2019 Vol. 39, No. 9
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2019, 39(9): 092101.
doi: 10.11883/bzycj-2018-0208
Abstract:
In recent years, Rotary Detonation Engine (RDE) has attracted more and more attention because of their higher combustion efficiency than conventional aerospace engines. For the key problems, ignition technique is particularly important. In order to establish a steady rotating detonation wave under one single ignition in a combustion chamber, a method based on controlling initial fuel distribution is proposed to start a rotating detonation engine under 0.4 MPa injection total pressure using hydrogen/air mixture as its propellant. Two-dimensional reactive Navier-Stokes equation coupled with the Arrhenius kinetic model and κ-ε model are used to simulate detonation process. Elementary chemical reaction model with 9 species 27 reversible reactions is applied to describe the evolution of reaction components. The finite volume method is conducted, and flux terms are solved by using the monotonic upstream-centered scheme for conservation laws, and the time integration is performed by using Euler method. Grid numbers are 600 (azimuthal direction) ×200 (axial direction), with mesh size of about 0.5 mm. Initial fuel filling rate (ϕ) is used to quantify the initial fuel distribution. The numerical study on the propagation characteristics of rotating detonation wave shows that the initial fuel filling rate is the key to the establishment of rotary detonation wave. This effect is particularly evident when the fuel injection pressure is low, which determines the height of the fuel layer(hf) for the first cycle of detonation wave development. When RDE operating steadily, hf is a function of the mixture sensitivity to detonation. But in initial stage, hf is affected by the fuel distribution and this affection can last more than one period. Once detonation wave or deflagration wave formed, it can either maintain rotating or die down, which is determined by the height of mixture layer ahead of it. Thus, keeping hf in an appropriate range by adjusting the initial fuel filling rate is the key to establish and maintain a rotating detonation wave in initial stage. Also, in this stage DW faces maximum possibility of extinguish. Based on this strategy, a rotating detonation wave is established successfully in combustion chamber with diameter of 95.5 mm and the length of chamber is 100 mm. The computed results give the rotating detonation wave has a velocity of 1 604 m/s and operational frequency is 5347.6 Hz. Furthermore, there are four operation modes of the engine due to different initial fuel filling rate, which are failed initiation of the detonation (0%−13.3%), stable rotating detonation (13.3%−20%), unstable detonation (20%−26.6%) and dying detonation (26.7%−100%). So the critical range of the initial fuel filling rate for steady rotating detonation is obtained. Moreover, the initial fuel distribution also influences the delay time of fuel deflagration to detonation transition.
In recent years, Rotary Detonation Engine (RDE) has attracted more and more attention because of their higher combustion efficiency than conventional aerospace engines. For the key problems, ignition technique is particularly important. In order to establish a steady rotating detonation wave under one single ignition in a combustion chamber, a method based on controlling initial fuel distribution is proposed to start a rotating detonation engine under 0.4 MPa injection total pressure using hydrogen/air mixture as its propellant. Two-dimensional reactive Navier-Stokes equation coupled with the Arrhenius kinetic model and κ-ε model are used to simulate detonation process. Elementary chemical reaction model with 9 species 27 reversible reactions is applied to describe the evolution of reaction components. The finite volume method is conducted, and flux terms are solved by using the monotonic upstream-centered scheme for conservation laws, and the time integration is performed by using Euler method. Grid numbers are 600 (azimuthal direction) ×200 (axial direction), with mesh size of about 0.5 mm. Initial fuel filling rate (ϕ) is used to quantify the initial fuel distribution. The numerical study on the propagation characteristics of rotating detonation wave shows that the initial fuel filling rate is the key to the establishment of rotary detonation wave. This effect is particularly evident when the fuel injection pressure is low, which determines the height of the fuel layer(hf) for the first cycle of detonation wave development. When RDE operating steadily, hf is a function of the mixture sensitivity to detonation. But in initial stage, hf is affected by the fuel distribution and this affection can last more than one period. Once detonation wave or deflagration wave formed, it can either maintain rotating or die down, which is determined by the height of mixture layer ahead of it. Thus, keeping hf in an appropriate range by adjusting the initial fuel filling rate is the key to establish and maintain a rotating detonation wave in initial stage. Also, in this stage DW faces maximum possibility of extinguish. Based on this strategy, a rotating detonation wave is established successfully in combustion chamber with diameter of 95.5 mm and the length of chamber is 100 mm. The computed results give the rotating detonation wave has a velocity of 1 604 m/s and operational frequency is 5347.6 Hz. Furthermore, there are four operation modes of the engine due to different initial fuel filling rate, which are failed initiation of the detonation (0%−13.3%), stable rotating detonation (13.3%−20%), unstable detonation (20%−26.6%) and dying detonation (26.7%−100%). So the critical range of the initial fuel filling rate for steady rotating detonation is obtained. Moreover, the initial fuel distribution also influences the delay time of fuel deflagration to detonation transition.
