Numerical simulations were performed to study the effects of pressure waves on the evolution and stability of flames propagating in tubes. The model is the fully compressible reactive Navier–Stokes ...equations coupled to a calibrated one-step chemical-diffusive model for combustion in a stoichiometric hydrogen–air mixture. The numerical solution method is high order in space and time, and adaptive mesh refinement provides adequate resolution of flames, boundary layers, acoustic waves, and all of their interactions. The influence of tube length scale and aspect ratio was examined for a range of tube sizes that produce tulip flames (TFs) and series of distorted tulip flames (DTFs). The simulations show that pressure waves and acoustic properties of the tube play an important role in the flame evolution, specifically in the formation and evolution of the series of increasingly wrinkled DTFs. A time scale and pressure wave analysis of the results, combined with a linear analysis to give the growth rate of the Rayleigh–Taylor instability (RTI), shows that the RTI is a primary cause for the initiation of DTFs.
Traditional leak location methods based on signal saltation points make it hard to locate the position of the weak leak event in the energy transportation system. To address it, a data-driven method ...based on signal attenuation mechanism is proposed in this paper. First, a wavelet adaptive threshold denoising procedure is proposed to obtain the pure signal from the collected data, and the decimal-coded genetic mechanism is designed to calculate the optimal threshold of wavelet decomposition for different layers. Second, the two-stage leak location method is proposed to calculate the position of the leak point through the combination analysis of pressure data change of both ends of the pipeline. Through the presented pressure signal attenuation mechanism, the leak location result is obtained from the data changes of both ends of the pipeline, not the time difference of arrived signal. With the above signal denoising and analysis way, the proposed method has the 1% location deviation of the leak point, which is superior to leak location methods based on signal saltation points such as wavelet transform. Finally, different experiment results are studied, and the analysis results show the effectiveness of the proposed method for the leak location problem.
•This study proposes a wavelet adaptive threshold denoising procedure.•This study proposes a two-stage leak location method.•The leak location result is obtained from the data changes of both ends of the pipeline.
We present a narrative of the eruptive events culminating in the cataclysmic January 15, 2022 eruption of Hunga Tonga-Hunga Ha'apai Volcano by synthesizing diverse preliminary seismic, ...volcanological, sound wave, and lightning data available within the first few weeks after the eruption occurred. The first hour of eruptive activity produced fast-propagating tsunami waves, long-period seismic waves, loud audible sound waves, infrasonic waves, exceptionally intense volcanic lightning and an unsteady volcanic plume that transiently reached—at 58 km—the Earth's mesosphere. Energetic seismic signals were recorded worldwide and the globally stacked seismogram showed episodic seismic events within the most intense periods of phreatoplinian activity, and they correlated well with the infrasound pressure waveform recorded in Fiji. Gravity wave signals were strong enough to be observed over the entire planet in just the first few hours, with some circling the Earth multiple times subsequently. These large-amplitude, long-wavelength atmospheric disturbances come from the Earth's atmosphere being forced by the magmatic mixture of tephra, melt and gasses emitted by the unsteady but quasi-continuous eruption from 0402±1–1800 UTC on January 15, 2022. Atmospheric forcing lasted much longer than rupturing from large earthquakes recorded on modern instruments, producing a type of shock wave that originated from the interaction between compressed air and ambient (wavy) sea surface. This scenario differs from conventional ideas of earthquake slip, landslides, or caldera collapse-generated tsunami waves because of the enormous (∼1000x) volumetric change due to the supercritical nature of volatiles associated with the hot, volatile-rich phreatoplinian plume. The time series of plume altitude can be translated to volumetric discharge and mass flow rate. For an eruption duration of ∼12 h, the eruptive volume and mass are estimated at 1.9 km3 and ∼2 900 Tg, respectively, corresponding to a VEI of 5–6 for this event. The high frequency and intensity of lightning was enhanced by the production of fine ash due to magma—seawater interaction with concomitant high charge per unit mass and the high pre-eruptive concentration of dissolved volatiles. Analysis of lightning flash frequencies provides a rapid metric for plume activity and eruption magnitude. Many aspects of this eruption await further investigation by multidisciplinary teams. It represents a unique opportunity for fundamental research regarding the complex, non-linear behavior of high energetic volcanic eruptions and attendant phenomena, with critical implications for hazard mitigation, volcano forecasting, and first-response efforts in future disasters.
