Shock Wave Characteristics Research Articles

Investigation on energy characteristics of shock wave in rock-breaking tests of high voltage electric pulse based on Hilbert-Huang transform

High voltage electric pulses (HVEPs) can damage hard rocks with electrical energy as the driving force. Fracture process of rock and energy characteristics of shock wave (SW) can better explain the fracture mechanism of HVEP. Self-developed HVEP system fractures rocks. By using high-speed camera technology, the extension of cracks can be shown in form of pictures. The Hilbert-Huang transform (HHT) is utilized to characterize the instability of rock fracture in terms of time domain-frequency domain-energy deposition. The results show that increased voltage leads to structural transformation of rock interior to instability. The peak energy of SWs occurs near 0 s, and decreases rapidly within 0.1 s 0–20 Hz is the region of concentrated distribution of SWs energy. In addition, instabilities occur at the moment of rock fracture, including an increase in the vibration frequency range of SWs and a shift in the main frequency of vibration. The occurrence of cracks suppresses waves propagation.

Numerical study of liquid jet and shock wave induced by two-bubble collapse in open field

The shock waves and high-speed jets induced by the violent collapse of bubbles can cause serious damage to nearby structures. To fully understand the shock wave and jet characteristics induced by bubble-bubble interaction, we developed a diffuse-interface method for the simulation of compressible two-phase flow, which combined interface compression technique with interface sharpening technique to keep the sharpness of the shock wave and phase interface. The thermodynamically consistent five-equation model was improved using interface compression technique to maintain a constant thickness of the phase interface. To further suppress numerical dissipation, the high-order scheme WENO (Weighted Essentially Non-Oscillatory) and interface sharpening function THINC (Tangent of Hyperbola for INterface Capturing) were used for the flux reconstruction at the grid boundary to ensure that the total variation at the cell boundary was minimized (Boundary Variation Diminishing, BVD), thus the spatial reconstruction scheme, named WENO-THINC-BVD, was developed. Moreover, we extended the present method to a block-structured adaptive mesh refinement framework to improve grid resolution and save computing resources. Numerical results of several benchmark tests fully demonstrated the advantages of the present method in simulating complex compressible flows containing shock-shock and shock-interface interactions. Based on the present high-fidelity numerical methods, we investigated the shock wave and liquid jet induced by the two-bubble interaction in an open space. A phase diagram of the liquid jet propagation direction as a function of the initial bubble pressure and the inter-bubble distance was summarized. Finally, according to the bubble-bubble interaction process, an empirical formula for the collapse strength and another for the attenuation of shock waves were developed.

Denoising method for weak velocity test signals under laser-induced shock waves based on attention-guided multi-scale convolutional neural network

In the research of characteristics of laser-induced shock waves via the laser interference velocity detection method, noise reduction for weak echo signals still relies on the manual setting of filtering parameters, alongside the problem of the loss of useful signals caused by global filtering and excessive filtering. To solve these problems, a multi-scale network for extraction of sparse features, in combination with the ECA channel module, was established in this study to acquire the features of multi-dimensional and multi-fine-granularity noise signals in a self-adaptive manner. By integrating various channel information of the deep/shallow features through skip connection, the deep features were fully observed without ignoring the impacts of the shallow features. Finally, the attention mechanism was adopted to adjust the weight of the features at different locations in the feature space to acquire an accurate representation of stochastic noise, and noise reduction for weak signals was achieved by reconstructing the module and removing the learned noise features from the noisy data. According to the simulation and test results, the method proposed in this study helped extract the noise information from weak signals in an accurate manner; unlimited by the forms and sizes of the noise and the working conditions and independent from manual setting of parameters, it eliminated the blind-source noise from weak echo signals effectively; with this method, the initial position and the coupled peak value were extracted accurately from the weak signals. In terms of the effects of the method, the phenomena of “peak clipping” and “breakpoint” caused by excessive filtering were avoided; compared to global filtering, time-frequency domain filtering and other methods, the method proposed outperformed the conventional ones for a peak value error of only 0.19%; as for the denoising velocity, simultaneous input of multiple pieces of data as well as simultaneous output of denoising outcomes in a real time manner were also achieved under this method, with the averaged processing time for a single piece of data (0.051 s) far superior to the result under other methods.