2019, 39(9): 092102.
doi: 10.11883/bzycj-2018-0183
Abstract:
Due to the complex form and long duration of the load from a confined explosion, it is usually difficult to propose an uniform simplified formula to describe the confined blast load effectively, which can be applied in the predicting the dynamic response of structures. In present paper, the explicit dynamic code Autodyn was employed to predict the response of steel plates under confined blast load numerically. The effectiveness of the numerical method was validated by comparing the numerical and experimental results, and then the characteristic of saturated impulse of steel plate was analyzed. The numerical simulations of 216 plates, which experience different load durations, were conducted. Based on analyzing the relationship between the duration of confined blast load and the subsequent dynamic response of these steel plates, a simplified formula was deduced to determine the saturated time that corresponding to the maximum deformation of plate, and a guide value of the parameter of the dimensionless saturated time was presented. Considering the influence of initial shock wave of confined explosion, combined with the law of saturation action time of explosion load, a rectangular load equivalent method for the confined blast load is proposed. The dynamic response of metal plate under 18 groups of simplified and fully-coupling load is compared, and the effectiveness of the equivalent method is verified.
Due to the complex form and long duration of the load from a confined explosion, it is usually difficult to propose an uniform simplified formula to describe the confined blast load effectively, which can be applied in the predicting the dynamic response of structures. In present paper, the explicit dynamic code Autodyn was employed to predict the response of steel plates under confined blast load numerically. The effectiveness of the numerical method was validated by comparing the numerical and experimental results, and then the characteristic of saturated impulse of steel plate was analyzed. The numerical simulations of 216 plates, which experience different load durations, were conducted. Based on analyzing the relationship between the duration of confined blast load and the subsequent dynamic response of these steel plates, a simplified formula was deduced to determine the saturated time that corresponding to the maximum deformation of plate, and a guide value of the parameter of the dimensionless saturated time was presented. Considering the influence of initial shock wave of confined explosion, combined with the law of saturation action time of explosion load, a rectangular load equivalent method for the confined blast load is proposed. The dynamic response of metal plate under 18 groups of simplified and fully-coupling load is compared, and the effectiveness of the equivalent method is verified.
2019, 39(9): 092201.
doi: 10.11883/bzycj-2018-0210
Abstract:
Since the information of detonation product is transmitted outward in the form of compression wave during underwater explosion, the purpose of this paper is to explore how to determine the equation of state (EOS) of detonation products using underwater explosion tests. Compared with conventional cylinder test, underwater explosion test has the advantages of simpler equipment, lower cost, less limited charge size, and wider range of calibration pressures, which makes it more suitable for the on-site testing of large or non-ideal explosives. Based on the measurable shock wave trajectory and post-shock pressure history in general underwater explosion test, an inverse method of characteristics (inverse MOC) is proposed to recover the gas-water interface from the shock and post-shock data, and a genetic algorithm is developed to determine the EOS of detonation products by the gas-water interface. Compared with virtual experimental data extracted from underwater explosion simulations, it is found that the inverse MOC can properly reproduce the position and pressure of gas-water interface. The lower limit of pressure range is close to 2 MPa, which is far lower than that of 0.1 GPa in cylinder test. Based on the inversed results of gas-water interface, it is also confirmed that the genetic algorithm can also stably optimize the parameters of JWL equation because the isentrope pressure error of eight commonly used explosives is less than 3% in the range of detonation pressure 0.01 GPa. The results show that it is by the inverse MOC and genetic algorithm that the EOS of detonation products can be properly and stably determined by the underwater explosion test data.
Since the information of detonation product is transmitted outward in the form of compression wave during underwater explosion, the purpose of this paper is to explore how to determine the equation of state (EOS) of detonation products using underwater explosion tests. Compared with conventional cylinder test, underwater explosion test has the advantages of simpler equipment, lower cost, less limited charge size, and wider range of calibration pressures, which makes it more suitable for the on-site testing of large or non-ideal explosives. Based on the measurable shock wave trajectory and post-shock pressure history in general underwater explosion test, an inverse method of characteristics (inverse MOC) is proposed to recover the gas-water interface from the shock and post-shock data, and a genetic algorithm is developed to determine the EOS of detonation products by the gas-water interface. Compared with virtual experimental data extracted from underwater explosion simulations, it is found that the inverse MOC can properly reproduce the position and pressure of gas-water interface. The lower limit of pressure range is close to 2 MPa, which is far lower than that of 0.1 GPa in cylinder test. Based on the inversed results of gas-water interface, it is also confirmed that the genetic algorithm can also stably optimize the parameters of JWL equation because the isentrope pressure error of eight commonly used explosives is less than 3% in the range of detonation pressure 0.01 GPa. The results show that it is by the inverse MOC and genetic algorithm that the EOS of detonation products can be properly and stably determined by the underwater explosion test data.
2019, 39(9): 092202.
doi: 10.11883/bzycj-2018-0255
Abstract:
In order to solve the issues of high cost and large risk factor of ammunition explosion in the battlefield damage test, the method of dimensional analysis is used to analyze the establishment method of cylindrical ammunition similar models. The explosive power field relationship between different similar models and an original model is studied. The AUTODYN finite element simulation software is used to simulate the explosive power field, and the effectiveness of the similar models is verified by real-experiment data. The results show that the simulated results are consistent with the results of both the dimensional analysis and the actual tests. Therefore, in the actual test, the similar model can be used instead of the original model. This study provides a theoretical basis for the use of the ammunition similar model in battlefield damage test and has certain engineering value.
