2022 Vol. 42, No. 3
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2022, 42(3): 032301.
doi: 10.11883/bzycj-2021-0188
Abstract:
A new emulsion explosive was obtained by introducing energetic microballoons containing alkane into emulsion matrix. Energetic microballoons were foamed in a constant temperature environment of 90 ℃ for 5 min to reach the maximum volume, and then energetic microballoons were mixed with emulsion matrix to prepare emulsion explosive with the energetic microballoon contents from 0.2% to 7%. The detonation velocity of emulsion explosives with different microballoons was measured by detonation velocity meter. In a steel explosion vessel with a diameter of 5 m and a depth of 5 m, the explosives were placed at a depth of 3 m, which were 0.8, 1.0, 1.2 and 1.4 m away from sensor. The underwater explosion pressure-time curve of emulsion explosive with microballoon contents from 0.2% to 7% was obtained through underwater explosion experiment. The parameters of underwater explosion, such as shock wave peak pressure, specific shock wave energy, specific bubble energy and specific explosion energy, were obtained by analysis and calculation, which was used to explore the influence of energetic microballoon contents on the underwater explosion property of explosive. The results show that the peak pressure of emulsion explosive with microballoon content of 0.2% is the largest and decreases with the increase of microballoon contents at the same testing distance. The specific bubble energy of emulsion explosive increases firstly and then decreases with the increase of the microballoon contents, and the specific bubble energy is the largest when the microballoon content is 4%. The specific shock wave energy and specific explosion energy decrease as microballoon contents increase. The attenuation rate of underwater shock wave peak pressure is negatively correlated with propagation distance. However, the specific shock wave energy, special bubble energy and special explosion energy do not change with the increase of propagation distance.
A new emulsion explosive was obtained by introducing energetic microballoons containing alkane into emulsion matrix. Energetic microballoons were foamed in a constant temperature environment of 90 ℃ for 5 min to reach the maximum volume, and then energetic microballoons were mixed with emulsion matrix to prepare emulsion explosive with the energetic microballoon contents from 0.2% to 7%. The detonation velocity of emulsion explosives with different microballoons was measured by detonation velocity meter. In a steel explosion vessel with a diameter of 5 m and a depth of 5 m, the explosives were placed at a depth of 3 m, which were 0.8, 1.0, 1.2 and 1.4 m away from sensor. The underwater explosion pressure-time curve of emulsion explosive with microballoon contents from 0.2% to 7% was obtained through underwater explosion experiment. The parameters of underwater explosion, such as shock wave peak pressure, specific shock wave energy, specific bubble energy and specific explosion energy, were obtained by analysis and calculation, which was used to explore the influence of energetic microballoon contents on the underwater explosion property of explosive. The results show that the peak pressure of emulsion explosive with microballoon content of 0.2% is the largest and decreases with the increase of microballoon contents at the same testing distance. The specific bubble energy of emulsion explosive increases firstly and then decreases with the increase of the microballoon contents, and the specific bubble energy is the largest when the microballoon content is 4%. The specific shock wave energy and specific explosion energy decrease as microballoon contents increase. The attenuation rate of underwater shock wave peak pressure is negatively correlated with propagation distance. However, the specific shock wave energy, special bubble energy and special explosion energy do not change with the increase of propagation distance.
2022, 42(3): 033101.
