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2025,
45(11):
111001.
doi: 10.11883/bzycj-2024-0284
Abstract:
Study on gas deflagration-to-detonation transition (DDT) is of great significance for the research and development of industrial explosion prevention and detonation propulsion technology. Staggered array of obstacles is a typical obstacle layout that may be involved in the gas ignition and explosion scenario. Its existence usually significantly promotes the occurrence of DDT. In view of the lack of understanding of DDT in staggered array of obstacles, high-precision algorithm and dynamic adaptive grid were applied to solve the two-dimensional, fully compressible reactivity Navier-Stokes equations coupled with a calibrated chemical-diffusive model. Numerical investigation on the initiation process of DDT of premixed hydrogen and air in staggered array of square obstacles under different obstacle spacings was carried out. The results showed that decreasing obstacle spacing is beneficial to increase flame surface area in the early stage of flame acceleration and enhance compression of unburned gas by shock wave in the later stage, thus shortening DDT run-up time and distance. However, when the obstacle spacing is reduced to a threshold value, stuttering detonation occurs and the DDT run-up distance increases. The occurrence of DDT is mainly caused by the interaction between the flame and the shock wave reflected from the front wall of obstacle. The detonation partially decouples when it diffracts around an obstacle. Detonation re-initiation may be triggered when the decoupled detonation collides with a wall or with the shock wave or failure detonation wave from the other side of the obstacle. If the obstacle spacing is too small, the shock wave intensity decays significantly during detonation decoupling. This can easily lead to detonation failure. In addition, shock waves can be reflected off the staggered array of square obstacles in the vertical and parallel directions to the flame propagation direction, which help shock waves to act on the flame and unburned gas mixture. Therefore, DDT is more likely to be initiated in the staggered array of square obstacles than that of circular obstacles.
Study on gas deflagration-to-detonation transition (DDT) is of great significance for the research and development of industrial explosion prevention and detonation propulsion technology. Staggered array of obstacles is a typical obstacle layout that may be involved in the gas ignition and explosion scenario. Its existence usually significantly promotes the occurrence of DDT. In view of the lack of understanding of DDT in staggered array of obstacles, high-precision algorithm and dynamic adaptive grid were applied to solve the two-dimensional, fully compressible reactivity Navier-Stokes equations coupled with a calibrated chemical-diffusive model. Numerical investigation on the initiation process of DDT of premixed hydrogen and air in staggered array of square obstacles under different obstacle spacings was carried out. The results showed that decreasing obstacle spacing is beneficial to increase flame surface area in the early stage of flame acceleration and enhance compression of unburned gas by shock wave in the later stage, thus shortening DDT run-up time and distance. However, when the obstacle spacing is reduced to a threshold value, stuttering detonation occurs and the DDT run-up distance increases. The occurrence of DDT is mainly caused by the interaction between the flame and the shock wave reflected from the front wall of obstacle. The detonation partially decouples when it diffracts around an obstacle. Detonation re-initiation may be triggered when the decoupled detonation collides with a wall or with the shock wave or failure detonation wave from the other side of the obstacle. If the obstacle spacing is too small, the shock wave intensity decays significantly during detonation decoupling. This can easily lead to detonation failure. In addition, shock waves can be reflected off the staggered array of square obstacles in the vertical and parallel directions to the flame propagation direction, which help shock waves to act on the flame and unburned gas mixture. Therefore, DDT is more likely to be initiated in the staggered array of square obstacles than that of circular obstacles.
2025,
45(11):
111401.
doi: 10.11883/bzycj-2024-0452
Abstract:
The leakage of combustible gas could lead to serious explosion accidents, which could cause great damage to people’s lives and property. Explosion suppression technology can effectively reduce the consequences of the explosion accidents, which is an important part of combustible gas explosion safety protection technology. As the core component of explosion suppression device, the performance of the explosion suppressant can directly affect the reliability of explosion suppression system. The research results in the field of explosion suppression at home and abroad are focused on, and the explosion suppression powder and its inhibition mechanism are systematically summarized and analyzed. Based on the different compositions, the explosion suppressing powder is divided into one-component and compound materials. According to the difference of the suppressing mechanism, the one-component suppressing powder is divided into active powder and inert powder. Due to the synergetic effects of different substances, the development of the compound material is the research hotspot. In the literature review part, this paper follows the structure “General introduction of powder materials—Related experimental and theoretical research—Suppression mechanism summary”. The first part provides the general introduction of the material, including the origin, structure and property. The second part offers the summary of the related research result about the material. The third part focuses on the physical and chemical suppression mechanism of different material, which contributes to the deeper understanding of the suppression effect. Finally, the existing problems of the research at present is summarized and the development of the future research work is discussed. In addition, this article proposes to standardize the testing process, emphasizes the use of numerical simulation to guide the suppressing of material synthesis and reduce the blindness of research. The aim of this review is to provide scientific understanding and technical support for the development of high-efficiency explosion suppression technology.
The leakage of combustible gas could lead to serious explosion accidents, which could cause great damage to people’s lives and property. Explosion suppression technology can effectively reduce the consequences of the explosion accidents, which is an important part of combustible gas explosion safety protection technology. As the core component of explosion suppression device, the performance of the explosion suppressant can directly affect the reliability of explosion suppression system. The research results in the field of explosion suppression at home and abroad are focused on, and the explosion suppression powder and its inhibition mechanism are systematically summarized and analyzed. Based on the different compositions, the explosion suppressing powder is divided into one-component and compound materials. According to the difference of the suppressing mechanism, the one-component suppressing powder is divided into active powder and inert powder. Due to the synergetic effects of different substances, the development of the compound material is the research hotspot. In the literature review part, this paper follows the structure “General introduction of powder materials—Related experimental and theoretical research—Suppression mechanism summary”. The first part provides the general introduction of the material, including the origin, structure and property. The second part offers the summary of the related research result about the material. The third part focuses on the physical and chemical suppression mechanism of different material, which contributes to the deeper understanding of the suppression effect. Finally, the existing problems of the research at present is summarized and the development of the future research work is discussed. In addition, this article proposes to standardize the testing process, emphasizes the use of numerical simulation to guide the suppressing of material synthesis and reduce the blindness of research. The aim of this review is to provide scientific understanding and technical support for the development of high-efficiency explosion suppression technology.
