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Showing papers on "Rarefaction published in 2011"


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28 Aug 2011

87 citations


Journal ArticleDOI
TL;DR: In this article, a complete classification of shock waves in a van der Waals fluid is undertaken, in order to gain a theoretical understanding of those shock-related phenomena as observed in real fluids which cannot be accounted for by the ideal gas model.
Abstract: A complete classification of shock waves in a van der Waals fluid is undertaken. This is in order to gain a theoretical understanding of those shock-related phenomena as observed in real fluids which cannot be accounted for by the ideal gas model. These relate to admissibility of rarefaction shock waves, shock-splitting phenomena, and shock-induced phase transitions. The crucial role played by the nature of the gaseous state before the shock (the unperturbed state), and how it affects the features of the shock wave are elucidated. A full description is given of the characteristics of shock waves propagating in a van der Waals fluid. The strength of these shock waves may range from weak to strong. The study is carried out by means of the theory of hyperbolic systems supported by numerical calculations.

74 citations


Journal ArticleDOI
TL;DR: Dam break and lock exchange flows are considered in a Boussinesq two-layer fluid system in a uniform two-dimensional channel in this paper, where the focus is on inviscid 'weak' dam breaks or lock exchanges, for which waves generated from the initial conditions do not break, but instead disperse in a so-called undular bore.
Abstract: Dam-break and lock-exchange flows are considered in a Boussinesq two-layer fluid system in a uniform two-dimensional channel. The focus is on inviscid 'weak' dam breaks or lock exchanges, for which waves generated from the initial conditions do not break, but instead disperse in a so-called undular bore. The evolution of such flows can be described by the Miyata-Camassa-Choi (MCC) equations. Insight into solutions of the MCC equations is provided by the canonical form of their long wave limit, the two-layer shallow water equations, which can be related to their single-layer counterpart via a surjective map. The nature of this surjective map illustrates that whilst some Riemann-type initial-value problems (dam breaks) are analogous to those in the single-layer problem, others (lock exchanges) are not. Previous descriptions of MCC waves of permanent form (cnoidal and solitary waves) are generalised, including a description of the effects of a regularising surface tension. The wave solutions allow the application of a technique due to El's approach, based on Whitham's modulation theory, which is used to determine key features of the expanding undular bore as a function of the initial conditions. A typical dam-break flow consists of a leftwards-propagating simple rarefaction wave and a rightward-propagating simple undular bore. The leading and trailing edge speeds, leading edge solitary wave amplitude and trailing edge linear wavelength are determined for the undular bore. Lock-exchange flows, for which the initial interface shape crosses the mid-depth of the channel, by contrast, are found to be more complex, and depending on the value of the surface tension parameter may include 'solibores' or fronts connecting two distinct regimes of long-wave behaviour. All of the results presented are informed and verified by numerical solutions of the MCC equations.

69 citations


Journal ArticleDOI
TL;DR: In this paper, a strong, post-reconnection pressure gradient forms in the field-aligned direction when dense and hot, active region core loops reconnect with neighboring tenuous and cool, open field lines.
Abstract: We conduct numerical experiments to determine whether interchange reconnection at high altitude coronal null points can explain the outflows observed as blueshifts in coronal emission lines at the boundaries between open and closed magnetic field regions. In this scenario, a strong, post-reconnection pressure gradient forms in the field-aligned direction when dense and hot, active region core loops reconnect with neighboring tenuous and cool, open field lines. We find that the pressure gradient drives a supersonic outflow and a rarefaction wave develops in both the open and closed post-reconnection magnetic field regions. We forward-model the spectral line profiles for a selection of coronal emission lines to predict the spectral signatures of the rarefaction wave. We find that the properties of the rarefaction wave are consistent with the observed velocity versus temperature structure of the corona in the outflow regions, where the velocity increases with the formation temperature of the emission lines. In particular, we find excellent agreement between the predicted and observed Fe XII 195.119 A spectral line profiles in terms of the blueshift (10 km s{sup -1}), full width at half-maximum (83 mA) and symmetry. Finally, we find that T{sub i} < T{sub e} in the open field region, whichmore » indicates that the interchange reconnection scenario may provide a viable mechanism and source region for the slow solar wind.« less

