2020 Vol. 40, No. 10
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2020, 40(10): 105101.
doi: 10.11883/bzycj-2020-0020
Abstract:
The calculation method based on the energy method for resisting perforation to the SC walls with tied bars was discussed. Based on the perforation mechanism of missile impacting on the SC walls, the dissipated energy was divided into four parts: the energy dissipated by the front and rear steel plates, the energy dissipated by internal concrete and tied bars, and a practical calculation formula of preventing perforation was proposed. The perforation velocity and the residual velocity of the SC walls with tied bars can be calculated by the practical calculation formula when the related parameters of the materials and geometry about the missile and SC walls are known, thus avoiding complex impacting numerical analysis of dynamic time history. In order to verify the reliability of the formula, the results calculated through the practical formula were compared with the existing test data, as well as the dynamic finite element (FE) analysis results. The perforation state of the SC walls can be judged by the practical calculation formula concretely, and the residual velocities of the missile given by the formula are in good agreement with the test results. To further verify the application extent of the formula, the FE models about 10 cases of an aircraft engine impacting on the SC walls were established, and the solid FE models and the front closed cylindrical shell FE models of the aircraft engine were described, respectively. The results calculated through the practical formula were compared with the 10 cases of the aircraft engine impacting on the SC wall. It indicates that the deviation value of one case is slightly more than 10%. In other cases, the deviation values are all less than 10%. The accuracy and effectiveness of the proposed method can be verified.
The calculation method based on the energy method for resisting perforation to the SC walls with tied bars was discussed. Based on the perforation mechanism of missile impacting on the SC walls, the dissipated energy was divided into four parts: the energy dissipated by the front and rear steel plates, the energy dissipated by internal concrete and tied bars, and a practical calculation formula of preventing perforation was proposed. The perforation velocity and the residual velocity of the SC walls with tied bars can be calculated by the practical calculation formula when the related parameters of the materials and geometry about the missile and SC walls are known, thus avoiding complex impacting numerical analysis of dynamic time history. In order to verify the reliability of the formula, the results calculated through the practical formula were compared with the existing test data, as well as the dynamic finite element (FE) analysis results. The perforation state of the SC walls can be judged by the practical calculation formula concretely, and the residual velocities of the missile given by the formula are in good agreement with the test results. To further verify the application extent of the formula, the FE models about 10 cases of an aircraft engine impacting on the SC walls were established, and the solid FE models and the front closed cylindrical shell FE models of the aircraft engine were described, respectively. The results calculated through the practical formula were compared with the 10 cases of the aircraft engine impacting on the SC wall. It indicates that the deviation value of one case is slightly more than 10%. In other cases, the deviation values are all less than 10%. The accuracy and effectiveness of the proposed method can be verified.
2020, 40(10): 105201.
doi: 10.11883/bzycj-2019-0445
Abstract:
Based on the field test of environmental vibration characteristics of subway tunnel millisecond delay blasting, considering the irregular characteristics of blasting load, a modified Davidenkov constitutive model based on asymmetric loading and unloading criterion is used to describe the dynamic nonlinear characteristics of the site soil. The transient air shock wave generated by the internal explosion on the surface of cylindrical blast hole is simulated by improving the Friedlander equation. And a three-dimensional refined finite element model of ground-blast-source system, involving the blast wave input and finite/infinite element coupling boundary, is realized. The effectiveness of the model method is verified by comparing with in-situ testing data. The environmental vibration features induced by 50 ms delay blasting and instantaneous blasting are numerically simulated. It is found that millisecond delay blasting can not only effectively reduce the surface peak vibration velocity, but also significantly change the frequency spectrum characteristics of surface vibration. The frequency band of surface vibration produced by millisecond delay blasting is relatively concentrated, which has a significant effect on dispersing blasting vibration energy. Moreover, the main frequency of surface velocity response is higher, which is far away from the natural frequency of building structure, it can significantly reduce the structural vibration level of adjacent buildings caused by blasting construction. The research results reveal the vibration characteristics and vibration reduction mechanism of millisecond delay blasting environment, which can provide scientific basis and reference for blasting construction of subway tunnel in complex urban environment.