2025,
45(11):
111402.
doi: 10.11883/bzycj-2024-0493
Abstract:
In order to ensure the safe transportation and storage of highly flammable and combustible gases, it is essential to implement effective prevention and control measures. Explosion venting is an effective way to prevent and control its explosion hazards. In order to improve the efficiency and safety of explosion venting means and to promote the further study of secondary explosion in the external flow field of explosion venting, the research status of combustible gas explosion and explosion venting at home and abroad is analyzed, and meanwhile, the theory and achievements of combustible gas explosion venting in recent 20 years are summarized. Existing researches have shown that the explosion characteristics of combustible gases has been studied systematically, providing underpinning data for the study of combustible gas venting characteristics. A comprehensive examination of the explosion parameters and flame development alterations was performed in the internal and external flow fields resulting from deflagration. The hazard of deflagration was found to be exacerbated by the coupling between pressure waves and flame waves in the internal and external flow fields. The effectiveness of deflagration was evaluated based on the results of the study. It is difficult to define the initiation of the secondary explosion because the secondary explosion in the vent outflow field is limited by the poorly recognized evolutionary mechanism of blast-flame coupling. A preliminary study of the effect of the secondary explosion on the variation of the deflagration parameters has been carried out. In the explosion venting research, it is still necessary to narrow the span of influencing factors in the experimental aspect and improve the explosion venting equipment. In the numerical simulation research, it is necessary to carry out the study of complex models, the prediction of explosion venting hazards and the evaluation of the effect of explosion venting, which still need a lot of data and good models. Accordingly, the safe transportation and storage of flammable gases can be realized and the applications of flammable gases can be broadened.
In order to ensure the safe transportation and storage of highly flammable and combustible gases, it is essential to implement effective prevention and control measures. Explosion venting is an effective way to prevent and control its explosion hazards. In order to improve the efficiency and safety of explosion venting means and to promote the further study of secondary explosion in the external flow field of explosion venting, the research status of combustible gas explosion and explosion venting at home and abroad is analyzed, and meanwhile, the theory and achievements of combustible gas explosion venting in recent 20 years are summarized. Existing researches have shown that the explosion characteristics of combustible gases has been studied systematically, providing underpinning data for the study of combustible gas venting characteristics. A comprehensive examination of the explosion parameters and flame development alterations was performed in the internal and external flow fields resulting from deflagration. The hazard of deflagration was found to be exacerbated by the coupling between pressure waves and flame waves in the internal and external flow fields. The effectiveness of deflagration was evaluated based on the results of the study. It is difficult to define the initiation of the secondary explosion because the secondary explosion in the vent outflow field is limited by the poorly recognized evolutionary mechanism of blast-flame coupling. A preliminary study of the effect of the secondary explosion on the variation of the deflagration parameters has been carried out. In the explosion venting research, it is still necessary to narrow the span of influencing factors in the experimental aspect and improve the explosion venting equipment. In the numerical simulation research, it is necessary to carry out the study of complex models, the prediction of explosion venting hazards and the evaluation of the effect of explosion venting, which still need a lot of data and good models. Accordingly, the safe transportation and storage of flammable gases can be realized and the applications of flammable gases can be broadened.
2025,
45(11):
111403.
doi: 10.11883/bzycj-2025-0128
Abstract:
Understanding the generation, transformation, and dissipation mechanisms of energy in high-pressure tanks during fire scenarios is of critical significance for the consequence assessment of explosion accidents. This study investigates the differences in properties between high-pressure hydrogen storage tanks and nitrogen tanks under fire conditions through comparative experiments. Fire tests were conducted using 6.8L-30MPa type Ⅲ tanks. The results indicate that fire exposure can significantly impair the pressure-bearing capacity of the tanks. Specifically, the critical bursting pressure decreased from 125.1 MPa at room temperature to 46.8 MPa under fire conditions, representing a reduction of 62.6%. The explosion dynamics of hydrogen tanks were characterized by typical physical-chemical composite features. A fireball with a diameter of 9 m was formed during the explosion. The peak shockwave pressure measured at a distance of 2 m reached 882.47 kPa, with a positive pressure duration of 168.11 ms. In contrast, nitrogen tanks experienced only physical explosions, with a peak shockwave pressure of 59.42 kPa and a positive pressure duration of merely 2.17 ms. This study analyzed the energy conversion pathways during explosions of high-compressed gas tanks (H2 and N2) in open environments. A novel method for assessing the blast power of hydrogen storage cylinder explosions in unconfined spaces was developed. Initially, the physical explosion energy was calculated based on fundamental parameters such as critical burst pressure, nominal volume, and initial filling pressure of the high-pressure tanks. The applicability of five mechanical energy calculation models was compared. Subsequently, the mass of hydrogen was determined using the actual gas equation, and the total chemical explosion energy was derived by integrating the heat of combustion of hydrogen. Finally, considering the contributions of mechanical and chemical energy to the shock wave intensity, the total explosion energy was converted into shock wave energy using an open space energy correction factor. Quantitative analysis and error verification were conducted in conjunction with measured data. The findings of this research provide essential support for enhancing risk assessment of explosion accidents involving high-pressure hydrogen storage devices.
