2023 Vol. 43, No. 2
Display Method:
PDF 
Cited by
Read OL
2023, 43(2): 022101.
doi: 10.11883/bzycj-2022-0068
Abstract:
To investigate the influence of the initial droplet diameter on the flow field of gas-liquid two-phase rotating detonation engine, an Eulerian-Lagrangian model of unsteady two-phase detonation is established based on the assumption of an initially uniform droplet diameter and considering atomization and evaporation processes. Non-premixed two-dimensional numerical simulations of detonation for liquid kerosene and high temperature air mixture are conducted. The results show that a single stable rotating detonation wave is formed in the initial droplet diameter range of 1–70 μm. For the global equivalent ratio of 1, the air area before the detonation wave front is larger than the vapor area of kerosene droplets, resulting in inhomogeneous mixing before the wave front. Both oil-rich and oil-poor areas form before the wave front. Due to the speed difference between two phases of the gas and droplets, the air is separated to form a low-temperature strip. When the initial diameter of kerosene droplets is small, the mixing process of reactants is mainly affected by evaporation and the detonation wave propagates stably. When the initial droplet diameter is reduced to 1 μm, evaporation occurs at the entrance, and the rotating detonation flow field shows the characteristics of gas phase propagation, and the structure of the detonation wave is smooth. When the initial diameter of kerosene droplets is relatively large, the mixing process of reactants before the wave front is mainly affected by droplet break-up. For the same fuel mass flow rate with different initial droplet diameters, the maximum residence time of kerosene droplets accounts for more than 80% of the detonation wave propagation time and the detonation velocity increases with the increased ratio of gaseous part of the fuel. The velocity of the detonation wave increases first and then decreases with the increased initial droplet diameter in the range of 10–70 μm.
To investigate the influence of the initial droplet diameter on the flow field of gas-liquid two-phase rotating detonation engine, an Eulerian-Lagrangian model of unsteady two-phase detonation is established based on the assumption of an initially uniform droplet diameter and considering atomization and evaporation processes. Non-premixed two-dimensional numerical simulations of detonation for liquid kerosene and high temperature air mixture are conducted. The results show that a single stable rotating detonation wave is formed in the initial droplet diameter range of 1–70 μm. For the global equivalent ratio of 1, the air area before the detonation wave front is larger than the vapor area of kerosene droplets, resulting in inhomogeneous mixing before the wave front. Both oil-rich and oil-poor areas form before the wave front. Due to the speed difference between two phases of the gas and droplets, the air is separated to form a low-temperature strip. When the initial diameter of kerosene droplets is small, the mixing process of reactants is mainly affected by evaporation and the detonation wave propagates stably. When the initial droplet diameter is reduced to 1 μm, evaporation occurs at the entrance, and the rotating detonation flow field shows the characteristics of gas phase propagation, and the structure of the detonation wave is smooth. When the initial diameter of kerosene droplets is relatively large, the mixing process of reactants before the wave front is mainly affected by droplet break-up. For the same fuel mass flow rate with different initial droplet diameters, the maximum residence time of kerosene droplets accounts for more than 80% of the detonation wave propagation time and the detonation velocity increases with the increased ratio of gaseous part of the fuel. The velocity of the detonation wave increases first and then decreases with the increased initial droplet diameter in the range of 10–70 μm.
2023, 43(2): 022301.
doi: 10.11883/bzycj-2022-0188
Abstract:
The effects of different diminished ambient pressure, temperature and altitude from sea level on blast wave parameters (overpressure, impulse and wave front trajectory) were investigated by employing the dimensional analysis theory and the AUTODYN software. Meanwhile, the relationship equations between the blast wave parameters with the diminished pressure and temperature were established, which were verified by numerical simulations and experimental data. Results indicate that the equations can evaluate the blast wave parameters at diminished temperature and pressure effectively. It is noted that the blast wave overpressure and far-field (scaled distance Z>0.2 m/kg1/3) impulse decrease, but the propagation velocity increases, as the ambient pressure decreases. The blast wave impulse increases, and the propagation velocity decreases, but has little effect on the overpressure, as the ambient temperature decreases. It is shown that when the altitude increases by 1000 m in the range from 0 to 9000 m above sea level, the overpressure and far-field impulse of the blast wave decrease in average by about 3.9% and 3.2%. In addition, the blast wave propagation velocity in the near field increases, but it in the farfield decreases with the altitude increase. The influences of the diminished pressure on the blast wave overpressure and impulse are greater than those of the diminished temperature at high altitudes. The blast wave propagation velocity depends on the diminished pressure in the near field, but on the diminished temperature in the far field.
The effects of different diminished ambient pressure, temperature and altitude from sea level on blast wave parameters (overpressure, impulse and wave front trajectory) were investigated by employing the dimensional analysis theory and the AUTODYN software. Meanwhile, the relationship equations between the blast wave parameters with the diminished pressure and temperature were established, which were verified by numerical simulations and experimental data. Results indicate that the equations can evaluate the blast wave parameters at diminished temperature and pressure effectively. It is noted that the blast wave overpressure and far-field (scaled distance Z>0.2 m/kg1/3) impulse decrease, but the propagation velocity increases, as the ambient pressure decreases. The blast wave impulse increases, and the propagation velocity decreases, but has little effect on the overpressure, as the ambient temperature decreases. It is shown that when the altitude increases by 1000 m in the range from 0 to 9000 m above sea level, the overpressure and far-field impulse of the blast wave decrease in average by about 3.9% and 3.2%. In addition, the blast wave propagation velocity in the near field increases, but it in the farfield decreases with the altitude increase. The influences of the diminished pressure on the blast wave overpressure and impulse are greater than those of the diminished temperature at high altitudes. The blast wave propagation velocity depends on the diminished pressure in the near field, but on the diminished temperature in the far field.
