Shock Wave Propagation Process Research Articles

Unsteady flow of droplet liquid in hydraulic systems of aircrafts and helicopters: models and analytical solutions

The subject of this study is the unsteady flow of liquid in pipelines, which are part of the design of airplanes and helicopters. This name means, first of all, the phenomenon of a sharp increase in pressure in the pipeline, which is known as a hydraulic shock. Although we have already learned to deal with this phenomenon in some parts of the systems, in many structural elements (flexible pipelines), inside which the working pressure reaches several hundred atmospheres, this phenomenon is still quite dangerous. As you know, the best way to deal with an unwanted phenomenon is through theoretical study. To date, there has been a huge amount of work in the direction of hydraulic shock research. This article does not fully cover these studies. It is limited to references to reviews and relevant works. Because the phenomenon of hydraulic shock has a significantly nonlinear character, analytical solutions of systems of equations corresponding to the simplest models were unknown until recently. This work presents, as an overview, already known analytical solutions describing the process of shock wave propagation. Most importantly, new achievements are given, both for the inviscid approximation and for considering internal viscous friction. It is shown that the internal friction within the considered model is negligible almost everywhere, except for the thin shock layer. The asymptotic is proportional to the tangent function and inversely proportional to the square root of the product of the Reynolds number and the dimensionless parameter characterizing the convection effect. Convection of the velocity field significantly affects the distribution of characteristics in hydraulic shock. If the self-similar solutions that were obtained earlier have a power-law character for the velocity distribution in the shock wave, then the simultaneous consideration in the model of convection and friction on the pipeline walls (according to the Weisbach-Darcy model) made it possible to obtain a distribution in the form of an exponential function that decays with increasing distance from the shock wave front. In addition, the work includes an original approach to solving a nonlinear system of differential equations that describes the propagation of a shock wave without considering the friction on the walls. Analytical solutions were obtained in the form of a function of pressure versus the velocity of shock wave propagation. Research methods. This work uses purely theoretical approaches based on the use of well-known fluid flow models, methods of analytical solution of differential equations and their systems, asymptotic methods, derivation of self-model equations, and finding their solutions. Conclusions. Analytical solutions of systems of differential equations were obtained, which describe models of hydraulic shock without considering viscous effects. A comparison of the obtained results with the results of other studies is given.

Attenuation effect of a preset bubble on hydrodynamic ram induced by fragments impacting fluid-filled tank

When the fluid-filled structure is impacted by a high-velocity penetrator, the hydrodynamic ram (HRAM) will appear and may induce catastrophic damage. Based on the damage mechanism of HRAM, a countermeasure through presetting a bubble inside the fluid-filled tank is proposed to attenuate the HRAM loads and thus alleviate the vulnerability of the tank structure under the impact of high-velocity projectile. Experimental tests are performed to compare the tank’s damage considering the effect of bubble by the charge-driven preset fragments. The experimental results show that the peak pressure and impulse of the initial impact wave acting on the tank rear plate are reduced by 78% and 88%, respectively, and the cavitation collapsing pressure acting on the rear plate almost disappeared. Meanwhile, the maximum deformation of the front plate is reduced by about 15%. In addition, numerical simulation is employed to reproduce the experimental process. By comparing the structural dynamic response and the shock wave propagation process, the attenuation mechanism of the preset bubble on HRAM is revealed. Furthermore, the influence of the bubble position and size on the attenuation effect is investigated. Numerical results show that a smaller distance between the bubble and the front plate, and a larger bubble size lead to a better attenuation effect.

