2015 Vol. 35, No. 3
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2015, 35(3): 289-295.
doi: 10.11883/1001-1455-(2015)03-0289-07
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Abstract:
On the basis of multi-group radiation hydrodynamics method of fireball radiation in strong explosion, operator splitting method is used to split the equations into convection items and source items, which are split into radiation groups due to the equation formation and solved individually.Numerical calculations show that the method used here overcomes strong instability when solving the equations directly because of the coupling items between radiation and fluid.In the meantime, the time step in the calculation is increased obviously.Fireball radiation spectrum is obtained in fine accordance with the result in the literature.
On the basis of multi-group radiation hydrodynamics method of fireball radiation in strong explosion, operator splitting method is used to split the equations into convection items and source items, which are split into radiation groups due to the equation formation and solved individually.Numerical calculations show that the method used here overcomes strong instability when solving the equations directly because of the coupling items between radiation and fluid.In the meantime, the time step in the calculation is increased obviously.Fireball radiation spectrum is obtained in fine accordance with the result in the literature.
2015, 35(3): 296-303.
doi: 10.11883/1001-1455-(2015)03-0296-08
Abstract:
TiNi tubes with and without lateral constraint subjected to radial impact were investigated experimentally for the purpose of developing repeatedly used energy absorption devices.By using a modified SHPB apparatus and wave separation technique, the signal recorded was extended to about 3ms, and then the load-compression curves were available.With a high speed CCD camera, the dynamic deformation process of the specimens was captured.The results show that TiNi tubes without lateral constraint have an excellent recoverable deformability with apparent loading platform.The tubes with lateral constraint have a much better performance of energy dissipation and are able to withstand higher speed impact.If properly choosing the combination of two constraints, it may improve its dynamic performance both in the large deformation and high energy dissipation and will be used in the future shock absorbing devices.
TiNi tubes with and without lateral constraint subjected to radial impact were investigated experimentally for the purpose of developing repeatedly used energy absorption devices.By using a modified SHPB apparatus and wave separation technique, the signal recorded was extended to about 3ms, and then the load-compression curves were available.With a high speed CCD camera, the dynamic deformation process of the specimens was captured.The results show that TiNi tubes without lateral constraint have an excellent recoverable deformability with apparent loading platform.The tubes with lateral constraint have a much better performance of energy dissipation and are able to withstand higher speed impact.If properly choosing the combination of two constraints, it may improve its dynamic performance both in the large deformation and high energy dissipation and will be used in the future shock absorbing devices.
2015, 35(3): 304-311.
doi: 10.11883/1001-1455-(2015)03-0304-08
Abstract:
A new experimental system of digital laser dynamic caustics was used and the distribution of dynamic stress field around empty holes and the influence of empty holes upon the main cracks expanding under the blasting loading were studied.Experimental results show that two blast-induced main cracks, which were oppositely expanding, deflected gradually to empty hole under the strong stress and penetrated empty hole.The angle between the principal stress direction and the line of two blasting holes center near the empty hole kept about 12°, and the principal stress direction did not change with the size of empty holes increasing; the interaction between explosive stress waves and empty holes produced reflective stretching waves, changed the stress field at the main crack tips, reduced expanding velocity of the main crack.The larger the diameter of empty hole was, the lower the main crack propagation velocity was.When the blast-induced main cracks expanded to empty hole, the dynamic stress intensity factor at crack tips appeared to rise again.
A new experimental system of digital laser dynamic caustics was used and the distribution of dynamic stress field around empty holes and the influence of empty holes upon the main cracks expanding under the blasting loading were studied.Experimental results show that two blast-induced main cracks, which were oppositely expanding, deflected gradually to empty hole under the strong stress and penetrated empty hole.The angle between the principal stress direction and the line of two blasting holes center near the empty hole kept about 12°, and the principal stress direction did not change with the size of empty holes increasing; the interaction between explosive stress waves and empty holes produced reflective stretching waves, changed the stress field at the main crack tips, reduced expanding velocity of the main crack.The larger the diameter of empty hole was, the lower the main crack propagation velocity was.When the blast-induced main cracks expanded to empty hole, the dynamic stress intensity factor at crack tips appeared to rise again.
