Explore the vast range of titles available.

The use of micro shock tubes has become common in many instruments requiring a high velocity and temperature flow field, for example in micro-propulsion systems and drug delivery devices for medical systems. A shock tube has closed ends, and the flow is generated by the rupture of a diaphragm separating a driver gas at high pressure from a driven gas at relatively low pressure. The rupture results in the movement of a shock wave and contact discontinuity into the low-pressure gas, and an expansion wave into the high pressure gas. The characteristics of the resulting unsteady flow for micro shock tubes are not well known as the physics of such tubes includes additional phenomena such as rarefaction and complex viscous effects at low Reynolds numbers. In the present study, computational fluid dynamics (CFD) calculations are made for unsteady compressible flow within a micro shock tube using the van-Leer MUSCL scheme and the two-layer k-ε turbulence model. Novel results have been obtained and discussed of the effects of using different diaphragm pressure ratios, shock tube diameters and wall boundary conditions, namely no slip and slip walls.

Using a shock wave simulator to simulate a shock wave loading environment is the most direct and effective technical means to study damage effects and protection performance. In order to ensure that the device can accurately simulate the real shock wave load environment, based on the experiment of the shock wave simulation device, SCDM and FLACS are used to establish a three-dimensional computational model of the shock wave simulation device driven by high-pressure air. The effectiveness of the computational model and the reliability of the modeling method are verified by comparing the shock wave over-pressure at different grid sizes with the measured over-pressure. This provides a theoretical basis and modeling computation method for accurately studying the propagation of shock waves in the shock wave simulation device in the future.

Firstly, the damaging effect of the internal explosion in a closed cabin by numerical simulation has been evaluated, which indicates that the pressure peak of the shock wave and the duration of positive pressure in the closed cabin has been increased at a large scale compared with the free field, and the corner-structures of the cabin have been damaged seriously under the shock wave at the same time. Then the explosion response effect of the hull superstructure which has an explosion venting hole has been analysed, and the pressure peak of the shock wave in a different location and the superstructure which has a different explosion venting hole size has been compared, which shows that the explosion venting holes have a strong impact on cabin explosion shock wave propagation, the scope and ratio of the venting explosion depend linearly on the characteristic length of explosion venting holes, and the explosion venting holes can protect the cabin corner structure within certain TNT limits. It is concluded that setting a reasonable size and proper location of the explosion venting holes can achieve the purpose of protecting the important compartments.

Wave propagation in channels with area changes is a topic of significant practical interest that involves a rich set of coupled physics. While the acoustic wave problem has been studied extensively, the shock propagation problem has received less attention. In addition to its practical significance, this problem also introduces deep fundamental issues associated with how energy in propagating large-amplitude disturbances is redistributed upon interaction with inhomogeneities. This paper presents a study of shock scattering and entropy and vorticity coupling for shock wave propagation through discrete area changes. It compares results from computational fluid dynamics to those of one-dimensional quasi-steady calculations. The solution space is naturally divided into five ‘regimes’ based upon the incident shock strength and area ratio. This paper also presents perturbation methods to quantify the dimensionless scaling of physical effects associated with wave reflection/transmission and energy transfer to other disturbances. Finally, it presents an analysis of the ‘energetics’ of the interaction, quantifying how energy that initially resides in dilatational disturbances and propagates at the shock speed is redistributed into finite-amplitude reflected and transmitted waves as well as convecting vortical and entropy disturbances.

The dynamic responses of both underground structures and their surrounding geoformations induced by tamped spherical detonation have been recognised as one of the key topics in both defence engineering and civil engineering. Proper understanding and evaluation of tamped detonation-induced particle movement, spherical stress wave propagation/attenuation, and dynamic crack propagation in geoformations require effective experimental methods and numerical tools. To capture the main characteristics of the spherical shock waves, including the wave propagation and attenuation, a systematic tamped spherical detonation test technique on PMMA has been designed in this study. A mini-explosive sphere with a diameter of 4 mm is generated to produce a small-scale explosion within the PMMA specimen. To monitor the movement of particles during explosion, an electronic measurement system consisting of embedded particle velocity sensors and high-intensity magnetic field generators, has been developed. For the modelling of tamped spherical detonation, a modified multibody failure criterion, equation of state (EOS), and Johnson–Holmquist–Beissel (JHB) model have been implemented in a four-dimensional lattice spring model, thus forming an improved JHB-4DLSM model (M-JHB-4DLSM). It is capable of reproducing the effects of large Poisson’s ratios, the strain rate and the high ratio of uniaxial compressive strength to the uniaxial tensile strength values (UCS/T). The developed M-JHB-4DLSM model has been validated through modelling the dynamic responses of both granite and PMMA. Results indicate that the dynamic process and fracturing patterns reproduced by M-JHB-4DLSM are consistent with experimental observations. M-JHB-4DLSM model is then applied to investigate the impact effects of tunnels subjected to close-in buried blasting.HighlightsA systematic experimental technique has been developed for the tamped spherical denotation test.A M-JHB-4DLSM model has been proposed for more realistic modelling of brittle materials subjected to blasting load.The proposed model has been validated through modelling the dynamic responses of both PMMA and granite.

