Numerical Simulation Software Research Articles

Wireless transmission method of electromagnetic wave of cross screw signal

Abstract Based on the near-bit azimuthing gamma measuring instrument developed by Changqing Drilling Company, this paper uses comsol multiphysics(COMSOL) numerical simulation software to build the electromagnetic wave wireless transmission model of cross-bolt signal while drilling. By using finite element method and a large amount of calculation and analysis, the influence law of source distance, drill wire conductivity, borehole and mud conductivity and other parameters on the response characteristics is obtained. The simulation modeling method presented in this paper and the conclusions obtained have important guiding significance for further optimizing and upgrading the near-bit wireless short-pass device and better understanding and mastering the signal transmission law of this kind of instrument.

Experimental and numerical investigations of bending mechanical properties and fracture characteristics of cemented tailings-waste rock backfill under three-point bending

The bending mechanical properties and fracture characteristics of cemented tailings-waste rock backfill (CT-WRB) have a significant impact on efficient mine production. In this study, the effects of waste rock content (WRC) and waste rock size (WRS) on the bending mechanical properties and macroscopic failure characteristics of CT-WRB were investigated through experiments. Concurrently, PFC3D numerical simulation software was used to establish a three-point bending numerical model of CT-WRB with actual waste rock shapes to explore the crack evolution law and microscopic damage characteristics. Results showed that adding appropriate waste rock improved the initial stiffness, flexural strength, and modulus of the backfill, with optimal WRC and WRS at 40 % and 4–6 mm, respectively. Simulations indicated that under load, the displacement field of CT-WRB formed a vortex, with tensile stress in the middle and lower parts and compressive stress in an upper arch. Cracks started at the bottom and extended upward, leading to failure. Compared to OCTB (without waste rock incorporation), CT-WRB had more total cracks and tension-shear composite failure of internal particles. Waste rock altered stress distribution and crack paths, resulting in curved, bifurcated, and discontinuous main cracks. These findings provide a reference for efficiently recycling tailings, waste rock and ensuring safe mine production.

Low Stress Level and Low Stress Amplitude Fatigue Loading Simulation of Concrete Components Containing Cold Joints under Fatigue Loading

Concrete linings containing cold joint defects may crack or detach under the aerodynamic fatigue loading generated by high-speed train operation, which posing a serious threat to the normal operation of high-speed trains. However, there is currently no simulation method specifically for fatigue damage of concrete linings containing cold joints. Based on the Roe-Siegmund cycle cohesive force model, a cohesive force fatigue damage elements were developed. A large dataset was constructed through numerical simulation software to build a BP neural network for back-calculated parameter of cohesive force fatigue damage elements. By combining experimental data, fatigue damage parameters corresponding to different pouring interval cold joints were back-calculated. These back-calculated parameters were then incorporated into the numerical model to compare simulation results with experimental results to validate the applicability of cohesive force fatigue damage elements and back propagation neural networks (BP neural network). The research results show that the difference between the fatigue life and fracture process calculated by numerical simulation and experimental data is small, verifying the applicability of the method proposed in this paper. The pouring interval directly affects the initial strength of the cold joint interface and the starting conditions of fatigue damage. The possibility of fatigue damage and fracture of concrete components containing cold joints increases with the increase of pouring interval, while the variability of fatigue life decreases with the increase of pouring interval. Interface strength and thickness are the main factors affecting the possibility of fatigue damage occurrence and the variability of fatigue life. The research results can be used to analyze the damage and cracking status of concrete linings containing cold joints under aerodynamic fatigue loading.