2023, 43(2): 023101.
doi: 10.11883/bzycj-2022-0203
Abstract:
One of the fundamental scientific problems of dynamic fracture of ductile metals is spallation of low melting point metals. The classical spallation and micro-spallation of single-crystal (SC) and nanocrystal (NC) tin were carried out using the non-equilibrium molecular dynamics (NEMD) at shock pressures of 13.5−61.0 GPa. In order to achieve the spallation in the SC and NC models, the piston-target method was utilized. Specifically, the rigid piston was assigned an initial velocity, then the piston impacted the target to generate stress wave, and the stress waveform was controlled by adjusting the loading time after the length of the model along the shock direction was determined. The simulation results show that: during the loading stage, the shock wave velocity has no influence on the waveform evolution of the SC Sn model, but it does have an effect on the waveform evolution of the NC Sn model, in which the front width of the stress wave in classical spallation of the NC Sn model is mainly affected by grain boundary sliding. The void nucleation sites in classical spallation and micro-spallation are found at high potential energies in the SC model. In the NC model, for the classic spallation, voids mostly nucleate at grain boundaries (including the triple junctions of the grain boundaries) and grow along grain boundaries, resulting in intergranular fractures; for the micro-spallation, voids nucleate at the grain boundary and inside the grain, resulting in intergranular fracture, intragranular fracture, and transgranular fracture. The void volume fraction increases exponentially, and the variation law of void volume fraction of SC and NC Sn is the same under the same impact velocity. The two turning points of the void volume fraction curve in classical spallation represent the transition from nucleation to growth and the catastrophic transition from damage to fracture.
One of the fundamental scientific problems of dynamic fracture of ductile metals is spallation of low melting point metals. The classical spallation and micro-spallation of single-crystal (SC) and nanocrystal (NC) tin were carried out using the non-equilibrium molecular dynamics (NEMD) at shock pressures of 13.5−61.0 GPa. In order to achieve the spallation in the SC and NC models, the piston-target method was utilized. Specifically, the rigid piston was assigned an initial velocity, then the piston impacted the target to generate stress wave, and the stress waveform was controlled by adjusting the loading time after the length of the model along the shock direction was determined. The simulation results show that: during the loading stage, the shock wave velocity has no influence on the waveform evolution of the SC Sn model, but it does have an effect on the waveform evolution of the NC Sn model, in which the front width of the stress wave in classical spallation of the NC Sn model is mainly affected by grain boundary sliding. The void nucleation sites in classical spallation and micro-spallation are found at high potential energies in the SC model. In the NC model, for the classic spallation, voids mostly nucleate at grain boundaries (including the triple junctions of the grain boundaries) and grow along grain boundaries, resulting in intergranular fractures; for the micro-spallation, voids nucleate at the grain boundary and inside the grain, resulting in intergranular fracture, intragranular fracture, and transgranular fracture. The void volume fraction increases exponentially, and the variation law of void volume fraction of SC and NC Sn is the same under the same impact velocity. The two turning points of the void volume fraction curve in classical spallation represent the transition from nucleation to growth and the catastrophic transition from damage to fracture.
2023, 43(2): 023201.
doi: 10.11883/bzycj-2022-0189
Abstract:
Based on the working mechanism of local resonance materials, a filter concrete with stress wave attenuation characteristics is designed by embedding metal balls wrapped with elastic layer (filter units) in the concrete matrix. First, the stress wave attenuation mechanism of filter concrete is analyzed by simplifying the filter concrete structure into a mass-spring mechanical system. Then, the propagation velocity and peak stress of stress wave in normal concrete model and filter concrete model under impact load are compared by using numerical simulation approach. Through parameter analysis, the influence of the density of metal ball, elastic modulus and thickness of elastic layer on the energy storage of filter units are studied. Finally, the spalling damage patterns of normal concrete model and filter concrete model under impact load are compared. The results show that the filter units can effectively reduce the stress wave propagation velocity and magnitude of peak stress in the concrete matrix. The vibration of the metal balls and the deformation of the elastic layer form a good energy storage mechanism for filter units and effectively reduce the energy exerted by the impact load on the concrete matrix. The larger the mass of the metal balls, the better the energy storage effect of the filter units, while the elastic modulus and thickness of the elastic layer need to be designed through a proper analysis to maximize the energy storage of the filter units. The concrete matrix around the elastic layer has obvious stress concentration and local damage may occur, but the local damage of the filter concrete matrix dissipates a large amount of energy produced by the load, effectively reducing the degree of destruction near the free surface of the structure. Combined with the attenuation effect of the filter units on the stress wave, the filter concrete has achieved good impact resistance.
