Increase Of Initial Pressure Research Articles

Numerical Simulation of Shock Wave in Gas–Water Interaction Based on Nonlinear Shock Wave Velocity Curve

In a gas–water interaction problem, the nonlinear relationship between shock wave velocity is introduced into a Hugoniot curve, and a Mie–Grüneisen Equation of state (EOS) is established by setting the Hugoiot curve as the reference state. Unlike other simple EOS based on the thermodynamics laws of gas (such as the Tait EOS), the Mie–Grüneisen EOS uses reference states to cover an adiabatic impact relationship and considers the thermodynamics law separately. However, the expression of the EOS becomes complex, and it is not adaptive to many methods. A multicomponent Mie–Grüneisen mixture model is employed in this study to conquer the difficulty of the complex form of an EOS. In this model, some coefficients in the Mie–Grüneisen EOS are regarded as variables and solved using newly constructed equations. The performance of the Mie–Grüneisen mixture model in the gas–water problem is tested by low-compression cases and high-compression cases. According to these two tests, it is found that the numerical solutions of the shock wave under the Mie–Grüneisen EOS agrees with empirical data. When compared to other simple-form EOSs, it is seen that the Mie–Grüneisen EOS has slight advantages in the low-compression case, but it plays an important role in the high-compression case. The comparison results show that the solution of the simple-form EOS clearly disagrees with the empirical data. A further study shows that the gap between the Mie–Grüneisen EOS and other simple-form EOSs becomes larger as the initial pressure and particle velocity increase. The impact effects on the pressure, density and particle velocity are studied. Moreover, the gas–water interaction in a spherical coordinate plane and a two-dimensional coordinate is a significant part of our work.

Study on combustion and emission characteristics of hydrogen/air mixtures in a constant volume combustion bomb

Hydrogen is an environmentally-friendly fuel with the characteristics of low carbon, high calorific value, and extensive combustible range, making it an optimal alternative fuel for internal combustion engines. In this study, an experiment using a spherical constant volume combustion bomb (CVCB) was conducted to investigate the combustion and emission characteristics of hydrogen/air mixtures. The results shows that the flame propagation velocity of hydrogen laminar flow initially increases and then decreases with the excess air coefficient (λ), reaching peak at λ = 0.6, and the flame becomes unstable on the side of lean burning (λ > 1.0). Both the NOx emissions and the average temperature in the CVCB initially rise before eventually declining with the λ, the peak values for both NOx emission and mean temperature are reached at λ = 1.0. The dilution of N2 inhibits the laminar combustion and emission of hydrogen. As the dilution rate of N2 increases, little change occurs in the Markstein length, while flame propagation velocity, NOx emission, and average temperature all decrease. An increase in initial pressure hinders the development of the initial flame, while promoting the formation of cellular structure within the flame. Consequently, unstable combustion leads to a rapid increase in flame propagation speed during later stages. The average temperature inside the CVCB and the NOx emission increase by 6.6 % and 25.9 %, respectively, with the initial pressure increasing from 0.1 MPa to 0.5 MPa. On the other hand, an increase in initial temperature can facilitate flame development and results in an increased flame propagation speed. Especially, Markstein length is less sensitive to changes in initial temperature than to changes in initial pressure. The average temperature and NOx emission present a pattern of increasing first and decreasing then with the increase in initial temperature. These results have provided empirical evidence for optimizing the combustion and emission control of hydrogen engines.

