2008 Vol. 28, No. 5
Display Method:
2008, 28(5): 385-390.
doi: 10.11883/1001-1455(2008)05-0385-06
PDF 
Cited by
Abstract:
The techniques of the high-speed schlieren photography, etc. were used to investigate the characteristics of the premixed methane-air flames with different equivalence ratios propagating through a closed tube. Based on the experimental results, the combustion behaviors and characteristics of the premixed flames were analyzed. Analyzed results show as follows: (1) the transformation process of the flame front bending to the unburned zone turning into bending to the burned zone during the flame propagation happens while the equivalence ratio volume approaches to 1, thus the typical tulip flame structure forms during the transformation; (2) the transformation process of the flame front does not happen while the equivalence ratio volume deviates from 1 to a certain extent, and the premixed flame shows the typical laminar combustion. (3) the tulip-flame structure forms in the period of the flame propagation velocity decreasing greatly and it can form only while the maximum deceleration is larger than a certain quantity; (4) the tulip-flame structure is a middle stage during the transformation of the premixed flame from the laminar combustion to the turbulent combustion.
The techniques of the high-speed schlieren photography, etc. were used to investigate the characteristics of the premixed methane-air flames with different equivalence ratios propagating through a closed tube. Based on the experimental results, the combustion behaviors and characteristics of the premixed flames were analyzed. Analyzed results show as follows: (1) the transformation process of the flame front bending to the unburned zone turning into bending to the burned zone during the flame propagation happens while the equivalence ratio volume approaches to 1, thus the typical tulip flame structure forms during the transformation; (2) the transformation process of the flame front does not happen while the equivalence ratio volume deviates from 1 to a certain extent, and the premixed flame shows the typical laminar combustion. (3) the tulip-flame structure forms in the period of the flame propagation velocity decreasing greatly and it can form only while the maximum deceleration is larger than a certain quantity; (4) the tulip-flame structure is a middle stage during the transformation of the premixed flame from the laminar combustion to the turbulent combustion.
2008, 28(5): 391-400.
doi: 10.11883/1001-1455(2008)05-0391-10
Abstract:
The flow field during the motion of an underwater explosion bubble is supposed as an inviscid, irrotational and incompressible ideal fluid to simulate the bubble motion in a free field using the boundary element method. An computational program is developed and in the calculation process, the numeric fair technique and elastic mesh technique are applied to avoid the numerical divergence induced by the mesh distortion. The error between the computed and experimental results is less than 10%. From the basic phenomenon of the underwater explosion bubble in the free field, the dynamic behavior of the bubble in the free field is investigated systematically by using the developed program. By analyzing the pressures of the fluid field in the different directions, it gains that the pressures in the directions of the bubble center movement and the jet attack are higher than those in other directions. It explains that the pressure loaded in the direction of the bubble jet attack is maximum and damages the underwater structure severely, showing the asymmetry of the bubble loading. Calculated velocity curves at the different positions in the fluid field reveal that the velocity of the retarded flow induced by the bubble motion decreases rapidly with the increase of the distance between the retarded flow and the bubble center, and the direction of the retarded flow reverses with the bubble expanding and collapsing. Attenuation and variation of the retarded flow are summed up.
The flow field during the motion of an underwater explosion bubble is supposed as an inviscid, irrotational and incompressible ideal fluid to simulate the bubble motion in a free field using the boundary element method. An computational program is developed and in the calculation process, the numeric fair technique and elastic mesh technique are applied to avoid the numerical divergence induced by the mesh distortion. The error between the computed and experimental results is less than 10%. From the basic phenomenon of the underwater explosion bubble in the free field, the dynamic behavior of the bubble in the free field is investigated systematically by using the developed program. By analyzing the pressures of the fluid field in the different directions, it gains that the pressures in the directions of the bubble center movement and the jet attack are higher than those in other directions. It explains that the pressure loaded in the direction of the bubble jet attack is maximum and damages the underwater structure severely, showing the asymmetry of the bubble loading. Calculated velocity curves at the different positions in the fluid field reveal that the velocity of the retarded flow induced by the bubble motion decreases rapidly with the increase of the distance between the retarded flow and the bubble center, and the direction of the retarded flow reverses with the bubble expanding and collapsing. Attenuation and variation of the retarded flow are summed up.