In order to solve the issues of high cost and large risk factor of ammunition explosion in the battlefield damage test, the method of dimensional analysis is used to analyze the establishment method of cylindrical ammunition similar models. The explosive power field relationship between different similar models and an original model is studied. The AUTODYN finite element simulation software is used to simulate the explosive power field, and the effectiveness of the similar models is verified by real-experiment data. The results show that the simulated results are consistent with the results of both the dimensional analysis and the actual tests. Therefore, in the actual test, the similar model can be used instead of the original model. This study provides a theoretical basis for the use of the ammunition similar model in battlefield damage test and has certain engineering value.
2019, 39(9): 092301.
doi: 10.11883/bzycj-2018-0256
Abstract:
Four kinds of aluminum/ titanium hydride/ polytetrafluoroethylene (Al/TiH2/PTFE) samples with different TiH2 contents were prepared by the mixed/compression/sintering method. The dynamic compression mechanical properties, impact sensitivity and reaction characteristics of the reaction materials were studied based on the split Hopkinson pressure bar (SHPB) and drop-weight impact tests. The results indicate that the four materials all show strain hardening and strain rate hardening effects, and the yield strength and hardening modulus increase with the increasing of the strain rate. Under the same loading strain rate, the yield strength of the material increases with the increasing of TiH2 content, and the compressive strength of the material increases first and then decreases. When the mass fraction of TiH2 is 5%, the compressive strength of the material reaches the maximum value of 166.4 MPa, which is 6.8% higher than that of the Al/PTFE. Within a certain range of mass fraction (less than 5%), adding TiH2 helps to improve the impact sensitivity and energy release level of the Al/PTFE material, while the impact sensitivity and the reaction degree gradually decrease when the mass fraction of TiH2 exceeds 10%. Compared with the Al/PTFE, there are sparks spraying from the reaction region of the TiH2-contained specimens, and this phenomenon is more significant with the increasing of TiH2 content.
Four kinds of aluminum/ titanium hydride/ polytetrafluoroethylene (Al/TiH2/PTFE) samples with different TiH2 contents were prepared by the mixed/compression/sintering method. The dynamic compression mechanical properties, impact sensitivity and reaction characteristics of the reaction materials were studied based on the split Hopkinson pressure bar (SHPB) and drop-weight impact tests. The results indicate that the four materials all show strain hardening and strain rate hardening effects, and the yield strength and hardening modulus increase with the increasing of the strain rate. Under the same loading strain rate, the yield strength of the material increases with the increasing of TiH2 content, and the compressive strength of the material increases first and then decreases. When the mass fraction of TiH2 is 5%, the compressive strength of the material reaches the maximum value of 166.4 MPa, which is 6.8% higher than that of the Al/PTFE. Within a certain range of mass fraction (less than 5%), adding TiH2 helps to improve the impact sensitivity and energy release level of the Al/PTFE material, while the impact sensitivity and the reaction degree gradually decrease when the mass fraction of TiH2 exceeds 10%. Compared with the Al/PTFE, there are sparks spraying from the reaction region of the TiH2-contained specimens, and this phenomenon is more significant with the increasing of TiH2 content.
2019, 39(9): 093101.
doi: 10.11883/bzycj-2018-0193
Abstract:
In this paper, a series of static/dynamic tensile tests are performed for unidirectionally reinforced GFRP composites. Using the combination of high-speed photography and DIC (digital image correlation) technology, true stress-strain curves in different directions and strain rates are obtained. We also obtained the dynamic failure strain of the material in different directions, which are used to accurately describe the dynamic tensile and failure behavior of the material. The experimental results show that there is a stiffness change point N in the fiber reinforcement direction under different strain rate (10−3, 10, 102 s−1) tensile conditions, and the modulus Echanged is 67.5%, 39% and 21.4% of the initial elastic modulus Einitial, respectively. The fiber has the highest strength in the 1 direction which is reinforced (608, 967 and 1 123 MPa, respectively) under different strain rates (10−3, 10 and 102 s−1). The direction 2 has the lowest strength (75, 67 and 58 MPa, respectively). The strength of direction 3 is a little weak (90, 151 and 221 MPa, respectively). With the combination of high-speed photography and the DIC technology, the dynamic failure parameters of different directions under the strain rate of 100 s−1 are obtained. The dynamic failure strain in 1−3 directions is 0.267, 0.078 and 0.099 respectively. The dynamic failure behavior of this unidirectional reinforced fiberglass composite can be more accurately described.