Investigating the laminar burning velocity of NH3/H2/air using the constant volume method: Experimental and numerical analysis

The fundamental combustion field of ammonia-hydrogen fuel is being extensively researched. However, studies on the laminar burning velocity (LBV) under high pressure with varying hydrogen concentration conditions are relatively scarce. This study innovatively used the constant volume method (CVM) to measure LBV of ammonia-hydrogen fuels with various hydrogen concentrations XH2 = 15%–30%, initial temperatures Ti = 298–428 K, initial pressures Pi = 1–3 bar, and equivalence ratios ϕ = 0.8–1.4. The LBV of the fuel mixture up to the temperature and pressure of 540 K and 7 bar under isentropic adiabatic assumption was determined with the CVM method. The results illustrate that the enhancing effect of hydrogen concentration on LBV is suppressed under high pressures, supporting the argument that the equivalence ratio associated with the maximum LBV is solely determined by the initial fuel composition. Chemical kinetics simulations were also analyzed including flame structure, sensitivity analysis, and reaction pathways. It indicated that the elementary reaction H + O2<=>O + OH predominantly governs the LBV of ammonia-hydrogen. An increase in hydrogen concentration intensifies this process by boosting the concentration of free radical hydrogen, albeit with a concomitant rise in NO emissions due to nitrogen-containing radical oxidation. Conversely, an increase in initial pressure diminishes NO emissions by strengthening the pathway from NO to NNH. The findings of this study enhance the LBV database of ammonia-hydrogen fuel at high pressures and high temperatures, and can further act as a reference for other experiments.

Effect of hydrogen concentration, initial pressure and temperature on mechanisms of hydrogen explosion in confined spaces

Hydrogen as a renewable clean energy raises industrial safety and environmental issues. Studying the mechanism of hydrogen explosion in confined space is significant for guiding the risk assessment and efficient use of hydrogen energy. This paper used a 20 L explosion chamber to explore the effect of initial concentration changes on the hydrogen explosion and verify the model, the CHEMKIN simulation software was used to qualitatively and quantitatively evaluate the dynamic behavior characteristics of hydrogen explosion in confined space under different initial conditions, and the variation law of physical process of hydrogen explosion under different influencing factors in confined space was revealed from macro-micro perspectives. This study shows that the maximum explosion temperature and pressure under fuel-rich conditions are generally higher than those under fuel-lean conditions. The induction period of the hydrogen explosion reaction gradually shortens as the initial pressure increases, there is a negative temperature coefficient effect of ignition delay at the initial temperature of 800 K. In addition, compared with the initial pressure, higher explosion temperature and faster reactant mixing speed significantly affect the gas explosion reaction rate. The molar fractions of free radicals H, O, and OH show an inverted V-shaped relationship with the initial hydrogen concentration, and there is a hysteresis phenomenon in the final molar fraction peak of H free radicals; Sensitivity analysis indicates that free radicals are mainly responsive to the intermediate reaction R16 (forward direction) and R9 (reverse direction), thereby affecting parameters such as explosion pressure and temperature. These research findings can provide theoretical support for developing hydrogen explosion suppression technology.

Ignition and flow combustion characteristics of hydroxylammonium nitrate - based liquid propellant based on electric method

Hydroxylamine nitrate (HAN)-based liquid propellants are characterized by high energy content and low toxicity ionic monopropellants, offering great potential application prospects in the space engine. This paper proposes an experimental system for electric ignition and combustion of HAN-based liquid propellant. The energy for decomposition, current, and combustion image of HAN-based liquid propellant are measured under different initial voltage, propellant volume, and the initial pressures in Ar and air atmospheres. The results show that the energy for decomposition decreased with an increase in initial voltage, propellant volume, and initial pressure. An increase in the initial voltage accelerates the reaction speed of HAN-based liquid propellant, and the energy for decomposition is approximately 3 J. An increase in the propellant volume decreases the equivalent resistance in the circuit, increasing the current and enhancing the thermal effect of the propellant. The accumulation of decomposition products and heat under high pressure reduced the energy for decomposition; the energy for decomposition is less than 1.5 J for the pressurization condition. Compared with the Ar atmosphere, the energy for decomposition of HAN-based liquid propellant shows better stability in the air atmosphere. The flow combustion device of HAN-based liquid propellant for the flow state is designed. The HAN-based liquid propellant is successfully ignited for different initial voltages and flow rates. The research results provide a reference for the design of space engine for HAN-based liquid propellant based on the electric ignition method.