The Safety Effect of Advanced Consolidation Grouted Rock under Blasting Shock Wave

Strong blasting disturbance leading to damage or even destruction of weak and fractured rock masses is a crucial problem to be solved during the construction process of underground engineering. For the blasting construction problem of advanced consolidation grouted rock near the excavation contour, the safety effect of blasting shock waves on grouted rock is investigated using a theoretical analysis method. The interaction process between blasting shock waves and grouted rock was studied based on the propagation characteristics of shock waves and the strain rate effect of rock strength. Considering the critical failure state, a safe vibration velocity model was established to analyze the effects of proportional distance, age, and grouting material. Results show that the first transmission and reflection effect creates the most dangerous state for grouted rock. SVV of super rapid strengthening cement is larger than that of ordinary cement. Choosing a suitable grouting material is essential to the following blasting design.

Non-ideal explosive underwater explosion shockwave model

The non-ideal behavior of aluminized explosives significantly affects the characteristics of underwater explosion shockwaves, rendering the classical model for underwater explosion shockwaves difficult to apply. In this paper, we analyze the underwater explosion shockwave characteristics of a new generation of aluminized explosives and propose a non-ideal explosive underwater explosion shockwave model incorporating a non-ideal explosive shockwave parameter correction function controlled by the Al/O ratio. First, we conducted underwater explosion tank experiments to obtain four groups of Al/O ratios of shockwave parameters of underwater explosion with aluminized explosives and analyzed the effect of the Al/O ratio on them. Subsequently, we calculated the equation of state of aluminized explosives and established a one-dimensional simulation model of underwater explosion. We verified the reliability of the mesh quality and equation of state using the experimental data. Finally, we used the model to calculate the underwater explosion shockwave parameters of aluminized explosives with Al/O ratios of 0.1–1.3. Based on data analysis, we established a calculation model of the pressure peak and energy flow density of the underwater explosion shockwave of aluminized explosives containing non-ideality correction functions. Our results demonstrate that shockwave pressure peak and energy increase and then decrease with an increase in the Al/O ratio, and the non-ideal behavior of aluminized explosives makes the shockwave energy of underwater explosion more sensitive to the Al/O ratio. The proposed model can better predict the experimental results and can be of high practical value as a general structure for underwater explosion shockwave models of other aluminized or metalized explosives.

Computational and Experimental Modeling in Magnetoplasma Aerodynamics and High-Speed Gas and Plasma Flows (A Review)

This paper provides an overview of modern research on magnetoplasma methods of influencing gas-dynamic and plasma flows. The main physical mechanisms that control the interaction of plasma discharges with gaseous moving media are indicated. The ways of organizing pulsed energy input, characteristic of plasma aerodynamics, are briefly described: linearly stabilized discharge, magnetoplasma compressor, capillary discharge, laser-microwave action, electron beam action, nanosecond surface barrier discharges, pulsed spark discharges, and nanosecond optical discharges. A description of the physical mechanism of heating the gas-plasma flow at high values of electric fields, which are realized in high-current and nanosecond (ultrafast heating) electric discharges, is performed. Methods for magnetoplasma control of the configuration and gas-dynamic characteristics of shock waves arising in front of promising and advanced aircraft (AA) are described. Approaches to the control of quasi-stationary separated flows, laminar–turbulent transitions, and static and dynamic separation of the boundary layer (for large PA angles of attack) are presented.

Study on The Method for Predicting The Explosion Source Point Based on The Characteristics of Shock Wave

To improve the accuracy in predicting the blast initiation position in tests from the measured data, a method of computing the blast source coordinates based on the average velocity of the blast shock and the corresponding correction and iteration methodology is proposed, and the accuracy of the method is verified and validated by comparing with the available data. The results show that: the accuracy of the method is good and its reliability is also high, and a spherical charge data correction method is proposed based on the characteristics of the shock wave, which can effectively improve the prediction accuracy. Using it, the coordinate error of the explosion source point is reduced from 0.656m to 0.084m, and the maximum relative error is reduced from 4.95% to 0.31%. The coordinate error of the dynamic explosion example is 1.68m, and the maximum relative error is 16.1%. The study found that the error of the original data has a great influence on prediction accuracy, and to ensure the high accuracy of the prediction results, the data with excessive errors should be excluded.

Experimental study on the pressure characteristics of laser-induced shock waves under different energy distribution

Laser shock peening has been widely used in anti-fatigue strengthening of metals. The different types of lasers (Flattop laser and Gaussian laser) used have influence on the pressure characteristics of shock wave and the strengthening effect. In this work, using PDV (photonic doppler velocimetry) system, the difference of peak pressure of Flattop laser-induced shock wave and Gaussian laser-induced shock wave is studied experimentally and theoretically. Research shows that the peak pressure of shock wave induced by Gaussian laser is higher than that of Flattop laser, because of the infinitesimal power density in the center of Gaussian laser spot is higher than that of Flattop laser. Furthermore, at the same power density, Gaussian laser can implant a larger and deeper residual stress field in the material.

