Shock Wave Pressure Research Articles

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.

Ultrafast measurement of laser-induced shock waves

We present measurements of laser-induced shockwave pressure rise time in liquids on a sub-nanosecond scale, using custom-designed single-mode fiber optic hydrophone. The measurements are aimed at the study of the shockwave generation process, helping to improve the effectiveness of various applications and decrease possible accidental damage from shockwaves. The developed method allows measurement of the fast shockwave rise time as close as 10 µm from an 8 µm sized laser-induced plasma shockwave source, significantly improving the spatial and temporal resolution of the pressure measurement over other types of hydrophones. The spatial and temporal limitations of the presented hydrophone measurements are investigated theoretically, with actual experimental results agreeing well with the predictions. To demonstrate the capabilities of the fast sensor, we were able to show that the shockwave rise time is linked to liquid viscosity exhibiting logarithmic dependency in the low viscosity regime (from 0.4 cSt to 50 cSt). Additionally, the shockwave rise time dependency on propagation distance close to the source in water was investigated, with shock wave rise times measured down to only 150 ps. It was found that at short propagation distances in water halving the shock wave peak pressure results in the rise time increase by approximately factor of 1.6. These results extend the understanding of shockwave behavior in low viscosity liquids.

Investigation of Formation Process and Intensity of Coal and Gas Outburst Shockwave

The shock wave of a coal and gas outburst is a high-pressure and high-speed impact airflow formed rapidly after the outburst. The propagation destroys the ventilation facilities and causes the destruction of the ventilation system. The theoretical research on the outburst shock wave is of great significance. In order to deeply understand the formation mechanism of the outburst shock wave, this paper draws on the shock wave theory to theoretically analyze the microscopic formation process of the outburst shock wave. The main difference between the formation process of a coal and gas outburst shock wave and the formation process of a general shock wave is that the outburst shock wave has a solid–gas flow zone in the high-pressure zone. The calculation formulas of pressure, density, temperature and other parameters before and after the outburst shock wave are derived. After the outburst shock wave passes through, the pressure, temperature and density of the roadway air will change suddenly. The relationship expression between outburst gas pressure and outburst shock wave intensity is derived, which can reflect the role of pulverized coal in the formation process of a shock wave. In order to facilitate the understanding and calculation, the concept of equivalent sound velocity of coal-gas flow is proposed, and the direct calculation of the impact strength of a coal and gas outburst is attempted. This paper is helpful to improve the understanding of the essence of a coal and gas outburst shock wave. It is also of great significance to outburst disaster relief.

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.

Determination of thickness parameters of detonation shell and safety performance analysis

AbstractOn the premise of security, it is necessary to ensure good operational performance and technical indicators for nonlethal weapons such as flash detonation bombs. To make the weight of a flash detonation grenade more convenient for hand throwing and material costs save, the outer dimensions of the grenade body are fixed, and the optimal parameters of outer shell thickness of the vertigo grenade are explored. Based on the maximum deformation energy theorem, the strength of the shell with the obtained maximum thickness of 8 mm is checked, and then the optimal shell thickness under the ideal air explosion condition is obtained by reducing the thickness; Then check the thread strength to obtain the inner casing fracture, shock wave, and sound pressure level. The fragmentation performance test, detonation test, and sound pressure level test were carried out for the projectiles involving the shell thickness of 4 and 5 mm, and the simulation results were verified from three aspects of sound intensity, shell strength, and fragments. The results show that the maximum equivalent stress is 232.6 MPa and the maximum deformation is 1.07 × 10−4 mm when the outer shell thickness of the vertigo grenade is 5 mm, which is less than the material failure strength standard and no plastic deformation could occur. The structural connection strength of the missile body meets the standard. Most of the fragments are trapped in the cavity. The average sound pressure level at 1.5 m can reach 159.7 dB. The relative error between the sound pressure level at 3 m and the live ammunition test results is 4.8%, which meets the expected operational technical indicators and has good safety performance. The results of the numerical simulation can provide a reference for the design optimization and performance evaluation of similar vertigo grenades.

