Amplitude Of Shock Wave Research Articles

VELOCITY AND EVOLUTION OF SHOCK WAVES IN SAND WITH INCREASING WATER CONTENT

Interest in the problems of shock wave propagation in saturated porous media is associated with studying seismic exploration issues, modeling the hummer effect during hydraulic fracturing, studying the water-gas impact on formations for the purpose of efficient oil production, etc. Experimental work on waves in bulk media is usually carried out in shock tubes. Traditionally, shock tubes are used to study the characteristics of the propagation of shock waves in various media, to analyze the wave properties of these media based on the speed of the shock waves and the change in the shape of the pulse along the passage of the first – main pulse. In a shock tube equipped with a section of bulk media, the wave is repeatedly reflected from the surface of the porous medium under study and the upper end of the tube. Re-reflected waves can be used to study changes in the environment that occurred under the influence of a shock wave, i.e. as probing pulses. In this article, sounding is understood as identifying acoustic properties (changing the shape of shock pulse diagrams and their velocities). This paper presents the results of experimental studies of the propagation of shock waves of small amplitude in sand with a volumetric content of liquid in the pore space from 0 to 40 %, and illustrates the influence of the presence of liquid in the pores on the shape of the main and probing pulses. The research was carried out using the Shock Tube installation, in the Laboratory of Experimental Hydrodynamics of the Mavlyutov Institute of Mechanics of Ufa Branch RAS. An increase in the speed of wave propagation was established with increasing water saturation of sand in the range from 0 to 40 %. An increase in the amplitude of reflected waves when passing through sand, the formation of peaks and stretching of pulses were discovered. The research results can be used in processing geophysical data to interpret seismograms of sandy deposits saturated with gas-liquid systems.

Effect of Combined Laser Thermal and Shock Wave Effects on the Mechanical and Tribological Properties of Steels.

Herein, we present the results of an experimental study on the mechanical properties of Fe-C alloys with different carbon contents (0.2, 0.45, and 0.8%) in a wide range of deformation rates (10-3-103 s-1) and abrasive wear resistance, which underwent combined laser thermal (laser surface hardening-LSH) and laser shock wave (Laser Shock Peening-LSP) processing. The combined treatment modes included a different sequence of exposure to laser thermal and laser-induced shock pulses on the material. The amplitude and duration of laser-induced shock waves were measured using a laser Michelson interferometer. The mechanical properties of steel samples were studied under conditions of uniaxial tension under static loads on a standard universal testing machine, the LR5KPlus, and under dynamic loading, tests were carried out on a specialized experimental complex according to the H. Kolsky method using a split Hopkinson rod. The abrasive wear resistance of hardened surfaces was studied using the Brinell-Haworth method. Studies have shown that the use of a combination of LSH and LSP treatments leads to an increase in both the mechanical properties of steels and abrasive wear resistance compared to traditional laser hardening. It has been established that in the combinations considered, the most effective is laser treatment, in which LSP treatment is applied twice: before and after LSH. Thus, after processing steels using this mode, an increase in the depth of the hardened layer was recorded-by 1.53 times for steel 20, by 1.41 times for steel 45, and by 1.29 times for steel U8-as well as a maximum increase in microhardness values by 22% for steel 20, by 27% for steel 45, and by 13% for U8 steel. The use of this mode made it possible to obtain the maximum strength properties of the studied materials under static and dynamic loading, which is associated with an increase in the volume fraction of the strengthened metal and high microhardness values of the strengthened layer of traditional LSH. The dependences of abrasive wear of the studied steels after various combinations of LSP and LSH impacts were established. It is shown that the greatest wear resistance of the studied steels is observed in the case when the LSH pulse is located between two LSP pulses. In this case, abrasive wear resistance increases by 1.5-2 times compared to traditional LSH.