Study on the characteristics of initial shock waves generated by cylindrical charge for underwater explosion

In order to provide a theoretical basis for studying the shock wave propagation and evolution generated by cylindrical charge of near-field underwater explosion, the characteristics of initial shock waves generated by cylindrical charge are studied. First, a new theoretical model for initial shock waves is proposed by the polar curve method. Based on the theoretical model and the simulated results, the influences of incident angle, length-to-diameter ratio and type of charge on the initial shock waves are analysed. Then the experiments of underwater explosion load tests are carried out to verify the theoretical and simulation results. Finally some instructive conclusions are drawn: i) The two-dimensional theoretical model can calculate the initial underwater shock wave pressure and its direction of cylindrical charge through detonation velocity, detonation pressure, explosive density and incident angle, which is provides a theoretical basic for studying the shock wave propagation and evolution studies. By comparing the theoretical results with the numerical results verified by experiments, the maximum error is not more than 9.93%. ii) Increasing the incident angle α 0 will reduce the initial shock wave pressure of cylindrical charge and make its direction deflect towards the material interface. When the incident angle α 0 is in the range of 0 - 10°, increasing the incident angle makes the initial shock wave pressure decrease rapidly as a power function. With the increasing of the incident angle, the attenuation rate of the initial shock wave firstly decreases and then increases when the incident angle α 0 is in the range of 10 - 72°. This phenomenon explains the reason that the axial and radial initial shock wave pressures are much higher than those in other directions after the central initiation of cylindrical charge. iii) According to the geometric relationship, the length-to-diameter ratio of the charge will limit the range of the incident angle. The length-to-diameter ratio will affect the initial shock wave pressure at the same initiation time. The pressure decreases with the increase of the length-to-diameter ratio when the initial shock wave is formed on the cylindrical surface of the charge.

Propagation characteristics of shock wave in wire explosive impact forming process

The theoretical analysis and numerical simulation are combined to explore the generation mechanism and propagation characteristics of the shock wave in WEIF process. The results show that with the increase of linear density of deposition energy, the propagation distance of shock wave in the same time is longer; as the propagation distance of shock wave increases, the propagation velocity on the wave front gradually decreases. In the early stage of the electric explosion of the metal wire, the shape of the shock wave generated is the expansion and evolution of the cylindrical wire source,and the pressure wave generated by the electric explosion of the metal wire is close to an ellipsoid. Since the expansion of the shock wave is radioactive, its shape gradually homogenizes to a sphere.

Investigation of shock wave propagation and water cavitation in a water-filled double plate subjected to underwater blast

Water-filled double hulls are a prevalent design for underwater warships. Studying the propagation of underwater shock wave in such structures is essential to comprehend their shock resistance. The aim of this paper is to investigate the propagation of underwater shock wave and water cavitation in a water-filled double plate. To achieve this objective, the paper establishes a Eulerian compressible fluid model that combines the isentropic single fluid model and Newton's second law. The accuracy of the numerical solver is confirmed through validation tests. The reflection and transmission characteristics of shock wave, the dynamic response of the plate, and the cavitation in external and gap water are analyzed. It also examines the effects of the supporting springs of outer and inner plates and the area density of the outer plate on the shock wave propagation and cavitation evolution. The findings indicate that the transmitted wave in the gap water is influenced by the area density and supporting spring of the outer plate. A thicker outer plate can reduce the peak value of the transmitted wave, and a stiffer supporting spring can decrease the transmitted impulse. On the other hand, if the outer plate is freestanding or softly supported, it has minimal effects on the response of the inner plate. Moreover, the water cavitation is determined by the supporting spring of the inner plate in the case of a softly supported outer plate, and the cavitation initially develops in the gap water near the inner plate before expanding towards the external water. When the supporting spring of the outer plate is stiff, it significantly reduces the occurrence of cavitation in the external water, while the cavitation in the gap water is still determined by the support spring of the inner plate. These research findings are valuable for analyzing the shock resistance of typical double-hull submarines.