Energy localization efficiency in 1,3,5-trinitro-2,4,6-triaminobenzene pore collapse mechanisms

Atomistic and continuum scale modeling efforts have shown that the shock-induced collapse of porosity can occur via a wide range of mechanisms dependent on pore morphology, the shockwave pressure, and material properties. The mechanisms that occur under weaker shocks tend to be more efficient at localizing thermal energy but do not result in high, absolute temperatures or spatially large localizations compared to mechanisms found under strong shock conditions. However, the energetic material 1,3,5-trinitro-2,4,6-triaminobenzene (TATB) undergoes a wide range of collapse mechanisms that are not typical of similar materials, leaving the collapse mechanisms and the resultant energy localization from the collapse, i.e., hotspots, relatively uncharacterized. Therefore, we present the pore collapse simulations of cylindrical pores in TATB for a wide range of pore sizes and shock strengths that trigger viscoplastic collapses that occur almost entirely perpendicular to the shock direction for weak shocks and hydrodynamic-like collapses for strong shocks that do not break the strong hydrogen bonds of the TATB basal planes. The resulting hotspot temperature fields from these mechanisms follow trends that differ considerably from other energetic materials; hence, we compare them under normalized temperature values to assess the relative efficiency of each mechanism to localize energy. The local intra-molecular strain energy of the hotspots is also assessed to better understand the physical mechanisms behind the phenomena that lead to a latent potential energy.

Моделирование волн давления при дефлаграционном горении облаков топливно- воздушных смесей

The paper examines the assumptions underlying a whole group of methods for estimating the parameters of shock waves (pressure waves) during the combustion of spherical fuel-air clouds - the so-called parametric formulas. The formulas allow to determine the parameters of pressure waves from the given energy release and combustion rate. To do this, a complete system of gas-dynamic equations is solved using high-precision numerical simulation. In this case, the combustion front is explicitly distinguished in the form of an infinitely thin discontinuity, on which the laws of conservation of mass, momentum, and energy are satisfied. The results of such a numerical calculation are compared with calculations using the corresponding parametric formulas. Clouds of a stoichiometric mixture hydrogen-air are considered. It is shown that the parametric formulas describe the expansion of clouds of hot products with a good degree of accuracy. Here, there is complete agreement with the direct numerical simulation. It is also shown that the parameters of pressure waves are satisfactorily described both in the calculation by parametric formulas and in direct numerical simulation. In this case, within the cloud, there is a greater increase in pressure than the parametric formulas predict. This is explained by the fact that the assumptions used in the formulas regarding the behavior of the flame front as an impenetrable piston do not fully reflect the physical processes: the combustion front is a semipermeable piston, and some of the mass of the initial mixture still penetrates through it. The third factor considered, which determines the achieved pressures, is the rarefaction wave that occurs in the air after the cloud burns out. This wave propagates in combination with the leading pressure front formed during combustion initiation. The extent of this complex remains practically constant, and its attenuation during spherical propagation is adequately described by the parametric formulas.

Numerical investigation on spall fracture in a metallic material caused by laser shock peening

Laser shock peening (LSP) is a very effective technology for metallic surface treatment, which has been widely used to improve fatigue life and the resistance of foreign object damage. However, when LSP is applied to a thin specimen, an undesirable result, spall fracture close to the free surface of the specimen, may occur. In this work, the spall fracture in Ti-17 alloy caused by LSP by numerical simulations is investigated. To this end, a three-dimensional (3D) finite element model is constructed, which consists of both finite elements and infinite elements in the commercial software Abaqus. In the simulation framework, the shock wave induced by laser is modeled as a pressure load varying in time and space, and the spall fracture criterion is a tensile failure model for high strain-rate dynamic problems. This simulation framework is verified and validated with the surface residual stress as the key result. Then, simulations of single-shock LSP process and multiple-shock LSP process are both conducted. The results show that spall fracture occurs within a very short time after the shock wave propagates into the specimen at a location very close to the free surface. Multiple layers of spall fracture occur inside the specimen after multiple shocks. The relation between the spall fracture and the specimen thickness, the peak pressure of shock wave and the shock number is thoroughly studied.