2015, 35(3): 312-319.
doi: 10.11883/1001-1455-(2015)03-0312-08
Abstract:
Several groups of compression tests at different strain rates(10-3~3 000 s-1)are carried out for MDYB-3 polymethyl methacrylate.Yield stress in the quasi-static tests and peak stress in the dynamic tests are obtained.Compression tests are performed along normal direction and parallel directions of samples to analyze the effect of orientation stretching on yield stress.Ree-Eyring model and Cooperative model are revised to describe the yield behavior of directional PMMA.Viscoplastic behaviors after yield are attempted to be described using Johnson-Cook model.The results of Cooperative yield model are shown to be closer to the test results than those of Ree-Eyring yield model.Cooperative yield model can describe the yield stress of quasi-static tests accurately.Peak stress in dynamic compression test is failure stress, which means that samples fail before yield at the strain rate above 1 500 s-1.The fitting results reveal that Johnson-Cook model can describe a single stress-strain curve well, but it cannot predict the dependence of strain rate.
Several groups of compression tests at different strain rates(10-3~3 000 s-1)are carried out for MDYB-3 polymethyl methacrylate.Yield stress in the quasi-static tests and peak stress in the dynamic tests are obtained.Compression tests are performed along normal direction and parallel directions of samples to analyze the effect of orientation stretching on yield stress.Ree-Eyring model and Cooperative model are revised to describe the yield behavior of directional PMMA.Viscoplastic behaviors after yield are attempted to be described using Johnson-Cook model.The results of Cooperative yield model are shown to be closer to the test results than those of Ree-Eyring yield model.Cooperative yield model can describe the yield stress of quasi-static tests accurately.Peak stress in dynamic compression test is failure stress, which means that samples fail before yield at the strain rate above 1 500 s-1.The fitting results reveal that Johnson-Cook model can describe a single stress-strain curve well, but it cannot predict the dependence of strain rate.
2015, 35(3): 320-325.
doi: 10.11883/1001-1455-(2015)03-0320-06
Abstract:
For investigating bubble pulse of small scale charge exploded under deepwater in the laboratory, an experiment platform of charge exploded under simulated deepwater is established by means of adding atmospheric pressure over the water surface to increase the hydrostatic pressure.Experiments of 3 small scale charges exploded under different simulated deepwater environments are conducted.Images of bubble pulse process are gained.The equivalence between experiments of small scale charge exploded under simulated deepwater and experiments under free-field is validated.The variations of the period and the maximum radius of bubble pulse depending on the water depth are analyzed.Passing through these experiments, the reflection effect from the containment vessel shell can be neglected for the bubble pulse process, and the simulated deepwater environment can be regarded as real free-field deepwater environment.When increasing the hydrostatic water depth, the attenuation coefficients of the period and the maximum radius of bubble pulse of small scale charge exploded under deepwater are-0.83 and-0.364, respectively.
For investigating bubble pulse of small scale charge exploded under deepwater in the laboratory, an experiment platform of charge exploded under simulated deepwater is established by means of adding atmospheric pressure over the water surface to increase the hydrostatic pressure.Experiments of 3 small scale charges exploded under different simulated deepwater environments are conducted.Images of bubble pulse process are gained.The equivalence between experiments of small scale charge exploded under simulated deepwater and experiments under free-field is validated.The variations of the period and the maximum radius of bubble pulse depending on the water depth are analyzed.Passing through these experiments, the reflection effect from the containment vessel shell can be neglected for the bubble pulse process, and the simulated deepwater environment can be regarded as real free-field deepwater environment.When increasing the hydrostatic water depth, the attenuation coefficients of the period and the maximum radius of bubble pulse of small scale charge exploded under deepwater are-0.83 and-0.364, respectively.
2015, 35(3): 326-334.
doi: 10.11883/1001-1455-(2015)03-0326-09
Abstract:
A new interface treating method is presented for the compressible-incompressible gas-water multi-phase flow.The Riemann problem is constructed at the compressible gas-water interface, and then solved according to the hypothesis that the sound speed tends to infinity in the water.The solution of Riemann problem provides the fluid states for compressible gas and incompressible water at the interface.Those states can then be used to define the interface boundary condition by coupling the ghost fluid method.The level set method is employed to track the interface.The numerical examples of one-dimension case are given in this paper, furthermore, several comparisons are made with other results to verify the algorithm.Numerical results show that the provided algorithm can capture the discontinuities accurately, which demonstrates the robustness and efficiency.
A new interface treating method is presented for the compressible-incompressible gas-water multi-phase flow.The Riemann problem is constructed at the compressible gas-water interface, and then solved according to the hypothesis that the sound speed tends to infinity in the water.The solution of Riemann problem provides the fluid states for compressible gas and incompressible water at the interface.Those states can then be used to define the interface boundary condition by coupling the ghost fluid method.The level set method is employed to track the interface.The numerical examples of one-dimension case are given in this paper, furthermore, several comparisons are made with other results to verify the algorithm.Numerical results show that the provided algorithm can capture the discontinuities accurately, which demonstrates the robustness and efficiency.
