2015 Vol. 35, No. 5
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2015, 35(5): 609-616.
doi: 10.11883/1001-1455(2015)05-0609-08
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A high-speed video camera was employed to record the flow field directly. Different explosion energy (discharging voltage) and explosion depth were examined. It is found that the surface jet formed in the narrow tube consists of a smooth upper body and a rough root, which differs from the general recognition of free surface jets. The bubble induced by the wire explosion underwent an expansion-collapse process, and the close-in collapse was characterized by a downward inner jet popping out from the bubble roof. The study also reveals that the strength of the surface jet increases with the explosion energy while decreases with explosion depth. A quasi-one-dimensional theoretical model was proposed to analyze the parametric dependences. It turns out not only the variation trend but also the exact value of both maximum bubble scale and jet velocity can be well predicted by this model.
A high-speed video camera was employed to record the flow field directly. Different explosion energy (discharging voltage) and explosion depth were examined. It is found that the surface jet formed in the narrow tube consists of a smooth upper body and a rough root, which differs from the general recognition of free surface jets. The bubble induced by the wire explosion underwent an expansion-collapse process, and the close-in collapse was characterized by a downward inner jet popping out from the bubble roof. The study also reveals that the strength of the surface jet increases with the explosion energy while decreases with explosion depth. A quasi-one-dimensional theoretical model was proposed to analyze the parametric dependences. It turns out not only the variation trend but also the exact value of both maximum bubble scale and jet velocity can be well predicted by this model.
2015, 35(5): 617-624.
doi: 10.11883/1001-1455(2015)05-0617-08
Abstract:
Small-angle oblique and vertical water entry experiments were carried out to observe the supercavitation generated by the blunt bodies with different initial velocities. The development features of the supercavitation in different cases were analyzed. Experimental results show that for small-angle oblique and vertical water entry, the the round-head and flat-head (disc cavitator) blunt bodies can form stable trajectories. When the initial water-entry velocity is lower, the closure mode of the cavity is deep closure. When the initial water-entry velocity is higher, the closure mode of the cavity is surface closure, and its speed decay rate is larger. For the supercavity generated by the small-angle oblique water entry of the blunt bodies, the front part of the supercavity contour is in agreement with the result by G.V. Logvinovich's semi-empirical formula. For the vertical water entry of the blunt bodies, the influences of the head shapes were discussed on the beginning points and morphologies of the supercavities.
Small-angle oblique and vertical water entry experiments were carried out to observe the supercavitation generated by the blunt bodies with different initial velocities. The development features of the supercavitation in different cases were analyzed. Experimental results show that for small-angle oblique and vertical water entry, the the round-head and flat-head (disc cavitator) blunt bodies can form stable trajectories. When the initial water-entry velocity is lower, the closure mode of the cavity is deep closure. When the initial water-entry velocity is higher, the closure mode of the cavity is surface closure, and its speed decay rate is larger. For the supercavity generated by the small-angle oblique water entry of the blunt bodies, the front part of the supercavity contour is in agreement with the result by G.V. Logvinovich's semi-empirical formula. For the vertical water entry of the blunt bodies, the influences of the head shapes were discussed on the beginning points and morphologies of the supercavities.
2015, 35(5): 625-632.
doi: 10.11883/1001-1455(2015)05-0625-08
Abstract:
A gridless method for simulation of reactive flows involving moving boundaries was investigated based on the linear basis least-squares gridless method. The Euler equations of arbitrary Lagrangian-Eulerian form were employed as governing equations. The numerical flux and chemical sources were calculated by the multi-component HLLC ((Harten-Lax-van Leer-Contact) scheme and finite rate reaction model, respectively. An elevated restructuring technique of local cloud was adopted to deal with the moving boundaries. The front advance method of fictitious boundaries was used during the restructuring. The flow around the cylinder and the shock-induced combustion flow field were simulated to validate the accuracy firstly. The muzzle flow of a 12.7 mm machine gun was simulated. The computational shadowgraphs agree well with the experimental photographs, the density and pressure contours are in agreement with the results by the unstructured mesh method. The numerical results show the coupling and interaction progress in the initial muzzle flow field, the under-expanding jet of explosive gas and high-speed projectile clearly, and the temporal, spatial distribution characteristics of the muzzle flash are reappeared plainly.
A gridless method for simulation of reactive flows involving moving boundaries was investigated based on the linear basis least-squares gridless method. The Euler equations of arbitrary Lagrangian-Eulerian form were employed as governing equations. The numerical flux and chemical sources were calculated by the multi-component HLLC ((Harten-Lax-van Leer-Contact) scheme and finite rate reaction model, respectively. An elevated restructuring technique of local cloud was adopted to deal with the moving boundaries. The front advance method of fictitious boundaries was used during the restructuring. The flow around the cylinder and the shock-induced combustion flow field were simulated to validate the accuracy firstly. The muzzle flow of a 12.7 mm machine gun was simulated. The computational shadowgraphs agree well with the experimental photographs, the density and pressure contours are in agreement with the results by the unstructured mesh method. The numerical results show the coupling and interaction progress in the initial muzzle flow field, the under-expanding jet of explosive gas and high-speed projectile clearly, and the temporal, spatial distribution characteristics of the muzzle flash are reappeared plainly.