52 citations


Journal ArticleDOI
TL;DR: In this article, a weak solution around a rarefaction wave to the Cauchy problem is constructed by approximating the system and regularizing the initial values which may contain vacuum states.
Abstract: In this paper, we study the asymptotic stability of rarefaction waves for the compressible isentropic Navier–Stokes equations with density-dependent viscosity. First, a weak solution around a rarefaction wave to the Cauchy problem is constructed by approximating the system and regularizing the initial values which may contain vacuum states. Then some global in time estimates on the weak solution are obtained. Based on these uniform estimates, the vacuum states are shown to vanish in finite time and the weak solution we constructed becomes a unique strong one. Consequently, the stability of the rarefaction wave is proved in a weak sense. The theory holds for large-amplitudes rarefaction waves and arbitrary initial perturbations.

50 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented two new self-similar solutions to the Chaplygin gas model in two space dimensions: simple waves and pressure delta waves, which are absent in one space dimension, but appear in the solutions to two-dimensional Riemann problems.
Abstract: We present two new types of self-similar solutions to the Chaplygin gas model in two space dimensions: Simple waves and pressure delta waves, which are absent in one space dimension, but appear in the solutions to the two-dimensional Riemann problems. A simple wave is a flow in a physical region whose image in the state space is a one-dimensional curve. The solutions to the interaction of two rarefaction simple waves are constructed. Comparisons with polytropic gases are made. Pressure delta waves are Dirac type concentration in the pressure variable, or impulses of the pressure on discontinuities. They appear in the study of Riemann problems of four rarefaction shocks. This type of discontinuities and concentrations are different from delta waves for the pressureless gas flow model, for which the delta waves are associated with convection and concentration of mass. By re-interpreting the terms in the Chaplygin gas system into new forms we are able to define distributional solutions that include the pressure delta waves. Generalized Rankine-Hugoniot conditions for pressure delta waves are derived.

49 citations


Journal ArticleDOI
TL;DR: A multi-wave approximation on rarefaction fan is proposed to avoid the occurrences of raref action shocks in computations and Computational efficiency comparisons show that the developed scheme is capable of reducing the computational time effectively with increasing the time step.

38 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the interaction of nonlinear fast magnetoacoustic waves with a magnetic null point in connection with the triggering of solar flares and found that only sufficiently smooth and low-amplitude initial pulses can reach the vicinity of the null point, create there current density spikes, and initiate magnetic reconnection by seeding anomalous electrical resistivity.
Abstract: We investigate the interaction of nonlinear fast magnetoacoustic waves with a magnetic null point in connection with the triggering of solar flares. Methods. We model the propagation of fast, initially axisymmetric waves towards a two-dimensional isothermal magnetic null point in terms of ideal magnetohydrodynamic equations. The numerical simulations are carried out with the Lagrangian remap code Lare2D. Results. Dynamics of initially axisymmetric fast pulses of small amplitude is found to be consistent with a linear analytical solution proposed earlier. The increase in the amplitude leads to the nonlinear acceleration of the compression pulse and deceleration of the rarefaction pulse and hence the distortion of the wave front. The pulse experiences nonlinear steepening in the radial direction either on the leading or the back slopes for the compression and rarefaction pulses, respectively. This effect is most pronounced in the directions perpendicular to the field. Hence, the nonlinear evolution of the fast pulse depends on the polar angle. The nonlinear steepening generates the sharp spikes of the electric current density. As in the uniform medium, the position of the shock formation also depends on the initial width of the pulse. Only sufficiently smooth and low-amplitude initial pulses can reach the vicinity of the null point, create there current density spikes, and initiate magnetic reconnection by seeding anomalous electrical resistivity. Steeper and higher amplitude initial pulses overturn at larger distance from the null point, and cannot trigger reconnection.

