Shock Waves In Air Research Articles

Opto-mechanical expulsion of individual micro-particles by laser-induced shockwave in air

It was recently demonstrated that laser filamentation was able to generate an optically transparent channel through clouds and fog for free-space optical communications applications. However, no quantitative measurement of the interaction between the laser-induced shockwave and the aerosol particles has been carried out so far, leaving the precise nature of the clearing mechanism up for discussion. A critical question was the maximum distance at which the filament could still act on the aerosol particle. Distances widely exceeding the filament diameter and its energy reservoir exclude other potential clearing effects like shattering or explosion by direct exposure to the laser. Here, we quantify the force exerted by the shockwave on a single aerosol microparticle. The force is measured by observing the ejection and displacement of the particle when trapped in an optical tweezer. We demonstrate that even for distances ranging from 1.5 to 5.5 mm away from the filament, thus widely exceeding the filamentary region, an acoustic force of 500 pN to 8 nN (depending on the initial laser power) acts on the aerosol particle and expels it away from the optical trap.

Energy Evolution Mechanism of Air Shock Wave Propagation and Attenuation Based on VMD–HT Energy Spectrum

Energy spectrum is an important tool for reflecting time–frequency characteristics of signals. The energy spectra of air shock wave at different explosion distances ware analyzed to investigate the energy evolution mechanism in the propagation and attenuation process. Waveforms of air shock wave were obtained from explosion tests and numerical simulations. Energy propagation and attenuation mechanisms of air shock wave were discussed on the basis of the wave theory of fluid. Instantaneous and marginal energy spectra of air shock wave were calculated using variational modal decomposition (VMD) and Hilbert transform (HT). Energy evolution laws of air shock wave with time, frequency, and explosion distance were analyzed according to the statistical results of the energy spectra. Results showed that the instantaneous energy peak of air shock wave is directly proportional to the square of its pressure peak while inversely proportional to the third power of propagation distance. Nonlinear attenuation of air shock wave will cause frequency dispersion and decelerate the attenuation rate of the total energy of air shock wave. The energy evolution laws of air shock wave with time and frequency reflected by instantaneous and marginal energy spectra were consistent with the theoretical analysis results.

Design and Execution of Demolition Works By Blasting of Industrial Constructions – Technical and Safety Aspects

Abstract The paper describes the practical way and security conditions of realizing the demolition of an industrial chimney located in an oil refinery platform, having in the immediate vicinity sensitive equipment and constructions. The chimney has a height of 150 m and consists of the outer tubular structure of reinforced concrete and an inner chimney made of refractory brick masonry. In order to establish the possible secondary effects generated by the blasting works, a risk assessment was made with reference to seismic wave, air shock wave, noise, dust and the level of shock generated by the impact of chimney construction with the soil. The demolition work was carried out successfully and due to protection and safety measures no unwanted events were recorded, and the measured values of the seismic wave generated by the impact with the ground of the chimney were non-dangerous, being below the values estimated in the risk assessment.

Interaction of Air Shock Waves with Parachute Stoppings in Mine Explosions

Interaction of Air Shock Waves with Parachute Stoppings in Mine Explosions

Heat and radiative fluxes in strongly nonequilibrium flows behind shock waves

State-to-state and two-temperature theoretical models for high-temperature strongly nonequilibrium reacting and radiating air flows are developed in the framework of the generalized Chapman - Enskog method. In the theoretical approach, the sets of governing equations for coupled fluid dynamics, chemical kinetics, internal energy transitions and radiation are derived; the algorithms for the calculation of state-resolved transport coefficients are developed and implemented. The proposed models are applied for 1-D simulations of shock waves in air under high-temperature conditions observed in flight experiments. Nonequilibrium mixture composition, temperatures and pressure profiles are obtained and compared for various models of chemical reaction rate coefficients. Flow variables strongly depend on both the kinetic-theory approach and chemical reaction model; species molar fractions and temperature show significantly different behaviour for the state-to-state and two-temperature simulations. Transport properties and radiative fluxes are calculated as functions of the distance from the shock front. It is found that diffusion provides a major contribution to the total energy flux whereas the role of heat conduction is weak due to the compensation effects. It is shown that under considered conditions, two-temperature models are not applicable for correct predictions of radiative heating.