2015, 35(5): 633-640.
doi: 10.11883/1001-1455(2015)05-0633-08
Abstract:
Assuming that sand grains are incompressible, a compaction equation for porous dry sand was derived by applying the dynamic systolic model of a spherical cavity and the generalized Mises strength criterion. Based on the Hugoniot jump condition and the Grüneisen parameter, the equation of state for dry sand was given by considering porous compaction. According to the associated flow rule, the elasto-plastic stress-strain relationships of dry sand under large deformation were obtained. By means of the dynamic finite element computing method, the above models were used to analyze the penetration process of dry sand by a projectile. The results show that the models can reflect the reverse influence of sand pore evolution on the stress-strain state in the high-velocity penetration process, and can accurately describe the dynamic response of dry sand under high-velocity penetration.
Assuming that sand grains are incompressible, a compaction equation for porous dry sand was derived by applying the dynamic systolic model of a spherical cavity and the generalized Mises strength criterion. Based on the Hugoniot jump condition and the Grüneisen parameter, the equation of state for dry sand was given by considering porous compaction. According to the associated flow rule, the elasto-plastic stress-strain relationships of dry sand under large deformation were obtained. By means of the dynamic finite element computing method, the above models were used to analyze the penetration process of dry sand by a projectile. The results show that the models can reflect the reverse influence of sand pore evolution on the stress-strain state in the high-velocity penetration process, and can accurately describe the dynamic response of dry sand under high-velocity penetration.
2015, 35(5): 641-650.
doi: 10.11883/1001-1455(2015)05-0641-10
Abstract:
For studying the chemical mechanism of thermal deflagration of gasoline-air mixture in the confined space, the temperature of the system, the concentration of main components and the generation rate of production in the deflagration process of C1-C4 alkane were simulated with CHEMICAL4.1 as a platform. Based on the analysis for the simulated data of the chemical mechanism, three results were obtained as follows. (1)By sensitivity analysis, rate-of-production analysis, path analysis and so on, the detailed oxidation mechanism of C1-C4 alkane was studied, and drew a reduced mechanism which consisted of 37 species and 80 reactions. The comparison of the two mechanisms was presented. (2) There existed three distinct stages in the thermal deflagration process based on the analysis for the mechanism, namely slow oxidation, rapid oxidation and reaction equilibrium. (3) In the whole chain reaction process, the reactions generating hydroperoxyl and hydrogen peroxide were the key reactions because the hydrogen and hydroxyl groups were largely generated from them so that they induced the deflagration happen finally.
For studying the chemical mechanism of thermal deflagration of gasoline-air mixture in the confined space, the temperature of the system, the concentration of main components and the generation rate of production in the deflagration process of C1-C4 alkane were simulated with CHEMICAL4.1 as a platform. Based on the analysis for the simulated data of the chemical mechanism, three results were obtained as follows. (1)By sensitivity analysis, rate-of-production analysis, path analysis and so on, the detailed oxidation mechanism of C1-C4 alkane was studied, and drew a reduced mechanism which consisted of 37 species and 80 reactions. The comparison of the two mechanisms was presented. (2) There existed three distinct stages in the thermal deflagration process based on the analysis for the mechanism, namely slow oxidation, rapid oxidation and reaction equilibrium. (3) In the whole chain reaction process, the reactions generating hydroperoxyl and hydrogen peroxide were the key reactions because the hydrogen and hydroxyl groups were largely generated from them so that they induced the deflagration happen finally.
2015, 35(5): 651-658.
doi: 10.11883/1001-1455(2015)05-0651-08
Abstract:
An experimental system of dynamic caustics was applied to carry out fracture experiments for pre-cracked beam-column specimens. The following dynamic fracture behaviors of the specimens under impact loads were discussed: the crack extension tracks, velocities and stress intensity factors at the beam-column joints, the beams and the column ends. The experimental results indicate the following findings. Under impact loads, first, the specimens were cracked at the beam-column joints, and in the process of crack extension, the specimens underwent apparent bending fracture, both of which can explain that the beam-column joints are most vulnerable to damage. The more the pre-cracks, the later the beam-column joints crack, which displays that the less the pre-cracks, the more concentrated and faster the energy can accumulate at the crack tips. For a specimen with pre-existing cracks at the ends, the time interval between the initiations of two cracks is longer than that for one with pre-existing cracks at the beam. However, the second crack, in most cases, tends to occur in the beam. This phenomenon indicates that the fracture of a fixed bearing requires more energy than a simply-supported beam. The bending fracture phenomenon of a beam weakens as the pre-existing cracks increases. This is because the partial energy accumulates at the crack tips of the column ends, accordingly the energy inducing the cracks at the beam to expand, decreases. Due in large part to the cracks on the columns, the tensile stresses and bending moments at the crack tips on the beams decrease, which affect the bending fracture phenomenon of the specimens.