Understanding the generation, transformation, and dissipation mechanisms of energy in high-pressure tanks during fire scenarios is of critical significance for the consequence assessment of explosion accidents. This study investigates the differences in properties between high-pressure hydrogen storage tanks and nitrogen tanks under fire conditions through comparative experiments. Fire tests were conducted using 6.8L-30MPa type Ⅲ tanks. The results indicate that fire exposure can significantly impair the pressure-bearing capacity of the tanks. Specifically, the critical bursting pressure decreased from 125.1 MPa at room temperature to 46.8 MPa under fire conditions, representing a reduction of 62.6%. The explosion dynamics of hydrogen tanks were characterized by typical physical-chemical composite features. A fireball with a diameter of 9 m was formed during the explosion. The peak shockwave pressure measured at a distance of 2 m reached 882.47 kPa, with a positive pressure duration of 168.11 ms. In contrast, nitrogen tanks experienced only physical explosions, with a peak shockwave pressure of 59.42 kPa and a positive pressure duration of merely 2.17 ms. This study analyzed the energy conversion pathways during explosions of high-compressed gas tanks (H2 and N2) in open environments. A novel method for assessing the blast power of hydrogen storage cylinder explosions in unconfined spaces was developed. Initially, the physical explosion energy was calculated based on fundamental parameters such as critical burst pressure, nominal volume, and initial filling pressure of the high-pressure tanks. The applicability of five mechanical energy calculation models was compared. Subsequently, the mass of hydrogen was determined using the actual gas equation, and the total chemical explosion energy was derived by integrating the heat of combustion of hydrogen. Finally, considering the contributions of mechanical and chemical energy to the shock wave intensity, the total explosion energy was converted into shock wave energy using an open space energy correction factor. Quantitative analysis and error verification were conducted in conjunction with measured data. The findings of this research provide essential support for enhancing risk assessment of explosion accidents involving high-pressure hydrogen storage devices.
2025,
45(11):
111404.
doi: 10.11883/bzycj-2024-0282
Abstract:
Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is suspectible to leakage and explosion accidents. The study used a 20-L spherical device to investigate the effects of hydrogen doping ratio and CO2 addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyze the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the pressure parameters of hydrogen-doped natural gas explosion and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, while both the rapid burn time and sustained burn time decrease progressively. The maximum rise rate of explosion pressure and flame propagation speed gradually increase when the hydrogen doping ratio is lower than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum rise rate of explosion pressure and flame propagation speed rise rapidly. The addition of CO2 has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is weak. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase. Meanwhile the concentration of active free radicals and the product formation rate increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO2 can reduce the laminar burning velocity, adiabatic flame temperature, active free radical concentration and product formation raten of the mixed gas, but adding CO2 does not change the reaction path of methane.Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is prone to leakage and explosion accidents. The study used a 20L spherical device to investigate the effects of hydrogen blending ratio and CO2 addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyse the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the hydrogen-doped natural gas explosion pressure parameters and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, the rapid burn time and sustained burn time are gradually decreasing. The maximum explosion pressure rise rate and flame propagation speed gradually increase when the hydrogen doping ratio is less than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum explosion pressure rise rate and flame propagation speed rise rapidly. The addition of CO2 has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is poor. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase, the mole fraction of active free radicals and the rate of product increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO2 can reduce the laminar burning velocity, adiabatic flame temperature, active free radical mole fraction and rate of production of the mixed gas, but adding CO2 does not change the reaction path of methane.
Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is suspectible to leakage and explosion accidents. The study used a 20-L spherical device to investigate the effects of hydrogen doping ratio and CO2 addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyze the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the pressure parameters of hydrogen-doped natural gas explosion and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, while both the rapid burn time and sustained burn time decrease progressively. The maximum rise rate of explosion pressure and flame propagation speed gradually increase when the hydrogen doping ratio is lower than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum rise rate of explosion pressure and flame propagation speed rise rapidly. The addition of CO2 has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is weak. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase. Meanwhile the concentration of active free radicals and the product formation rate increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO2 can reduce the laminar burning velocity, adiabatic flame temperature, active free radical concentration and product formation raten of the mixed gas, but adding CO2 does not change the reaction path of methane.Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is prone to leakage and explosion accidents. The study used a 20L spherical device to investigate the effects of hydrogen blending ratio and CO2 addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyse the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the hydrogen-doped natural gas explosion pressure parameters and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, the rapid burn time and sustained burn time are gradually decreasing. The maximum explosion pressure rise rate and flame propagation speed gradually increase when the hydrogen doping ratio is less than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum explosion pressure rise rate and flame propagation speed rise rapidly. The addition of CO2 has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is poor. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase, the mole fraction of active free radicals and the rate of product increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO2 can reduce the laminar burning velocity, adiabatic flame temperature, active free radical mole fraction and rate of production of the mixed gas, but adding CO2 does not change the reaction path of methane.
2025,
45(11):
111405.
doi: 10.11883/bzycj-2024-0434
Abstract:
Polypropylene (PP) is widely utilized in industrial production, yet PP dust generated during its production and transportation can form explosive dust clouds, leading to severe dust explosion accidents that threaten personnel and equipment safety. To address this issue, a novel explosion suppressant, NiP@Fe-SBA-15, was synthesized to inhibit the propagation of PP dust combustion flames. The synthesis involved modifying SBA-15 mesoporous silica with Fe ions and subsequently loading NiP, resulting in a composite powder with uniformly dispersed active components and a well-preserved mesoporous structure. Characterization via SEM-Mapping and N2 adsorption-desorption experiments revealed that NiP@Fe-SBA-15 maintains a high specific surface area, exhibits a regulated pore structure, and shows no significant particle agglomeration. The Hartman tube explosive testing system was employed to evaluate the effect of NiP@Fe-SBA-15 on PP dust deflagration. Results indicated that as the NiP@Fe-SBA-15 additive increased, the flame propagation speed, brightness, and flame length of PP deflagration decreased significantly, with flame propagation almost completely inhibited by a suppressant dosage with the mass fraction of 70 %. The dual explosion suppression mechanism of NiP@Fe-SBA-15 was analyzed. Physically, NiP@Fe-SBA-15 occupies reaction space, reducing oxygen and combustible volatile concentrations, while the SBA-15 molecular sieve, exposed by thermal decomposition of the suppressant, absorbs heat and forms a physical barrier, thereby reducing combustion intensity. Chemically, NiP decomposition releases Ni· and P· radicals that consume key free radicals (H·, O·, OH·) in combustion reactions, interrupting explosion chain reactions. Meanwhile, Fe-based species rapidly oxidize to Fe3O4, reducing oxygen availability and further weakening combustion intensity. In summary, NiP@Fe-SBA-15 was proven to be an effective explosion suppressant for PP dust explosions, reducing combustion intensity through combined physicochemical synergies. This research provides a new approach to enhancing polypropylene industry safety. Future work will focus on optimizing the industrial application of NiP@Fe-SBA-15 explosion suppressants while addressing cost, environmental sustainability, and stability issues to further advance dust explosion prevention technology.