34 citations


Journal ArticleDOI
TL;DR: In this paper, the authors considered the first stage of the dam-break of a lock-released gravity current in a two-layer model, where the parameters R = ρL/ρH and H = H*/h0 were considered.
Abstract: We consider the dam-break initial stage of propagation of a gravity current released from a lock of length x0 and height h0 into an ambient fluid in a channel of height H*. The system contains heavy and light fluids, of densities ρH and ρL, respectively. When the Reynolds number is large, the resulting flow is governed by the parameters R = ρL/ρH and H = H*/h0. We focus attention on non-Boussinesq effects, when the parameter R is not close to 1; in this case significant differences appear between the ‘light’ (top surface) current and the ‘heavy’ (bottom) current. We use a shallow-water two-layer formulations. We show that ‘exact’ solutions of the thickness and speed of the current and ambient can be obtained by the method of characteristics. However, this requires a careful matching with the conditions at the front (ambient) and the back (reservoir). We show that a jump, instead of a rarefaction wave, propagates into the reservoir when H 1, including comparisons with the one-layer model results of Ungarish (J. Fluid Mech., vol. 579, 2007, p. 373).Overall, the shallow-water two-layer theory yields consistent, self-contained, and physically acceptable analytical solutions for the dam-break problem over the full physical range of the R and H parameters, for both light-into-heavy and heavy-into-light gravity currents. The solution can be closed without adjustable constants or predetermined properties of the flow field. The thickness solution is formally valid until the jump, or rarefaction wave, hits the backwall; the speed of propagation prediction is valid until this reflected wave hits the nose, i.e. until the end of the slumping stage. This theory is a significant extension of the Boussinesq problem (recovered by the present solution for R = 1), which elucidates the non-Boussinesq effects during the first stage of propagation of lock-released gravity currents.

28 citations


Journal ArticleDOI
TL;DR: In this paper, a rarefied gas flow through a thin slit into vacuum is calculated on the basis of the kinetic model equations applying the discrete velocity method, for the whole range of the gas rarefaction from the free molecular regime to the hydrodynamic one.

26 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the development of linear micro-fault systems that can be traced for several meters in length, and which predominantly trend radially from the point of impact.

Journal ArticleDOI
TL;DR: In this paper, a multi-phase constitutive model that considers strength effects to describe the observed response under shock loading of polytetrafluoroethylene (PTFE) material is presented.
Abstract: Polytetrafluoroethylene (PTFE) is a polymer with a simple atomic structure that shows complex behavior under pressure and demonstrates a highly variable metastable phase structure in shock waves with amorphous and crystalline components In turn, the crystalline component has four known phases with the high-pressure transition of the crystalline domain from crystalline phase IV at ambient through phase II to III At the same time, as has been recently studied using spectrometry, the crystalline region nucleates from the amorphous one with load Stress and velocity shock-wave profiles acquired recently with embedded gauges demonstrate features that may be related to the impedance mismatch between the phase domains subjected to such transitions resulting in variations of mechanical and thermophysical characteristics We consider the inter-phase non-equilibrium and the amorphous-to-crystalline and inter-crystalline transitions that are associated with the high pressure and temperature transformations under shock wave loading as possible candidates for the analysis The present work utilizes a multi-phase constitutive model that considers strength effects to describe the observed response under shock loading of the PTFE material Experimental plate impact shock-wave histories are compared with calculated profiles using kinetics describing the transitions The study demonstrates that the inter-phase pressure non-equilibrium of the state parameters plays the key role in the delay of the shock wave attenuation At the same time, the forward transition associated with the crystallization might be responsible for the velocity spike in the experimental velocity profiles at high impact velocity and the modulus variation at low impact velocity On the other hand, an accelerated attenuation of the velocity in the rarefaction wave is associated with another transition resulting in the residual crystallinity change during unloading

Journal ArticleDOI
Abstract: The manuscript is devoted to nonisentropic solutions of simple wave type of the gas dynamics equations. For an isentropic flow these equations (in one-dimensional and steady two-dimensional cases) are reduced to the equations written in the Riemann invariants. The system written in the Riemann invariants is hyperbolic and homogeneous. It allows obtaining simple waves, which are also called Riemann waves. For nonisentropic flows there are no Riemann invariants. The question is: what solutions could substitute the Riemann waves? By the method of differential constraints such types of solutions are found here. For these classes of solutions one can integrate the gas dynamics equations: finite formulas with one parameter are obtained. These solutions have some properties similar to simple Riemann waves. For example, they describe a nonisentropic rarefaction wave. The rarefaction waves play the main role in many applications such as the problem of pulling a piston, decay of arbitrary discontinuity and others.

