Simulation Of Shock Waves Research Articles

Molecular dynamics simulation of strong shock waves propagating in dense deuterium, taking into consideration effects of excited electrons.

We present a molecular dynamics simulation of shock waves propagating in dense deuterium with the electron force field method [J. T. Su and W. A. Goddard, Phys. Rev. Lett. 99, 185003 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.185003], which explicitly takes the excitation of electrons into consideration. Nonequilibrium features associated with the excitation of electrons are systematically investigated. We show that chemical bonds in D_{2} molecules lead to a more complicated shock wave structure near the shock front, compared with the results of classical molecular dynamics simulation. Charge separation can bring about accumulation of net charges on large scales, instead of the formation of a localized dipole layer, which might cause extra energy for the shock wave to propagate. In addition, the simulations also display that molecular dissociation at the shock front is the major factor that accounts for the "bump" structure in the principal Hugoniot. These results could help to build a more realistic picture of shock wave propagation in fuel materials commonly used in the inertial confinement fusion.

Shock Mechanism Analysis and Simulation of High-Power Hydraulic Shock Wave Simulator

The simulation of regular shock wave (e.g., half-sine) can be achieved by the traditional rubber shock simulator, but the practical high-power shock wave characterized by steep prepeak and gentle postpeak is hard to be realized by the same. To tackle this disadvantage, a novel high-power hydraulic shock wave simulator based on the live firing muzzle shock principle was proposed in the current work. The influence of the typical shock characteristic parameters on the shock force wave was investigated via both theoretical deduction and software simulation. According to the obtained data compared with the results, in fact, it can be concluded that the developed hydraulic shock wave simulator can be applied to simulate the real condition of the shocking system. Further, the similarity evaluation of shock wave simulation was achieved based on the curvature distance, and the results stated that the simulation method was reasonable and the structural optimization based on software simulation is also beneficial to the increase of efficiency. Finally, the combination of theoretical analysis and simulation for the development of artillery recoil tester is a comprehensive approach in the design and structure optimization of the recoil system.

DSMC study of oxygen shockwaves based on high-fidelity vibrational relaxation and dissociation models

This work evaluates high-fidelity vibrational-translational (VT) energy relaxation and dissociation models for pure O2 normal shockwave simulations with the direct simulation Monte Carlo (DSMC) method. The O2–O collisions are described using ab initio state-specific relaxation and dissociation models. The Macheret-Fridman (MF) dissociation model is adapted to the DSMC framework by modifying the standard implementation of the total collision energy (TCE) model. The O2–O2 dissociation is modeled with this TCE+MF approach, which is calibrated with O2–O ab initio data and experimental equilibrium dissociation rates. The O2–O2 vibrational relaxation is modeled via the Larsen-Borgnakke model, calibrated to experimental VT rates. All the present results are compared to experimental data and previous calculations available in the literature. It is found that, in general, the ab initio dissociation model is better than the TCE model at matching the shock experiments. Therefore, when available, efficient ab initio models are preferred over phenomenological models. We also show that the proposed TCE + MF formulation can be used to improve the standard TCE model results when ab initio data are not available or limited.

Gaseous microflow modeling using the Fokker-Planck equation.

We present a comparative study of gaseous microflow systems using the recently introduced Fokker-Planck approach and other methods such as: direct simulation Monte Carlo, lattice Boltzmann, and variational solution of Boltzmann-BGK. We show that this Fokker-Plank approach performs efficiently at intermediate values of Knudsen number, a region where direct simulation Monte Carlo becomes expensive and lattice Boltzmann becomes inaccurate. We also investigate the effectiveness of a recently proposed Fokker-Planck model in simulations of heat transfer, as a function of relevant parameters such as the Prandtl, Knudsen numbers. Furthermore, we present simulation of shock wave as a function of Mach number in transonic regime. Our results suggest that the performance of the Fokker-Planck approach is superior to that of the other methods in transition regime for rarefied gas flow and transonic regime for shock wave.