Polypropylene (PP) is widely utilized in industrial production, yet PP dust generated during its production and transportation can form explosive dust clouds, leading to severe dust explosion accidents that threaten personnel and equipment safety. To address this issue, a novel explosion suppressant, NiP@Fe-SBA-15, was synthesized to inhibit the propagation of PP dust combustion flames. The synthesis involved modifying SBA-15 mesoporous silica with Fe ions and subsequently loading NiP, resulting in a composite powder with uniformly dispersed active components and a well-preserved mesoporous structure. Characterization via SEM-Mapping and N2 adsorption-desorption experiments revealed that NiP@Fe-SBA-15 maintains a high specific surface area, exhibits a regulated pore structure, and shows no significant particle agglomeration. The Hartman tube explosive testing system was employed to evaluate the effect of NiP@Fe-SBA-15 on PP dust deflagration. Results indicated that as the NiP@Fe-SBA-15 additive increased, the flame propagation speed, brightness, and flame length of PP deflagration decreased significantly, with flame propagation almost completely inhibited by a suppressant dosage with the mass fraction of 70 %. The dual explosion suppression mechanism of NiP@Fe-SBA-15 was analyzed. Physically, NiP@Fe-SBA-15 occupies reaction space, reducing oxygen and combustible volatile concentrations, while the SBA-15 molecular sieve, exposed by thermal decomposition of the suppressant, absorbs heat and forms a physical barrier, thereby reducing combustion intensity. Chemically, NiP decomposition releases Ni· and P· radicals that consume key free radicals (H·, O·, OH·) in combustion reactions, interrupting explosion chain reactions. Meanwhile, Fe-based species rapidly oxidize to Fe3O4, reducing oxygen availability and further weakening combustion intensity. In summary, NiP@Fe-SBA-15 was proven to be an effective explosion suppressant for PP dust explosions, reducing combustion intensity through combined physicochemical synergies. This research provides a new approach to enhancing polypropylene industry safety. Future work will focus on optimizing the industrial application of NiP@Fe-SBA-15 explosion suppressants while addressing cost, environmental sustainability, and stability issues to further advance dust explosion prevention technology.
2025,
45(11):
111406.
doi: 10.11883/bzycj-2024-0359
Abstract:
Oxy-fuel combustion is one of the effective means to reduce greenhouse gases. To grasp the combustion characteristics of the clean fuel acetylene in O2/CO2 atmosphere and to investigate the effect of different CO2 volume fraction on the lower flammable limit of acetylene, the lower flammable limit of acetylene was experimentally measured in a 5 L cylindrical explosive reaction device. With the increase of CO2 volume fraction from 14% to 85%, the experimental value of the lower flammable limit of acetylene increased from 2.64% to 3.93%, which was linearly increased in a small range. Compared with hydrocarbon fuels such as ethylene, ethane, and propylene, the lower flammability limit of alkanes, olefins, alkynes decrease sequentially, indicating that alkynes have a larger combustion range and a higher hazard factor. Based on the calculation model of limiting laminar burning velocity method, a prediction model applicable to the lower flammability limit of acetylene was established. Through the verification of experimental data, the average absolute error of this prediction model using the USC Ⅱ combustion reaction mechanism is at 0.52%, and the model is accurate and reliable. To explain the reason for the existence of the lower flammability limit from the perspective of the competition between the temperature rise of the heat generation from fuel consumption and the temperature drop of the heat dissipation from the expansion of the fuel body, this study examines the thermodynamic, chemical, and transport effects of CO2 on the lower flammability limit. The combustion reaction mechanism of USC Ⅱ is modified to incorporate the virtual substances FCO2, TCO2, and MCO2, and comparing the flammability limits of the three virtual substances as well as those of the five atmospheres of N2 and CO2. The thermodynamic, chemical and transport effects of CO2 on the lower flammability limit were discussed. The results show that the average proportion of thermodynamic effect is 64%, chemical effect is 35% and transportation effect is 1%.
Oxy-fuel combustion is one of the effective means to reduce greenhouse gases. To grasp the combustion characteristics of the clean fuel acetylene in O2/CO2 atmosphere and to investigate the effect of different CO2 volume fraction on the lower flammable limit of acetylene, the lower flammable limit of acetylene was experimentally measured in a 5 L cylindrical explosive reaction device. With the increase of CO2 volume fraction from 14% to 85%, the experimental value of the lower flammable limit of acetylene increased from 2.64% to 3.93%, which was linearly increased in a small range. Compared with hydrocarbon fuels such as ethylene, ethane, and propylene, the lower flammability limit of alkanes, olefins, alkynes decrease sequentially, indicating that alkynes have a larger combustion range and a higher hazard factor. Based on the calculation model of limiting laminar burning velocity method, a prediction model applicable to the lower flammability limit of acetylene was established. Through the verification of experimental data, the average absolute error of this prediction model using the USC Ⅱ combustion reaction mechanism is at 0.52%, and the model is accurate and reliable. To explain the reason for the existence of the lower flammability limit from the perspective of the competition between the temperature rise of the heat generation from fuel consumption and the temperature drop of the heat dissipation from the expansion of the fuel body, this study examines the thermodynamic, chemical, and transport effects of CO2 on the lower flammability limit. The combustion reaction mechanism of USC Ⅱ is modified to incorporate the virtual substances FCO2, TCO2, and MCO2, and comparing the flammability limits of the three virtual substances as well as those of the five atmospheres of N2 and CO2. The thermodynamic, chemical and transport effects of CO2 on the lower flammability limit were discussed. The results show that the average proportion of thermodynamic effect is 64%, chemical effect is 35% and transportation effect is 1%.
