Shock Wave Propagation Research Articles

Studies on Thermal Separation and the Effects of Geometrical and Operating Parameters on the Performance of Pressure Wave Refrigerators

Abstract Thermal separation in a pressure wave refrigerator (PWR) occurs primarily through the propagation of shock waves and reverse-moving rarefied waves produced by injecting a high-pressure gas into a low-pressure residual gas in a receiving tube or channel. The major advantages of PWRs are simple design, low cost, high reliability, low rotational speed, and efficiency comparable to the conventional turbo-expanders. The objectives of this work are to understand the thermal separation in PWRs and to study the effects of various geometrical and operating parameters on the performance of PWRs. Two-dimensional computational fluid dynamics (CFD) simulation using a finite volume method is adopted for this study. The results indicate that the temperature and pressure profiles of the fluid inside the receiving tube just before the discharge, in the region about half the tube length from the inlet nozzle, strongly govern the performance of a PWR. The operating frequency at which the isentropic efficiency attains the first peak value is determined in a generalized way. Within the chosen geometrical and operating parameters, the optimized tube length, operating frequency, and pressure ratio are 2 m, 50 Hz, and 2.5, respectively. The findings in this article will be useful in designing and operating PWRs optimally.

Parametric Study of a Switchable Vortex Generator for Load Alleviation in Transonic Conditions

This paper investigates the impact of introducing a switchable vortex generator (SVG), acting as a minitab, on the aerodynamic performance of a high-aspect-ratio wing’s outer section in transonic regime. A parametric study is conducted employing computational fluid dynamics two-dimensional simulations, focusing on the aerodynamic effects of changing the chordwise position and height of the vane of a SVG located on the airfoil upper surface in both nominal cruise conditions and for varying angles of attack. The analysis reveals that minitabs can strongly affect the aerodynamic forces produced by the wing section, showing great potential for load alleviation and control, but also emphasizing the need for a careful parameter selection to reduce undesirable effects such as the generation of shock waves. In cruise conditions, lift reduction increases with the vane height and has its maximum for chordwise positions at 60% of the chord length. However, SVGs located in the first half of the chord length yield more robust performance for varying angle of attack, without sharp lift variations or generated shock waves, and a delayed stall onset. High SVGs (greater than or equal to 3% chord length) can also lead to strong shock waves on the airfoil lower surface at small or negative angle of attack, while small SVGs (less than 1% chord length) can generate normal shock waves on the upper surface, with limited lift reduction in cruise conditions and at higher incidence.

Effects of the shock tube diameter on shock wave propagation in a diaphragmless shock tube

Effects of the shock tube diameter on shock wave propagation in a diaphragmless shock tube

Observations of umbral flashes in the resonant sunspot chromosphere

Context. In sunspot umbrae, the core of some chromospheric lines exhibits periodic brightness enhancements known as umbral flashes. The consensus is that they are produced by the upward propagation of shock waves. This view has recently been challenged by the detection of downflowing umbral flashes and the confirmation of a resonant cavity above sunspots. Aims. We aim to determine the propagating or standing nature of the waves in the low umbral chromosphere and confirm or refute the existence of downflowing umbral flashes. Methods. Spectroscopic temporal series of Ca II 8542 Å, Ca II H, and Hα in a sunspot were acquired with the Swedish Solar Telescope. The Hα velocity was inferred using bisectors. Simultaneous inversions of the Ca II 8542 Å line and the Ca II H core were performed using the code NICOLE. The nature of the oscillations were determined and insights into the resonant oscillatory pattern were gained by analyzing the phase shift between the velocity signals and examining the temporal evolution. Results. Propagating waves in the low chromosphere are more common in regions with frequent umbral flashes, where the transition region is shifted upward, making resonant cavity signatures less noticeable. In contrast, areas with fewer umbral flashes show velocity fluctuations that align with standing oscillations. Evidence suggests dynamic changes in the location of velocity-resonant nodes due to variations in the transition region height. Downflowing profiles appear at the onset of some umbral flashes, but upflowing motion dominates during most of the flash. These downflowing flashes are more common in standing umbral flashes. Conclusions. We confirm the existence of a chromospheric resonant cavity above sunspot umbrae. It is produced by wave reflections at the transition region. The oscillatory pattern depends on the transition region height, which exhibits spatial and temporal variations due to the impact of the waves.