IMPROVED CRITERION IN METHOD OF ASSESSMENT OF THE SAFETY LEVEL OF THE PROCESS OF LAND RECULTIVATION OF PLACES OF AMMUNITION DISPOSAL AND DESTRUCTION

The relevance of the research and the need to develop methods that allow assessing the level of safety of the disposal and destruction of ammunition sites are shown not only at the present time, but also in the future when land reclamation measures are applied. An improved criterion for assessing the safety level of the reclamation process of the lands of the disposal and destruction of ammunition sites was developed based on the use of a regulatory approach, and significant indicators were determined, namely: the probability of an explosion, the amount of excessive pressure in the air shock wave, and the level of degradation of the lands of the disposal and destruction of ammunition sites. An improved method of assessing the safety level of the process of land reclamation of the disposal and destruction of munitions by using an improved criterion for assessing the safety level of the process has been developed. The proposed method is suitable not only for long-term evaluation, but also for operational safety management of similar objects. The main advantage of the proposed method in comparison with those used today is to take into account the entire complex of active factors of explosion risk and environmental danger, while minimizing the number of significant environmental quality indicators. Thanks to this, it becomes possible to reduce the amount of calculations required for accurate assessment by a set of regulatory criteria, and also simplifies the assessment procedure without loss of accuracy.

Vibration effect and ocean environmental impact of blasting excavation in a subsea tunnel

Drill-blast method is one of the important methods in the current subsea tunnel excavation construction. Controlling the vibration effect during blasting construction and its impact on the marine environment has been a key topic in the construction of subsea tunnels. This paper takes the Xiamen subsea tunnel excavation and blasting project as the background, combines blast vibration monitoring in the tunnel and underwater sound pressure testing in seawater, analyzes the attenuation law of subsea tunnel blast vibration propagation along the rockmass, studies of the characteristics of shock waves formed in water following the propagation of blast stress waves to seawater. Based on the dynamic finite element numerical calculation, the impact of blasting vibration effect of mainline tunnel on the adjacent built service tunnel structure and the characteristics of shock wave pressure distribution in water excited by blasting vibration are analyzed. Considering the influence of the burial depth of tunnel blasting source, a mathematical prediction model of the attenuation law of underwater sound pressure in water caused by subsea tunnel blasting is established. Based on the pressure control standard of marine organism safety, the control range of marine organism safety under the influence of subsea tunnel blasting is proposed.

Method of calculations and substantiation of requirements for engineering protection of critical infrastructure objects from UAVs with warheads

Abstract. Aim of the study. The purpose of the work is to develop a methodology for calculations and substantiation of requirements for elements of engineering protection of key infrastructure objects (KIO) of the electric power and gas transportation systems of Ukraine against UAVs of the "Shahed" type. Methodology. The characteristics and design of the "Shahed" UAV were considered. It has been established that UAVs of the "Shahed-136" type pose the greatest danger, as they have the largest warhead. For large and/or key KIO structures, the case of a direct hit by a UAV is considered. The requirements for the arrangement are substantiated and a principled solution for the first-order circular engineering protection of the most important structures and equipment of KIO is proposed. It includes two layers: a protective screen and an impenetrable shell. The protective screen is designed to destroy the UAV or prematurely detonate its charge. The protective shell, from which the screen is located at some distance, is designed to retain debris and withstand the wave from the explosion. Findings. The method of calculations and substantiation of requirements for elements of engineering protection of OKIS was obtained. The sequence and analytical methods of calculations of both levels of protection are presented. When designing a protective screen, a concentrated impact from a UAV collision is calculated, and for a protective shell, shock wave pressure and debris permeability are calculated. Scientific innovation. The method of calculations and substantiation of requirements for elements of engineering protection of key infrastructure objects is proposed in the work for the first time. Practical value. A constructive solution was developed for the engineering protection of the process gas treatment plant against direct hits of the "Shahed-136" UAV using steel structures and sand filling. The procedure for carrying out work on the installation of the protection system is proposed.

Dynamics of Laser-Induced Shock Waves in Supercritical CO2

We studied the dynamics of laser-induced shock waves in supercritical CO2 (scCO2) for different pressures and temperatures under nanosecond optical breakdown. We estimated the shock wave pressure and energy, including their evolution during shock wave propagation. The maximal shock wave pressure ~0.5 GPa was obtained in liquid-like scCO2 (155 bar 55 °C), where the fluid density is greater. However, the maximal shock wave energy ~25 μJ was achieved in sub-critical conditions (67 bar, 55 °C) due to a more homogeneous microstructure of fluid in comparison with supercritical fluid. The minimal pressure and energy of the shock wave are observed in the Widom delta (a delta-like region in the vicinity of the critical point) due to the clusterization of scCO2, which strongly affects the energy transfer from the nanosecond laser pulse to the shock wave.