The laminar burning velocity of propyl acetate at high pressures and temperatures

Since propyl acetate has the potential to be used as a biofuel in heat engines, it is necessary to ascertain and comprehend its combustion properties. Using equivalence ratios of 0.7–1.4, the laminar burning velocity of propyl acetate was studied in the constant volume combustion vessel at the initial pressures of 1, 2, and 4 bar and initial temperatures of 390 K, 420 K, and 450 K. The constant volume method was used to determine the burning velocity via extrapolations at the initial condition. In addition, a ten-fitted empirical correlation was formulated to calculate the burning velocity for pressures and temperatures as high as 8 bar and 534 K, respectively. The extrapolated burning velocity showed good agreement with the numerical simulation burning velocity, and the correlated burning velocity agreed well with the extrapolated burning velocity. The laminar burning flux was also investigated and was ascertained that laminar burning flux increases as the initial pressure and temperature increase. The fuel mixture density significantly influences the burning flux as the initial pressure rises, whereas the laminar burning velocity has a notable impact on the burning flux as the initial temperature rises. In summary, this study advances our knowledge of propyl acetate combustion, particularly concerning its flame propagation at higher pressures and temperatures and its potential application in combustion engines, and the data are of great engineering value for developing and understanding the combustion science of propyl acetate.

Effect of low blockage ratio obstacle on explosion characteristic in methane/air mixture

Methane/air explosion is one of the common hazards in process and mining industries. In this study, the methane explosion propagation is studied, and two-dimensional configuration is considered. The gas phase equations are solved using an OpenFOAM code for compressible reacting flow, EXiFOAM. The effects of the low blockage ratio (LBR) obstacles are investigated. The results show that the flame propagation speed, flame structure, shock wave propagation, and gas flow are considerably affected by LBR obstacles. Specifically, the flame propagation speed first increases and then decreases. As the initial pressure increases, the flame propagation speed gradually increases. The maximum speed is up to 500 m/s, when the initial pressure is 1.5 MPa. If the flame propagation is prevented, resulting in the flame deformation. Moreover, the flame disruptive phenomenon is captured due to the reflected waves. In front of the obstacle, the cellular structures of the high-pressure distribution are formed. Note that the tiny cellular structures are produced in the wake of the leading shock. Furthermore, a high-speed flow region and two low-speed flow regions are produced around the LBR obstacles. It is found that as the initial pressure increases, the explosion pressure is larger, while the temperature change is not obvious. These research findings have implications for enhancing safety production in coal mines.

Study on the influence factors of rock breaking by supercritical CO2 thermal fracturing

At present, there is a growing demand for safe and low-pollution rock-breaking technology. The rock breaking technology of supercritical CO2 thermal fracturing has many advantages, such as no dust noise, no explosion, high efficiency, controllable shock wave and so on. Fully considering the combustion rate of energetic materials, heat and mass transfer, CO2 phase change and transient nonlinear flow process, a multi-field coupled numerical model of rock breaking by supercritical CO2 thermal fracturing was established based on the existing experiments. The influence factors of CO2 thermal fracturing process were studied to provide theoretical guidance for site construction parameters optimization. The numerical simulation results were in good agreement with the experimental observation results. The results showed that the maximum temperature of CO2 and the growth rate of CO2 pressure during the fracturing process would decrease accordingly with the increase of CO2 initial pressure. But the change in CO2 peak pressure wasn't significant. Appropriately increasing the heat source power could improve the heating and pressurization rate of CO2 and accelerate the damage rate of rock. The relevant results were of great importance for promoting the application of rock breaking by supercritical CO2 thermal fracturing technology.