In this paper, a series of static/dynamic tensile tests are performed for unidirectionally reinforced GFRP composites. Using the combination of high-speed photography and DIC (digital image correlation) technology, true stress-strain curves in different directions and strain rates are obtained. We also obtained the dynamic failure strain of the material in different directions, which are used to accurately describe the dynamic tensile and failure behavior of the material. The experimental results show that there is a stiffness change point N in the fiber reinforcement direction under different strain rate (10−3, 10, 102 s−1) tensile conditions, and the modulus Echanged is 67.5%, 39% and 21.4% of the initial elastic modulus Einitial, respectively. The fiber has the highest strength in the 1 direction which is reinforced (608, 967 and 1 123 MPa, respectively) under different strain rates (10−3, 10 and 102 s−1). The direction 2 has the lowest strength (75, 67 and 58 MPa, respectively). The strength of direction 3 is a little weak (90, 151 and 221 MPa, respectively). With the combination of high-speed photography and the DIC technology, the dynamic failure parameters of different directions under the strain rate of 100 s−1 are obtained. The dynamic failure strain in 1−3 directions is 0.267, 0.078 and 0.099 respectively. The dynamic failure behavior of this unidirectional reinforced fiberglass composite can be more accurately described.
2019, 39(9): 093102.
doi: 10.11883/bzycj-2018-0191
Abstract:
To explore the mechanical behavior of SFRC beams subjected to both impact and fire loadings, 4 beams were tested with high-performance drop-weight test system, four point bending test machine and assembled electric furnace. The beams were firstly subjected to impact loadings and then exposed to fire with a constant load. During the test process, the crack patterns of beams were observed while the time histories of mid-span deflections and rebar strain were recorded. Then, the fire resistance of these beams was discussed. Based on the experiment, three-dimensional macroscopic finite element numerical model considering the effects of strain rate and high temperature was established. The impact loading process was simulated firstly; and then taking simulation results as the initial state, SFRC beams subjected to both fire and constant loading were simulated with a sequentially coupled thermal-stress analysis method. Moreover, considering the heterogeneity of concrete’s internal structure, a meso-scale simulation was also conducted with the procedures similar to that in macroscopic simulation. Good agreement between both the macro-/meso-scale simulation results and the test results illustrates the rationality and effectiveness of the present numerical analysis methods. The advantages of mesoscopic model were indicated through the comparison of macro-/meso-scopic results. It has been found that when the impact energy is low, the local concrete is cracked but a small overall deformation is remained. Nevertheless, this degrades the fire resistance of SFRC beams to some ex-tent. When the steel fiber dosage increases, resulting in an increasing shear strength of concrete matrix, the coexistence phenomenon of bending and shear cracks of beams under the impact load is changed to bending cracks as a dominant. Moreover, when subjected to elevated temperatures with a constant load, the distribution of cracks on the impact-damaged SFRC beams is relatively concentrated and a brittle failure occurs.
To explore the mechanical behavior of SFRC beams subjected to both impact and fire loadings, 4 beams were tested with high-performance drop-weight test system, four point bending test machine and assembled electric furnace. The beams were firstly subjected to impact loadings and then exposed to fire with a constant load. During the test process, the crack patterns of beams were observed while the time histories of mid-span deflections and rebar strain were recorded. Then, the fire resistance of these beams was discussed. Based on the experiment, three-dimensional macroscopic finite element numerical model considering the effects of strain rate and high temperature was established. The impact loading process was simulated firstly; and then taking simulation results as the initial state, SFRC beams subjected to both fire and constant loading were simulated with a sequentially coupled thermal-stress analysis method. Moreover, considering the heterogeneity of concrete’s internal structure, a meso-scale simulation was also conducted with the procedures similar to that in macroscopic simulation. Good agreement between both the macro-/meso-scale simulation results and the test results illustrates the rationality and effectiveness of the present numerical analysis methods. The advantages of mesoscopic model were indicated through the comparison of macro-/meso-scopic results. It has been found that when the impact energy is low, the local concrete is cracked but a small overall deformation is remained. Nevertheless, this degrades the fire resistance of SFRC beams to some ex-tent. When the steel fiber dosage increases, resulting in an increasing shear strength of concrete matrix, the coexistence phenomenon of bending and shear cracks of beams under the impact load is changed to bending cracks as a dominant. Moreover, when subjected to elevated temperatures with a constant load, the distribution of cracks on the impact-damaged SFRC beams is relatively concentrated and a brittle failure occurs.
2019, 39(9): 093103.
doi: 10.11883/bzycj-2018-0270
Abstract:
The dynamic strength of three kinds of ice specimens at −18 ℃ were tested by the split Hopkinson pressure bar (SHPB) method. The pulse-shaping technology was used to achieve constant strain rate loading and stress equalization. The double-peak phenomena of reflection wave and transmission wave were explained by comparing with stress waveforms. The compression stress of distill-water ice in the strain rate range from 700 to 2 700 s−1 is 14.5−49.3 MPa, and it is much higher than the static data. Generally, the dynamic compression stress of the impurity-water ice is higher than that of the distill-water ice, this indicate that the ice specimens become harder after adding impurities, and the capability to resist deformation is enhanced. Compared with a-type and c-type specimens, the crack stress of b-type specimens becomes higher and its dispersiveness is lower. This indicates that the adhesive forces between impurities and ice crystals become stronger, and the expending and nucleate process of cracks is restrained.