2025,
45(11):
111407.
doi: 10.11883/bzycj-2025-0048
Abstract:
Coal-to-hydrogen is an effective solution for the low-carbon transformation of coal energy. However, transporting hydrogen via the natural gas pipeline network poses significant explosion safety challenges. To address these concerns, the effect of non-premixed CO2 injection on the explosion characteristics of hydrogen-doped natural gas was investigated. An experimental explosion platform was independently designed and constructed to actively release CO2 into the hydrogen-doped methane explosion via a high-pressure gas injection device. The CO2 injection was initiated prior to ignition, creating a non-premixed turbulent atmosphere. The volume of CO2 injection was controlled by injection pressure (0, 0.5, 0.75, and 1.00 MPa) and injection time (0, 60, 120, and 180 ms). The dynamics of explosion flame propagation and pressure behavior under non-premixed CO2 injection were analyzed. Results showed that injection pressure and injection time significantly influence the premixed explosion process. The injection of non-premixed CO2 into the premixed explosion induces turbulence, causing flame wrinkling. Structural changes in wrinkled flames increase the flame surface area, leading to accelerate flame propagation and enhance explosion intensity. For a given injected time (e.g., 0 or 120 ms), increasing the injection pressure introduces more CO2, which enhances localized turbulence and disturbance in the flame, leading to further flame acceleration and more severe explosion consequences. As the injection time increases, the maximum explosion pressure of different injection pressures increases and then decreases. CO2 injection in the explosion plays a competitive relationship between turbulence promotion and dilution effect, with a critical injection time. Excessive CO2 injection can enhance its dilution effect, weakening the CO2 injection on the explosion of turbulence perturbation ability, which reduces the explosion intensity. Moreover, a higher injection pressures correspond to shorter injection time. Meanwhile, the maximum explosion pressure at larger injection pressures is more sensitive to changes in injection time. Injection pressure and injection time are the key parameters governing the impact of CO2 injection on the explosion hazard of hydrogen-doped natural gas. The findings provide fundamental guidelines for the safety prevention and control strategy of hydrogen transportation in the natural gas pipeline network.
Coal-to-hydrogen is an effective solution for the low-carbon transformation of coal energy. However, transporting hydrogen via the natural gas pipeline network poses significant explosion safety challenges. To address these concerns, the effect of non-premixed CO2 injection on the explosion characteristics of hydrogen-doped natural gas was investigated. An experimental explosion platform was independently designed and constructed to actively release CO2 into the hydrogen-doped methane explosion via a high-pressure gas injection device. The CO2 injection was initiated prior to ignition, creating a non-premixed turbulent atmosphere. The volume of CO2 injection was controlled by injection pressure (0, 0.5, 0.75, and 1.00 MPa) and injection time (0, 60, 120, and 180 ms). The dynamics of explosion flame propagation and pressure behavior under non-premixed CO2 injection were analyzed. Results showed that injection pressure and injection time significantly influence the premixed explosion process. The injection of non-premixed CO2 into the premixed explosion induces turbulence, causing flame wrinkling. Structural changes in wrinkled flames increase the flame surface area, leading to accelerate flame propagation and enhance explosion intensity. For a given injected time (e.g., 0 or 120 ms), increasing the injection pressure introduces more CO2, which enhances localized turbulence and disturbance in the flame, leading to further flame acceleration and more severe explosion consequences. As the injection time increases, the maximum explosion pressure of different injection pressures increases and then decreases. CO2 injection in the explosion plays a competitive relationship between turbulence promotion and dilution effect, with a critical injection time. Excessive CO2 injection can enhance its dilution effect, weakening the CO2 injection on the explosion of turbulence perturbation ability, which reduces the explosion intensity. Moreover, a higher injection pressures correspond to shorter injection time. Meanwhile, the maximum explosion pressure at larger injection pressures is more sensitive to changes in injection time. Injection pressure and injection time are the key parameters governing the impact of CO2 injection on the explosion hazard of hydrogen-doped natural gas. The findings provide fundamental guidelines for the safety prevention and control strategy of hydrogen transportation in the natural gas pipeline network.
2025,
45(11):
112301.
doi: 10.11883/bzycj-2024-0269
Abstract:
Modeling powder is used to simulate the highly fragmented state of pressed explosives resulting from collisions, and the gap extrusion ignition behavior of PBX modeling powder is studied. Experiments were designed based on the way of projectile impact method. To ensure that no flow space exists except the designed gap, the surface of the sample was covered with cushion and coated with grease for sealing. The movement and reaction of molding powder squeezing into the gap were recorded by high-speed photography. By changing the ratio of gap area to sample cross-sectional area, the influence of compaction on ignition was studied. The results show that in the absence of grease seal, PBX molding powder undergoes particle crushing and compaction, and then the compacted molding powder is extruded from the clearance near the cushion, and ignition occurs in the extrusion process. The ignition position is at the interface between explosive and cushion. In the case of grease seal, PBX molding powder does not ignite for a period of time after compaction. When the indenter moves halfway, a wedge-shaped slip zone is formed, and a slip-dead zone interface could be seen in high-speed camera photos. Then the deformation mode evolves from single-wedge slip zone to double-wedge slip zone, and the shear effect of slip-dead zone interface does not cause ignition. At the later stage of loading, the indenter travels close to the gap surface, and the wedge-shaped slip zone disappears. Before and after the collision between the indenter and the gap, the explosive ignites once in each instance. Compaction effect has an important influence on ignition behavior. After compaction, the threshold value of ignition speed is obviously reduced, with the impact speed required to cause ignition being merely 4.5 m/s.
