2016 Vol. 36, No. 4
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2016, 36(4): 433-440.
doi: 10.11883/1001-1455(2016)04-0433-08
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In order to study the ballistic limits and damage properties of the basalt/Kevlar stuffed shields, hypervelocity impact tests were carried out by non-power two-stage light-gas gun facilities. The ballistic limit curves were fitted with the test data, and compared with those of the Nextel/Kevlar stuffed shields and the all-aluminum triple-wall shields with the same areal density. The results indicate that the protection property of the basalt/Kevlar stuffed shields is the same as that of the Nextel/Kevlar stuffed shields, and better than that of the all-aluminum triple-wall shields. Further, the hypervelocity impact damage properties of the first bumper, the stuffed layer, and the rear wall were investigated. The reasons were analyzed which caused the damage types of the bumpers different, and the protection mechanisms of the basalt/Kevlar stuffed shields were explored. The results show that the basalt fabrics broke the aluminum projectiles into pieces, and the Kevlar fabrics absorbed and dissipated the energy of the aluminum projectiles or debris clouds.
In order to study the ballistic limits and damage properties of the basalt/Kevlar stuffed shields, hypervelocity impact tests were carried out by non-power two-stage light-gas gun facilities. The ballistic limit curves were fitted with the test data, and compared with those of the Nextel/Kevlar stuffed shields and the all-aluminum triple-wall shields with the same areal density. The results indicate that the protection property of the basalt/Kevlar stuffed shields is the same as that of the Nextel/Kevlar stuffed shields, and better than that of the all-aluminum triple-wall shields. Further, the hypervelocity impact damage properties of the first bumper, the stuffed layer, and the rear wall were investigated. The reasons were analyzed which caused the damage types of the bumpers different, and the protection mechanisms of the basalt/Kevlar stuffed shields were explored. The results show that the basalt fabrics broke the aluminum projectiles into pieces, and the Kevlar fabrics absorbed and dissipated the energy of the aluminum projectiles or debris clouds.
2016, 36(4): 441-448.
doi: 10.11883/1001-1455(2016)04-0441-08
Abstract:
The detonation initiation distance for stoichiometric C2H4/O2 mixture gas in a narrow gap was experimentally studied at the initial pressure of 5.0-50.0 kPa. The channels were formed by the 10, 20, 30 mm×1.0 mm cross-sections and 1 220 mm long, respectively. the initiation positions were determined by the soot records and the high-speed digital imagings. The influence of initial pressure and gap width on detonation initiation distance was analyzed. The results indicate that: (1) initiation distance decreases with the increase of gap width at the initial pressure of 21.0-30.0 kPa; (2) with the increase of gap width, initiation distance initially decreases and then increases at the initial pressure of 35.0-42.5 kPa, and remains unchanged at the initial pressure of 45.0-50.0 kPa; (3) the non-dimensional change curves between detonation initiation distance and initial pressure are different corresponding to the three different gap widths.
The detonation initiation distance for stoichiometric C2H4/O2 mixture gas in a narrow gap was experimentally studied at the initial pressure of 5.0-50.0 kPa. The channels were formed by the 10, 20, 30 mm×1.0 mm cross-sections and 1 220 mm long, respectively. the initiation positions were determined by the soot records and the high-speed digital imagings. The influence of initial pressure and gap width on detonation initiation distance was analyzed. The results indicate that: (1) initiation distance decreases with the increase of gap width at the initial pressure of 21.0-30.0 kPa; (2) with the increase of gap width, initiation distance initially decreases and then increases at the initial pressure of 35.0-42.5 kPa, and remains unchanged at the initial pressure of 45.0-50.0 kPa; (3) the non-dimensional change curves between detonation initiation distance and initial pressure are different corresponding to the three different gap widths.
2016, 36(4): 449-456.
doi: 10.11883/1001-1455(2016)04-0449-08
Abstract:
On the basis of the three-wave theory and Whitham's method, the flow fields associated with regular reflection and Mach reflection in high explosives with waveshapers were investigated, and the relevant theoretical model for deriving the detonation configuration was proposed. The calculated results of pressure, flow velocity and triple point growth angle of Mach stem were presented and the Mach stem height was also determined based on the modified Whitham's method. The finite element code was used to numerically simulate the detonation processes of the high explosives with waveshapers. The shock initiation of the cylindrical charge was described by the Jones-Wilkins-Lee(JWL) and Lee-Travel models. The calculated results show that the Mach stem height increases with the propagation of detonation wave. The numerical results are consistent with the predictions based on the presented model, which shows that the analytical model provides reasonably accurate predictions of the Mach reflection process.