The dynamic strength of three kinds of ice specimens at −18 ℃ were tested by the split Hopkinson pressure bar (SHPB) method. The pulse-shaping technology was used to achieve constant strain rate loading and stress equalization. The double-peak phenomena of reflection wave and transmission wave were explained by comparing with stress waveforms. The compression stress of distill-water ice in the strain rate range from 700 to 2 700 s−1 is 14.5−49.3 MPa, and it is much higher than the static data. Generally, the dynamic compression stress of the impurity-water ice is higher than that of the distill-water ice, this indicate that the ice specimens become harder after adding impurities, and the capability to resist deformation is enhanced. Compared with a-type and c-type specimens, the crack stress of b-type specimens becomes higher and its dispersiveness is lower. This indicates that the adhesive forces between impurities and ice crystals become stronger, and the expending and nucleate process of cracks is restrained.
2019, 39(9): 093104.
doi: 10.11883/bzycj-2018-0221
Abstract:
It is very important to establish the material model for the explosive forming and penetration simulation of ZrCuNiAlAg bulk amorphous alloy. In this paper, the JH-2 model parameters of the ZrCuNiAlAg bulk amorphous alloy were calculated by the experimental results. In order to verify the accuracy of the ZrCuNiAlAg bulk amorphous alloy JH-2 model, the finite element model of plate impact test was established by Autodyn. The deformation process of ZrCuNiAlAg bulk amorphous alloy under high pressure and high strain rate was simulated. Compared with the experimental results, the average velocity deviation of the free surface particles on the back surface of the target plate is less than 3%. It is shown that the JH-2 model of ZrCuNiAlAg bulk amorphous alloy can well describe the mechanical behavior of the material under large deformation, high strain rate, high pressure and other environmental conditions, and the accuracy of JH-2 model of ZrCuNiAlAg bulk amorphous alloy is verified.
It is very important to establish the material model for the explosive forming and penetration simulation of ZrCuNiAlAg bulk amorphous alloy. In this paper, the JH-2 model parameters of the ZrCuNiAlAg bulk amorphous alloy were calculated by the experimental results. In order to verify the accuracy of the ZrCuNiAlAg bulk amorphous alloy JH-2 model, the finite element model of plate impact test was established by Autodyn. The deformation process of ZrCuNiAlAg bulk amorphous alloy under high pressure and high strain rate was simulated. Compared with the experimental results, the average velocity deviation of the free surface particles on the back surface of the target plate is less than 3%. It is shown that the JH-2 model of ZrCuNiAlAg bulk amorphous alloy can well describe the mechanical behavior of the material under large deformation, high strain rate, high pressure and other environmental conditions, and the accuracy of JH-2 model of ZrCuNiAlAg bulk amorphous alloy is verified.
2019, 39(9): 093201.
doi: 10.11883/bzycj-2018-0212
Abstract:
Based on the ALE algorithm in LS-DYNA software, the numerical simulation of the pulsation process of underwater explosion near water surface is carried out and compared with the experimental results. The correctness of the finite element model and parameter setting of the near-wall hybrid boundary near the water surface is verified. The different explosion conditions are set up, and the influence of air bubbles and their broken waves on the floating shock platform is explored. The results show that during the underwater explosion, the bubble, free surface and floating shock platform will have strong coupling effect, in the bubble pulsation stage. The bubble will induce the inrush current and the water ripple effect, affecting the safety and usability of the floating shock platform; the shock wave is the main factor affecting the shock environment of the floating shock platform. Due to the low frequency of the bubble, the bubble pulsation and the water ripple on the floating shock platform The direct shock effect will increase the spectral velocity value and spectral displacement value of the shock environment of the floating shock platform to a small extent, and has almost no effect on the spectral acceleration value; the waves and bubbles formed by the water slamming water surface are broken and waved, which is caused by the floating shock platform. The excitation load is periodic with the same period as the wave period. The excitation load of the wave changes the shock environment of the platform only by exciting the floating shock platform resonance of its corresponding frequency. The wave load is small and has little shock on the shock environment of the floating shock platform.
Based on the ALE algorithm in LS-DYNA software, the numerical simulation of the pulsation process of underwater explosion near water surface is carried out and compared with the experimental results. The correctness of the finite element model and parameter setting of the near-wall hybrid boundary near the water surface is verified. The different explosion conditions are set up, and the influence of air bubbles and their broken waves on the floating shock platform is explored. The results show that during the underwater explosion, the bubble, free surface and floating shock platform will have strong coupling effect, in the bubble pulsation stage. The bubble will induce the inrush current and the water ripple effect, affecting the safety and usability of the floating shock platform; the shock wave is the main factor affecting the shock environment of the floating shock platform. Due to the low frequency of the bubble, the bubble pulsation and the water ripple on the floating shock platform The direct shock effect will increase the spectral velocity value and spectral displacement value of the shock environment of the floating shock platform to a small extent, and has almost no effect on the spectral acceleration value; the waves and bubbles formed by the water slamming water surface are broken and waved, which is caused by the floating shock platform. The excitation load is periodic with the same period as the wave period. The excitation load of the wave changes the shock environment of the platform only by exciting the floating shock platform resonance of its corresponding frequency. The wave load is small and has little shock on the shock environment of the floating shock platform.
