Shock-wave Processes Research Articles

Features of Shock-Wave Processes and Fracture in Anisotropic Materials

For the description of the behavior of anisotropic materials within the framework of the phenomenological approach the model which is taking into account distinctions in strength on compression and a stretching is offered. The model as allows carrying out researches with any orientation of properties of a material concerning system of coordinates. Numerical modeling is carried out in three-dimensional statement. The range of velocities of interaction up to 3000 m/sec is considered.

Numerical Simulation of Underwater Explosive Welding Process

Recently, underwater explosive welding shows its advantage in some difficult-to-weld combinations such as material with thin thickness, high hardness, and fragile quality. The pattern of the typical wave morphology in the interface of the welding specimen indicates the suitability of the selected experimental parameters and sound strength of the laminates. For the existence of the water, traditional Gurney formula and Aziz formula can not directly be used to evaluate the velocity and acceleration process of the flyer plate. Numerical simulation is necessary and irreplaceable for existing knowledge. Underwater explosive welding process was numerically simulated by ANSYS/LS-DYNA to explore the underwater shock wave and deformation process of the flyer plate. Velocity and pressure distribution of welding plates were obtained. The velocity of the flyer plate could satisfy the minimum velocity in explosive welding. It was found that water prevented the gross distortion and ensured the integrity of the composite laminate. Welding rate was increased by expanding the size of the explosive.

Mathematical modeling of shock-wave processes under gas solid boundary interaction

The results of numerical simulations are presented for planar air flows in a bounded volume of square cross section diminishing due to a uniform motion of the walls, for a flow of a propane-air mixture under sinusoidal variation of the size of the square domain, and for three-dimensional supersonic air and propane-air flows in channels of variable square cross section. Specific features of shock-wave processes that are associated with the piston effect and cumulation are established. The hypersonic analogy between planar and spatial flows is confirmed, which allows one to use two-dimensional solutions in estimating three-dimensional flows. The equations of a multicomponent ideal perfect gas and one-stage kinetics of chemical reactions are used to describe the flows. The method of numerical simulations is based on S.K. Godunov’s scheme and implemented within an original software package.

Investigating shock-wave transient processes in explosives by means of synchrotron radiation

The results from studying the transient processes induced by a shock in porous TATB, obtained using an original and tested method based on employing the soft X-ray component of synchrotron radiation, are presented. The method enables us to determine the parameters of a shock-wave striker, the distribution of velocity and density behind the front of the shock and detonation wave, and the characteristics of flow after a shock wave is reflected from a rigid wall, all in one experiment. Trials with charges 1.8 and 1.9 g/cm3 in density show that modes such as the absence of detonation and initiation in direct and reflected shock waves, are possible depending on the loading conditions.

On a Nonsymmetric Keyfitz-Kranzer System of Conservation Laws with Generalized and Modified Chaplygin Gas Pressure Law

This paper is devoted to the study of a nonsymmetric Keyfitz-Kranzer system of conservation laws with the generalized and modified Chaplygin gas pressure law, which may admit delta shock waves, a topic of interest. Firstly, we solve the Riemann problems with piecewise constant data having a single discontinuity. For the generalized Chaplygin gas pressure law, the solution consists of three different structures:R+J,S+J, andδ. Existence and uniqueness of delta shock solution are established under the generalized Rankine-Hugoniot relation and entropy condition. For the modified Chaplygin gas pressure law, the structures of solution areR+JandS+J. Secondly, we discuss the limits of Riemann solutions for the modified Chaplygin gas pressure law as the pressure law tends to the generalized Chaplygin gas one. In particular, for some cases, the solutionS+Jtends to a delta shock wave, and it is different from the delta shock wave for the generalized Chaplygin gas pressure law with the same initial data. Thirdly, we simulate the Riemann solutions and examine the formation process of delta shock wave by employing the Nessyahu-Tadmor scheme. The numerical results are coincident with the theoretical analysis.

Shock wave negative pressure characteristics of underwater plasma sound source

The propagation process of intense acoustic shock wave, generated by the discharge of underwater plasma sound source, is analyzed based on a modified Rayleigh model. The bunching sound field model of underwater plasma sound source is established by using the Euler equation as the control equations. The formation mechanism of the shock wave negative pressure is analyzed theoretically and intuitively through the sound field charts obtained by simulation. The results demonstrate that the waters around the bunching wave will be stretched and form a zone of negative pressure with the combination of the rarefaction wave and the inertia of water. It will make the waters to form a discontinuous phenomenon if the stretching force is great than the ultimate tensile strength of the water, the phenomenon of cavitation bubble will appear at this time. Besides that, negative pressure will be aggravated by the diffracted wave generated at the edge of the energy-gathered reflector, and the shock wave negative pressure will reach the maximum value by the superimposition of the edge diffraction wave and the stretch wave. The reasons for the formation of the shock wave negative pressure is testified and revealed further by comparing the waveforms of simulation and experiment. The study results provide a theoretical guide for understanding the propagation law of underwater shock wave and further improving the design of the underwater plasma sound source.