Selection of Material and Thickness of the Protective Wall in the Conditions of a Hydrogen Explosion of Various Power

The main purpose of this study is a numerical assessment of the consequences of an explosion of a hydrogen-air cloud on the personnel of a hydrogen fueling station and the strength of a protective solid wall of certain dimensions. An explosive gas mixture is formed as a result of the destruction of high-pressure cylinders, the number of which determines the size of the cloud, the power of the explosion, and the scale of the consequences of environmental impact. To obtain the spatio-temporal distribution of the maximum overpressure and the impulse of the shock wave compression phase, a mathematical model of the dispersion of an active gaseous admixture is used, taking into account the chemical interaction with air oxygen. The probable consequences of the shock-impulse impact on the personnel at the control point are carried out using probit analysis. The values of the maximum bending moment and stress at the base of the protective wall, which result from the impact of the blast wave, are used to deterministically estimate the minimum wall thickness necessary for the safe operation of the protective device. The mathematical model takes into account the complex terrain and the three-dimensional non-stationary nature of the shock wave propagation process, and it is a source of data necessary to solve the problem of the strength of solid objects located in the area of baric perturbation of the gaseous medium. The developed methodology makes it possible to carry out a comparative analysis of the effectiveness of protective structures in relation to the power of the explosion.

Numerical investigation and analysis of indoor gas explosion: A case study of “6·13” major gas explosion accident in Hubei Province, China

Taking the ' 6·13 ′ major gas explosion accident in Shiyan, Hubei Province, China as an example, three problems were studied in this work: (1)The determination of the volume of natural gas involved in the explosion; (2)The propagation process of shock wave inside the building and the damage evolution process of the accident-related building; (3)The overpressure and fragment injury to the person outside the building. Through the numerical simulation in ANSYS/LS-DYNA software, the volume of natural gas involved in the explosion is determined to be 10240 × 1400 × 400 cm (length × width × height) from three perspectives: the damage to the building, the distribution of overpressure inside the building, and the TNT equivalent of the explosion energy. The simulation results are in good line with the accident, which verifies the effectiveness of the scheme and the accuracy of the numerical model. Based on the reasonable filling scheme, the propagation process of shock waves inside the building, the damage evolution process of the building, and the injury ranges of overpressure and fragments outside the building are analyzed. It can be found that the propagation of shock waves in confined space is complex and variable. The explosion shock waves are first reflected and superimposed in the watercourse, resulting in pressure rise. At about 8ms, the shock waves rushed into the first-floor space of the building, and the maximum overpressure was about 0.56 MPa. At about 50 ms, the shock waves rushed into the second-floor space, and the maximum overpressure was about 0.139 MPa. The first and second-floor slabs and infilled walls were almost completely destroyed. The interior walls of the infilled walls are mainly collapsed, and the exterior walls are ejection around the building as the center. The peak displacement and peak velocity of the interior walls of each floor are about 15% of the exterior walls. The fragments which cause fragment injury mainly come from the retaining wall above the watercourse, the maximum velocity is about 89 m/s, and the maximum displacement is 8.9 m. The safety distance of fragment injury is about 8.8 m, while the safety distance of overpressure injury is about 4.6 m. The lethal distance of fragment injury is greater than that of overpressure injury. Compared with the distance between different damage levels of overpressure injury, the difference in fragment injury is small. Therefore, the safety assessment at the engineering level only needs to consider the safety distance of fragment injury. This study can provide suggestions for evaluating the damage of natural gas cloud explosions in confined spaces and is helpful for accident investigation and safety protection.

An h-adaptive local discontinuous Galerkin method for second order wave equation: Applications for the underwater explosion shock hydrodynamics