Based on the working mechanism of local resonance materials, a filter concrete with stress wave attenuation characteristics is designed by embedding metal balls wrapped with elastic layer (filter units) in the concrete matrix. First, the stress wave attenuation mechanism of filter concrete is analyzed by simplifying the filter concrete structure into a mass-spring mechanical system. Then, the propagation velocity and peak stress of stress wave in normal concrete model and filter concrete model under impact load are compared by using numerical simulation approach. Through parameter analysis, the influence of the density of metal ball, elastic modulus and thickness of elastic layer on the energy storage of filter units are studied. Finally, the spalling damage patterns of normal concrete model and filter concrete model under impact load are compared. The results show that the filter units can effectively reduce the stress wave propagation velocity and magnitude of peak stress in the concrete matrix. The vibration of the metal balls and the deformation of the elastic layer form a good energy storage mechanism for filter units and effectively reduce the energy exerted by the impact load on the concrete matrix. The larger the mass of the metal balls, the better the energy storage effect of the filter units, while the elastic modulus and thickness of the elastic layer need to be designed through a proper analysis to maximize the energy storage of the filter units. The concrete matrix around the elastic layer has obvious stress concentration and local damage may occur, but the local damage of the filter concrete matrix dissipates a large amount of energy produced by the load, effectively reducing the degree of destruction near the free surface of the structure. Combined with the attenuation effect of the filter units on the stress wave, the filter concrete has achieved good impact resistance.
2023, 43(2): 023202.
doi: 10.11883/bzycj-2022-0196
Abstract:
The study of thermal-mechanical coupling mechanism is of great significance to deep rock engineering such as rock tunnel fire, nuclear waste treatment and geothermal development. To investigate the effect of high temperature on the impact mechanical properties of granite, the real-time high temperature impact compression test was carried out on the granite specimen at 20～800 ℃. The Caledonian granite in the construction area of Sejila Mountain on Sichuan-Tibet Railway was taken as the research object, real-time high temperature impact compression tests were carried out on the specimens under five different temperatures ( 20, 200, 400, 600 and 800 ℃) with three average loading rates ( 72.8, 144.97 and 230.29 s−1) by using the split Hopkinson pressure bar (SHPB) and synchronous box-type resistance furnace. The effects of high temperature and loading strain rate on the fracture characteristics, dynamic compressive strength and fractal dimension of the specimens were analyzed. The variation law of dissipated energy per unit volume was also studied and discussed. In addition, the intrinsic correlation between the change of mineral composition and the dynamic strength of granite was analyzed based on X-ray powder crystal diffraction. The results show that the brittle fracture of the specimens at 20 to 400 ℃ is dominant, and the fragments are spindle-shaped with sharp ends. The specimens at 600 ℃ are dominated by plastic failure, and their shapes tend to be round. The peak stress of specimens increases first and then decreases with the increase of temperature, reaches the strength threshold at 200 ℃, and then decreases continuously. The dissipated energy per unit volume of rock has a positive linear correlation with the loading strain rate and a quadratic function with the temperature, which shows a good fitting effect. The content fluctuation and phase change of the three main mineral components of quartz, mica and feldspar lead to the gradual deterioration of the dynamic strength of granite after 200 ℃.
The study of thermal-mechanical coupling mechanism is of great significance to deep rock engineering such as rock tunnel fire, nuclear waste treatment and geothermal development. To investigate the effect of high temperature on the impact mechanical properties of granite, the real-time high temperature impact compression test was carried out on the granite specimen at 20～800 ℃. The Caledonian granite in the construction area of Sejila Mountain on Sichuan-Tibet Railway was taken as the research object, real-time high temperature impact compression tests were carried out on the specimens under five different temperatures ( 20, 200, 400, 600 and 800 ℃) with three average loading rates ( 72.8, 144.97 and 230.29 s−1) by using the split Hopkinson pressure bar (SHPB) and synchronous box-type resistance furnace. The effects of high temperature and loading strain rate on the fracture characteristics, dynamic compressive strength and fractal dimension of the specimens were analyzed. The variation law of dissipated energy per unit volume was also studied and discussed. In addition, the intrinsic correlation between the change of mineral composition and the dynamic strength of granite was analyzed based on X-ray powder crystal diffraction. The results show that the brittle fracture of the specimens at 20 to 400 ℃ is dominant, and the fragments are spindle-shaped with sharp ends. The specimens at 600 ℃ are dominated by plastic failure, and their shapes tend to be round. The peak stress of specimens increases first and then decreases with the increase of temperature, reaches the strength threshold at 200 ℃, and then decreases continuously. The dissipated energy per unit volume of rock has a positive linear correlation with the loading strain rate and a quadratic function with the temperature, which shows a good fitting effect. The content fluctuation and phase change of the three main mineral components of quartz, mica and feldspar lead to the gradual deterioration of the dynamic strength of granite after 200 ℃.
2023, 43(2): 023203.
doi: 10.11883/bzycj-2022-0202
Abstract:
In order to improve the uniformity of the fragments of the fragmentation warhead and enhance the axial lethality of the warhead, it was proposed to use a wave shape controller to control the scattering direction of the fragments. The shape of the wave shape controller was designed based on the law of detonation wave reflection at the wave shape controller interface and the Shapiro formula. The LS-DYNA software and ALE（arbitrary Lagrange-Euler） algorithm were used to numerically simulate the scattering process of fragments, and the static explosion test of the warhead prototype was carried out to verify the rationality of using the wave shape controller to improve the scattering characteristic of fragments. The difference in the fragment scattering processes with and without the wave shape controller were compared. The law of fragment scattering velocity and scattering angle of the warhead was analyzed and summarized when there was no wave shape controller and when the wave shape controller materials were nylon, polyurethane and PTFE（polytetrafluoroethylene）, respectively. The results show that the wave shape controller can reduce the difference in the scattering velocities of the fragments between the center and both ends of the warhead, and evenly change the direction angles of the fragments scattering from the center to both ends, so that the fragments are distributed more uniformly along the axial direction. The wave shape controllers made of different materials have different effects on the scattering characteristics of the fragments, while the use of the wave shape controller reduces the fragment scattering velocity, reduces the fragment scattering angle, and increases the fragment distribution density. The error between the numerical calculation values and experimental values of fragment scattering angle is within 6.53%. Compared with that without a wave shape controller, the fragment scattering angles of the warhead prototypes with the wave shape controller and the material is nylon, polyurethane and PTFE reduced by 40.00%, 44.00% and 46.67%, respectively.