doi: 10.11883/bzycj-2021-0262
Abstract:
Metal spallation phenomenon often occurs when shock waves are reflected and unloaded on a free surface. If there is a secondary shock wave impact, the metal spallation zone will be compressed again, and the metal in the tensile state will be gradually recompressed into a dense material until the spallation zone disappears. The above process is referred to as the recompression process of the metal spallation zone. The main difficulty of the recompression process simulation is that the initial tensile state of the spallation zone is hard to be determined, and it is difficult to accurately measure the recompaction state experimentally. These bring great difficulties in verifying the reliability of macro-simulations under complex loading. In this case, direct numerical simulations with the ability to describe the internal details of the spallation zone become an effective means to verify the reliability of the macro-simulation. Firstly, in direct simulation modeling, the initial tensile state of the metal spallation zone is set to three situations: containing only spalls, only holes, and both holes and spalls. After that, through direct numerical simulations of different porosity, recompression rate, number of spalls and number of holes, the recompression states of the metal spallation zone under the corresponding working conditions are statistically obtained. Finally, under the condition that the constitutive model and parameters of the direct simulation and macro-simulation have good comparability, macro-modeling and simulation analysis of the spallation recompression process are carried out. The results show that: if there are spalls in the spallation zone, the macro-simulation can better simulate the recompression process and the state of the metal spallation zone when the mesh fracture post-processing algorithm is "set stress to zero and keep temperature constant". If the initial state of the recompression process contains only holes, then macro-simulations cannot well simulate the recompression process and the recompression state no matter whether the hole collapse forms surface material ejections or not.
Metal spallation phenomenon often occurs when shock waves are reflected and unloaded on a free surface. If there is a secondary shock wave impact, the metal spallation zone will be compressed again, and the metal in the tensile state will be gradually recompressed into a dense material until the spallation zone disappears. The above process is referred to as the recompression process of the metal spallation zone. The main difficulty of the recompression process simulation is that the initial tensile state of the spallation zone is hard to be determined, and it is difficult to accurately measure the recompaction state experimentally. These bring great difficulties in verifying the reliability of macro-simulations under complex loading. In this case, direct numerical simulations with the ability to describe the internal details of the spallation zone become an effective means to verify the reliability of the macro-simulation. Firstly, in direct simulation modeling, the initial tensile state of the metal spallation zone is set to three situations: containing only spalls, only holes, and both holes and spalls. After that, through direct numerical simulations of different porosity, recompression rate, number of spalls and number of holes, the recompression states of the metal spallation zone under the corresponding working conditions are statistically obtained. Finally, under the condition that the constitutive model and parameters of the direct simulation and macro-simulation have good comparability, macro-modeling and simulation analysis of the spallation recompression process are carried out. The results show that: if there are spalls in the spallation zone, the macro-simulation can better simulate the recompression process and the state of the metal spallation zone when the mesh fracture post-processing algorithm is "set stress to zero and keep temperature constant". If the initial state of the recompression process contains only holes, then macro-simulations cannot well simulate the recompression process and the recompression state no matter whether the hole collapse forms surface material ejections or not.
2022, 42(3): 033102.
doi: 10.11883/bzycj-2021-0050
Abstract:
Fibre reinforced plastic (FRP) laminates have been widely used in various engineerings due to their excellent mechanical properties. However, FRP laminates may be subjected to impact loading and delamination is one of the major concerns which is caused by the poor performance of matrix and the poor bonding between fibre and matrix. To improve the bonding strength, some toughening technologies have been developed including the modification of matrix by adding nano fillers such as carbon nanotubes. In this paper, numerical simulations of the response and failure of carbon nanotube/carbon fibre reinforced plastic (CNT/CFRP) under low velocity impact loading were performed. Firstly, on the basis of the previous work, a new dynamic progressive damage model for FRP laminates was developed by introducing a matrix toughening factor and a residual strength factor into the damage criterion and damage evolution equation respectively, together with an improved damage coupling equation which was changed from the original sum form to product form. The new dynamic progressive damage model was used to describe the intralaminar damage, and a cohesive element model to describe the interlaminar damage of the CNT/CFRP laminates. Both models were incorporated into the ABAQUS/Explicit finite element program by the user-defined material subroutine VUMAT. Then, numerical simulation was conducted for the response and failure of CNT/CFRP composites subjected to low velocity impact loading. Finally, the numerical results were compared with some available experimental data and the influence of impact velocity was discussed. It transpires that the results predicted from the present model are found to be in good agreement with the test data for CNT/CFRP laminates in terms of load-displacement curve and failure pattern, and the delamination damage at the interlaminar interface decreases gradually with increasing CNT content. It also transpires that the impact velocity affects the ratio of compression and tensile failure of FRP laminates, and under the same impact energy, a larger impact velocity will cause more tensile failure.
