Blast waveform tailoring using controlled venting in blast simulators and shock tubes

A critical challenge of any blast simulation facility is in producing the widest possible pressure-impulse range for matching against equivalent high-explosive events.Shock tubes and blast simulators are often constrained with the lack of effective ways to control blast wave profiles and as a result have a limited performance range.Some wave shaping techniques employed in some facilities are reviewed but often necessitate extensive geometric modifications,inadvertently cause flow anomalies,and/or are only applicable under very specific configurations.This paper investigates controlled venting as an expedient way for waveforms to be tuned without requiring extensive modifications to the driver or existing geometry and could be widely applied by existing and future blast simulation and shock tube facilities.The use of controlled venting is demonstrated experimentally using the Advanced Blast Simulator(shock tube)at the Australian National Facility of Physical Blast Simulation and via numerical flow simulations with Computational Fluid Dynamics.Controlled venting is determined as an effective method for mitigating the impact of re-reflected waves within the blast simulator.This control method also allows for the adjustment of parameters such as tuning the peak overpressure,the positive phase duration,and modifying the magnitude of the negative phase and the secondary shock of the blast waves.This paper is concluded with an illustration of the potential expanded performance range of the Australian blast simulation facility when controlled venting for blast waveform tailoring as presented in this paper is applied.

Propagation law of shock waves and gas flow in cross roadway caused by coal and gas outburst

In order to study the propagation law of shock waves and gas flow during coal and gas outburst,we analyzed the formation process of outburst shock waves and gas flow and established the numerical simulation models of the roadways with 45°intersection and 135°intersection to simulate the propagation of outburst gas flow and the process of gas transport.Based on the analysis of the simulation results,we obtained the qualitative and quantitative conclusions on the characteristics and patterns of propagation and attenuation of outburst shock waves and gas flow.With the experimental models,we investigated the outburst shock waves and gas flow in the roadways with the similar structures to the simulated ones.According to the simulation results,when the angle between the driving roadway and the adjacent roadway increased,the sudden pressure variation range in adjacent roadway and the influencing scope of gas flow increased and the sudden pressure variation duration decreased.The intersection between the driving roadway and the adjacent roadway has no effect on airflow reversal induced by the shock waves and gas flow.

Molecular dynamics study of thermal stress and heat propagation in tungsten under thermal shock

Using molecular dynamics （MD） simulation, we study the thermal shock behavior of tungsten （W）, which has been used for the plasma facing material （PFM） of tokamaks. The thermo-elastic stress wave, corresponding to the collective displacement of atoms, is analyzed with the Lagrangian atomic stress method, of which the reliability is also analyzed. The stress wave velocity corresponds to the speed of sound in the material, which is not dependent on the thermal shock energy. The peak pressure of a normal stress wave increases with the increase of thermal shock energy. We analyze the temperature evolution of the thermal shock region according to the Fourier transformation. It can be seen that the “obvious” velocity of heat propagation is less than the velocity of the stress wave; further, that the thermo-elastic stress wave may contribute little to the transport of kinetic energy. The heat propagation can be described properly by the heat conduction equation. These results may be useful for understanding the process of the thermal shock of tungsten.

New method for rekindling the explosive waves in Maxwellian space plasmas

Our interest is to study the nonlinear wave phenomena in complex plasma constituents with Maxwellian electrons and ions. The main aim is to use a new method known as the(G′/G)method to exhibit the effects of dust charge fluctuations on the evolution of nonlinear waves. The coherent features of the shock and solitary waves along with the generation of high-energy waves have been amplified through the solution of the Korteweg–de Vries–Burgers equation,and the different natures of the waves were found successfully. Results are discussed graphically with the thoughtful choice of typical plasma parameters from different space plasma environments, exactly those found in cosmic dusty plasmas laden in ionospheric auroral region,radial spokes of Saturn's rings, planetary nebulae and solar F-corona region. All conclusions are in good accordance with the actual occurrences and could be of interest to further investigations of space. Moreover, the applicability of the present method is hoped to be a great enhancement by its use as ingenious mechanism used to evaluate the soliton dynamics and Burgers shock waves.