2015, 35(3): 335-342.
doi: 10.11883/1001-1455-(2015)03-0335-08
Abstract:
Flight trajectory experiments were conducted with⌀60 mm diameter EFP warhead in order to investigate the effect of eccentric initiation on the flight characteristics of EFP.The results indicate that the projectile flight stability with perforations nearly circular in the net target when eccentricity is less than 2 mm.The accuracy of strike is lower and terminal effects are less harmful because the projectile overturns during the flight, with the eccentric value of 4 mm.The forming of EFP and its flight characteristics with different eccentricity was numerically analyzed by using LS-DYNA and CFX.EFP is asymmetrical under the conditions of the eccentric initiation.It changes the symmetry of the flow field which leads to instability during flight.The research results provide a reference to detonation parameter of EFP warhead.
Flight trajectory experiments were conducted with⌀60 mm diameter EFP warhead in order to investigate the effect of eccentric initiation on the flight characteristics of EFP.The results indicate that the projectile flight stability with perforations nearly circular in the net target when eccentricity is less than 2 mm.The accuracy of strike is lower and terminal effects are less harmful because the projectile overturns during the flight, with the eccentric value of 4 mm.The forming of EFP and its flight characteristics with different eccentricity was numerically analyzed by using LS-DYNA and CFX.EFP is asymmetrical under the conditions of the eccentric initiation.It changes the symmetry of the flow field which leads to instability during flight.The research results provide a reference to detonation parameter of EFP warhead.
2015, 35(3): 343-349.
doi: 10.11883/1001-1455-(2015)03-0343-07
Abstract:
Aiming at rockburst geological disaster induced by discontinuity such as faults or joints in deep lay rock mass, numerical model is presented according to distributional characteristics and geometrical aspects of potential seismic faults in underground tunnel.Subsequently, excavation response of deep lay surrounding rock with rigid flat faults is simulated via distinct element codes, and varied features of stress state in surrounding rock are examined while excavation process approaches and then passes through fault zones.Finally, Mechanism of action is discussed on the base of stress state change induced by available faults.Energy releases sharply via rockburst under high stress, and it is revealed that faulted structure occur movement within a certain region of excavation section.Rockburst impacts on surrounding rock intensely, and the mechanism is similar to fault stick slip in earthquake process.
Aiming at rockburst geological disaster induced by discontinuity such as faults or joints in deep lay rock mass, numerical model is presented according to distributional characteristics and geometrical aspects of potential seismic faults in underground tunnel.Subsequently, excavation response of deep lay surrounding rock with rigid flat faults is simulated via distinct element codes, and varied features of stress state in surrounding rock are examined while excavation process approaches and then passes through fault zones.Finally, Mechanism of action is discussed on the base of stress state change induced by available faults.Energy releases sharply via rockburst under high stress, and it is revealed that faulted structure occur movement within a certain region of excavation section.Rockburst impacts on surrounding rock intensely, and the mechanism is similar to fault stick slip in earthquake process.
2015, 35(3): 350-358.
doi: 10.11883/1001-1455(2015)03-0350-09
Abstract:
To meet higher security requirements for blasting vibration from urban tunnel excavation under dense buildings, a new blasting technology was proposed and the corresponding method for obtaining parameters was explored.The proposed blasting technology uses non-electric detonators to precisely control blasting vibration.Chongqing Yuzhong connecting tunnel was taken as the research background.By applying Fourier function and MATLAB software, the vibration velocity curves were fitted for single-hole blasting with different charges and the quantification data of vibration superposition at different millisecond intervals from 1 to 50 ms were analyzed.The vibration-reduction effect was discussed for different millisecond intervals.The parameters about blasting charge and detonating time delayed were determined under given vibration velocities.Interval characteristics of each period between detonators in the field were measured and analyzed.Accordingly, the blasting scheme was designed, which using hole-by-hole cut blasting to control vibration.The blasting vibration velocity measured in the field is below 1.00 cm/s, and the corresponding reasonable single-hole charge is 1.2 kg for avoiding vibration superposition.The vibration velocity peak occurs after the detonation of the first or second-period detonator in the main cut area, which is consistent with the theoretical results.And the vibration velocity decreases by more fifty percent after 60 ms of hole-by-hole blasting. So blasting vibration can be precisely controlled by using non-electric detonators under high safety standard.
