Shock Wave Propagation Research Articles

Efficient two-dimensional simulation of primary reference fuel ignition under engine-relevant thermal stratification

Despite vast research on engine knock, there remains a limited understanding of the interaction between reaction front propagation, pressure oscillations, and fuel chemistry. To explore this through computational fluid dynamics, the adoption of advanced numerical methods is necessary. In this context, the current study introduces ARCFoam, a computational framework that combines dynamic mesh balancing, chemistry balancing, and adaptive mesh refinement with an explicit, density-based solver designed for simulating high-speed flows in OpenFOAM. First, the validity and performance of the solver are assessed by simulating directly initiated detonation in a hydrogen/air mixture. Second, the study explores the one/two-dimensional (1D/2D) hotspot ignition for the primary reference fuel and illuminates the impact of transitioning to 2D simulations on the predicted combustion modes. The 2D hotspot simulations reveal a variety of 2D physical phenomena, including the appearance of converging shock/detonation fronts as a result of negative temperature coefficient (NTC) behavior and shock wave reflection-induced detonation. The main results of the paper are as follows: (1) NTC chemistry is capable of drastically changing the anticipated reaction front propagation mode by manipulating the local/global reactivity distribution inside and outside the hotspot, (2) subsonic hotspot ignition can induce detonation (superknock) through the generation of shock waves and subsequent wall reflections, and (3) while the 1D framework predicts the initial combustion mode within the hotspot, significant differences between 1D and 2D results may emerge in scenarios involving ignition-to-detonation transitions and curvature effect on shock/detonation front propagation.

Shock wave generation in water by nanosecond pulse laser irradiation with 1064 and 2940 nm wavelengths

Shock wave generation in water by nanosecond pulse laser irradiation with 1064 and 2940 nm wavelengths

Propagation of magnetogasdynamics spherical shock wave in a gravitating gas with radiation heat flux

This article presents a mathematical model for characterizing the dynamic behavior of spherical shock waves in a self-gravitating, radiating ideal gas with the presence of an azimuthal magnetic field, emphasizing adiabatic conditions. The analysis assumes that the environment just ahead of the shock wave is stationary, and it accounts for variations in density, magnetic field, and fluid velocity within the disturbed medium just behind the shock front. Furthermore, the impact of thermal radiation within the context of an optically thin limit is incorporated into the energy equation of the governing system. Employing the Lie invariance method, the set of partial differential equations governing the flow within this medium is transformed into a system of nonlinear ordinary differential equations through the use of similarity variables. Four distinct cases of similarity solutions are derived by selecting different values for the arbitrary constants associated with the generators. Among these four cases, only two yield similarity solutions, one assuming a power-law shock path and the other an exponential-law shock path. In the case of a power-law shock path, the resulting set of nonlinear ordinary differential equations is numerically solved using the 4th-order Runge-Kutta method in MATLAB software. The article thoroughly discusses the influence of various parameters, including γ (adiabatic index of the gas), Ma−2 (Alfvén–Mach number), ϕ (ambient density exponent), and G0 (gravitational parameter), on the flow properties. The findings are presented graphically to provide a comprehensive understanding of the effects of these parameters.

Long‐term results of Alzheimers’ dementia treated with transcranial pulse stimulation

AbstractBackgroundThe treatment of the brain with focused extracorporal shock waves (ESW) in patients with unresponsive wakefulness syndrome dates back to 2006 (1). This was followed by preliminary investigations for the treatment of Alzheimer’s dementia and Parkinson’s disease in the years up to 2014.The introduction of a shock wave generator with a navigation system in 2016 (Neurolith, Storz Medical) was a breakthrough for the precise treatment of brain structures. This method of brain treatment was then called TPS. After a 3 month study with people living with Alzheimer’s dementia in 2019 (2), we now present patients with long‐term follow‐up over 3 years during continous monthly TPS treatment as a critical undertaking for future treatments.Method6 persons living with mild Alzheimer’s dementia (Mini Mental Status >18) were treated initially 6 times during 2 weeks with TPS. Subsequently, they received one TPS session monthly over 3 years. The results were assessed with the CERAD Plus score and compared with the data of the expected natural development with standard medication according to the ALSOVA study of Hallikainen.ResultWhile cognitive skills improved by 12% over 12 months, outcomes returned to the baseline in the second year. A two‐week booster of 6 sessions with TPS improved outcomes again by 4.5% compared to the baseline. After 3 years, the results were at the level of the expected natural development with standard medication.ConclusionA symptomatic improvement of Alzheimer’s symptoms with low‐energy TPS over several years seems to be possible. It was a methodological mistake not to examine the patients more frequently neuropsychologically. It is conceivable that this would achieve a better long‐term result.(1.) H. Lohse‐Busch, U. Reime and R. Falland, (2014) Symptomatic treatment of unresponsive wakefulness syndrome with transcranially focused extracorporeal shock waves. NeuroRehabilitation 35 (2014) 235‐244(2.) Beisteiner R, Matt E, …… Lohse‐Busch H (2019) Transcranial pulse stimulation with ultrasound in Alzheimer’s disease—A new navigated focal brain therapy. Adv Sci (Weinh) 23;7(3):1902583.

