Showing papers on "Overpressure published in 2023"

Visualising fluid migration due to hydrate dissociation: implications for submarine slides

Abstract: The impact of gas hydrate dissociation on submarine landslides has become an increasingly significant issue. However, previous models cannot interpret the newly discovered non-conformity between the slide surface and the base of the gas hydrate stability zone. Here, the authors design an experimental approach for visualising fluid migration during hydrate dissociation at atmospheric pressure. The results identify the lateral and vertical fluid migration pathways. Weak layers propagate nearly laterally beyond the hydrate zone, which lengthens the potential slide surface. Vertical pathways branch and deviate from their original paths, generating a shallower slide surface. Furthermore, the findings show that fluid overpressure under the overlying layer leads to steepening slopes. The lubrication effect and the underestimated inclination of slopes at failure may account for the low-angle failure of clay slopes. The results support a new conceptual model that reconciles the non-conformity between the slide surface and the base of the gas hydrate stability zone and offer a new perspective for the large-scale failure of low-angle submarine slopes. It will be interesting and important to confirm these implications in the future.

Damage Assessment of Roadway Wall Caused by Dynamic and Static Load Action of Gas Explosion

Abstract: In order to obtain the damage characteristics of a roadway wall caused by a gas explosion, the damage evaluation theory of a roadway wall under the dynamic and static loads of a gas explosion is analyzed in this paper. Meanwhile, an evaluation method (overpressure–impulse criterion) is selected to evaluate the damage of the roadway wall under the impact load of the gas explosion. A mathematical model and a physical analysis model of the roadway wall damage are established by LS-DYNA software. The dynamic response of the roadway wall caused by the dynamic and static loads of the gas explosion is numerically simulated. The overpressure and impulse of gas explosion propagation are measured, while the damage data of the roadway wall under different overpressure and impulse loads are obtained. The P-I curves of the roadway wall under different dynamic and static loads of gas explosion are drawn. The fitting formula of P-I curves of the roadway wall is obtained. The influence of different geostress loads (0–20 MPa) on the P-I curve is analyzed. The shape of the P-I curve is similar under different geostress conditions. The difference is mainly shown in different sizes of P0 and I0. The numerical simulation results show that the P-I curve and the effect of geostress on roadway wall damage could reflect the dynamic response of the roadway wall. The damage degree and damage range of the roadway wall increase with the increase in explosion load energy. Under the action of different geostresses, the overpressure asymptote P0 and the impulse asymptote I0 show linear changes. The above research results could provide a theoretical basis and data support for the evaluation of roadway wall damage caused by gas explosions.

Temporally and Spatially Resolved Reflected Overpressure Measurements in the Extreme Near Field

Abstract: The design of blast-resistant structures and protective systems requires a firm understanding of the loadings imparted to structures by blast waves. While empirical methods can reliably predict these loadings in the far field, there is currently a lack of understanding on the pressures experienced in the very near field, where physics-based numerical modelling and semi-empirical fast-running engineering model predictions can vary by an order of magnitude. In this paper, we present the design of an experimental facility capable of providing definitive spatially and temporally resolved reflected pressure data in the extreme near field (Z<0.5 m/kg1/3). The Mechanisms and Characterisation of Explosions (MaCE) facility is a specific near-field evolution of the existing Characterisation of Blast Loading (CoBL) facility, which uses an array of Hopkinson pressure bars embedded in a stiff target plate. Maraging steel pressure bars and specially designed strain gauges are used to increase the measurement capacity from 600 MPa to 1800 MPa, and 33 pressure bars in a radial grid are used to improve the spatial resolution from 25 mm to 12.5 mm over the 100 mm radius measurement area. In addition, the pressure bar diameter is reduced from 10 mm to 4 mm, which greatly reduces stress wave dispersion, increasing the effective bandwidth. This enables the observation of high-frequency features in the pressure measurements, which is vital for validating the near-field transient effects predicted by numerical modelling and developing effective blast mitigation methods.