Projectile target response model for normal penetration process based on mechanical vibration theory
2019, 39(9): 093301.
doi: 10.11883/bzycj-2018-0242
Abstract:
In order to provide exact mechanics input for anti-high-overload optimal design of penetration fuze, the mechanical vibration theory is introduced into theoretical analysis on normal penetration and a projectile target response model combining the rigid body motion with the first order axial vibration is proposed. On the basis of force analysis for normal penetration process, a rigid body motion model for projectile is built by adopting Newton second law. The first-order axial vibration model is built based on single DOF spring-mass-damper system. Then, numerical integration calculation is carried out and the trend of each physical variable in normal penetration process is obtained. To verify the credibility of the model proposed, artillery test is carried out and the acceleration signal in the penetration process is collected. Considering that the calculated values agree well with the experimental ones, it could be concluded that the model taking axial vibration effect into account is suitable to analyze force conditions, therefore, could be applied to guide the optimal design of penetration fuze.
In order to provide exact mechanics input for anti-high-overload optimal design of penetration fuze, the mechanical vibration theory is introduced into theoretical analysis on normal penetration and a projectile target response model combining the rigid body motion with the first order axial vibration is proposed. On the basis of force analysis for normal penetration process, a rigid body motion model for projectile is built by adopting Newton second law. The first-order axial vibration model is built based on single DOF spring-mass-damper system. Then, numerical integration calculation is carried out and the trend of each physical variable in normal penetration process is obtained. To verify the credibility of the model proposed, artillery test is carried out and the acceleration signal in the penetration process is collected. Considering that the calculated values agree well with the experimental ones, it could be concluded that the model taking axial vibration effect into account is suitable to analyze force conditions, therefore, could be applied to guide the optimal design of penetration fuze.
2019, 39(9): 094101.
doi: 10.11883/bzycj-2018-0175
Abstract:
In order to increase the reliability to obtain fragments’ velocities and velocity attenuation coefficients in static explosion experiments, a vision-measurement method based on high-speed photography is proposed in this paper. We use high speed cameras to acquire images and visually solve the fragment trajectory. A kinematic model is then applied to fit fragments’ initial velocities and velocity attenuation coefficients. Experimental results show that the test method is valid which can considerably increase the accuracy of the data.
In order to increase the reliability to obtain fragments’ velocities and velocity attenuation coefficients in static explosion experiments, a vision-measurement method based on high-speed photography is proposed in this paper. We use high speed cameras to acquire images and visually solve the fragment trajectory. A kinematic model is then applied to fit fragments’ initial velocities and velocity attenuation coefficients. Experimental results show that the test method is valid which can considerably increase the accuracy of the data.
2019, 39(9): 094201.
doi: 10.11883/bzycj-2018-0312
Abstract:
To obtain more accurate images of the shock wave formation process, pressure and flame propagation velocity, and flow field evolution of flame-inert flame retarding interaction duringpremixed gas/air deflagration in a blast shock tube, by analyzing the time response’s characteristics and the control modes of multiple targets in the shock tube test system, we designed two experimental schemes using an ultrahigh speed camera, a photomultiplier tube, a time delayer, a solid state relay, a charge amplifier and a data acquisition system, and tested the response time of the high pressure ignition system and the inert medium flame retarding injection system. The results showed that the response time of the spark ignition is microsecond, and that of the flame retarding injection system is millisecond. Based on the response time, we realized the multi-objective synchronous control by setting a precise delay time, thus laying a foundation for the display of a micro-flow field of premixed gas/air deflagration in a shock tube.
To obtain more accurate images of the shock wave formation process, pressure and flame propagation velocity, and flow field evolution of flame-inert flame retarding interaction duringpremixed gas/air deflagration in a blast shock tube, by analyzing the time response’s characteristics and the control modes of multiple targets in the shock tube test system, we designed two experimental schemes using an ultrahigh speed camera, a photomultiplier tube, a time delayer, a solid state relay, a charge amplifier and a data acquisition system, and tested the response time of the high pressure ignition system and the inert medium flame retarding injection system. The results showed that the response time of the spark ignition is microsecond, and that of the flame retarding injection system is millisecond. Based on the response time, we realized the multi-objective synchronous control by setting a precise delay time, thus laying a foundation for the display of a micro-flow field of premixed gas/air deflagration in a shock tube.
2019, 39(9): 095101.
doi: 10.11883/bzycj-2018-0073
Abstract:
In order to investigate the properties of crack fracture time, propagation speed and arrest period in the surrounding rock of tunnel under different impact loading speed, the dynamic tests were performed by self-developed adjustable speed drop weight impact test system, and the tight green sandstone was selected to make the cracked tunnel specimens. A crack propagation gauge (CPG) was applied to measure dynamic initiation time, propagation speeds and arrest time, respectively. The properties of crack propagation velocity, crack fracture time and crack arrest period were discussed and analyzed. The corresponding numerical simulation was carried out by AUTODYN code, and the simulation results showed that the crack propagation speeds and crack fracture time generally agree with the experimental results, and crack arrest period also was calculated. The results show that crack propagation speeds increase with impact loading speed, but as the impact loading speed is larger than a certain value, the crack speeds tend toward a stable value; Crack fracture time decreases with the increase of impact loading speed, and as the loading rate is larger than a certain value, it tends toward a stable value; With the increase of the impact loading speed, the crack arrest period in the crack propagation path gradually decreases.