An experimental system of dynamic caustics was applied to carry out fracture experiments for pre-cracked beam-column specimens. The following dynamic fracture behaviors of the specimens under impact loads were discussed: the crack extension tracks, velocities and stress intensity factors at the beam-column joints, the beams and the column ends. The experimental results indicate the following findings. Under impact loads, first, the specimens were cracked at the beam-column joints, and in the process of crack extension, the specimens underwent apparent bending fracture, both of which can explain that the beam-column joints are most vulnerable to damage. The more the pre-cracks, the later the beam-column joints crack, which displays that the less the pre-cracks, the more concentrated and faster the energy can accumulate at the crack tips. For a specimen with pre-existing cracks at the ends, the time interval between the initiations of two cracks is longer than that for one with pre-existing cracks at the beam. However, the second crack, in most cases, tends to occur in the beam. This phenomenon indicates that the fracture of a fixed bearing requires more energy than a simply-supported beam. The bending fracture phenomenon of a beam weakens as the pre-existing cracks increases. This is because the partial energy accumulates at the crack tips of the column ends, accordingly the energy inducing the cracks at the beam to expand, decreases. Due in large part to the cracks on the columns, the tensile stresses and bending moments at the crack tips on the beams decrease, which affect the bending fracture phenomenon of the specimens.
2015, 35(5): 659-667.
doi: 10.11883/1001-1455(2015)05-0659-09
Abstract:
To confirm and reveal the characteristics of the flow field of the abrasive supercritical CO2 jet, the structure of the jet and the influence of the ambient factors were analyzed through numerical simulation, with the computational fluid dynamics software. Results show that the axial velocities of the fluid and particles on the wall firstly increase and then descend as the standoff distance increases, as well as the impact pressure of the fluid, which means that there is an optimal standoff distance where their peak values exist respectively and it is 3-6 times of the jet nozzle diameter at the differential pressure of 10-30 MPa; given fixed jet differential pressure, increase of the confining pressure from 10 MPa to 30 MPa has a weak negative effect on the axial velocity of the jet fluid. The supercritical CO2 jet-breaking-rock experiment was conducted to provide test to the results of the numerical simulation. The velocities of the fluid and particles increase as the temperature goes up from 333 K to 413 K, while the impact pressure of the supercritical CO2 fluid becomes weaker because of fluid density decrease as the volume fraction of the abrasive particles is set from 3.0% to 11.0% in a row, the velocity of each phase gradually decreases and the variation gradually gets smaller.
To confirm and reveal the characteristics of the flow field of the abrasive supercritical CO2 jet, the structure of the jet and the influence of the ambient factors were analyzed through numerical simulation, with the computational fluid dynamics software. Results show that the axial velocities of the fluid and particles on the wall firstly increase and then descend as the standoff distance increases, as well as the impact pressure of the fluid, which means that there is an optimal standoff distance where their peak values exist respectively and it is 3-6 times of the jet nozzle diameter at the differential pressure of 10-30 MPa; given fixed jet differential pressure, increase of the confining pressure from 10 MPa to 30 MPa has a weak negative effect on the axial velocity of the jet fluid. The supercritical CO2 jet-breaking-rock experiment was conducted to provide test to the results of the numerical simulation. The velocities of the fluid and particles increase as the temperature goes up from 333 K to 413 K, while the impact pressure of the supercritical CO2 fluid becomes weaker because of fluid density decrease as the volume fraction of the abrasive particles is set from 3.0% to 11.0% in a row, the velocity of each phase gradually decreases and the variation gradually gets smaller.
2015, 35(5): 668-674.
doi: 10.11883/1001-1455(2015)05-0668-07
Abstract:
To research the analytical method and affecting factors of the additional impact load, an integral expression formula was derived for the additional impact load. Three major parameters affecting the additional impact load were obtained. A numerical model was built for the adaptive base. And the correctness of this modeling method was verified by the test. Based on the built numerical model, a mathematic model was developed by combining the MISO (multiple-input, single-output) multivariate generalized polynomials neural network to describe the mechanical properties of the adaptive base. Thereby, the intelligent decision analysis was conducted for the affecting factors of the additional impact load. The analysis results show that the affecting factors for the additional impact load from high to low levels are cord modulus, section area and cord spacing. If the change of one parameter would cause the additional load to increase, the affecting factor by the corresponding parameter on the additional impact load decreases.
To research the analytical method and affecting factors of the additional impact load, an integral expression formula was derived for the additional impact load. Three major parameters affecting the additional impact load were obtained. A numerical model was built for the adaptive base. And the correctness of this modeling method was verified by the test. Based on the built numerical model, a mathematic model was developed by combining the MISO (multiple-input, single-output) multivariate generalized polynomials neural network to describe the mechanical properties of the adaptive base. Thereby, the intelligent decision analysis was conducted for the affecting factors of the additional impact load. The analysis results show that the affecting factors for the additional impact load from high to low levels are cord modulus, section area and cord spacing. If the change of one parameter would cause the additional load to increase, the affecting factor by the corresponding parameter on the additional impact load decreases.