On the basis of the three-wave theory and Whitham's method, the flow fields associated with regular reflection and Mach reflection in high explosives with waveshapers were investigated, and the relevant theoretical model for deriving the detonation configuration was proposed. The calculated results of pressure, flow velocity and triple point growth angle of Mach stem were presented and the Mach stem height was also determined based on the modified Whitham's method. The finite element code was used to numerically simulate the detonation processes of the high explosives with waveshapers. The shock initiation of the cylindrical charge was described by the Jones-Wilkins-Lee(JWL) and Lee-Travel models. The calculated results show that the Mach stem height increases with the propagation of detonation wave. The numerical results are consistent with the predictions based on the presented model, which shows that the analytical model provides reasonably accurate predictions of the Mach reflection process.
2016, 36(4): 457-464.
doi: 10.11883/1001-1455(2016)04-0457-08
Abstract:
A series of experiments were conducted to study the factors influencing gas explosion venting in methane-air mixture explosion in linked vessels. For the linked vessels, the maximum explosion venting pressure in both the big vessel and the small vessel increases when the rupture disk bursting pressure and the dimensionless ratio of the vent area to the vessel volume decrease. At the same dimensionless ratio, the maximum explosion venting pressure in the secondary vessel increases with the pipe length regardless of the ignition occurring in the big or in the small vessel. The maximum explosion venting pressures in the primary and in the secondary vessels are higher than that in the single vessel for ignition in the big vessel without a rupture disk. However, when the pipe length is 0.45 m, the maximum explosion venting pressures in the primary and in the secondary vessel are lower than that in the single vessel for ignition occurring in the small vessel without a rupture disk. At the same dimensionless ratio of the vent area to the vessel volume, the maximum explosion venting pressure in the big vessel and that in the small one are close to each other when the pipe length is 0.45 m for explosion venting in linked vessels without a rupture disk. However, when the pipe length is 2.45 m, the maximum explosion venting pressure in the primary vessel is higher than that in the secondary vessel for ignition in the small vessel. When the pipe length is 4.45 m or 6.45 m, the maximum explosion venting pressure in the secondary vessel is higher than that in the primary vessel.
A series of experiments were conducted to study the factors influencing gas explosion venting in methane-air mixture explosion in linked vessels. For the linked vessels, the maximum explosion venting pressure in both the big vessel and the small vessel increases when the rupture disk bursting pressure and the dimensionless ratio of the vent area to the vessel volume decrease. At the same dimensionless ratio, the maximum explosion venting pressure in the secondary vessel increases with the pipe length regardless of the ignition occurring in the big or in the small vessel. The maximum explosion venting pressures in the primary and in the secondary vessels are higher than that in the single vessel for ignition in the big vessel without a rupture disk. However, when the pipe length is 0.45 m, the maximum explosion venting pressures in the primary and in the secondary vessel are lower than that in the single vessel for ignition occurring in the small vessel without a rupture disk. At the same dimensionless ratio of the vent area to the vessel volume, the maximum explosion venting pressure in the big vessel and that in the small one are close to each other when the pipe length is 0.45 m for explosion venting in linked vessels without a rupture disk. However, when the pipe length is 2.45 m, the maximum explosion venting pressure in the primary vessel is higher than that in the secondary vessel for ignition in the small vessel. When the pipe length is 4.45 m or 6.45 m, the maximum explosion venting pressure in the secondary vessel is higher than that in the primary vessel.
2016, 36(4): 465-471.
doi: 10.11883/1001-1455(2016)04-0465-07
Abstract:
The combustion-gas generator and liquid-filled cylindrical chamber are designed to study the expansion characteristics of annular four wall combustion-gas jets under high temperature and high pressure in a confined space. The expansion processes of Taylor cavities formed by combustion-gas jets are observed by means of a high-speed digital photographic system. It is shown that the irregular interface induced by the Kelvin-Helmholtz instability exists in the entire expansion process of the jets. The axial and radial displacements at different times are obtained from a series of expansion photographs of gas jets. The effects of the blasting injection pressure and the parameters of the nozzle structure on the expansion characteristics of the annular four wall combustion-gas jets are discussed. The experimental results indicate that, the larger the nozzle orifice area, the greater the axial expansion velocity of the wall jets in the prime stage. Meanwhile, the axial expansion velocity attenuates more quickly due to the effect of turbulent mixing and interference. The higher the blasting injection pressure, the earlier the four jets begin converging. Moreover, the axial expansion velocity of the wall jet increases substantially and the gas-liquid turbulent mixing effect becomes much stronger when the blasting injection pressure increases from 12 MPa to 20 MPa.