Modeling powder is used to simulate the highly fragmented state of pressed explosives resulting from collisions, and the gap extrusion ignition behavior of PBX modeling powder is studied. Experiments were designed based on the way of projectile impact method. To ensure that no flow space exists except the designed gap, the surface of the sample was covered with cushion and coated with grease for sealing. The movement and reaction of molding powder squeezing into the gap were recorded by high-speed photography. By changing the ratio of gap area to sample cross-sectional area, the influence of compaction on ignition was studied. The results show that in the absence of grease seal, PBX molding powder undergoes particle crushing and compaction, and then the compacted molding powder is extruded from the clearance near the cushion, and ignition occurs in the extrusion process. The ignition position is at the interface between explosive and cushion. In the case of grease seal, PBX molding powder does not ignite for a period of time after compaction. When the indenter moves halfway, a wedge-shaped slip zone is formed, and a slip-dead zone interface could be seen in high-speed camera photos. Then the deformation mode evolves from single-wedge slip zone to double-wedge slip zone, and the shear effect of slip-dead zone interface does not cause ignition. At the later stage of loading, the indenter travels close to the gap surface, and the wedge-shaped slip zone disappears. Before and after the collision between the indenter and the gap, the explosive ignites once in each instance. Compaction effect has an important influence on ignition behavior. After compaction, the threshold value of ignition speed is obviously reduced, with the impact speed required to cause ignition being merely 4.5 m/s.
2025,
45(11):
112901.
doi: 10.11883/bzycj-2024-0245
Abstract:
The defective cracks were prefabricated on the wall of the notch holes by using polymethyl methacrylate (PMMA) material, which were parallel or vertical to the notch, and the distance from the defective cracks to the hole center was 2, 3, and 4 mm. The influence of notch hole wall defects on the crack propagation of notch blasting was investigated by using a digital dynamic caustic experimental system with numerical simulation. At the same time, triacetone triperoxide (TATP) explosives were employed as a charge, which served to mitigate the effect of gun smoke on the dynamic caustic experimental system and to improve the experimental design. The results demonstrate that the reflection of the stress wave at parallel defects results in a downward shift in the direction of crack initiation at the notch, but the refraction of the stress wave at vertical defects has no effect on the direction of crack initiation. The presence of wall defects in the hole impedes the impact of stress waves and blast gases on the cracks at the notch, resulting in a reduction in the length, expansion rate, and strength factor values of the cracks, and the degree of inhibition is contingent upon the distance of the defects from the centre of the borehole. As the distance between the parallel defects and the centre of the borehole increases, the inhibition effect of the parallel defects on both sides of the notch cracks gradually decreases. The inhibition effect of vertical defects on the far side of the notch cracks gradually decreases, while the inhibition effect on the proximal side of the notch cracks gradually enhances. The left and right notch cracks of vertical defects are more significantly affected by the boundary reflected stress wave than those of parallel defects. The notch cracks on the left side do not exhibit a clear pattern, owing to the pre-existing reflected stress wave at the defects. In contrast, the notch cracks on the right side are substantially diminished by the boundary-reflected stress wave as the vertical defects move away from the centers of the notch holes.
The defective cracks were prefabricated on the wall of the notch holes by using polymethyl methacrylate (PMMA) material, which were parallel or vertical to the notch, and the distance from the defective cracks to the hole center was 2, 3, and 4 mm. The influence of notch hole wall defects on the crack propagation of notch blasting was investigated by using a digital dynamic caustic experimental system with numerical simulation. At the same time, triacetone triperoxide (TATP) explosives were employed as a charge, which served to mitigate the effect of gun smoke on the dynamic caustic experimental system and to improve the experimental design. The results demonstrate that the reflection of the stress wave at parallel defects results in a downward shift in the direction of crack initiation at the notch, but the refraction of the stress wave at vertical defects has no effect on the direction of crack initiation. The presence of wall defects in the hole impedes the impact of stress waves and blast gases on the cracks at the notch, resulting in a reduction in the length, expansion rate, and strength factor values of the cracks, and the degree of inhibition is contingent upon the distance of the defects from the centre of the borehole. As the distance between the parallel defects and the centre of the borehole increases, the inhibition effect of the parallel defects on both sides of the notch cracks gradually decreases. The inhibition effect of vertical defects on the far side of the notch cracks gradually decreases, while the inhibition effect on the proximal side of the notch cracks gradually enhances. The left and right notch cracks of vertical defects are more significantly affected by the boundary reflected stress wave than those of parallel defects. The notch cracks on the left side do not exhibit a clear pattern, owing to the pre-existing reflected stress wave at the defects. In contrast, the notch cracks on the right side are substantially diminished by the boundary-reflected stress wave as the vertical defects move away from the centers of the notch holes.
2025,
45(11):
112902.
doi: 10.11883/bzycj-2024-0252
Abstract:
To investigate the explosive energy release of Zr-based reactive material (Zr-RM) casings and the ignition effect of fragments driven by the explosion on fuel, casings composed primarily of zirconium (Zr), copper (Cu), nickel (Ni), aluminum (Al), and ytterbium (Y) were fabricated using alloy melting and casting techniques. The casings mentioned above had an outer diameter of 40 mm, a height of 80 mm, and a wall thickness of 5 mm. For comparison of subsequent damage effects, steel casings made of 45 steel with the same dimensions and mass were also prepared. Both types of casings were filled with JH-2 explosive charges. The charged structures were placed on a polyvinyl chloride pipe stand 1.5 m above the ground, and a fuel box containing 2.5 L of gasoline was positioned 2.0 m away from the explosion center. During the explosion-driven tests, a high-speed camera was utilized to capture the formation and propagation of the explosion fireball, the shockwave, and the impact process of casing fragments on the fuel tank. The fireball duration, shockwave velocity, and fragment impact effects were measured and analyzed. Additionally, the ignition and destruction effects of the fragments on the fuel were observed and recorded. The experimental results demonstrate that, when compared to steel casings of equal mass, Zr-RM casings under explosion-driven conditions exhibit a longer duration of firelight and faster shockwave velocities. Specifically, the fireball duration of Zr-RM casings is approximately 25.84 times that of steel casings, and the shockwave velocity is roughly 1.17 times faster. Zr-RM casings exhibit an enhancement effect on air shockwaves under explosion-driven conditions. Fragments of different materials cause structural damage to fuel tanks, including perforation and plastic deformation. After piercing the fuel tank, the reactive material ignites the fuel inside, demonstrating the ability to ignite gasoline. On the contrary, steel casings of equal mass do not ignite the fuel within the tank. This research provides a reference for the application of Zr-RM casing warheads.