In order to improve the uniformity of the fragments of the fragmentation warhead and enhance the axial lethality of the warhead, it was proposed to use a wave shape controller to control the scattering direction of the fragments. The shape of the wave shape controller was designed based on the law of detonation wave reflection at the wave shape controller interface and the Shapiro formula. The LS-DYNA software and ALE（arbitrary Lagrange-Euler） algorithm were used to numerically simulate the scattering process of fragments, and the static explosion test of the warhead prototype was carried out to verify the rationality of using the wave shape controller to improve the scattering characteristic of fragments. The difference in the fragment scattering processes with and without the wave shape controller were compared. The law of fragment scattering velocity and scattering angle of the warhead was analyzed and summarized when there was no wave shape controller and when the wave shape controller materials were nylon, polyurethane and PTFE（polytetrafluoroethylene）, respectively. The results show that the wave shape controller can reduce the difference in the scattering velocities of the fragments between the center and both ends of the warhead, and evenly change the direction angles of the fragments scattering from the center to both ends, so that the fragments are distributed more uniformly along the axial direction. The wave shape controllers made of different materials have different effects on the scattering characteristics of the fragments, while the use of the wave shape controller reduces the fragment scattering velocity, reduces the fragment scattering angle, and increases the fragment distribution density. The error between the numerical calculation values and experimental values of fragment scattering angle is within 6.53%. Compared with that without a wave shape controller, the fragment scattering angles of the warhead prototypes with the wave shape controller and the material is nylon, polyurethane and PTFE reduced by 40.00%, 44.00% and 46.67%, respectively.
2023, 43(2): 023301.
doi: 10.11883/bzycj-2022-0435
Abstract:
The blast resistance of sacrificial cladding has been extensively studied in the field of blast protection. As a polymer material with a cellular structure, non-water reactive foaming polyurethane also has the potential to act as a sacrificial cladding due to its good mechanical properties. In order to study the blast damage mitigation effect of polymer sacrificial cladding on reinforced concrete structures, a contact explosion test on the reinforced concrete slab with polymer sacrificial cladding was carried out, while an ordinary reinforced concrete slab was set as the control group, and the effect of polymer sacrificial cladding on the damage characteristics of the reinforced concrete slab was compared and analyzed. In addition, the SPH-FEM (coupled smooth particle hydrodynamics and finite element method) coupling model of the field explosion test was established by using AUTODYN software, and the reliability of the coupling model was verified by comparing with the test results. On this basis, the effects of explosive charge, the density, and the thickness of polymer sacrificial cladding on the damage features and energy absorption characteristics of reinforced concrete slabs with polymer sacrificial cladding were investigated through parametric sensitivity analysis. The results show that the polymer sacrificial cladding can effectively disperse the blast loads and mitigate the impact of the blast loads on the reinforced concrete slab with good protective performance under contact explosions. The polymer sacrificial cladding can maintain a high level of energy absorption even with the explosive charge increased within limits. Increasing the density and thickness of the cladding is beneficial to enhance the energy absorption ability of the polymer sacrificial cladding, while the change in thickness will cause a change in the damage mode of the protected reinforced concrete slab. The research results are helpful in providing a relevant reference for the further research and application of the new non-water reactive foaming polyurethane in the field of blast protection of engineering structures.
The blast resistance of sacrificial cladding has been extensively studied in the field of blast protection. As a polymer material with a cellular structure, non-water reactive foaming polyurethane also has the potential to act as a sacrificial cladding due to its good mechanical properties. In order to study the blast damage mitigation effect of polymer sacrificial cladding on reinforced concrete structures, a contact explosion test on the reinforced concrete slab with polymer sacrificial cladding was carried out, while an ordinary reinforced concrete slab was set as the control group, and the effect of polymer sacrificial cladding on the damage characteristics of the reinforced concrete slab was compared and analyzed. In addition, the SPH-FEM (coupled smooth particle hydrodynamics and finite element method) coupling model of the field explosion test was established by using AUTODYN software, and the reliability of the coupling model was verified by comparing with the test results. On this basis, the effects of explosive charge, the density, and the thickness of polymer sacrificial cladding on the damage features and energy absorption characteristics of reinforced concrete slabs with polymer sacrificial cladding were investigated through parametric sensitivity analysis. The results show that the polymer sacrificial cladding can effectively disperse the blast loads and mitigate the impact of the blast loads on the reinforced concrete slab with good protective performance under contact explosions. The polymer sacrificial cladding can maintain a high level of energy absorption even with the explosive charge increased within limits. Increasing the density and thickness of the cladding is beneficial to enhance the energy absorption ability of the polymer sacrificial cladding, while the change in thickness will cause a change in the damage mode of the protected reinforced concrete slab. The research results are helpful in providing a relevant reference for the further research and application of the new non-water reactive foaming polyurethane in the field of blast protection of engineering structures.