Based on the field test of environmental vibration characteristics of subway tunnel millisecond delay blasting, considering the irregular characteristics of blasting load, a modified Davidenkov constitutive model based on asymmetric loading and unloading criterion is used to describe the dynamic nonlinear characteristics of the site soil. The transient air shock wave generated by the internal explosion on the surface of cylindrical blast hole is simulated by improving the Friedlander equation. And a three-dimensional refined finite element model of ground-blast-source system, involving the blast wave input and finite/infinite element coupling boundary, is realized. The effectiveness of the model method is verified by comparing with in-situ testing data. The environmental vibration features induced by 50 ms delay blasting and instantaneous blasting are numerically simulated. It is found that millisecond delay blasting can not only effectively reduce the surface peak vibration velocity, but also significantly change the frequency spectrum characteristics of surface vibration. The frequency band of surface vibration produced by millisecond delay blasting is relatively concentrated, which has a significant effect on dispersing blasting vibration energy. Moreover, the main frequency of surface velocity response is higher, which is far away from the natural frequency of building structure, it can significantly reduce the structural vibration level of adjacent buildings caused by blasting construction. The research results reveal the vibration characteristics and vibration reduction mechanism of millisecond delay blasting environment, which can provide scientific basis and reference for blasting construction of subway tunnel in complex urban environment.
2020, 40(10): 102101.
doi: 10.11883/bzycj-2019-0416
Abstract:
In order to investigate the closed explosion and venting characteristics of gasoline-air mixture, two kinds of explosion modes were studied by using a visualized square tube, and numerical simulation was carried out based on the wall-adapting local eddy-viscosity (WALE) model and Zimont premixed flame model. The results show the followings. (1) The number of the peaks on the overpressure time series curve for the vented explosion is greater than that for the closed explosion, and there is a violent oscillation similar to a simple harmonic vibration on the overpressure time series curve of the vented explosion, while the characteristic parameters of explosion overpressure in the closed explosion are significantly higher than those in the vented explosion. (2) The maximum flame propagation speed in the closed explosion is significantly lower than that in the vented explosion, but the former reaches the maximum at the beginning of flame propagation, while the latter reaches the maximum at the end of flame propagation. (3) Tulip-shaped flame appears in the closed explosion condition, while mushroom-shaped flame appears in the venting condition. The formation of the tulip-shaped flame is related to the coupling effects of flame front, flow field and dynamic pressure of flow field in the pipe, while the mushroom-shaped flame is caused by the combined action of turbulence and baroclinic effect in the external flow field.
In order to investigate the closed explosion and venting characteristics of gasoline-air mixture, two kinds of explosion modes were studied by using a visualized square tube, and numerical simulation was carried out based on the wall-adapting local eddy-viscosity (WALE) model and Zimont premixed flame model. The results show the followings. (1) The number of the peaks on the overpressure time series curve for the vented explosion is greater than that for the closed explosion, and there is a violent oscillation similar to a simple harmonic vibration on the overpressure time series curve of the vented explosion, while the characteristic parameters of explosion overpressure in the closed explosion are significantly higher than those in the vented explosion. (2) The maximum flame propagation speed in the closed explosion is significantly lower than that in the vented explosion, but the former reaches the maximum at the beginning of flame propagation, while the latter reaches the maximum at the end of flame propagation. (3) Tulip-shaped flame appears in the closed explosion condition, while mushroom-shaped flame appears in the venting condition. The formation of the tulip-shaped flame is related to the coupling effects of flame front, flow field and dynamic pressure of flow field in the pipe, while the mushroom-shaped flame is caused by the combined action of turbulence and baroclinic effect in the external flow field.