Solar Energetic Particle Event of 2005 January 20:Release Times and Possible Sources

Based on cosmic ray data obtained by neutron monitors at the Earth＇s surface, and data on near-relativistic electrons measured by the WIND satellite, as well as on solar X-ray and radio burst data, the solar energetic particle （SEP） event of 2005 January 20 is studied. The results show that this event is a mixed event where the flare is dominant in the acceleration of the SEPs, the interplanetary shock accelerates mainly solar protons with energies below 130 MeV, while the relativistic protons are only accelerated by the solar flare. The interplanetary shock had an obvious acceleration effect on relativistic electrons with energies greater than 2 MeV. It was found that the solar release time for the relativistic protons was about 06：41 UT, while that for the near-relativistic electrons was about 06：39 UT. The latter turned Out to be about 2 rain later than the onset time of the interplanetary type HI burst.

Near-source characteristics of two-phase gas-solid outbursts in roadways

Coal and gas outbursts compromise two-phase gas-solid mixtures as they propagate as shock waves and flows from their sources.Propagation is influenced by the form of the outburst,proximity to source,the structure and form of the transmitting roadways and the influence of obstacles.The following characterizes the propagation of coal and gas outbursts as two-phase gas-solid flows proximal to source where the coupled effects of pulverized coal and gas flows dominate behavior.The characteristics of shock wave propagation and attenuation were systematically examined for varied roadway geometries using experiments and numerical models.The results demonstrate that the geometry of roadway obstructions is significant and may result in partial compression and sometimes secondary overpressurization in blocked and small comer roadways leading to significant attenuation of outburst shock waves.The shock waves attenuate slowly in both straight and abruptly expanding roadways and more significantly in T-shaped roadways.The most significant attenuation appears in small angle comers and bifurcations in roadways with the largest attenuation occurring in blocked roadways.These results provide basic parameters for simplifying transport in complex roadway networks in the far-field,and guidance for the design of coal and gas outburst prevention facilities and emergency rescue.

Numerical method for sound propagation with acoustic shock waves in transonic flow ducts

The fourth order MacCormack scheme with fourth viscous term is used to improve the shocked solutions for sound propagation in varying cross area and hard-wall ducts with transonic flow. The artificial viscous coefficient is given out by an empirical formula. It is shown from three calculation examples of acoustic shock waves that the new method is much better than the second order MacCormack method which is the best one of second order schemes. Moreover, CPU times of both methods are almost the same.

Numerical Simulation of Flow Characteristics in Micro Shock Tubes

Recently micro shock tubes have been widely used in many engineering and industrial fields, but the characteristics of unsteady flow are not well known to date in micro shock tubes. Compared to conventional shock tubes with macro scales, flows related to shock waves in micro shock tubes are highly complicated. Stronger viscous and dissipative interactions make shock wave dynamic behaviors significantly different from theoretical predictions. In the present study, a CFD work was applied to the unsteady compressible Navier-Stokes equations which were solved using a fully implicit finite volume scheme. The diaphragm pressure ratio and shock tube diameter were varied to investigate their effects on micro shock tube flows. Different wall boundary conditions were also performed to observe shock wave and contact surface propagation with no slip and slip walls. Detailed flow characteristics at the foot of shock wave and contact surface propagation were known from the present numerical simulations.

Analysis of shock wave reflection from fixed and moving boundaries using a stabilized particle method

In the present paper, the efficiency of an enhanced formulation of the stabilized corrective smoothed particle method （CSPM） for simulation of shock wave propagation and reflection from fixed and moving solid boundaries in compressible fluids is investigated. The Lagrangian nature and its accuracy for imposing the boundary conditions are the two main reasons for adoption of CSPM. The governing equations are further modified for imposition of moving solid boundary conditions. In addition to the traditional artificial viscosity, which can remove numerically induced abnormal jumps in the field values, a velocity field smoothing technique is introduced as an efficient method for stabilizing the solution. The method has been implemented for one- and two-dimensional shock wave propagation and reflection from fixed and moving boundaries and the results have been compared with other available solutions. The method has also been adopted for simulation of shock wave propagation and reflection from infinite and finite solid boundaries.