SPH simulation of oblique shocks in compressible flows

AbstractThe Lagrangian smoothed particle hydrodynamics (SPH) method is used to simulate shock waves in inviscid, supersonic (compressible) flow. It is shown for the first time that the fully Lagrangian SPH particle method, without auxiliary grid, can be used to simulate shock waves in compressible flow. The wall boundary condition is treated with ghost particles combined with a suitable repulsive potential function, whilst corners are treated by a novel ‘angle sweep’ technique. The method gives accurate predictions of the flow field and of the shock angle as compared with the analytical solution. The study shows that SPH is a good potential candidate to solve complex aerodynamic problems, including those involving rarefied flows, such as atmospheric re‐entry. Copyright © 2016 John Wiley & Sons, Ltd.

Predictions of Detonation Propagation Through Open Cell Foam Embedded in Chemically Sensitized Nitromethane

We report results of Eulerian hydrodynamic simulations of detonation shock waves propagating through open cell foams constructed of aluminum, polymethylmethacrylate, and lead at approximately 20 % relative density in nitromethane. By varying pore sizes, as well as material impedance, we predict the dynamic responses at the mesoscale using a reactive flow model in the ALE3D software package. We explain predictions of the detonation profile of each explosive system, along with the stress-strain response of the foams therein. Finally, we describe predictions of a radially expanding detonation front and apply the theory of Detonation Shock Dynamics to the expansion rate of the shock front.

Generation of laser plasma bunches with a high efficiency of energy concentration for laboratory simulation of collisionless shock waves in magnetised cosmic plasma

We present the results of first experiments on the formation of collisionless shock waves (CSWs) in background plasma by injecting laser plasma bunches transverse to the magnetic field (as a piston) with a maximum energy up to per unit of solid angle and with a high enough degree of ion magnetisation. With this aim in view, on a unique KI-1 facility at the Institute of Laser Physics, Siberian Branch of the Russian Academy of Sciences (ILP), a plastic (polyethylene) target irradiated by a laser in the most energy-efficient regime (near the plasma formation threshold) and a highly ionised hydrogen plasma with a high concentration in a large volume (not less than ) have been employed. As a result of model experiments performed on the basis of a model of collisionless interaction of plasma flows, developed at the VNIIEF and being adequate to the problem under consideration, not only an intensive, background-induced, deceleration of a super-Alfven laser plasma flow, but also the formation in that flow of a strong perturbation having the properties of a subcritical CSW and propagating transverse to the magnetic field, have been first registered in the laboratory conditions.

Relaxation of heavy ions in collisionless shock waves in cosmic plasma

We report on the results of hybrid particle-in-cell simulation of shock waves (SWs) in the cosmic plasma with admixture of heavy weakly charged ions. The dependence of ion relaxation and the SW structure on the angle between the magnetic field and the normal to the wavefront is analyzed. The conditions for invariability of the anisotropic ion velocity distribution behind the front of quasi-transverse SWs are indicated on scales substantially exceeding the width of the collisionless SW front (up to the Coulomb relaxation length). The obtained results are essential for determining the effectiveness of heating of heavy ions and observation diagnostic of collisionless SWs in the cosmic plasma.

Development of a simulation for supersonic aircraft signature propagation through turbulence

For the next generation of quiet supersonic civilian aircraft, minimizing the acoustic signature is important. To inform the design process, a model of the effect of shock wave propagation through the atmosphere is required. For such a model to be accurate, both the weak nonlinear effects on the supersonic signature and the distortion due to atmospheric turbulence could be important. To best predict the variability of waveforms heard at multiple locations on the ground, a propagation simulation requires multiple random realizations of the turbulent field. In the present model, a finite difference implementation of the two-dimensional, nonlinear KZK propagation equation is combined with a statistical turbulence model to simulate shock wave propagation through the atmosphere. For this initial work, a KZK simulation for focused sources developed at the University of Texas by Y. Lee was modified and extended for atmospheric propagation. [Work supported by NASA via a subcontract from Wyle.]

English

English

Characteristics of energy exchange between inter- and intramolecular degrees of freedom in crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) with implications for coarse-grained simulations of shock waves in polyatomic molecular crystals.