2020, 40(10): 102102.
doi: 10.11883/bzycj-2019-0481
Abstract:
The impact of nozzle configuration on the performance of rotating detonation with different equivalence ratios was studied through tests on rotating detonating engines (RDEs) without a nozzle and with a convergent nozzle, a divergent nozzle and a convergent-divergent nozzle, respectively. Pre-combustion cracked kerosene and 30% oxygen-enriched air were used as the fuel and oxidizer, respectively. The results show that the rotating detonation engines can operate smoothly with the equivalence ratio ranging from 0.73 to 1.30. Three operating modes including single wave, unstable two counter-rotating waves and stable two counter-rotating waves were found in the experiments. The nozzle configurations strongly affect the mode transition and the detonation wave velocity. The convergent nozzle and the convergent-divergent nozzle can promote the generation of new detonation waves, making the working modes mainly to be two counter-rotating waves, while the detonation mainly operates in the single wave mode with a divergent nozzle installed. The results further show that the maximum propagating velocity deviates from the stoichiometric ratio when the convergent or convergent-divergent nozzles are installed, and the convergent-divergent nozzle can increase the detonation wave velocity.
The impact of nozzle configuration on the performance of rotating detonation with different equivalence ratios was studied through tests on rotating detonating engines (RDEs) without a nozzle and with a convergent nozzle, a divergent nozzle and a convergent-divergent nozzle, respectively. Pre-combustion cracked kerosene and 30% oxygen-enriched air were used as the fuel and oxidizer, respectively. The results show that the rotating detonation engines can operate smoothly with the equivalence ratio ranging from 0.73 to 1.30. Three operating modes including single wave, unstable two counter-rotating waves and stable two counter-rotating waves were found in the experiments. The nozzle configurations strongly affect the mode transition and the detonation wave velocity. The convergent nozzle and the convergent-divergent nozzle can promote the generation of new detonation waves, making the working modes mainly to be two counter-rotating waves, while the detonation mainly operates in the single wave mode with a divergent nozzle installed. The results further show that the maximum propagating velocity deviates from the stoichiometric ratio when the convergent or convergent-divergent nozzles are installed, and the convergent-divergent nozzle can increase the detonation wave velocity.
2020, 40(10): 102201.
doi: 10.11883/bzycj-2019-0398
Abstract:
The scattering of steady-state shear horizontal (SH) guided waves from the elastic strip media with multiple semi-cylindrical depressions on the surface was studied and the analytical solution was given. Firstly, the guided wave expansion method was used to construct SH guided waves. Then, the scattered waves satisfying the zero-stress boundary conditions of the upper and lower surfaces in the strip were constructed by employing the repeated image method. Finally, according to the condition that the shear stress of the edge of the depression is zero, the definite solution equation was derived. The accuracy of repeated image method, the dynamic stress concentration around a depression and the displacement amplitude at the upper and lower boundaries were analyzed by examples. The numerical results show that when there is only one depression, the incident waves with middle and high frequency and the strip with small thickness cause higher dynamic stress concentration around the depression, and the maximum displacement amplitude of the upper boundary occurs near the incident surface of the depression. When there are two depressions, in most cases, the second depression amplifies the dynamic stress concentration around the first depression. And in the ideal elastic strip, even if the two depressions are infinitely far apart, the influence between them still exists.
The scattering of steady-state shear horizontal (SH) guided waves from the elastic strip media with multiple semi-cylindrical depressions on the surface was studied and the analytical solution was given. Firstly, the guided wave expansion method was used to construct SH guided waves. Then, the scattered waves satisfying the zero-stress boundary conditions of the upper and lower surfaces in the strip were constructed by employing the repeated image method. Finally, according to the condition that the shear stress of the edge of the depression is zero, the definite solution equation was derived. The accuracy of repeated image method, the dynamic stress concentration around a depression and the displacement amplitude at the upper and lower boundaries were analyzed by examples. The numerical results show that when there is only one depression, the incident waves with middle and high frequency and the strip with small thickness cause higher dynamic stress concentration around the depression, and the maximum displacement amplitude of the upper boundary occurs near the incident surface of the depression. When there are two depressions, in most cases, the second depression amplifies the dynamic stress concentration around the first depression. And in the ideal elastic strip, even if the two depressions are infinitely far apart, the influence between them still exists.