To investigate the explosive energy release of Zr-based reactive material (Zr-RM) casings and the ignition effect of fragments driven by the explosion on fuel, casings composed primarily of zirconium (Zr), copper (Cu), nickel (Ni), aluminum (Al), and ytterbium (Y) were fabricated using alloy melting and casting techniques. The casings mentioned above had an outer diameter of 40 mm, a height of 80 mm, and a wall thickness of 5 mm. For comparison of subsequent damage effects, steel casings made of 45 steel with the same dimensions and mass were also prepared. Both types of casings were filled with JH-2 explosive charges. The charged structures were placed on a polyvinyl chloride pipe stand 1.5 m above the ground, and a fuel box containing 2.5 L of gasoline was positioned 2.0 m away from the explosion center. During the explosion-driven tests, a high-speed camera was utilized to capture the formation and propagation of the explosion fireball, the shockwave, and the impact process of casing fragments on the fuel tank. The fireball duration, shockwave velocity, and fragment impact effects were measured and analyzed. Additionally, the ignition and destruction effects of the fragments on the fuel were observed and recorded. The experimental results demonstrate that, when compared to steel casings of equal mass, Zr-RM casings under explosion-driven conditions exhibit a longer duration of firelight and faster shockwave velocities. Specifically, the fireball duration of Zr-RM casings is approximately 25.84 times that of steel casings, and the shockwave velocity is roughly 1.17 times faster. Zr-RM casings exhibit an enhancement effect on air shockwaves under explosion-driven conditions. Fragments of different materials cause structural damage to fuel tanks, including perforation and plastic deformation. After piercing the fuel tank, the reactive material ignites the fuel inside, demonstrating the ability to ignite gasoline. On the contrary, steel casings of equal mass do not ignite the fuel within the tank. This research provides a reference for the application of Zr-RM casing warheads.
2025,
45(11):
113101.
doi: 10.11883/bzycj-2025-0101
Abstract:
Lattice mechanical metamaterials have been widely used in various fields due to the lightweight, flexible designability and excellent impact resistance. In this paper, an enhanced X-shaped lattice mechanical metamaterial was designed and fabricated by selective laser melting. The dynamic crushing behavior and energy absorption mechanism of this metamaterials subjected to low-velocity impact were explored experimentally and numerically. The influence of impact velocity on the deformation mode and energy absorption capability of the enhanced X-shaped lattice mechanical metamaterials was analyzed. It is shown that the impact velocity has significant effects on the deformation modes of the mechanical metamaterials. At the lower impact velocities, the deformation mode of lattice mechanical metamaterials resembles that observed under quasi-static compression, characterized by the layer-by-layer crushing mode of the cells around the shear band. At the higher impact velocities, the deformation mode of lattice mechanical metamaterials transitions from X-shaped shear band to V-shaped shear band, and finally evolves into an arc-shaped shear band. The further study suggests that enhanced X-shaped lattice mechanical metamaterial exhibits a certain degree of velocity sensitivity. With the increase of the impact velocity, the initial peak stress, plateau stress, and specific energy absorption all increase correspondingly.
Lattice mechanical metamaterials have been widely used in various fields due to the lightweight, flexible designability and excellent impact resistance. In this paper, an enhanced X-shaped lattice mechanical metamaterial was designed and fabricated by selective laser melting. The dynamic crushing behavior and energy absorption mechanism of this metamaterials subjected to low-velocity impact were explored experimentally and numerically. The influence of impact velocity on the deformation mode and energy absorption capability of the enhanced X-shaped lattice mechanical metamaterials was analyzed. It is shown that the impact velocity has significant effects on the deformation modes of the mechanical metamaterials. At the lower impact velocities, the deformation mode of lattice mechanical metamaterials resembles that observed under quasi-static compression, characterized by the layer-by-layer crushing mode of the cells around the shear band. At the higher impact velocities, the deformation mode of lattice mechanical metamaterials transitions from X-shaped shear band to V-shaped shear band, and finally evolves into an arc-shaped shear band. The further study suggests that enhanced X-shaped lattice mechanical metamaterial exhibits a certain degree of velocity sensitivity. With the increase of the impact velocity, the initial peak stress, plateau stress, and specific energy absorption all increase correspondingly.
2025,
45(11):
113901.
doi: 10.11883/bzycj-2024-0273
Abstract:
Prestressed reinforced concrete (RC) T-beam bridges are commonly employed in highway bridges construction. After explosive attacks, the deck damage mostly exists in the form of breaches and affects its traffic capacity. While significant attention has been devoted to evaluating post-blast residual capacity of RC beam bridge piers and girders in existing blast damage assessment studies, there remains a critical gap in methodologies enabling intuitive and rapid damage assessment method for bridge serviceability. Therefore, the rapid assessment of bridge deck damage is investigated in this study by combining numerical simulation with multivariate nonlinear regression analysis, in which the breach size of the prestressed RC T-beam bridge deck subjected to explosive loading is taken as the damage index. Through comparative analysis of the transverse size of the deck breach under blast loading, it was revealed that concrete strength exhibits relatively minor influence, whereas parameters including explosion location, deck thickness, diaphragm spacing, TNT equivalent, and scaled distance demonstrate more pronounced effects. Owing to the pronounced reinforcing and constraining effects of webs and diaphragms on the bridge deck, comparative analyses under identical conditions demonstrate that transverse size of the breach caused by explosion above deck areas between webs and diaphragms is significantly smaller than that by explosion directly above the web, while on-bridge explosion exhibit lower damage compared to under-bridge explosion. Based upon the aforementioned parameters with significant influence, utilizing transverse size of the breach as the damage index, a rapid blast damage assessment formula is proposed for predicting the post-blast traffic capacity of bridges.
