Propagation Of Rarefaction Waves Research Articles

Numerical simulation of shaped charge jet forming and penetrating characteristics of anti-armor and anti-personnel composite warhead

Abstract The anti-armor and anti-personnel composite warhead is a kind of high-efficiency warhead with both anti-armor and anti-personnel effect, which is suitable for weapons such as cruise missile and UAV-brone ammunition. Based on the ANSYS/LS-DYNA numerical simulation software, the influence of the structural parameters of the biconical warhead on the forming characteristics and anti-armor power of the shaped charge jet was studied. The results show that the main mechanism of fragment influence on jet forming characteristics is to reduce the driving pressure of detonation by reducing the charge mass. Prefabricated fragments have little delay effect on radial rarefaction wave propagation in detonation products, and the existence of fragments increases the penetration depth by 1.41% under the same charge mass. The research results provide a useful reference for the overall structure design, material selection and structure optimization of the anti-armor and anti-personnel composite warhead.

Study on the Influence of a Rigid Wall on Cavitation in Underwater Explosions Near the Free Surface

A two-fluid, phase transition-based multiphase flow model is employed to simulate the dynamics of phase transition between liquid and vapor phases during shock wave and rarefaction wave propagation in underwater explosions. The aim is to understand the influence of a rigid wall on the cavitation evolution process and the cavitation collapse load, considering various charge quantities and water depths. The evolution of crucial physical qualities, such as the density, pressure, and the cavitation domain, within the flow field are analyzed and summarized. The presence of a rigid wall is found to significantly impact the cavitation evolution process in underwater explosions. It affects the shape, size, and dynamics of the cavitation domain, as well as the interaction between the explosion and the surrounding fluid. Specifically, the reflected wave on the wall influences the cavitation collapse load, leading to notable differences in the collapse time and collapse pressure compared to free-field conditions. Under different operating conditions, the size and position of the cavitation domain exhibit distinct changes. The proximity of the rigid wall results in unique patterns of cavitation domain evolution, which in turn lead to variations in the pressure distribution and the emergence of new cavitation regions. The findings of this study provide valuable insights into the behavior of cavitation and atomization induced by underwater explosions near the free surface. The understanding gained from these investigations can contribute to the development of effective safety measures and protective strategies in marine and underwater engineering applications. By accurately predicting and mitigating the effects of cavitation, it is possible to enhance the design and operation of underwater structures, ensuring their integrity and minimizing the potential risks associated with underwater explosions.

Experimental and numerical analysis of rarefaction wave propagation across an orifice plate with varying thickness and diameter

Experimental and numerical analysis of rarefaction wave propagation across an orifice plate with varying thickness and diameter

Internal shocks hydrodynamics: the collision of two cold shells in detail

ABSTRACT Emission in many astrophysical transients originates from a shocked fluid. A central engine typically produces an outflow with varying speeds, leading to internal collisions within the outflow at finite distances from the source. Each such collision produces a pair of forward and reverse shocks with the two shocked regions separated by a contact discontinuity (CD). As a useful approximation, we consider the head-on collision between two cold and uniform shells (a slower leading shell and a faster trailing shell) of finite radial width, and study the dynamics of shock propagation in planar geometry. We find significant differences between the forward and reverse shocks, in terms of their strength, internal energy production efficiency, and the time it takes for the shocks to sweep through the respective shells. We consider the subsequent propagation of rarefaction waves in the shocked regions and explore the cases where these waves can catch up with the shock fronts and thereby limit the internal energy dissipation. We demonstrate the importance of energy transfer from the trailing to leading shell through pdV work across the CD. We outline the parameter space regions relevant for models of different transients,e.g. Gamma-ray burst internal shock model, fast radio burst blast wave model, Giant flare due to magnetars, and superluminous supernovae ejecta. We find that the reverse shock likely dominates the internal energy production for many astrophysical transients.

Numerička simulacija prometnog toka

The paper discusses the concept of traffic flow described by hyperbolic differential equations. In this paper the Lighthill-Whitham-Richards model (LWR model) is used to describe traffic flow. The said model uses two parameters to describe the traffic flow – density and average speed of vehicles. Numerical approximation of the LWR model is formulated through scalar conservation laws. The finite volume method is used for numerical results. The term of shock wave and propagation of rarefaction wave in traffic flow are described. This paper focuses on numerical simulation of traffic flow via fluid dynamics model for a single road with a traffic light. The results obtained in this paper are compared with previous studies.

