Pressure Relief Process Research Articles

Electromagnetic signal analysis and recognition of coal and rock properties during the borehole pressure relief process: Simulation and experiment

Borehole pressure relief is an important measure to prevent and control rock bursts for high stress mine. However, the complex and changeable coal and rock properties cannot be effectively identified during the borehole pressure relief process, resulting in instability phenomena such as drill pipe jumping, drill sticking, and drill holding in the borehole system, which seriously affects the borehole pressure relief efficiency and operation safety. To perceive the drilling status of coal and rock in real time, this paper provides an in-depth analysis of the electromagnetic signals of coal and rock during drilling through simulations and experiments, so as to accurately identify the coal and rock properties. First, a small-size coaxially fed microstrip antenna that can be used on a specific drill pipe is designed, and some simulations are performed to analyze the propagation characteristics of electromagnetic signals under different drilling conditions. The electromagnetic signals of different coal and rock properties are significantly different in the range of 4-8 GHz, and the frequencies corresponding to the S11 extremes are 5.432 GHz, 5.436 GHz, 5.532 GHz, 5.552 GHz, 5.516 GHz, and 5.468 GHz, respectively. Then, the electromagnetic signals are mapped into time-frequency diagrams through continuous wavelet transform to provide training samples for coal and rock properties recognition model. Subsequently, the MobileNetV3-EACS model is proposed by embedding the efficient multi-channel attention mechanism and modifying the classification network structure to improve the detection accuracy and classification adaptability, achieving the effective recognition of coal and rock properties. Finally, an experimental platform of coal and rock borehole system is built and multiple sets of comparative experiments are conducted. The experimental results show that the MobileNetV3-EACS has a prediction accuracy of 99.11%, which is increased by 1.78% compared to the classical MobileNetV3, verifying the effectiveness and superiority of the proposed coal and rock properties recognition method.

An experimental study of fire development under varying ventilation conditions during the depressurization process in pressurized buildings

Hermetic pressurized buildings are a new type of building in high-altitude areas that efficiently addresses issues such as high-altitude reactions. The indoor pressure is higher than the external pressure under working conditions, and pressure relief must be carried out first during emergencies. The emergency pressure relief process during a fire may lead to complex fire behavior that is different from that in regular buildings. In this study, we focus on the impact of ventilation conditions and the status of doors in such buildings on fire evolution and smoke plume characteristics through experiments. The temperature variation in the fire room and corridor is measured under different ventilation power, ventilation time, and door opening width conditions. This shows that the width of the door has the greatest impact on fire development. A smaller gap in the door opening restricts air circulation between the interior and exterior of the room, resulting in a rapid decrease in the oxygen concentration within the fire room and a decrease in the combustion reaction rate of wood fires. The ventilation power exerts the most significant influence on the temperature variation in the corridor. These findings provide empirical data and a basis for fire science studies in high-altitude hermetic pressurized buildings and can guide existing fire protection design and management for improved safety.

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.

Dynamic pressure-induced amorphous transition and crystallization behavior of 4-methylpyridine

The phase transitions of 4-methylpyridine (4MP) were studied under static pressure and dynamic pressure by in situ Raman spectroscopy. Under static compression, 4-methylpyridine underwent three phase transitions: a liquid to crystal I transition at 0.44 GPa; followed by transformation into crystal II at 2.17 GPa and crystal III at 10.36 GPa. Under dynamic compression, 4-methylpyridine was compressed into an amorphous phase as the pressure increased from 0.36, 0.38, and 0.33 GPa to 4.42, 6.80, and 11.53 GPa within 5 ms, respectively. Through the fitting of partial Raman peak linewidth with pressure, the compression rate has a significant effect on the disorder degree of crystal structure. During the pressure relief process, the amorphous 4-methylpyridine transformed into a new crystal Ⅰ’ at 2.40 GPa, and then returned to the initial liquid state at roughly 0.58 GPa. The phase transitions of 4-methylpyridine dynamic pressure can be explained by the faster compression rate that drives systems to break chemical equilibrium and generate a new phase.