Correction to: Abstract P804: Lopsided Blood-Thinning Drug Increases the Risk of Internal Flow Choking and Shock Wave Generation Causing Asymptomatic Stroke.

Correction to: Abstract P804: Lopsided Blood-Thinning Drug Increases the Risk of Internal Flow Choking and Shock Wave Generation Causing Asymptomatic Stroke.

The appearance of standing wave structures in the reaction medium during the diffusion development of the chain reaction process

Relevance. Understanding the dynamic behavior of radicals in reactors undergoing gas-phase oxidation of organic substances is crucial for optimizing reactor design and safety across industries. Purpose. This study aims to elucidate the emergence of standing wave structures influenced by feedback mechanisms in reactors with cylindrical and spherical symmetry, using mathematical principles governing the propagation of oscillations and shock waves in diffusion-driven chain reactions. Methodology. Materials and methods for the research included a computer simulation using MATHCAD 2001i, and comparative analysis of experimental data obtained from reactor experiments. The computational modeling revealed vivid formations of standing wave structures in reactors influenced by feedback mechanisms. Results. The impact of reverse connections in reactors with cylindrical and spherical symmetry significantly contributed to the formation of various standing wave structures of radical concentrations within the reaction zone. It was found that these structures were largely imperceptible visually and could only be observed when the reaction was accompanied by intense light emission. These visual representations served as compelling evidence of the intricate interplay between reaction kinetics and feedback effects. The study emphasized the importance of understanding and predicting the root causes of instabilities, ultimately enhancing the reliability and safety of reactors across various industries. The results demonstrated a correlation between specific feedback mechanisms and the spatial distribution of standing wave structures. Conclusions. The derived computational patterns, as presented in this paper, provide compelling evidence supporting the feasibility of standing wave structure formation within reactors when influenced by feedback mechanisms. The study unveiled the potential for fine-tuning reactor parameters to influence the formation and stability of these structures. The findings represented a significant stride towards a more comprehensive understanding of dynamic regimes in reactors, with implications for reactor design, operation, and safety protocols. The insights garnered from uncovering standing wave structures influenced by feedback mechanisms offered valuable opportunities to optimize reactor design and operational safety, leading to more efficient and sustainable processes

Numerical and experimental analysis of dynamic process of laser ablation epoxy resin

The numerical simulation of polymer laser ablation is essential for applications such as laser propulsion and laser deposition. Based on the pyrolysis effect of polymers, this paper establishes a dynamics model of polymer laser ablation. Numerical solution software FLUENT was used to solve the equations involving mass, momentum, and energy. With user-defined functions (UDF) and dynamic mesh, the deposition of laser energy, the depression of the material surface, and the generation of high-temperature pyrolysis gas plumes were simulated. Epoxy resin was selected as the experimental material, and its surface changes were observed after exposure to various laser pulse powers. High-speed shadow imaging techniques were employed to examine epoxy resin's dynamic laser ablation process. Compared to experimental results, numerical calculations accurately reflected the dynamic behaviours of epoxy resin after pulse laser interaction, such as the expansion of pyrolysis gas plumes and the propagation of shockwaves.

Comparison of Biomechanical Outcome Measures From Characteristically Different Blast Simulators and the Influence of Exposure Location.