Journal ArticleDOI
TL;DR: An empirical relation of Poiseuille number which contains the two opposite effects and has a better physical meaning is proposed in the form of multiplicative decomposition, and then is validated by available experimental and numerical results.
Abstract: Poiseuille number of rarefied gas flow in channels with designed roughness is studied and a multiplicative decomposition of Poiseuille number on the effects of rarefaction and roughness is proposed. The numerical methodology is based on the mesoscopic lattice Boltzmann method. In order to eliminate the effect of compressibility, the incompressible lattice Boltzmann model is used and the periodic boundary is imposed on the inlet and outlet of the channel. The combined bounced condition is applied to simulate the velocity slip on the wall boundary. Numerical results reveal the two opposite effects that velocity gradient and friction factor near the wall increase as roughness effect increases; meanwhile, the increments of the rarefaction effect and velocity slip lead to a corresponding decrement of friction factor. An empirical relation of Poiseuille number which contains the two opposite effects and has a better physical meaning is proposed in the form of multiplicative decomposition, and then is validated by available experimental and numerical results.

Journal ArticleDOI
TL;DR: The theoretical model presented here gives a coherent and complete description of the rarefaction shock and its effects on the ion acceleration process and an excellent agreement is obtained.
Abstract: The one-dimensional collisionless expansion into a vacuum of a plasma with a bi-Maxwellian electron distribution function and a single ion species is studied both theoretically and numerically. A shock wave occurs when the ratio of the temperatures between the hot and the cold electrons is larger than $5+\sqrt{24}$ [B. Bezzerides, D. W. Forslund, and E. L. Lindman, Phys. Fluids 21, 2179 (1978)]. The theoretical model presented here gives a coherent and complete description of the rarefaction shock and its effects on the ion acceleration process. Analytical expressions of the characteristics of the shock are given. The analytical findings are compared to the results of a hybrid code describing the plasma expansion, and an excellent agreement is obtained.

Journal ArticleDOI
TL;DR: In this paper, the authors show that the spherical shock waves arising in a liquid during cavitation bubble collapse can lead to formation of deep needle-like pits on the solid surface.
Abstract: The purpose of this work is to show that the spherical shock waves arising in a liquid during cavitation bubble collapse can lead to formation of deep needle-like pits on the solid surface. The nature of dynamic damage during cavitation erosion is the spallation caused by interference of rarefaction waves. Rarefaction at spherical wave impact arises when the velocity of contact surface boundary becomes less than the speed of sound in a target. If the tension caused by the focused rarefaction wave exceeds the spall strength of material, channel spall cracks can arise. At low pulsed loading, spall cracks are formed in a dynamic fatigue mode. Needle-like damage arises upon focusing rarefaction waves. In terms of our model, a system of cylindrical spall cracks is consecutively formed around a deeper axial spall needle-like crack. Upon subsequent loading, each crack acts as a source of new rarefaction wave. Newly formed cylindrical spall cracks suppress the growth of the cracks of previous generation and give birth to the cracks of next generation. A distinctive feature is that the cracks are first formed at the periphery of damageability zone, subsequent cracks having a lower depth.

Journal ArticleDOI
TL;DR: In this paper, an isothermal steady rarefied gas flow in a long channel (tube) of elliptical or rectangular cross-section under the action of a given pressure gradient (Poiseuille flow) is studied on the basis of the Bhatnagar-Gross-Krook model.
Abstract: An isothermal steady rarefied gas flow in a long channel (tube) of elliptical or rectangular cross-section under the action of a given pressure gradient (Poiseuille flow) is studied on the basis of the Bhatnagar-Gross-Krook model. The solution is obtained using a conservative higher-order method. The velocity field in a channel cross-section is investigated as a function of the rarefaction degree and the cross-section geometry parameters. The main calculated function is the gas flow rate through the tube. The solutions obtained are compared with the available results.