Experimental Study on Pressure Wave-induced Explosion of Different Types of Deposited Coal Dust

Abstract: When the gas explosion occurs in a coal mine, the pressure wave will induce coal dust (CD) to participate in the explosion reaction, which will further expand the accident and eventually cause more serious casualties. Based on this hazard, experiments were performed on three representative types of CD with the aid of a self-built experimental pipeline for gas/CD explosion. The explosion characteristics under the condition that pressure waves entrain different CD to participate in the explosion were studied. Furthermore, the influence of volatile content in CD on the compound explosion was analyzed from a microscopic perspective. The following beneficial conclusions were obtained: The overpressure peak value and the flame propagation velocity in the compound explosion are positively correlated with the volatile content in CD. Under those three conditions, the maximum overpressure is obtained at P2 position, and obvious stratification occurs in the process of flame propagation. However, compared with the other two working conditions, the average flame propagation speed of the composite explosion system with anthracite decreased by 51.2% and 52.6%, respectively, and flame surface breaks and becomes discontinuous earlier. After the explosion, the volatile content of three kinds of CD is significantly reduced, and the volatile content of lignite, bituminous coal and anthracite is 75.6%, 75.7% and 44.7% of the industrial analysis value of raw coal, respectively. With reference to the analysis on the microscopic test results, the amount of volatile gas decomposed from volatiles determines the intensity of the homogeneous reaction in the whole combustion process, while the coke formed after the reaction determines the intensity of the non-homogeneous reaction. Therefore, the volatile content in CD is a key factor affecting CD explosion. The research results provide an important scientific and theoretical basis for the prevention, control and reduction of CD explosion disasters.

Study on flame propagation of H2/LPG premixed gas in a tube

Abstract: This work aims to is to study the flame propagation characteristics of the hydrogen/liquefied petroleum gas (LPG) premixed gas in a closed tube. With the aid of a self-developed square glass explosion tube and a high-speed camera, the characteristic parameters (i.e., flame structure, flame tip speed, maximum explosion overpressure, maximum rate of explosion pressure rise, deflagration index) were obtained and analyzed the explosion characteristics of the premixed gas. The results show that the time for the flame to reach the end of the pipe decreased, and the maximum explosion overpressure increases as the hydrogen addition ratio increases. However, the explosion overpressure and flame propagation velocity increased slowly when the hydrogen addition ratio was less than 40%, While the explosion overpressure and flame propagation velocity increased drastically in the range of hydrogen addition ratio 40–80%. Therefore, the key turning point for LPG hydrogenation is when the hydrogen volume fraction is 40%. The peak explosion flame propagation velocity and the peak explosion pressure showed the change law of increasing first and then decreasing with the equivalent ratio increasing. The Pmax and Vmax are 6.4 bar and 71.2 m/s respectively. The explosive flame structure of the premixed gas formed a "multiple tulip" structure after the typical tulip flame structure due to the influence of hydrodynamic. In addition, the propagation law of H2-LPG-Air premixed flame in the pipeline was influenced by the interaction of pressure wave and flame front velocity, and Pmax trajectory and Vmax curve showed similar oscillation law. Hence, the study provides crucial data for the prevention and control of H2-LPG-Air gas mixture combustion and explosion accidents.

Analysis of flow field in a blast simulator combined-driven by explosive charge and compressed gas