Shock-wave Processes Modelling on Railway Vehicles Using a Scaled Model Utilizing Viscoelastic Properties

The shock impacts on the railway vehicles with two-stage spring suspension excite in working mode. These impacts change the kinematics components of the movement, i.e. linear and angular speeds at the end of the shock process and free damped vibrations of the mechanical system arise. In this paper, our aim is to perform a dynamic scaling of the original model in order to build up a new double mass model utilizing viscoelastic properties which is smaller with small masses and is easier to work even possible in laboratory conditions. The new dynamically scaled model is supposed to perform the same behaviour as the original one if its natural frequencies are the same with the original model. The two masses M1 and M2 of the new double mass scaled utilizing viscoelastic properties model are calculated after optimization performed with numerical calculations of the characteristic polynomial varying with masses in order to fit the same natural frequencies. The objective of the work presented in this paper is to model the shock-vibrations response of the railway vehicle using a scaled model utilizing viscoelastic properties and to compare the results derived here with the results obtained using the original model.

Identification of the model of nonlinear viscoelasticity of filled polymer materials in millisecond time range

Determination of mechanical characteristics of filled polymer materials in shock wave processes is of interest in calculations of the strength of these materials. The standard computation methods are based on the use of the linear theory of viscoelasticity, where there is no distinction between the active and passive deformation processes. In the present paper, dynamical experiment and theoretical modeling are used to illustrate the important role played by the sharp decrease in the resistance of a filled polymer material in unloading (in the millisecond time range). The higher the degree of filling of this material, the more significant this effect is.

Numerical simulation of shock wave processes in elastic media and structures. Part II: Application results

The authors present finite difference algorithms for solving nonstationary problems on dynamics of elastic media and structures, and perform numerical modeling of the following applied problems: stroke on an elastic half-plane by a rigid die; shock piling; generation of a pendulum wave in a blocky medium by a local impulse effect. One of the goals of the presented modeling is driving the problem solutions with minimized influence of spurious effects inherent to numerical approximation. Finally, the authors compare the results obtained in different models of elastic media.

Study of shock-wave flows in the channel by schlieren and background oriented schlieren methods

The results of recording gas flow in a shock tube by the schlieren and background oriented schlieren (BOS) methods after initiating a pulsed (surface or volume) discharge are presented. Simultaneous recording of the flow field by the two methods allows a complete qualitative and quantitative analysis of the shock-wave processes resulting from the interaction of a pulse discharge with high-velocity flow. The vector displacement field of the BOS method was determined by the cross-correlation method. The density field was obtained by solving the Poisson equation with special boundary conditions. It was shown that the BOS method yields a good quality map of the flow structure that corresponds to the classical schlieren method and provides reliable quantitative results except in areas of high gradients. A modification of the BOS method was proposed and tested to measure the density jump at the shock-wave front. Recording was performed at an angle to the plane of the wave front. Various Schemes of processing of digital flow images were tested. The proposed method provides a resolution of large density gradients at the shock-wave front. The obtained quantitative results are consistent with the calculated values.

Modeling of shock-wave deformation of polymethyl metacrylate

A model of a Maxwellian elastoplastic body is constructed to describe the behavior of polymethyl metacrylate (C5O2H8)n under loading. A principal feature of this model is supplementing the governing equations with the relaxation time of shear stresses in the form of a continuous dependence on parameters characterizing the state of the medium. The analytical form of the dependence is chosen with allowance for microstructural and mesostructural mechanisms of irreversible deformation. Another specific feature of the model is the equation of state of the medium, which includes the dependence of the internal energy on the first and second invariants of the strain tensor. Such an approach allows obtaining a unified mathematical description of all physical states of polymers. Particular attention is paid at the stage of model verification to comparisons of model predictions with experimental data for the temperature of the shock-compressed material and decay of the shock wave due to its interaction with overtaking and side rarefaction waves. This comparison shows that the model provides an adequate description of shock-wave processes in polymethyl metacrylate.

Numerical simulation of shock-wave processes in elastic media and structures. Part I: Solving method and algorithms

Finite-difference algorithms for solving non-stationary wave problems are presented, which allow to obtain the description of fronts and front zones with a minimal influence of spurious effects of numerical approximation. The principal condition of the construction of calculation algorithms is the convergence of domains of dependence of continual and difference equations. It is shown that the fulfillment of this condition provides a maximally exact wave fronts description. Numerical solutions of several one-dimensional and two-dimensional wave problems are presented. In the second part of the paper, we will give examples of numerical simulation of applied problems of structure dynamics and geodynamics — impact driving of piles into the soil, formation of pendulum waves in a block massif, stress state of a homogeneous massif in the zone of interaction with a punch, fracture of a layered solid under the action of a local pulse, and high-speed penetration of a layered target.

