Shock Waves最新文献

Evidence suggests that low-level blast (LLB) overpressure exposure from military heavy weapons training is associated with subclinical adverse brain health and performance (H &P) outcomes. Existing DOD safety policies related to blast overpressure exposure are not specific to LLB-related brain health effects. This study sought to synthesize the available literature and analyze the relevancy of a specific blast metric to LLB exposures and the manifestation of adverse brain H &P outcomes. A literature search yielded 311 unique articles, from which 220 were identified as human studies on LLB published from 2010 to 2021. After more exhaustive exclusion criteria were applied, 14 articles met the criteria for inclusion. Findings on brain H &P changes were examined in relation to quantified LLB measurements (e.g., peak overpressure) to identify trends. Overall, the included studies suggested that alterations of reaction time, a metric for neurocognitive performance, as well as symptom reporting can occur following cumulative LLB exposures above 4 psi (27.6 kPa). Biomarkers and neurosensory changes have not demonstrated consistent associations with LLB exposures. These findings suggest that cumulative blast overpressure exposures above 4 psi (27.6 kPa) based on current measurement methodologies for body-worn sensors may be associated with adverse brain H &P outcomes. Current research efforts seek to better quantify LLB exposure, the relationships between LLB (e.g., intensity, duration, dose) and brain health, as well as to assess brain H &P domains more comprehensively. These efforts will serve to promote a better understanding of the interaction between LLB exposures and adverse brain H &P outcomes.

The neurological consequences of combat blast-induced neurotrauma (BINT) pose important clinical concerns for military service members and veterans. Previous studies have shown that low-intensity blast (LIB) results in BINT with multifaceted characteristics in mice exposed to open-field blast in prone position. Although the prone position is natural for rodents, experimental models of blast using this position do not represent common scenarios of human standing while being exposed to blast during deployment or military training. In this study, we used our previously developed BINT mouse model of open-field LIB with mice in an upright position and then used quantitative proteomics and multiple bioinformatic approaches to analyze brain tissue taken from multiple subregions during the acute post-injury phase. We identified: (1) region-specific BINT-induced proteome changes, which were significantly and differently influenced by animal positioning (upright vs. prone): the upright positioning caused more significant protein alterations in cortex and cerebellum, which were less significant in striatum as compared to prone position; (2) synapse- and mitochondrion-related damage contributed to BINT in both positions; and (3) some molecular signatures were exclusively and/or oppositely regulated in two positions. This study delineates the molecular signatures of the position-dependent blast effects, indicating the importance of brain–body position for BINT translational studies and for modeling the location and extent of position-related blast injuries.

Towards a better characterization of the increasing blast overpressure threat, person-borne sensors are being considered for large military population segments potentially subjected to explosive blast and firing of crew served weapons. Training and field data, tracked longitudinally across a soldier’s entire career, can help with the diagnosis of blast injuries and the improvement of standard operating procedures for both explosive forced entry and large weapons firing. However, a current challenge with person-born blast dosimeters resides with the position of the overpressure sensors themselves. Often, the sensors are not fully exposed to the blast locally, resulting in pressure measurements not representative of the blast conditions surrounding an individual. While fielding multiple individual and uncoupled dosimeter units around the body increases the likeliness of catching the representative blast exposure, issues arise from differences in internal clock, potential partial triggering, and the complexity of merging data from different sources. Instead, integrating multiple overpressure sensors pointing in different directions, within a single device that captures and records all data simultaneously, proves highly beneficial for data analysis and interpretation. This paper presents algorithms that combine the overpressure data collected from such multiple coupled sensors for each blast event to minimize the effect of blast directionality. In particular, an algorithm estimating the equivalent side-on blast overpressure is presented, facilitating injury estimates from existing established blast injury models adapted for the outputs from the blast dosimeters. An algorithm is also presented that estimates the orientation or provenance of an explosive blast relative to the soldier.