Abstract: The flow field characteristics of blast simulators with the explosive-driven method and compression-driven method have been extensively investigated; however, limited effort has been made to the flow field in blast simulators combined-driven by explosive charge and compressed gas. In this paper, the finite volume method governed by the Navier–Stokes equation based on an explosive detonation and k-omega SST turbulence equation was used to analyze the flow field characteristics of blast simulators with three kinds of drive methods, namely, explosive-driven method, compression-driven method, and combined-driven method. The results show that the numerical method could simulate the flow field characteristics of the blast simulators with the explosive-driven method and compression-driven method accurately by comparing to the experimental data. Also, the influence of air turbulence on the explosion flow field cannot be neglected in the case of long running time. It is obtained that the combined-driven method could increase the pressure peak value of shock waves and extends positive pressure duration effectively, owing to the interaction of the shock waves generated from the explosive detonation and the rarefaction wave formed by rupturing the diaphragm. The first overpressure peak value, the second overpressure peak value, and the positive pressure duration obtained by the combined-driven method of 5 kg TNT and 0.3 MPa compressed gas were 1.669 times, 2.172 times, and 2.308 times more than those obtained by the explosive-driven method of 5 kg TNT, respectively. The maximum overpressure and positive pressure duration obtained by the combined-driven method of 5 kg TNT and 0.3 MPa compressed gas were 2.56 times and 1.162 times more than those obtained by the compression-driven method of 0.3 MPa compressed gas, respectively. Moreover, various shock wave environments could be simulated by controlling the charge mass of explosive charge and the initial pressure of compressed gas.

Obstacle Impacts on Methane-Air Flame Propagation Properties in Straight Pipes

Abstract: Accidental flame initiation to propagation in pipes carrying flammable gases is a significant safety concern that can potentially result in loss of life and substantial damage to property. The understanding of flame propagation characteristics caused by methane–air mixtures within various extractive and associated process industries such as coal mining is critical in developing effective and safe fire prevention and mitigation countermeasures. The aim of this study is to investigate and visualise the fire and explosion properties of a methane–air mixture in a straight pipe with and without obstacles. The experimental setup included modular starting pipes, an array of sensors (flame, temperature, and pressure), a gas injection system, a gas analyser, data acquisition and a control system. The resulting observations indicated that the presence of obstacles within a straight pipe eventuated an increase in flame propagation speed and deflagration overpressure as well as a reduction in the elapsed time of flame propagation. The maximum flame propagation speed in the presence of an orifice with a 70% blockage ratio at multiple spots was increased around 1.7 times when compared to the pipe without obstacles for 10% methane concentration. The findings of this study will augment the body of scientific knowledge and assist extractive and associated process industries, including stakeholders in coal mining to develop better strategies for preventing or reducing the incidence of methane–air flame propagation caused by accidental fires.

Pressure Relief-Type Overpressure Distribution Prediction Model Based on Seepage and Stress Coupling

Abstract: At present, great progress has been made in the prediction of undercompaction and fluid expansion overpressure. However, in recent years, the field has frequently encountered pressure relief-type overpressure. Different from primary overpressure, such as undercompaction and fluid expansion, this type of overpressure belongs to secondary overpressure, which has a certain concealment in response to seismic velocity and logging data. Based on this, a geological analysis model of pressure relief-type overpressure was established according to the seepage and stress coupling theory. The model can realize the prediction of pressure relief range and pressure distribution, which provides a new way to predict this kind of overpressure. The influence of the laws of porosity, permeability, and geological movement on pressure relief were analyzed. The research results provide a new method for the prediction of pressure relief-type overpressure and improving the basic guarantee of safe and efficient drilling.

Flame oscillation instability of H2/CO/air at different ignition positions in an open-ended vertical narrow channel

Abstract: ABSTRACT The propagation instability of a premixed H2/CO/air mixture flame in an open-ended vertical narrow channel was investigated in this paper. The mixture was ignited at five different ignition positions: IP-50, IP-250, IP-500, IP-750, and IP-950. This paper presents a new method for flame image processing. The flame front curve is generally an exponential outflow from the ignition to the top opening at any ignition. The oscillation frequency increases with the increase of flame front curvature. The flame front curvature fluctuates with time when the oscillation propagation occurs, and the flame decelerates and inverts when the curvature is larger. The dominant frequencies are different depending on ignition position, which has a certain effect on frequency. Five different ignition positions of dominant frequency are 78.00 Hz, 125.07 Hz, 170.5 Hz, 125.1 Hz, 170.7 Hz, respectively. Interestingly, IP-500, IP-750 and IP-950 have secondary frequency values of 356.9 Hz, 357.1 Hz and 331.8 Hz, respectively. The secondary frequency is about twice the dominant frequency, and it is caused by parametric instability. Flame oscillation propagation is affected by dimensionless temperature and Lewis value. The interaction between flame and overpressure wave promotes the deformation and oscillation of the flame front. The overpressure, flame front position, flame front curvature, and flame speed coupled oscillation.