Upon interaction with underwater shock waves, bubbles can collapse and produce high-speed liquid jets in the direction of the wave propagation. This work experimentally investigates the impact of laser-induced underwater impulsive shock waves, i.e. shock waves with a short, finite width, of variable peak pressure on bubbles of radii in the range 10–500 $\\mathrm {\\mu }$m. The high-speed visualisations provide new benchmarking of remarkable quality for the validation of numerical simulations and the derivation of scaling laws. The experimental results support scaling laws describing the collapse time and the jet speed of bubbles driven by impulsive shock waves as a function of the impulse provided by the wave. In particular, the collapse time and the jet speed are found to be, respectively, inversely and directly proportional to the time integral of the pressure waveform for bubbles with a collapse time longer than the duration of shock interaction and for shock amplitudes sufficient to trigger a nonlinear bubble collapse. These results provide a criterion for the shock parameters that delimits the jetting and non-jetting behaviour for bubbles having a shock width-to-bubble size ratio smaller than one. Jetting is, however, never observed below a peak pressure value of 14 MPa. This limit, where the pressure becomes insufficient to yield a nonlinear bubble collapse, is likely the result of the time scale of the shock wave passage over the bubble becoming very short with respect to the bubble collapse time scale, resulting in the bubble effectively feeling the shock wave as a spatially uniform change in pressure, and in an (almost) spherical bubble collapse.

We report our analysis of ionospheric disturbances from the 15 January 2022 Tonga volcano eruption, using GPS data from the International GNSS Service network and ionosonde data in the Australian sector. Wave fluctuations with amplitudes of ∼1 TECU and altitude variations of ∼100 km were observed in the GPS and ionosonde data, respectively. In near‐field region around Tonga shortly after the eruption, our analysis reveals that the ionospheric disturbances had an azimuthally anisotropic velocity profile, with a peculiar minimum in southwestward direction. Close resemblance is identified between the velocity profile of near‐field ionospheric disturbances and the Tonga tsunami, suggesting a coupling between water and atmospheric waves. In far‐field, the disturbances propagated at ∼300 m/s, circling the globe for at least three days and possibly until 21 January 2022, in agreement with several previous reports of the event. Arrival times of ionospheric disturbances observed by GPS receivers and ionosondes provide consistent picture. Plain Language Summary Massive eruption of the Hunga‐Tonga volcano on 15 January 2022 generated tsunami waves in the ocean and shock waves in the Earth's atmosphere. The shock waves from the eruption also propagated upward into space and reached the Earth's ionosphere, creating some ripples. We detected these ionospheric ripples with the help of radio frequency signals transmitted from ground stations and from GPS satellites. The scientific measurement data were recorded by ionosonde stations around Australia, and by network of GPS receiver stations that are distributed internationally. While several previous research works have examined the global nature of the Tonga disturbances, here we contrasted the disturbance profiles in both near‐field and far‐field. Far away from the Tonga volcano, the ionospheric disturbances propagated uniformly with velocity close to 300 m/s in all directions around the globe. This pattern is consistent with previous reports. Near the Tonga volcano, however, these ionospheric ripples spread out unevenly, showing complex patterns whereby the wave speed varied with direction. The uneven ripple patterns in the ionosphere around Tonga were found to be correlated with the uneven tsunami wavefront within the Tonga basin. Key Points We investigated near‐field and far‐field traveling ionospheric disturbance (TID) from the 15 January 2022 Tonga volcano eruption using GPS total electron content and ionosondes TID velocity profile in near‐field around Tonga shows directional asymmetry, likely connected to the anisotropy of tsunami waves In far‐field, TID velocity profile isotropizes in all directions, approaching 300 m/s Lamb wave speed reported previously by others