2008, 28(5): 401-406.
doi: 10.11883/1001-1455(2008)05-0401-06
Abstract:
Algorithms for the flow field of detonation products behind 2D curved detonation waves are given. Detonation propagation is described by detonation shock dynamics, and detonation front positions are computed by the LS methods. Detonation propagation and coupling between the detonation front and the flow field of detonation products behind the detonation front are calculated by a program burn method, in which the reaction process variable is defined by the LS functions. Calculated results for 2D detonation wave diffraction from a rigid finer tube to a coarser tube show that chemical reaction rates do not influence the flow field distribution behind the detonation front, only affects the reaction zone structure. The proposed method can deal with the driven problems of insensitive explosives.
Algorithms for the flow field of detonation products behind 2D curved detonation waves are given. Detonation propagation is described by detonation shock dynamics, and detonation front positions are computed by the LS methods. Detonation propagation and coupling between the detonation front and the flow field of detonation products behind the detonation front are calculated by a program burn method, in which the reaction process variable is defined by the LS functions. Calculated results for 2D detonation wave diffraction from a rigid finer tube to a coarser tube show that chemical reaction rates do not influence the flow field distribution behind the detonation front, only affects the reaction zone structure. The proposed method can deal with the driven problems of insensitive explosives.
2008, 28(5): 407-414.
doi: 10.11883/1001-1455(2008)05-0407-08
Abstract:
The high-amplitude single-mode Richtmyer-Meshkov instability is simulated by using the high-resolution ghost-fluid method. The initial conditions and computational domain are modeled after the single-mode, 1.15-Mach， shock tube experiment by Jourdan G, et al. Four test examples are presented with the evolutions of the air-CO2, air-SF6, air-N2 and air-He interfaces, including density and shading contours. The simulated amplitudes are in agreement with the experimental data and the predictions of the theoretical models. The perturbation growths for the light-heavy (air-SF6 and air-CO2) cases agree well with the nonlinear model of Sadot O, et al. At the close density (air-N2) interface acting with the weak shock wave, the slow evolution can be described by the linear theory.
The high-amplitude single-mode Richtmyer-Meshkov instability is simulated by using the high-resolution ghost-fluid method. The initial conditions and computational domain are modeled after the single-mode, 1.15-Mach， shock tube experiment by Jourdan G, et al. Four test examples are presented with the evolutions of the air-CO2, air-SF6, air-N2 and air-He interfaces, including density and shading contours. The simulated amplitudes are in agreement with the experimental data and the predictions of the theoretical models. The perturbation growths for the light-heavy (air-SF6 and air-CO2) cases agree well with the nonlinear model of Sadot O, et al. At the close density (air-N2) interface acting with the weak shock wave, the slow evolution can be described by the linear theory.
2008, 28(5): 415-420.
doi: 10.11883/1001-1455(2008)05-0415-06
Abstract:
The method and technology, which can be used to make three-dimensional numerical simulations on the whole process of a long-rod projectile penetrating and exploding in a thick concrete target, are investigated. The related method and key techniques for the corresponding numerical simulations are presented. The suitable constitutive model and the appropriate parameters for the target material, C30 concrete, are determined. The three-dimensional numerical simulations are carried out on the whole physical process of an ogive-nosed rod projectile penetrating to a depth and then exploding in a C30 concrete target. The pictures of damaging effects of the C30 concrete target are shown for penetration and explosion respectively. The simulated penetration results are compared with the experimental ones, and they reach good agreement qualitatively.
The method and technology, which can be used to make three-dimensional numerical simulations on the whole process of a long-rod projectile penetrating and exploding in a thick concrete target, are investigated. The related method and key techniques for the corresponding numerical simulations are presented. The suitable constitutive model and the appropriate parameters for the target material, C30 concrete, are determined. The three-dimensional numerical simulations are carried out on the whole physical process of an ogive-nosed rod projectile penetrating to a depth and then exploding in a C30 concrete target. The pictures of damaging effects of the C30 concrete target are shown for penetration and explosion respectively. The simulated penetration results are compared with the experimental ones, and they reach good agreement qualitatively.