Shockwave velocimetry using wave-based image processing to measure anisotropic shock emission

Noninvasive optical measurements of the shockwave propagation velocity using multiple pulse illumination allow deducing the shockwave pressure amplitude through Hugoniot relations and an appropriate equation of state of the medium. This technique is particularly useful for spatially resolved measurements near the shockwave emission site. Due to diffraction, however, a shockwave front can significantly change its morphology, rendering precise velocity measurements non-trivial. As solution we propose a wave front evolution (WaFE) velocimetry technique, which applies Huygens principle. We take a shadowgraph of the wave front at subsequent times as initial condition for the acoustic Helmholtz equation and numerically propagate the fronts in time. From the instance of time, when two subsequently taken wave front shadows numerically interfere and form one sharp wave front, the local shock velocity is obtained and the local shock pressure amplitude measured. With artificial test images, it is shown that this technique has excellent sub-pixel accuracy, robustness to noise, and can work with low contrast images and even overlapping and interfering wave fronts. The software is made available freely and can be applied to general shock front velocity measurements. We apply WaFE to determine the anisotropic shockwave emission from an elongated laser-induced plasma in water from shadowgraphs of the shockwave front imaged four times onto the same camera frame using multiple pulse illumination at a repetition rate of 60 MHz. The direction dependence of attenuation of the shockwave pressure amplitude is measured at distances of 50–300 μm to the plasma.

Effects of electrical parameters on weak shock waves induced by spark discharge

The effects of the electrical parameters, including storage capacitance, additional inductance, charging voltage, and electrode gap, on the shock wave induced by spark discharge in gas were experimentally investigated. The results showed that the shock waves induced by spark discharge conform to the attenuation law for weak spherical shock waves outside the spark core. The shock wave amplitude is approximately proportional to the electrode gap and storage energy and decreases with increasing inductance. The effect of the charging voltage on the shock wave amplitude can be almost ignored if the storage energy is the same. The average power in the first quarter cycle of spark discharge was found to be closely related to the shock wave amplitude. An empirical equation was given between the shock wave amplitude and the average discharge power, which provides convenient access to set appropriate electrical parameters to generate shock waves of specified amplitude induced by spark discharge.

Energy-load Matching and Shockwave Analysis of Electrical Explosion

Electrical explosion shockwave is a technique for inducing formation resonance by the interruption of formation pressure balance. By matching complex nonlinear influencing factors, this paper optimizes the engineering parameters and estimates the influence range of the shockwave. It achieves the objective of efficient shockwave acquisition and amplitude control. The test apparatus rapidly discharges the stored energy of various capacitance-voltage schemes, causing the load of various diameter-length structures to generate shaped shockwaves. By characterizing the discharge circuit and the shockwave signal, the energy and load matching was studied. Extraction of shockwave signal characteristics for decomposition and reconstruction analysis. The matching results indicate that the 10 MW loop oscillation is generated within 5 μs of discharge time, with the load diameter structure getting a major effect on the deposited energy. The 50 MPa shaped shockwave is generated in a 100 mm diameter region. And the peak pressure is influenced primarily by the load length structure and voltage scheme. The optimal load structure is D = 0.2 mm and L = 25 mm, controlling 2 to 5 times the input power’s enthalpy and increasing the voltage to create the shockwave more efficiently. The results of shockwave analysis indicate that the signal’s time-domain characteristics correspond precisely with its propagation path. The wavelet packet analysis indicates that the shockwave possesses a broad frequency and a high peak. The detection signal is composed of the principal shock wave, the radiation pressure wave, and the resonance error. The results provide theoretical basis for engineering application.

On the shock wave structures in anisotropy magnetoplasmas

In this work, the propagation of nonlinear electrostatic shock wave structures in an anisotropy pressure magnetoplasma composed of warm inertial ions and inertia-less Maxwellian electrons is reported. For this purpose, the technique of reductive perturbation is applied for reducing fluid equations of the current model to the Korteweg–de Vries Burgers (KdVB) equation with a second-order dissipative term and the KdVB–Kuramoto (KBK) equation with both second- and fourth-order dissipative terms. The impact of various plasma parameters, including the parallel ion pressure, perpendicular ion pressure, and dissipation parameter, on the significant characteristics of the shock wave profile is examined and discussed. In addition, a comparison between the profiles of KdVB shocks and KdVB–Kuramoto shocks is reported. We expect that KBK shock wave amplitudes become larger than the KdVB ones by taking the fourth-order dissipative into consideration. Thus, the results of the KBK equation may treat the difference between the theoretical and laboratory results or satellite observations.