The effect of ethane on the chain reaction characteristics of methane–air mixtures explosions

In order to study the effect of ethane on gas explosions, the macroscopic properties, thermodynamics and kinetics of gas explosions were investigated using Chemkin numerical simulation software with the GRI-Mech 3.0 mechanism. Ethane was added to methane-air mixtures at seven different concentrations, such as 0%, 0.1%, 0.3% and so on, at constant initial temperature (1200 K) and pressure(0.9atm), respectively. The results show that the maximum explosion pressure, explosive power and ·H content was all maximized when the volume fraction of ethane was 3%, which was the most effective volume addition to promote gas explosion. Ethane reduced the time to peak energy of key radical reactions from 0.049s to 0.003s and reduced the sensitivity factors for reactions such as R155 and R158. When the added ethane was 8%, R158 and R98 shifted from inhibiting methane consumption to promoting methane consumption. Calculated by Arrhenius and Lindemann formulae found that ethane can act as the third molecule in unimolecular reactions, increasing the reaction rate constant and decreasing the activation energy, so accelerating the reaction. Due to the low addition of ethane, there was still a large amount of N2 acting as the third molecule, so the decrease in activation energy was small.

Scale parameters of soft structures for surrounding rock erosion prevention in rockburst-prone roadways

Practical experience in coal mines has suggested that establishing a loose and soft structure in the surrounding rock of roadways can play a role in wave attenuation, energy absorption and erosion prevention, which is conducive to the prevention of and reduction in the severity of rockburst disasters in coal mines. The scale parameters of soft structures includes two aspects: the size and the fracture degree of soft structures. The FLAC3D numerical simulation software was used to study the failure characteristics of roadways with different impact positions (roof impact, side impact) and different impact energies (104, 105, 106, and 107 J). The stress reduction rates of soft structures with different sizes and fracture degrees were calculated. Based on the stress reduction rate of the soft structure, the energy absorption effect of the soft structure around the roadway was obtained as a logarithmic function of the soft structure size, which is a power function related to its fracture degree, and the intersection range of the two curves was fitted. The stress reduction rate was 30% when the soft structure size of the surrounding rock of the roadway was 10–15 m and the fracture degree was represented by 30–40% of the coal strength, which was the most reasonable range of scale parameters. The research conclusions provide a parametric basis for improving the theory and practice of rockburst prevention and support in coal mine roadways.

Annual cyclical variations of urban green space cold island(GSCI) effect by combining remote sensing inversion and ENVI-met simulation

Combining multiple methods offers a practical approach to studying long-term variations in the urban green space cold island(GSCI) effect. This research integrates remote sensing inversion and numerical simulation to investigate the annual cycle of the GSCI in Huachong Park, Hefei City. Initially, 59 remote sensing images from various seasons between 2010 and 2020 were retrieved using Landsat series image data and atmospheric correction methods to invert Land Surface Temperatures(LST), which preliminary identified the GSCI's annual cycle variations. Subsequently, meteorological data for Hefei from 2010 to 2020 were extracted using the Solar Terms Typical Meteorological Day(STTMD) method to obtain representative annual meteorological data. These data were then input into the ENVI-met software for numerical simulations of the study area, capturing diurnal variations of the cold island effect at 24-time points and predicting annual changes in cold island intensity. The results indicate that: (1) The GSCI exhibits an annual cycle and seasonal variations characterized by “strong in summer and weak in winter, cooler in summer and warmer in winter”; (2) A progressive relationship exists between remote sensing inversion and ENVI-met numerical simulation in studying the temporal variation of the GSCI, with the integration of these methods yielding a more comprehensive spatiotemporal analysis of the GSCI over long-term scales;(3) The STTMD method effectively simplifies representative meteorological data, progressively combining remote sensing retrievals and numerical simulations to facilitate the acquisition of comprehensive spatiotemporal variations of the green space heat effect over extended periods. These findings advance understanding of the long-term dynamics of cold island effects within urban green spaces, providing valuable insights for urban planners and environmental researchers.