2015, 35(5): 675-681.
doi: 10.11883/1001-1455(2015)05-0675-07
Abstract:
Experiments were carried out to explore the mechanical properties of the attenuation of shock waves respectively interacted with wooded plates, open and closed cellular foams. Based on the experimental data, the peak overpressure and positive impulse loss of shock waves were quantitatively analyzed as well as the positive impulses of the incidence, reflection and transmission shock waves. The experimental results show that the attenuation capacity of foams to shock waves is mainly due to the shock wave reflection and energy dissipation inside the foam microstructure. And the mechanical phenomena of open foam to shock wave are not fully consistent with those of closed foam, while the attenuation capacity of open foam to shock wave is more effective than that of closed foam.
Experiments were carried out to explore the mechanical properties of the attenuation of shock waves respectively interacted with wooded plates, open and closed cellular foams. Based on the experimental data, the peak overpressure and positive impulse loss of shock waves were quantitatively analyzed as well as the positive impulses of the incidence, reflection and transmission shock waves. The experimental results show that the attenuation capacity of foams to shock waves is mainly due to the shock wave reflection and energy dissipation inside the foam microstructure. And the mechanical phenomena of open foam to shock wave are not fully consistent with those of closed foam, while the attenuation capacity of open foam to shock wave is more effective than that of closed foam.
2015, 35(5): 682-688.
doi: 10.11883/1001-1455(2015)05-0682-07
Abstract:
On the basis of the industrial experiment of medium-depth hole caving in Jinchanggouliang Gold Mine, the authers carried out the optimization research of hole pattern blasting parameters. ANSYS/LS-DYNA was used to make several schemes of numerical simulation. Then the distribution features of the blasting stress fields under different hole pattern parameters and the formation process of the fractured blasting regions under the constrained blasting effect of narrow vein were obtained. The results show that when the resistance line is between 0.8 and 1.2 m, under the same hole spacing, the effective stress peak of the central free surface decreases with the increasing resistance line; when the hole spacing is between 0.9 and 1.6 m, it increases with the rising hole spacing under the same resistance line. As the bore hole density coefficient increases, the stress increments slow down, and the ore loss and dilution aggravate, if the bore hole density coefficient is more than 1.5. Comparison of all the schemes displays that the 1.0 m×1.4 m hole pattern parameter is the best. After employing the optimization results for the field experiment and with the CMS evaluating the blasting effect, the actual blasting zone volume covers 91.8% of the designed volume. The blast, with sound effect, did not cause the top and bottom side wall orebody to cave.
On the basis of the industrial experiment of medium-depth hole caving in Jinchanggouliang Gold Mine, the authers carried out the optimization research of hole pattern blasting parameters. ANSYS/LS-DYNA was used to make several schemes of numerical simulation. Then the distribution features of the blasting stress fields under different hole pattern parameters and the formation process of the fractured blasting regions under the constrained blasting effect of narrow vein were obtained. The results show that when the resistance line is between 0.8 and 1.2 m, under the same hole spacing, the effective stress peak of the central free surface decreases with the increasing resistance line; when the hole spacing is between 0.9 and 1.6 m, it increases with the rising hole spacing under the same resistance line. As the bore hole density coefficient increases, the stress increments slow down, and the ore loss and dilution aggravate, if the bore hole density coefficient is more than 1.5. Comparison of all the schemes displays that the 1.0 m×1.4 m hole pattern parameter is the best. After employing the optimization results for the field experiment and with the CMS evaluating the blasting effect, the actual blasting zone volume covers 91.8% of the designed volume. The blast, with sound effect, did not cause the top and bottom side wall orebody to cave.
2015, 35(5): 689-695.
doi: 10.11883/1001-1455(2015)05-0689-07
Abstract:
Aimed to the safety of an explosive charge in a projectile during penetration, the visco-statistical crack mechanics (Visco-SCRAM) model was applied to numerically calculate the bulk heat of the explosive charge, the heat produced by the friction between explosive charge cracks, and the heat induced by the friction between the explosive charge and the projectile inner wall. The contribution of the above three mechanisms to the temperature rise of the explosive charge were analyzed, the ignition mechanism of the explosive charge was discussed, and the critical initial penetration velocity of the projectile was obtained corresponding to the ignition of the explosive charge. The investigated results show as follows: (1) the heat induced by the friction between the explosive charge and the projectile inner wall has a certain contribution to the temperature rise of the explosive charge, and this contribution gradually increases as the initial penetration velocity of the projectile increases; (2) the bulk temperature rise produced by the viscosity, damage and adiabatic volume change plays a weak role in the ignition of the explosive charge; (3) the hot spot formation by the friction between the explosive charge cracks is the physical mechanism for the ignition of the explosive charge; (4) the Visco-SCRAM model can be used to predict the ignition responses of explosive charges to low strength and long pulse loads
Aimed to the safety of an explosive charge in a projectile during penetration, the visco-statistical crack mechanics (Visco-SCRAM) model was applied to numerically calculate the bulk heat of the explosive charge, the heat produced by the friction between explosive charge cracks, and the heat induced by the friction between the explosive charge and the projectile inner wall. The contribution of the above three mechanisms to the temperature rise of the explosive charge were analyzed, the ignition mechanism of the explosive charge was discussed, and the critical initial penetration velocity of the projectile was obtained corresponding to the ignition of the explosive charge. The investigated results show as follows: (1) the heat induced by the friction between the explosive charge and the projectile inner wall has a certain contribution to the temperature rise of the explosive charge, and this contribution gradually increases as the initial penetration velocity of the projectile increases; (2) the bulk temperature rise produced by the viscosity, damage and adiabatic volume change plays a weak role in the ignition of the explosive charge; (3) the hot spot formation by the friction between the explosive charge cracks is the physical mechanism for the ignition of the explosive charge; (4) the Visco-SCRAM model can be used to predict the ignition responses of explosive charges to low strength and long pulse loads
2015, 35(5): 696-702.