In order to investigate the properties of crack fracture time, propagation speed and arrest period in the surrounding rock of tunnel under different impact loading speed, the dynamic tests were performed by self-developed adjustable speed drop weight impact test system, and the tight green sandstone was selected to make the cracked tunnel specimens. A crack propagation gauge (CPG) was applied to measure dynamic initiation time, propagation speeds and arrest time, respectively. The properties of crack propagation velocity, crack fracture time and crack arrest period were discussed and analyzed. The corresponding numerical simulation was carried out by AUTODYN code, and the simulation results showed that the crack propagation speeds and crack fracture time generally agree with the experimental results, and crack arrest period also was calculated. The results show that crack propagation speeds increase with impact loading speed, but as the impact loading speed is larger than a certain value, the crack speeds tend toward a stable value; Crack fracture time decreases with the increase of impact loading speed, and as the loading rate is larger than a certain value, it tends toward a stable value; With the increase of the impact loading speed, the crack arrest period in the crack propagation path gradually decreases.
2019, 39(9): 095401.
doi: 10.11883/bzycj-2018-0249
Abstract:
In order to study the characteristics of methane explosion under different vented end faces, explosion tests of methane with different concentrations are carried out in a vertical 5 L quartz duct with the upper end sealed by different films. The results show that the properties of the vented end faces have significant effects on methane explosion. The explosion overpressure of methane with different concentrations is largely dependent upon the vent burst pressure of the vented end faces, which increases with the increasing vent burst pressure. Specially, by covering the end of the duct by a single layer of PVC film, neither the flame nor the overpressure oscillation will be aroused by the rupture of the PVC film, while the rupture of the paper which generates drastic discharge and reflux of the air flow will severely reverse and distort the flame, such that cause the overpressure oscillation in the duct. Moreover, as the two works together, the PVC film will hinder the venting of the air flow, resulting in accelerating the reduction of the overpressure and suppressing the flame and overpressure oscillation. However, this effect gradually decreases with the increasing layers of paper films. Indeed, as the vent burst pressure reaches a certain value, the difference among the explosion overpressure of different concentrations of methane gradually diminishes owing to the same vent burst pressure, which is the maximum pressure of the overpressure history, resulting in a similar overpressure amongst different concentrations of methane. Significantly, the overpressure attenuation curves of methane explosion with different concentrations completely coincide with each other in the first half of the period. At this point, the differential overpressure between the internal and external duct is the key factor leading to the overpressure oscillation, while the influence of the combustion rate of methane with different concentrations on the overpressure oscillation can be ignored.
In order to study the characteristics of methane explosion under different vented end faces, explosion tests of methane with different concentrations are carried out in a vertical 5 L quartz duct with the upper end sealed by different films. The results show that the properties of the vented end faces have significant effects on methane explosion. The explosion overpressure of methane with different concentrations is largely dependent upon the vent burst pressure of the vented end faces, which increases with the increasing vent burst pressure. Specially, by covering the end of the duct by a single layer of PVC film, neither the flame nor the overpressure oscillation will be aroused by the rupture of the PVC film, while the rupture of the paper which generates drastic discharge and reflux of the air flow will severely reverse and distort the flame, such that cause the overpressure oscillation in the duct. Moreover, as the two works together, the PVC film will hinder the venting of the air flow, resulting in accelerating the reduction of the overpressure and suppressing the flame and overpressure oscillation. However, this effect gradually decreases with the increasing layers of paper films. Indeed, as the vent burst pressure reaches a certain value, the difference among the explosion overpressure of different concentrations of methane gradually diminishes owing to the same vent burst pressure, which is the maximum pressure of the overpressure history, resulting in a similar overpressure amongst different concentrations of methane. Significantly, the overpressure attenuation curves of methane explosion with different concentrations completely coincide with each other in the first half of the period. At this point, the differential overpressure between the internal and external duct is the key factor leading to the overpressure oscillation, while the influence of the combustion rate of methane with different concentrations on the overpressure oscillation can be ignored.