Study on Gas Explosion Propagation Law and Explosion Venting in an Excavation Roadway

Abstract: Gas explosions are the biggest threat to coal mine safety, which often result in sudden massive destruction. When a gas explosion occurs in a mine, it often causes a large number of casualties and property losses, which significantly restricts the development of the coal industry. In this study, a numerical model was established for the excavation and main roadways under the condition of a forward blasting chamber and a blasting wall, and the law of overpressure propagation and the flame temperature were studied. The results show that the overpressure curve first increases and then decreases with time, exhibiting a fluctuating state, and finally tends to stabilize. The overpressure curve with an explosion venting chamber and explosion venting wall oscillates many times; compared with the roadway overpressure reduced by 10% and explosive impulse reduced by 8.5%, the explosion venting chamber and explosion venting wall have a certain explosion venting effect. The flame temperature exhibits a gradual increase in the early stage, a sharp increase in the temperature at the measuring point, a fluctuation in the temperature curve in the later stage, and a significant decrease after the roadway turns. The explosion venting chamber and explosion venting wall with different explosion venting pressures have a slight effect on the temperature of each measuring point in the roadway after a gas explosion.

Effect of Vent Area on Dynamic Characteristics of Premixed Methane/Air Explosions in End-vented Channels with Different Length/Diameter Ratios

Abstract: Further elucidate the interaction mechanism of pressure-flame-wall in channels under the effects of length/diameter ratio (L/D) and vent area, which helps to propose more effective decompression means. Experiments of premixed methane-air explosions in end-vented channels with L/D of 10, 15 and 20 were conducted under initial conditions (301 ± 2 K and 1 atm). The results demonstrate that L/D and vent area are critical external factors causing tulip flames and distorted tulip flames. When the vent area is 60 mm × 60 mm~40 mm × 40 mm, the distorted tulip flame can be generated at L/D of 20. Notably, the critical intrinsic factor causing distorted tulip flame is the interaction of reflected pressure waves-flame. It is deduced that flames stagnate or decelerate during the initial stages of irregular flames because rarefaction waves attenuate the driving force of flames. The new overpressure peaks (Ptulip, Pdis-tulip, and Pirr-tulip) induced by tulip flames, distorted tulip flames and irregular tulip flames are identified. Moreover, the drop size and drop ratio of the maximum overpressure decrease with increasing L/D.

Numerical Study on Protective Measures for a Skid-Mounted Hydrogen Refueling Station

Abstract: Hydrogen refueling stations are one of the key infrastructure components for the hydrogen-fueled economy. Skid-mounted hydrogen refueling stations (SHRSs) can be more easily commercialized due to their smaller footprints and lower costs compared to stationary hydrogen refueling stations. The present work modeled hydrogen explosions in a skid-mounted hydrogen refueling station to predict the overpressures for hydrogen-air mixtures and investigate the protective effects for different explosion vent layouts and protective wall distances. The results show that the explosive vents with the same vent area have similar overpressure reduction effects. The layout of the explosion vent affects the flame shape. Explosion venting can effectively reduce the inside maximum overpressure by 61.8%. The protective walls can reduce the overpressures, but the protective walls should not be too close to the SHRS because high overpressures are generated inside the walls due to the confined shock waves. The protective wall with a distance of 6 m can effectively protect the surrounding people and avoid the secondary overpressure damage to the container.