2008, 28(5): 421-426.
doi: 10.11883/1001-1455(2008)05-0421-06
Abstract:
The layer-directional compressive mechanical properties of 2-demensional carbon-fiber-reinforced silicon carbide ceramic matrix composites (2D-C/SiC CMCs) were investigated at the strain rates of 10-4~ 2.8 103 s-1. The static experiments were done by using the electronic universal testing machine, and the dynamic experiments were done by using the SHPB system. The results show that the dynamic compressive stress-strain curve is non-linear. The failure strength and the elasticity modulus increase, and the failure strain decreases with the strain rate. The elastic modulus is linear to the logarithm of the strain rate. A new constitutive equation, in which the rate-dependent and damage-softening effects are considered, was proposed. This equation agrees well with the experimental results.
The layer-directional compressive mechanical properties of 2-demensional carbon-fiber-reinforced silicon carbide ceramic matrix composites (2D-C/SiC CMCs) were investigated at the strain rates of 10-4~ 2.8 103 s-1. The static experiments were done by using the electronic universal testing machine, and the dynamic experiments were done by using the SHPB system. The results show that the dynamic compressive stress-strain curve is non-linear. The failure strength and the elasticity modulus increase, and the failure strain decreases with the strain rate. The elastic modulus is linear to the logarithm of the strain rate. A new constitutive equation, in which the rate-dependent and damage-softening effects are considered, was proposed. This equation agrees well with the experimental results.
2008, 28(5): 427-432.
doi: 10.11883/1001-1455(2008)05-0427-06
Abstract:
In order to high-accurately measure air shock wave, a theoretical frequency response property calculation of the measuring system was presented with sound-vibration coupling analysis. Dynamic response experiments of the measuring system were carried out in a shock tube. The suitable diameters of the damper holes in probes were obtained for three different ranges. Results show that the calculated values of the diameters of damper holes in probes and the jump time of pressure waveform are in basical agreement with the measured ones. The shock pressure waveform measured by the measuring system in intense explosions presents fine frequency response properties.
In order to high-accurately measure air shock wave, a theoretical frequency response property calculation of the measuring system was presented with sound-vibration coupling analysis. Dynamic response experiments of the measuring system were carried out in a shock tube. The suitable diameters of the damper holes in probes were obtained for three different ranges. Results show that the calculated values of the diameters of damper holes in probes and the jump time of pressure waveform are in basical agreement with the measured ones. The shock pressure waveform measured by the measuring system in intense explosions presents fine frequency response properties.
2008, 28(5): 433-437.
doi: 10.11883/1001-1455(2008)05-0433-05
Abstract:
The rapid dispersal process and phenomena of high explosive, aluminized explosive and thermobaric explosive were investigated experimentally by using a high-speed framing camera. By comparing the characteristics of the dispersal process and afterburning of the three kinds of explosive, two processes of explosion and afterburn of the thermobaric explosive, and the development history of the afterburn fireball were observed. Based on the experimental results, a formula was proposed to discribe the variation of the dispersal radius of the thermobaric explosive explosion production with time.
The rapid dispersal process and phenomena of high explosive, aluminized explosive and thermobaric explosive were investigated experimentally by using a high-speed framing camera. By comparing the characteristics of the dispersal process and afterburning of the three kinds of explosive, two processes of explosion and afterburn of the thermobaric explosive, and the development history of the afterburn fireball were observed. Based on the experimental results, a formula was proposed to discribe the variation of the dispersal radius of the thermobaric explosive explosion production with time.
2008, 28(5): 438-442.
doi: 10.11883/1001-1455(2008)05-0438-05
Abstract:
The level set method based on adaptive Cartesian grids is used to simulate multi-material flow problems. An quadtree-based algorithm is applied to generate adaptive Cartesian grids. The Euler equations are solved by the finite volume method and the flux of the control face is computed by the HLLC （Hartern, Lax, van Leer, Contact）approximate Riemann method. The level set equations are solved by the finite volume method and the flux is computed by the Lax-Friedchs method. The narrow band method is used to reduce computational costs and the ghost fluid method is used to treat the interface. The explicit two-stage Runge-Kutta time-integration scheme can achieve second-order time-accuracy and the space accuracy is second order. The shock-tube problem containing two different ideal gases with different specific heat ratios is computed and the numerical results agree with the exact solution. Simulated results on interaction of air with helium bubble are satisfactory.