Simulation of blast exposure in the laboratory has been inconsistent across laboratories. This is primarily because of adoption of the shock wave-generation techniques that are used in aerodynamic tests as opposed to application of blast exposures that are relevant to combat and training environments of a Warfighter. Because of the differences in blast signatures, characteristically different pathological consequences are observed among the preclinical studies. This is also further confounded by the varied exposure positioning of the animal subject (e.g., inside the blast simulator vs. at the mouth of the simulator). In this study, we compare biomechanical responses to blast exposures created in an advanced blast simulator (ABS) that generates "free-field"-like blast exposure with those produced by a traditionally applied cylindrical blast simulator (CBS) that generates a characteristically different blast signature. In addition, we have tested soft-armor vest protective responses with the ABS and CBS to compare the biomechanical responses to this form of personal protective equipment in each setting in a rodent model. Anesthetized male Sprague-Dawley rats (n = 6) were surgically probed with an intrathoracic pressure (ITP) transducer and an intracranial pressure (ICP) transducer directed into the lateral cerebral ventricle (Millar, Inc.). An ABS for short-duration blast or a CBS for long-duration blast was used to expose animals to an incident blast overpressure of 14.14 psi (impulse: 30.27 psi*msec) or 16.3 psi (impulse: 71.9 psi*msec) using a custom-made holder (n = 3-4/group). An external pitot probe located near the animal was used to measure the total pressure (tip) and static gauge (side-on) pressure. Data were recorded using a TMX-18 data acquisition system (AstroNova Inc.). MATLAB was used to analyze the recordings to identify the peak amplitudes and rise times of the pressure traces. Peak ICP, peak ITP, and their impulses were normalized by expressing them relative to the associated peak static pressure. Normalized impulse (ABS: 1.02 ± 0.03 [vest] vs. 1.02 ± 0.01 [no-vest]; CBS: 1.21 ± 0.07 [vest] vs. 1.01 ± 0.01 [no-vest]) and peak pressure for ICP (ABS: 1.03 ± 0.03 [vest] vs. 0.99 ± 0.04 [no-vest]; CBS: 1.06 ± 0.08 [vest] vs. 1.13 ± 0.06 [no-vest]) remained unaltered when comparisons are made between vest and no-vest groups, and the normalized peak ITP (ABS: 1.50 ± 0.02 [vest] vs. 1.24 ± 0.16 [no-vest]; CBS: 1.71 ± 0.20 [vest] vs. 1.37 ± 0.06 [no-vest]) showed a trend of an increase in the vest group compared to the no-vest group. However, impulses in short-duration ABS (0.94 ± 0.06 [vest] vs. 0.92 ± 0.13 [no-vest]) blast remained unaltered, whereas a significant increase of ITP impulse (1.21 ± 0.07 [vest] vs. 1.17 ± 0.01 [no-vest]) in CBS was observed. The differences in the biomechanical response between ABS and CBS could be potentially attributed to the higher dynamic pressures that are imparted from long-duration CBS blasts, which could lead to chest compression and rapid acceleration/deceleration. In addition, ICP and ITP responses occur independently of each other, with no evidence of thoracic surge.

Effect of dimensionless vent ratio on the flame-shock wave evolution dynamics of blended LPG/DME gas explosion venting

To reveal the flow field-shock wave-flame coupling evolution law of LPG/DME blended gas explosion venting under different dimensionless vent ratio(KV), the numerical model for multi-blended gas explosion venting was established and research of blended gas explosion venting at KV = 0.02–0.21 was carried out based on experimental verification. The results show that, after the vent opens, the turbulence intensity increases, the velocity gradient of the flow field increases, the maximum explosion wind velocity(Vmax) of the outfield varies linearly with KV, and the flame of “mushroom shape” is elongated, and “break flame” occurs under the action of the relative motion of “primary and secondary vortex group”. When KV＞0.02, the flame propagation velocity increases locally because of the thermal-mass diffusion instability, and with increasing KV, the average flame propagation velocity decreases from 258.29 m/s to 226.58 m/s. In the process of explosion venting, a typical shock wave fluctuating pressure waveform curve is formed in the outfield. Under the combined action of the infield pressure venting effect and the outfield turbulence intensity, the maximum explosion overpressure in the outfield (Pmax) reaches maximum 423.97 kPa at KV = 0.07. Meanwhile, the larger the KV, the greater the shock wave velocity due to the lead role of the infield explosion venting shock wave and outfield flame compression shock wave on the shock wave propagation velocity.