Numerical study on the thermal environment of the vertical greening system based on infrared thermal imaging

ABSTRACT Since the design and construction of the building envelope affects approximately 20–60% of the energy used to heat and cool the building, it is important to improve the energy efficiency of the building envelope. This study intends to obtain an optimal thermal environment model of vertical greening through software simulation in the later stage. For some countries and cities that are still relatively backward in green development, we can provide technical support and guidance. In this study, infrared imaging equipment was used to obtain the thermal environment parameters of vertical greening, and the corresponding thermal environment characteristics were analyzed to provide support for the construction of the thermal environment model of the vertical greening system. Secondly, a new microclimate numerical simulation software ENVI-met was used to establish a vertical greening system model, quantify the changes of thermal environment parameters under different conditions, and output the numerical simulation analysis results, including temperature and thermal comfort evaluation indicators, to evaluate the role relationship and influence mechanism under different conditions. It provides theoretical support for the development, application and prediction of vertical greening. This will improve the energy efficiency of buildings.

The Effect of Distance between Jet Fans on Gas Transport, Energy Conservation, and Emission Reduction in Long Highway Tunnels

With the rapid development of the national economy, China’s transportation industry is experiencing accelerated development, and, at the same time, the number of long tunnels is constantly increasing. In order to examine the influence of jet fan spacing on gas transport law during the construction of long highway tunnels, this study used the Baima Highway Tunnel in Sichuan as an engineering prototype and established a numerical tunnel ventilation model based on Fluent numerical simulation software. The gas transport characteristics of jet fans in tunnels at different spacings (200 m, 400 m, 600 m, and 800 m) were studied. The results showed that with the increase in jet fan spacing (200 m, 400 m, 600 m, and 800 m), the gas concentration at the tunnel face showed a trend of decreasing and then increasing. Moreover, by analyzing the gas distribution cloud map and the wind flow line diagram, it was determined that the ventilation system effect was the best when the jet fan spacing was 600 m, which met the requirements of a gas concentration of less than 0.5% at the tunnel face and a minimum wind speed of 0.25 m/s. At the same time, according to the optimal spacing for the optimization of the site ventilation system, it was observed that after the ventilation was stabilized (after 600 s), the minimum value of the gas concentration in the left and right tunnel holes diminished from 0.38% to 0.31% and from 0.41% to 0.31%, with rates of reduction of 18.42% and 24.39%, respectively. This indicated that after optimizing the ventilation system at the tunnel site, the concentration significantly decreased compared with before the optimization. Moreover, when the jet fan spacing was 600 m compared with 200 m and 400 m, the annual energy savings were 1900.8 MW·h and 950.4 MW·h, respectively. The research results clarified the optimal layout parameters of jet fans in the Baima Highway Tunnel, providing a reference for the rational layout of jet fans in long-distance tunnels. In addition, the results of this study provide an important theoretical basis for the gas prevention and safe construction of long highway tunnels. Furthermore, this study contributes to research in energy conservation, emission reduction, and sustainable development of energy in the ventilation process during tunnel construction.

Simulation and Analysis of Hydrodynamic Behavior in Different Nozzles and Its Corresponding Fluidized Beds

Uniform air distribution is the basic condition for the stable operation of circulating fluidized beds and closely related to the hole layout of nozzles and the air outlet conditions. In this paper, CAD modeling software is used to establish different opening types for nozzles and the corresponding gasifier models, and Fluent simulation software for numerical simulations (k-ε model) is introduced to the hydrodynamic behavior of the upper opening, the side opening and the combined opening types of nozzles, as well as the corresponding single-nozzle fluidized bed gasifiers. The flow field distribution under the above opening modes is obtained, including the velocity distribution, static pressure distribution, and total pressure distribution, and the influence of the boundary conditions, including the inlet gas velocity and outlet pressure, on the flow field distribution inside the nozzle and in the single-nozzle fluidized bed gasifier is also investigated. The simulation results show that the suitable optimal operating conditions for the coal gasifier can be achieved with an inlet velocity of 30 m/s and an outlet pressure of 25 kPaG. Under the above conditions, the local fluidization dead zone at the elbow and top of the nozzle is narrower, the uniformity of the wind velocity can be improved, the pressure drop of the inner core tube of the nozzle is gentle, and the pressure distribution tends to be stable. Theoretically, the anti-slag performance of the nozzle is improved, which will enhance the stability and reliability of the operation of the gasification unit.