A semi-analytical model for fractured horizontal wells production considering imbibition during shut-in periods

After hydraulic fracturing in tight oil reservoirs, part of the fracturing fluid is retained in the formation. Therefore, it’s essential to investigate the pressure and saturation distributions during and after fracturing to further understand the impact of fluid loss on productivity. Concerning the capillary pressure, fracture propagation, and fracture volume changes, a semi-analytical model was established innovatively. Comparisons between the model’s calculations and actual measurements demonstrate a high level of agreement, validating the model’s accuracy. Furthermore, the impacts of capillary pressure, shut-in time, injection rate, initial reservoir pressure, and initial water saturation on actual production performance were investigated. The results show that the effect of capillary pressure on production in the tight reservoir cannot be ignored. A reasonable shut-in operation should be carried out according to the actual situation. A smaller injection rate should be selected to achieve a larger fracture length and imbibition area. The proportion of oil produced by capillary pressure decreases with the increase of initial pressure. The initial water saturation is positively correlated with oil production and negatively correlated with water production. The imbibition effect of shut-in operation is more obvious in tight reservoirs with low initial pressure and low water saturation.

Study on Numerical Simulation of Large-Diameter Borehole Pressure Relief in Deep High-Gas Soft Coal Seams.

The deep highly gassy soft coal seam has the characteristics of high ground stress, high gas pressure, and low permeability. In the process of coal roadway excavation, there are problems such as frequent gas concentration exceeding the limit and easy induction of gas dynamic disasters. To investigate the pressure relief and disaster reduction efficiency of large-diameter boreholes in a deep high-gas soft coal seam, the 8002 high-gas working face of the Wuyang coal mine was taken as the engineering background to study the deformation law of large-diameter boreholes in deep high-gas soft coal seams. A coupled damage-stress-seepage model for pressure relief of large-diameter boreholes in gas-bearing coal seams was constructed based on the Hoek-Brown criterion, the correlation between the damage area and the gas pressure distribution in the gas-bearing coal seam after the pressure relief of boreholes of different apertures was analyzed, and the pressure relief efficiency of different technical parameters "three flower holes" in the roadway head was determined. The law of stress transfer, gas migration, and energy release in the coal seam after pressure relief of a large-diameter borehole under different initial gas pressures was revealed, and the power function equations of the damage range and borehole diameter, maximum stress at the roadway head, and driving distance after pressure relief of a gas-bearing coal seam were determined. Results showed that under the confining pressure of the 8002 working face roadway in the Wuyang coal mine, the pressure relief effect of 250 mm aperture is better, the drilling plastic zone is "butterfly" or "X″-type distribution, and the plastic zone range is positively correlated with the aperture size. Under the arrangement of "three flower holes", the plastic zone is larger and the pressure relief effect is better when the hole spacing is 1.4 m. With the increase of initial gas pressure, the vertical stress above the borehole increases and the pressure relief efficiency decreases. According to the vertical stress distribution within 200 h of borehole pressure relief, the pressure relief process is divided into a coal damage and failure stage, stress balance stage, and hole collapse stability stage. The research results provide a theoretical basis for the prevention and control of coal rock gas dynamic disasters by large-diameter drilling in a deep high-gas soft coal seam.

Enhanced forming height and accuracy of thin-walled aluminum alloy by impact pneumatic forming

To enhance the plastic deformation capacity of hard-to-deform metal materials, the utilization of impact pneumatic forming technology is proposed for shaping complex thin-walled structures within milliseconds at room temperature. In this study, an efficient numerical simulation model is established and experiments were performed to investigate the forming height, limits, and accuracy of aluminum alloy components. The experimental results show a 21.4 % increase in the ultimate forming height when employing impact pneumatic forming as compared to quasi-static pneumatic forming. Moreover, as the initial gas pressure increases, part forming height experiences an increase but the gas compression rate experiences a decline. The simulation results reveal a maximum deformation velocity of 43.19 m/s and a limited strain rate exceeding 134 s−1, affirming the connection between increased forming height and high strain rate. Furthermore, the actual contours of parts under different gas pressures align with the simulation results, validating the reliability of the simulation. It is shown that a high gas pressure of more than 20 MPa applied for a long time can improve the forming accuracy of flat bottom and wave parts. Microstructural analysis shows that dislocations in the specimens subjected to IPF conditions are better distributed, and the dimples at the fracture sites are more pronounced. This further substantiates that the IPF process improves the plastic deformation capacity of hard-to-deform materials.