2023, 43(2): 023302.
doi: 10.11883/bzycj-2022-0294
Abstract:
To meet the requirements of a tandem penetrating warhead for high penetration depth and large perforation, a jetting projectile charge (JPC) was designed. The damage test of a large-scale reinforced concrete wall was carried out to analyze the impact of standoff distance on the damaging effect. By constructing a large air domain covering the whole reinforced concrete wall for the transmission of explosion shock wave and JPC, the coupling damage of JPC high-speed penetration and explosion shock wave to the reinforced concrete wall was considered. The damage evolution, strain rate and other parameters of the Karagozian & Case (K&C) model were modified, based on which a numerical model was established to simulate the whole process of the combined damage of JPC and explosion shock wave to the reinforced concrete wall. The reliability of the numerical model was fully verified by comparing the simulation and test results from the failure mode, crater depth and crater diameter of the reinforced concrete wall. On this basis, the combined damage effect of JPC and explosion shock wave on the reinforced concrete wall was further studied, and the influence of wall thickness on the damaging effect was analyzed. The results show that JPC can penetrate the reinforced concrete wall with a thickness of 80 cm (6.67 times of charge diameter) at the standoff distance of 1.67 times and 2.50 times of charge diameter, and form cylindrical holes with a diameter of more than 6 cm (0.50 times of charge diameter). The multi-load damage characteristic of shaped charge determines the damage result of the reinforced concrete wall, and the explosion shock wave can intensify the damage range of the front crater and back crater of the reinforced concrete wall. The wall thickness has no significant effect on the diameter and depth of the crater on the front of the wall and the diameter of the internal penetration hole. With the increase of the wall thickness, the crater diameter on the back gradually decreases and the crater depth on the back gradually increases.
To meet the requirements of a tandem penetrating warhead for high penetration depth and large perforation, a jetting projectile charge (JPC) was designed. The damage test of a large-scale reinforced concrete wall was carried out to analyze the impact of standoff distance on the damaging effect. By constructing a large air domain covering the whole reinforced concrete wall for the transmission of explosion shock wave and JPC, the coupling damage of JPC high-speed penetration and explosion shock wave to the reinforced concrete wall was considered. The damage evolution, strain rate and other parameters of the Karagozian & Case (K&C) model were modified, based on which a numerical model was established to simulate the whole process of the combined damage of JPC and explosion shock wave to the reinforced concrete wall. The reliability of the numerical model was fully verified by comparing the simulation and test results from the failure mode, crater depth and crater diameter of the reinforced concrete wall. On this basis, the combined damage effect of JPC and explosion shock wave on the reinforced concrete wall was further studied, and the influence of wall thickness on the damaging effect was analyzed. The results show that JPC can penetrate the reinforced concrete wall with a thickness of 80 cm (6.67 times of charge diameter) at the standoff distance of 1.67 times and 2.50 times of charge diameter, and form cylindrical holes with a diameter of more than 6 cm (0.50 times of charge diameter). The multi-load damage characteristic of shaped charge determines the damage result of the reinforced concrete wall, and the explosion shock wave can intensify the damage range of the front crater and back crater of the reinforced concrete wall. The wall thickness has no significant effect on the diameter and depth of the crater on the front of the wall and the diameter of the internal penetration hole. With the increase of the wall thickness, the crater diameter on the back gradually decreases and the crater depth on the back gradually increases.
2023, 43(2): 024101.
doi: 10.11883/bzycj-2022-0160
Abstract:
The expanding ring experimental technology mainly refers to the explosion expanding ring and the electromagnetic expanding ring experimental technology. During the experiment, the loading strain rate of the expansion ring decreases rapidly with the expansion of the ring after reached the peak value, which creates great inconvenience to the study of tension fragmentation of strain-rate sensitive solids. In this paper, a constant strain-rate loading technology is developed on the basis of the liquid-driving expanding ring experimental technology. Since it is not possible to apply sudden loading to the expansion ring during the experiment, it is assumed that the strain rate of the expansion ring during the expansion process is divided into linear growth stage and stable stage of the strain rate. By reasonably controlling the loading velocity and loading time of the liquid, an approximate expression of the liquid-driving loading curve required to realize the constant strain-rate expansion of the metal ring is deduced theoretically. The tension fragmentation process of the 1060-O aluminum ring under liquid-driving loading is simulated by the fluid-solid coupling numerical simulation. Under the liquid-driving loading curve, the hoop strain rate of the expanding ring fluctuates within a maximum of 20% in the stable stage of the strain rate. Before occurring of the significant necking of the expansion ring, the circumferential velocity of the expansion ring is basically zero, indicating that the expansion ring is under uniform tensile loading and there is no stress wave propagation in the circumferential direction. When the expansion ring is significantly necked, an obvious sudden change in the circumferential velocity will take place, indicateing that a Mott wave from the fracture site propagates to the corresponding position. The influence of the loading curve on the strain rate during the fracture process is further studied. Then an expanding ring experiment was carried out on the 1060-O aluminum ring on the liquid-driving expanding ring experimental device to verify the feasibility of the constant strain rate loading technology.