Study on the Fire Characteristics of Dual Fire Sources and the Difference in Power Temperature of Different Fire Sources in Tunnel

To investigate the combustion characteristics of multiple fire sources in the tunnel caused by ‘jumping’ discontinuous fire spread, we utilized scaled model experiments, numerical simulation software, and theoretical research. Our study focused on analyzing the influence of different fire source powers on the temperature characteristics of double fire sources in the tunnel. We examined the temperature characteristics, critical wind speed, and change rule under various wind speeds, fire source spacing, and fire source powers. Additionally, we explored the temperature characteristics, critical wind speed, and change rule of different fire source powers under varying wind speed conditions. The mathematical model for roof temperature decay and the temperature decay coefficients of dual source fires were established through the analysis of scale-down model experiments and numerical simulations. In comparison to single-source fires, the temperature variations in the tunnel of dual source fires exhibit a more intricate pattern, with higher average temperature and temperature peak values. These values are influenced by factors such as fire source spacing and power. Numerical simulation software was utilized to investigate the impact of fire source spacing at 10 m, 15 m, and 20 m, as well as the effect of varying fire source power on the temperature distribution within a tunnel under consistent fire source position and growth coefficient. The study revealed that, with consistent double fire source position and ventilation conditions in the tunnel, the upstream fire source exhibited greater power than the downstream fire source, resulting in the lowest average and peak temperatures in the tunnel. This observation could potentially enhance escape and rescue operations within the tunnel. Similarly, the lowest average and peak temperatures in the tunnel were also identified, offering potential benefits for optimizing escape and rescue strategies in tunnel scenarios.

Topographic variation and fluid flow characteristics in rough contact interface

Understanding flow characteristics of fluid near rough contact is important for the design of fluid-based lubrication and basic of tribology physics. In this study, the spreading and seepage processes of anhydrous ethanol in the interface between glass and rough PDMS are observed by a homemade optical in-situ tester. Digital image processing technology and numerical simulation software are adapted to identify and extract the topological properties of interface and thin fluid flow characteristics. Particular attention is paid to the dynamic evolution of the contact interface morphology under different stresses, the distribution of microchannels in the interface, the spreading characteristics of the fluid in contact interface, as well as the mechanical driving mechanism. Original surface morphology and the contact stress have a significant impact on the interface topography and the distribution of interfacial microchannels, which shows that the feature lengths of the microchannels, the spreading area and the spreading rate of the fluid are inversely proportional to the load. And the flow path of the fluid in the interface is mainly divided into three stages: along the wall of the island, generating liquid bridges, and moving from the tip side to the root side in the wedge-shaped channel. The main mechanical mechanism of liquid flow in the interface is the equilibrium between the capillary force that drives the liquid spreading and viscous resistance of solid wall to liquid. In addition, the phenomenon of “trapped air” occurs during the flow process due to the irregular characteristics of the microchannel. This study lays a certain theoretical foundation for the research of microscopic flow behavior of the liquid in the rough contact interface, the friction and lubrication of the mechanical system, and the sealing mechanism.

Artificial neural network for geometric design and optimization of three-stage segmented thermoelectric generators