Comparative analysis of permeability rebound and recovery of tectonic and intact coal: Implications for coalbed methane recovery in tectonic coal reservoirs

The permeability rebound and recovery of coal reservoirs is one of the key factors affecting the efficient recovery of coalbed methane (CBM). Most studies focus on the permeability rebound and recovery of intact coal reservoirs. Conversely, the permeability rebound characteristics of tectonic coal have only been rarely investigated. In this paper, an improved fully coupled mathematical model for methane transport of tectonic coal and intact coal seam was established. Then, the phenomenon of permeability rebound and recovery was analyzed theoretically, and the permeability rebound time, rebound value and recovery time were proposed to compare the difference in permeability evolution. In addition, the permeability rebound characteristics of tectonic and intact coal were evaluated for different geological parameters of coal reservoirs. The results indicate that the rebound time and recovery time of both intact and tectonic coal increase with the increase of initial gas pressure. As the initial permeability increases, the permeability rebound time of intact and tectonic coal show a decreasing trend. The permeability rebound time of intact coal decreases with increasing initial diffusion coefficient, while that of tectonic coal shows the opposite trend. Furthermore, the change in permeability recovery time for tectonic coal is 6.59 times larger than for intact coal, indicating that the effect of permeability rebound phenomenon is more significant during gas extraction in tectonic coal reservoirs. Finally, a conceptual model was proposed to explain the differential mechanism of permeability rebound between tectonic and intact coal, and its implications for CBM recovery in tectonic coal reservoirs was discussed. Therefore, the results presented in this paper can provide a theoretical basis for the efficient development of CBM in tectonic coal reservoirs.

Omnidirectional simulation analysis of thermo-mechanical coupling mechanism in inertia friction welding of Ni-based superalloy

The coupling between heat and pressure is the kernel of inertia friction welding (IFW) and is still not fully understood. A novel 3D fully coupled finite element model based on a plastic friction pair was developed to simulate the IFW process of a Ni-based superalloy and reveal the omnidirectional thermo-mechanical coupling mechanism of the friction interface. The numerical model successfully simulated the deceleration, deformation processes, and peak torsional moments in IFW and captured the evolution of temperature, contact pressure, and stress. The simulated results were validated through measured thermal history, optical macrography, and axial shortening. The results indicated that interfacial friction heat was the primary heat source, and plastic deformation energy only accounted for 4% of the total. The increase in initial rotational speed and friction pressure elevated the peak temperature, reaching a maximum of 1525.5 K at an initial rotational speed of 2000 r/min and friction pressure of 400 MPa. The interface heat generation could form an axial temperature gradient exceeding 320 K/mm. The radial inhomogeneities of heat generation and temperature were manifested in a concentric ring distribution with maximum heat flux and temperature ranging from 2/5 to 2/3 radius. The radial inhomogeneities were caused by increasing linear velocity along the radius and an opposite distribution of contact pressure, which could reach 1.7 times the set pressure at the center. The circumferential inhomogeneity of thermo-mechanical distribution during rotary friction welding was revealed for the first time, benefiting from the 3D model. The deflection and transformation of distribution in contact pressure and Mises stress were indicators of plastic deformation and transition of quasi-steady state welding. The critical Mises stress was 0.5 times the friction pressure in this study. The presented modeling provides a reliable insight into the thermo-mechanical coupling mechanism of IFW and lays a solid foundation for predicting the microstructures and mechanical properties of inertia friction welded joints.