Fibre reinforced plastic (FRP) laminates have been widely used in various engineerings due to their excellent mechanical properties. However, FRP laminates may be subjected to impact loading and delamination is one of the major concerns which is caused by the poor performance of matrix and the poor bonding between fibre and matrix. To improve the bonding strength, some toughening technologies have been developed including the modification of matrix by adding nano fillers such as carbon nanotubes. In this paper, numerical simulations of the response and failure of carbon nanotube/carbon fibre reinforced plastic (CNT/CFRP) under low velocity impact loading were performed. Firstly, on the basis of the previous work, a new dynamic progressive damage model for FRP laminates was developed by introducing a matrix toughening factor and a residual strength factor into the damage criterion and damage evolution equation respectively, together with an improved damage coupling equation which was changed from the original sum form to product form. The new dynamic progressive damage model was used to describe the intralaminar damage, and a cohesive element model to describe the interlaminar damage of the CNT/CFRP laminates. Both models were incorporated into the ABAQUS/Explicit finite element program by the user-defined material subroutine VUMAT. Then, numerical simulation was conducted for the response and failure of CNT/CFRP composites subjected to low velocity impact loading. Finally, the numerical results were compared with some available experimental data and the influence of impact velocity was discussed. It transpires that the results predicted from the present model are found to be in good agreement with the test data for CNT/CFRP laminates in terms of load-displacement curve and failure pattern, and the delamination damage at the interlaminar interface decreases gradually with increasing CNT content. It also transpires that the impact velocity affects the ratio of compression and tensile failure of FRP laminates, and under the same impact energy, a larger impact velocity will cause more tensile failure.
2022, 42(3): 033103.
doi: 10.11883/bzycj-2021-0173
Abstract:
In order to investigate the impact protection performance of partially liquid filled multicell structure, the two-dimensional FEM numerical analysis of the impact dynamic characteristics of liquid filled inner concave cell structure, unfilled inner concave cell structure, partially liquid filled inner concave multicell structure and unfilled inner concave multicell structure was established by combining the drop hammer impact test of liquid filled and unfilled inner concave cell structure. The deformation/failure mode of partially liquid filled inner concave multicell structure was obtained, and the dynamic response characteristics and energy absorption characteristics of partially liquid filled inner concave multicell structures at different impact velocities were discussed by using the initial load weakening factor and the strain energy per unit volume, respectively. The results show that after the breakage of the liquid filled cell, the water medium will flow into the adjacent unfilled cell, developing a secondary bulging energy absorption effect, thus effectively increasing the deformation energy absorption level of the structure wall; the deformation damage modes of the liquid filled and unfilled regions of the structure are bulging tension and flexural bending, respectively; the strain energy per unit volume of the structure and the weakening effect on the initial impact load are enhanced with the increase of the impact velocity. The transverse filling method can be equated with tandem arrangement of variable stiffness springs, which only affects the local stiffness of the structure. And the longitudinal filling method can be equated with a parallel arrangement of multiple layers of variable stiffness springs, which affects the overall stiffness of the structure; the equivalent stiffness of the filled and unfilled regions changes dynamically, and the deformation mode of the structure is determined by the equivalent stiffness of each region in real time. When the load impact velocity is high, both transverse and longitudinal partially liquid filled inner concave multicell structures are superior to the unfilled inner concave multicell structure in weakening the initial impact load.