The expanding ring experimental technology mainly refers to the explosion expanding ring and the electromagnetic expanding ring experimental technology. During the experiment, the loading strain rate of the expansion ring decreases rapidly with the expansion of the ring after reached the peak value, which creates great inconvenience to the study of tension fragmentation of strain-rate sensitive solids. In this paper, a constant strain-rate loading technology is developed on the basis of the liquid-driving expanding ring experimental technology. Since it is not possible to apply sudden loading to the expansion ring during the experiment, it is assumed that the strain rate of the expansion ring during the expansion process is divided into linear growth stage and stable stage of the strain rate. By reasonably controlling the loading velocity and loading time of the liquid, an approximate expression of the liquid-driving loading curve required to realize the constant strain-rate expansion of the metal ring is deduced theoretically. The tension fragmentation process of the 1060-O aluminum ring under liquid-driving loading is simulated by the fluid-solid coupling numerical simulation. Under the liquid-driving loading curve, the hoop strain rate of the expanding ring fluctuates within a maximum of 20% in the stable stage of the strain rate. Before occurring of the significant necking of the expansion ring, the circumferential velocity of the expansion ring is basically zero, indicating that the expansion ring is under uniform tensile loading and there is no stress wave propagation in the circumferential direction. When the expansion ring is significantly necked, an obvious sudden change in the circumferential velocity will take place, indicateing that a Mott wave from the fracture site propagates to the corresponding position. The influence of the loading curve on the strain rate during the fracture process is further studied. Then an expanding ring experiment was carried out on the 1060-O aluminum ring on the liquid-driving expanding ring experimental device to verify the feasibility of the constant strain rate loading technology.
2023, 43(2): 024201.
doi: 10.11883/bzycj-2022-0155
Abstract:
The self-driven rotary sprayer using ultra-high-pressure water jet is widely used in the rust removal of ship hulls, and its layout directly affects the efficiency and quality of ship derusting. Hitherto, the design of sprayer layout primarily depends on practical engineering experiences, due to the lack of support from accurate optimization techniques and theoretical analysis. In order to solve the layout optimization problem associated with self-driven rotary sprayers using ultra-high-pressure water jet, an improved elitist strategy genetic algorithm (ESGA) based on conventional genetic algorithm (GA) is proposed. By designing appropriate evolutionary operations, the ESGA algorithm can skip crossover and mutation operations on the fittest individuals in the population, and then directly copy the fittest individual to the next generation. Thus, the global convergence ability and robustness of the algorithm are improved effectively. By fully combining the sweep impinging performance and trajectory characteristics of rotary sprayer, a sweep impinging discrete-time model for self-driven rotary sprayer using ultra-high-pressure water jet is developed to quantify the evenness of impinging energy distribution on target surface perpendicular to the sprayer movement path. Aiming at enhancing the evenness of impinging energy distribution and improving hydrodynamic performance, the layout of self-driven rotary sprayer is optimized via the GA and ESGA algorithms. It is found that the evenness of the impinging energy distribution related to the self-driven rotary sprayer with a rod-like shape, which is optimized by the ESGA algorithm, is improved by 47.2% compared with that of the original layout scheme. The ESGA algorithm provides faster convergence speed and higher convergence precision, superior to the conventional GA. The experimental test results indicated that the rust-removing efficiency of self-driven rotary sprayer, optimized by the ESGA algorithm, is increased by 42.0% when compared with original layout scheme. It is worth noting that the improved ESGA algorithm optimization approach is feasible, and some sprayer layouts with better hydrodynamic performance can be easily achieved in fewer convergence iterations, providing adequate theoretical basis and application support for the layout optimization.
The self-driven rotary sprayer using ultra-high-pressure water jet is widely used in the rust removal of ship hulls, and its layout directly affects the efficiency and quality of ship derusting. Hitherto, the design of sprayer layout primarily depends on practical engineering experiences, due to the lack of support from accurate optimization techniques and theoretical analysis. In order to solve the layout optimization problem associated with self-driven rotary sprayers using ultra-high-pressure water jet, an improved elitist strategy genetic algorithm (ESGA) based on conventional genetic algorithm (GA) is proposed. By designing appropriate evolutionary operations, the ESGA algorithm can skip crossover and mutation operations on the fittest individuals in the population, and then directly copy the fittest individual to the next generation. Thus, the global convergence ability and robustness of the algorithm are improved effectively. By fully combining the sweep impinging performance and trajectory characteristics of rotary sprayer, a sweep impinging discrete-time model for self-driven rotary sprayer using ultra-high-pressure water jet is developed to quantify the evenness of impinging energy distribution on target surface perpendicular to the sprayer movement path. Aiming at enhancing the evenness of impinging energy distribution and improving hydrodynamic performance, the layout of self-driven rotary sprayer is optimized via the GA and ESGA algorithms. It is found that the evenness of the impinging energy distribution related to the self-driven rotary sprayer with a rod-like shape, which is optimized by the ESGA algorithm, is improved by 47.2% compared with that of the original layout scheme. The ESGA algorithm provides faster convergence speed and higher convergence precision, superior to the conventional GA. The experimental test results indicated that the rust-removing efficiency of self-driven rotary sprayer, optimized by the ESGA algorithm, is increased by 42.0% when compared with original layout scheme. It is worth noting that the improved ESGA algorithm optimization approach is feasible, and some sprayer layouts with better hydrodynamic performance can be easily achieved in fewer convergence iterations, providing adequate theoretical basis and application support for the layout optimization.