Liquid Jet Blasting Using Ultra-High Frequency Supersonic Pulsed Air Jet

This paper reports an experimental study on a liquid injector assembly integrated with an ultra-high frequency pulsed air jet that operates at 21 kHz. The active air-blasting assembly steadily injects a liquid through four micro-nozzles of 0.4 mm diameters each, positioned around a 1 mm nozzle through which the pulsed actuation jet flows out at supersonic velocity. High-frequency compressible air vortexes and shock waves generated by the injector atomize the liquid stream into finer droplets and distribute them to a larger area to improve mixing with the ambiance. The paper presents the design details and preliminary studies on the flow field characteristics of this novel injection scheme, which is a potential candidate for high-speed flow mixing and control applications.

Interaction of Air Shock Waves with Parachute Stoppings in Mine Explosions

Interaction of Air Shock Waves with Parachute Stoppings in Mine Explosions

Gas-Dynamic Approach to the Calculation of an Underground Structure for the Impact of an Air Shock Wave

Gas-Dynamic Approach to the Calculation of an Underground Structure for the Impact of an Air Shock Wave

Seismic design of NPP structures taking into account foundation slab compliance

The present article proposes a mathematical method for factoring in the compliance of foundation slabs in NPP structures under dynamic loading. In many cases, such an approach allows the analysis results to be significantly improved, whereas sometimes it is simply a necessary part of the procedure, i.e., when structures having “detached” exterior walls are exposed to an air shock wave generated by an aircraft crash.The presented method applies soil springs and dampers as per ASCE 4-16, specially distributed along the foundation slab bottom of a building.The conclusion presents the results of calculating the integral characteristics of soil springs and dampers according to the realistic (saddle-shaped) law of their distribution along the foundation slab bottom of a typical building.

The impact of heavy object on an underground structure when falling onto the ground surface

At the objects of space infrastructure and at nuclear power facilities there are industrial structures, the main task of which is to protect a person, equipment or machinery from emergencies such as, for example, explosions, falling of various objects, fragments. In accordance with the requirements of the Federal Law On the Protection of the Population and Territories from Natural and Technogenic Emergencies, when calculating such structures, all types of loads corresponding to their functional purpose must be taken into account. So, for structures located in the area of a possible accident and the fall of space rockets, it is necessary to calculate for the fall of the destroyed parts of the rocket engine. For nuclear power plant facilities, such accidents occur when containers and other heavy objects fall on the ground, affecting underground structures located in the ground, and for civil defense protective structures built into the basement floors of buildings, it is necessary to consider situations in which the overlying floors of a building collapse when exposed to there is an air shock wave on them. Therefore, this problem is relevant, and in this study, a finite-element method for calculating an underground structure in a non-linear dynamic setting has been developed when a large overall object collides with the ground.

Experimental investigations of direct measurement of borehole wall pressure under decoupling charge

Decoupling charge is quite widely applied in smooth blasting, pre-splitting blasting, and bench blasting. The borehole wall pressure (BWP) is an indispensable condition for analyzing blasting action as it is the main initial parameter that determines the stress wave generated in the rock. In this study, a full-scale concrete model (4.0 m in length × 3.0 m in width × 1.6 m in height) with two boreholes was utilized to directly measure the BWP under decoupling charging. PVDF (polyvinylidene fluoride) gauges were employed as pressure-sensing devices to develop a technique for direct measuring high dynamic pressure due to its superior characteristics. The values of measured peak pressures of the borehole wall ranged from 1461 to 205 MPa within 0.1–1.1 m from the explosive charge end along the borehole axis. BWP of decoupling charge are responses to air shock wave loading and explosion gas loading, in which the responses near the explosive charge are the results of air shock wave and explosion gas working together, while the responses far from the charge are merely loaded by the air shock wave. The strain rates varied from 2.12 to 0.73 s−1 for the test range, which has confirmed that decoupling blast loading is a quasi-dynamic process. By fitting the experimental data, it is found that the peak value of BWP along the borehole axisdecreases as a power function with the increase of the distance from the explosive. The findings may be of great significance to mechanism analysis of rock blasting, scientific design of blasting schemes, and numerical simulation of rock blasting.