Models of shock wave propagation for diverging metallic structures

In the present study we have considered shock waves propagating freely in some diverging metallic structures. The characteristic equation along with boundary conditions provides a differential equation that is used to evaluate certain flow variables and parameters. The Chisnell-Chester-Whitham (CCW) method forms the basis to obtain the analytical relations for shock velocity, shock strength and pressure behind the shock wave. The variation of pressure with parameter  (compression behind the shock) and propagation distance r is obtained for cylindrical (barrel) shock waves. It is found that shock velocity decreases and the shock strength increases as the shock wave progresses in both the Al and Cu metals. The pressure behind the shock also decays with propagation distance. The rate of decay of pressure in case of Al differs with that in Cu metal. Adiabatic sound velocity c and the parameter  both shows a decreasing trend with propagation distance for both materials but the rate of decay is higher for the former.

Effects of Orifices on the Damage Characteristics of an Arch Dam Subjected to Underwater Contact Explosion

Orifices designed into an arch dam for flood discharge significantly reduce the ability of the dam to resist an explosion, especially when an explosive charge is detonated close to an orifice, and the dam may suffer considerable damage in consequence. We created a fully coupled model to represent the dynamic interactions between reservoir water, explosive, arch dam and abutments. Shock wave propagation and damage initiation and propagation were compared between arch dams with and without orifices. The effects of orifices on damage modes and the spatial distribution of damage were investigated. Damage characteristics of the top and middle orifices subjected to explosive loads were also analyzed. Results showed that the top and middle orifices designed into an arch dam have an important effect on the impact resistance of arch dams, especially when an explosive is detonated at an orifice inlet. At a certain mass of explosive, complete failure of the dam wall at the adjacent sluice piers of the top orifices can occur, and penetration failure may also occur at the middle orifice.

On the formation and propagation of dust acoustic shock waves in a magnetic quantum dusty plasma

On the formation and propagation of dust acoustic shock waves in a magnetic quantum dusty plasma

APPLICATION OF CABARET AND WENO SCHEMES FOR SOLVING THE NONLINEAR TRANSPORT EQUATION IN THE MODELING OF SOUND WAVE PROPAGATION IN THE ATMOSPHERE

The most convenient model for describing the phenomenon of shock wave propagation in the atmosphere is the extended Burgers equation. This work investigates the influence of the numerical scheme on the results of solving the equation, which accounts for the nonlinear nature of shock wave propagation in the atmosphere. This equation is a key component of the extended Burgers equation and defines the transformation of the perturbed pressure profile during its propagation. Two numerical schemes were applied for the solution: CABARET and WENO, which are quasi-monotonic finite difference schemes that allow for solutions without significant numerical oscillations. An analysis of the applicability of these schemes for solving the considered problem was conducted.

Molecular dynamics simulations on shock response and plasticity behaviors of semi-coherent {001} Ni/Al laminate composite

Abstract Molecular dynamics (MD) simulations were used to explore the shock response and plasticity behaviors of a semi-coherent {001} Ni/Al laminate composite premised on interfaces. Firstly, the impedance-matching theory can reasonably explain the impacts that interfaces have on the propagation of shock waves. The findings illustrate that “reflection-unloading” occurs at the Ni-Al interfaces; however, “reflection-loading” occurs at the Al-Ni interfaces. The interfaces have been observed to have discontinuities of shock wave stress, characterized by elastic-plastic properties of heterogeneous materials adjoining the interfaces. Secondly, the stacking fault pyramids and dislocation activities in the Al layers were derived using shock modeling of a multilayer target. Thirdly, we studied the formation of stacking fault pyramids, a process involving decomposition and synthesis of perfect dislocations, and the process of FCC→BCC→HCP continuous phase transition.