The underwater explosion (UNDEX) phenomenon involves hydrodynamic behaviors with a wide range of spatial scales, from macroscopic cavitation regions to refined areas with fluid-structure interactions around the shock wavefront. Correct description of the refined shock wavefront is important for determining the shock wave position and pressure peak. In this work, the local discontinuous Galerkin (LDG) method for the two-dimensional wave equation, which allows for the local triangular meshes refinement and merging during the shock wave propagation process, is presented to model the UNDEX shock hydrodynamics. This article is an extension of our previous work, where we discretize the UNDEX total wave formulation in the LDG framework and simulate the UNDEX shock wave and cavitation phenomenon. In order to save computational cost (including CPU time and computational storage) and capture the shock wavefront more accurately, the LDG method is extended to be in combination with the mesh adaption technique. The troubled-cell indicator, depending on the local jump of the pressure, is adopted to identify elements which require to be refined or coarsened. Typical numerical examples are tested to assess the capability of the present h-adaptive LDG method for capturing the UNDEX shock wave. The numerical results clearly demonstrate that the mesh adaption technique enables us to dynamically increase the mesh resolution in close proximity to the flow discontinuities with a large pressure jump. The local increase of the mesh resolution results in a substantial increase in the accuracy of the pressure peak. In terms of the computational efficiency, the h-adaptive LDG method can save nearly half of the calculation time in comparison to the non-adaptive LDG method on uniform meshes, whose mesh resolution is the same as that of the maximum level of refinement of the h-adaptive LDG method.

Research on the distribution characteristics of explosive shock waves at different altitudes

There are great differences in the distribution characteristics of shock waves produced by ammunition explosions at different altitudes. At present, there are many studies on plain explosion shock waves, but there are few studies on the distribution characteristics of plateau explosion shock waves, and there is still a lack of complete analysis and evaluation methods. This paper compares and analyzes shock wave overpressure data at different altitudes, obtains the attenuation effect of different altitudes on the shock wave propagation process and proposes a calculation formula for shock wave overpressure considering the effect of altitude. The data analysis results show that at the same TNT equivalent and the same distance from the measuring point, the shock wave overpressure at high altitude is lower than that at low altitude. With the increase in the explosion center distance of the measuring point, the peak attenuation rate of the shock wave overpressure at high altitudes is smaller than that at low altitudes, and the peak attenuation rate of the shock wave overpressure at high altitudes gradually intensifies with increasing proportional distance. The average error between the shock wave overpressure and measured shock wave overpressure in a high-altitude environment obtained by using the above calculation formula is 11.1389%. Therefore, this method can effectively predict explosion shock wave overpressure in plateau environments and provides an effective calculation method for practical engineering tests.

Effects of Internal Fluid on the Dynamic Behaviors of Double Cylindrical Shells Subjected to Underwater Explosion

Abstract Fluid-filled double cylindrical shells were widely used in the marine engineering field and their blast resistance was considerably concerned. In this paper, the dynamic behaviors of fluid-filled double cylindrical shells subjected to underwater explosion were studied through a combination of experimental and numerical methods. First, a series of comparative underwater explosion tests were carried out on the scaled empty and fluid-filled double cylindrical shells. Then, more detailed numerical simulations were developed to give more results, and the model was verified by comparing with the data gathered from tests. Based on the experimental and numerical results, the effects of internal fluid on the shock wave propagation process, deformation modes, dynamic response, and energy characteristics of structures were analyzed. It is shown that the internal fluid is helpful to resist the structural deformation of outer shell and significantly decreased the axial strains of inner shell. Meanwhile, the dynamic response of the inner shell of fluid-filled shells was more violent. Besides, the internal and kinetic energy of outer shell decreased markedly. Above results would provide a reference for the protection of fluid-filled structures.

Comparative study between turbulence models in unsteady cavitating flow with special emphasis on shock wave propagation