The combustion-gas generator and liquid-filled cylindrical chamber are designed to study the expansion characteristics of annular four wall combustion-gas jets under high temperature and high pressure in a confined space. The expansion processes of Taylor cavities formed by combustion-gas jets are observed by means of a high-speed digital photographic system. It is shown that the irregular interface induced by the Kelvin-Helmholtz instability exists in the entire expansion process of the jets. The axial and radial displacements at different times are obtained from a series of expansion photographs of gas jets. The effects of the blasting injection pressure and the parameters of the nozzle structure on the expansion characteristics of the annular four wall combustion-gas jets are discussed. The experimental results indicate that, the larger the nozzle orifice area, the greater the axial expansion velocity of the wall jets in the prime stage. Meanwhile, the axial expansion velocity attenuates more quickly due to the effect of turbulent mixing and interference. The higher the blasting injection pressure, the earlier the four jets begin converging. Moreover, the axial expansion velocity of the wall jet increases substantially and the gas-liquid turbulent mixing effect becomes much stronger when the blasting injection pressure increases from 12 MPa to 20 MPa.
2016, 36(4): 472-482.
doi: 10.11883/1001-1455(2016)04-0472-11
Abstract:
Tanking account of the mass conservation conditions, incompressible conditions and boundary conditions, this paper described the dynamic behaviors of the medium based on the plastic-rigid model and established the compatible dynamic velocity field in the plastic zone. In addition, utilizing the limit equilibrium theory, this paper derived the equations of material resistance to explosions in both the infinite and the semi-infinite medium. Combined with the initial and boundary conditions, the equations of motion can be solved and the critical depth can be obtained. Besides, this paper has obtained a dimensionless impact factor which reflects the integrated nature of explosive sources and media. The calculated results illustrated that the critical depth and the dimensionless impact factor have a proportional relationship. Finally, the comparative analysis of the empirical formulas with the derived equations proved that our calculation methods are valid and widely applicable.
Tanking account of the mass conservation conditions, incompressible conditions and boundary conditions, this paper described the dynamic behaviors of the medium based on the plastic-rigid model and established the compatible dynamic velocity field in the plastic zone. In addition, utilizing the limit equilibrium theory, this paper derived the equations of material resistance to explosions in both the infinite and the semi-infinite medium. Combined with the initial and boundary conditions, the equations of motion can be solved and the critical depth can be obtained. Besides, this paper has obtained a dimensionless impact factor which reflects the integrated nature of explosive sources and media. The calculated results illustrated that the critical depth and the dimensionless impact factor have a proportional relationship. Finally, the comparative analysis of the empirical formulas with the derived equations proved that our calculation methods are valid and widely applicable.
2016, 36(4): 483-490.
doi: 10.11883/1001-1455(2016)04-0483-08
Abstract:
By using a split Hopkinson pressure bar (SHPB) technique, impact experiments were carried out on the jointed rock specimens simulated by cement-based mortar specimens. The dynamic responses of the simulated jointed rock material with different joint angles at different strain rates were analyzed including stress-strain curve characteristics, failure modes, energy transmission and dissipation. The experimental results show that, with the increase of strain rate, the dynamic elastic moduli increase, and the specimens become more fragile. The peak intensity decreases with the increase of the joint angles whereas when the strain rate increases to a certain extent, the influence of the joint angles on the rock damage formation is no longer obvious. The incident energy, the reflective energy, the transmission energy, and the dissipation energy of the different specimens nonlinearly increase with the increase of the strain rate. The energy dissipation rates of the specimens with inclination joint angles are higher than those of the intact specimens with the increase of the strain rate.