On the Theory of Shock Waves in Isotropic Hardening Plastic Media

Based on the thermomechanical model of plastic deformation of an elastically compressible isotropic hardening medium, the system of relations for describing plastic shock waves of finite amplitude is obtained, which satisfies the maximum entropy production principle at the front of strong discontinuity. A classification of admissible shock-wave transitions is performed within the framework of the model of isotropic hardening under the von Mises plasticity condition.

Model of a stationary thermal detonation wave in the “liquid lead – water” system for safety analysis of NPP with the reactor BREST-OD-300 during heat exchanger tube break accident

This paper presents a mathematical model of a stationary wave of thermal detonation in the “liquid lead - water” system, which can occur after the rupture of a steam generator tube of the reactor BREST-OD-300. The model is based on the mechanics of multiphase fluid flows. The system under study includes a continuous phase of liquid lead, in which drops of water surrounded by a steam film are dispersed. Heat exchange between high-temperature molten lead and water drops is carried out in the film boiling mode. A shock wave propagating in this multiphase system causes all phases in motion. Due to the significant difference in density between liquid lead and water, a difference in velocities arises between dispersed water drops and liquid lead, which cause the fragmentation of water droplets. The shock wave velocity and amplitude are determined by constructing the shock adiabat and the Hugoniot adiabat for the parameters of the studied multiphase mixture. To describe the fragmentation of water droplets, heat transfer between phases, and interfacial friction, the empirical correlations of the thermal detonation theory are used. The obtained numerical solutions describe the distributions of parameters in the zone of melt – water interaction.

Monitoring cavitation dynamics evolution in tissue mimicking hydrogels for repeated exposures via acoustic cavitation emissions

Acoustic cavitation emission (ACE)/shockwave signals generated by cavitation during histotripsy have been demonstrated to undergo characteristic changes correlated with the level of damage generated in select target media following repeated cavitation exposures, and may allow assessment of therapy-induced tissue damage during histotripsy. Here we investigate the impacts of nucleation medium on the evolutions of cavitation dynamics and ACE signals during repeated cavitation exposures. Repeated cavitation is generated in agarose, gelatin, and polyacrylamide hydrogels using a 700-kHz histotripsy array. High-speed imaging, broadband hydrophones, and histotripsy array elements are used to measure ACE signals and bubble dynamics. Bubble lifespans and collapse shockwave amplitudes were observed to be equivalent in optical and acoustic measurements. However, the evolutions of these properties, as well as bubble maximum radii, varied significantly across materials. Maximum radii initially increased and then decreased in agarose, but remained constant in gelatin and polyacrylamide. Lifespans increased monotonically in agarose and gelatin, but decreased in polyacrylamide. Collapse shockwave amplitudes evolved differently in all materials. The observed evolutions of the maximum radii, lifespans, and collapse shockwave amplitudes between media suggest that these features are dependent on the structure and stiffness of the nucleation medium and must be further investigated in tissues.

MESO-MACRO ENERGY EXCHANGE IN SHOCK-WAVE PROCESSES AND DYNAMIC STRENGTH OF AB2 STEEL

Impact tests of low-alloy martensitic-bainitic steel AB2 showed that the scale of dynamic deformation and the fracture mechanism change in a threshold manner. The change in the mechanism and scale of fracture is triggered by the resonant excitation of large-scale structural elements of the material (grain conglomerates) due to plastic flow oscillations. In this case, the grain-boundary mechanism of dynamic fracture is replaced by a transcrystalline one. Beyond the strain rate threshold, mesoscopic elementary carriers of dynamic deformation are divided into two groups: low-velocity and high-velocity. Accordingly, the velocity distribution of mesoparticles shows two humps. The velocity spread of mesoparticles sharply increases under these conditions, while the mass velocity defect (change in the shock wave amplitude) becomes negative. The latter fact indicates the local acceleration of mesoparticles in discrete regions of the target (the so-called shooting of mesoparticles in the shock wave direction). Transcrystalline cracks are randomly distributed throughout the sample and have a random orientation.

Monitoring cavitation dynamics evolution in tissue mimicking hydrogels for repeated exposures via acoustic cavitation emissions.