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.

Piezochromic luminescence of excimers formed by anthracene plane slip

Excimer materials are frequently applied to organic chemistry, optoelectronic devices and stimulus response. Specific research on the entire process of excimer generation in solid materials, as well as the intricate mechanism of piezochromic luminescence based on excimer, are still absent and need to be examined in-depth through comprehensive experiments. Therefore, we designed an anthracene-based molecule CZPAN, which adopts no overlap area between anthracene molecules in its crystal at ambient conditions, to investigate the piezochromic luminescence behavior and expect the anthracene group to form excimers under high-pressure stimulation. As pressure increases, CZPAN gradually changes from blue monomer luminescence to green excimer luminescence accompanied with the considerably red-shifted emission spectra, and exhibits a discontinuity of fluorescence quenching during the formation of excimers (in the pressure range of 5.3–6.6 GPa). Moreover, the pressure relief process is fully reversible. This study presents abundant piezochromic luminescence of CZPAN and proves that the formation of excimers requires a certain overlap area between molecules. Pursuing the appropriate strength of π–π interactions will thus be the focus of future research on excimer materials of high luminescence efficiency, so that excimers can be better applied in sensors and imaging devices.

Numerical Simulation Analysis of Acoustic Emission Characteristics during the Drilling Pressure Relief Process in Coal Seams under Different Influencing Factors

Numerical Simulation Analysis of Acoustic Emission Characteristics during the Drilling Pressure Relief Process in Coal Seams under Different Influencing Factors

Numerical investigation of the effect of the opening mode on the pressure relief process of engine nacelle

The pressure relief door (PRD) is a vital structure to ensure the safety and reliability of the engine. This paper established a zero-dimensional transient simulation mathematical model to study the plenum compartment pressure threshold and maximum opening angle effects on the nacelle pressure relief process under different opening modes. Then, a computational fluid dynamics model verified by experimental literature data was used to simulate the nacelle pressure relief process and to determine the influence of two different opening modes on the force and discharge characteristics of the PRD. The results of this study show that different opening modes strongly impact the nacelle pressure relief process. Reducing the nacelle compartment pressure threshold of the PRD opening can reduce the time required for the pressure relief process to reach the equilibrium stage. Reducing the maximum opening angle may increase the nacelle compartment pressure during the equilibrium stage. In addition, under the same nacelle compartment pressure thresholds and maximum opening angles, the pressure relief process under the vertical opening mode can reach a lower nacelle compartment pressure during the pressure relief equilibrium stage compared to that under the horizontal opening mode. Therefore, the vertical opening mode is better than the horizontal opening mode. This paper provides two lower calculation costs and high accuracy research models for studying the nacelle pressure relief process.

Experimental Study on Damage Fracture Law of Coal from Solid-Propellant Blasting

The low permeability of coal seams has always been the main bottleneck restricting coalbed methane drainage. In this paper, a coal seam anti-reflection technology with solid-propellant blasting was proposed, and the composition and proportion of the solid propellants were determined based on the principle of oxygen balance. The authors designed a solid-propellant blasting damage fracture experiment of simulation coal, tested the impact pressure on a blast hole wall, measured the ultrasonic wave velocity, explosive strain and crack propagation velocity, and then revealed the blasting damage fracture process and mechanism of coal based on the experimental results and damage fracture mechanics theory. The history curve of impact pressure time can be divided into three processes including the slow pressurization process, dramatic increase process, and nonlinear pressure relief process. The pressure distribution along the whole blasting hole was uneven, and the peak pressure was relatively small, but the pressure action time was long. The damage and fracture process of coal solid-propellant blasting can be divided into two stages including the rapid damage fracture development stage and the stable slow damage fracture development stage. Firstly, the explosion stress wave produced and rapidly accelerated the radial cracks extension; secondly, the cracks slowly expanded over a large area by the combined effects of the high-pressure gases, the gas, and the original rock stress.