Subcontinuum scale analysis of diamond lattice films through spatial multi-level coarsening method

In this study, a multilevel scalable spatial-coarsening method for diamond structures was developed to selectively scale the space represented by the particles. The bonding relationship between the particles of the interlayer facing different spatial regions is explained by the combination of the potential energies that dominate each side. The proposed method reproduces the tensor properties of the diamond crystal material with high accuracy under thermodynamic equilibrium covering a wide temperature range. Additionally, shock wave characteristics are examined for Si thin-films in which only the surface area is left as the all-atom level and upscaling is performed in the thickness direction. The change in particle velocity and stress due to the potential energy transferred in the thickness direction is maintained even after penetrating the interlevel layer, successfully predicting the all-atom model and experimental results.

Insight into the underwater implosion mechanisms of thin-walled metallic cylindrical shells

Underwater hollow structures are prone to implosion due to high hydrostatic pressure and structural imperfections. The implosion deformation patterns and induced shock wave impulses are quite involved, and the underlying mechanisms are still not clear. This paper presents an investigation of the implosion mechanisms of metallic cylindrical tubes. The finite element model is first established and validated by the existing experimental results. Numerical simulations are then performed for the aluminum alloy (6061-T6) cylindrical tubes with different length diameter and wall thickness. The deformation features, as well as the induced implosion shock wave characteristics, are analyzed, and the boundaries for the switch of deformation modes are derived. Furthermore, a comparison between the implosion of the cavity and that of the cylindrical shells is implemented. Results show that with the variation of geometrical dimensions, three deformation modes are developed for the cylindrical shells. The implosion shock wave pressure is non-uniformly distributed in the nearby fluid field, and the higher peak is generated in the area around the valleys of the deformed shells. The finding of this work can help understand the implosion mechanics and facilitate the design of underwater hull structures.

Stress wave analysis of high-voltage pulse discharge rock fragmentation based on plasma channel impedance model

High-voltage pulse discharge (HVPD) rock fragmentation controls a plasma channel forming inside the rock by adjusting the electrical parameters, electrode type, etc. In this work, an HVPD rock fragmentation test platform was built and the test waveforms were measured. Considering the effects of temperature, channel expansion and electromagnetic radiation, the impedance model of the plasma channel in the rock was established. The parameters and initial values of the model were determined by an iterative computational process. The model calculation results can reasonably characterize the development of the plasma channel in the rock and estimate the shock wave characteristics. Based on the plasma channel impedance model, the temporal and spatial distribution characteristics of the radial stress and tangential stress in the rock were calculated, and the rock fragmentation effect of the HVPD was analyzed.

Interferometric measurements of laser-induced shockwaves in air: Variable laser energy

When focused to a small spot size in air, a sufficiently energetic laser pulse initiates a rapidly expanding plasma. After a delay, a shockwave detaches from the plasma boundary and propagates. General features of the shockwaves can be deduced from condenser microphone measurements. However, the minimum range is limited by damage thresholds, and the presence of the microphone introduces a number of measurement artifacts. Distortion of the signal is caused by diffraction around the sensor, and the limited bandwidth does not allow rise times to be correctly quantified. In contrast, optical interferometry is a nonintrusive diagnostic for quantifying shockwave characteristics. In this study, a Nd:YAG laser is focused through a converging lens in order to generate laser-induced shockwaves. By using a variable attenuator, four laser energy outputs are examined: 25, 50, 75, and 100% of the maximum energy transmission. Heterodyne Mach–Zehnder interferometer measurements are made from 10 mm to 200 mm from the focal point of the lens. Virtual velocity signals, proportional to the time derivative of optical phase differences, are used to estimate density and pressure time histories, along with peak pressure as a function of distance.

Cavitation-induced shock wave behaviour in different liquids

This paper follows our earlier work where a strong high frequency pressure peak has been observed as a consequence of the formation of shock waves due to the collapse of cavitation bubbles in water, excited by an ultrasonic source at 24 kHz. We study here the effects of liquid physical properties on the shock wave characteristics by replacing water as the medium successively with ethanol, glycerol and finally a 1:1 ethanol–water solution. The pressure frequency spectra obtained in our experiments (from more than 1.5 million cavitation collapsing events) show that the expected prominent shockwave pressure peak was barely detected for ethanol and glycerol, particularly at low input powers, but was consistently observed for the 1:1 ethanol–water solution as well as in water, with a slight shift in peak frequency for the solution. We also report two distinct features of shock waves in raising the frequency peak at MHz (inherent) and contributing to the raising of sub-harmonics (periodic). Empirically constructed acoustic pressure maps revealed significantly higher overall pressure amplitudes for the ethanol–water solution than for other liquids. Furthermore, a qualitative analysis revealed that mist-like patterns are developed in ethanol–water solution leading to higher pressures.