In this report, we characterize the kinetics and dynamics of energy exchange between intramolecular and intermolecular degrees of freedom (DoF) in crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). All-atom molecular dynamics (MD) simulations are used to obtain predictions for relaxation from certain limiting initial distributions of energy between the intra- and intermolecular DoF. The results are used to parameterize a coarse-grained Dissipative Particle Dynamics at constant Energy (DPDE) model for TATB. Each TATB molecule in the DPDE model is represented as an all-atom, rigid-molecule mesoparticle, with explicit external (molecular translational and rotational) DoF and coarse-grained implicit internal (vibrational) DoF. In addition to conserving linear and angular momentum, the DPDE equations of motion conserve the total system energy provided that particles can exchange energy between their external and internal DoF. The internal temperature of a TATB molecule is calculated using an internal equation of state, which we develop here, and the temperatures of the external and internal DoF are coupled using a fluctuation-dissipation relation. The DPDE force expression requires specification of the input parameter σ that determines the rate at which energy is exchanged between external and internal DoF. We adjusted σ based on the predictions for relaxation processes obtained from MD simulations. The parameterized DPDE model was employed in large-scale simulations of shock compression of TATB. We show that the rate of energy exchange governed by σ can significantly influence the transient behavior of the system behind the shock.

密度変調場を通過する衝撃波のシミュレーション

密度変調場を通過する衝撃波のシミュレーション

Simulation of Shock Wave Assisted Free and Shape Forming of Metallic Plates in a Shock Tube

Due to their complexity, certain engineering problems like finding shock strength, Mach number etc. and the interaction of shock wave with a structure in free and restricted metal forming techniques cannot be achieved in a single experimentation, these can be obtained only through a number of trials and that leads to increase in cost and time. In such cases both cost and time can be reduced by adopting numerical simulations. In this projectcommercial software ANSYS is used to simulate the propagation shock wave through a shock tube, free and shape forming of metallic plates subjected to this shock wave. Shock Mach numbers up to 2.12 have been generated by varying the driver to driven pressure ratios. Thin copper plates of diameter 60mm and thickness of 0.5mm and 0.3mm are subjected to shock wave loadingin order to form into dies.These dies,madeof structural steel are modelled with pre-defined shapes. The plate peakoverpressures ranging from 9 to 20bar have been generated.The midpoint deflection, Von Mises stress and strain are calculated for free forming copper plates. The simulated results are compared with the experimental values available in literature. The simulated results match well with the experimental values.

The multicomponent self-consistent Ornstein—Zernike application for CO2, N2, O2 shock Hugoniots simulation

A multicomponent equation of state with wide range of applicability is required to simulate shock waves in CxNyOz mixtures. This problem demands fine molecular interaction model due to competition between repulsion and attraction forces during shock compression process. A self-consistent Ornstein-Zernike application (SCOZA) based on distribution function integral equation theory can be used for it. The hypernetted-chain/soft core mean spherical approximation (HMSA) for SCOZA has been successfully applied to dense fluid systems with ambidextrous interactions. However, it was not designed to simulate mixtures, such as shock products of CxNyOz system. The convenient way to simulate multicomponent systems is the van der Waals one-fluid model (vdWlf). It has been shown, that vdWlf is not good enough for CO2 shock products at pressures higher, than 50 GPa. The multicomponent HMSA closure application based on partial version of the virial theorem has been offered in this paper. It is verified by molecular Monte-Carlo simulation at pressures up to 160 GPa with accuracy about 1–2%.

Determination of the third-order elastic constants of diamond by shock wave simulations

A new methodology comprising finite-strain theory, Hugoniot jump conditions, second-order elastic constants (SOECs) and their pressure derivatives, has been developed and was used to estimate the third-order elastic constants (TOECs) of diamond. Density functional theory was used to compute SOECs and their pressure derivatives. The required shock wave Hugoniots were estimated along the , and directions by classical molecular dynamics simulations. Calculated SOECs and TOECs were compared with available experimental and theoretical results. For SOECs, a fairly good agreement with experimental data was obtained and for TOECs our methodology predicts a better agreement with experimental data compared to other theoretical methods.