The level set method based on adaptive Cartesian grids is used to simulate multi-material flow problems. An quadtree-based algorithm is applied to generate adaptive Cartesian grids. The Euler equations are solved by the finite volume method and the flux of the control face is computed by the HLLC （Hartern, Lax, van Leer, Contact）approximate Riemann method. The level set equations are solved by the finite volume method and the flux is computed by the Lax-Friedchs method. The narrow band method is used to reduce computational costs and the ghost fluid method is used to treat the interface. The explicit two-stage Runge-Kutta time-integration scheme can achieve second-order time-accuracy and the space accuracy is second order. The shock-tube problem containing two different ideal gases with different specific heat ratios is computed and the numerical results agree with the exact solution. Simulated results on interaction of air with helium bubble are satisfactory.
2008, 28(5): 443-447.
doi: 10.11883/1001-1455(2008)05-0443-05
Abstract:
Based on the nucleation-and-growth model of microvoids and the phenomenological assumption, a microvoid damage evolution equation was acquired. The material constitutive relation considering the effects of damage and temperature softening was developed. The damage evolution and material constitutive equations were embedded into the fininte element software ABAQUS with its material interface to simulate numerically the impact spallations of DA6C and 921 steel plates. The simulated results are in good agreement with the experiments.
Based on the nucleation-and-growth model of microvoids and the phenomenological assumption, a microvoid damage evolution equation was acquired. The material constitutive relation considering the effects of damage and temperature softening was developed. The damage evolution and material constitutive equations were embedded into the fininte element software ABAQUS with its material interface to simulate numerically the impact spallations of DA6C and 921 steel plates. The simulated results are in good agreement with the experiments.
2008, 28(5): 448-454.
doi: 10.11883/1001-1455(2008)05-0448-07
Abstract:
Stress uniformity along the axial direction in specimens of split Hopkinson pressure bar (SHPB) tests was investigated. By theory of one-dimensional elastic stress wave, the temporal and spatial distribution of stress in specimen induced by incident pulses with any rising shape was derived. Wave propagation processes in specimens were calculated under rectangular, trapezoidal and sloping waves, which were uniquely expressed as the trapezoidal type by the parameter of rise time. Stress uniformity histories were obtained, and the influences of relative rise time of incident pulse and specimen-bar relative mechanical impedance on relative time required for stress uniformity were investigated. Researched results can provide guidelines to design and analyze SHPB tests.
Stress uniformity along the axial direction in specimens of split Hopkinson pressure bar (SHPB) tests was investigated. By theory of one-dimensional elastic stress wave, the temporal and spatial distribution of stress in specimen induced by incident pulses with any rising shape was derived. Wave propagation processes in specimens were calculated under rectangular, trapezoidal and sloping waves, which were uniquely expressed as the trapezoidal type by the parameter of rise time. Stress uniformity histories were obtained, and the influences of relative rise time of incident pulse and specimen-bar relative mechanical impedance on relative time required for stress uniformity were investigated. Researched results can provide guidelines to design and analyze SHPB tests.
2008, 28(5): 455-461.
doi: 10.11883/1001-1455(2008)05-0455-07
Abstract:
This paper presents a newly-designed loading truncated cone, its associated two gland bushes, and an analytical formula for testing dynamic fracture toughness of anthracite. The impact fracture tests were carried out by using the SHPB and the newly-designed loading components. The dynamic fracture toughness of anthracite was measured on the short-bar anthracite specimens with the V-shaped notch. The relationship between the fracture toughness and loading ratelg(dF/dt) of anthracite was obtained by combining with the experimental data gained from the quasi-static tests. The fracture toughness of anthracite increases gradually whenlg(dF/dt), and it increases rapidly whenlg(dF/dt). The tests prove that the newly-developed truncated cone is better than the conventional knife-wedge for measuring the dynamic fracture toughness of short-rod specimens of rocklike materials.
This paper presents a newly-designed loading truncated cone, its associated two gland bushes, and an analytical formula for testing dynamic fracture toughness of anthracite. The impact fracture tests were carried out by using the SHPB and the newly-designed loading components. The dynamic fracture toughness of anthracite was measured on the short-bar anthracite specimens with the V-shaped notch. The relationship between the fracture toughness and loading ratelg(dF/dt) of anthracite was obtained by combining with the experimental data gained from the quasi-static tests. The fracture toughness of anthracite increases gradually whenlg(dF/dt), and it increases rapidly whenlg(dF/dt). The tests prove that the newly-developed truncated cone is better than the conventional knife-wedge for measuring the dynamic fracture toughness of short-rod specimens of rocklike materials.