Injury and death to armored passenger-vehicle occupants and ground personnel from explosive shock waves

This study evaluated the risks for injury and death to occupants from blast waves to the side and underbody of an armored passenger-vehicle and to ground personnel from free-field blast waves. The Kingery-Bulmash empirical relationships for explosive shock waves were augmented by the Swisdak empirical relations for stand-off distances up to Z = 39.8 m/kg1/3 to tabulate shock-wave characteristics using the Friedlander wave-shape. A 15 kg, hemispherical explosion was analyzed in detail for the shock wave velocity and compression of air behind the wave front. An armored SUV was analyzed with Z = 1.6 m/kg1/3 (4 m) standoff distance from pressure loading on the near-side, far-side and underbody. The rigid body displacement was 0.36 m and 7.8° yaw for a side loading. When a segment of the occupant compartment accelerates inward, there are risks for injury from the intrusion. Energy is transferred to the occupant by deformation of their body (Ed) and by velocity increasing the kinetic energy of the body region (Ek). Body deformation injures an occupant by exceeding the tolerable compression (crush mechanism) or exceeding the rate-dependent tolerance, which is defined by the rate times the extent of compression (viscous mechanism). The risk for injury and death to ground personnel was analyzed for free-field blast waves by stand-off distance and TNT weight. A 15 kg charge posed a 99% risk of death at 3.9 m, 50% risk at 5.2 m, 1% risk at 7.8 m and injury threshold at 8.2 m. A 100 kg charge posed a 99% risk of death at 8.5 m, 50% risk at 11.6 m, 1% risk at 17.3 m and injury threshold at 18.0 m. The study describes the steps to analyze blast loading of an armored passenger-vehicle for risks of occupant injury. It describes the steps to analyze injury risks to ground personnel from blast wave pressure.

Non-intrusive, imaging-based method for shock wave characterization in bubbly gas–liquid fluids

A novel experimental imaging-based method is presented for the non-intrusive determination of shock wave characteristics (i.e. shock wave speed and magnitude, and shock-induced liquid velocity) in a bubbly flow solely from gas bubble velocities. Shock wave speeds are estimated by the relative motion between gas bubbles at two locations by splitting the camera field-of-view using a mirror construction, increasing the dynamic spatial range of the measurement system. Although gas bubbles have in general poor tracing properties of the local fluid velocity, capturing the relative dynamics provides accurate estimates for the shock wave properties. This proposed imaging-based method does not require pressure transducers, the addition of tracer particles, or volumetric reconstruction of the gas bubbles. The shock wave magnitude and shock-induced liquid velocity are computed with a hydrodynamic model, which only requires non-intrusively measured variables as input. Two reference measurements, based on pressure transducers and the liquid velocity field by particle image velocimetry, show that the proposed method provides reliable estimates for the shock wave front speed and the shock-induced liquid velocity within the experimental range of 70 < U_textrm{s}< 400 m/s.Graphical abstract

Propagation characteristics of blast shock waves in low-pressure environment

Propagation characteristics of blast shock waves in low-pressure environment

Анализ эффективности противоударной стойкости двух групп керамических и композитных материалов

Complex experimental and theoretical studies of shock-wave characteristics and penetration parameters are conducted to develop physical and mathematical models of deformation and fracture of ceramic and composite materials under high-velocity loading. The purpose of this work is to investigate the fracture of ceramic and composite targets and their efficiency in ceramic-containing structures. The experiments are performed using a ballistic test stand (Research Institute of Applied Mathematics and Mechanics, National Research Tomsk State University). The deformation and fracture of ceramic (aluminum oxide Al2O3, aluminum oxide (KVP-98, corundum), zirconium dioxide ZrO2, silicon carbide SiC) and composite (TiC-NiCr and TiB2-B4C) materials are studied experimentally in the impact velocity range of 0.5 - 6.5 km/s. The dynamics of the fracture of ceramic plates (silicon carbide and aluminum oxide) is analyzed. The fragments of the plates and their size distribution are given. The study of the impact resistance of ceramic and composite samples reveals two groups of materials with essentially different levels of efficiency. For both groups, the dependence of the efficiency parameter on the impact velocity demonstrates a decrease in the velocity range from 0.5 to 3.0 - 4.5 km/s and a subsequent increase when the impact velocity tends to 6.5 km/s. The obtained experimental results may be used during the validation and verification of numerical and analytical models, approaches, and software packages.