Microwave diagnostics of shock-wave and detonation processes

A method for measuring the parameters of shock-wave and detonation processes using a microwave interferometer is proposed. The experimental technique used in the study and the employed method of processing experimental data are described. Examples of experimental studies carried out using a radio interferometer of the three-millimeter range are considered.

Review about acceleration of plasma by nonlinear forces from picoseond laser pulses and block generated fusion flame in uncompressed fuel

AbstractIn addition to the matured “laser inertial fusion energy” with spherical compression and thermal ignition of deuterium-tritium (DT), a very new alternative for the fast ignition scheme may have now been opened by using side-on block ignition aiming beyond the DT-fusion with igniting the neutron-free reaction of proton-boron-11 (p-11B). Measurements with laser pulses of terawatt power and ps duration led to the discovery of an anomaly of interaction, if the prepulses are cut off by a factor 108(contrast ratio) to avoid relativistic self focusing in agreement with preceding computations. Applying this to petawatt (PW) pulses for Bobin-Chu conditions of side-on ignition of solid fusion fuel results after several improvements in energy gains of 10,000. This is in contrast to the impossible laser-ignition of p-11B by the usual spherical compression and thermal ignition. The side-on ignition is less than ten times only more difficult than for DT ignition. This is essentially based on the instant and direct conversion the optical laser energy by the nonlinear force into extremely high plasma acceleration. Genuine two-fluid hydrodynamic computations for DT are presented showing details how ps laser pulses generate a fusion flame in solid state density with an increase of the density in the thin flame region. Densities four times higher are produced automatically confirming a Rankine-Hugoniot shock wave process with an increasing thickness of the shock up to the nanosecond range and a shock velocity of 1500 km/s which is characteristic for these reactions.

Investigation of shock-wave processes in a bubble liquid during the interaction with a barrier

The parametric analysis the process of reflection a shock wave in a gas-liquid mixture from solid wall is conducted. The results are compared with the experimental data for mixture of water and nitrogen bubbles.

Shock-wave induced damage in lipid bilayers: a dissipative particle dynamics simulation study

The effects of shock-wave impact on the damage of lipid bilayer membranes are investigated with dissipative particle simulations at constant energy (DPDE). A coarse-grained model for the phospholipid bilayer in aqueous environment is employed, which models single lipids as short chains consisting of a hydrophilic head and two hydrophobic tail beads. Water is modeled by mapping four H2O molecules to one water bead. Using the DPDE method enables us to faithfully simulate the non-equilibrium shock-wave process with a coarse-grained model as the correct heat capacity can be recovered. At equilibrium, we obtain self-stabilizing bilayer structures that exhibit bending stiffness and compression modulus comparable to experimental measurements under physiological conditions. We study in detail the damage behavior of the coarse-grained lipid bilayer upon high-speed shock-wave impact as a function of shock impact velocity and bilayer stability. A single damage parameter based on an orientation dependent correlation function is introduced. We observe that mechanical bilayer stability has only small influence on the resulting damage after shock-wave impact, and inertial effects play almost no role. At shock-front velocities below ≲ 3000 ms−1, we observe reversible damage, whereas for speeds ≳ 3900 ms−1 no such recovery, or self-repair of the bilayer, could be observed.

Experimental investigation of shock-wave processes in the pulsed ionization of the surface of a shock-tube channel

The interaction of a shock wave and the gas flow behind it with the plasma formed by a surface electric discharge in a shock tube was investigated.

Localization of a strain wave propagating in damaged material

Distribution of a strain wave propagation in nonlinear-elastic damaged material is studied. It is shown that damage leads to spatial localization of the wave process and formation of a weak shock wave.

Explosive plasma-vortex optical radiation sources

The results of experimental study of explosive radiation sources based on pulsed injection of a cumulative plasma jet into atmospheric air are considered. The injection process is accompanied with intense vortex formation as well as the formation of a large-scale toroidal plasma vortex. High-power electromagnetic radiation in the optical range is generated due to shock-wave processes during deceleration of a plasma jet in air and plasma-chemical processes in the vortex. The temporal structure of a radiation pulse being generated contains components from the micro- and millisecond range. For a 20-g mass of the explosive charge, a peak radiation power of 300 kW/sr and an energy yield of 400–600 J/sr integrated over the emission spectrum are attained. The efficiency of conversion of the chemical energy of the explosive into radiation is 5.0–7.5%.

An axisymmetric electric discharge as a means for remote heating of gas and for ignition of combustible gas mixture

Experimental and theoretical investigations are performed of gasdynamic phenomena accompanying a ring electric discharge excited in air at atmospheric pressure. It is experimentally demonstrated that the discharge generates a toroidal (three-dimensional) shock wave which cumulatively converges toward the axis. A mathematical model is constructed, which describes the process of focusing of the toroidal shock wave. The results of measurements of shock-wave processes accompanying the discharge are in good agreement with the calculation results; this enables one to estimate the gas temperature which may be attained in the region of cumulative convergence at some distance from the ring center. Results are given of first experiments in the excitation of a ring shock wave in a combustible gas mixture (stoichiometric mixture of CH4:O2).