In order to investigate the impact protection performance of partially liquid filled multicell structure, the two-dimensional FEM numerical analysis of the impact dynamic characteristics of liquid filled inner concave cell structure, unfilled inner concave cell structure, partially liquid filled inner concave multicell structure and unfilled inner concave multicell structure was established by combining the drop hammer impact test of liquid filled and unfilled inner concave cell structure. The deformation/failure mode of partially liquid filled inner concave multicell structure was obtained, and the dynamic response characteristics and energy absorption characteristics of partially liquid filled inner concave multicell structures at different impact velocities were discussed by using the initial load weakening factor and the strain energy per unit volume, respectively. The results show that after the breakage of the liquid filled cell, the water medium will flow into the adjacent unfilled cell, developing a secondary bulging energy absorption effect, thus effectively increasing the deformation energy absorption level of the structure wall; the deformation damage modes of the liquid filled and unfilled regions of the structure are bulging tension and flexural bending, respectively; the strain energy per unit volume of the structure and the weakening effect on the initial impact load are enhanced with the increase of the impact velocity. The transverse filling method can be equated with tandem arrangement of variable stiffness springs, which only affects the local stiffness of the structure. And the longitudinal filling method can be equated with a parallel arrangement of multiple layers of variable stiffness springs, which affects the overall stiffness of the structure; the equivalent stiffness of the filled and unfilled regions changes dynamically, and the deformation mode of the structure is determined by the equivalent stiffness of each region in real time. When the load impact velocity is high, both transverse and longitudinal partially liquid filled inner concave multicell structures are superior to the unfilled inner concave multicell structure in weakening the initial impact load.
2022, 42(3): 033301.
doi: 10.11883/bzycj-2021-0178
Abstract:
Ultra high toughness cementitious composites (UHTCC) have ultra-high toughness, good durability and excellent energy consumption effect. These characteristics make UHTCC have broad applications in protection engineering. To better investigate the penetration resistance of UHTCC composite structure subjected to second strike conditions, the basic mechanical parameters of the UHTCC and polyvinl alcohol fiber reinforced concrete (FRC) were measured first. Then, a 25 mm caliber ballistic smoothbore gun was used against a cylindrical UHTCC, FRC and UHTCC-FRC composite targets with a diameter of 750 mm and a height of 600 mm. The targets were subjected to two-time penetration tests of 550 m/s. The damage data of the projectile and the three types of targets were obtained, including the penetration depth of the projectile, the abrasion of the projectile, the crater diameter and area of the target’s strike surface, the crater depth, the number of cracks and the maximum crack width on the strike surface. On this basis, the influence of aggregate, structure type and distance between two strikes on the penetration resistance of UHTCC composite targets was analyzed. The results show that under the same test conditions, compared with the normal concrete and ultra-high performance concrete, the UHTCC can effectively reduce the crater diameter of the strike surface, but the penetration depth of the projectile increases; the 50mm UHTCC placing on the front surface of the functionally graded target can effectively reduce the cratering diameter of the strike surface; the secondary penetration depth of the projectile is greater than the primary penetration depth of the projectile, and the crater area of the target under the secondary impact is smaller than the crater area of the target under the first impact.
Ultra high toughness cementitious composites (UHTCC) have ultra-high toughness, good durability and excellent energy consumption effect. These characteristics make UHTCC have broad applications in protection engineering. To better investigate the penetration resistance of UHTCC composite structure subjected to second strike conditions, the basic mechanical parameters of the UHTCC and polyvinl alcohol fiber reinforced concrete (FRC) were measured first. Then, a 25 mm caliber ballistic smoothbore gun was used against a cylindrical UHTCC, FRC and UHTCC-FRC composite targets with a diameter of 750 mm and a height of 600 mm. The targets were subjected to two-time penetration tests of 550 m/s. The damage data of the projectile and the three types of targets were obtained, including the penetration depth of the projectile, the abrasion of the projectile, the crater diameter and area of the target’s strike surface, the crater depth, the number of cracks and the maximum crack width on the strike surface. On this basis, the influence of aggregate, structure type and distance between two strikes on the penetration resistance of UHTCC composite targets was analyzed. The results show that under the same test conditions, compared with the normal concrete and ultra-high performance concrete, the UHTCC can effectively reduce the crater diameter of the strike surface, but the penetration depth of the projectile increases; the 50mm UHTCC placing on the front surface of the functionally graded target can effectively reduce the cratering diameter of the strike surface; the secondary penetration depth of the projectile is greater than the primary penetration depth of the projectile, and the crater area of the target under the secondary impact is smaller than the crater area of the target under the first impact.
