Shock Waves In Air Research Articles

Dynamic Interaction of the two Incompressible Plates and Soil Set with a Layered Elastic Half-space

Genesis of the problem descends from the need to implement shelters for military and civil defense purposes. In designing of the stationary shelters structures we must take into account the risks arising from the ability to use of the nuclear means of destruction.Admitted to the analysis system is a model that reflects the reality structure, consisting of the shelter with the soil and concrete overlay. This system rests on the layer soil surface. The analyzed dynamic interaction is caused by air shock wave. The main interaction factors are the wave stress processes in all soil layers. These processes are subject to wave interference with unsteady boundary conditions. Taking into account the spatial aspects of the problem we were used our own one-dimensional discrete calculation model which is characterized by the high accuracy of the wave processes analysis, expressed by the zero-error of the method. This model has a specific structure of each elementary discrete component. These are two half-masses with deformable connector.As a result, of the numerical experiments one obtained extensive information about the properties of the dynamic interaction of the consider set with the multi layered subsoil.Click

Spherical piezoceramic sensors for measuring shock-wave parameters

The results of the development and the main performance characteristics of spherical piezoceramic sensors of four sizes (with diameters of the sensitive elements of 5, 10, 15, and 32 mm), which are intended for measuring the parameters of pulse pressures behind the front of air shock waves in the range of 0.0001–2.0 MPa, are described. Examples of the practical use of spherical piezoceramic sensors for measuring the parameters of air shock waves in shock tubes and explosive experiments are presented.

Mining induced collapse in 1997 and seismic records at Changyu, SE China

Quarry induced collapse, an issue of particular concern in the mining industry, is a typical form of manmade disaster. Identification of the morphological characteristics of such collapses is commonly based on seismic records but comprehensive studies regarding the mechanism and energy conversion mode utilizing the seismic record is seldom undertaken. A huge collapse event at the Biyutan mining cavern at Changyu Dongtian in Wenling city, China, lasting for about 20 seconds, was observed on August 11, 1997. After the collapse, nearly 11 million m 3 of rock blocks were left on the floor. By conducting a field survey on engineering geology, retrospectively analyzing the collapsing process through interviewing local residents, referring to related documents, and identifying the seismic records obtained from 3 surrounding seismic stations, it was established the roof collapse at the Biyutan cavern, excavated in massive tuff, was due to over excavation of several pillars, which substantially affected the stress field in cavern roof giving rise to a local failure of the roof that gradually developing into a widespread failure in an area EW 800m long, SN 460m wide. During the collapse, outbursts of water and air shock waves result in loss of life and property within a distance of 150m from the mine opening. This reminds us that reasonable allocation of sufficiently strong safety pillars and installation of monitoring system are absolutely essential in quarrying operations to avoid overall failure and ensure the safety of the people nearby.

Numerical Analysis of Blast Load from Explosive Materials Using Finite Volume Method

A method of numerical analysis of the phenomenon of the air shock wave propagation is presented. The paper describes an explicit own solution. It uses Finite Volume Method (FVM). It also takes into account energy losses due to a heat transfer. For validation, the results of numerical analysis were compared with the literature reports. Both one-dimensional (an explosion in the pipe) and three-dimensional (explosion within the compartment) flow of a shock wave were analysed. Values of impulse, pressure, and its duration were studied. Finally, an overall good convergence of numerical results with experiments was achieved. Also the most important parameters were well reflected.

Features of vortex formation under the impact of a pressure pulse on a gas region bounded by the foam layer

The features of the dynamic processes related to the interaction between air shock waves and aqueous foam barriers accompanied by formation of vortex flows are simulated numerically and investigated. The method of solving is based on the two-phase gas-liquid mixture model generalized for solving spatial problems with the use of the equations of state in the analytic form which describe the thermodynamic properties of the mixture components.

A methodology to predict shock overpressure decay in a tunnel produced by a premixed methane/air explosion

A methodology for estimating the blast wave overpressure decay in air produced by a gas explosion in a closed-ended tunnel is proposed based on numerical simulations. The influence of the tunnel wall roughness is taken into account in studying a methane/air mixture explosion and the subsequent propagation of the resulting shock wave in air. The pressure time-history is obtained at different axial locations in the tunnel outside the methane/air mixture. If the shock overpressure at two, or more locations, is known, the value at other locations can be determined according to a simple power law. The study demonstrates the accuracy of the proposed methodology to estimate the overpressure change with distance for shock waves in air produced by methane/air mixture explosions. The methodology is applied to experimental data in order to validate the approach.

On peculiarities of near-threshold initiation of powder density explosive by air shock wave and by solid impactor

The features of near-threshold mode of initiating by gas-tight piston and high- enthalpy gas flow was evaluated for a powder density explosive PETN. Both methods lead to the development of detonation in about 10 μs time. The synchrotron radiation diagnostics have shown that the initial stages of the process were significantly different, that diversity being caused by the influence of the gas flow in the pores of the charge. In this work, the effect of the gas flow on the mode of initiation was studied experimentally.