•A non-spherical airgun-bubble model is established based on BIM.•A model is proposed to consider the process of air release from the airgun port.•The essential physics in the experiments are well ...reproduced by the model.•The effects of the port opening time, airgun firing depth and gravity are studied.
A thorough understanding of the dynamics of meter-sized airgun-bubbles is very crucial to seabed geophysical exploration. In this study, we use the boundary integral method to investigate the highly non-spherical airgun-bubble dynamics and its corresponding pressure wave emission. Moreover, a model is proposed to also consider the process of air release from the airgun port, which is found to be the most crucial factor to estimate the initial peak of the pressure wave. The numerical simulations show good agreement with experiments, in terms of non-spherical bubble shapes and pressure waves. Thereafter, the effects of the port opening time Topen, airgun firing depth, heat transfer, and gravity are numerically investigated. We find that a smaller Topen leads to a more violent air release that consequently causes stronger high-frequency pressure wave emissions; however, the low-frequency pressure waves are little affected. Additionally, the non-spherical bubble dynamics is highly dependent on the Froude number Fr. Starting from Fr=2, as Fr increases, the jet contains lower kinetic energy, resulting in a stronger energy focusing of the bubble collapse itself and thus a larger pressure peak during the bubble collapse phase. For Fr ≥ 7, the spherical bubble theory becomes an appropriate description of the airgun-bubble. The new findings of this study may provide a reference for practical operations and designing environmentally friendly airguns in the near future.
•Obtained the mechanism of pressure wave variation under different geothermal distributions.•Studied and summarized the influence of different geothermal distributions on the pressure wave ...peak.•Obtained the variation law of the dynamic temperature field in the tunnel.
In this paper, experiments and numerical simulations are used to study the pressure wave transient laws, propagation characteristics and dynamic temperature field changes in tunnels located near geothermal hot springs. To simulate different temperature distributions, areas of 0–80 m, 80–160 m, 160–240 m and 270–350 m are heated, and the tunnel pressure wave peak value and train surface pressure wave peak value are studied accordingly. The research shows that when the heating zone is 0–80 m, the influence on the initial pressure wave is the greatest, the change rate is 8–10 %, and the initial expansion wave change rate is 5–10 %. When the heating zone is 80–160 m, there is little change in the pressure wave peak value in the first and second stages, and the expansion wave peak value is larger than the normal temperature in the third stage. When the heating zone is 160–240 m, the change rate of the pressure wave peak is small. When the heating zone is 270–350 m, there is a negligible change in the initial compression wave and expansion wave peaks in the first and second stages, and the change rate in the third stage is 2–4 %. Moreover, the heating zone located in front of the tunnel has a greater impact on the pressure at the tip of the train's nose, and the heating zones located in the middle and end of the tunnel have little effect on the initial positive peak value of the train pressure wave but a greater effect on the negative peak value. This study explores the influence mechanism of different geothermal distributions on pressure waves, which can provide more accurate boundary data for improving passenger comfort and the train thermal structural performance in high-temperature tunnels.
Aims: In t he arterial tree, a pressure gradient of the systolic blood pressure (SBP) is observed from the center to the periphery, with the pressure being higher in the periphery because of pressure ...wave reflection. However, this gradient is attenuated, with elevation of the central SBP (cSBP), in cases with abnormal pressure wave reflection in the arterial tree. It remains unclear if increase of the cSBP might be an independent risk factor for accelerated progression of arterial stiffness. We conducted this prospective observational study using latent growth curve model (LGCM) analyses to examine if elevated cSBP might be an independent risk factor for accelerated progression of the arterial stiffness in middle-aged Japanese men. Methods: In this 9-year prospective observational study, we analyzed the data of 3862 middle-aged Japanese men (43±10years old) without cerebrocardiovascular disease at the study baseline who had undergone repeated annual measurements of the brachial-ankle pulse wave velocity (baPWV) and cSBP, as represented by the second peak of the radial pressure waveform (SBP2) in radial pressure waveform analysis. Results: During the follow-up period (6.3±2.5years), significant increases of both the baPWV and SBP2 were observed in all the subjects. Analysis using the LGCM confirmed that the SBP2, a marker of the cSBP (B=0.260, P＜0.001), was a significant determinant of the slope of the annual changes of the baPWV during the study period. Conclusions: Our fi nding may appear to confirm elevated cSBP as an independent risk factor for accelerated progression of the arterial stiffness in middle-aged Japanese men.