doi: 10.11883/1001-1455(2015)05-0696-07
Abstract:
The failure mode and mechanism of floating-roof oil storage tanks under the blast impact through the combustible gas explosion were discussed, on the basis of the scaled model tests and the numerical simulations comprehensively. It is found that the coupled impact effect of the blast wave and the liquid resulted in the bulking failure and damage of the oil storage tank body. In the process of the violent vibration, the stress concentration appeared on the upper area of the scaled model, and the tank body lost its stability and generated the concave formation and dynamic buckling area.
The failure mode and mechanism of floating-roof oil storage tanks under the blast impact through the combustible gas explosion were discussed, on the basis of the scaled model tests and the numerical simulations comprehensively. It is found that the coupled impact effect of the blast wave and the liquid resulted in the bulking failure and damage of the oil storage tank body. In the process of the violent vibration, the stress concentration appeared on the upper area of the scaled model, and the tank body lost its stability and generated the concave formation and dynamic buckling area.
2015, 35(5): 703-710.
doi: 10.11883/1001-1455(2015)05-0703-08
Abstract:
The interaction between explosion waves in soil and underground structures is the theory basis of underground protective structures design. Based on the tests, the rational media dynamic constitutive relationships were introduced and the wave propagation problems were solved. The recent advancements of calculation models and analytical methods on the interaction between explosion waves in soil and underground structures were reviewed. They were categorized into three parts: the dynamic constitutive models of soil, the explosion wave propagation in free field and the interaction between blast waves and underground structures such as box-framed structures, circular structures and horseshoe structures. The conventional dynamic constitutive models of unsaturated soil and saturated soil were itemized in details. The integrated elastoplastic dynamic constitutive model for soil was introduced, which can reflect relaxation effects of soil. The research achievements for one-dimensional plane wave propagation in inhomogeneous or layered media and the explosion load for underground structures were emphatically described. The applicable range and main deficiencies of various calculation models and analytical methods were analyzed.
The interaction between explosion waves in soil and underground structures is the theory basis of underground protective structures design. Based on the tests, the rational media dynamic constitutive relationships were introduced and the wave propagation problems were solved. The recent advancements of calculation models and analytical methods on the interaction between explosion waves in soil and underground structures were reviewed. They were categorized into three parts: the dynamic constitutive models of soil, the explosion wave propagation in free field and the interaction between blast waves and underground structures such as box-framed structures, circular structures and horseshoe structures. The conventional dynamic constitutive models of unsaturated soil and saturated soil were itemized in details. The integrated elastoplastic dynamic constitutive model for soil was introduced, which can reflect relaxation effects of soil. The research achievements for one-dimensional plane wave propagation in inhomogeneous or layered media and the explosion load for underground structures were emphatically described. The applicable range and main deficiencies of various calculation models and analytical methods were analyzed.
2015, 35(5): 711-716.
doi: 10.11883/1001-1455(2015)05-0711-06
Abstract:
Experiments and numerical simulations were carried out to explore a mechanical method for discarding the sabot of a high-velocity projectile by a laminated wood target. First, the feasibility and parametric regular pattern of an orthotropic material model for wood in numerical simulation were discussed. And the numerical simulation program was verified and validated by combining with the hyper-speed penetration experimental data of U.S. Army. Then, the penetration/perforation phenomena were analyzed for a sabot-contained projectile impacting a laminated wood target under different conditions. The numerically simulated and experimental results show the followings. Under normal impact, the sabot of a sub-caliber projectile can be discarded effectively by a reasonably-designed laminated wood target, the projectile can penetrate vertically into the target and its velocity attenuation can be controllable. Under oblique impact, a laminated wood target can induce the attack angel of the projectile to increase. With the increasing of impact velocity, the consumption of a projectile's kinetic energy increases, which indicates that wood has an apparent strain-rate strengthening effect.
Experiments and numerical simulations were carried out to explore a mechanical method for discarding the sabot of a high-velocity projectile by a laminated wood target. First, the feasibility and parametric regular pattern of an orthotropic material model for wood in numerical simulation were discussed. And the numerical simulation program was verified and validated by combining with the hyper-speed penetration experimental data of U.S. Army. Then, the penetration/perforation phenomena were analyzed for a sabot-contained projectile impacting a laminated wood target under different conditions. The numerically simulated and experimental results show the followings. Under normal impact, the sabot of a sub-caliber projectile can be discarded effectively by a reasonably-designed laminated wood target, the projectile can penetrate vertically into the target and its velocity attenuation can be controllable. Under oblique impact, a laminated wood target can induce the attack angel of the projectile to increase. With the increasing of impact velocity, the consumption of a projectile's kinetic energy increases, which indicates that wood has an apparent strain-rate strengthening effect.