Mechanism and destruction status of CO2 BLEVE during CO2 geological storage and enhanced oil recovery injection process

In CO2-oil recovery enhancement technology, the occurrence of a Boiling Liquid Expansion Vapor Explosion (BLEVE) can result in dangerous events that endanger the lives and health of workers, while also leading to significant economic losses. This happens when there is an excessive injection concentration and volume of CO2, coupled with container defects. To address the limited research on the mechanism and destruction of BLEVE, this study conducts experiments to explore these issues. The experimental results reveal that the bursting piece ruptures at a temperature of 36 °C, and the specimen explodes when the pressure intensity exceeds the residual strength of the specimen, reaching 69.97 MPa. The findings indicate that parameters, such as initial pressure, initial temperature, and failure pressure, can impact the risk of CO2 BLEVE occurrence and the propagation of explosion shock waves. The pressure inside the container during the BLEVE process fluctuates due to the joint action of the leakage rate and gasification rate of liquid CO2. This research provides a framework for evaluating the risk of CO2 BLEVE during CO2 geological storage and enhanced oil recovery injection processes, offering theoretical support for BLEVE prevention and control.

Numerical simulation of shock wave propagation over a dense particle layer using the Baer–Nunziato model

The present study examines the possibility of numerical simulation of a strong shock wave propagating over the surface of a dense layer of particles poured onto an impermeable wall using the Baer–Nunziato two-phase flow model. The setting of the problem follows the full-scale experiment. The mathematical model is based on a two-dimensional system of Baer–Nunziato equations and takes into account intergranular stresses arising in the solid phase of particles. The computational algorithm is based on the Harten–Lax–van Leer–Contact method with a pressure relaxation procedure. The developed algorithm proved to be workable for two-phase problems with explicit interfacial boundaries and strong shock waves. These issues are typical of problems arising from the interaction of a shock wave with a bed or a layer of particles. A comparison with the simulations and full-scale experiments of other authors is carried out. A reasonable agreement with the experiment is obtained for the angles of the transmitted compaction wave and granular contact, including their dependency on the intensity of the propagating shock wave. The granular contact angle increases with the incident shock wave Mach number, while the transmitted compaction wave angle decreases. An explanation is given of the phenomenon of the decrease in thickness of the compacted region in the layer with the increase in intensity of the propagating shock wave. The main reason is that the maximal value of the particle volume fraction in the plug of compacted particles in the layer rises with the increase in shock wave intensity.

Experimental investigation of the shock wave/boundary layer interaction at a compression corner and an incident shock wave generator

The separation of the boundary layer is one of the main failures in scramjets due to its influence on the amount of oxygen used in combustion, reducing thrust and specific impulse. The main objective of this paper was to perfom experimental investigations to study the shock wave/boundary layer interaction and boundary layer separation. The experimental investigation was done in the T2 shock tunnel using the throats/nozzles for theoretical Mach numbers of 6.5 and 8.3. Compression ramp (30° and 20°) models made of aluminum and printed on plastic filament in the 3D printer were designed and produced, as well as two shock generators models with 30°. The flow analysis was performed using pressure sensors and the schlieren image technique. In the cases of shock generators, the incident shock wave caused an increase in pressure and reached a plateau inside the separation bubble (from 81.84 kPa to 360.01 kPa). The highest pressure values were related to the reattachment line. Then, the expansion waves cause a reduction in pressure and adjacent phenomena cause increase in pressure. The ramps caused an increase in pressure and an effect close to a plateau. Then, the boundary layer is replaced and the pressure continues to increase until the end of the ramp, obtaining values from 15.9 kPa to 93.8 kPa. The highest pressure values were observed in the region of interaction of the incident shock wave with the reattachment shock. The pressure values between the aluminum and plastic filament models measured different values along the ramp (45.6 kPa and 28.8 kPa) in the last sensor. The images in schlieren were of excellent quality and the technique was highly efficient to visualize the phenomena. As results of these campaigns, it was possible to visualize the adverse pressure gradient, the flow separation structure, including the separation bubble and reattachment of the boundary layer.