•We point out the inappropriate classification of combining condensation shock and collapse-induced pressure wave mechanisms in the literature.•X-ray phase contrast imaging enhances significantly the ...vapour-liquid interfaces enabling a more detailed visualization of the two-phase structures.•Three different types of mechanisms responsible for large cloud shedding are revealed using experimental measurements.
The conventional high-speed images of cavitation with a set of X-ray phase contrast images reveal the presence of three different types of mechanisms responsible for large cloud shedding: re-entrant jet mechanism, condensation shock wave mechanism, and collapse-induced pressure wave mechanism. At higher cavitation numbers, the sheet cavity is relatively short and the cavity detachment is a consequence of a re-entrant jet pinching off the cavity from its leading edge. At lower cavitation numbers, the re-entrant jet plays a smaller role in the cavitation instabilities and the primary reason for periodic cloud shedding is the condensation shock mechanism where a void fraction discontinuity propagates upstream until collapsing the entire cavity. If the amount of shed vapour cloud reaches a certain extent, the collapse will emit a pressure wave strong enough to disturb the growing cavity, and subsequently make it detached from the wall. This is the third mechanism observed in the experiments. We point out the inappropriate classification of combining condensation shock and collapse-induced pressure wave mechanisms in the literature, since we identify pronounced differences between them: (i) the pressure increase across the condensation front is very weak (a few kPa) while the amplitude of collapse-induced pressure wave can be hundreds of kPa, (ii) the travelling velocity of the collapse-induced pressure wave within the cavity is much faster than the condensation shock, and (iii) the collapse-induced pressure wave does not result in an obvious discontinuity in void fraction when it propagates through the cavity, in contrary to the condensation shock.
The transient pressure waves in the intake and exhaust systems directly affect the intake and exhaust processes of diesel engines, thus further affecting the combustion process and the performance of ...diesel engines. The variation rules of the intake and exhaust pressure waves at different engine speeds and loads in a high-pressure common-rail diesel engine were studied. Then, the effects of EGR rate and VNT nozzle opening on the intake and exhaust pressure waves were systematically studied by bench test and one-dimensional simulation analysis. The results show that at 2000 r·min-1 full-load, when the EGR rate increases from 0 to 10%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms of the intake pressure and the exhaust pressure change significantly. The fluctuation intensity of the intake pressure decreases by 58.6%, and the fluctuation intensity of the exhaust pressure increases by 77.2%. As the EGR rate increases from 10% to 30%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms are basically unchanged. The increasing magnitudes of the intake and exhaust pressure fluctuation intensities are 16.6% and 20.5%, respectively. As the VNT nozzle opening increases, the average intake pressure and the average exhaust pressure both decrease. The corresponding phases of the intake pressure wave crest and trough are delayed. The fluctuation waveforms of the intake and exhaust pressure are basically unchanged, and the fluctuation intensities do not change significantly.
The development and evolution of tulip and distorted tulip flames in closed channels were simulated by solving the fully compressible reactive Navier–Stokes equations using a high-order numerical ...method and a single-step Arrhenius model for the reactions and energy release in a stoichiometric mixture of hydrogen and air. Important features of the simulations include (1) the development and propagation of acoustic waves and their effects on flame evolution, (2) the formation and collapse of flame cusps, both at the flame front and near the sidewalls, and the effects of cusp collapse on flame propagation, and (3) the appearance of adverse pressure gradients at the onset of the tulip or a distorted tulip flame, which result in reverse flow in the unburned gas. The simulations highlight the coupling between pressure waves, adverse pressure gradients, boundary layers, and the propagating flame front. Whereas the formation of the tulip flame can be attributed to several effects (such as pressure waves, vortex motion and Landau–Darrieus instabilities), the onset of the distorted tulip flame is strongly influenced by the Rayleigh–Taylor instability.
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