Experimental investigation on detonation characteristics of boron-rich gelled propellant in static premixed combustible gases

A detonation in multiphase air-kerosene-boron mixtures is studied experimentally and the initiation and propagation characteristics of multiphase pulse detonation are emphasized. The boron-rich kerosene gelled propellants are taken as the fuel to analyze its detonation characteristics in static premixed combustible gases. The factors affecting detonation initiation including component, atomization, and ignition method of propellant are elucidated respectively. Considering atomization, evaporation and combustion, a small molecular organic compound is employed to fabricate metallized gelled propellants enriched with substantial boron particles. The dynamic atomization of gelled propellant with varying boron content is imaged by means of visual observation devices, and the ejecting parameters are optimized properly from actual initiation conditions. A flame jet by hot turbulent jet is applied to amplify the ignition energy of deflagration to detonation transition in boron-rich gelled propellant, which has not been seen ever. Results show that the ignition energy is positively correlated with initial pressure formed by combustible gas products. The multiphase detonation wave of boron-rich gelled propellant is successfully induced by premixed H2/O2 mixtures, and its detonation propagation characteristic is closely associated with the increase of initial pressure of premixed gas and mass mixing ratio of working medium. The pressure peak and propagation velocity of detonation wave show a considerable improvement with increasing initial pressure of premixed combustible gas and mass mixing ratio, and the highest values can reach up to 8.65 MPa and 2750 m/s respectively.

The effects of different equivalence ratios and initial pressures on the explosion of methane/air premixed gas in closed space

Methane/air is a widely used fuel. The effects of equivalent ratio (0.8–1.2) and initial pressure (1.0 atm–1.2 atm) on the flame propagation process and explosion overpressure of methane/air premixed gas were studied using a high-speed camera and pressure sensor in a rectangular closed container. Four flame modes in the late propagation stage are distinguished according to the different modes of secondary cup movement. The flame propagation velocity and structure evolution are analyzed by defining the characteristic times. The relationship between the flame structure evolution and the growth of flame propagation velocity and explosion overpressure is revealed. The results show that, in lean combustion, the maximum flame propagation velocity increases with initial pressure increase, and the explosion overpressure fluctuates more significantly. However, the opposite is true with fuel-rich combustion. The interaction between pressure waves and flame fronts can enhance the growth of explosion overpressure in fuel-rich combustion but can inhibit the growth in lean combustion. This work can provide more data support and reference for the application prospect and safe application of methane.

Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action

Abstract In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.

Flame evolution and pressure dynamics of premixed stoichiometric ammonia/hydrogen/air in a closed duct

Ammonia is regarded as a promising energy carrier due to its zero-carbon emissions and its suitability for long-distance, large-scale storage, and transportation. Ammonia/hydrogen mixed combustion is an important way to solve the problem of high ignition temperature and low flame speed in the process of ammonia combustion. This study systematically investigates the evolution of flames and pressure dynamics in a closed duct for ammonia/hydrogen/air mixtures with varying hydrogen blending ratio (0–100 %). Simultaneously, the study assesses the impact of flame instability and heat release on the evolution of ammonia/hydrogen/air flames and pressure dynamics. The results show that the flame tip speed and overpressure increase with the increase of hydrogen blending ratio and initial pressure, and when the hydrogen blending ratio is more than 25 %, the growth range of flame tip speed peak and overpressure peak value increases significantly. At the same time, the flame thickness decreases after hydrogen blending, the hydrodynamic instability increases, and the degree of wrinkles on the flame surface increases, which promotes flame acceleration. The Froude number increases significantly, the influence of buoyancy instability gradually weakens, and the flame core does not undergo significant displacement. In the later stage of flame propagation, both the flame front propagation velocity and pressure show significant pulsation phenomena. The heat release calculation results show that hydrogen blending significantly increases the adiabatic flame temperature. Consistent with the evolution law of overpressure, when the hydrogen blending ratio is greater than 25 %, the net heat release increases significantly. The elementary reaction with the highest heat release rate changes from the chain termination reaction R41 to the chain termination reaction R3. The research results can provide theoretical basis and experimental data support for the formulation of safety standards during the regulation and utilization of the combustion structure of ammonia/hydrogen/air mixtures.