To meet higher security requirements for blasting vibration from urban tunnel excavation under dense buildings, a new blasting technology was proposed and the corresponding method for obtaining parameters was explored.The proposed blasting technology uses non-electric detonators to precisely control blasting vibration.Chongqing Yuzhong connecting tunnel was taken as the research background.By applying Fourier function and MATLAB software, the vibration velocity curves were fitted for single-hole blasting with different charges and the quantification data of vibration superposition at different millisecond intervals from 1 to 50 ms were analyzed.The vibration-reduction effect was discussed for different millisecond intervals.The parameters about blasting charge and detonating time delayed were determined under given vibration velocities.Interval characteristics of each period between detonators in the field were measured and analyzed.Accordingly, the blasting scheme was designed, which using hole-by-hole cut blasting to control vibration.The blasting vibration velocity measured in the field is below 1.00 cm/s, and the corresponding reasonable single-hole charge is 1.2 kg for avoiding vibration superposition.The vibration velocity peak occurs after the detonation of the first or second-period detonator in the main cut area, which is consistent with the theoretical results.And the vibration velocity decreases by more fifty percent after 60 ms of hole-by-hole blasting. So blasting vibration can be precisely controlled by using non-electric detonators under high safety standard.
2015, 35(3): 359-365.
doi: 10.11883/1001-1455(2015)03-0359-07
Abstract:
Aimed at the selection problem of priming parameters of two-point explosion in concrete, a method for optimizing the parameters was proposed based on the gray theory.The experimental program was developed by the orthogonal experimental design technique, static explosion experiments were simulated by the software AUTODYN under different priming parameters.The gray relational degree and the gray incidence coefficient between the priming parameters and crater diameter as well as crater depth were calculated.The optimization of the priming parameters was done based on the single-objective function and the multi-objective function, and the additional production experiments were completed.The results show that the crater diameter increases 4%-42%, the left crater depth increases(0-29)%and the right crater depth increases(0-32)%by means of the optimized parameters, the damage effect of two-point explosion in concrete is improved than before.
Aimed at the selection problem of priming parameters of two-point explosion in concrete, a method for optimizing the parameters was proposed based on the gray theory.The experimental program was developed by the orthogonal experimental design technique, static explosion experiments were simulated by the software AUTODYN under different priming parameters.The gray relational degree and the gray incidence coefficient between the priming parameters and crater diameter as well as crater depth were calculated.The optimization of the priming parameters was done based on the single-objective function and the multi-objective function, and the additional production experiments were completed.The results show that the crater diameter increases 4%-42%, the left crater depth increases(0-29)%and the right crater depth increases(0-32)%by means of the optimized parameters, the damage effect of two-point explosion in concrete is improved than before.
2015, 35(3): 366-371.
doi: 10.11883/1001-1455(2015)03-0366-07
Abstract:
Due to the huge differences in pressure and duration of dynamic loading process and quasistatic loading process in high-pressure water jet impacting HTPB propellant, possible ignition modes were prejudged on the basis of the calculation of water hammer pressure and stagnation pressure, and the safety of dynamic loading process and quasi-static loading process were analyzed through model analogy and experimental study respectively.The results show that there is no detonation risk in the dynamic loading process of high pressure water jet with the outlet pressure less than 300 MPa, but in the quasi-static loading process of high pressure water jet the outlet pressure of which is above 100 MPa.It is possible that internal temperature has a sudden rise, which may cause thermal ignition or even thermal explosion.
Due to the huge differences in pressure and duration of dynamic loading process and quasistatic loading process in high-pressure water jet impacting HTPB propellant, possible ignition modes were prejudged on the basis of the calculation of water hammer pressure and stagnation pressure, and the safety of dynamic loading process and quasi-static loading process were analyzed through model analogy and experimental study respectively.The results show that there is no detonation risk in the dynamic loading process of high pressure water jet with the outlet pressure less than 300 MPa, but in the quasi-static loading process of high pressure water jet the outlet pressure of which is above 100 MPa.It is possible that internal temperature has a sudden rise, which may cause thermal ignition or even thermal explosion.