By using a split Hopkinson pressure bar (SHPB) technique, impact experiments were carried out on the jointed rock specimens simulated by cement-based mortar specimens. The dynamic responses of the simulated jointed rock material with different joint angles at different strain rates were analyzed including stress-strain curve characteristics, failure modes, energy transmission and dissipation. The experimental results show that, with the increase of strain rate, the dynamic elastic moduli increase, and the specimens become more fragile. The peak intensity decreases with the increase of the joint angles whereas when the strain rate increases to a certain extent, the influence of the joint angles on the rock damage formation is no longer obvious. The incident energy, the reflective energy, the transmission energy, and the dissipation energy of the different specimens nonlinearly increase with the increase of the strain rate. The energy dissipation rates of the specimens with inclination joint angles are higher than those of the intact specimens with the increase of the strain rate.
2016, 36(4): 491-496.
doi: 10.11883/1001-1455(2016)04-0491-06
Abstract:
A convenient method for fabricating a layered impactor with a sample backed up by high hardness materials was developed to overcome the obstacle of the shock-reload experiments in the self-consistent yield strength technique. This method was validated by a series of ideal shock-reload particle velocities of aluminum, tin, and Zr-based bulk metallic glass obtained from the reverse-impact experiments at the peak shock stresses from 28 GPa to 48 GPa. The sum of the shear stresses for these materials in the reload process from the shocked state was estimated, and compared with the previously reported data in the release process. It is shown that the yield strength under a high pressure for the materials investigated will underestimate 20%-50% if without the reload data. Thus, shock-reload experiments are essential for the self-consistent yield strength method.
A convenient method for fabricating a layered impactor with a sample backed up by high hardness materials was developed to overcome the obstacle of the shock-reload experiments in the self-consistent yield strength technique. This method was validated by a series of ideal shock-reload particle velocities of aluminum, tin, and Zr-based bulk metallic glass obtained from the reverse-impact experiments at the peak shock stresses from 28 GPa to 48 GPa. The sum of the shear stresses for these materials in the reload process from the shocked state was estimated, and compared with the previously reported data in the release process. It is shown that the yield strength under a high pressure for the materials investigated will underestimate 20%-50% if without the reload data. Thus, shock-reload experiments are essential for the self-consistent yield strength method.
2016, 36(4): 497-502.
doi: 10.11883/1001-1455(2016)04-0497-06
Abstract:
The Mei extinction detection system and the self-developed 20 L pulse pneumatic spray multiphase explosion test system were applied to experimentally investigate the explosion parameters of the diethyl ether mist/air mixtures. By regulating pneumatic pressure and designing spray dose, the explosion parameters of the diethyl ether mist/air mixtures with the same particle size and different mass concentrations were obtained including explosion overpressure, explosion temperature and ignition delay time. The results show that when the Sauter mean diameter of diethyl ether mist is 22.90 μm, the lower explosion limit of diethyl ether mist/air mixtures is 80.261 g/m3, the upper explosion limit is 417.34 g/m3, the highest peak overpressure is 0.78 MPa which occurs with the mass concentration as 278.23 g/m3, the highest peak temperature is 1 260 ℃ which occurs with the mass concentration as 228.29 g/m3, and the ignition delay time takes on a U-shaped distribution in the explosion limit range.
The Mei extinction detection system and the self-developed 20 L pulse pneumatic spray multiphase explosion test system were applied to experimentally investigate the explosion parameters of the diethyl ether mist/air mixtures. By regulating pneumatic pressure and designing spray dose, the explosion parameters of the diethyl ether mist/air mixtures with the same particle size and different mass concentrations were obtained including explosion overpressure, explosion temperature and ignition delay time. The results show that when the Sauter mean diameter of diethyl ether mist is 22.90 μm, the lower explosion limit of diethyl ether mist/air mixtures is 80.261 g/m3, the upper explosion limit is 417.34 g/m3, the highest peak overpressure is 0.78 MPa which occurs with the mass concentration as 278.23 g/m3, the highest peak temperature is 1 260 ℃ which occurs with the mass concentration as 228.29 g/m3, and the ignition delay time takes on a U-shaped distribution in the explosion limit range.
2016, 36(4): 503-508.
doi: 10.11883/1001-1455(2016)04-0503-06
Abstract:
To solve the problems of bad convergence and to satisfy the strict requirement to initial conditions in the calculation of detonation parameters, a new calculation method was proposed based on the principles of chemical equilibrium and the method of minimum free energy by introducing the genetic algorithm, and the calculated results of typical explosives were compared with the experimental data to verify the validity and the accuracy of the new method. It is demonstrated that, by the new method, the calculated results of detonation pressure and velocity of the explosives correspond well with the experimental data with the errors under 5%, which can be applied to predict explosive properties. Also, the computational process is convenient with little manual intervention and entails only the verification of the moles variation form of the few major ingredients, which may be used for multi-formula optimization design.