Effects of methane addition on the laminar burning velocity and Markstein length of methanol/air premixed flame

Adding methane to methanol can solve the problem of difficult cold starts of methanol engines. Therefore, it is important to understand the combustion of methane and methanol fuel blends. Because of this, this study explores the effect of methane addition on the laminar burning velocity and Markstein length of methanol/methane premixed flames under stoichiometric conditions at the initial temperatures of 353 K, 373 K, and 393 K, initial pressures of 1 bar, 2 bar, and 4 bar, using methane addition ratios of 0%, 25%, 50%, 75%, and 100% in a constant volume combustion chamber. The results show that the laminar burning velocity decreases linearly with the increase of methane addition ratio due to the linear decrease of the Arrhenius factor. The sensitivity analysis revealed that the kinetic effect is the main reason for the inhibition of laminar burning velocity, which is insensitive to initial temperature but enhanced at a high initial pressure. The Markstein length decreases with the addition of methane and the increase of initial pressure, which is mainly caused by the high mass diffusivity of methane and the decrease of flame thickness due to the increase of initial pressure.

The effect of the initial temperature, pressure, and shape of carbon nanopores on the separation process of SiO2 molecules from water vapor by molecular dynamics simulation

Today, with the advancement of science in nanotechnology, it is possible to remove dust nanostructures from the air breathed by humans or other fluids. In the present study, the separation of SiO2 molecules from H2O vapor is studied using molecular dynamics (MD) simulation. This research studied the effect of initial temperature, nanopore geometry, and initial pressure on the separation of SiO2 molecules. The obtained results show that by increasing the temperature to 500 K, the maximum velocity (Max-Vel) of the samples reached 2.47 Å/fs. Regarding the increasing velocity of particles, more particles pass via the nanopores. Moreover, the shape of the nanopore could affect the number of passing particles. The results show that in the samples with a cylindrical nanopore, 20 and 40% of SiO2 molecules, and with the sphere cavity, about 32 and 38% of SiO2 particles passed in the simulated structure. So, it can be concluded that the performance of carbon nanosheets with a cylindrical pore and 450 K was more optimal. Also, the results show that an increase in initial pressure leads to a decrease in the passage of SiO2 particles. The results reveal that about 14 and 54% of Silica particles passed via the carbon membrane with increasing pressure. Therefore, for use in industry, in terms of separating dust particles, in addition to applying an EF, temperature, nanopore geometry, and initial pressure should be controlled.

Stability Analysis of Surrounding Rock in Deep Underground Engineering Under Fluid-solid Interaction

The geological environment of deep rock masses is extreme and complex, characterized by typical deep geological features such as high geostress, high permeation water pressure, and high geotemperature. Geological disasters like water and mud inrush, high-intensity rock bursts, and large-volume collapses occur frequently in engineering construction, presenting more complex mechanisms of disaster than shallower rock masses and severely impacting the construction and operational safety of deep underground projects. Utilizing three-dimensional numerical simulation methods, this study investigated the deformation, stress, and plastic zone characteristics of surrounding rock under multi-field coupling conditions during the construction of deep caverns, revealing the stability influencing factors of deep caverns under multi-field coupling. A funnel-shaped precipitation area forms near the excavation surface of the cavern, gradually expanding as the initial pore water pressure increases. The concentration of seepage vectors in the sidewalls and arch feet continues to increase, with local seepage rates reaching 5.1×10^-6. The cavern's crown and sidewalls are particularly sensitive to changes in pore water pressure, with the maximum tensile stress appearing 1 m and 3 m axially along the sidewalls of the cavern. The plastic zone experiences its greatest increase at a water pressure of 4 MPa.