A 700 kHz histotripsy array is used to generate repeated cavitation events in agarose, gelatin, and polyacrylamide hydrogels. High-speed optical imaging, a broadband hydrophone, and the narrow-band receive elements of the histotripsy array are used to capture bubble dynamics and acoustic cavitation emissions. Bubble radii, lifespan, shockwave amplitudes are noted to be measured in close agreement between the different observation methods. These features also decrease with increasing hydrogel stiffness for all of the tested materials. However, the evolutions of these properties during the repeated irradiations vary significantly across the different material subjects. Bubble maximum radius initially increases, then plateaus, and finally decreases in agarose, but remains constant across exposures in gelatin and polyacrylamide. The bubble lifespan increases monotonically in agarose and gelatin but decreases in polyacrylamide. Collapse shockwave amplitudes were measured to have different-shaped evolutions between all three of the tested materials. Bubble maximum radii, lifespans, and collapse shockwave amplitudes were observed to express evolutions that are dependent on the structure and stiffness of the nucleation medium.

ON THE DESTRUCTION AND PREFRACTURING OF SOLID ROCKS UNDER BLASTING IN FORMATION CONDITIONS

Purpose and task. Analysis and specification of mechanisms of softening and change of structure of monolithic and low-fractured rocks under blasting of single and dispersed charges, definition of the reasons and model of their evolution in a formation. To solve this goal, the followingscientific tasks were set in the work:1. Estimation of force factors of external action on rock.2. Thermodynamic analysis and detection of mechanisms of structural changes in rocks at a considerable distance from the well, which provide a change in its productivity.Research methods. To solve the set tasks, the following were performed: calculations of the attenuation of shock wave amplitudes generated during the explosion of spherical and elongated charges; analysis of the results of explosive treatments of oil and gas wells; energy analysis of processes and mechanisms of changes that occur around the well in the reservoir.The main results. Studies have shown that structural changes in rocks during low-energy explosions, as well as other low-energy methods of external action on the reservoir occur in the form of increased cracking of rocks at micro and macro levels due to cooperative effects of external action, internal reservoir energy and physico-chemical effects of reservoir fluids.The main results. The mechanisms of decompaction of the rocks in rock formation conditions in the presence of rock and reservoir pressure at low-energy external actions are considered. Experiments on the operation of oil, oil and gas and gas wells show that the transition of the system "well - formation" from one thermodynamic state to another occurs in a time that depends on the internal energy of the formation. The transition is the result of the cooperative effects of the combined action of external influences, the internal energy of the formation and rock pressure. For gas wells this time does not exceed a few hours or days, for oil and oil and gas with depths of 3000… 4000 m the typical time of the well to reach maximum productivity is ≈ (30 - 90) days.Conclusions and practical significance. The analysis of the results of industrial tests of explosive intensification technology and calculations of attenuation of compression wave amplitudes show that under rock pressure conditions structural changes in rock after explosions of several charges occur at distances up to ≈ (80… 100) R0. Under reservoir conditions, the main reasons for the appearance of such long zones of increased permeability around the well are the cooperativeeffects of the combined action of blast waves, reservoir gases (methane, carbon dioxide, helium and possibly hydrogen), as well as changes in rock pressure in the process of its development. Of practical importance is to understand the sequence of technological operations in the work tointensify the inflow of oil and gas.

Mitigating Forced Shock-Wave Oscillation with Two-Dimensional Wavy Surface

Oscillating flow is one challenge for wide-Mach-number-range flight with supersonic/hype-rsonic vehicles. Aiming to mitigate the large-amplitude forced shock-wave oscillation, a 2D wavy surface has been implemented onto the flat-bottomed wall of the Sajben diffuser under downstream pressure disturbance. The oscillating SBLI in the diffuser is captured using the finite volume method with the second-order implicit dual-time-stepping method. Impacts of the wavy surface on the forced shock-wave oscillation are numerically investigated. It is found that increasing the wavy surface’s depth benefits mitigation of the shock-wave oscillation amplitudes on the walls under the given conditions, but that decreasing the wavy surface’s length may increase or decrease the oscillation amplitudes, depending on the specific value. The mitigating mechanism is interpreted from two viewpoints, i.e., the shock-wave stability and the work performed by a moving shock-wave. The transient second shock-wave temporally appears in the flow field and can be explained by the post-shock expansion.