The Godunov Method for Calculating Multidimensional Flows of a One-Velocity Multicomponent Mixture

Computational formulas of the Godunov method are given for the equations of a generalized-equilibrium model of a heterogeneous medium on a curvilinear grid; with the use of this method, the problems of interaction of air shock waves with bubbles of various gases are investigated. Flow of a gas–liquid mixture in a nozzle mouthpiece is considered. The Prandtl–Meyer flow of a water–air mixture is calculated and compared with a self-similar solution.

Experimental study on ground vibration of blasting the boulder with tandem shaped charging warhead

Hazardous effects of blasting the boulder with the new breaking-blasting equipment-tandem shaped charging warhead are mainly air shock wave, seismic wave and blast slung shot. Blast-induced ground vibration is one of the inevitable effects and may cause substantial damage to nearby structures. Started from the formation process and mechanism of ground vibration to study the seismic wave, the research attained curve of vibration velocity of monitoring points by TC-4850 and carried out differential and fast Fourier transform analysis of the curve. And the results concluded that blasting vibration with tandem shaped charging warhead mainly comes from prime charge; the attenuation law can be predicted by Sadev’s Formula. Explosion vibration frequency range is 20-150 Hz, while with the increase of distance from the blasting center, blasting vibration intensity attenuates rapidly, vibration duration increases and vibration frequency gradually reduces. Compared with general rock blasting, its attenuation rate of blasting vibration is faster with higher frequency and smaller impact on buildings, but the harm effects should not be ignored for the special application environment.

Planar shock wave sliding over a water layer

In this work, we conduct experiments to study the interaction between a horizontal free water layer and a planar shock wave that is sliding over it. Experiments are performed at atmospheric pressure in a shock tube with a square cross section ( $$200\times 200\,\hbox {mm}^2$$ ) for depths of 10, 20, and 30 mm; a 1500-mm-long water layer; and two incident planar shock waves having Mach numbers of 1.11 and 1.43. We record the pressure histories and high-speed visualizations to study the flow patterns, surface waves, and spray layers behind the shock wave. We observe two different flow patterns with ripples formed at the air–water interface for the weaker shock wave and the dispersion of a droplet mist for the stronger shock wave. From the pressure signals, we extract the delay time between the arrival of the compression wave into water and the shock wave in air at the same location. We show that the delay time evolves with the distance traveled over the water layer, the depth of the water layer, and the Mach number of the shock wave.

International Conference on Gravitation Cosmology and Continuum Mechanics (dedicated to the centenary of Kirill Petrovich Staniukovich)

International Conference on Gravitation Cosmology and Continuum Mechanics (dedicated to the centenary of Kirill Petrovich Staniukovich)

Nano-second Laser-induced Plasma Shock Wave in Air for Non-contact Vibration Tests

Herein a vibration test method is discussed based on a non-contact, non-destructive excitation input using a laser-induced plasma (LIP) shock wave and a non-contact input estimation using Newton’s second law of motion. We have previously introduced a non-contact vibration test method using an excitation force generated by laser ablation, but it cannot be used when the target structure is lightweight, fragile, and small-sized because a crater with a diameter of several micrometers is created. The LIP generates a highly reproducible shock wave, which become an excitation force to a target structure. This shock wave depends on the gas density, gas specific heat ratio, laser fluence, and ambient environment. If these parameters are constant, the LIP excitation force can be estimated beforehand, allowing only the output measurement to determine the frequency response measurement of an input–output relationship of the target structure. After calibrating the LIP excitation, the frequency response function of a target structure can be obtained.

Study on the collinear delay double pulse laser induced air plasma expansion by optical interference

In this paper, the air plasma expansion dynamics induced by collinear delayed double nanosecond laser pulses are studied by optical interference method, and comparative analyzed the difference of the air plasma expansion generated by single pulse laser and collinear delayed double pulse laser. The experimental results show that the air plasma expansion distance, expansion velocity and shock wave pressure produced by collinear delay double pulse laser are all larger than that of single pulse because of existing the second laser pulse interaction with the air plasma formed by the first one, and the plasma action time is effectively delay. Finally the mechanisms of the inter-pulse delay time effect on air plasma expansion process are analyzed.

Non-contact ultrasonic acquisition of femtosecond laser-driven ablative Mbar-level shock waves on Ti alloy surface

Mbar-level ablative plume pressures, produced by single-shot femtosecond laser ablation of a dry Ti alloy surface and driving shock waves in air and in the solid target, were characterized using non-contact broad-band ultrasonic measurements. X-ray diffraction measurements reveal the resulting shock-wave induced sub-GPa residual compressive stresses over multi-micrometer depths inside the target, indicating GPa-level residual compressive stresses on its surface.