Journal ArticleDOI
TL;DR: In this article, the authors compared three different continuum-based models to study oscillatory flow in the transition regime and found that the regularized 26 moment model can follow kinetic theory in terms of both Knudsen numbers but the regularised 13 moment equations can only be used up to the upper limit of the hydrodynamic regime.
Abstract: We present results using three different continuum-based models to study oscillatory flow in the transition regime. Data obtained from numerical solutions of the Boltzmann equation and the direct simulation Monte Carlo method, are used to assess the ability of the continuum models to capture important rarefaction effects. We further highlight the need to consider two Knudsen numbers: one based upon the length scale and the other upon the time scale. It is found that the regularized 26 moment model can follow kinetic theory in the early transition regime in terms of both Knudsen numbers but the regularized 13 moment equations can only be used up to the upper limit of the hydrodynamic regime. However, the subtle interplay of the length and time scales on oscillatory non-equilibrium flow causes the Navier–Stokes equations to fail even in the hydrodynamic regime. In addition, the effect of modifying the accommodation coefficient is also considered. It is found that reducing the accommodation coefficient on the stationary wall alone will increase the motion of the gas. However, gaseous movement will be reduced by changing both walls from diffusive to specular reflection.

Journal ArticleDOI
TL;DR: In this paper, a wave equation including nonlinear terms up to the second order for a thermoviscous Newtonian fluid is proposed, which preserves the Hamiltonian structure, in contrast to the Kuznetsov equation, a model often used in nonlinear acoustics.
Abstract: A wave equation including nonlinear terms up to the second order for a thermoviscous Newtonian fluid is proposed. In the lossless case this equation results from an expansion to third order of the Lagrangian for the fundamental non-dissipative fluid dynamical equations. Thus it preserves the Hamiltonian structure, in contrast to the Kuznetsov equation, a model often used in nonlinear acoustics. An exact traveling wave front solution is derived from a generalized traveling wave assumption for the velocity potential. Numerical studies of the evolution of a number of arbitrary initial conditions as well as head-on colliding and confluent wave fronts exhibit several nonlinear interaction phenomena. These include wave fronts of changed velocity and amplitude along with the emergence of rarefaction waves. An analysis using the continuity of the solutions as well as the boundary conditions is proposed. The dynamics of the rarefaction wave is approximated by a collective coordinate approach in the energy balance equation.

Posted Content
TL;DR: In this paper, the convergence of the Boltzmann equaiton to the compressible Euler equations when the Knudsen number tends to zero has been a long standing open problem in the kinetic theory.
Abstract: The convergence of the Boltzmann equaiton to the compressible Euler equations when the Knudsen number tends to zero has been a long standing open problem in the kinetic theory. In the setting of Riemann solution that contains the generic superposition of shock, rarefaction wave and contact discontinuity to the Euler equations, we succeed in justifying this limit by introducing hyperbolic waves with different solution backgrounds to capture the extra masses carried by the hyperbolic approximation of the rarefaction wave and the diffusion approximation of contact discontinuity.

Posted Content
TL;DR: It is shown that the density of any weak solution satisfying the natural energy and entropy estimates will converge to the rarefaction wave connected to vacuum with arbitrary strength in sup-norm time-asymptotically.
Abstract: In this paper, we study the large time asymptotic behavior toward rarefaction waves for solutions to the 1-dimensional compressible Navier-Stokes equations with density-dependent viscosities for general initial data whose far fields are connected by a rarefaction wave to the corresponding Euler equations with one end state being vacuum. First, a global-in-time weak solution around the rarefaction wave is constructed by approximating the system and regularizing the initial data with general perturbations, and some a priori uniform-in-time estimates for the energy and entropy are obtained. Then it is shown that the density of any weak solution satisfying the natural energy and entropy estimates will converge to the rarefaction wave connected to vacuum with arbitrary strength in super-norm time-asymptotically. Our results imply, in particular, that the initial vacuum at far fields will remain for all the time which are in contrast to the case of non-vacuum rarefaction waves studied in \cite{JWX} where all the possible vacuum states will vanish in finite time. Finally, it is proved that the weak solution becomes regular away from the vacuum region of the rarefaction wave.