Optical Emission Spectroscopy of Underwater Spark Generated by Pulse High-Voltage Discharge with Gas Bubble Assistant

This paper is aimed at the investigation of the acoustic and spectral characteristics of underwater electric sparks generated between two plate electrodes, using synchronized gas bubble injection. There are two purposes served by discharge initiation in the bubble. Firstly, it creates a favorable condition for electrical breakdown. Secondly, the gas bubble provides an opportunity for the direct spectroscopy of plasma light emission, avoiding water absorption. The effect of water absorption on captured spectra was studied. It was observed that the emission intensity of the Ha line and a shockwave amplitude generated by discharge strongly depend on the size of the gas bubble in the moment of the discharge initiation. It was found that the plasma in the underwater spark channel does not correspond to a source of black-body radiation. This study can be also very useful for understanding the difference between discharges produced directly in a liquid and discharges produced in gas/vapor bubbles surrounded by a liquid.

Shock Wave Characterization Using Different Diameters of an Optoacoustic Carbon Nanotube Composite Transducer

Carbon nanotube–polymethyl siloxane (CNT-PDMS) composite transducers generate shock waves using optoacoustic technology. A thin layer of thermally conductive CNT and elastomeric polymer, PDMS, is applied on the concave surface of transparent polymethylmethacrylate (PMMA) to convert laser energy to acoustic energy using the thermoelastic effect of the composite transducer. The efficient conversion of laser energy requires an optimum utilization of the different properties of composite transducers. Among these properties, the diameter of composite transducers is a significant parameter. To practically verify and understand the effect of the diameter of composite transducers on the properties of shock waves, CNT-PDMS composite transducers with different diameters and focal lengths were constructed. Increases in the diameter of the composite transducer and input laser energy resulted in increased peak pressures of the shock waves. The maximum positive and negative pressures of the shock waves generated were 53 MPa and −25 MPa, respectively. This practically demonstrates that high peak amplitudes of shock waves can be achieved using larger transducers, which are suitable for practical applications in transcranial studies.

Deep learning-based monitoring of surface residual stress and efficient sensing of AE for laser shock peening

• A multi-channel acoustic emission real-time efficient signal detection method and acquisition system. • A novel spatio-temporal complementary model (CNN-LSTM) for fusion of time-varying AE signal. • Dual circulation LSTM explains the decay mechanism of AE using temporal sampling points. • Stronger correlation between information from AE attenuation profile and surface quality. Laser shock peening (LSP) is one of the main anti-fatigue technologies in high-end manufacturing industries. However, guaranteeing its quality consistency is difficult due to its process complexity. Acoustic emission (AE) is a promising solution to accurately monitoring the surface quality of LSP, although, the large scale of monitoring data is still challenging for industrial applications. This paper studied the in-situ evaluation of surface residual compressive stress (SRCS) for 7075 aluminum alloy in LSP and the efficient sensing of AE based on deep learning methods. Firstly, a monitoring system of LSP with four types of AE sensors was developed in order to simultaneously acquire both the ultra-high and ultra-low amplitude of shock wave. The performance of those sensors is further quantitatively evaluated via long-short term memory (LSTM). Then, a new spatio-temporal parallel CNN-LSTM model for SRCS classification was proposed and experimentally validated to outperform CNN and LSTM after parameters optimization. Finally, aiming to efficient sensing of AE, the importance of different frames of AE signal was analyzed by means of the proposed dual circulation LSTM (DC-LSTM) model, which can accurately locate the key frame of time series signal. Besides, the effects of different frames of AE on classification performance was discussed. It was found that the broadband AE sensor without attenuator shows the highest classification accuracy, while the fast decay stage of AE signal has more contribution to the SRCS classification. This paper provides guidance for real-time non-destructive evaluation of residual stress via AE in laser manufacturing.