Numerical Simulation of the Dynamics of a Reinforced Concrete Slab under an Air Shock Wave

Numerical Simulation of the Dynamics of a Reinforced Concrete Slab under an Air Shock Wave

Evaluation of blast mitigation effects of hollow cylindrical barriers based on water and foam

Using structurally weak materials to construct blast barriers is a promising approach for blast mitigation because these materials have multiple potential energy-dissipation modes and barely produce secondary hazards. This research experimentally and numerically investigated the blast mitigation effects of different hollow cylindrical barriers using water or/and polyurethane (PU) foam. In view of the characteristics that momentum acquired by the barrier debris might increase the near-field blast loading, a sliding impulse witness device was designed to determine the loadings induced by the air shock waves and debris impact. Six explosive experiments were performed to study the influences of the barrier’s materials and structures in terms of pressure, impulse, structure response, etc. Numerical models corresponding to experiments were established, which can reproduce the dynamic response of the barriers. The experimental results show that among water or/and PU barriers, the protective performance of the PU_water barrier has advantages in comprehensive evaluation, whose mitigation efficiency for a scaled mass is 48% higher than that of the water barrier. The corresponding impulse is significantly lower because the foam is restrained by water, without premature disintegration to form a large debris impact. However, the pressure distribution of different barriers was not improved with the material arrangement, since that the main factor affecting it is the deflection of the blast wave through shadowing effect. The simulation results further revealed that although the dominant energy absorption mechanism and efficiency of the foam can be changed by material arrangement, the energy dissipated by the foam is negligible compared to the heat of explosion, resulting in a minimal effect on the overpressure distribution.

High-order numerical scheme for compressible multi-component real gas flows using an extension of the Roe approximate Riemann solver and specific Monotonicity-Preserving constraints

The purpose of this paper is to develop a high-order shock-capturing scheme capable of predicting flows where shock waves with high-temperature jumps interact with multi-component real gas mixtures, assuming a local thermodynamic equilibrium. We first propose a generalization of the Roe solver for distinct species with non-ideal thermodynamic properties that relies on the original method proposed by Vinokur & Montagné [1]. This method uses an approximation of compressibility factors to estimate a coherent value of the speed of sound at the Roe averaged state.This Roe averaged state is introduced in the One-Step Monotonicity-Preserving (OSMP) scheme, originally developed by Daru and Tenaud [2], to obtain an extension to the high-order with Lax-Wendroff procedure adequate for dealing with non-ideal gas flows. To avoid thermodynamic inconsistencies in the evolution of the Roe average state over a large stencil, we propose to reformulate the discrete total energy flux of the initial solver. This new formulation uses a combination of Riemann invariants related to the species mass fractions and avoids the influence of the independent values of the compressibility factors in the total energy flux computation. An additional M-P constraint on this new combination allows dealing with discontinuities. Based on the averaged speed of sound estimated by our proposed extension of the Vinokur & Montagné method, we demonstrate that this new formulation is equivalent to selecting a new combination of compressibility factors that completely fulfill the jump relationships of the Riemann problem.To properly capture discontinuities while optimizing the number of numerical cells, the new high-order OSMP scheme is combined with an Adaptive Multiresolution [3] procedure to automatically refine grid in regions where steep gradients occur and coarsen grid elsewhere. The order of the numerical method is evaluated on the convection of density and mass fraction waves. Its capability of capturing discontinuities is validated on a 1-D shock tube problem with a mixture of Nitrogen, Oxygen and dense refrigerant R22 gases. We show that smooth solutions, as well as discontinuities, are recovered with high accuracy. The 2-D interaction between a shock wave in Air with a cylindrical bubble initially filled with dense refrigerant R22 gas is also considered. Present results compare very well with both a recent fully resolved numerical solution of ideal gases and experimental results obtained with real gases. Compared to ideal gas solutions corresponding to calorically perfect gas, drastic changes are recorded on the predicted temperature and the bubble flow patterns that fully justify the use of relevant thermodynamics and the proposed numerical method to account for real gas properties.