This note presents a vapor-based seeding apparatus, named the external alkali seeding instrument (EASI), which is designed to introduce alkali metal vapors into experimental facilities without using precursors or large auxiliary equipment. The device vaporizes small amounts of alkali metals, potassium in this work, which are then carried away by an inert gas. In a benchtop flow cell, carrier gas flow rate (6–(200~hbox {cm}^3/hbox {s})) and device temperature (150–(250,^{circ }hbox {C})) most strongly affected potassium-vapor concentrations. Higher values of either quantity lead to increased potassium-vapor concentrations. When using the EASI to seed a shock tube experiment, vapor-phase potassium was detected immediately after the incident and reflected shockwaves using a laser absorption diagnostic. Mole fraction time histories stay within a factor of 2 over the test time as compared with those from a precursor-based seeding approach, which may span multiple orders of magnitude. This suggests potassium is nearly homogeneously distributed throughout the test gas. This design can be extended to other low-vapor-pressure elements, such as other alkalis or sulfur, with minimal modifications. The EASI simplifies seeding for laboratory experiments targeting potassium and other alkali metals—enabling advances in fundamental spectroscopy, diagnostic development, and chemical kinetics.

An experimental investigation was carried out to study the fluid–structure interactions on a compliant panel subjected to an impinging shock wave and an incoming turbulent boundary layer. These experiments were aimed at understanding the time-averaged and unsteady characteristics of fluid–structure interaction at Mach 2. Two shock impingement locations on the panel (aspect ratio of 2.82), namely the central and three-fourths of the panel length, were tested. The shock boundary layer interactions on a rigid flat plate served as a baseline case. Measurements include shadowgraph and surface oil flow visualizations, panel deflections using a capacitance probe, cavity acoustics using a pressure sensor, surface pressures using discrete pressure sensors, and pressure-sensitive paints. Results show that the interaction on the compliant panel is relatively three-dimensional as compared to a rigid plate with a nominally two-dimensional interaction. Pressure fluctuations on the compliant panel are significantly higher than on the rigid plate, and the fluctuation spectra are multi-modal. Strong coupling at some frequencies was observed between the shock and the panel for both shock impingement locations. The present study suggests that for a compliant panel, the shape of pressure spectra is sensitive to the measurement location on the panel, the panel modifies the pressure distribution around the interaction, and the energy in dominant modes depends on the shock impingement location.

Far-field blast loading has been studied extensively for decades. Close-in, confined, and semi-confined detonations less so, partly because it is difficult to obtain good experimental data. The increase in computational power in recent years has made it possible to conduct studies of this kind numerically, but the results of such simulations ultimately depend on experimental validation and verification. This work thus aims at using reliable experiments to validate and verify numerical models developed to represent blast loading in general. Test rigs consisting of massive steel cylinders with pressure sensors were used to measure the pressure profiles of semi-confined detonations with different charge sizes. The experimental data set was then used to assess numerical models appropriate for simulating blast loading. In general, the numerical results were in excellent agreement with the experimental data, in both qualitative and quantitative terms. These results may in turn be used to analyse structures exposed to internal blast loads, which constitutes the next phase of this research project.

Numerical simulation results of a convecting shielded vortex interacting with a normal shock using a compact scheme in the convecting upwind and split pressure framework are presented. We explore the parameter space spanned by vortex Mach number and incident Mach number to look for combinations of the parameters which lead to vortex breakdown. The incident and vortex Mach numbers covered are on the higher side, where relatively less information is available. It is well known that for a weak shock, the vortex retains its original shape and for stronger shocks it breaks down. In-between these two extremes, there is a region where the vortex neither retains its original shape nor does it break into small pieces. We determine the vortex breakdown and transition regions that have not so far been reported in shock–vortex interaction studies. A number of cases have been studied, and a vortex breakdown criterion for the cases considered is proposed.

Variations in the experimental constraints applied within blast simulations can result in dramatically different measured biomechanical responses. Ultimately, this limits the comparison of data between research groups and leads to further inquisitions about the “correct” biomechanics experienced in blast environments. A novel bilayer surrogate brain was exposed to blast waves generated from advanced blast simulators (ABSs) where detonation source, boundary conditions, and ABS geometry were varied. The surrogate was comprised of Sylgard 527 (1:1) as a gray matter simulant and Sylgard 527 (1:1.2) as a white matter simulant. The intracranial pressure response of this surrogate brain was measured in the frontal region under primary blast loading while suspended in a polyurethane spherical shell with 5 mm thickness and filled with water to represent the cerebrospinal fluid. Outcomes of this work discuss considerations for future experimental designs and aim to address sources of variability confounding interpretation of biomechanical responses.