Experimental Study on Rapid Pressure Relief in the Cargo Compartment of Civil Aircraft

The rapid pressure relief device in the cargo compartment of civil aircraft can avoid the structural damage of aircraft caused by sudden pressure relief in a pressurized compartment. Based on a typical rapid pressure relief device in the cargo hold of civil aircraft, a test bench was built to carry out experimental research on the pressure magnitude and pressure relief process of the device. To simulate the real pressure relief situation of the aircraft pressurized cabin, two experimental studies of forwarding pressure and reverse pressure were carried out, and the pressure relief process of the device was analyzed. The experimental results show that the pressure relief time of the fast pressure relief device is basically the same, and the peak pressure difference of the pressure relief device is within the specified design range of 0.82 ~ 1.62psi. It provides method support for the research and experimental design of the same type of rapid pressure relief device in the cargo hold.

Experimental Study on Rapid Pressure Relief in the Cargo Compartment of Civil Aircraft

The rapid pressure relief device in the cargo compartment of civil aircraft can avoid the structural damage of aircraft caused by sudden pressure relief in a pressurized compartment. Based on a typical rapid pressure relief device in the cargo hold of civil aircraft, a test bench was built to carry out experimental research on the pressure magnitude and pressure relief process of the device. To simulate the real pressure relief situation of the aircraft pressurized cabin, two experimental studies of forwarding pressure and reverse pressure were carried out, and the pressure relief process of the device was analyzed. The experimental results show that the pressure relief time of the fast pressure relief device is basically the same, and the peak pressure difference of the pressure relief device is within the specified design range of 0.82 ~ 1.62psi. It provides method support for the research and experimental design of the same type of rapid pressure relief device in the cargo hold.

Controllable Preparation of Porous Polypropylene Piezoelectrets Using Crystallization Self‐Reinforcement Method Induced by the Variable Thermal History

AbstractA porous linear isostatic polypropylene (iPP) piezoelectret with oriented cell structure is controllably prepared by crystallization self‐reinforcement method based on a unique variable thermal history. In this multi‐step one‐pot foaming strategy, the iPP sheet placed in a 1D confined space undergoes appropriate initial heating, quenching, reheating, and pressure relief process assisted with supercritical CO2 (scCO2). The crystallization self‐reinforcement of iPP is realized by inducing the formation of closely packed crystals, whose residual lamellae in the melt serve as the nodes to enhance the melt strength during reheating. The above closely packed lamellae are used as the heterogeneous nucleating cell sites as well as the crystal nuclei in the CO2 relief process. This makes the cells easier to deform in a 1D restricted space and form uniformly oriented cells. Furthermore, the static piezoelectric coefficient of the porous iPP piezoelectret with the optimal expansion ratio and orientation ratio of 18.8 and 6.6 is 700 pC/N, reaching 1.5 times that of commercial porous PP piezoelectret. Moreover, piezoelectric energy harvester made with porous iPP piezoelectret can light up 22 LED lights arranged in ZJU word. Therefore, the novel foaming strategy provides a new insight for uniform preparation of the polymer foams with oriented cells.

Numerical simulation study and application of coal seepage evolution law around water injection borehole in the stope “dynamic-static” pressure zone

A pressure relief anti-reflection model of a borehole along a coal seam goaf was constructed to analyze the stress-plastic spatiotemporal evolution characteristics of a borehole, and the implementation process of pressure relief anti-outbursts from the underground mine of the Huaibei Qingdong Coal Mine was used as the research background. A simulation of the mathematical relationship between the permeability of the coal seam sample and the overburden-gas pressure was performed, incorporating the dynamic balance parameters of the stress after the borehole was constructed along the coal seam; in addition, the water injection pressure relief process and the plastic deformation mechanism of the boreholes in the “dynamic-static” pressure zone were simulated. These simulations were performed to explore the evolution of stress permeability of the coal body before and after water injection. The results showed that after water injection, the stress unloading in the stress relief region was 12.8 ∼ 31.1%, and the permeability was increased by 23.5 ∼ 42.9%; the stress unloading in the stress concentration region was 26.7 ∼ 58.4%, and the permeability was increased by 263.7 ∼ 563.5%. With the application of water injection technology in the drilling zone of a bedding layer at the 726 working face of the Qingdong Coal Mine, the average cutting volume in the water injection area decreased by 17.19%, the K1 and Δh2 values decreased by 40.3% and 12.2%, respectively, and the return gas concentration decreased by 31%. Thus, pressure relief had an outstanding anti-outburst effect.