2022, 42(3): 033302.
doi: 10.11883/bzycj-2021-0448
Abstract:
In view of the projectile fuze system in the process of penetration, the vibration characteristics of the threaded connection between a projectile and a fuze were studied. An elastic model for the missile fuze threaded connection between projectile and fuze was established. This model took the uneven distribution characteristics of the thread load into consideration. Not only the distribution law of the thread load was given, but also the equivalent stiffness and vibration frequency of the threaded connection structure were given. At the same time, in order to verify the correctness of the model, the finite element simulation and the static tensile and impact tests of the spring thread connection structure were carried out. The frequency characteristics of the system were obtained by calculating the vibration characteristics of each structure and analyzing the measured overload signals. Finally, the vibration frequency of the projectile-fuze system was compared with the time-frequency analysis results of the measured overload signal. For impact load and static load, the results of calculation and test show that the load on the first thread close to the force action point is the largest, and the load on the threads far away from the action point decreases gradually. Compared with the static load, the first thread supports more load under the impact load. The stiffness of the screw connection structure is obviously lower than that of the fixed connection structure. By increasing the stiffness of the thread material, increasing the screw length and reducing the pitch, the natural frequency of the threaded connection structure can be effectively increased. Based on the time-frequency analysis of the penetration overload test signals, it is found that there is a signal having the same vibration frequency with that of the threaded connection structure. Moreover, the amplitude of this signal is very high and it has a great impact on the overload signal.
In view of the projectile fuze system in the process of penetration, the vibration characteristics of the threaded connection between a projectile and a fuze were studied. An elastic model for the missile fuze threaded connection between projectile and fuze was established. This model took the uneven distribution characteristics of the thread load into consideration. Not only the distribution law of the thread load was given, but also the equivalent stiffness and vibration frequency of the threaded connection structure were given. At the same time, in order to verify the correctness of the model, the finite element simulation and the static tensile and impact tests of the spring thread connection structure were carried out. The frequency characteristics of the system were obtained by calculating the vibration characteristics of each structure and analyzing the measured overload signals. Finally, the vibration frequency of the projectile-fuze system was compared with the time-frequency analysis results of the measured overload signal. For impact load and static load, the results of calculation and test show that the load on the first thread close to the force action point is the largest, and the load on the threads far away from the action point decreases gradually. Compared with the static load, the first thread supports more load under the impact load. The stiffness of the screw connection structure is obviously lower than that of the fixed connection structure. By increasing the stiffness of the thread material, increasing the screw length and reducing the pitch, the natural frequency of the threaded connection structure can be effectively increased. Based on the time-frequency analysis of the penetration overload test signals, it is found that there is a signal having the same vibration frequency with that of the threaded connection structure. Moreover, the amplitude of this signal is very high and it has a great impact on the overload signal.
2022, 42(3): 033303.
doi: 10.11883/bzycj-2021-0081
Abstract:
In recent years, as a hot area of computational mechanics, peridynamic has attracted the attention of researchers. The peridynamic theory attempts to unify the mathematical models of continuum, cracks, and particles into one framework, which is essentially a mechanical model independent of the scope of continuum mechanics. The governing equation of peridynamic adopts the spatial integral form, and the continuity of the field function is no longer required. Compared with the traditional methods based on continuum mechanics, this method has a great advantage in dealing with discontinuity problems, such as crack propagation and other fracture problems. In this paper, the peridynamic method was used to study the damage characteristics of composite structures under the impact of a fragment group and to analyze the enhancement effect on the penetration ability during the destruction process. Through a self-programmed peridynamic model, the penetration process of a fragment group into a composite laminate was simulated to explore the influence of the fragment velocity, fragment number and fragment spacing on the penetration ability enhancement. The results show that the damage modes of the laminate structure under the action of high-velocity fragment group penetration are diverse and related to the number, velocity and spacing of the fragments. The increase in the fragment number has a significant effect on the penetration ability of the fragments. The fragment spacing is negatively correlated with the enhancement effect. When the fragment spacing decreases, the damage effect increases. The fragment velocity directly determines the penetration time, and the increase in the fragment velocity decreases the penetration time. The superimposition effect of the stress waves is not enough to affect the penetration ability of the fragment group.