2015, 35(3): 372-379.
doi: 10.11883/1001-1455-(2015)03-0372-08
Abstract:
Experiments were conducted to investigate the effect of conveying airflow characteristics on flame structure for the electric spark ignition in air flow of lycopodium dust.Hot wire anemometers were used to measure the distributions of velocity and turbulent intensity along the diameter in a 6 cm diameter and 4 m length horizontal acrylic tube of a blow-type pneumatic conveying system.The measured dust-air mixtures flowing velocities ranged between 10 and 30 m/s.A high-speed video camera was utilized to record the flame propagation process and to obtain the direct light emission photographs.Two apparently different types of flames appeared in the flame propagation process under different airflow conditions.Type A flame was characterized by a regular and continuous structure with the yellow light-emitting zone in the center surrounding by the red luminous zone.Type B flame was discrete in the space and the structure of the luminous zone was irregular.Furthermore, the flame propagation velocities, vortex structures, formation conditions and relative burning velocities of the two types flames under different airflow velocities were discussed in detail.
Experiments were conducted to investigate the effect of conveying airflow characteristics on flame structure for the electric spark ignition in air flow of lycopodium dust.Hot wire anemometers were used to measure the distributions of velocity and turbulent intensity along the diameter in a 6 cm diameter and 4 m length horizontal acrylic tube of a blow-type pneumatic conveying system.The measured dust-air mixtures flowing velocities ranged between 10 and 30 m/s.A high-speed video camera was utilized to record the flame propagation process and to obtain the direct light emission photographs.Two apparently different types of flames appeared in the flame propagation process under different airflow conditions.Type A flame was characterized by a regular and continuous structure with the yellow light-emitting zone in the center surrounding by the red luminous zone.Type B flame was discrete in the space and the structure of the luminous zone was irregular.Furthermore, the flame propagation velocities, vortex structures, formation conditions and relative burning velocities of the two types flames under different airflow velocities were discussed in detail.
2015, 35(3): 380-385.
doi: 10.11883/1001-1455-(2015)03-0380-06
Abstract:
The square tube with pre-designed corrugations shape is presented and the folding angles formula of the corrugated tubes is established in this study base on geometrical relationship.Buckling modes and energy absorption of square tube and six kinds of corrugated tubes under axial impacting are compared and analyzed by LS-DYNA.The simulation result shows that deformation of tubes can be divided into three stages, including the initial peak stage, the stable progress buckling stage and the densification stage.The folding angle is one of important influence factors on the initial peak force and mean force.The pre-designed corrugations demonstrate some obvious advantages at reducing initial peak force and the fluctuation range of impact force curves which are smoother than the square tube.In addition, the specific energy absorption of the corrugated tubes are lower than the square tube, while the crush force efficiency and specific total efficiency of corrugated tube with a certain folding angle are higher than those of the square tube.
The square tube with pre-designed corrugations shape is presented and the folding angles formula of the corrugated tubes is established in this study base on geometrical relationship.Buckling modes and energy absorption of square tube and six kinds of corrugated tubes under axial impacting are compared and analyzed by LS-DYNA.The simulation result shows that deformation of tubes can be divided into three stages, including the initial peak stage, the stable progress buckling stage and the densification stage.The folding angle is one of important influence factors on the initial peak force and mean force.The pre-designed corrugations demonstrate some obvious advantages at reducing initial peak force and the fluctuation range of impact force curves which are smoother than the square tube.In addition, the specific energy absorption of the corrugated tubes are lower than the square tube, while the crush force efficiency and specific total efficiency of corrugated tube with a certain folding angle are higher than those of the square tube.
2015, 35(3): 386-392.
doi: 10.11883/1001-1455(2015)03-0386-07
Abstract:
Monolithic and three-layered plates were normally impacted by hemispherically-nosed projectiles.The residual velocity-the initial velocity curves of the projectiles and ballisitic limit velocities were constructed.The penetration process of metal plates impacted by rod projectiles has been studied with numerical simulation code ABAQUS/EXPLICIT.The validation of models and parameters of materials has been proved by comparing the experiment results with numerical simulations.We investigated the influence of combination configuration of target on the ballistic characteristic, including the ballistic resistance and failure models.Furthermore, the impact process was also analyzed.The results indicated that the ballistic limit velocity of multi-layered plate was higher than that of monolithic plate.The dominant failure model of monolithic plate was shearing, but the dominant failure models of multi-layered plate were global dishing and local bulging.Moreover, the failure models of plates of multi-layered plates were in relation to their order in targets.
Monolithic and three-layered plates were normally impacted by hemispherically-nosed projectiles.The residual velocity-the initial velocity curves of the projectiles and ballisitic limit velocities were constructed.The penetration process of metal plates impacted by rod projectiles has been studied with numerical simulation code ABAQUS/EXPLICIT.The validation of models and parameters of materials has been proved by comparing the experiment results with numerical simulations.We investigated the influence of combination configuration of target on the ballistic characteristic, including the ballistic resistance and failure models.Furthermore, the impact process was also analyzed.The results indicated that the ballistic limit velocity of multi-layered plate was higher than that of monolithic plate.The dominant failure model of monolithic plate was shearing, but the dominant failure models of multi-layered plate were global dishing and local bulging.Moreover, the failure models of plates of multi-layered plates were in relation to their order in targets.