The generation and propagation of shock waves are important sources of cavitation instability and material damage. This paper describes an evaluation of the predictive ability of different turbulence models in a compressible cavitation flow for shock wave propagation. The Schnerr–Sauer cavitation model is used to model cavitation and the volume of fluid method is used to capture the water/vapor interface. The pressure pulsations and cavity evolution given by numerical simulations and experimental results are compared to evaluate the correctness of the numerical method and the prediction accuracy of different turbulence models. The propagation mechanism of the shock wave, the evolution of vortex structures, and the temporal and spatial distribution characteristics of the cavitating flow are analyzed. The results show that the results predicted by the large-eddy simulation (LES) model are in good agreement with the experimental results. The shock wave is caused by a pressure wave that is generated by the collapse of the previously detached cloud cavity. This pressure wave hits the trailing edge of the cavity, thus inhibiting the development of the cavity and delaying the period of the cavity. In the process of shock wave propagation, the peak pressure and the peak lift (drag) coefficient appear at the same time. The propagation of the shock wave strongly disturbs the motion of the vortices, causing the large-scale vortex structure on the trailing edge of the hydrofoil to be depressed and the stable vortex on the hydrofoil to lift. The vortex stretching term and vortex dilatation term dominate the transmission process of the eddy current, and the vortex dilatation term is the most important in the process of shock wave propagation. The pressure fluctuations in the evolution of the cavity lead to changes in the statistical structure of the velocity field. Moreover, the anisotropy of velocity fluctuations in the cloud-cavity region is higher than that in the region of the sheet cavity. The Reynolds-averaged Navier–Stokes (RANS) model underestimates the cavity volume and the pulsation characteristics of the flow field, and cannot capture the negative X-direction velocity and vortex structure changes in the shock wave propagation process. Moreover, the RANS model and detached-eddy simulation (DES) model cannot accurately predict the characteristics of the flow field near the wall, and overestimate the dominant frequency of the cavity oscillations. The LES model is better at capturing the flow field characteristics in unsteady dynamics, and reproduces the shock wave propagation process well.

Controlling Vibration Speed in Tunnel Excavation Using Fine Blasting Method under Complex Environmental Conditions

It is very important to reduce the impact of blasting vibration on the surrounding structures during the tunnel drilling-blasting excavation. Taking the diversion tunnel of the urban water supply project in Zhumadian, Henan Province, China, as an example, the segmentation linear function between the drilling rig and borehole depth was established by fining blasting design. The test of the blasting number and particle vibration velocity was designed. The propagation and attenuation characteristics of blast vibration velocity in the surrounding rocks of the tunnel were analyzed by using theoretical calculation and field monitoring methods. Results show that the fine blasting design can realize the superposition of negative phase of shock waveform to reduce the vibration speed. With the increase of the blasting number, the attenuation of the particle vibration velocity shows a negative exponential function, and the dimensionless vibration velocity loss increases in a power function. The greater the loss, the greater the energy loss during the shock wave propagation process, which is more conducive to ensuring the stability of the protected buildings. The research results can provide the reference for similar engineering practices.

Effects of confining layer and ablating layer on laser-induced shock wave characteristics during laser shock processing by PVDF gauge

The PVDF sensor is used to obtain the time variation curves of the shock wave pressure in the four states of the laser shock peening with or without confining layer and with or without ablating layer, the effects of confining layer and ablating layer on shock wave characteristics are analyzed. The results show that the confining layer limits the plasma expansion area, and the inverse bremsstrahlung absorption effect is enhanced, so that the peak pressure and pulse width of the shock wave are increased to 10 times and 2 times that under the condition of the without confining layer; The ablating layer significantly increases the peak pressure of the shock wave by improving the laser energy coupling efficiency. However, the influence of the ablating layer on the peak pressure tends to saturate with the increase of power density, the difference of the peak pressure is only 8.5% when the laser power density is 4.53GW/cm2. In addition, the ablating layer complicates the shock wave propagation process, and the shock wave curve presents a multi-peak structure.

Numerical Modelling of Gas Explosion Overpressure Mitigation Effects

The main aims of this study are to assess numerically the mitigation effects caused by the solid wall installed at the fueling station in order to protect personnel from the consequences of the emergent gas explosion, evaluate the optimal location of the wall and choose the appropriate material the wall have to be made of in order not to be destructed. A three-dimensional mathematical model of an explosion of hydrogen-air cloud is used. A computer technology how to define the personnel damage probability fields on the basis of probit analysis of the explosion wave is developed. The mathematical model takes into account the complex terrain and three-dimensional non-stationary nature of the shock wave propagation process. The model allows obtaining time-spatial distribution of damaging factors (overpressure in the shock wave front and the compression phase impulse) required to determine the three-dimensional non-stationary damage probability fields based on probit analysis. The developed computer technology allows to carry out an automated analysis of the safety situation at the fueling station and to conduct a comparative analysis of the effectiveness of different types of material the protective facilities made of.