Facilitated ignition and detonation initiation of hydrogen-oxygen mixtures by ozone doping

This work computationally studies homogeneous and inhomogeneous ozone addition in hydrogen-oxygen ignition and transition to detonation, with emphasis on the ozone-induced two-stage behaviors in the chemical kinetics and wave dynamics. In 0D homogenous ignitions, ozone addition induces an additional first-stage reaction and substantially reduces the ignition delay time (IDT). At intermediate initial temperatures, e.g. T0 = 600 K, a critical value, αcr, is identified to delineate different regimes for ozone fraction in the total oxidizer, α. Specifically, the first-stage ignition occurs several orders earlier than IDT for α<αcr, while the IDTs for two stages are comparable for α>αcr. Mechanistically, low-to-intermediate temperature HO2 chemistry introduces a quasi-steady intermediate state in the former regime, whereas ozone reactions directly accelerate high-temperature H2O2 reactions in the latter one. Furthermore, according to the Zel'dovich mechanism, ozone concentration non-uniformity can establish reactivity gradient and hence further initiate double spontaneous waves with multiple dynamics. Coherent coupling between the second-stage heat release and pressure (shock) wave can further evolve into detonation, whereas such synchronized enhancement is not observed in the first-stage ignition due to its large excitation time. Corresponding to the multi-timescales in 0D ignition, when the initial α interval are respectively below, across and above αcr, the low- and high- temperature reaction fronts always separate, first separate then merge, and always merge, respectively. It is also noted that at higher initial temperatures αcr decreases, and that the first-stage reaction becomes less concentrated. Consequently, detonation can be initiated with smaller amounts of ozone and is minimally influenced by the first-stage reaction.

Shockwave and dynamic pressure propagation law of methane–air explosion in full-scale pipe network

ABSTRACT Methane explosions are the main cause of coal mine disasters. Considering the scale effect involved in the process of methane explosion, small-scale methane explosion experiments can only obtain a qualitative trend of explosion parameters. It is necessary to study methane explosions in a full-size complex pipe network. In this study, the No. 501 experiment at the Lynn Lake Experimental Mine in the United States was used as the background case. GASFLOW-MPI was used to study the oscillation, attenuation, and dynamic pressure evolution laws of the explosion shockwaves in a full-size complex pipe network with consideration of the heat loss. The results showed that the numerical simulation results considering heat loss were more accurate than the adiabatic simulation results, and the average error of the peak pressure was only 4.25%. The pressure – time history curve of methane explosion shockwaves in a complex pipe network differed from that in a single pipe. The pressure peak was a bimodal curve near the explosion source, the dynamic pressure changes significantly, and both forward and reverse wind reaching 200 m/s occurred. The pressure curve far from the explosion source was a unimodal peak curve, and only the forward wind occurred. This reasonably explains the bidirectional deformation of rock bolted plates found in the US UBB accident. The results are expected to provide theoretical support for emergency mine rescue operations and mitigating the effects of methane explosions.

Research on vibration compensation technology of pressure sensors in shock wave overpressure measurement

In the dynamic pressure test of explosion shock wave, the interference of seismic wave and mechanical shock makes the interpretation of shock wave pressure measurement more difficult. In this paper, a comparative test is designed to peel off the vibration signal, and the source of vibration in shock wave measurement and the cause of acceleration parasitic effect of pressure sensor are analyzed combined with the data; Then, according to the experimental conclusions and the working principle of the sensor, a new pressure sensor with vibration compensation function is designed; Finally, the feasibility of the new sensor structure for vibration compensation is analyzed by finite element simulation. The results show that the vast majority of vibration interference signals are output by the sensor’s sensitive elements, and the new sensor with double sensitive element compensation can effectively suppress or eliminate the parasitic output caused by vibration interference. The design of the new structure sensor provides ideas for the design of vibration compensation structure of other pressure sensors, and has a certain reference value.