Структурні особливості детонаційного потоку

The subject of this research is the processes that occur during the formation and propagation of a detonation wave in a flat channel. The goal of this work is to study the features of the complex multiform structure of the detonation wave and its influence on the integral parameters of the detonation flow. The task of the research was to identify regularities during the formation process and propagation of the detonation wavefront, establish the nature of the influence of the detonation front structure on the processes that occur in the zone of stable flow parameters, and analyze the gas-dynamic parameters of the flow at the final stage of the process - at the stage of propagation of rarefaction waves. The main research method is mathematical simulation using CFD technologies (ANSYS Fluent package). The main results of the study: it was established that the values of gas-dynamic parameters at the triple points of shock waves are significantly greater than the corresponding values at the Neumann peak, and in the areas between the triple points are significantly smaller; the values of the parameters averaged over the cross-section of the detonation wave front almost do not differ from the values of the parameters at the Neumann peak; the propagation velocity of the detonation wave averaged over the cross-section of the flow also corresponds to the calculated velocity according to the Chapman-Jouguet model; outside the zone of chemical reaction, the formation of triple configurations is impossible, therefore the speed of the detonation wave front will be lower than the values of Chapman-Jouguet, which will affect the further processes of propagation of the detonation; the processes of formation and propagation of the detonation wave front in a certain way influence the distribution of steady flow parameters, while the wave processes spread to the Taylor zone, which leads to significant turbulence of the wall layer; due to the turbulence of the wall layer, the intensity of convective heat fluxes into the channel wall increases. Conclusion: the obtained results are in good agreement with the results of known experimental studies and can be used in the calculation of the integral impulse characteristics of the detonation engine chamber and in the design of its cooling system.

Theoretical analyses on the one-dimensional charged particle transport in a decaying plasma under an electrostatic field

The spatiotemporal evolutions of a one-dimensional collisionless decaying plasma bounded by two electrodes with an externally applied electrostatic field are studied by theoretical analyses and particle-in-cell (PIC) simulations with the ion extraction process in a laser-induced plasma as the major research background. Based on the theoretical analyses, the transport process of the charged particles including electrons and ions can be divided into three stages: electron oscillation and ion matrix sheath extraction stage, sheath expansion and ion rarefaction wave propagation stage and the plasma collapse stage, and the corresponding criterion for each stage is also presented. Consequently, a complete analytical model is established for describing the ion extraction flux at each stage during the decaying of the laser-induced plasmas under an electrostatic field, which is also validated by the PIC modeling results. Based on this analytical model, influences of the key physical parameters, including the initial electron temperature and number density, plasma width and the externally applied electric voltage, on the ratio of the extracted ions are predicted. The calculated results show that a higher applied electric potential, smaller initial plasma number density and plasma width lead to a higher ratio of the extracted ions during the first stage; while in this stage, the initial electron temperature shows little effect on it. Meanwhile, more ions will be extracted before the plasma collapse once a higher electric potential is applied. The theoretical model presented in this paper is helpful not only for a deep understanding to the charged particle transport mechanisms for a bounded decaying plasma under an applied electrostatic field, but also for an optimization of the ion extraction process in practical applications.

Investigation on the cavitation and atomization characteristics of multiphase fluids in underwater explosion near a free surface

The characteristics of cavitation and atomization induced by underwater explosion near a free surface have been investigated by the multiphase fluid model based on two-fluid phase transition. This numerical method can provide the phase transition between liquid and its vapor phases during shock wave and rarefaction wave propagation at any time in underwater explosion. The detailed density, pressure, vapor, and liquid phases of volume fraction contours in cavitation and atomization zones can be obtained. The phase transition model was first used to quantitatively research the phenomenon of vapor liquefaction after shock wave propagation in initial water containing different trace amounts of vapor. Then the contribution of phase transition to the formation of cavitation and atomization in underwater explosion was investigated through a shock tube test and two typical underwater explosion cases. It is found that the phase transition effect between the vapor and liquid phases contributes more than 60% to the formation of the cavitation zone. Two charges under two different water surface conditions have been investigated by comparison with the case of a single charge. We can conclude that it is very necessary to introduce the phase transition model into the simulation of underwater explosion, which can provide details of the flow field in the cavitation and atomization zones that cannot be obtained by the one-fluid cavitation model.

Analysis and particle-in-cell simulation on the similarity relation during an ion extraction process

Ion extraction time is one of the key parameters for an ion extraction process. Particle-in-cell (PIC) simulation can provide a detailed description on the charged-particle behaviours during the ion extraction process in a decaying plasma. However, the PIC modelling is a very time-consuming task with very small space step (~ Debye length) and time step (~ inverse of plasma frequency), as well as a massive number of macro-particles, especially for the cases in multi-dimensions and large geometrical sizes. In this paper, based on the sheath expansion and ion-acoustic rarefaction wave propagation model, a similarity relation of ion extraction time with different geometrical sizes of the ion extraction regions is established. The theoretical analysis shows that, by changing the magnitude of the externally applied voltage to keep the ion extraction flux equal, the ion extraction time is proportional to the geometrical size ratio. Then, the PIC simulations on the ion extraction process are conducted, which show that there exists a good consistency with the theoretical analysis and previous experimental data. This research is helpful for promoting numerical simulations facing actual ion extraction processes with large geometrical sizes and provides theoretical guidance for improving the ion extraction efficiencies in applications.