The quest for greener power generation is a major driver for the development of thermoelectric generators. Segmented thermoelectric generators are an effective means to significantly improve the efficiency. Given the complexity of multiple geometric parameters in a three-stage segmented thermoelectric generator, the conventional practice is to use software for numerical simulation and geometric optimization before manufacturing. While this method saves time and increases production efficiency, it lacks reproducibility. However, artificial neural networks offer a solution to this problem by further reducing the computational time required. In this work, artificial neural networks are used to replace these processes by using optimization algorithms to guide the neural network in calculating the optimal thermoelectric conversion efficiency. First, a dataset of 3000 three-stage segmented thermoelectric generator configurations is generated using a COMSOL simulation model. A backpropagation neural network is then constructed and trained on this dataset, using particle swarm optimization to adjust the network weights and computational parameters. The trained neural network accurately predicted the conversion efficiency of three-stage segmented thermoelectric generators over various temperature ranges. When compared to COMSOL calculations, the values are generally within the 95% confidence interval of the backpropagation neural network predictions. Finally, genetic algorithms and artificial fish swarm algorithms are used to drive the neural network to calculate the optimal thermoelectric conversion efficiency. Compared to COMSOL, the thermoelectric conversion efficiency increased by 2.48% and 3.61%, respectively. Despite the initial dataset construction time, the artificial neural network can determine the optimal geometric structure and conversion efficiency of a three-stage segmented thermoelectric generator within 5 min. This method is expected to significantly improve the design and production efficiency of three-stage segmented thermoelectric generators.

Characteristic Study of a Typical Satellite Solar Panel under Mechanical Vibrations.

As the most common energy source of spacecraft, photovoltaic (PV) power generation has become one of the hottest research fields. During the on-orbit operation of spacecraft, the influence of various uncertain factors and the unbalanced inertial force will make the solar PV wing vibrate and degrade its performance. In this study, we investigated the influence of mechanical vibration on the output characteristics of PV array systems. Specifically, we focused on a three-segment solar panel commonly found on satellites, analyzing both its dynamic response and electrical output characteristics under mechanical vibration using numerical simulation software. The correctness of the simulation model was partly confirmed by experiments. The results showed that the maximum output power of the selected solar panel was reduced by 5.53% and its fill factor exhibited a decline from the original value of 0.8031 to 0.7587, provided that the external load applied on the panel increased to 10 N/m2, i.e., the vibration frequency and the maximal deflection angle were 0.3754 Hz and 74.9871°, respectively. These findings highlight a significant decrease in the overall energy conversion efficiency of the solar panel when operating under vibration conditions.

Non-pillar mining of upper coal seam layers with double-roadway driving using a flexible-formwork pre-cast partition wall

Abstract When mining layered coal seams, three-soft coal seams, high-gas coal seams, or hard-roof coal seams with the application of gob-side entry retention technology, various practical problems that seriously threaten construction safety arise, such as roadway deformation, shear failure of the roadway supporting body, and air leakage in the goaf. To effectively address these issues, in this work, a novel, pillar-free, coal mining technique based on a flexible-formwork pre-cast partition wall was proposed and applied to a case study: working face 2301 (upper) at Yuecheng Coal Mine, China. The principles of the technique and the characteristics of the movement in the surrounding rock were comprehensively examined. Through theoretical analysis and numerical simulation, the support parameters of the roadway and flexible-formwork pre-cast partition wall were determined and applied in the case study. From our analysis, it was demonstrated that the parameters of the flexible-formwork pre-cast partition wall and roadway support are reasonably designed, achieving effective roadway retention. Combined with a top cutting and pressure relief process, the roadway deformation can be eventually stabilised with the mining of the working face and does not affect the subsequent use of the roadway. From the acquired data, a good agreement between the field real-time measurements and the numerical simulation software measurements was found, which is helpful for the analysis of technological perspectives of the proposed framework. The introduced technology can effectively solve the technical problems existing in the traditional gob-side entry retention. It can not only realize non-pillar mining, but also double-roadway driving without coal pillars in 2301 working face can be achieved, which significantly improves the technical and economic index of the mine.

Simulation and verification of discrete element parameter calibration of pulverized coal particles