2020, 40(10): 103101.
doi: 10.11883/bzycj-2019-0479
Abstract:
Due to the excavation unloading effect and the amplitude attenuation of stress wave, the rock masses locating the different distances away from the blasting source are subjected to different geostress and impact loadings during the blasting excavation of underground rock mass. The construction of relationship between rock dynamic failure properties with impact loadings has more important engineering practical significance compared with representating them with strain rate. In order to investigate the effect of the values of impact loading and the geostress on the characteristics of rock failure and energy dissipation, impact experiments of red sandstone were carried out with a modified split Hopkinson pressure bar testing system, the impact velocities and axial static stresses were set seven levels, respectively. The effects of impact velocity on the failure mode and mechanism of red sandstone under different axial static stresses were researched based on the broken rock specimens. By analyzing the energy values of stress waves under different experimental conditions, the effects of the impact velocity and the axial static stress on energy dissipation of red sandstone were investigated. The fragment fractal dimensions of red sandstone under different impact velocities and axial static stresses were studied based on the sieve test results of the broken specimens. The results show that the increase of impact velocity will aggravate the destroy degree of the red sandstone. The main part after macroscopic failure remains a circular cylinder when a red sandstone specimen is subjected to impact loading and no axial static stress, the failure of the specimen is resulted from its insufficiency of resistance to tensile deformation; but the main part after macroscopic failure represents a hourglass shape when the specimen is under coupled axial static stress and impact loading, the failure mechanism is mixed tension and shear fracture. The dissipation energy of the red sandstone increases in a quadratic function with increasing the impact velocity, the higher the axial static stress, the smaller the increasing amplitude. With the increase of impact velocity, the fractal dimension of the red sandstone increases from zero gradually. For a rock specimen subjected to specific axial static stress, there is a critical impact velocity which signifies that the fractal dimension of the specimen will change from zero to greater than zero, and the critical impact velocity increases first and then decreases with the increase of axial static stress.
Due to the excavation unloading effect and the amplitude attenuation of stress wave, the rock masses locating the different distances away from the blasting source are subjected to different geostress and impact loadings during the blasting excavation of underground rock mass. The construction of relationship between rock dynamic failure properties with impact loadings has more important engineering practical significance compared with representating them with strain rate. In order to investigate the effect of the values of impact loading and the geostress on the characteristics of rock failure and energy dissipation, impact experiments of red sandstone were carried out with a modified split Hopkinson pressure bar testing system, the impact velocities and axial static stresses were set seven levels, respectively. The effects of impact velocity on the failure mode and mechanism of red sandstone under different axial static stresses were researched based on the broken rock specimens. By analyzing the energy values of stress waves under different experimental conditions, the effects of the impact velocity and the axial static stress on energy dissipation of red sandstone were investigated. The fragment fractal dimensions of red sandstone under different impact velocities and axial static stresses were studied based on the sieve test results of the broken specimens. The results show that the increase of impact velocity will aggravate the destroy degree of the red sandstone. The main part after macroscopic failure remains a circular cylinder when a red sandstone specimen is subjected to impact loading and no axial static stress, the failure of the specimen is resulted from its insufficiency of resistance to tensile deformation; but the main part after macroscopic failure represents a hourglass shape when the specimen is under coupled axial static stress and impact loading, the failure mechanism is mixed tension and shear fracture. The dissipation energy of the red sandstone increases in a quadratic function with increasing the impact velocity, the higher the axial static stress, the smaller the increasing amplitude. With the increase of impact velocity, the fractal dimension of the red sandstone increases from zero gradually. For a rock specimen subjected to specific axial static stress, there is a critical impact velocity which signifies that the fractal dimension of the specimen will change from zero to greater than zero, and the critical impact velocity increases first and then decreases with the increase of axial static stress.