Strategy for Calculating the Speed of Trans Media Small Targets Using Stereo Vision Fusion Object Detection

Abstract The velocity calculation of the projectile entering water involves fluid dynamics, shock wave propagation and other aspects of the problem. Traditional photoelectric, radar and laser velocimeters suffer from reduced accuracy due to trans-media effects. At the same time, the projectile entering the water will create a large splash, which affects the parameter measurement of the projectile entering water. In order to address the above problems, a trans-media projectile entry system is constructed, a binocular high-speed camera is used to capture the dynamic process of the projectile entering the water, and a deep learning model is trained for the detection of the projectile target, which assists in the computation of the projectile’s three-dimensional coordinates and then. calculates the speed of the projectile at the moment it enters the water. The experimental results show that the binocular camera provides a better reconstruction of the 3D coordinates of the projectile, and the target detection combined with edge detection makes it easier to obtain the contour information as well as the pixel coordinates of the projectile. The mAP0.5 of the target detection model is 95.43%. Using this target detection model to extract useful images of projectile water entry frames from the video stream saves more than 90% of the time compared with manual extraction, providing an efficient calculation for calculating the velocity of trans media small targets.

Numerical investigation of the multi-physics coupling effect of supersonic projectile on the cross section of terminal ballistics

Abstract This study investigates the multiphysics effects the shock waves from the supersonic projectile on the cross section of its terminal ballistics, and this purpose is to effectively extract attitude information of projectiles in terminal ballistics。Firstly, the acoustic effects are used to study the propagation and attenuation laws of shock waves on the terminal ballistic plane, comparing the spectral characteristics of acoustic pressure signals and photoelectric signals; Secondly, through numerical simulations using COMSOL, the study analyses shock wave attenuation, refractive index changes, and pressure distribution at different Mach numbers. Results show that shock waves significantly affect the refractive index, which can be effectively detected using optical methods. The proposed method demonstrates improved accuracy over conventional techniques, particularly in capturing critical flight parameters of supersonic projectiles. This research lays the groundwork for developing advanced measurement techniques for hypersonic weapon systems, addressing current limitations in projectile detection and measurement accuracy.

Evolution characteristics of shock wave in microsecond-scale underwater electrical wire explosion

The underwater electrical wire explosion (UEWE) is a physical phenomenon initiated by the rapid injection of electrical energy, triggering an explosive event. UEWE offers advantages in energy conversion efficiency, repeatability, and controllability, making it valuable in various industrial applications. Building upon established zero-dimensional (0D) and one-dimensional (1D) models, this paper proposes an enhanced 0D-1D coupled cold-start model to describe the plasma channel expansion and subsequent shock wave (SW) propagation characteristics. The model comprises two submodules: a 0D magnetohydrodynamics model that describes plasma channel boundary expansion during the explosion, and a 1D hydrodynamics model using an artificial viscosity algorithm to depict SW propagation. The constructed numerical model facilitates investigation of plasma characteristics, SW propagation behavior, and energy conversion efficiency throughout the UEWE process. Additionally, the influences of wire dimensions and discharge frequency on these characteristics were analyzed. The results indicate that SW propagation characteristics are primarily governed by thermal pressure variations within the wire and that different wire dimensions markedly affect SW amplitude, attenuation, and impulse. The efficiency of electrical-to-SW energy conversion remains relatively low; however, thicker and shorter wires can enhance SW amplitude and improve conversion efficiency. Higher discharge frequencies produce greater impact forces and impulses near the explosion site, while also improving energy conversion rates. This study offers a theoretical basis and technical guidance for prospective engineering applications.