Numerical Simulation and Analysis of Muzzle Flow During a Rarefaction Wave Gun Firing

AbstractRarefaction wave gun can significantly reduce the recoil and the barrel heat without affecting projectile velocity during the launching process. This paper aims to improve the understanding of the muzzle flow characteristics during a rarefaction wave gun firing and clarify the different ballistic behaviors between the rarefaction wave gun and the traditional gun. First, the mathematical models and the numerical methods of the muzzle flow with the interior ballistic process were established. Then, the numerical simulation results were compared with the experimental data to validate the reliability and accuracy. Next, the rarefaction wave propagation behavior was described, and the interior ballistic process of the rarefaction wave gun was compared with that of the traditional gun. Then the development law of the muzzle flow field for the rarefaction wave gun coupled with the interior ballistics process was studied. Finally, the different detailed results of the muzzle flow between the traditional gun and the rarefaction wave gun were investigated. The development processes of the muzzle flow in both guns are generally similar, but the strength of the main flow parameters and the ballistic performances for the rarefaction wave gun are smaller than that for the traditional gun due to the rarefaction wave influence. This paper could provide a valuable reference for the research and design on the rarefaction wave gun.

The Vlasov-Poisson-Landau system near a local Maxwellian

In this paper, we construct the global solutions near a local Maxwellian to the Vlasov-Poisson-Landau system with slab symmetry for the physical Coulomb interaction. The fluid quantities of this local Maxwellian are the approximate rarefaction wave solutions to the associated one-dimensional compressible Euler equations. We prove for the first time that for the Cauchy problem on this system, such a local Maxwellian is time asymptotically stable under suitably small smooth perturbations and global solutions tend in large time to the rarefaction waves of the compressible Euler system with the corresponding Riemann data. As a byproduct, the nonlinear stability of the same rarefaction waves for the pure Landau equation is also proved. This illustrates in our setting that the electric field does not affect the propagation of rarefaction waves to the Landau equation.

Three-Dimensional Numerical Simulation of the Development of Instability of a Contact Boundary of Colliding Metal Plates within the Gas-Dynamic Approximation

The development of the initial stage of instability of a contact boundary of colliding metal plates has been numerically simulated. The mathematical model is based on the Euler system of equations for a medium obeying the two-term equation of state. The parameters of the equation of state are calibrated proceeding from the calculated and experimental data based on real wide-range equations of state for metals. The computational algorithm is based on the Harten–Lax–van Leer scheme. The initial sinusoidal perturbation of the contact boundary between the plates after the propagation of rarefaction waves from the free plate boundaries becomes crater-shaped, which qualitatively corresponds to natural experiments.

Analysis of Some Modifications of the Large-Particle Method to Model Wave Dynamics Problems

We perform a numerical analysis of various modifications of the large-particle method applied to problems of wave dynamics (gas dynamics). We use modifications of the large-particle method to solve the problems on calculation of the decay of an arbitrary discontinuity, propagation of shock waves and propagation of rarefaction waves. Calculations of the propagation of stationary shock waves show that all considered modifications of the large-particle method allow to calculate correctly a pressure behind the shock wave, despite the fact that a width of the shock transition zone and a profile of the shock wave pressure in the zone depend on the modification of the large-particle method. During solving the problem on the decay of an arbitrary discontinuity, we show that the solution obtained by modified large-particle method with recalculation of pressure at the Euler stage best coincides with the analytical solution to the problem, both in the region of the shock wave and in the rarefaction wave region. A significant advantage of this modification is the fact that the considered problems can be solved without introducing the artificial viscosity into the laws of conservation.

Dam break flow solution using artificial neural network

The ability of a mathematical model to simulate the dam break shock-wave and rarefaction wave propagation is beneficial in the context of modeling shock dominated engineering problems. In this study, a novel technique based on artificial neural network (ANN) along with an equation is proposed and detailed for the solution of the one-dimensional dam break problems without source terms. The research is motivated by the fact that the classic numerical models show severe oscillations in the results, besides; all the existing analytical solutions are complex piecewise functions. Accordingly, a quick solution with a single equation and smooth results can be helpful for analyzing the problem. The model is developed with five parameters consisting the channel length, upstream and downstream water depths, time, and the distance factors as the input data, while the water depths and flow velocities are considered as the outputs. The model is well validated against several numerical and analytical solutions. Findings indicate that the ANN is capable of simulating the dam break flow problem satisfactorily and that the proposed model has outperformed the classical numerical results while its CPU time is one-third that of the numerical scheme.