2020, 40(10): 103102.
doi: 10.11883/bzycj-2019-0475
Abstract:
The deformation mode and energy absorption property of aircraft sub-structure are of great significance for occupant protection during aircraft crash. The load transfer and failure mode of joint structures are one of important factors affecting aircraft structural deformation. This paper tries to study the dynamic failure behavior of aviation of hi-lock bolt joints under impact loads. Based on the shear resistance hi-lock bolt, the single-bolt single lap joints with two kinds of base metals (2024-T3 and 7050-T7451) were designed. The dynamic tensile tests of the joints were carried out by a high-speed material testing machine under four loading velocities, 0.01、0.10、1.00 and 3.00 m/s. The dynamic response, the ultimate load, the energy absorption and the failure mode of hi-lock bolt joints were measured and analyzed. The results show that the failure mode of the joints is greatly affected by the material strength of the base metal and the high lock bolt / nut, but less affected by the loading speed; as increasing the speed from 0.01 m/s to 3 m/s, the ultimate load and the energy absorption of 2024-T3 joints increase by 2.17% and 34.43% respectively, and the ultimate load and the energy absorption of 7050-T7451 joints increase by 5.53% and 6.58% respectively.
The deformation mode and energy absorption property of aircraft sub-structure are of great significance for occupant protection during aircraft crash. The load transfer and failure mode of joint structures are one of important factors affecting aircraft structural deformation. This paper tries to study the dynamic failure behavior of aviation of hi-lock bolt joints under impact loads. Based on the shear resistance hi-lock bolt, the single-bolt single lap joints with two kinds of base metals (2024-T3 and 7050-T7451) were designed. The dynamic tensile tests of the joints were carried out by a high-speed material testing machine under four loading velocities, 0.01、0.10、1.00 and 3.00 m/s. The dynamic response, the ultimate load, the energy absorption and the failure mode of hi-lock bolt joints were measured and analyzed. The results show that the failure mode of the joints is greatly affected by the material strength of the base metal and the high lock bolt / nut, but less affected by the loading speed; as increasing the speed from 0.01 m/s to 3 m/s, the ultimate load and the energy absorption of 2024-T3 joints increase by 2.17% and 34.43% respectively, and the ultimate load and the energy absorption of 7050-T7451 joints increase by 5.53% and 6.58% respectively.
2020, 40(10): 103103.
doi: 10.11883/bzycj-2019-0249
Abstract:
In order to reveal the mechanical properties of a polyvinyl chloride elastomer under static and dynamic loading, the stress-strain curves of the polyvinyl chloride elastomer at six different strain rates (0.001, 0.01, 0.1, 1 510, 2 260 and 3 000 s−1) were obtained by using a universal material testing machine and a modified split Hopkinson pressure bar experimental device. The shaping effects of the three shaper materials including copper, coated paper and plumbum were compared by using the yield strength as the optimized parameter of the shapers. It is difficult to obtain a unified parametric constitutive expression directly using the original ZWT nonlinear viscoelastic constitutive model, and the constitutive model is less efficient in describing the mechanical properties of the materials under static and dynamic loading. Therefore, the modified ZWT nonlinear viscoelastic constitutive model was used to describe the mechanical properties of the material under static and dynamic loading. The results show that the polyvinyl chloride elastomer has a strain-rate effect and significant hyperelastic properties under static load. It exhibits a more obvious strain-rate effect and strong resistance to deformation under dynamic loading, and the mechanical behaviors under static and dynamic loading are greatly affected by the strain histories. Coated paper has the best shaping effect among the three shaper materials. The modified ZWT nonlinear viscoelastic constitutive model can obtain constitutive expressions with uniform parameters, and the fitting results at various strain rates are in good agreement with the experimental results.