2015, 35(5): 717-722.
doi: 10.11883/1001-1455(2015)05-0717-06
Abstract:
Reinforcing design for the opening on a certain experiment-used spherical explosive containment vessel was carried out referring to the pressure vessel code GB150-2011. The relationships between the effective plastic strain around the opening and the geometrical parameters of the nozzle and the reinforcing ring were investigated by numerical simulation. And a reinforcing scheme was proposed which included a nozzle with the wall thickness equal to 5/3 times of the wall thickness of the main spherical shell and a 10°-reinforcing ring with the same thickness to the main spherical shell wall. Experiments were performed to validate the reliability of the simulation results and the rationality of the reinforcing scheme.
Reinforcing design for the opening on a certain experiment-used spherical explosive containment vessel was carried out referring to the pressure vessel code GB150-2011. The relationships between the effective plastic strain around the opening and the geometrical parameters of the nozzle and the reinforcing ring were investigated by numerical simulation. And a reinforcing scheme was proposed which included a nozzle with the wall thickness equal to 5/3 times of the wall thickness of the main spherical shell and a 10°-reinforcing ring with the same thickness to the main spherical shell wall. Experiments were performed to validate the reliability of the simulation results and the rationality of the reinforcing scheme.
2015, 35(5): 723-728.
doi: 10.11883/1001-1455(2015)05-0723-06
Abstract:
A new discrete rod warhead named profiled rod warhead was proposed to improve the damage aftereffect, and the experimental research on detonation-driven profiled rod dispersing was employed. The initial velocity of the rods were obtained. The dispersion characteristics and flight attitude of the rods and their damage effect to the aming steel plates were analyzed. The flight attitudes of the rods changed in the detonation-driven process. Experimental results show that the expected design effects were achieved.
A new discrete rod warhead named profiled rod warhead was proposed to improve the damage aftereffect, and the experimental research on detonation-driven profiled rod dispersing was employed. The initial velocity of the rods were obtained. The dispersion characteristics and flight attitude of the rods and their damage effect to the aming steel plates were analyzed. The flight attitudes of the rods changed in the detonation-driven process. Experimental results show that the expected design effects were achieved.
2015, 35(5): 729-734.
doi: 10.11883/1001-1455(2015)05-0729-06
Abstract:
To research the influence of the T-shaped branch structure during the explosions of gasoline-air mixture in pipelines, the explosion wave overpressure of gasoline-air mixture explosion in the T-shaped branch pipeline and the straight pipeline at different initial volune fractions were measured through contrast experiments, and the flame propagation rules were researched in an organic glass pipeline by visualized study. The results show that the T-shaped branch pipe can strengthen the explosions of gasoline-air mixture in pipelines, which is the most obvious within the volume fraction range of oilgas from 1.2% to 1.6%. The effect of the T-shaped branch pipe to strengthen the explosion of gasoline-air mixture comes from three aspects: the sudden enlargement of the pipeline cross section, the reinforcement of the disturbance and the obstacles, and the influence of the reflection and diffraction of the waves. When the flame propagates to the T-shaped branch pipeline, the flame front creases distorted, the flame surface area and combustion rate increase significantly, which enhances the heat and the transport rate of active material and improves the strength of the explosion waves. Near the T-shaped branch pipe, the pressure of gasoline-air mixture explosion increased suddenly, both because of the temperature effect caused by the pressure wave reflection and diffraction, and the turbulence intensity increased by explosion waves.
To research the influence of the T-shaped branch structure during the explosions of gasoline-air mixture in pipelines, the explosion wave overpressure of gasoline-air mixture explosion in the T-shaped branch pipeline and the straight pipeline at different initial volune fractions were measured through contrast experiments, and the flame propagation rules were researched in an organic glass pipeline by visualized study. The results show that the T-shaped branch pipe can strengthen the explosions of gasoline-air mixture in pipelines, which is the most obvious within the volume fraction range of oilgas from 1.2% to 1.6%. The effect of the T-shaped branch pipe to strengthen the explosion of gasoline-air mixture comes from three aspects: the sudden enlargement of the pipeline cross section, the reinforcement of the disturbance and the obstacles, and the influence of the reflection and diffraction of the waves. When the flame propagates to the T-shaped branch pipeline, the flame front creases distorted, the flame surface area and combustion rate increase significantly, which enhances the heat and the transport rate of active material and improves the strength of the explosion waves. Near the T-shaped branch pipe, the pressure of gasoline-air mixture explosion increased suddenly, both because of the temperature effect caused by the pressure wave reflection and diffraction, and the turbulence intensity increased by explosion waves.