Study on pressure relief effect of upper protective coal seam mining based on distributed optical fiber sensing monitoring

On site real-time monitoring of protective layer mining is an important method to deeply study its pressure relief mechanism. It is proposed that the distributed optical fiber sensing technology (BOTDA) based on Brillouin optical time domain analysis is used to conduct mining industry tests on the deformation law and pressure relief effect of the underlying coal and rock mass during the mining of the upper protective layer. Taking the 21,104 comprehensive mechanized working face of Hulusu Coal Mine as an example, the strain transmission relationship between the coal and rock mass and the force-bearing optical fiber sensor is analyzed, and the design scheme, implantation scheme and installation process of the optical fiber sensor monitoring system are introduced. Implemented the accuracy analysis of the optical fiber sensing monitoring system and the spatial positioning of the sensors. According to the mining progress of the working face, the optical fiber sensing monitoring system regularly collects data, and by analyzing the strain distribution characteristics of the sensing optical cable and its dynamic change process, the deformation law of the underlying coal and rock mass in the mining of the upper protective layer is obtained. The monitoring results show that the underlying coal and rock mass undergoes a dynamic process of compressive strain increase, tensile strain increase and tensile strain recovery during the mining of the upper protective layer, and the scale of increase and decrease of strain of coal and rock mass at different depths are different; The intensity of coal rock deformation and pressure relief effect are characterized by the fluctuation amplitude of optical fiber strain increment. The pressure relief process can be divided into three stages: the pressure relief start stage is 40.8 m, the pressure relief active stage is 68.3 m, and the pressure relief decline stage; Finally, the strike pressure relief angle of the upper protective layer mining is 58.7°, the inclined pressure relief angle is 63.6°, the pressure relief lag distance is 14.2 m, and the maximum vertical distance of pressure relief is 28.4 m. The research shows that the application of BOTDA distributed optical fiber sensing technology in monitoring the pressure relief effect of protective layer mining can provide a reliable basis for coal mine safety mining.

Coal pillar’s breaking and fracture development mechanism and numerical simulation

This study explores the influence of a repeated mining process on an upper coal pillar in a close coal seam group. The pillar's breaking and instability processes are emphasized, and the influence of fracture development on the oxidation and spontaneous combustion of coal pillars is revealed. A numerical simulation is used to simulate the dynamic evolution characteristics of stress, displacement of the upper coal pillar, and the numerical results elucidate that the mining of the lower adjacent coal seam is a pressure relief process for the upper coal pillar. The theoretical length of the fracture along the strike of the upper coal pillar is also obtained for the upper coal pillar.

Transient simulation on pressure relief process of engine nacelle

Transient simulation on pressure relief process of engine nacelle

Pressure-Relief Impact Control of Open Circuit Hydraulic Pump-Controlled Forging Press System

Taking the open circuit hydraulic pump-controlled forging press system as the research object, according to the problems of pressure-relief impact of this system, the pressure-relief rules, mathematic models of the energy release rules, and the flow release rules were established, and the pressure-relief performance in different stages of each pressure-relief curve was analyzed. Based on the different requirements of the pressure gradient decrease, the combined pressure-relief curve (CPRC) was proposed to realize variable-pump eccentric magnitude planning. An experimental study on the pressure-relief process with CPRC was carried out. The results show that the pressure fluctuation of the pressure-relief pipe was reduced and the suppression effect of pressure-relief impact was better than that of the single regular pressure-relief curve. When the initial pressures were 10 MPa and 15 MPa, the pressure impact of the pressure-relief tube decreased by 45.45% and 37.5%, respectively, which realized the smooth pressure relief of the main cylinder.