A two-phase model to simulate the 1-D shock wave propagation in porous metal foam

A two-phase model is proposed to simulate the dynamic behavior of porous metal foam. The model is applied to known experimental data describing equations of state for different aluminum foams. To analyze impact and shock problems in compressible media with analytical, semi-analytical and numerical methods, the corresponding Riemann problem solution is required. Its solution for a metal foam medium has been obtained. The possible wave configurations have been analyzed and the corresponding equations for the contact pressure and velocity evaluation have been derived. The effect of the volumetric air content in a metal foam medium on the Riemann problem solution has been investigated. The proposed equation of state has been successfully used to simulate shock waves propagation in the Alporas foam. The comparisons of the present model predictions with numerical results computed with LS-Dyna as well as with experimental data show very good correspondence and demonstrate the power of the present approach.

Numerical simulation of shock wave and contact surface propagation in micro shock tubes

Micro shock tubes have been widely used in many engineering and industrial applications, but their performance and detailed flow characteristics are not well known. Compared to macro shock tubes, unsteady flows related to the moving shock waves in micro shock tubes are highly complicated due to more active viscous dissipation and rarefaction effects. This makes shock wave dynamics significantly different from theoretical predictions. One of the major flow behaviors related to the shock wave propagation in micro shock tube is that the boundary layer growth leads to stronger dissipative shock wave. Due to effects of the scale, more shock wave attenuation happens in micro shock tubes. We used a CFD approach to understand the flow characteristics in a micro shock tube with finite diameter. A fully implicit finite volume scheme has been employed to solve the unsteady compressible Navier-Stokes equations. The diaphragm pressure ratio and diameter of the shock tube were varied to investigate their effects on micro shock tube flows. Based on the predicted results, some wave diagrams were built to characterize the micro shock tube flows. Detailed flow structures between the contact surface and moving shock wave were analyzed during the present study.

Hybrid simulation of collisionless shock waves in space plasma

A new version of a multiprocessor 3D hybrid code is described, which makes it possible to simulate the formation and evolution of collisionless shock waves in a multicomponent space plasma with ions of different masses and charge states. The algorithm ensures exact conservation of zero magnetic field divergence and self-consistent electric field dynamics and is of the second order of accuracy in time. The peculiarities of the effect of the boundary conditions at the reflecting wall on the formation of quasi-parallel and quasi-perpendicular shock waves are analyzed. It is shown that the rates of collisionless relaxation of ions to quasi-equilibrium distributions for quasi-longitudinal and quasi-transverse shock waves are substantially different.

Application of Compressible Multi-component Flow in Underwater Explosion Problems

High-order accurate shock-capturing schemes had been proposed to resolve compressible flow movement that involving shockwave problem in single-fluid Riemann problems previously. However, when different fluids appear, oscillations often generate at the multi-component interfaces without deep implementations. An underwater explosion (UNDEX) event is typical multi-component problem with different flows phase evolvement. In order to simulate underwater explosion, we extend the numerical schemes which include five-order WENO reconstruction and HLLC approximate Riemann solver to capture interface between the explosive gas and water. Our method is high-order accurate, quasi-conservative and interface-capturing, which has been verified by 2D problems, and produce good agreement between analytical solution and experiment result. At last we attempted to use the method to simulate shock wave loading and underwater explosion (UNDEX) near a free surface

Simulation of radiative shock waves in Xe of last PALS experiments

We present the radiative hydrodynamic simulation code ARWEN applied to study laboratory astrophysics phenomena. Our aim is to reproduce the results obtained from laser-produced radiative shock waves experiments held in PALS in 2011, focusing on the velocity of the shock wave and the length of the radiative precursor formed. We describe the main features of the simulation code as well as the parameters and data (EOS and opacities) used to simulate a target consisting of a Xe gas filled tube illuminated by a 60 J laser during 0.35 ns. A radiative precursor of about 165 μm is formed ahead of a shock wave traveling at velocity of 47.8 km/s, in agreement with the experimental data.