To solve the problems of bad convergence and to satisfy the strict requirement to initial conditions in the calculation of detonation parameters, a new calculation method was proposed based on the principles of chemical equilibrium and the method of minimum free energy by introducing the genetic algorithm, and the calculated results of typical explosives were compared with the experimental data to verify the validity and the accuracy of the new method. It is demonstrated that, by the new method, the calculated results of detonation pressure and velocity of the explosives correspond well with the experimental data with the errors under 5%, which can be applied to predict explosive properties. Also, the computational process is convenient with little manual intervention and entails only the verification of the moles variation form of the few major ingredients, which may be used for multi-formula optimization design.
2016, 36(4): 509-515.
Abstract:
Both aleatory uncertainty and epistemic uncertainty exist in the initial and boundary conditions when we numerically solve the CFD with sharp discontinuity. In this paper, mixed uncertainty quantification approaches are developed to deal with this situation. Specifically, the outer level uncertainty is linked to epistemic uncertainties, and the inner uncertainty is linked to aleatory uncertainty. The non-intrusive polynomial chaos method is utilized to cope with the aleatory uncertainties, while the P-box theory is used to deal with the epistemic uncertainties, and the upwind scheme and Riemann solver are used to solve the deterministic system. We apply this method to the Sod problem in the CFD, and acquire preferable effect. This method evaluates the influence of input uncertainty such as density (aleatory uncertainty) and polytrophic exponent (epistemic uncertainty) on the output uncertainty, the efficiency of this method is also proved. This method is also helpful in evaluating the degree of confidence and validation of the result from modeling and simulation by other models.
Both aleatory uncertainty and epistemic uncertainty exist in the initial and boundary conditions when we numerically solve the CFD with sharp discontinuity. In this paper, mixed uncertainty quantification approaches are developed to deal with this situation. Specifically, the outer level uncertainty is linked to epistemic uncertainties, and the inner uncertainty is linked to aleatory uncertainty. The non-intrusive polynomial chaos method is utilized to cope with the aleatory uncertainties, while the P-box theory is used to deal with the epistemic uncertainties, and the upwind scheme and Riemann solver are used to solve the deterministic system. We apply this method to the Sod problem in the CFD, and acquire preferable effect. This method evaluates the influence of input uncertainty such as density (aleatory uncertainty) and polytrophic exponent (epistemic uncertainty) on the output uncertainty, the efficiency of this method is also proved. This method is also helpful in evaluating the degree of confidence and validation of the result from modeling and simulation by other models.
2016, 36(4): 516-524.
doi: 10.11883/1001-1455(2016)04-0516-09
Abstract:
On the basis of the smoothed particle hydrodynamics (SPH) method with fully variable smoothing lengths, the modified Ott-Schnetter SPH method was used to cope with the computational instability in the large density gradient problems. The Holmquist-Johnson-Cook constitutive model was used to cope with the deformation and damage of concrete under impact. By comparing with the corresponding ones simulated by the non-linear finite element program LS-DYNA, the changing courses of the von-Mises stress and cracks in the concrete targets, and the velocities at the some special points of the jet head were analyzed, which proved the feasibility and accuracy of the SPH method. Other two concrete plates with different sizes penetrated by shaped charge jets were also simulated. The results are in good agreement with the physical principle. So this method can be used to deal with the multi-material and large deformation problems such as detonation and impact.
On the basis of the smoothed particle hydrodynamics (SPH) method with fully variable smoothing lengths, the modified Ott-Schnetter SPH method was used to cope with the computational instability in the large density gradient problems. The Holmquist-Johnson-Cook constitutive model was used to cope with the deformation and damage of concrete under impact. By comparing with the corresponding ones simulated by the non-linear finite element program LS-DYNA, the changing courses of the von-Mises stress and cracks in the concrete targets, and the velocities at the some special points of the jet head were analyzed, which proved the feasibility and accuracy of the SPH method. Other two concrete plates with different sizes penetrated by shaped charge jets were also simulated. The results are in good agreement with the physical principle. So this method can be used to deal with the multi-material and large deformation problems such as detonation and impact.