Numerical Study on the Propagation Law of Shock Wave in Turning Tunnel

To study the propagation law of the shock wave in turning tunnel, the propagation process of shock wave in underground turning tunnels of 15°, 30°, 45°, 60°, 75° and 90° was simulated based on ANSYS/LS-DYNA. Results show that at the turning corner, the overpressure on the outside wall is 2 times that on the inside wall. According to the overpressure ratio criterion, the length of the turbulent zone is no more than 3.2 times the equivalent diameter of the tunnel. With the increase of the turning angle, the attenuation coefficient of shock wave decreases gradually, which indicates that the overpressure attenuation becomes less obvious. The results can provide an important reference for the protection design of the turning tunnel.

Study on the Pressure Characteristics of Shock Wave Propagating across Multilayer Structures during Underwater Explosion

The propagation of the shock wave across multilayer structures during underwater explosion is a very complex physical phenomenon, involving violent fluid-structure interaction (FSI) problems. In this paper, the coupled Eulerian–Lagrangian (CEL) method in AUTODYN is used to simulate the process of shock wave propagation and solve FSI problems. Firstly, the governing equation and the treatment of fluid and structure interface of the CEL method are briefly reviewed. Afterwards, two underwater explosion numerical models are established, and the results are compared with the empirical formula and experimental data, respectively, to verify the reliability of numerical solutions. The results obtained by this method show good agreements with those of the empirical formula and experiment. Furthermore, the model of the multilayer structures composed of two hemispherical shells and the fluid filled between the shells subjected to underwater explosion is established, and the pressure characteristics of the shock wave propagating across the multilayer structures are analyzed regarding the wave reflection and transmission. Finally, the effects of the shell thickness and the filled fluid type among the multilayer structures on the wave reflection and transmission are studied.

Assessing safety conditions in underground excavations after a methane-air mixture explosion

A technique for evaluation of shock wave impulse after a methane-air mixture explosion is elaborated. The numerical model developed in previous studies has been verified in the laboratory by using laser initiation of explosives and measuring the pressure impulses of explosion products on a ballistic pendulum. To evaluate the mechanical impulse the functional correlations between its magnitude, the swing angle, and the pendulum characteristics have been derived analytically. The reliability of experimental results is ensured by calibrating the sensor that measures the pendulum swing angle and estimating the impulse measurement errors caused by specifics of angle measurements by a digital voltmeter, pendulum axis friction, and the pauses between measurements. Testing the developed technique to evaluate the shock wave impact showed satisfactory consistency of experimental and theoretical results with the momentum deviation below 9%, which confirms model applicability and correct reproducibility of the shock wave propagation process.

Characterization of laser-driven shock compression by time-resolved Raman spectroscopy

To characterize the laser-driven shock wave propagation process in anthracene molecules, the time-resolved Raman spectroscopy experiments were performed. After establishing a pressure distribution formula and using Lorenz profile to simulate the experimental Raman spectrum, the pressure distribution in the gauge layer during the pressure loading and unloading processes will be clarified in real time. The velocity of shock wave in the gauge layer, calculated through the shock front location at various delay time, is about 2.99 km s−1. Noticing that the relative intensity of compressed Raman mode is proportional to the velocity of the shock wave, in this work, this relationship was identified in a new mathematical expression after establishing a physical model. The velocity of shock wave calculated from the new formula is about 3.02 km s−1, which was in great agreement with the previous method and both methods are corresponded to practice.