2023, 43(2): 025201.
doi: 10.11883/bzycj-2022-0081
Abstract:
To explore the influences of the opening angle of bilinear shaped charge on the effective utilization rate and energy gathering effect, the boundary equation of effective shaped charge was deduced through the theory of instantaneous detonation hypothesis. The effective utilization ratio of the shaped charge structure blasting with 60°, 65°, 70°, 75°, and 80° shaped charge angles was analyzed using the visual implicit functions of SymPy package based on Python language. Through the physical model tests of single-hole Plexiglas and double-hole cement mortar, the crack formation law of pre-cracked holes with different energy-gathering opening angles was studied. Using the LS-DYNA numerical simulation software, five numerical models with energy-gathered opening angles of 60°, 65°, 70°, 75°, and 80° were established to reveal the penetration process of the bilinear energy-gathered structure charge jet and the stress evolution law of the rock unit on the blast-hole wall with different energy-gathered opening angles. The research results show that the effective utilization ratio of the shaped explosives is the highest when the energy-gathered opening angle is 75°. The pre-split hole formation effect when the opening angle of the energy-concentrating groove of the shaped charge is 75° is better than that when the opening angle is 60°, and the stress concentration effect and penetration depth along the direction of the energy-concentrating groove are the best, and the rock unit on the blast-hole wall reaches the peak stress first. The pre-split blasting field tests of two lithologies of Slate and Dolomite were carried out for the double-line shaped energy-concentrated structure charge with the energy-gathering opening angle of 75°. In two different lithologies of Slate and Dolomite, under the condition that hole spacing was increased by 20%, the double-linear pre-split blasting effect of the shaped energy is better than that of the conventional pre-split blasting.
To explore the influences of the opening angle of bilinear shaped charge on the effective utilization rate and energy gathering effect, the boundary equation of effective shaped charge was deduced through the theory of instantaneous detonation hypothesis. The effective utilization ratio of the shaped charge structure blasting with 60°, 65°, 70°, 75°, and 80° shaped charge angles was analyzed using the visual implicit functions of SymPy package based on Python language. Through the physical model tests of single-hole Plexiglas and double-hole cement mortar, the crack formation law of pre-cracked holes with different energy-gathering opening angles was studied. Using the LS-DYNA numerical simulation software, five numerical models with energy-gathered opening angles of 60°, 65°, 70°, 75°, and 80° were established to reveal the penetration process of the bilinear energy-gathered structure charge jet and the stress evolution law of the rock unit on the blast-hole wall with different energy-gathered opening angles. The research results show that the effective utilization ratio of the shaped explosives is the highest when the energy-gathered opening angle is 75°. The pre-split hole formation effect when the opening angle of the energy-concentrating groove of the shaped charge is 75° is better than that when the opening angle is 60°, and the stress concentration effect and penetration depth along the direction of the energy-concentrating groove are the best, and the rock unit on the blast-hole wall reaches the peak stress first. The pre-split blasting field tests of two lithologies of Slate and Dolomite were carried out for the double-line shaped energy-concentrated structure charge with the energy-gathering opening angle of 75°. In two different lithologies of Slate and Dolomite, under the condition that hole spacing was increased by 20%, the double-linear pre-split blasting effect of the shaped energy is better than that of the conventional pre-split blasting.
2023, 43(2): 025401.
doi: 10.11883/bzycj-2022-0174
Abstract:
By using a self-designed 5.00-m-long duct with a cross-section of 0.30 m × 0.30 m, a seris of experiments were performed on premixed hydrogen-air gases in which volume fraction of hydrogen was 30%. And the effects of vent burst pressure (pv) on the flame propagation and pressure-time histories in the duct were experimentally iveatigated. The explosion flames were recorded by a high-speed camera at a frequency of 2.5 kHz. Five piezoelectric pressure transducers were employed to record the internal and external overpressure. The duct had been evacuated using a vacuum pump before the experiment, and the premixed hydrogen-air gases with volume fraction of 30% was prepared according to Dalton’s law of partial pressure. The variation of the vent burst pressure was achieved by changing the thickness of the aluminum foil which was used as vent cover. The results show that the first three stages of the flame structure in the duct are hemispherical, finger-shaped and tulip flame, respectively. pv has a significant effect on the structure of tulip flame and its subsequent development. Three pressure peaks (pb, pout, pext) can be distinguished from the pressure-time histories monitored by the pressure transducer near the vent, corresponding to three different generation mechanisms: burst of the aluminum film, venting of burned mixtures, and the external explosion, respectively. The three pressure peaks increase with an increase in pv. pb is the dominant pressure peak in most cases. The maximum internal overpressure increases as pv increases, and the position where the maximum internal overpressure was measured depended on pv. The maximum internal overpressure was obtained at the center of the duct (PT2) when pv≤42 kPa, but near the open end of the duct (PT3) if pv>42 kPa. When the flame reached the vent, it ejected from the vent and then ignited the external combustible cloud. Therefore, the external explosion is triggered. pv significantly affects the flame evolution outside the duct, but there is no significant difference in the maximum length of the external flame at various pv. A non-monotonic trend between the maximum external overpressure and pv was observed.