2016, 36(4): 525-531.
doi: 10.11883/1001-1455(2016)04-0525-07
Abstract:
To explore the mitigating mechanism of detonation of a high explosive surrounded by water, experiments of explosion with and without water were carried out in an open-ended steel cylinder. The particle velocity and the displacement of the outer surface of the cylinder were obtained by an optical-fiber displacement interferometer. The results indicate that shock wave will not be formed in air by the product of detonation until the water surrounding the product is separated to a fissure, which causes the later appearance and lower magnitude of shock wave with a longer duration compared with an explosion without water. It means that two-dimensional or three-dimensional numerical models are required to conduct the simulations of explosions with water. It is also observed that the augment of blast load decreases with the decrease of the density of the water container as well as its thickness.
To explore the mitigating mechanism of detonation of a high explosive surrounded by water, experiments of explosion with and without water were carried out in an open-ended steel cylinder. The particle velocity and the displacement of the outer surface of the cylinder were obtained by an optical-fiber displacement interferometer. The results indicate that shock wave will not be formed in air by the product of detonation until the water surrounding the product is separated to a fissure, which causes the later appearance and lower magnitude of shock wave with a longer duration compared with an explosion without water. It means that two-dimensional or three-dimensional numerical models are required to conduct the simulations of explosions with water. It is also observed that the augment of blast load decreases with the decrease of the density of the water container as well as its thickness.
2016, 36(4): 532-540.
doi: 10.11883/1001-1455(2016)04-0532-09
Abstract:
Under shock loading a specimen undergoes a uniaxial-strain loading process and a lateral release process, both of which have an influence on the residual structure, while the influence of the latter is often underestimated or even totally neglected. The plastic work generated in these two processes is calculated in this paper, and the stress history from the beginning of the shock loading to the specimen entering the recovery bin is given. It is found that after the lateral release process begins, the specimen experiences cyclic tension and compression load and the amplitude of the cyclic load reaches its maximum under moderate impact pressure. If the amplitude of the cyclic load is larger than the spall strength, the center of the specimen will be destroyed and the specimen cannot be recovered successfully. The ratio of the plastic work produced during the lateral release to that produced during the uniaxial-strain loading decreases as the impact velocity increases. When the impact velocity reaches a certain critical value, the plastic work produced during the lateral release is equal to that produced during the uniaxial-strain loading. At a certain impact velocity, decreasing the initial yield stress of the materials reduces the lateral release effects. Theoretical analysis of the ideally plastic material shows that the ratio of the plastic work produced during the lateral release to that produced during the uniaxial-strain loading decreases as the ratio of the impact velocity to the yield strength increases, which is consistent with the numerical results.
Under shock loading a specimen undergoes a uniaxial-strain loading process and a lateral release process, both of which have an influence on the residual structure, while the influence of the latter is often underestimated or even totally neglected. The plastic work generated in these two processes is calculated in this paper, and the stress history from the beginning of the shock loading to the specimen entering the recovery bin is given. It is found that after the lateral release process begins, the specimen experiences cyclic tension and compression load and the amplitude of the cyclic load reaches its maximum under moderate impact pressure. If the amplitude of the cyclic load is larger than the spall strength, the center of the specimen will be destroyed and the specimen cannot be recovered successfully. The ratio of the plastic work produced during the lateral release to that produced during the uniaxial-strain loading decreases as the impact velocity increases. When the impact velocity reaches a certain critical value, the plastic work produced during the lateral release is equal to that produced during the uniaxial-strain loading. At a certain impact velocity, decreasing the initial yield stress of the materials reduces the lateral release effects. Theoretical analysis of the ideally plastic material shows that the ratio of the plastic work produced during the lateral release to that produced during the uniaxial-strain loading decreases as the ratio of the impact velocity to the yield strength increases, which is consistent with the numerical results.
2016, 36(4): 541-547.
doi: 10.11883/1001-1455(2016)04-0541-07
Abstract:
Experiments were carried out and the dynamic response test of the tube wall was conducted simultaneously to characterize the flame and pressure wave propagation generated by methane-air mixture explosion in a shock tube. Our results show that in the closed tube, the reflected compression wave from the end wall produces a positive interference that increases the flame brightness, on the other hand, the compression wave reflected from the front end wall may bring about flame separation and thus lead to flame quenching and recrudescence in the reaction region. In addition, in contrast with the open-ended experimental configuration, the multiple reflections from both of the end walls exhibit a continuous load effect on the tube shell, which results in a larger dynamic elastic strain in the closed blast tube.