Modeling of weak shock waves propagation in aqueous foam layer

Dynamics of low-intensity air shock waves in the shock tube containing an aqueous foam layer is theoretically investigated. Modeling of studied process is carried out using two-phase model of aqueous foam developed by the authors in single-pressure, single-speed and two-temperature approximations. The model takes into account the Ranz-Marshall interphase contact heat transfer, effective Herschel-Bulkley viscosity, which describes foam behavior as a non-Newtonian fluid, and elastic properties of aqueous foam under a weak shock impaction without destruction of foam structure. Properties of air and water as the foam components are described by realistic equations of state. Computer implementation of the aqueous foam model is carried out in the solver, developed by the authors in OpenFOAM software. The influence of aqueous foam viscoelastic properties on the intensity and structure of a shock wave has been investigated. When analyzing the obtained solutions, reliability of the proposed model and method of numerical modeling is estimated by comparative analysis of the found solutions and literature experimental data.

Исследование и разработка компонентов газогенераторных составов на основе нитрата аммония для повышения безопасности производства взрывных работ

The article is devoted to the study and development of the components of gas generator compositions based on the ammonium nitrate to improve safety of blasting operations. This is primarily due to the low cost of ammonium nitrate, low sensitivity to mechanical and detonation effects and a significantly lower content of harmful compounds in the combustion products compared to the analogues. PA-4 aluminum powder was used as fuel, carbon black powder — as a gas-forming agent. The effect was studied concerning different amounts of aluminum powder on the combustion characteristics of a gas generator composition based on the ammonium nitrate. Calculated and experimental data showed that it is unreasonable to introduce more than 5 % of aluminum into the composition. According to the results of the conducted study, a gas generator composition based on the ammonium nitrate was developed to increase blasting operations efficiency and safety. Laboratory and polygon studies confirmed the efficiency and safety of using gas generator compositions at the destruction of stone. Destruction of the stone occurred without scattering of individual fragments, formation, and propagation of an air shock wave. Thus, the urgent task is to ensure blasting operations safety using gas generator compositions, which will allow to eliminate the formation of harmful, toxic gases and the high explosive effect.

Вибухо-індукована нейротравма (патофізіологічні та патоморфологічні особливості)

The article presents the results of pathophysiological and pathomorphological features which were studied in experimental blust-induced neurotrauma in rats. The relevance of this study is associated with the frequent blust neurotrauma resulting from the use of explosives in military conflicts. At the same time, neurotrauma is more common, which is clinically manifested by cognitive impairment, even with mild and moderate severity. This, in turn, leads to complications and disability for young people. The purpose of the work was to study the consequences of the air-shock wave influence on the functional and morphological states of the central nervous system. Materials and methods. The studies were carried out on 36 white male Wistar rats 5-7 months old, weighing 180-220 g. The rats were divided into two groups: I – experimental group (n=18), the animals of which were anesthetized with halothane, fixed and explosion-induced neurotraum was simulated by generating a baroacoustic wave with an excess pressure of 26.4 ± 3.6 kPa. II group was a control group (n=18). Functional changes were investigated in the Barnes maze. For pathomorphological examination, brain sections were stained with hematoxylin and eosin. The animals were kept in standard conditions and in the standard diet of the vivarium, all studies were conducted in accordance with modern international requirements and norms of humane treatment of animals (Council of Europe Convention dated 18.03.1986 (Strasbourg); Helsinki Declaration 1975, revised and supplemented in 2000, Law of Ukraine dated 21.02.2006 No. 3447-IV), which is evidenced by an extract from the protocols of the meeting of the commission on biomedical ethics. Results and discussion. Analysis of the results of memory studies in the Barnes maze showed a significant (Р <0.05) increase in the latent time of entering the shelter in rats of the experimental group in the acute and early post-traumatic period, which indicates memory impairment. General characteristics of the rats behavior in the experimental group showed an increase in anxiety and disorientation. The increase in research on "fake shelters" and the chaotic movement around the facility was evidenced. Analysis of frontal histological sections of the rat brain in the dynamics of the explosion-induced neurotrauma development showed the presence of characteristic signs in the form of diffuse microhemorrhages in the hippocampus zone in the acute period of injury, diffuse areas of perivascular and pericellular edema in the early post-traumatic period and paretic dilated capillaries in the structure of the cerebral region on 2nd-3rd week of the post-traumatic period. Conclusion. Thus, quantitative (increased latent time) and qualitative (increased anxiety) signs of impaired orientational-spatial memory and the development of specific pathomorphological signs of explosive brain damage in rats of the experimental group were established

Analysis of the ignition induced by shock wave focusing equipped with conical and hemispherical reflectors