2015, 35(3): 393-400.
doi: 10.11883/1001-1455-(2015)03-0393-08
Abstract:
Gas explosion is the leading accident in underground coal mining in China.In order to prevent mine gas explosion effectively, methane, the dominant sector of mine gases, was taken as experimental medium.A quartz tube test system, in which the ratio of length to diameter is 18, was designed and made.A high-speed camera and numerical simulation software FLACS was employed to study the characteristics of methane explosion.The impact of CO2at various concentrations on the suppression of 9%methane explosion was investigated.Fluctuations were observed on the explosion pressure, the velocity of the flame front and the velocity of the mixed gases during the propagation of the gas explosion.The time to reach the maximum for the pressure was not simultaneous with that for velocity.Additionally, carbon dioxide can effectively suppress the reaction between methane and oxygen and the larger the concentration of CO2is, the better the suppression effect will be.Simulation results are in accordance with the experiments.
Gas explosion is the leading accident in underground coal mining in China.In order to prevent mine gas explosion effectively, methane, the dominant sector of mine gases, was taken as experimental medium.A quartz tube test system, in which the ratio of length to diameter is 18, was designed and made.A high-speed camera and numerical simulation software FLACS was employed to study the characteristics of methane explosion.The impact of CO2at various concentrations on the suppression of 9%methane explosion was investigated.Fluctuations were observed on the explosion pressure, the velocity of the flame front and the velocity of the mixed gases during the propagation of the gas explosion.The time to reach the maximum for the pressure was not simultaneous with that for velocity.Additionally, carbon dioxide can effectively suppress the reaction between methane and oxygen and the larger the concentration of CO2is, the better the suppression effect will be.Simulation results are in accordance with the experiments.
2015, 35(3): 401-408.
doi: 10.11883/1001-1455-(2015)03-0401-08
Abstract:
The model of circular honeycomb structures randomly filled with rigid inclusions which keeps the relative density as a constant is developed.And then the effects of impact velocity and packing ratio on the deformation modes, dynamic plateau stress and energy absorption capacities are discussed in detail.Research results show that the rigid inclusions have pinning effect in the process of deformation and the deformation modes can still be classified as quasi-static mode, transitional mode and dynamic mode.The plateau stress is proportional to the square of the impact velocity when the honeycombs are deformed at transitional mode or dynamic mode, which shows obvious speed effect. The energy absorption capacities of circular honeycombs are higher than these of the regular honeycombs at high-velocity impact.These results can provide valuable suggestions in the study and design of the functionally gradient honeycombs.
The model of circular honeycomb structures randomly filled with rigid inclusions which keeps the relative density as a constant is developed.And then the effects of impact velocity and packing ratio on the deformation modes, dynamic plateau stress and energy absorption capacities are discussed in detail.Research results show that the rigid inclusions have pinning effect in the process of deformation and the deformation modes can still be classified as quasi-static mode, transitional mode and dynamic mode.The plateau stress is proportional to the square of the impact velocity when the honeycombs are deformed at transitional mode or dynamic mode, which shows obvious speed effect. The energy absorption capacities of circular honeycombs are higher than these of the regular honeycombs at high-velocity impact.These results can provide valuable suggestions in the study and design of the functionally gradient honeycombs.
2015, 35(3): 409-415.
doi: 10.11883/1001-1455-(2015)03-0409-07
Abstract:
In order to analyze influences of multistage divergent chamber structure of combustion light gas gun on the combustion characteristics of hydrogen-oxygen mixed gas, the propellant combustion launching process in the multistage divergent chamber and standard cylinder chamber combustion light gas gun was simulated with the computational fluid dynamics method respectively.Comparative results show that the pressure fluctuations in the chamber of combustion light gas gun are significantly reduced by using the multistage divergent combustion chamber structure, while the stability of hydrogen-oxygen mixed gas combustion is improved.Recirculation zones would be formed in the multistage divergent chamber, which can reduce the flow axial velocity.The flame shape and the divergent chamber structure coincide with each other during its expanding.The surface of combustion zones develops steady.The multistage divergent combustion chamber structure has considerable impact on the flame expansion process and pressure fluctuations in the combustion chamber.