In order to reveal the mechanical properties of a polyvinyl chloride elastomer under static and dynamic loading, the stress-strain curves of the polyvinyl chloride elastomer at six different strain rates (0.001, 0.01, 0.1, 1 510, 2 260 and 3 000 s−1) were obtained by using a universal material testing machine and a modified split Hopkinson pressure bar experimental device. The shaping effects of the three shaper materials including copper, coated paper and plumbum were compared by using the yield strength as the optimized parameter of the shapers. It is difficult to obtain a unified parametric constitutive expression directly using the original ZWT nonlinear viscoelastic constitutive model, and the constitutive model is less efficient in describing the mechanical properties of the materials under static and dynamic loading. Therefore, the modified ZWT nonlinear viscoelastic constitutive model was used to describe the mechanical properties of the material under static and dynamic loading. The results show that the polyvinyl chloride elastomer has a strain-rate effect and significant hyperelastic properties under static load. It exhibits a more obvious strain-rate effect and strong resistance to deformation under dynamic loading, and the mechanical behaviors under static and dynamic loading are greatly affected by the strain histories. Coated paper has the best shaping effect among the three shaper materials. The modified ZWT nonlinear viscoelastic constitutive model can obtain constitutive expressions with uniform parameters, and the fitting results at various strain rates are in good agreement with the experimental results.
2020, 40(10): 103301.
doi: 10.11883/bzycj-2019-0428
Abstract:
Under the threat of earth penetration weapons (EPWs), the protective fortification should be further enhanced. The bursting layer is commonly used to increase the protective strength of the fortification. A hard spherical aggregate (aggregate for short) is often used to construct the bursting layer. The mechanism of a high-speed projectile into the aggregate was studied, and the dominant factors were investigated in the present paper. Based on the dynamic spherical cavity expansion theory, the model for the drag force of the projectile was constructed considering the free surface effect of the target and the strength of the aggregate. Detaching the projectile response from the target, the resistant force of the target was loaded on the projectile surface as a force boundary. The deformation and movement of the projectile was numerically researched when it obliquely penetrated into the high-strength concrete target including aggregates. The influences of aggregate strength, location and dimensions upon the projectile response were investigated. It indicates that the sheltering effect of the aggregate is mainly dominated by the gesture of the projectile impacting on the aggregate. However, the variation of the gesture does not follow a distinct law. It is shown that the higher the strength of the aggregate, the better the sheltering effect of the aggregate. The main sheltering mechanism transforms from ballistic trajectory deflection into combination of ballistic trajectory deflection and augment of the drag force of the projectile, when the radius of the aggregate increases from 1 time of projectile diameter to 10 times. Based on the above analyses, for the bursting layer made of one layer, the diameter of the aggregate should be larger than 10 times of the projectile diameter. However, when the size of the aggregate decreases, the bursting layers should be constructed by multiple and staggered layers of aggregates with total layer thickness larger than 10 times of the projectile diameter, in order to achieve the effective sheltering effect.
Under the threat of earth penetration weapons (EPWs), the protective fortification should be further enhanced. The bursting layer is commonly used to increase the protective strength of the fortification. A hard spherical aggregate (aggregate for short) is often used to construct the bursting layer. The mechanism of a high-speed projectile into the aggregate was studied, and the dominant factors were investigated in the present paper. Based on the dynamic spherical cavity expansion theory, the model for the drag force of the projectile was constructed considering the free surface effect of the target and the strength of the aggregate. Detaching the projectile response from the target, the resistant force of the target was loaded on the projectile surface as a force boundary. The deformation and movement of the projectile was numerically researched when it obliquely penetrated into the high-strength concrete target including aggregates. The influences of aggregate strength, location and dimensions upon the projectile response were investigated. It indicates that the sheltering effect of the aggregate is mainly dominated by the gesture of the projectile impacting on the aggregate. However, the variation of the gesture does not follow a distinct law. It is shown that the higher the strength of the aggregate, the better the sheltering effect of the aggregate. The main sheltering mechanism transforms from ballistic trajectory deflection into combination of ballistic trajectory deflection and augment of the drag force of the projectile, when the radius of the aggregate increases from 1 time of projectile diameter to 10 times. Based on the above analyses, for the bursting layer made of one layer, the diameter of the aggregate should be larger than 10 times of the projectile diameter. However, when the size of the aggregate decreases, the bursting layers should be constructed by multiple and staggered layers of aggregates with total layer thickness larger than 10 times of the projectile diameter, in order to achieve the effective sheltering effect.