Attenuation and inflection of initially planar shock wave generated by femtosecond laser pulse

Evolution of wavefront geometry during propagation and attenuation of initially planar shock waves generated by femtosecond laser pulses in aluminum is studied. We demonstrate that three stages of shock front inflection take place in consistent hydrodynamics and molecular dynamics simulations.During the first stage, the distance traveled by a near-planar wave DSW≲RL is smaller than the radius of heated laser spot RL. Wave attenuation is associated with one-dimensional plane (1D) rarefaction wave coming from the free surface. Such rarefaction wave shapes the shock wave to a 1D triangular pressure profile along direction normal to target surface with a shock front followed by an unloading tail. The second transitional stage starts after propagation of DSW∼RL, at which the unloading lateral waves begin to arrive to a symmetry axis of flow and initiate inflection of the initially planar shock front. Next at the third stage, the wavefront geometry is finally rounded and rapid attenuation of shock pressure begins at DSW≳RL.It is shown that such divergent shock wave cannot generate plastic deformations in aluminum shortly after propagation of DSW∼RL. Thus, we may estimate the maximal peening depth as a radius of focal spot, which sets an upper limit for the laser shock peening.The cessation of plastic deformation is caused by the fall of the shockwave amplitude below the elastic limit. In this case, the elastic-plastic wave transitions to a purely elastic mode of propagation. For large-sized light spots, this transition ends in the 1D mode of propagation.

Experiments and modeling of the effect of the internal air on the shock response of a porous material

The present experiments consider the shock loading of porous samples under statically evacuated, atmospheric, and pressurized interparticle air conditions. An additively manufactured foam with interconnected pores, made from a titanium alloy, is used as the sample material. Loading by a moderate amplitude shock wave has shown that the effect of the internal air on the mechanical response is noticeable for the sample under pressurized conditions, differing from the responses at atmospheric and evacuated conditions. These observations agree with considerations of the air effect within a two-phase constitutive modeling approach.

The concept of improvement high-strength aluminum alloys FSW joint properties via post-weld explosive treatment

The study describes the theoretical background and technological aspects of the post-weld explosive treatment of high-strength aluminum alloy FSW joints. Although FSW allows to effective join high-strength aluminum alloys, the heat generated during the process causes undesirable changes in the strengthening phase, giving a joint efficiency of about 80%. The load-carrying capabilities of these joints can be increased via post-weld treatment (e.g. shot peening, laser shock peening). The new, potential post-weld treatment that is presented in this paper is based on the affection of the welded joint by a shock wave generated during the detonation of explosive material. Such post-weld explosive treatment would result in the hardening of the low-hardness zone, which often determines the mechanical properties of precipitation-hardened aluminum alloy FSW joints. Studies show that explosive welding of annealed aluminum alloys increases their microhardness by about 25% as the result of a high-velocity collision. If a similar effect can be achieved in explosive hardening, the microhardness of the low-hardness zone will increase entailing an improvement of entire joint mechanical properties. The variety of explosives materials used in metalworking (covering the values of detonation velocity from about 2000 m/s to 8000 m/s) and different systems for shock-wave affection gives many technological possibilities. In this work are discussed two different explosive hardening systems: with direct placement of explosive material on a treated welded plate and with an additional driven plate, which provides a higher pressure impulse. Considering that affecting of high amplitude shock wave introduces defects into the structure and decreases residual stresses in the welded joints, the application of an appropriate technological system creates a potential for improving the load-carrying capacities of discussed joints, especially in a condition of cyclic loading.

Numerical Simulation of Diffracted U-Shaped Sonic Boom Waveform

U-shaped sonic booms associated with the dive maneuver of a supersonic vehicle are numerically simulated in this paper. Usual prediction tools for ordinary sonic booms are not suitable for such a waveform because of the breakdown of geometrical acoustics near the caustic. In this paper, nonlinear Tricomi equation approach is used near the caustic to take diffraction into account, whereas augmented Burgers equation analysis is applied away from the caustic where geometrical acoustics is applicable. The U-shaped waveforms predicted by this method are in good agreement with measured data. The effects of atmospheric turbulence are also considered by replacing one-dimensional analysis using augmented Burgers equation with multidimensional wave propagation analysis near the ground surface. Results with the atmospheric turbulence effects show better agreement with measured U-shaped waveform than ones without such effects. It is also found that the amplitude of the tail shock wave, which is much larger than the front shock wave, is more sensitive than the front shock to atmospheric turbulence.