2019, 39(9): 095402.
doi: 10.11883/bzycj-2018-0121
Abstract:
The explosion characteristics of methanol under different ambient temperature, material temperature and spray concentration were investigated by using the 20 L spherical explosion experiment system. The results show that the explosion limit of methanol spray droplets in the 20 L explosion vessel is 118.8−594.0 g/cm3. Compared with the limit range of pure gas explosion (78.6−628.6 g/cm3), the limit range of methanol spray droplets explosion is narrower, and the sensitivity of spray droplets is lower than that of pure gas methanol vapor. As the ambient temperature in the explosion vessel increases, the limit range of methanol spray explosion becomes wider, and the probability of successful ignition of gas-liquid spray in the confined space increases. When the temperature of the methanol or the ambient temperature of the explosion vessel remains unchanged, parameters of the corresponding explosion characteristic firstly increase, and then decrease after the inflection point of Φ=1.8. When Φ=1.8, there is a maximum over pressure peak in the methanol spray explosion. The increasing ambient temperature and material temperature can improve the atomization and then promote diffusion combustion. However, the effect of ambient temperature is more significant than the factor of material temperature on the characteristic parameters of methanol droplet spray explosion. The ambient temperature and stoichiometric ratio affect the strength value of methanol spray explosion. When Φ=1.8 and the ambient temperature is 303.15 K, the intensity of methanol spray explosion is greater than the intensity of methane gas explosion.
The explosion characteristics of methanol under different ambient temperature, material temperature and spray concentration were investigated by using the 20 L spherical explosion experiment system. The results show that the explosion limit of methanol spray droplets in the 20 L explosion vessel is 118.8−594.0 g/cm3. Compared with the limit range of pure gas explosion (78.6−628.6 g/cm3), the limit range of methanol spray droplets explosion is narrower, and the sensitivity of spray droplets is lower than that of pure gas methanol vapor. As the ambient temperature in the explosion vessel increases, the limit range of methanol spray explosion becomes wider, and the probability of successful ignition of gas-liquid spray in the confined space increases. When the temperature of the methanol or the ambient temperature of the explosion vessel remains unchanged, parameters of the corresponding explosion characteristic firstly increase, and then decrease after the inflection point of Φ=1.8. When Φ=1.8, there is a maximum over pressure peak in the methanol spray explosion. The increasing ambient temperature and material temperature can improve the atomization and then promote diffusion combustion. However, the effect of ambient temperature is more significant than the factor of material temperature on the characteristic parameters of methanol droplet spray explosion. The ambient temperature and stoichiometric ratio affect the strength value of methanol spray explosion. When Φ=1.8 and the ambient temperature is 303.15 K, the intensity of methanol spray explosion is greater than the intensity of methane gas explosion.
2019, 39(9): 095403.
doi: 10.11883/bzycj-2018-0265
Abstract:
In order to study the variation law of coal dust explosion pressure with different metamorphic degrees, the maximum pressure pmax and maximum pressure rise rate (dp/dt)max are characterized. The variation of explosion pressure characteristics of lignite, long flame coal, non-coking coal and gas coal is investigated by using a near-spherical coal dust explosion device. It is found that, among the selected coal dust samples, lignite has the largest pmax and (dp/dt)max, up to 0.71 MPa and 65.69 MPa/s, respectively. With the increase of metamorphism, the pmax and (dp/dt)max of long-flame coal, non-coking coal and gas coal are significantly reduced. Characterizing the explosion intensity by the explosion pressure characteristics, the four coal dust explosion strengths are then ranked from lignite, long flame coal, non-coking coal to gas coal. By comparing the volatile matter content of coal dust before and after the explosion, it is concluded that the proportion of volatile matter involved in the explosion is 46.28%−68.19%. At dispersion pressure p0=2.0 MPa and ignition delay time t0=100 ms, the pmax values of the four types of coal dust reach the maximum 0.71, 0.60, 0.55 and 0.47 MPa, respectively. However, lignite, non-viscous coal and gas coal have the highest (dp/dt)max at p0=2.0 MPa and t0=80 ms, while long-flame coal reaches the maximum (dp/dt)max at p0=2.0 MPa and t0=100 ms. The results are of significance for mastering explosion pressure characteristics under different test conditions.
In order to study the variation law of coal dust explosion pressure with different metamorphic degrees, the maximum pressure pmax and maximum pressure rise rate (dp/dt)max are characterized. The variation of explosion pressure characteristics of lignite, long flame coal, non-coking coal and gas coal is investigated by using a near-spherical coal dust explosion device. It is found that, among the selected coal dust samples, lignite has the largest pmax and (dp/dt)max, up to 0.71 MPa and 65.69 MPa/s, respectively. With the increase of metamorphism, the pmax and (dp/dt)max of long-flame coal, non-coking coal and gas coal are significantly reduced. Characterizing the explosion intensity by the explosion pressure characteristics, the four coal dust explosion strengths are then ranked from lignite, long flame coal, non-coking coal to gas coal. By comparing the volatile matter content of coal dust before and after the explosion, it is concluded that the proportion of volatile matter involved in the explosion is 46.28%−68.19%. At dispersion pressure p0=2.0 MPa and ignition delay time t0=100 ms, the pmax values of the four types of coal dust reach the maximum 0.71, 0.60, 0.55 and 0.47 MPa, respectively. However, lignite, non-viscous coal and gas coal have the highest (dp/dt)max at p0=2.0 MPa and t0=80 ms, while long-flame coal reaches the maximum (dp/dt)max at p0=2.0 MPa and t0=100 ms. The results are of significance for mastering explosion pressure characteristics under different test conditions.