Research on the collapse process of a near-wall bubble

The effect of wall on the bubble collapse is significant. A compressible numerical simulation method based on the state equation was used to numerically calculate the collapse process of bubbles at different leaving wall distances. The results show that when the dimensionless distance between the bubble center and the wall is greater than zero, the bubble generates a high-pressure region at the top of the interface, which induces a jet toward the wall. When the dimensionless distance is less than zero, the jet is generated from the vicinity of the contact position between the bubble and the wall and moves along the wall towards the center axis of the bubble. When the dimensionless distance is equal to zero, that is, the center of the bubble coincides with the center of the wall, the bubble shrinks uniformly, and its collapse process is consistent with that of a single bubble in free space under the same parameter conditions. Comparison of these three typical cases of dimensionless distance from the wall reveals that the presence of the wall induces an asymmetric effect and a pressure gradient effect in the flow field around the bubble, and the farthest point away from the center of the attached wall is a high-pressure region, which induces destabilization of the bubble interface and the occurrence of jets.

Insights into microstructural evolution and deformation behaviors of a gradient textured AZ31B Mg alloy plate under hypervelocity impact

We have for the first time elucidated the microstructural evolution and deformation behaviors of a gradient textured AZ31 B Mg alloy plate under the ultrahigh strain rate of ~10~6 s^(-1) that is generated by a two-stage light gas gun with the hypervelocities of 1.6-4.4 km s^(-1). The hypervelocity impact cratering behaviors indicate that the cratering deformation of AZ31 B Mg alloy is mainly affected by the inertia and strength of the target material. The crater prediction equation of AZ31 B Mg alloy target under impact velocity of 5 km s^(-1) is given. The 2017 Al projectile completely melts in the Mg alloy target plate at the impact velocities of 3.8 km s^(-1) and 4.4 km s^(-1), and the microstructural evolution around the crater is: dynamic recrystallization zone, high-density twinning zone, low-density twinning zone, and Mg alloy matrix. It is found that the dynamic recrystallization, twinning and cracking are the main deformation behaviors for the AZ31 B Mg alloy to absorb the shock wave energy and release the stress generated by the hypervelocity impact. The main plastic deformation mechanisms of the Mg alloy target during hypervelocity impact are twinning and dislocation slip. Microstructure analysis shows the interactions of twins-twins, dislocations-dislocations, and twins-dislocations determine the strain hardening during the hypervelocity impact process, which eventually contributes the dynamic mechanical properties. The evolution of microhardness around the crater further demonstrates the microstructural evolutions and their interactions under the hypervelocity impacts.

An improve d smoothe d particle hydrodynamics approach using new inverse kernel function

The main limitation of Smoothed Particle Hydrodynamics(SPH)method that resists the method’s poten-tial is its lack of providing stability and accuracy to the numerical technique.We improve the accuracy of the standard SPH technique,by formulating a new inverse logarithmic kernel function.This new kernel function is derived based on the underlying properties of kernel functions.The approximation technique used here is based on the Moving Least Squares based technique.The adequacy of the proposed ker-nel function is tested by simulation of 2D shock wave propagation and 3D dam-break free surface flow against a cuboidal obstacle.The method was validated against experimental data by Kleefsman et al.,[1].The numerical results reveal that our new SPH approach using inverse logarithmic kernel function outper-forms existing ones in particle restoration,zero error,better accuracy and enhanced efficiency in kernel approximation.This new kernel function showed some improvement over existing kernels by showing very less error approximation value of 0.035h 2.The results showed some improvements over standard technique by being capable of handling problems with large deformations accurately and precisely.