In order to analyze influences of multistage divergent chamber structure of combustion light gas gun on the combustion characteristics of hydrogen-oxygen mixed gas, the propellant combustion launching process in the multistage divergent chamber and standard cylinder chamber combustion light gas gun was simulated with the computational fluid dynamics method respectively.Comparative results show that the pressure fluctuations in the chamber of combustion light gas gun are significantly reduced by using the multistage divergent combustion chamber structure, while the stability of hydrogen-oxygen mixed gas combustion is improved.Recirculation zones would be formed in the multistage divergent chamber, which can reduce the flow axial velocity.The flame shape and the divergent chamber structure coincide with each other during its expanding.The surface of combustion zones develops steady.The multistage divergent combustion chamber structure has considerable impact on the flame expansion process and pressure fluctuations in the combustion chamber.
2015, 35(3): 416-422.
doi: 10.11883/1001-1455-(2015)03-0416-07
Abstract:
As the metal fragments of penetration can not be effectively simulated by finite element method(FEM), a three-dimensional(3D)calculation code was developed to simulate penetration problem of multi-layered spaced metal plates based on theory of 3D FE-SPH adaptive coupling algorithm.Numerical models are approximated initially by tetrahedral elements.When equivalent plastic strain of elements reaches a specified value, they are converted into particles and are calculated by Smoothed Particle Hydrodynamics(SPH)method.Then the regions of large deformation and crush are simulated by SPH method, as SPH method overcome the distortion of elements in FEM.Contact method and coupling algorithm are used to calculate the interface between FEM and SPH method. Two numerical examples are presented to validate the 3D FE-SPH code by representing penetration process of spaced multi-layered metallic targets.The numerical simulation results show that good accuracy and stability are compared to experiment, when equivalent plastic strain is used as criterion of conversion.
As the metal fragments of penetration can not be effectively simulated by finite element method(FEM), a three-dimensional(3D)calculation code was developed to simulate penetration problem of multi-layered spaced metal plates based on theory of 3D FE-SPH adaptive coupling algorithm.Numerical models are approximated initially by tetrahedral elements.When equivalent plastic strain of elements reaches a specified value, they are converted into particles and are calculated by Smoothed Particle Hydrodynamics(SPH)method.Then the regions of large deformation and crush are simulated by SPH method, as SPH method overcome the distortion of elements in FEM.Contact method and coupling algorithm are used to calculate the interface between FEM and SPH method. Two numerical examples are presented to validate the 3D FE-SPH code by representing penetration process of spaced multi-layered metallic targets.The numerical simulation results show that good accuracy and stability are compared to experiment, when equivalent plastic strain is used as criterion of conversion.
2015, 35(3): 423-427.
doi: 10.11883/1001-1455(2015)03-0423-05
Abstract:
The mixing induced by Richtmyer-Meshkov instability under lower and high compression ratios is studied by using buoyancy-drag model.It is found by the comparison between the experimental and theoretical analytic results that in order to achieve good agreement, the range of the drag coefficient value chosen in Richtmyer-Meshkov instability is much wider than that in Rayleigh-Taylor instability; while in Richtmyer-Meshkov instability the uncertainty of the drag coefficient under high compression is larger than that under lower compression.It is pointed that the further improvement of the model needs to be validated by more accurate experiment.Moreover the study reveals that the exponent in empirical expression varies with calculation conditions remarkably and the use of the empirical expression in current engineering design is rough.
The mixing induced by Richtmyer-Meshkov instability under lower and high compression ratios is studied by using buoyancy-drag model.It is found by the comparison between the experimental and theoretical analytic results that in order to achieve good agreement, the range of the drag coefficient value chosen in Richtmyer-Meshkov instability is much wider than that in Rayleigh-Taylor instability; while in Richtmyer-Meshkov instability the uncertainty of the drag coefficient under high compression is larger than that under lower compression.It is pointed that the further improvement of the model needs to be validated by more accurate experiment.Moreover the study reveals that the exponent in empirical expression varies with calculation conditions remarkably and the use of the empirical expression in current engineering design is rough.