2015, 35(5): 735-740.
doi: 10.11883/1001-1455(2015)05-0735-06
Abstract:
To investigate the characteristics of rocket launching noise and the acoustic distribution around the nozzle, the gas jet noise was studied experimentally and numerically. Three main components (turbulent mixing noise, screech tone and broadband shock noise radiation) and respective features of supersonic jet noise were explored, which revealed that the speed disturbance of the turbulent jet is the principal factor influencing noise radiation. The sound pressure level peaks of the jet noise at different test points were analyzed, and the distribution rule of the jet noise was got in the axial and radial directions. The investigated results show that with increasing the distance from the nozzle exit, the attenuation of noise in the axial direction is higher than that in the radical direction. Based on the experiments, the sound pressure level peaks of the supersonic jet noise were calculated by large eddy simulation and Ffowcs Williams-Hawkings acoustic analogy. The calculated results are in agreement with the experimental ones, which can provide reference for further study of controlling jet noise.
To investigate the characteristics of rocket launching noise and the acoustic distribution around the nozzle, the gas jet noise was studied experimentally and numerically. Three main components (turbulent mixing noise, screech tone and broadband shock noise radiation) and respective features of supersonic jet noise were explored, which revealed that the speed disturbance of the turbulent jet is the principal factor influencing noise radiation. The sound pressure level peaks of the jet noise at different test points were analyzed, and the distribution rule of the jet noise was got in the axial and radial directions. The investigated results show that with increasing the distance from the nozzle exit, the attenuation of noise in the axial direction is higher than that in the radical direction. Based on the experiments, the sound pressure level peaks of the supersonic jet noise were calculated by large eddy simulation and Ffowcs Williams-Hawkings acoustic analogy. The calculated results are in agreement with the experimental ones, which can provide reference for further study of controlling jet noise.
2015, 35(5): 741-746.
doi: 10.11883/1001-1455(2015)05-0741-06
Abstract:
The basic principle of regression analysis was considered for the prediction formula of blasting vibration velocity. On the basis of the considered principle, an opinion was put forward that certain reliability indexes should be chosen according to the safety levels of buildings. And the calculation process was deduced for the safety assurance coefficient included in the prediction formula of blasting vibration velocity. To simplify the calculation process, an empirical calculation formula was proposed for the safety assurance coefficient based on the parameters consisting of amount of monitoring data, correlation coefficient of regression analysis, and reliability index. The accuracy and reliability of the empirical calculation formula was verified by the monitoring data in actual projects. The investigated results show that the empirical calculation formula can meet the practical needs and it can make up the shortcoming that the accuracy of Sadov's formula is not enough. So the empirical calculation formula proposed can provide a reference for the design of safety blasting surrounding important buildings.
The basic principle of regression analysis was considered for the prediction formula of blasting vibration velocity. On the basis of the considered principle, an opinion was put forward that certain reliability indexes should be chosen according to the safety levels of buildings. And the calculation process was deduced for the safety assurance coefficient included in the prediction formula of blasting vibration velocity. To simplify the calculation process, an empirical calculation formula was proposed for the safety assurance coefficient based on the parameters consisting of amount of monitoring data, correlation coefficient of regression analysis, and reliability index. The accuracy and reliability of the empirical calculation formula was verified by the monitoring data in actual projects. The investigated results show that the empirical calculation formula can meet the practical needs and it can make up the shortcoming that the accuracy of Sadov's formula is not enough. So the empirical calculation formula proposed can provide a reference for the design of safety blasting surrounding important buildings.
2015, 35(5): 747-752.
doi: 10.11883/1001-1455(2015)05-0747-06
Abstract:
Flammability limits for the binary mixtures of CH4/N2 and CH4/CO2 were measured, and the ternary mixtures of CH4/N2/CO2 with three different diluent volume ratios were studied. A method based on the adiabatic flame temperature was introduced to estimate the flammability limits of the mixtures, and the experimental results were compared with the estimated values. The average absolute deviation between the experimental results and estimated values of the lower flammability limit for the two binary mixtures is 0.15%, and for the upper flammability limit is 0.34%. The average absolute deviation between the experimental results and estimated values of the lower flammability limit for the three ternary mixtures is 0.20%, and for the upper flammability limit is 0.43%. The results showed that the method is available for estimating the flammability limits of the binary and ternary mixtures of methane with diluent gases.
Flammability limits for the binary mixtures of CH4/N2 and CH4/CO2 were measured, and the ternary mixtures of CH4/N2/CO2 with three different diluent volume ratios were studied. A method based on the adiabatic flame temperature was introduced to estimate the flammability limits of the mixtures, and the experimental results were compared with the estimated values. The average absolute deviation between the experimental results and estimated values of the lower flammability limit for the two binary mixtures is 0.15%, and for the upper flammability limit is 0.34%. The average absolute deviation between the experimental results and estimated values of the lower flammability limit for the three ternary mixtures is 0.20%, and for the upper flammability limit is 0.43%. The results showed that the method is available for estimating the flammability limits of the binary and ternary mixtures of methane with diluent gases.