Protective performance of helmets based on the shock wave from rocket launcher

Abstract Traumatic brain injury(TBI) is one of the most common cause of major casualties in the battlefield. Soldiers may be endangering their brains when they operate certain shoulder-fired weapons or large-caliber artillery for long periods of time. It is necessary to pay attention to protection and prevention of brain injury in daily training. In this paper, the characteristic of shock wave propagation on the head with/without helmet protection when soldiers operated shoulder-fired rocket-propelled grenade launcher. The head-helmet surrogate was constructed in combination with pressure sensors. The pressure sensors were installed on the forehead, temples, top, and back of the head surrogate respectively and the sensors kept a plane with the surface of the head surrogate. The pressure variation of the shock wave flow field under different working conditions was analyzed in three types such as with/without combat helmet and integrated helmet. The results show that the peak overpressure of the shock wave from the back of the head can reach 80∼105kPa without combat helmet. The combat helmet can effectively reduce the shock wave overpressure. The integrated helmet has the best protection and can reduce the overpressure on the forehead, temple, top, and back of the head by 73%, 58%, 80%, and 83% respectively. Meanwhile the shock wave is prone to reflection and diffraction as it transmits inside the helmet. This significantly increase the overpressure of the shock wave on the forehead and the duration of the shock wave in the helmet, which has a negative effect on the protection provided by the shock wave.

Propagation characteristics of explosion shock waves in air under different temperature and pressure conditions

Abstract In order to study the propagation characteristics of explosion shock waves in air under different temperature and pressure conditions, stress wave theory and detonation wave theory were first used to analyze the propagation characteristics of shock waves. Combined with numerical simulation results, the propagation characteristics of explosion shock waves were comprehensively analyzed and verified. The following conclusion was drawn: the higher the pressure, the larger the peak value of shock waves at the same spatial position, and the greater the specific impulse of shock waves, Shortening of shock wave propagation distance; The higher the temperature, the less the peak pressure changes at the same spatial position, the smaller the specific impulse of the shock wave, and the longer the propagation distance of the shock wave.

Improvements of the damage responses and failure modes of an RC vehicle over pass bridge under contact explosion using FEM-SPH coupled computational frameworks

Winds, earthquakes, and blasts are unpredictable and most challenging dynamic loads. However, the blast is relatively new, and its protection over infrastructure is a vital concern. Conversely, bridges play a critical role in the transport system, and their loss may affect the Nation’s growth. However, the literature says that experimental and numerical simulation is an excellent option to predict the blast impacts. Most of the data from the experiments are collected by photos or videography at high temperatures. Therefore, the reliability of those data is a genuine concern, particularly for bridges. Conversely, if correctly explored, numerical simulation is an option to get into the blast field with high accuracy. A mesh-based method like Finite Element Method (FEM) is excellent for numerical simulation up to a specific temperature. Beyond that, it starts a mesh tangling. Element erosion and remeshing processes may overcome this issue if the mesh-free method simulates. Smoothed Particle Hydrodynamics (SPH) is a mesh-free particle method that can naturally handle massive deformation due to adaptive features. Finally, the current study has coupled two discretisation systems to avoid instability and increase run time. Therefore, FEM-SPH coupling has been adopted to explore the direct damage-reduction, complete damage-time response, damaged contours of the shock wave propagations, damaged contours of particle formation, the effective plastic strain (EPS) and different failure modes of the Vehicle Over Pass typed bridge without and with the protective layer of non-Explosive Reactive Armour (nERA). Finally, the improvement of the bridge is eye-catching as the nERA effectively reduces the deformation, damage, particle formation, EPS, and failure modes.

Numerical Analysis of the Possibility of High-Speed Screw Feeding of Charges for Solid-Fuel Shock Wave Generators

Numerical Analysis of the Possibility of High-Speed Screw Feeding of Charges for Solid-Fuel Shock Wave Generators

Isotropization by shock waves generation in anisotropic hydrodynamics

Anisotropic hydrodynamics (aHydro) has proven successful in modeling the evolution of quark-gluon matter created in heavy-ion collisions. The hydrodynamic description of quark-gluon plasma has also been widely used to study sound phenomena, such as shock waves. It has recently been shown that initial fluctuations in energy density and supersonic partons can generate fairly strong shock waves. However, significant anisotropic properties of the system due to the rapid longitudinal expansion of matter have not been taken into account in such studies. Moreover, the process of isotropization and its characteristic time-scales were not considered along with the question of the shock waves formation. Previous studies on shock discontinuous solutions in anisotropic hydrodynamics assumed constant anisotropy, leading to flow refraction towards the anisotropy axis and flow acceleration, characteristics of rarefaction waves, indicating limitations in this approach. This paper investigates discontinuous solutions for normal shock waves without flow refraction, introducing two compression parameters for longitudinal and transverse pressures. The resulting analytical solutions, as well as numerical computations, provide an isotropization mechanism of the system.