By using a self-designed 5.00-m-long duct with a cross-section of 0.30 m × 0.30 m, a seris of experiments were performed on premixed hydrogen-air gases in which volume fraction of hydrogen was 30%. And the effects of vent burst pressure (pv) on the flame propagation and pressure-time histories in the duct were experimentally iveatigated. The explosion flames were recorded by a high-speed camera at a frequency of 2.5 kHz. Five piezoelectric pressure transducers were employed to record the internal and external overpressure. The duct had been evacuated using a vacuum pump before the experiment, and the premixed hydrogen-air gases with volume fraction of 30% was prepared according to Dalton’s law of partial pressure. The variation of the vent burst pressure was achieved by changing the thickness of the aluminum foil which was used as vent cover. The results show that the first three stages of the flame structure in the duct are hemispherical, finger-shaped and tulip flame, respectively. pv has a significant effect on the structure of tulip flame and its subsequent development. Three pressure peaks (pb, pout, pext) can be distinguished from the pressure-time histories monitored by the pressure transducer near the vent, corresponding to three different generation mechanisms: burst of the aluminum film, venting of burned mixtures, and the external explosion, respectively. The three pressure peaks increase with an increase in pv. pb is the dominant pressure peak in most cases. The maximum internal overpressure increases as pv increases, and the position where the maximum internal overpressure was measured depended on pv. The maximum internal overpressure was obtained at the center of the duct (PT2) when pv≤42 kPa, but near the open end of the duct (PT3) if pv>42 kPa. When the flame reached the vent, it ejected from the vent and then ignited the external combustible cloud. Therefore, the external explosion is triggered. pv significantly affects the flame evolution outside the duct, but there is no significant difference in the maximum length of the external flame at various pv. A non-monotonic trend between the maximum external overpressure and pv was observed.
2023, 43(2): 025402.
doi: 10.11883/bzycj-2021-0531
Abstract:
The shock waves and flame produced by explosions of methane (CH4) and other combustible gas explosion can cause huge casualties and property damage. Therefore, the explosion-proof isolating technologies have always been a hotspot in the fields of industrial explosion protection. Foamed metal has attracted attention as a new type of explosion-isolating material which can simultaneously block the propagation of gas explosion shock waves and flame waves. Its explosion-isolating performance is a key factor affecting its application. However, there are few researches on improving the explosion-isolating performances of materials by changing the overall structures of foamed metals. A new method was proposed to change the structure of the blast front of a foamed metal and increase the contact area of the blast front with the explosion flame, so as to improve the flame-proof performance of the foamed metal. In this experiment, the experimental material with the thickness of 20 mm was prepared by wire cutting. Under the premise of the foundation thickness of 15 mm, the explosive effect surface was prepared into serrated ripples with the thickness of 5 mm and the angles of 30°, 60° and 90°. The processed foamed metal materials with different explosive effect surfaces were installed in the diffusion pipe near the end of the experimental equipment. The sensors placed at different positions and with different distances were used to collect the relevant data, and thereby the attenuation ratios of explosion overpressure, flame propagation velocity and flame temperature were calculated. The explosion-proof performances of the foamed metal with different saw tooth angles were evaluated by combining the explosion-extinguishing parameters. The results show that under the premise of the same thickness, the increase of a certain zigzag wave on the explosive effect surface of the material will improve the overall isolating explosion performance. The attenuation ratios of explosion overpressure, flame velocity, and flame temperature increase with the decrease of the sawtooth angle. When the front surface of the foamed metal has a sawtooth of 30°, the attenuation ratios of explosion overpressure, flame velocity, and flame temperature are 74.0%, 76.18%, and 91.93%, respectively. The explosion overpressure decay rate is 30.76 MPa/s, and the explosion is extinguished at the rear end of the material. The quenching parameter at the rear-end of the material is 17.68 MPa·℃, and the isolating explosion effect is better.
The shock waves and flame produced by explosions of methane (CH4) and other combustible gas explosion can cause huge casualties and property damage. Therefore, the explosion-proof isolating technologies have always been a hotspot in the fields of industrial explosion protection. Foamed metal has attracted attention as a new type of explosion-isolating material which can simultaneously block the propagation of gas explosion shock waves and flame waves. Its explosion-isolating performance is a key factor affecting its application. However, there are few researches on improving the explosion-isolating performances of materials by changing the overall structures of foamed metals. A new method was proposed to change the structure of the blast front of a foamed metal and increase the contact area of the blast front with the explosion flame, so as to improve the flame-proof performance of the foamed metal. In this experiment, the experimental material with the thickness of 20 mm was prepared by wire cutting. Under the premise of the foundation thickness of 15 mm, the explosive effect surface was prepared into serrated ripples with the thickness of 5 mm and the angles of 30°, 60° and 90°. The processed foamed metal materials with different explosive effect surfaces were installed in the diffusion pipe near the end of the experimental equipment. The sensors placed at different positions and with different distances were used to collect the relevant data, and thereby the attenuation ratios of explosion overpressure, flame propagation velocity and flame temperature were calculated. The explosion-proof performances of the foamed metal with different saw tooth angles were evaluated by combining the explosion-extinguishing parameters. The results show that under the premise of the same thickness, the increase of a certain zigzag wave on the explosive effect surface of the material will improve the overall isolating explosion performance. The attenuation ratios of explosion overpressure, flame velocity, and flame temperature increase with the decrease of the sawtooth angle. When the front surface of the foamed metal has a sawtooth of 30°, the attenuation ratios of explosion overpressure, flame velocity, and flame temperature are 74.0%, 76.18%, and 91.93%, respectively. The explosion overpressure decay rate is 30.76 MPa/s, and the explosion is extinguished at the rear end of the material. The quenching parameter at the rear-end of the material is 17.68 MPa·℃, and the isolating explosion effect is better.