The interaction of a plane shock wave in air with concave profiles has been used in the past to understand the nature of shock wave focusing. The current study examines the complex two-dimensional flow field resulting from the interaction of a plane shock wave entering a symmetrical cavity with a curved end wall. The development of reflection patterns of the incident shock wave at the profile wall and the process of gas dynamic focus are of particular interest. In this study, numerical and experimental studies are performed to understand the ignition behavior in a stoichiometric methane-oxygen-argon mixture due to shock wave reflection from a variety of shapes, including planar, 60° and 90° conical and hemispherical reflectors. The numerical simulation reveals the complex two-dimensional flow field when the shock wave collides head-on with different reflectors and the propagation behavior of the reflected waves in the process of focusing. The instantaneous maximum temperature and pressure as a function of shock wave intensity in four reflectors are given and analyzed. The experimental results show that two ignition modes, namely, weak ignition and strong ignition, occur in those reflectors when the incident shock wave velocity (Vi) is greater than a critical value, and the separatrix between the weak and strong ignition for each reflector is demonstrated to be highly dependent on Vi. The critical values of Vi for the 60° conical, 90° conical and hemispherical reflectors are 740, 775 and 780 m/s, respectively. The ignition delay time (tign) of the combustible mixture under shock wave focusing for various reflectors is provided. The results show that in the weak ignition mode, tign is shorter in the hemispherical reflector than in the others, and therefore, its Pign (the maximum pressure after ignition) is higher. However, the result is completely opposite in the strong ignition mode, which is mainly because the ignition temperature of hot spots in the hemispherical reflectors is much lower than those in the conical reflectors. This study provides new simulation and experimental evidence of the ignition behavior in various reflectors, supporting the effect of enhancing shock wave focusing on the ignition performance.

Damage assessment of prefabricated prestressed channel slab under plane charge blast

The study of the mechanical properties of prestressed concrete channel slabs under different plane charge air blasts for applications in civil defense engineering is significant. For this reason, similar simulation tests were conducted on the anti-explosive performance of three 1:3 scale prestressed concrete channel slabs under 9 times plane charge air blast. The positive duration was more than 260 ms to simulate the uniform distribution load of a strong blast air shock wave on the prestressed concrete channel slab. The results showed that the designed prestressed concrete channel slab had good displacement ductility without brittle destruction, which significantly reduced the damage of the blasting impact on the structure. The channel slab could resist an air shock load of 0.467 MPa without damage. On the other hand, the positive duration was not only related to the quality of the overlying soil but also related to the air shock wave overpressure design value. The channel plate is regarded as a rigid-plastic component to calculate its plastic dynamic response under explosive load. In addition, the reliability of the theoretical calculation results and ABAQUS software simulation were verified by experimental data, which provided a feasible analytical method for calculation and simulation research in civil air defense engineering.

Numerical and experimental studies of deflections of conventional and strengthened reinforced concrete bendable elements under short-term dynamic loading

The relevance of this study is conditioned by the technical complexity of the design solutions for construction projects of ground-based space infrastructure. It is associated with the possibility of special loads in the form of an air shock wave in the event of a launch abort, a fall of a fragment, an emergency shutdown of engines, an air shock wave from the indirect impact of nuclear weapons, seismic loads, accidental cargo falls, terrorist attacks, etc. Such impacts with a high degree of probability lead to damage to building structures and in the future, they need to be reinforced. These building structures must have survivability under special loads and deform without collapsing. Under the dynamic loading, the energy intensity of the bendable structures is important, to determine which it is necessary to know the magnitude of the acting force and deflections. The effective load in a wide class of problems refers to the initial data, and the determination of reliable values of the dynamic deflection of the bendable structure is an actual problem. The purpose of this study is to conduct a numerical and experimental investigation of the deflection of conventional and strengthened reinforced concrete structures under short-term dynamic loading. This study used the following research methods: measurements of deflections and loads by strain measurement, graphical analytic research using Microsoft Excel, numerical calculation in the environment of the Explicit Dynamics module of the Ansys software package. As a result of the study, experimental investigation of conventional and strengthened bendable reinforced concrete elements under short-term dynamic loading was carried out, the values of the effective force and deflections were obtained. The same experiment was modelled in the environment of the Explicit Dynamics module of the Ansys software package. A comparison of the deflection parameters was made, based on the results of numerical and physical experiments on the example of a specific design, which showed satisfactory convergence.