Experiments were carried out and the dynamic response test of the tube wall was conducted simultaneously to characterize the flame and pressure wave propagation generated by methane-air mixture explosion in a shock tube. Our results show that in the closed tube, the reflected compression wave from the end wall produces a positive interference that increases the flame brightness, on the other hand, the compression wave reflected from the front end wall may bring about flame separation and thus lead to flame quenching and recrudescence in the reaction region. In addition, in contrast with the open-ended experimental configuration, the multiple reflections from both of the end walls exhibit a continuous load effect on the tube shell, which results in a larger dynamic elastic strain in the closed blast tube.
2016, 36(4): 548-556.
doi: 10.11883/1001-1455(2016)04-0548-09
Abstract:
In this work, based on the determination of the rockfall impact energy and using the dynamic finite element numerical method, we analyzed dynamic responses of large-span shed-tunnels of mountain tunnels under rockfall impact, and investigated the characteristics of damages suffered by the shed-tunnel structure's reinforced-concrete. The impact depth time-history curve and impact force time-history curve under different conditions were presented for comparison and different buffering effects were also summarized for comparison between the common soil and the light soil on which shed-tunnels were constructed. Meanwhile, suggestions concerning the choice of backfilled soil and the propriety of its thickness were proposed. The results from our study will be valuable for the design of mountain tunnels' large-span shed-tunnels and the prevention of rockfall that may damage them.
In this work, based on the determination of the rockfall impact energy and using the dynamic finite element numerical method, we analyzed dynamic responses of large-span shed-tunnels of mountain tunnels under rockfall impact, and investigated the characteristics of damages suffered by the shed-tunnel structure's reinforced-concrete. The impact depth time-history curve and impact force time-history curve under different conditions were presented for comparison and different buffering effects were also summarized for comparison between the common soil and the light soil on which shed-tunnels were constructed. Meanwhile, suggestions concerning the choice of backfilled soil and the propriety of its thickness were proposed. The results from our study will be valuable for the design of mountain tunnels' large-span shed-tunnels and the prevention of rockfall that may damage them.
2016, 36(4): 562-567.
doi: 10.11883/1001-1455(2016)04-0562-06
Abstract:
The experimental system with a closed bomb was employed to discuss the characteristics of 4/7 high-nitrogen solid propellant burning rate enhanced by plasma. The plasma energy transferred into the closed bomb was measured by the utilization efficiency of the plasma generator electrical energy. A transient burning rate formula of propellant including the influence of pressure gradient and an enhanced gas generation rates coefficient by electrical power was presented. The enhanced gas generation rates coefficient of 4/7 high-nitrogen solid propellant is equal to 0.005 MW-1. Compared with the burning rate formula given by Woodley, the pressure curve simulated by the transient burning rate formula is in better agreement with the tests. And the transient burning rate formula can describe the combustion process of solid propellant by plasma more accurately.
The experimental system with a closed bomb was employed to discuss the characteristics of 4/7 high-nitrogen solid propellant burning rate enhanced by plasma. The plasma energy transferred into the closed bomb was measured by the utilization efficiency of the plasma generator electrical energy. A transient burning rate formula of propellant including the influence of pressure gradient and an enhanced gas generation rates coefficient by electrical power was presented. The enhanced gas generation rates coefficient of 4/7 high-nitrogen solid propellant is equal to 0.005 MW-1. Compared with the burning rate formula given by Woodley, the pressure curve simulated by the transient burning rate formula is in better agreement with the tests. And the transient burning rate formula can describe the combustion process of solid propellant by plasma more accurately.
2016, 36(4): 568-572.
doi: 10.11883/1001-1455(2016)04-0568-05
Abstract:
The detonation reaction of CL-20 composite explosive was numerically simulated to analyze its detonation reaction characteristics, and then an experimental setup was designed for measuring the particle velocity at the explosive-window interface. The laser interference method was used to measure the particle velocity at the interface between the LiF window and the C-1 explosive, and ninety-four percent of the C-1 explosive is CL-20 and six percent is binder by weight. And the measured particle velocity-time curves were processed by the method of derivation and piecewise fitting to determine the corresponding CJ point. According to the corresponding CJ velocity, the reaction time and CJ pressure were determined. The detonation reaction time of the C-1 explosive with the density of 1.943 g/cm3 is 38 ns and the CJ pressure is 34.2 GPa.