In recent years, as a hot area of computational mechanics, peridynamic has attracted the attention of researchers. The peridynamic theory attempts to unify the mathematical models of continuum, cracks, and particles into one framework, which is essentially a mechanical model independent of the scope of continuum mechanics. The governing equation of peridynamic adopts the spatial integral form, and the continuity of the field function is no longer required. Compared with the traditional methods based on continuum mechanics, this method has a great advantage in dealing with discontinuity problems, such as crack propagation and other fracture problems. In this paper, the peridynamic method was used to study the damage characteristics of composite structures under the impact of a fragment group and to analyze the enhancement effect on the penetration ability during the destruction process. Through a self-programmed peridynamic model, the penetration process of a fragment group into a composite laminate was simulated to explore the influence of the fragment velocity, fragment number and fragment spacing on the penetration ability enhancement. The results show that the damage modes of the laminate structure under the action of high-velocity fragment group penetration are diverse and related to the number, velocity and spacing of the fragments. The increase in the fragment number has a significant effect on the penetration ability of the fragments. The fragment spacing is negatively correlated with the enhancement effect. When the fragment spacing decreases, the damage effect increases. The fragment velocity directly determines the penetration time, and the increase in the fragment velocity decreases the penetration time. The superimposition effect of the stress waves is not enough to affect the penetration ability of the fragment group.
2022, 42(3): 033304.
doi: 10.11883/bzycj-2021-0080
Abstract:
In recent years, as a hot area of computational mechanics, an emerging meshless method, namely peridynamic, has attracted the attention of researchers. The peridynamic theory attempts to unify the mathematical models of continuum, cracks, and particles into one framework, so it is essentially a mechanical model independent of the scope of continuum mechanics. The governing equation of peridynamic adopts the spatial integral form, and the continuity of the field function is no longer required. Compared with the traditional methods based on continuum mechanics, the peridynamic method has a great advantage in dealing with discontinuity problems, such as crack propagation and other fracture problems. In this paper, the peridynamic method is adopted to study the damage characteristics of composite structure under the combined action of shock wave and fragment group. The damage mode of the laminated plate and reinforced plate structures are analyzed, and the influence of the load sequence and other factors on the damage ability is considered. The results show that the damage degree of the composite structure under the combined action is mainly related to the shock wave strength, the penetration ability of the fragment group, and the order of action. The main damage modes are delamination failure, matrix damage, shear damage and large structural deformation. When the shock wave acts first, the structural damage is serious and the damage range is larger. The ribs of the reinforced plate significantly reduce the impact of the shock wave action, and then affect the joint action, hence its deformation, displacement and structural damage are greatly reduced compared to the laminates, the damage is more serious when fragment group acting first.
In recent years, as a hot area of computational mechanics, an emerging meshless method, namely peridynamic, has attracted the attention of researchers. The peridynamic theory attempts to unify the mathematical models of continuum, cracks, and particles into one framework, so it is essentially a mechanical model independent of the scope of continuum mechanics. The governing equation of peridynamic adopts the spatial integral form, and the continuity of the field function is no longer required. Compared with the traditional methods based on continuum mechanics, the peridynamic method has a great advantage in dealing with discontinuity problems, such as crack propagation and other fracture problems. In this paper, the peridynamic method is adopted to study the damage characteristics of composite structure under the combined action of shock wave and fragment group. The damage mode of the laminated plate and reinforced plate structures are analyzed, and the influence of the load sequence and other factors on the damage ability is considered. The results show that the damage degree of the composite structure under the combined action is mainly related to the shock wave strength, the penetration ability of the fragment group, and the order of action. The main damage modes are delamination failure, matrix damage, shear damage and large structural deformation. When the shock wave acts first, the structural damage is serious and the damage range is larger. The ribs of the reinforced plate significantly reduce the impact of the shock wave action, and then affect the joint action, hence its deformation, displacement and structural damage are greatly reduced compared to the laminates, the damage is more serious when fragment group acting first.