Multi-scale modeling of shock wave propagation in energetic solid-state composites

We present a novel structural dynamics code for modeling shock and detonation waves in Polymer-Bonded Explosives (PBXs), which are crucial for conventional munitions and propulsion components. Our code uses a stable and efficient solution strategy based on a Taylor–Galerkin finite element (FE) discretization to accurately predict PBX behavior under extreme shock loading. To model the PBXs, we implement equations of state for the solid unreacted material and gaseous reaction products using a pressure mixture rule governed by pressure-based reaction rates. We verify the FE model using analytical solutions for SOD shock and ZND detonation models. In addition to the continuum model, we also introduce a first-order multi-scale model that uses a Taylor approach to compute macro-scale fluxes and properties from the underlying microstructural sub-problems using averaging schemes. Our numerical results demonstrate the effectiveness of our multi-scale model in accurately predicting pressure profiles and detonation velocities for microstructures with varying mass fractions. These findings have significant implications for microstructure design and highlight the importance of considering microstructural variability in PBX behavior. Overall, our structural dynamics code represents a significant step towards improving the understanding and design of PBXs under extreme shock loading conditions.

Underwater microsecond timescale electrical explosions of aluminum and copper foils

We present results on underwater electrical explosions of thin aluminum and copper foils using a generator delivering ∼200 kA current amplitude, ∼0.9 μs rise time pulses. Time-resolved shadow imaging displays the generation of a strong planar shock wave in water in the vicinity of the exploding foil. Using time-resolved spectroscopy, aluminum oxide (AlO) absorption bands were observed in a Planckian-like spectrum, indicating that aluminum combustion starts when aluminum vaporizes. It is also shown that the strongest shock wave is obtained for the largest linear energy deposition rate to the foil.

Numerical simulation of the propagation and distribution of explosion shock waves in trenches

Trenches, as important military defense measures, have significant practical significance in studying the impact of trench terrain on the propagation patterns of explosive shock waves. This research is based on numerical simulations and establishes six trench models with depths of 0 mm, 200 mm, 400 mm, 600 mm, 800 mm, and 1000 mm, as well as five different lengths of trenches: 400 mm, 600 mm, 800 mm, 1000 mm, and 1200 mm. The internal and front-to-back shock wave pressures within the trenches were numerically calculated. The research findings indicate that as the depth of the trench increases, the pressure at the midpoint of the trench bottom gradually decreases within a depth of 800 mm, and then slowly increases beyond 800 mm. As the length of the trench increases, the pressure on the trench bottom significantly decreases when the length does not exceed 600 mm, but steadily increases after reaching 600 mm.

Recent developments in MHz radioscopy: Towards the ultimate temporal resolution using storage ring-based light sources

Hard X-ray imaging with ultra-high speed acquisition rates using synchrotron-based sources or free-electron lasers has recently gained significant attention: commercially available CMOS-based cameras as basis for indirect detection allow for the use of radioscopy with MHz acquisition rates in a routine manner. Hence, an increasing number of experiments are reported in the literature studying with ultra-high speed radioscopy phenomena ranging from materials research (additive manufacturing), astrophysics (meteorite formation) to dynamic compression (propagation of shock and compression waves). By using the high flux beamline BL40XU of the SPring-8 synchrotron light source this MHz radioscopy approach has been developed further: the outstanding high photon flux density at narrow bandwidth of beamline BL40XU allowed for reaching unprecedented temporal resolution at high X-ray imaging sensitivity. Furthermore, a proto-type of a new ultra-high speed framing camera was integrated, demonstrating that frame rates close to the native radio frequency of the storage ring should become feasible in the future, i.e. an approach towards GHz radioscopy.

Impact Velocity and Temperature Effects on the Shock Wave Propagation and Spallation of Hydroxyl-Terminated Polybutadiene: A Molecular Dynamics Study

Impact Velocity and Temperature Effects on the Shock Wave Propagation and Spallation of Hydroxyl-Terminated Polybutadiene: A Molecular Dynamics Study

On the unsteady cavitation characteristics of compressible liquid nitrogen flows through a venturi tube