Proceedings ArticleDOI
01 Jan 2011
TL;DR: In this article, the authors used an upgraded version of the Direct Simulation Monte Carlo (DSMC) method to study binary gas flows driven by pressure gradient through short microtubes.
Abstract: Binary gas flows driven by pressure gradient through short microtubes are studied by using an upgraded version of the Direct Simulation Monte Carlo (DSMC) method. Two types of mixtures, He/Xe and Ne/Ar, are examined. Several values of the channel length to radius ratio, the downstream to upstream pressure ratio and a wide range of the gas rarefaction are considered. Results are presented for the species and total flow rates and for the axial distributions of the macroscopic quantities. There is a pronounced difference of the flow behavior of the two mixtures due to the different molecular mass ratios. The flow rate of the He/Xe mixture for very short channels and large pressure drops is increased with increasing gas rarefaction, while the flow rate of the Ne/Ar mixture shows a different rarefaction dependence. The obtained results can be useful in optimal design of microfluidic or vacuum devices.Copyright © 2011 by ASME

Proceedings ArticleDOI
27 Jun 2011
TL;DR: In this article, three-dimensional laminar hypersonic boundary-layer flows are investigated applying the compressible bi-global linear stability theory (B-LST) in flow crossplanes.
Abstract: Three-dimensional laminar hypersonic boundary-layer flows are investigated applying the compressible bi-global linear stability theory (B-LST) in flow crossplanes. The flat-plate flow is altered by an obliquely placed discrete fence-like roughness element that is about half the boundary-layer thickness high. Roughness setup and flow conditions resemble the STS-119 flight experiment. A cold-flow case and hot-flow cases are considered. The influence of non-perfect gas properties such as variable chemical composition, or thermal energy relaxation are included. The steady base flows are extracted from Navier-Stokes simulations. The underlying gas modell for reacting and non-reacting air accounts for thermal as well as chemical nonequilibrium. Rarefaction effects are considered in terms of a slip condition for velocity and temperature at the wall. Stability properties of the roughness wake under cold, hot, and hot rarefied flow conditions are compared in terms of local and integral growth.

Journal Article
TL;DR: In this paper, a closed form expression describing the shape of the strongly nonlinear rarefaction wave is exact for n = 1/2 and agrees well with the shape and width of the pulses resulting from discrete simulations.
Abstract: We investigate rarefaction waves in nonlinear periodic systems with a 'softening' power-law relationship between force and displacement to understand the dynamic behavior of this class of materials. A closed form expression describing the shape of the strongly nonlinear rarefaction wave is exact for n = 1/2 and agrees well with the shape and width of the pulses resulting from discrete simulations. A chain of particles under impact was shown to propagate a rarefaction pulse as the leading pulse in initially compressive impulsive loading in the absence of dissipation. Compression pulses generated by impact quickly disintegrated into a leading rarefaction solitary wave followed by an oscillatory train. Such behavior is favorable for metamaterials design of shock absorption layers as well as tunable information transmission lines for scrambling of acoustic information.

Journal ArticleDOI
TL;DR: In this article, a dynamic sheath expansion in front of a target biased with a negative, highvoltage pulse is investigated in a non-uniform plasma, taking into account the influence of ion drift, which is inevitable in diffusive plasmas with a nonuniform density profile.
Abstract: Dynamic sheath expansion in front of a target biased with a negative, high-voltage pulse is investigated in a non-uniform plasma, taking into account the influence of ion drift, which is inevitable in diffusive plasmas with a non-uniform density profile. Temporal evolutions of a sheath edge and a rarefaction wave measured in a low-pressure argon plasma diffusing towards the target agree well with numerical predictions of their transient behaviors as obtained using a dynamic sheath model for non-uniform plasmas with ion drift. It is found that the thickness of the expanding sheath edge is reduced considerably by the ion drift velocity when compared with the thickness without ion drift. Moreover, because the ion drift prevents the propagation of the rarefaction wave significantly, the phase velocity of the wave is observed to be much less than the Bohm speed. The propagating characteristics of the rarefaction wave confirm that the ion drift velocity plays an important role in the dynamic sheath expansion in non-uniform plasmas with ion drift. The results are expected to be useful in analyzing the dose and energy of implanted ions as well as understanding the sheath dynamics in a real plasma source ion implantation system in which the plasma sheath commonly evolves in a non-uniform plasma with ion drift.