Mitigating hydrodynamic ram effect by a novel perforated lattice filled tank

High-velocity impact on fluid-filled structures has become an increasingly critical issue for the vulnerability of aircraft fuel tanks. Hydrodynamic Ram (HRAM) is a typical phenomenon that occurs when a flying object impacts against a fluid-filled tank with a high velocity, leading to excessive structural damage and catastrophic failure. Thus, an effective HRAM mitigation method is highly desired to provide better protection for the aircraft fuel tanks. In this paper, a novel perforated lattice filled tank was proposed by filling the empty space inside a fuel tank to mitigate HRAM effect and reduce the shock wave pressure. Perforated lattices were utilized to reduce the cavity expansion and structural damage while the holes on the lattice walls could guarantee the connectivity for each unit cells. Experimental tests were conducted to investigate the impact response and cavity evolution of the perforated lattice filled tanks with 1 × 1, 3 × 3 and 5 × 5 unit cells. The deformations of the front, back and lateral walls of the lattice-filled tanks were recorded by using a high-speed video camera and strain gauges (SG). Besides, A fluid–structure interaction finite element model of the fuel tank based on the SPH method was established to study the mitigation performance of HRAM phenomenon. A parametric analysis was conducted to explore the influence of unit-cell number, impact velocity, volume fraction of fluid and liquid level pressure on the impact response. The results indicated that the structural deformation and damage can be alleviated by the lattice-filled design, and it could be considered as an effective solution to mitigate the HRAM effect.

Characterization of laser-induced shock waves generated during infrared laser ablation of copper by the optical beam deflection method

The shock waves generated during laser ablation of a copper target are investigated using the optical beam deflection method. The fluence of nanosecond pulsed infrared laser beam was in the range of 15-700J/cm2. The density jumps related with the influx of the shock wave at two interaction points were detected with the help of He-Ne laser probes. In general, a supersonic shock wave is produced, which propagates through air and gradually decays into an acoustic wave. Experiments were carried out to study the impact of laser fluence and propagation distance on the shock wave velocity and pressure. The shock wave velocity varies with laser fluence as v∝Fl0.3 and with propagation distance as v∝d-1.5. These results are compared with the predictions of the theoretical models. In the investigated fluence range, shock wave pressure rises by an order of magnitude (∼1-10MPa). We demonstrated that shock wave pressure and ablated mass can be related, yielding mass-specific shock wave pressure that increases linearly with laser fluence. We have also noticed the shock-wave-induced probe beam focusing under certain conditions, which indicates that the shock wave modifies the refractive index of the compressed layer of air. The reported results are useful for the fundamental understanding and pave the way for new applications of laser-induced shock waves.

In vitro prediction of the lower/upper-critical biofluid flow choking index and in vivo demonstration of flow choking in the stenosis artery of the animal with air embolism

<i>In vitro</i> prediction of the lower/upper-critical biofluid flow choking index and <i>in vivo</i> demonstration of flow choking in the stenosis artery of the animal with air embolism

Influence of Ground Impedance on Explosive Shock Wave Test Accuracy

Different propagation media have different effects on explosion shock wave attenuation during the propagation process. Studying the attenuation effect of dielectric impedance on shock wave pressure is of great significance to accurately measure shock wave pressure and evaluate the ammunition damage power. This study analyzes the measured shock wave overpressure peak data of TNT bare charge (60 kg) on soil, sand soil, and concrete grounds. Dimensional analysis was used to establish the medium impedance expressed by material densityρ, burst center distancer, equivalent TNT quality ω, and impedance coefficient η. Based on this, the mapping relationship between the propagation medium impedance coefficientηand the shock wave overpressure peak value was established. The test data were analyzed, and the results showed that in the same explosive environment, different ground propagation media had different impedance effects on the shock wave pressure, which is specifically expressed as ηsoil>ηsandsoil>ηconcrete; the modified calculation model of shock wave pressure established using material impedance coefficient has a fitting accuracy of 93.39% to the measured data, which can well represent the attenuation law between different ground propagation media and shock wave overpressure peak. This provides a theoretical basis and method for obtaining shock wave pressure data in explosion field and verifying validity of the test data.

Multi-frame multi-exposure shock wave imaging and pressure measurements.

Shock wave visual detection was traditionally performed using streak cameras, limited to homogeneous shock wave emission, with the corresponding shock wave pressure measurements available at rather large distances or numerically estimated through equation of state for water. We demonstrate a multi-frame multi-exposure shock wave velocity measurement technique for all in-plane directions of propagation, based on custom-built illumination system allowing multiple illumination pulses within each frame at multi-MHz frame rates and at up to 200 MHz illumination pulse repetition frequency at sub-nanosecond pulse durations. The measurements are combined and verified using a fiber-optic probe hydrophone, providing independent shock wave pressure and time-of-flight measurements, creating a novel all-optical measurement setup. The measured pressures at distances around 100 µm from the plasma center exceed 500 MPa, while camera-based measurements at even shorter distances indicate pressures above 1 GPa.