In this paper, the unsteady cavitating flows of liquid nitrogen (LN2) through a three-dimensional (3D) venturi tube in different thermal cavitation modes are modeled based on the mixture multiphase model with the LES method and Sauer-Schnerr cavitation model. A numerical framework considering compressibility and the thermal effects of cryogenic fluids is developed, and the modified temperature-dependent Tait equations of state provide the mathematical closure. The numerical results are compared with those from previous experiments that we have conducted, and it is indicated that the simulations and experiments agree well. Condensation shock wave propagation is observed to be initiated by the impingement of the collapse-induced pressure waves from the previously shedding cloud, and details of the process are presented. The impacts of the thermal effect on the cavitation dynamics, especially the evolution of cavitation patterns and dynamic interactions between cavitation and vortex, are analyzed. The numerical results show that the formulation of condensation shock generated at the rear of the cavity varies with temperature. In addition to the pressure waves caused by shed vapor collapse, the violent mass transfer process at the closure region of the cavity releases a substantial quantity of latent heat, initiating further condensation towards the cavity as liquid temperature decreases. The entropy production theory is derived and implemented, and different entropy production terms are established in unsteady LN2 cavitating flow with different thermal effects to understand the interactions between cavitation and entropy production. The present study provides insight into the interactions of cavitation-condensation shock in the LN2 cavitating flow and contributes to a better understanding of the influences of thermal effects on cryogenic cavitation dynamics.

Numerical modeling and simulation of underwater explosions interacting with discrete rigid bodies

The smoothed particle hydrodynamics (SPH) method is widely used to simulate underwater explosion phenomena. However, previous studies have focused on the interaction between the underwater explosion and continuous structures (e.g., steel plates and dams), while studies on the interaction between the explosion and discrete objects (e.g., debris) have not been reported. In this study, a multi-media coupled model containing water, explosion gas, discrete objects, and steel plates is developed based on the SPH method. The discrete object is modeled as a rigid body with a certain shape, which is discretized by SPH particles. The interaction between the discrete object and the adjacent fluid particles is realized by the kernel approximation, while the collision between different objects is realized by the contact algorithm. To improve the numerical stability, an artificial viscous term containing a threshold switch is added to the SPH momentum equation, while a density dissipation term is introduced into the continuity equation to reduce the noise of the pressure field. Subsequently, the established SPH model is used to simulate the underwater explosion process containing discrete rigid bodies, and the effects of the distribution, stacking form, and number of rigid bodies on the propagation of shock waves, bubble expansion, and deformation of steel plates and the effect of damage are analyzed. The results show that the rigid body will hinder the propagation of shock waves, help reduce the peak pressure of the shock wave behind, and then affect the direction of the diffusion of the explosion energy. Shock waves would produce diffraction, reflection, and transmission when passing through the rigid bodies, and the superposition of various waves would make the pressure distribution near the liquid–gas interface irregular. The rigid bodies stacked above the explosives would enhance the damage effect of the explosion on the steel plates below, and the damage effect is affected by the stacking form. The established model can simulate the multi-medium coupling process in a unified framework without coupling other methods and can effectively restore the complex interaction process between underwater explosion, discrete object, and structure.

Symmetry and scaling in one-dimensional compressible two-phase flow

Investigations of shock compression of heterogeneous materials often focus on the shock front width and overall profile. The number of experiments required to fully characterize the dynamic response of a material often belie the structure–property relationships governing these aspects of a shock wave. Recent observations measured a pronounced shock-front width on the order of 10 s of ns in particulate composites. Here, we focus on particulate composites with disparate densities and investigate whether the mechanical interactions between the phases are adequate to describe this emergent behavior. The analysis proceeds with a general Mie–Grüneisen equation of state for the matrix material, a general drag force law with general power-law scaling for the particle-matrix coupling of the phases, and a volume fraction-dependent viscosity. Lie group analysis is applied to one-dimensional hydrodynamic flow equations for the self-consistent interaction of particles embedded in a matrix material. The particle phase is characterized by a particle size and volume fraction. The Lie group analysis results in self-similar solutions reflecting the symmetries of the flow. The symmetries lead to well-defined scaling laws, which may be used to characterize the propagation of shock waves in particle composites. An example of the derived scaling laws for shock attenuation and rise time is shown for experimental data on shock-driven tungsten-loaded polymers. A key result of the Lie analysis is that there is a relationship between the exponents characterizing the form of the drag force and the exponent characterizing the shock velocity and its attenuation in a particulate composite. Comparison to recent experiments results in a single exponent that corresponds to a conventional drag force.