ABSTRACT To enhance the simulation efficiency of the EDEM discrete element numerical simulation software for coal powder mineral particles, experimental data on the rest angle of coal powder particles were collected as the response variable. Five parameters related to coal powder particles within the Hertz-Mindlin no-slip contact model were selected for investigation. Initially, the Plackett-Burman experiment identified three parameters: collision restitution coefficient, static friction coefficient, and rolling friction coefficient, significantly influencing the resting angle. Subsequently, the steepest ascent experiment determined the significant parameter ranges as follows: the collision restitution coefficient ranged from 0.20 to 0.40, the particle-particle static friction coefficient ranged from 0.30 to 0.50, and the particle-particle dynamic friction coefficient ranged from 0.06 to 0.10. Finally, the second-order regression model for the angle of repose and the saliency parameters was developed and optimized using the Box-Behnken experimental design. The following parameter combination was obtained: the collision recovery coefficient was 0.30, the particle-particle static friction coefficient was 0.49, and the particle-particle dynamic friction coefficient was 0.09. This study aimed to compare the angle of repose between the simulation experiment and the actual experiment. The relative error was only 1.02%, indicating that the simulation experiment achieved the optimal parameter combination.

Influence of porous media and substrate rotation on AlN growth in MNVPE reactors based on CFD simulations

AlN is an important III-V wide-bandwidth semiconductor material. Its maximum (ultra-wide) direct bandgap of up to 6.2 eV at room temperature and excellent physical properties make it have great application prospects in the fields of high-power high-frequency electronics and high-efficiency optoelectronic devices. In this paper, based on Computational Fluid Dynamics (CFD), the finite volume method was employed to investigate the process of growing AlN thin films by MNVPE using CFD simulation software for three-dimensional numerical simulation. By optimizing the chamber structure, it was devoted to improving the growth rate and uniformity of AlN thin films. Different thicknesses of porous media were placed in front of the substrate respectively, and the flow field analysis showed that the presence of eddy currents can be effectively suppressed to reduce the pre-reaction, and the best growth effect was achieved when the thickness reached 7 cm. With the increasing of porosity, more gas reached the substrate surface and improved the growth rate of AlN films. Secondly, for the 90° substrate, substrate rotation created a pumping effect and the growth rate was higher with the increase of the rotation speed. At 160 rpm, the growth rate reached 11.29 μm/h and the coefficient of variation decreased to less than 5 %.

Simulation analysis of the evolution law of creep rupture crack extension in X-fractured rock body

Creep is the macroscopic manifestation of the process of generation, expansion, and penetration of microscopic cracks in a rock body. In this study, the GDEM continuous–discontinuous numerical simulation software was used to model a rock body containing X-fractured for the purposes of exploring creep crack expansion and rupture in the rock body, analyzing the effects of various factors on X-fractured the rock body under the rule of change of the creep curve, and assessing the influences of the intersection angle of the fracture and other factors on the non-parallel fractured rock body on the creep rupture process. The results show that an X-fractured rock body exhibits a mixed tensile–shear damage mode, with tensile damage being the main type of damage. In the isotropic creep stage of a rock body with X-fractured , the steady-state creep rate initially increases and then decreases as the sub- fracture length increases, with the change of the fracture angle of the creep rate of the w-type; the sub-fracture length of h is 14 mm, the rock body is the first to enter into the accelerated creep stage, for the different fracture intersection angle of the rock body For the rock mass with different fracture angles, the time sequence of entering the accelerated creep stage is consistent with the creep rate; when the fracture intersection angle is 45°, and the sub-fracture length is 12 mm, the rock mass has the largest degree of fragmentation, which has a significant impact on the creep damage; after using a single variable processing, it is found that the fracture intersection angle, the sub-fracture length and other factors compared to the fracture intersection angle has a greater impact on the creep damage of the X-fractured rock body. This paper can provide theoretical basis and reference for the study of rock engineering creep damage law and mechanical properties of X-fractured rock body.