The interaction between a planar shock wave propagating in air and a polygonal bubble (composed of two triangles) containing two different gases is studied numerically. Studying the interaction between an oncoming shock wave with front- and rear-facing triangles containing light and heavy gases is of great importance in understanding the complex shock wave propagation, interaction and hydrodynamic instabilities as well as their effect on mitigating or enhancing the colliding shock/blast wave. Two different cases were studied: in the first case, the front triangle contained sulfur hexafluoride (SF 6 ) and the rear one contained helium (He); while in the second case, He is in the front and SF 6 in the rear triangle. As the speed of sound in He is significantly higher than that in SF 6 and in air, different flow fields were evolved. When SF 6 is placed in the front triangle, the shock wave transmitted through the SF 6 is reflected back from the interface separating the two gases and starts propagating downstream; over the He segment of the bubble, the incident shock wave (in the open air) is already seen over the He section and it submits compression waves into the He gas. These compression waves travel upstream and downstream; in their upstream movement they generate compression waves into the ambient air ahead of the incident shock wave. The part moving downstream will hit the interface separating SF 6 and He, resulting in a complex wave pattern. A completely different wave pattern is visible when He is placed in the front triangle. Now the fastest shock is the transmitted shock wave in the He section; it reaches the membrane separating the two gases well before the incident shock wave reaches this location. Unlike the previous case, now the resulting flow in the rear triangle of the bubble is affected not only by the incident shock wave but also by the transmitted compression waves from the helium section. Furthermore, when helium is placed in the front section of the bubble, the compression waves in the He impacts the rear triangle of the bubble (containing SF 6 ) almost like a planar shock wave. This is different from the previous case where SF 6 was in the front section; then the shock wave impacting on the rear bubble containing He had a completely different shape due to its propagation into the SF 6 bubble. This resulted in completely different peak pressures.

The Earth’s magnetosphere and its bow shock, which is formed by the interaction of the supersonic solar wind with the terrestrial magnetic field, constitute a rich natural laboratory enabling in situ investigations of universal plasma processes. Under suitable interplanetary magnetic field conditions, a foreshock with intense wave activity forms upstream of the bow shock. So-called 30 s waves, named after their typical period at Earth, are the dominant wave mode in the foreshock and play an important role in modulating the shape of the shock front and affect particle reflection at the shock. These waves are also observed inside the magnetosphere and down to the Earth’s surface, but how they are transmitted through the bow shock remains unknown. By combining state-of-the-art global numerical simulations and spacecraft observations, we demonstrate that the interaction of foreshock waves with the shock generates earthward-propagating, fast-mode waves, which reach the magnetosphere. These findings give crucial insight into the interaction of waves with collisionless shocks in general and their impact on the downstream medium.The Earth’s bow shock results from the interaction of the solar wind with the terrestrial magnetic field. With global numerical simulations and spacecraft observations, the transmission of fast magnetosonic waves through the bow shock is revealed.

On 18 November 2023, SpaceX launched the Starship, the tallest and the most powerful rocket ever built. The Super Heavy engine separated from the Starship spacecraft and exploded at 90 km of altitude, while the main core Starship continued to rise up to 149 km and exploded after ∼8 min of flight. In this work, we used data from ground‐based GNSS receivers and we analyzed total electron content (TEC) response to the Starship flight and the two explosions. For the first time, we observed large‐distance northward propagation of intensive 2,000 km V‐shaped ionospheric disturbances from the rocket trajectory. The observed perturbations, most likely, represent shock waves propagating with the cone angle of ∼14° on the North and ∼7° on the South against the flight track that corresponds to the Mach angle of the shock waves in the lower atmosphere. The Starship explosion also produced a non‐chemical depletion in the ionospheric TEC. Plain Language Summary On 18 November 2023, SpaceX launched the Starship, the tallest and the most powerful rocket ever built. About 2 min and 40 s after the liftoff, the Super Heavy engine separated from the Starship spacecraft and exploded at an altitude of 90 km. The main core Starship continued to rise to 149 km and exploded as well. The rocket launch and explosion produced an unexpected response in the ionosphere—the ionized part of the Earth's atmosphere. The Starship flew at a velocity, exceeding the local sound speed, and generated cone‐like atmospheric shock‐acoustic waves. Most unexpectedly, the observed disturbances represented long and intensive multi‐oscillation wave structures that propagated northward, which is unusual for disturbances driven by a rocket launch. The Starship explosion also generated a large‐amplitude total electron content depletion that could have been reinforced by the impact of the spacecraft's fuel exhaust in the lower atmosphere. This study appears to be the first‐time detection of a non‐chemical ionospheric hole produced by a man‐made explosion. Key Points The 18 November 2023 Starship flight and explosions generated large‐scale multi‐oscillation supersonic conic waves in the ionosphere The cone angle of the V‐shaped ionospheric disturbances corresponds to the Mach angle of shock waves propagating in the lower ionosphere The shock waves from the Starship explosion caused a depletion in total electron content (TEC)