Specific features of modeling of nonequilibrium radiation behind the shock wave in air in the vacuum ultraviolet spectral range

A physical-chemical model of generation of nonequilibrium molecular radiation in the vacuum ultraviolet (VUV) spectral range behind the shock wave in air for shock wave velocities from 4.5 to 9.5 km/s is developed. Experimental results obtained in a shock tube in investigations of photoionization of air ahead of the shock wave front are used for verification of the numerical model of VUV radiation in the wavelength range from 85 to 105 nm. Model calculations show that nonequilibrium VUV radiation arises in a very thin high-temperature layer behind the shock wave front and is affected by heavy particles and electrons.

Особенности моделирования неравновесного излучения ударной волны в воздухе в области вакуумного ультрафиолетового спектра

Особенности моделирования неравновесного излучения ударной волны в воздухе в области вакуумного ультрафиолетового спектра

Blast load estimation using Finite Volume Method and linear heat transfer

From the point of view of people and building security one of the main destroying factor is the blast load. Rational estimating of its results should be preceded with knowledge of complex wave field distribution in time and space. As a result one can estimate the blast load distribution in time. In considered conditions, the values of blast load are estimating using the empirical functions of overpressure distribution in time ( Δp(t) ). The Δp(t) functions are monotonic and are the approximation of reality. The distributions of these functions are often linearized due to simplifying of estimating the blast reaction of elements. The article presents a method of numerical analysis of the phenomenon of the air shock wave propagation. The main scope of this paper is getting the ability to make more realistic the Δp(t) functions. An explicit own solution using Finite Volume Method was used. This method considers changes in energy due to heat transfer with conservation of linear heat transfer. For validation, the results of numerical analysis were compared with the literature reports. Values of impulse, pressure, and its duration were studied.

Wind tunnel experiments on flow separation control of an Unmanned Air Vehicle by nanosecond discharge plasma aerodynamic actuation**Project supported by the National Natural Science Foundation of China (Grant Nos. 61503302, 51207169, and 51276197), the China Postdoctoral Science Foundation (Grant No. 2014M562446), and the Natural Science Foundation of Shaanxi Province, China (Grant No. 2015JM1001).

Plasma flow control (PFC) is a new kind of active flow control technology, which can improve the aerodynamic performances of aircrafts remarkably. The flow separation control of an unmanned air vehicle (UAV) by nanosecond discharge plasma aerodynamic actuation (NDPAA) is investigated experimentally in this paper. Experimental results show that the applied voltages for both the nanosecond discharge and the millisecond discharge are nearly the same, but the current for nanosecond discharge (30 A) is much bigger than that for millisecond discharge (0.1 A). The flow field induced by the NDPAA is similar to a shock wave upward, and has a maximal velocity of less than 0.5 m/s. Fast heating effect for nanosecond discharge induces shock waves in the quiescent air. The lasting time of the shock waves is about 80 μs and its spread velocity is nearly 380 m/s. By using the NDPAA, the flow separation on the suction side of the UAV can be totally suppressed and the critical stall angle of attack increases from 20° to 27° with a maximal lift coefficient increment of 11.24%. The flow separation can be suppressed when the discharge voltage is larger than the threshold value, and the optimum operation frequency for the NDPAA is the one which makes the Strouhal number equal one. The NDPAA is more effective than the millisecond discharge plasma aerodynamic actuation (MDPAA) in boundary layer flow control. The main mechanism for nanosecond discharge is shock effect. Shock effect is more effective in flow control than momentum effect in high speed flow control.

Diagnostics of the loss of stability of loaded constructions and the development of the sites of breakdown during the action of seismic explosion and air shock waves

One of the challenging problems for mining enterprises, namely, predicting the decrease in the strength of the structure elements in guarded buildings and constructions during blasting, is solved in terms of a stress concentration factor, the time of exceeding the long-term tensile strength, and the crack growth rate. It is shown that the existence of stress concentrators in the form of natural heterogeneities or defects in the building materials of the building elements subjected to the action of seismic explosion and air shock waves results in crack growth. The distribution of cracks in samples of some materials and the ultimate tensile strength of these materials are determined to find the surface energy. The size distribution of cracks is used to calculate the effective crack length.

Contact and non-contact ultrasonic diagnostics of shock waves driven by single-shot femtosecond laser ablation of titanium

Initial pressures and expansion speeds of air shock waves, driven by single-shot femtosecond laser ablation of titanium surface at fluences up to 6 J/cm2, were acquired by means of front-side non-contact time-of-flight ultrasonic measurements. Similar contact ultrasonic measurements on the rear side of the titanium target demonstrate general correlation of ultrasonic amplitudes the measured in the contact and non-contact modes at high ablative pressures (above 100 GPa, superelastic propagation regime), and strong deviation of these dependences at lower ablative pressures (strong dissipation regime) without any indications of new titanium phases, besides the initial α-Ti phase.