Journal Article
TL;DR: In this paper, the dynamics of ultrashort shock waves induced by femtosecond laser pulses were explored in nickel-glass and free-standing nickel films by molecular dynamics simulations.
Abstract: The dynamics of ultrashort shock waves induced by femtosecond laser pulses were explored in nickel-glass and free-standing nickel films by molecular dynamics simulations. Ultrafast laser heating causes stress-confinement, which is characterized by formation of a strongly pressurized 100-nm-thick zone just below the surface of the film. For low-intensity laser pulses, only a single elastic shock wave was formed despite pressures several times greater than the experimental Hugoniot elastic limit. Because the material remains uniaxially compressed for < 50 ps, comparatively slow processes of dislocation formation are not activated. For high intensity laser pulses, the process of double wave breaking was observed with formation of split elastic and plastic shock waves. Presence of a trailing rarefaction wave acts to attenuate the plastic wave until it disappears. Agreement between the experimental and simulated Hugoniot was facilitated by a new EAM potential designed to simulate nickel in a wide range of pressures and temperatures.

Journal ArticleDOI
TL;DR: In this paper, the ion rarefaction response to a high negative voltage pulse (U0 >> kTe/e) applied to a metal plate immersed in a low pressure argon plasma, for time duration lower than ion plasma period, is experimentally examined.
Abstract: The ion rarefaction response to a high negative voltage pulse (U0 >> kTe/e) applied to a metal plate immersed in a low pressure argon plasma, for time duration lower than ion plasma period, is experimentally examined. In the present experiment the pulse duration is kept intermediate between the ion and electron plasma response times. Such a pulse duration is chosen so that ions are collectively undisturbed and, according to general understanding, no force is given to ions. Hence no ion rarefaction wave should be excited. But contrary to the general understanding, excitation of a rarefaction wave is observed. The results indicate that the speed of the rarefaction waves for various conditions (like plasma density, applied pulse magnitude, and pulse duration) is supersonic. After a distance from the exciter (biased plate), typically three-fourth of the exciter diameter, the rarefaction waves are turned into ion acoustic waves. The experimental results indicate that even though the bias durations are shorter ...

Journal ArticleDOI
TL;DR: In this article, it was shown that collisions of compression shock waves and rarefaction solitons lead to the generation of nuclei of new phases, which evolve according to the domino principle.
Abstract: It is shown that the generation of nonlinear soliton, breather, and shock waves at high dynamic excitations leads to martensitic phase transformations in crystalline materials of the α-uranium type. Investigations have been performed by modeling the atomic microdynamics with the use of the modified interaction potential. It is shown that collisions of compression shock waves and rarefaction solitons lead to the generation of nuclei of new phases, which evolve according to the domino principle. The phonon spectra of systems with phase interfaces are investigated. A new effect of the total internal phonon reflection has been discovered. It is shown that surface phonons of radically a new type (different from the Rayleigh surface waves) are excited on interfaces. The results are adapted to materials of the α-uranium type, where solitons have been found at slow-neutron scattering.


Journal ArticleDOI
TL;DR: The interconversion of shock and rarefaction waves during the equation's evolution displays in accordance with a Markov process, which has a stationary transition probability matrix with the elements satisfying universal functions and, when the time interval is much greater than the corresponding characteristic value, exhibits the scale-invariant property.
Abstract: A numerical and statistical study is performed to describe the positive and negative local subgrid energy fluxes in the one-dimensional random-force-driven Burgers turbulence (Burgulence). We use a subensemble method to decompose the field into shock wave and rarefaction wave subensembles by group velocity difference. We observe that the shock wave subensemble shows a strong intermittency which dominates the whole Burgulence field, while the rarefaction wave subensemble satisfies the Kolmogorov 1941 (K41) scaling law. We calculate the two subensemble probabilities and find that in the inertial range they maintain scale invariance, which is the important feature of turbulence self-similarity. We reveal that the interconversion of shock and rarefaction waves during the equation's evolution displays in accordance with a Markov process, which has a stationary transition probability matrix with the elements satisfying universal functions and, when the time interval is much greater than the corresponding characteristic value, exhibits the scale-invariant property.