Prestressed reinforced concrete (RC) T-beam bridges are commonly employed in highway bridges construction. After explosive attacks, the deck damage mostly exists in the form of breaches and affects its traffic capacity. While significant attention has been devoted to evaluating post-blast residual capacity of RC beam bridge piers and girders in existing blast damage assessment studies, there remains a critical gap in methodologies enabling intuitive and rapid damage assessment method for bridge serviceability. Therefore, the rapid assessment of bridge deck damage is investigated in this study by combining numerical simulation with multivariate nonlinear regression analysis, in which the breach size of the prestressed RC T-beam bridge deck subjected to explosive loading is taken as the damage index. Through comparative analysis of the transverse size of the deck breach under blast loading, it was revealed that concrete strength exhibits relatively minor influence, whereas parameters including explosion location, deck thickness, diaphragm spacing, TNT equivalent, and scaled distance demonstrate more pronounced effects. Owing to the pronounced reinforcing and constraining effects of webs and diaphragms on the bridge deck, comparative analyses under identical conditions demonstrate that transverse size of the breach caused by explosion above deck areas between webs and diaphragms is significantly smaller than that by explosion directly above the web, while on-bridge explosion exhibit lower damage compared to under-bridge explosion. Based upon the aforementioned parameters with significant influence, utilizing transverse size of the breach as the damage index, a rapid blast damage assessment formula is proposed for predicting the post-blast traffic capacity of bridges.
2025,
45(11):
114201.
doi: 10.11883/bzycj-2024-0411
Abstract:
In order to address the needs of modern combat vehicles for both personnel protection and lightweight design, optimizing their blast-resistant structures is necessary. Due to the high cost of physical experiments, finite element simulation has been commonly used instead. However, simulations of explosion and vehicle responses require extensive computational resources and incur high computational costs, leading to limited data availability for the optimization of explosion-proof structures. Since structural optimization demands sufficient data support, larger amount of valid data can improve the accuracy of the surrogate model and the precision of the optimal solution, yielding better optimization results. To overcome these challenges, a data-driven optimization method for vehicle’s explosion-proof structures was proposed, integrating data augmentation and semi-supervised regression. To address the limitations of generative adversarial networks (GANs) in handling numerical data, an improved model, a Gaussian density estimation-Wasserstein generative adversarial network (GDE-WGAN), was developed by modifying both the generator and discriminator of the WGAN model, a variant of the GANs. The feasibility of the proposed method was demonstrated based on the principle of information gain. The data generated by the GDE-WGAN were incorporated into a self-training framework, where an adaptive confidence assessment mechanism dynamically adjusted the way that the semi-supervised support vector regression model utilizes the generated data. The feasibility and superiority of the method were validated by comparing the enhanced performance of the semi-supervised regression model using different numerical data expansion techniques. Finally, multi-objective optimization was performed to obtain the optimal solutions of the data-augmented semi-supervised regression model and the initial model, followed by verification and comparison with finite element simulation results. It shows that the GDE-WGAN significantly enhances the performance of the semi-supervised regression model, and the generated data exhibit greater randomness and diversity through the network structure of the GANs, which benefits semi-supervised learning. When handling semi-supervised regression for high-dimensional nonlinear numerical data, both global and local data distribution similarities play a crucial role. Furthermore, finite element simulations indicate that the improved model predicts results more accurately than the initial model and achieves superior optimization outcomes.
In order to address the needs of modern combat vehicles for both personnel protection and lightweight design, optimizing their blast-resistant structures is necessary. Due to the high cost of physical experiments, finite element simulation has been commonly used instead. However, simulations of explosion and vehicle responses require extensive computational resources and incur high computational costs, leading to limited data availability for the optimization of explosion-proof structures. Since structural optimization demands sufficient data support, larger amount of valid data can improve the accuracy of the surrogate model and the precision of the optimal solution, yielding better optimization results. To overcome these challenges, a data-driven optimization method for vehicle’s explosion-proof structures was proposed, integrating data augmentation and semi-supervised regression. To address the limitations of generative adversarial networks (GANs) in handling numerical data, an improved model, a Gaussian density estimation-Wasserstein generative adversarial network (GDE-WGAN), was developed by modifying both the generator and discriminator of the WGAN model, a variant of the GANs. The feasibility of the proposed method was demonstrated based on the principle of information gain. The data generated by the GDE-WGAN were incorporated into a self-training framework, where an adaptive confidence assessment mechanism dynamically adjusted the way that the semi-supervised support vector regression model utilizes the generated data. The feasibility and superiority of the method were validated by comparing the enhanced performance of the semi-supervised regression model using different numerical data expansion techniques. Finally, multi-objective optimization was performed to obtain the optimal solutions of the data-augmented semi-supervised regression model and the initial model, followed by verification and comparison with finite element simulation results. It shows that the GDE-WGAN significantly enhances the performance of the semi-supervised regression model, and the generated data exhibit greater randomness and diversity through the network structure of the GANs, which benefits semi-supervised learning. When handling semi-supervised regression for high-dimensional nonlinear numerical data, both global and local data distribution similarities play a crucial role. Furthermore, finite element simulations indicate that the improved model predicts results more accurately than the initial model and achieves superior optimization outcomes.