2008, 28(5): 462-466.
doi: 10.11883/1001-1455(2008)05-0462-05
Abstract:
Three pure aluminum specimens with different grain sizes were obtained by the controlled heat treatment process. The stress-strain curves of the three pure aluminum specimens at 102~104 s-1 were obtained by using the split Hopkinson pressure bar technique. The yield stress and flow stress increase with the decrease of the grain size. A Hall-Petch relationship of pure aluminum under dynamic loadings was fitted out. Spall tests were performed for the three specimens by utilizing a one-stage gas gun. The results show that the grain size can hardly influence the spall properties of pure aluminum.
Three pure aluminum specimens with different grain sizes were obtained by the controlled heat treatment process. The stress-strain curves of the three pure aluminum specimens at 102~104 s-1 were obtained by using the split Hopkinson pressure bar technique. The yield stress and flow stress increase with the decrease of the grain size. A Hall-Petch relationship of pure aluminum under dynamic loadings was fitted out. Spall tests were performed for the three specimens by utilizing a one-stage gas gun. The results show that the grain size can hardly influence the spall properties of pure aluminum.
2008, 28(5): 467-470.
doi: 10.11883/1001-1455(2008)05-0467-04
Abstract:
Different additives were added to ANFO to enhance its detonator initiation sensitivity and work capacity. Based on the principle of the plate trace test, the test device and method were proposed to compare detonator initiation sensitivity and work capacity of ANFO containing additives. The results show that all the selected additives can improve detonator initiation sensitivity and work capacity of ANFO. Among these additives, Al and AP have stronger effects on the work capacity of ANFO than glass microballoon particles, AC foaming agent and NaNO2. The effect mechanisms of these additives were analyzed respectively.
Different additives were added to ANFO to enhance its detonator initiation sensitivity and work capacity. Based on the principle of the plate trace test, the test device and method were proposed to compare detonator initiation sensitivity and work capacity of ANFO containing additives. The results show that all the selected additives can improve detonator initiation sensitivity and work capacity of ANFO. Among these additives, Al and AP have stronger effects on the work capacity of ANFO than glass microballoon particles, AC foaming agent and NaNO2. The effect mechanisms of these additives were analyzed respectively.
2008, 28(5): 471-475.
doi: 10.11883/1001-1455(2008)05-0471-05
Abstract:
The infrared thermography method was used to investigate the detonation temperature of thermobaric explosives (TBE). The experimental result shows that the temperature of TBEs detonation cloud is higher than that of TNT with the same weight. The duration of high temperature and the volume of the high temperature cloud are 2~5 and 2~10 times as much as those of TNT, respectively. This implies that TBE is superior to the traditional high explosive on the temperature field. The high-temperature environment formed by the explosive explosion is sufficient to maintain the afterburning of the aluminum powder，which can provide assistance to boost up the blast wave.
The infrared thermography method was used to investigate the detonation temperature of thermobaric explosives (TBE). The experimental result shows that the temperature of TBEs detonation cloud is higher than that of TNT with the same weight. The duration of high temperature and the volume of the high temperature cloud are 2~5 and 2~10 times as much as those of TNT, respectively. This implies that TBE is superior to the traditional high explosive on the temperature field. The high-temperature environment formed by the explosive explosion is sufficient to maintain the afterburning of the aluminum powder，which can provide assistance to boost up the blast wave.
2008, 28(5): 476-480.
doi: 10.11883/1001-1455(2008)05-0476-05
Abstract:
Three layered defense models were designed based on the multiplayer defense structure of a warship. Contact explosion experiments with three different masses of explosive were carried out three times in the centers of the outside plates. The defense effects of multiplayer structures were explored by analyzing the dimension and shape of crevasses. Experimental results show： (1) the vacant cabin of the multiplayer defense structure has great importance to expand and decompress the effect of detonation products and shock wave; (2) liquid cabin can alleviate the damage of fragments, detonation products and shock wave. The multiplayer defense structure has great importance to diminish the damage of contact explosion.
Three layered defense models were designed based on the multiplayer defense structure of a warship. Contact explosion experiments with three different masses of explosive were carried out three times in the centers of the outside plates. The defense effects of multiplayer structures were explored by analyzing the dimension and shape of crevasses. Experimental results show： (1) the vacant cabin of the multiplayer defense structure has great importance to expand and decompress the effect of detonation products and shock wave; (2) liquid cabin can alleviate the damage of fragments, detonation products and shock wave. The multiplayer defense structure has great importance to diminish the damage of contact explosion.