The impact of nozzle parameters and water injection pressure on the application effect of hydraulic punching enhanced permeability technology in high ground stress coal seam

High-stress coal seams are different from ordinary coal seams in terms of their low hardness, low permeability, and certain degree of fluidity, making them more difficult to enhance permeability. Hydraulic punching enhanced transmission technology can quickly create voids in coal seams, but existing hydraulic punching techniques are suitable for shallow coal seams, and the effect of creating voids is greatly reduced when applied to high-stress coal seams. To optimize the application effect of hydraulic punching enhanced transmission technology in high-stress coal seams, theoretical research was conducted on the parameters of hydraulic punching nozzles and injection water pressure. A simulation model was established using COMSOL numerical simulation software to optimize the nozzle parameters and explore the combined effect of nozzle parameters and injection water pressure on enhancing permeability. Field experiments were conducted in the Zhaotong Tunnel of the China high-speed railway to determine the optimal combination of nozzle parameters and injection water pressure, thereby increasing the overall permeability of the coal seam and improving gas extraction efficiency. The results indicate that: (1)Through theoretical calculations, numerical simulations, and experimental verification, it has been proven that the perforation effect of a jetting device with three the long oblique nozzle with an oblique length of 15 mm and a size of 3 mm × 6mm is the best among the comparative results under a water injection pressure of 5 MPa；(2)Compared to the perforation effect before optimization, the water consumption for perforation after optimization is reduced to 0.6 times that before optimization, and the perforation efficiency after optimization is 3.556 times that before optimization. The perforation efficiency has been effectively improved；(3)The similarity between the theoretical results, simulation results, and experimental results in this study is all above 85%. The consistency of the results provides mutual verification and has certain engineering guidance significance.

Numerical research on disastrous mechanism of seepage instability of karst collapse column considering variable mass effect

In order to reveal the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect, a variable mass fluid–solid coupling mechanical model of water inrush is established, by considering the random distribution characteristics of a collapse column. Taking Qianjin coal mine as the research background, based on the Weibull distribution theory, the heterogeneous distribution characteristics of rock mass is described, and COMSOL Multiphysics numerical simulation software is employed to simulate the seepage characteristics and inrush water changes in collapse columns under different conditions of homogeneity, water pressure, and initial porosity. The research results show that the greater the homogeneity is, the more water conduction channels are formed, and the porosity increases accordingly, when considering the influence of different homogeneity on the seepage characteristics of broken rock mass, which eventually leads to water inrush accidents and a sharp increase in water inflow. Besides, when studying the seepage evolution law of different water pressures on a broken rock mass, an elevation of water pressure dramatically increases the porosity and seepage rate of the water. Over time, the broken rock particles gradually migrate and the fine particles are transported and eroded by the water flow, resulting in changes in the seepage characteristics and the formation of potential water diversion channels. Finally, when taking into account the effect of different initial porosity on the fractured rock mass seepage characteristics, the greater the original porosity is, the higher the seepage velocity is, and the particle migration increases the permeability. This leads to a more pronounced conductive water passage formation, which reveals the disastrous mechanism of seepage instability of karst collapse column considering variable mass effect.

Research on Resistance Characteristics of Fire Zone of Mine Tunnel Fire and Construction of Calculation Model

To investigate resistance change in the fire area of a roadway caused by roadway fires, a mathematical calculation model for thermal resistance is developed. Theoretical research is conducted to analyze the factors influencing resistance change through theoretical derivation, revealing that temperature is a key factor contributing to the change in thermal resistance. By leveraging the correlation between changes in CO concentration and temperature on the downwind side of the roadway within the fire zone, researchers developed mathematical models to predict temperature increases at various points downwind of the fire source. These models were then used to determine the mathematical relationship governing the change in thermal resistance. The accuracy of the numerical simulation software was validated using Fluent numerical simulation software and scaled-down model experiments. Full-scale numerical simulation experiments were conducted to investigate the fire characteristics of roadway fires and validate the thermal resistance mathematical model. The results indicate that the thermal resistance in the numerical simulation is 7.55 Pa at 20m from the fire source and 5.54 Pa at the end of the roadway. The decrease in resistance is linear. The minimum error between the thermal resistance calculated by the mathematical model and the gradient of the pressure drop in the numerical simulation is 0.03 Pa, approximately 2.3%. Furthermore, the fitting degree of the pressure drop in each section is as high as 97.7%. The calculation model demonstrates high accuracy and offers a theoretical foundation for investigating fire resistance in tunnel fire.