Collapse of microbubbles over an elastoplastic wall

The collapse of a vapour bubble over a material surface has been widely studied over the past few decades, but a comprehensive and quantitative analysis of the cavitation dynamics and its effects on solid materials at the mesoscale (nanometre up to micrometre), which would be of particular interest in applications exploiting cavitation power, is still lacking. In this work, we adopt a diffuse interface model to describe the microbubble dynamics, and a dynamic plasticity model for the solid. The former is particularly suited to studying the rich phenomenology characterising bubble collapse at the mesoscale, which comprises transitions to supercritical conditions, emission and propagation of shock waves, generation of liquid microjets and topological transitions, whereas the latter is used to characterise the permanent plastic deformation caused by the bubble collapse, and has been augmented to consider inertial effects, to assess whether or not an interaction between elastic and plastic waves may influence the resulting deformation. Results concerning the collapse of a microbubble at different liquid overpressures and initial standoff ratios are discussed, and the elastoplastic wave propagation in the solid, together with plastic deformation, is studied for different cases, depending on elastic and plastic material parameters.

Numerical Investigation of Network-Based Shock Wave Propagation of Designated Methane Explosion Source in Subsurface Mine Ventilation System Using 1D FDM Code

In coal mining operations, methane explosions constitute a severe safety risk, endangering miners’ lives and causing substantial economic losses, which, in turn, weaken the production efficiency and economic benefits of the mining industry and hinder the sustainable development of the industry. To address this challenge, this article explores the application of decoupling network-based methods in methane explosion simulation, aiming to optimize underground mine ventilation system design through scientific means and enhance safety protection for miners. We used the one-dimensional finite difference method (FDM) software Flowmaster to simulate the propagation process of shock waves from a gas explosion source in complex underground tunnel networks, covering a wide range of scenarios from laboratory-scale parallel network samples to full-scale experimental mine settings. During the simulation, we traced the pressure loss in the propagation of the shock wave in detail, taking into account the effects of pipeline friction, shock losses caused by bends and obstacles, T-joint branching connections, and cross-sectional changes. The results of these two case studies were presented, leading to the following insights: (1) geometric variations within airway networks exert a relatively minor influence on overpressure; (2) the positioning of the vent positively contributes to attenuation effects; (3) rarefaction waves propagate over greater distances than compression waves; and (4) oscillatory phenomena were detected in the conduits connecting to the surface. This research introduces a computationally efficient method for predicting methane explosions in complex underground ventilation networks, offering reasonable engineering accuracy. These research results provide valuable references for the safe design of underground mine ventilation systems, which can help to create a safer and more efficient mining environment and effectively protect the lives of miners.

Numerical study of the spontaneous ignition mechanisms of pressurized hydrogen released inside pipes with different structures

Hydrogen is considered a key clean energy carrier to achieve the global goal of carbon neutrality. But spontaneous ignition can occur when pressurized hydrogen is released into pipes, and the presence of different pipe structures will significantly affect the ignition mechanism. In this work, the effects of varied pipe structures on the shock wave propagation and spontaneous ignition characteristics are investigated by numerical simulation with the DNS-like approach, EDC combustion model, and 21-step detailed hydrogen combustion mechanism. Results show that the simulation is in well agreement with the experimental data. Five dominant spontaneous ignition mechanisms are provided depending on different pipe structures. Among all types of pipe structures investigated, contraction structures can lead to a greater increase in shock wave pressure due to more severe shock wave reflection and convergence. While enlargement structures can contribute to more mixing of hydrogen and air, causing more sufficient combustion. This study provides a comprehensive understanding and clear safety guidance to inform the practical application of hydrogen energy.