2022, 42(3): 033305.
doi: 10.11883/bzycj-2021-0092
Abstract:
When a small-caliber projectile is moving underwater at a high speed, the water around the projectile will cavitate. The cavitation effect can greatly reduce the resistance of the moving vehicle, and the geometric shape of the warhead with the best drag coefficient corresponds to the supercavitating state where the projectile is completely enveloped by cavitation. Aiming at a small-caliber projectile, the computational fluid dynamics method is used to numerically simulate the gas-liquid two-phase flow with cavitation phenomenon, while the relationships of the cavitation shape and the drag coefficient with the geometry of the projectile’s head shape are explored. The three-segment cone type is selected as the basic projectile type, and the shape of the projectile is optimized by step optimization method. First, seven parameters are used to describe the three-segment cone shape of the projectile, and then the projectile is optimized in the order of the first section cone, the second and the third section cone. This method is used because the seven parameters are not independent of each other, and it is difficult to quantitatively determine the relationship between an individual parameter and the performance of the projectile. At the same time, the neural network is employed to perform nonlinear fitting with a large number of CFD numerical simulation results as learning samples, and the approximate calculation model of the shape parameters-drag coefficient of the projectile is established by neural network. Finally, the sequential quadratic programming (SQP) algorithm is introduced to find the optimal solution of the approximate calculation model. The use of neural network and SQP algorithm reduces the amount of calculation in the optimization process and the total time required for optimization work. After two rounds of optimization, the optimized projectile has a better ability to form supercavitation, and its drag coefficient has also been significantly improved compared to the original projectile, with a reduction about 30% compared to the projectile before optimization.
When a small-caliber projectile is moving underwater at a high speed, the water around the projectile will cavitate. The cavitation effect can greatly reduce the resistance of the moving vehicle, and the geometric shape of the warhead with the best drag coefficient corresponds to the supercavitating state where the projectile is completely enveloped by cavitation. Aiming at a small-caliber projectile, the computational fluid dynamics method is used to numerically simulate the gas-liquid two-phase flow with cavitation phenomenon, while the relationships of the cavitation shape and the drag coefficient with the geometry of the projectile’s head shape are explored. The three-segment cone type is selected as the basic projectile type, and the shape of the projectile is optimized by step optimization method. First, seven parameters are used to describe the three-segment cone shape of the projectile, and then the projectile is optimized in the order of the first section cone, the second and the third section cone. This method is used because the seven parameters are not independent of each other, and it is difficult to quantitatively determine the relationship between an individual parameter and the performance of the projectile. At the same time, the neural network is employed to perform nonlinear fitting with a large number of CFD numerical simulation results as learning samples, and the approximate calculation model of the shape parameters-drag coefficient of the projectile is established by neural network. Finally, the sequential quadratic programming (SQP) algorithm is introduced to find the optimal solution of the approximate calculation model. The use of neural network and SQP algorithm reduces the amount of calculation in the optimization process and the total time required for optimization work. After two rounds of optimization, the optimized projectile has a better ability to form supercavitation, and its drag coefficient has also been significantly improved compared to the original projectile, with a reduction about 30% compared to the projectile before optimization.
2022, 42(3): 034101.
