaction of the plasma flow with frozen in it magnetic field, with the
spherical obstacle. Parameters of the flow correspond to a laser plasma ablation produced in the laboratory during irradiation
of the target by a 3 J laser. Magnetic fields in the plasma flow and around the obstacle are created by the currents produced
by the pulse power ZEBRA voltage generator. With the appropriate set of initial conditions imposed on the flow collisionless
shocks can be created in such a system. Using independent generators for plasma flow and magnetic field allows for the exploration
of a wide range of shock parameters. We present simulations of the formation of supercritical collisionless shock relevant
to the experiment, performed with the 2D version of the hybrid code based on the CAM-CL algorithm [Planet. Space Sci. 51,
649, 2003]. 相似文献
16.
C. Michaut E. Falize C. Cavet S. Bouquet M. Koenig T. Vinci A. Reighard R. P. Drake 《Astrophysics and Space Science》2009,322(1-4):77-84
Radiative shocks (RS) occur in astrophysical systems and in high-energy density laboratory experiments. Aided by three dimensionless parameters, we propose a classification of RS into four types, integrating previous work that has focused independently on optical depth and on Mach number. Specific terms, such as a cooling function, a radiative flux, or radiative energy and pressure must be added to the Euler equations in order to model these various kinds of shocks. We examine how these terms correspond to the radiative classification regimes. In astrophysics, observed RS arise generally in optically thin material. Thus, radiation escapes without interaction with the surrounding gas, except perhaps to ionize it, and the energy loss in such shocks can be modeled by a cooling function Λ. In this case only the post-shock region is structured by the radiation cooling. We found the analytical solution for hydrodynamic equations including Λ∝ ρ ε P ζ x θ for arbitrary values of ε, ζ, θ. This is a completely new result. An application of this calculation for the accretion shock in cataclysmic variables of polar type is given in astrophysical terms. We also draw a parallel between RS experiments performed using the LULI2000 laser facility, in France and the Omega laser Facility, in USA. RS developed in these laboratories are more or less optically thick. These high-Mach number RS present a radiative precursor. 相似文献
17.
A. C. Calder 《Astrophysics and Space Science》2005,298(1-2):25-32
The growing field of Laboratory Astrophysics seeks to study the extreme environments found in many astrophysical events in
the controlled setting of a laboratory. In addition to the opportunity to perform basic research into the nature and properties
of materials in astrophysical environments, laboratory astrophysics experiments serve beautifully for validating calculations
performed by simulation codes designed to model astrophysical phenomena. I present results from our ongoing validation effort
for FLASH, a parallel adaptive-mesh hydrodynamics code for the compressible, reactive flows of astrophysical environments.
The first test case is a laser-driven shock propagating though a multilayer target introducing Rayleigh–Taylor and Richtmyer–Meshkov
fluid instabilities at the material interfaces. The second is an accelerating fluid interface that is subject to the Rayleigh–Taylor
instability. We found good agreement between simulations and experiment for the multilayer target case, but disagreement between
experiment and simulation in the Rayleigh–Taylor case. I discuss our findings and possible reasons for the disagreement. 相似文献
18.
A. D. Edens R. G. Adams P. K. Rambo I. C. Smith J. L. Porter T. Ditmire 《Astrophysics and Space Science》2007,307(1-3):127-130
We have performed a series of experiments examining the properties of high Mach number blast waves. Experiments were conducted
on the Z-Beamlet laser at Sandia National Laboratories. We created blast waves in the laboratory by using ∼1000 J laser pulses
to illuminate millimeter scale solid targets immersed in gas. Our experiments studied the validity of theories forwarded by
Ryu and Vishniac (1987, 1991) and Vishniac (1983) to explain the dynamics of perturbations on astrophysical blast waves. These
experiments consisted of a systematic scan of the decay rates of perturbations of known primary mode number induced on the
surface of blast waves by means of a regularly spaced wire array. The amplitude of the induced perturbations relative to the
radius of the blast wave was tracked and fit to a power law in time. Measurements were taken for a number of different mode
numbers in a mixed gas consisting of 7.5 Torr xenon and 2.5 Torr nitrogen and the results are compared to theoretical predictions.
It is found that two of the three mode numbers imply one polytropic index while the third case, which is the most complicated
for several reasons, implies a higher polytropic index. 相似文献
19.
A. Frank E. G. Blackman A. Cunningham S. V. Lebedev D. Ampleford A. Ciardi S. N. Bland J. P. Chittenden M. G. Haines 《Astrophysics and Space Science》2005,298(1-2):107-114
We present new data from High-Energy Density (HED) laboratory experiments designed to explore the interaction of a heavy hypersonic
radiative jet with a cross wind. The jets are generated with the MAGPIE pulsed power machine where converging conical plasma
flows are produced from a cylindrically symmetric array of inclined wires. Radiative hypersonic jets emerge from the convergence
point. The cross wind is generated by ablation of a plastic foil via soft-X-rays from the plasma convergence region. Our experiments
show that the jets are deflected by the action of the cross wind with the angle of deflection dependent on the proximity of
the foil. Shocks within the jet beam are apparent in the data. Analysis of the data shows that the interaction of the jet
and cross wind is collisional and therefore in the hydrodynamic regime. We consider the astrophysical relevance of these experiments
applying published models of jet deflection developed for AGN and YSOs. We also present results of 3-D numerical simulations
of jet deflection using a new astrophysical Adaptive Mesh Refinement code. These simulations show highly structured shocks
occurring within the beam similar to what was observed in the experiments. 相似文献
20.