Numerical simulation analysis of explosion process and destructive effect by gas explosion accident in buildings

Every year, the widespread use of natural gas in buildings results in a number of accidental gas explosions. On December 7th, 2015, a gas explosion accident occurred within buildings in the Shijingshan District of Beijing, China. Three people were slightly injured when a flammable concentration of natural gas had accumulated in the enclosed building space and ignited, resulting in a gas explosion. To study the process of this explosion and its destructive effect, a physical model that was consistent with the actual event was firstly established, using accident data from the above accident. Windows and doors in the building were designed for pressure relief. According to different leakages and scopes, numerical simulation of gas explosion was carried out by computational fluid dynamics explosion simulation software. In the simulation, the finite volume method was used to solve the compressible N-S equation in the three-dimensional Cartesian grid.In this paper, the shock wave propagation process in the building was analyzed and typical blast-wave curves were plotted at different locations. By comparing numerical simulation results with actual event, the most consistent filling scheme and equivalent ratio of gas reactions were obtained, and the calculation showed that the overpressure field and temperature field were consistent with the actual scene.Simulation results agreed well with actual destruction in the accident and verified the validity of the scheme. This research can provide suggestions for evaluating injuries and damages when gas explosions occur and might help in anti-blast designs and accident investigations.

Numerical simulation of detonation initiation induced by shock wave reflection in a rapid compression machine

This paper presents numerical study of detonation initiation induced by shock wave reflection which is photoed by high speed camera in a rapid compression machine. It is found that detonation initiates near the wall of combustion chamber. In the numerical study, the process of shock wave propagation, the interaction between shock wave and wall, and the detonation initiation by shock wave reflection are analysed with a CFD software. The numerical simulation demonstrates that mach reflection occurs near the wall during the propagation of the shock wave in the combustion chamber. The temperature of the region between the slip plane and the wall becomes higher. The auto-ignition of a hot spot in the high temperature region forms shock wave which is coupled with the reaction surface, resulting in the detonation finally.

Experimental Investigation of a Novel Blast Wave Mitigation Device

A novel blast wave mitigation device was investigated experimentally in this paper. The device consists of a piston-cylinder assembly. A shock wave is induced within the cylinder when a blast wave impacts on the piston. The shock wave propagates inside the device and is reflected repeatedly. The shock wave propagation process inside the device lengthens the duration of the force on the base of the device to several orders of magnitude of the duration of the blast wave, while it decreases the maximum pressure over an order of magnitude. Two types of experiments were carried out to study the blast wave mitigation device. The first type of experiments was done with honeycomb structures protected by the blast wave mitigation device. Experimental results show that the device can adequately protect the honeycomb structure. A second type of experiments was done using a Hopkinson bar to measure the pressure transmitted through the blast wave mitigation device. The experimental results agree well with results from a theoretical model.

OS1718 高速飛翔体衝突における衝撃波光学可視化計測

This paper reports the preliminarily experimental results of shock wave propagation visualization by hypervelocity impact. An experimental investigation of hypervelocity impact was performed by using a ballistic range at Institute of Fluid Science, Tohoku University. The process of shock wave propagation by hypervelocity impact was visualized by shadowgraph method and recorded by high-speed video camera.

Study on Influence Scope of Shock Wave and Smoke Flow after Gas Explosion

Gas explosion is very disastrous accident all over the world. Influence scope analysis of shock wave and smoke after gas explosion is of great importance and significance. The results indicate that, during the process of shock wave propagation destroying the air throttle, the shock wave energy will be consumed as part of air throttle destruction, which causes the overpressure reduced. However, the shock wave continues to be propagated and attenuated to a certain distance. Results on analyzing influence scope of smoke flow show that the smoke temperature and concentration in roadway are higher before restoring ventilation. The smoke is diluted by the fresh air through diffusion. After restoring ventilation, the temperature and concentration of smoke flow are lowered greatly. In conclusion, the influence scope study of shock and smoke flow is of full practice.