2015, 35(3): 428-436.
doi: 10.11883/1001-1455-(2015)03-0428-09
Abstract:
In view of the fact that the jointed rockmass contains both macroscopic flaws such as the joint and crack and the mesoscopic flaws such as the microcrack and microhole, the viewpoint that the above two kinds of flaws should be considered at the same time in the dynamic damage constitutive model of the jointed rockmass is proposed.Therefore, the rock classic dynamic damage constitutive model namely TCK model based on mesoscopic dynamic fracture mechanism is discussed, then the compound damage variable(tensor)comprehensively considering macroscopic and mesoscopic flaws based on Lemaitre equivalent strain hypothesis is deduced.Finally, the corresponding dynamic damage constitutive model is established, and the effect law of the load strain ratio and joint set on rock mass dynamic mechanical property is discussed with this model.The results show that under different load strain rates, the initial deformation stage of the samples coincides with each other, and then with increase of strain, the climax strength, strain and the total strain of the samples all increase.With increase in joint sets, the climax strength of the samples gradually decreases, but the reduction degree gradually becomes little and tends to a certain value.The basic law between the above research conclusions and the current experimental and theoretical results is the same, which demonstrates the rationality of this model.
In view of the fact that the jointed rockmass contains both macroscopic flaws such as the joint and crack and the mesoscopic flaws such as the microcrack and microhole, the viewpoint that the above two kinds of flaws should be considered at the same time in the dynamic damage constitutive model of the jointed rockmass is proposed.Therefore, the rock classic dynamic damage constitutive model namely TCK model based on mesoscopic dynamic fracture mechanism is discussed, then the compound damage variable(tensor)comprehensively considering macroscopic and mesoscopic flaws based on Lemaitre equivalent strain hypothesis is deduced.Finally, the corresponding dynamic damage constitutive model is established, and the effect law of the load strain ratio and joint set on rock mass dynamic mechanical property is discussed with this model.The results show that under different load strain rates, the initial deformation stage of the samples coincides with each other, and then with increase of strain, the climax strength, strain and the total strain of the samples all increase.With increase in joint sets, the climax strength of the samples gradually decreases, but the reduction degree gradually becomes little and tends to a certain value.The basic law between the above research conclusions and the current experimental and theoretical results is the same, which demonstrates the rationality of this model.
2015, 35(3): 437-441.
doi: 10.11883/1001-1455(2015)03-0437-05
Abstract:
Air blast experiments of small-scale charges were conducted in an explosion containment vessel.The shock wave velocity was measured by sensor series.And the approximately theoretic peak pressure was determined from the shock wave velocity by using the Rankine-Hugoniot relationship. The sensor was then calibrated, and the relative error of the sensitivity was small.The shock wave parameters were measured and post processed by using the modified-Friedlander equation.The results show that the nonlinear regression by fixing the overpressure is close to the physical fact, and the fitting by fixing the duration has a high precision.Error analysis reveals that the sensor properties and the post-processing methods can produce errors.Experimental results display that the shock wave parameter measuring and post-processing method suggested has a high precision.By this suggested method, the sensor calibration and parameter measurement can be conducted simultaneously.
Air blast experiments of small-scale charges were conducted in an explosion containment vessel.The shock wave velocity was measured by sensor series.And the approximately theoretic peak pressure was determined from the shock wave velocity by using the Rankine-Hugoniot relationship. The sensor was then calibrated, and the relative error of the sensitivity was small.The shock wave parameters were measured and post processed by using the modified-Friedlander equation.The results show that the nonlinear regression by fixing the overpressure is close to the physical fact, and the fitting by fixing the duration has a high precision.Error analysis reveals that the sensor properties and the post-processing methods can produce errors.Experimental results display that the shock wave parameter measuring and post-processing method suggested has a high precision.By this suggested method, the sensor calibration and parameter measurement can be conducted simultaneously.
2015, 35(3): 442-448.
doi: 10.11883/1001-1455(2015)03-0442-07
Abstract:
On the basis of conservation of mass and momentum, a mechanical model was established for high-pressure water jets impinging on coal.By using this model, the mechanical characteristics were analyzed for the intact water jet, cracked water jet, and the crushing zone and crater expansion zone of the coal.The system of ordinary differential equations was obtained to describe the process of high-pressure water jets impinging on coal.And the theoretical values were compared with the numerical simulation and the experimental results.The theoretical values are consistent with the numerical simulation and the experimental results.So the established mechanical model can reflect the actual process of high-pressure water jets impinging on coal.
On the basis of conservation of mass and momentum, a mechanical model was established for high-pressure water jets impinging on coal.By using this model, the mechanical characteristics were analyzed for the intact water jet, cracked water jet, and the crushing zone and crater expansion zone of the coal.The system of ordinary differential equations was obtained to describe the process of high-pressure water jets impinging on coal.And the theoretical values were compared with the numerical simulation and the experimental results.The theoretical values are consistent with the numerical simulation and the experimental results.So the established mechanical model can reflect the actual process of high-pressure water jets impinging on coal.