2020, 40(10): 104101.
doi: 10.11883/bzycj-2020-0041
Abstract:
Aimed to the recovery of expansive metal cylindrical shells subjected to internal explosive loading, the freezing recovery test method was developed to realize the freezing recovery of the metallic cylindrical shells at different moments after detonation. Based on the integrated shell, three improved structures were proposed, and the expansion and fracture processes of the four cylindrical shell structures under internal explosive loading were numerically simulated. It was found that the two-stage shell was the most beneficial to reduce the influence of the non-initiation end on the middle shell expected to be recovered. According to the selected optimal shell structure and the shape expansion characteristics of metal cylindrical shells at different moments after detonation, the freezing recovery devices matching with the shells were designed, and the freezing recovery tests were carried out. The test results show that the developed freezing recovery test method can realize the recovery of the expanded metallic cylindrical shells. The axial and radial dimensions of the recovery shells are in good agreement with the ideal design values, and the overall error can be controlled within 10%.
Aimed to the recovery of expansive metal cylindrical shells subjected to internal explosive loading, the freezing recovery test method was developed to realize the freezing recovery of the metallic cylindrical shells at different moments after detonation. Based on the integrated shell, three improved structures were proposed, and the expansion and fracture processes of the four cylindrical shell structures under internal explosive loading were numerically simulated. It was found that the two-stage shell was the most beneficial to reduce the influence of the non-initiation end on the middle shell expected to be recovered. According to the selected optimal shell structure and the shape expansion characteristics of metal cylindrical shells at different moments after detonation, the freezing recovery devices matching with the shells were designed, and the freezing recovery tests were carried out. The test results show that the developed freezing recovery test method can realize the recovery of the expanded metallic cylindrical shells. The axial and radial dimensions of the recovery shells are in good agreement with the ideal design values, and the overall error can be controlled within 10%.
2020, 40(10): 104201.
doi: 10.11883/bzycj-2019-0478
Abstract:
To investigate the influence of water depth on the evolution characteristics of the muzzle flow field of an underwater submerged launched ballistic gun, a two-dimensional axisymmetric transient muzzle flow field model was established. The fluid volume function multiphase flow model, standard k-ε turbulence model, Schnerr-Sauer cavitation model, combined with dynamic grid and user-defined function technology, are used to numerically simulate the evolution process of underwater muzzle flow field. An underwater visualized shooting experimental platform for a ballistic gun was built. The evolution process of the muzzle flow field when the 12.7 mm ballistic gun was fully submerged in water was observed, and the rationality of the numerical model was verified. Based on this, the evolution characteristics of the muzzle flow field at different water depths (h=1−100 m) are analyzed and compared. Through comparison, it is found that within the range of the muzzle flow field, the projectile displacement meets the exponential function with time under different water depths; the deeper the water, the longer it takes for the typical wave structure of the muzzle flow field to form, and the lower the peak temperature and pressure of the gas at the axial Mach disc, the smaller the pressure oscillation amplitude, the faster it stabilizes. but in the radial direction, the deeper the water depth, the longer the duration of pressure oscillations.