The detonation reaction of CL-20 composite explosive was numerically simulated to analyze its detonation reaction characteristics, and then an experimental setup was designed for measuring the particle velocity at the explosive-window interface. The laser interference method was used to measure the particle velocity at the interface between the LiF window and the C-1 explosive, and ninety-four percent of the C-1 explosive is CL-20 and six percent is binder by weight. And the measured particle velocity-time curves were processed by the method of derivation and piecewise fitting to determine the corresponding CJ point. According to the corresponding CJ velocity, the reaction time and CJ pressure were determined. The detonation reaction time of the C-1 explosive with the density of 1.943 g/cm3 is 38 ns and the CJ pressure is 34.2 GPa.
2016, 36(4): 573-576.
doi: 10.11883/1001-1455(2016)04-0573-04
Abstract:
In order to investigate the characteristics of the thermobaric explosives, the 25 g charge of thermobaric explosive was ignited in the sealed explosion chamber of 5.8 L volume, and the explosion pressure and temperature were measured and the gas productions were analyzed by the gas chromatography under the vacuum and air conditions, respectively. The experimental results show that the equilibrium pressure and equilibrium temperature under the air condition are significantly higher than those under the vacuum condition, and the oxygen in the air participates in the oxidation of aluminum, so that there is after-combustion occurring when the thermobaric explosive is ignited in air.
In order to investigate the characteristics of the thermobaric explosives, the 25 g charge of thermobaric explosive was ignited in the sealed explosion chamber of 5.8 L volume, and the explosion pressure and temperature were measured and the gas productions were analyzed by the gas chromatography under the vacuum and air conditions, respectively. The experimental results show that the equilibrium pressure and equilibrium temperature under the air condition are significantly higher than those under the vacuum condition, and the oxygen in the air participates in the oxidation of aluminum, so that there is after-combustion occurring when the thermobaric explosive is ignited in air.
2016, 36(4): 509-515.
doi: 10.11883/1001-1455(2016)04-0509-07
Abstract:
Both aleatory uncertainty and epistemic uncertainty exist in the initial and boundary conditions when we numerically solve the CFD with sharp discontinuity. In this paper, mixed uncertainty quantification approaches are developed to deal with this situation. Specifically, the outer level uncertainty is linked to epistemic uncertainties, and the inner uncertainty is linked to aleatory uncertainty. The non-intrusive polynomial chaos method is utilized to cope with the aleatory uncertainties, while the P-box theory is used to deal with the epistemic uncertainties, and the upwind scheme and Riemann solver are used to solve the deterministic system. We apply this method to the Sod problem in the CFD, and acquire preferable effect. This method evaluates the influence of input uncertainty such as density (aleatory uncertainty) and polytrophic exponent (epistemic uncertainty) on the output uncertainty, the efficiency of this method is also proved. This method is also helpful in evaluating the degree of confidence and validation of the result from modeling and simulation by other models.
Both aleatory uncertainty and epistemic uncertainty exist in the initial and boundary conditions when we numerically solve the CFD with sharp discontinuity. In this paper, mixed uncertainty quantification approaches are developed to deal with this situation. Specifically, the outer level uncertainty is linked to epistemic uncertainties, and the inner uncertainty is linked to aleatory uncertainty. The non-intrusive polynomial chaos method is utilized to cope with the aleatory uncertainties, while the P-box theory is used to deal with the epistemic uncertainties, and the upwind scheme and Riemann solver are used to solve the deterministic system. We apply this method to the Sod problem in the CFD, and acquire preferable effect. This method evaluates the influence of input uncertainty such as density (aleatory uncertainty) and polytrophic exponent (epistemic uncertainty) on the output uncertainty, the efficiency of this method is also proved. This method is also helpful in evaluating the degree of confidence and validation of the result from modeling and simulation by other models.
2016, 36(4): 557-561.
doi: 10.11883/1001-1455(2016)04-0557-05
Abstract:
Using the line array Doppler pins system(DPS) test technique, the velocity history of the collision region of a tungsten alloy plate was measured, and 16 test points were arranged within the 4-mm-long range in the collision region. The velocity curves were processed to obtain the experimental information such as velocity change, pressure distribution, bulge evolution and plate surface damage. Experimental results show that regular reflection occured after two shock waves colliding, and the pressure of the collision region after colliding was 2.5 times of one before colliding. Meanwhile, the pressure distribution in the collision region after colliding dominated the bulge contour of the collision region. And the collision region of the tungsten alloy flying layer took on a tip-shaped structure.