Influence of the pressure relief door area and aspect ratio on discharge and force characteristics

Purpose The purpose of this paper is to analyze the effects of the PRD geometric parameters, including the area and aspect ratio, on the discharge and force characteristics of pressure relief process under various plenum compartment pressures and Mach numbers. Design/methodology/approach Under various plenum compartment pressures and Mach numbers, the effect of the area and aspect ratio on the discharge and force characteristics of the PRD are numerically investigated via a three-dimensional steady Reynolds-averaged Navier–Stokes equations solver based on structured grid technology. Findings When the aspect ratio remains constant, the discharge coefficient CD, thrust coefficient CT and moment coefficient CM are not affected by the PRD. When the area is constant, the aspect ratio dramatically impacts the discharge and force characteristics because the aspect ratio increases, the discharge coefficient CD of the PRD decreases, and the thrust coefficient CT and the moment coefficient CM both increase. When the aspect ratio is 2, the discharge coefficient CD decreases by 14.7 per cent, the thrust coefficient CT increases by 10-15 per cent, and the moment coefficient CM increases by 10-23 per cent compared with when the aspect ratio is 1. Practical implications This study provides detailed data and conclusions for nacelle PRD researchers and actual engineering applications. Originality/value On the basis of considering the influence of operating conditions on the discharge and force characteristics of the nacelle PRD, the impact of geometric parameters, including the area and aspect ratio on the discharge and force characteristics is comprehensively considered.

Influence of Casing Pressure Test on Seal Integrity of Cementing First Interface

Casing pressure test is an important link of the oil and gas well cementing, but excessive casing pressure test may cause stress failure or plastically deformation of the cement sheath, and generate micro-annulus on the casing-cement sheath cemented surface, then lose seal integrity of the cement sheath. According to the basic theory of elastoplastic mechanics and considering the volume invariance of plastic strain and the influence of elastic strain on volume change, the Mohr-Coulomb criterion is used to establish the casing-cement sheath-surrounding rock combination model. The paper also derived the formula for calculating the micro-annulus of the casing pressure test, and analyzed the influence of the internal pressure of the casing during the pressure test and the elastic modulus of the cement sheath on the radial contact stress of the cement sheath cementation interface after the cementing operation is completed. Results show that: (1) The generation of micro-annulus of casing pressure test is determined by the pressure increase process and the pressure relief process. The pressure increase process may lead the cement sheath into plasticity, and the radial stress at the interface turns into tensile stress and the micro-annulus could appear at the first interface by the decrease of internal pressure during pressure relief process. (2) The varying internal pressure has a great influence on the fatigue failure of the cement sheath, so the continuous multiple casing pressure test should be avoided after the cementing is completed. (3) Under the condition of maintaining the integrity of the cement sheath, increasing the tensile strength of the cement stone and reducing the elastic modulus of the cement stone can improve the pressure bearing capacity of the first interface during the casing pressure test. The model can provide a theoretical basis for the mechanical parameter design of the cement sheath, and provide guidance for on-site construction to reduce or avoid the risk of failure of the first interface seal integrity for the casing pressure test.

Coal Temperature Variation Mechanism during Gas Desorption Process

To further reveal the mechanism of coal gas migration, the reasons for coal temperature changes during the methane desorption process were analyzed from the aspect of molecular motion and the thermodynamic theory. The temperature change mechanism was investigated, and the mathematical equation was established to describe the variation of temperature change during the methane desorption and diffusion process. The established equation was applied for the calculation of temperature change for two types of coal samples, and the measured and theoretical values of temperature changes were obtained. The results show that the temperature changes in the coal gas desorption process are mainly caused by the heat adsorption. The heat adsorption phenomenon was also caused by free gas expansion during the pressure relief process. The gas diffusion and work done for gas seepage also need heat adsorption. The temperature change is positively correlated to the coal gas pressure, quantity, and limit value of gas desorption volume. Due to the poor insulation in the test system, the difference between the theoretical and the measured temperature change values increase with the adsorption equilibrium pressure. It is helpful to further reveal the mechanism of coal and gas outburst. It also has an important reference value for controlling gas dynamic disasters in coal mines.