To investigate the influence of water depth on the evolution characteristics of the muzzle flow field of an underwater submerged launched ballistic gun, a two-dimensional axisymmetric transient muzzle flow field model was established. The fluid volume function multiphase flow model, standard k-ε turbulence model, Schnerr-Sauer cavitation model, combined with dynamic grid and user-defined function technology, are used to numerically simulate the evolution process of underwater muzzle flow field. An underwater visualized shooting experimental platform for a ballistic gun was built. The evolution process of the muzzle flow field when the 12.7 mm ballistic gun was fully submerged in water was observed, and the rationality of the numerical model was verified. Based on this, the evolution characteristics of the muzzle flow field at different water depths (h=1−100 m) are analyzed and compared. Through comparison, it is found that within the range of the muzzle flow field, the projectile displacement meets the exponential function with time under different water depths; the deeper the water, the longer it takes for the typical wave structure of the muzzle flow field to form, and the lower the peak temperature and pressure of the gas at the axial Mach disc, the smaller the pressure oscillation amplitude, the faster it stabilizes. but in the radial direction, the deeper the water depth, the longer the duration of pressure oscillations.
2020, 40(10): 104202.
doi: 10.11883/bzycj-2019-0435
Abstract:
In the article a thermodynamically consistent diffuse interface model is proposed in order to numerically simulate the interaction between solid explosive detonation and compressible inert media. The chemical reaction of detonation course in solid explosive is simplified as the solid-phase reactant changing into the gas-phase product, thus the mixture within a control volume is regarded to be composed by three kinds of components: solid-phase reactant, gas-phase product and inert media, and all components are thought to be in mechanical equilibrium and thermal nonequilibrium because of their having distinct thermodynamic properties or equations of state. The starting point based on the energy conservation of the mixture and pressure equivalence among components within the control volume is adopted to derive the evolution equation for volume fraction of every component, in which the equation for energy conservation of the mixture is decomposed into a family of equations for energy conservation of the all components with the heat exchange resulting from thermal nonequilibrium. Thus, the governing equations of proposed diffuse interface model include: the conservation equation for mass of every component and the conservation equations for momentum and total energy of the mixture, and the evolution equations for volume fraction of every component and for pressure of the mixture. The important character of the present model is that the mass transfer due to chemical reaction and the heat exchange due to thermal nonequilibrium are involved. In this model, pressure is solved directly from the governing equations instead of computed next from the obtained conservative variables. The present model may apply to arbitrary expression of equation of state and allow for any number of inert media. The partially differential governing equations of the diffuse interface model are numerically solved by a temporal-spatial second-order Godunov-type finite volume scheme with wave propagation algorithm. From numerical examples, the proposed diffuse interface model can eliminate the unphysical oscillations near the material interfaces, and obtain the agreeable results with the physical mechanism.
In the article a thermodynamically consistent diffuse interface model is proposed in order to numerically simulate the interaction between solid explosive detonation and compressible inert media. The chemical reaction of detonation course in solid explosive is simplified as the solid-phase reactant changing into the gas-phase product, thus the mixture within a control volume is regarded to be composed by three kinds of components: solid-phase reactant, gas-phase product and inert media, and all components are thought to be in mechanical equilibrium and thermal nonequilibrium because of their having distinct thermodynamic properties or equations of state. The starting point based on the energy conservation of the mixture and pressure equivalence among components within the control volume is adopted to derive the evolution equation for volume fraction of every component, in which the equation for energy conservation of the mixture is decomposed into a family of equations for energy conservation of the all components with the heat exchange resulting from thermal nonequilibrium. Thus, the governing equations of proposed diffuse interface model include: the conservation equation for mass of every component and the conservation equations for momentum and total energy of the mixture, and the evolution equations for volume fraction of every component and for pressure of the mixture. The important character of the present model is that the mass transfer due to chemical reaction and the heat exchange due to thermal nonequilibrium are involved. In this model, pressure is solved directly from the governing equations instead of computed next from the obtained conservative variables. The present model may apply to arbitrary expression of equation of state and allow for any number of inert media. The partially differential governing equations of the diffuse interface model are numerically solved by a temporal-spatial second-order Godunov-type finite volume scheme with wave propagation algorithm. From numerical examples, the proposed diffuse interface model can eliminate the unphysical oscillations near the material interfaces, and obtain the agreeable results with the physical mechanism.