Rarefaction wave propagation in tapered granular columns

The study of stress waves in granular materials is of some importance in several industrial bulk materials handling systems. In particular, the growth in the magnitude of rarefaction waves due to friction has been thought to play an important role in the silo quaking phenomenon. To this end, this paper examines the propagation of rarefaction waves in granular columns subject to Coulomb wall friction, focusing on the effect of geometry by examining converging and diverging tapered columns. A one-dimensional dynamic model of these systems is developed and analytical solutions of this model are compared to a numerical model based on the Arbitrary Lagrangian–Eulerian formulation in a finite element analysis. This numerical model was first validated using the known behaviour of cylindrical columns. In all cases, the rarefaction waves examined in this work grew with the distance travelled up the column; however, the rate was shown to depend on the half-angle of the taper. Over a range of small angles, the analytical model was found to accurately predict this behaviour.

Modelling of pressure pulse evolution at the contact of cold liquid with saturated vapor

The process of rarefaction wave propagation in saturated vapor at sudden contact with cold liquid is studied.

Air-Blast Effects on Structural Shapes of Finite Width

In blast engineering, many designs begin with simplified hand procedures with the loading parameters determined based upon a reflective surface of infinite size. Individual structural members such as columns have finite widths and should be considered as finite surfaces for blast loading calculations. A study was performed to investigate the effect of finite flange width on blast loadings on structural components. The diffraction of a blast wave around the leading edges of the cross section and the propagation of rarefaction waves from the leading edges to the column centerline leads to a more rapid reduction in reflected pressure than that of an infinite surface: a process that is widely known as clearing. A series of analyses were performed using the computational fluid dynamics code Air3d. Peak reflected pressures are not changed by the “finiteness” of the section, although the reflected impulse can be substantially reduced by clearing. For a given charge mass, held constant for a range of stand-off distances, R, impulse is approximately proportional to 1/R when considering an infinite surface. If clearing is considered, the reflected impulse is still proportional to 1/R, but can be 50% lower than the value computed for an infinite surface, which has significant implications for blast resistant design of structural components.

Evolution of pressure and temperature upon sudden contact of cold water and saturated steam

The process of rarefaction wave propagation upon sudden contact of cold water and saturated vapor is studied. It is shown that the most intensive steam condensation occurs over a time interval of about 0.01 ms, during which the water surface heats up. Then a constant temperature difference of 2-3 degrees is formed between the water surface and the steam and thus the condensation intensity is reduced.

Hydrodynamic Effects in Internal Shock of Relativistic Outflows

We study both analytically and numerically hydrodynamic effects of two colliding shells, the simplified models of internal shock in various relativistic outflows such as gamma-ray bursts and blazars. We pay particular attention to three interesting cases: a pair of shells with the same rest-mass density (equal rest-mass density), a pair of shells with the same rest mass (equal mass), and a pair of shells with the same bulk kinetic energy (equal energy) measured in the interstellar medium frame. We find that the density profiles are significantly affected by the propagation of rarefaction waves. A split feature appears at the contact discontinuity of two shells for the equal-mass case, while no significant split appears for the equal-energy and equal rest-mass density cases. The shell spreading within a few 10% of the speed of light is also shown as a notable aspect caused by rarefaction waves. The conversion efficiency of bulk kinetic energy to internal energy is numerically evaluated. The time evolutions of the efficiency show deviations from the widely used inelastic two-point mass-collision model.

Interaction of rarefaction waves with wet foam

The interaction of rarefaction waves of different shapes with wet water foams is studied experimentally. It is found that the observed values of the pressure are greater, while the surface velocity is lower than the corresponding values predicted by the pseudogas model. The foam breakdown starts as the pressure decreases by 0.3 atm relative to the initial pressure. During downstream propagation of the rarefaction-wave leading edge the propagation velocity decreases. Using of water-based foams as effective screens for damping blast waves in different technological processes has caused considerable interest in studying wave propagation in such systems. The pressure wave dynamics in a foam have been investigated in much detail, both experimentally and theoretically [1–3]. However, the interaction of rarefaction waves with foam has practically never been studied, although it was mentioned in [4] that the unloading phase following the compression wave phase is one of the factors defining the damaging action of blast waves. Besides blast-wave damping, rarefaction wave propagation takes place if such waves are used to breakup foam in oil-producing wells [5]. Below, the interaction of rarefaction waves of different shapes with wet water foams is studied. The vertical shock tube described in detail in [3] was used in these experiments.