2015, 35(5): 753-757.
doi: 10.11883/1001-1455(2015)05-0753-05
Abstract:
Explosion characteristics of dimethyl ether (DME)/air and DME/air/ argon (Ar) mixtures were studied by using a 20-L spherical explosion-containment vessel under different initial conditions. This paper analyzed the effects of different initial conditions (e.g., pressures, Ar dilution) on the explosion parameters including explosion limits, maximum explosion pressure and maximum rise rate of explosion pressure. A dome-shaped relationship was found between maximum explosion pressure and DME concentration. And there lies a dome-shaped relationship between maximum explosion pressure rise rate and DME concentration. Their maximum values appear in the vicinity of the stoichiometric composition. Lowering the initial pressure can significantly decrease the upper flammability limit, but has no influence on the lower explosion limit. For fuel-rich DME/air mixtures, Ar dilution can greatly decrease the maximum explosion pressure and the maximum rise rate of explosion pressure. For fuel-lean ones, in a certain range of Ar concentration, the maximum explosion pressure and the maximum rise rate of explosion pressure increase with the increasing of Ar concentration. And these explosion parameters decrease eventually with the increasing of Ar concentration over 20%.
Explosion characteristics of dimethyl ether (DME)/air and DME/air/ argon (Ar) mixtures were studied by using a 20-L spherical explosion-containment vessel under different initial conditions. This paper analyzed the effects of different initial conditions (e.g., pressures, Ar dilution) on the explosion parameters including explosion limits, maximum explosion pressure and maximum rise rate of explosion pressure. A dome-shaped relationship was found between maximum explosion pressure and DME concentration. And there lies a dome-shaped relationship between maximum explosion pressure rise rate and DME concentration. Their maximum values appear in the vicinity of the stoichiometric composition. Lowering the initial pressure can significantly decrease the upper flammability limit, but has no influence on the lower explosion limit. For fuel-rich DME/air mixtures, Ar dilution can greatly decrease the maximum explosion pressure and the maximum rise rate of explosion pressure. For fuel-lean ones, in a certain range of Ar concentration, the maximum explosion pressure and the maximum rise rate of explosion pressure increase with the increasing of Ar concentration. And these explosion parameters decrease eventually with the increasing of Ar concentration over 20%.
2015, 35(5): 758-762.
doi: 10.11883/1001-1455(2015)05-0758-05
Abstract:
There is an oscillation signal superposition on measured acceleration signals during the process of penetrating multilayer hard targets, which can cause a misjudgement of the target layer number. To overcome the above problem, a time-frequency analysis method was adopted to study the Choi-Williams energy distribution features of the acceleration signals in the directions of projectile main axes. Based on the energy distribution of the acceleration signals during penetration process, a target layer identification method was put forward. The acceleration data were processed, and these data were measured from the penetration of eight concrete slabs with the same thickness by a projectile. The processed results show that the layer identification method put forward can identify the layer number rapidly and accurately. The problem, that the low-pass filtering method can not acquire the accurate layer number, was solved. So the layer identification method put forward can provide basis for the real-time control of initiation positions.
There is an oscillation signal superposition on measured acceleration signals during the process of penetrating multilayer hard targets, which can cause a misjudgement of the target layer number. To overcome the above problem, a time-frequency analysis method was adopted to study the Choi-Williams energy distribution features of the acceleration signals in the directions of projectile main axes. Based on the energy distribution of the acceleration signals during penetration process, a target layer identification method was put forward. The acceleration data were processed, and these data were measured from the penetration of eight concrete slabs with the same thickness by a projectile. The processed results show that the layer identification method put forward can identify the layer number rapidly and accurately. The problem, that the low-pass filtering method can not acquire the accurate layer number, was solved. So the layer identification method put forward can provide basis for the real-time control of initiation positions.
2015, 35(5): 763-767.
doi: 10.11883/1001-1455(2015)05-0763-05
Abstract:
Based on the Gurney velocity formula for cylindrical shells with finite length, the average strain rate was estimated by the average radius of the shell. And by taking into account the differences between the shear fracture surface length of the shell and the radial thickness, the Grady-Kipp method was modified to give a full expression for the number of the circumferential fragments of the cylindrical shell. The number of the circumferential fragments number calculated by the modified Grady-Kipp method can better match with the experimental result than one by the Grady theory. The 20# low-carbon steel was taken as an example to numerically simulate the expansion and fracture of low-carbon steel shells under TNT explosion loading. The numbers of the circumferential fragments of the low-carbon steel shells by numerical simulation are in agreement with the experimental one.
Based on the Gurney velocity formula for cylindrical shells with finite length, the average strain rate was estimated by the average radius of the shell. And by taking into account the differences between the shear fracture surface length of the shell and the radial thickness, the Grady-Kipp method was modified to give a full expression for the number of the circumferential fragments of the cylindrical shell. The number of the circumferential fragments number calculated by the modified Grady-Kipp method can better match with the experimental result than one by the Grady theory. The 20# low-carbon steel was taken as an example to numerically simulate the expansion and fracture of low-carbon steel shells under TNT explosion loading. The numbers of the circumferential fragments of the low-carbon steel shells by numerical simulation are in agreement with the experimental one.