doi: 10.11883/bzycj-2021-0303
Abstract:
The measurement of the interior ballistic projectile velocity in a two-stage light gas gun or powder gun and the observation of the state of the precursor gas in the launch tube are very important for the design and calculation of the interior ballistic and for the analysis of the abnormal ballistic. In order to obtain the better results, two microwave interferometers in the Ka-band and X-band were designed by the Dopple principle, since the transmission and reflection characteristics of microwave are related with the caliber of launch tube and objects materials respectively. A combination of the short-time Fourier transform and phase calculation was used to process the interference signal, and then the velocity, acceleration, displacement, projectile bottom pressure and other information were obtained by calculation. Complete interior ballistic data for a two-stage light gas gun and a high-speed powder gun were obtained experimentally. The difference in the projectile velocity measured by the microwave interferometer and the optical beam blocking (OBB) device is less than 0.5%. Moreover, it was demonstrated in our experiments that under some conditions, shock waves may cause premature breaking of the diaphragm in the high pressure section, which results in the projectile having a secondary loading at high pressure, and then becoming fragmented with a probability. In addition, based on the reflection and transmission characteristics of the ionized gas at different microwave wavelengths, the velocity of the precursor H2 gas in the launch tube of the two-stage light gas gun was measured using the X-band microwave interferometer for the first time, which can provide data for studying the temperature, pressure, ionization and other states of the high-speed ionized gas.
The measurement of the interior ballistic projectile velocity in a two-stage light gas gun or powder gun and the observation of the state of the precursor gas in the launch tube are very important for the design and calculation of the interior ballistic and for the analysis of the abnormal ballistic. In order to obtain the better results, two microwave interferometers in the Ka-band and X-band were designed by the Dopple principle, since the transmission and reflection characteristics of microwave are related with the caliber of launch tube and objects materials respectively. A combination of the short-time Fourier transform and phase calculation was used to process the interference signal, and then the velocity, acceleration, displacement, projectile bottom pressure and other information were obtained by calculation. Complete interior ballistic data for a two-stage light gas gun and a high-speed powder gun were obtained experimentally. The difference in the projectile velocity measured by the microwave interferometer and the optical beam blocking (OBB) device is less than 0.5%. Moreover, it was demonstrated in our experiments that under some conditions, shock waves may cause premature breaking of the diaphragm in the high pressure section, which results in the projectile having a secondary loading at high pressure, and then becoming fragmented with a probability. In addition, based on the reflection and transmission characteristics of the ionized gas at different microwave wavelengths, the velocity of the precursor H2 gas in the launch tube of the two-stage light gas gun was measured using the X-band microwave interferometer for the first time, which can provide data for studying the temperature, pressure, ionization and other states of the high-speed ionized gas.
2022, 42(3): 034201.
doi: 10.11883/bzycj-2021-0196
Abstract:
Viscoelastic artificial boundary is a commonly used numerical simulation method to deal with the wave propagation problems in an infinite domain. When the explicit time-domain stepwise integration algorithm is adopted for such numerical analysis, the stability conditions of the artificial boundary area are more stringent than those of the internal domain due to the influence of the damping and stiffness of the viscoelastic artificial boundary. However, there is currently no clear and practical stability criterion for this problem, which affects the reasonable selection of the integral time step when using the viscoelastic artificial boundaries, and further restricts the application of viscoelastic artificial boundary in the explicit dynamic analysis. Aiming at the two-dimensional (2D) viscoelastic artificial boundary, two typical types of boundary subsystem that can represent the localized characteristics of the overall numerical model, namely the edge boundary subsystem and the corner boundary subsystem, were established and their motion equations as well as the transfer matrixes were obtained according to the stability analysis method based on the local subsystem. Then through the stability criteria based on the spectral radius of the transfer matrix, the analytical solutions of the stability conditions of different local subsystems were derived. Through the comparative analysis of the stability conditions of different calculation areas and their influencing factors, it is found that the stability of the overall model is controlled by the corner boundary subsystem. On that basis, a uniform stability criterion and a simplified practical calculation method of the stability condition for the overall model with 2D viscoelastic artificial boundary in explicit dynamic calculations were proposed. In practical applications, the dynamic calculation of the overall model can be successfully completed once the integral time step meets the proposed stability condition of the numerical system. This study provides theoretical guidance for the reasonable selection of the integral time step when applying 2D viscoelastic artificial boundaries in explicit dynamic calculations.
Viscoelastic artificial boundary is a commonly used numerical simulation method to deal with the wave propagation problems in an infinite domain. When the explicit time-domain stepwise integration algorithm is adopted for such numerical analysis, the stability conditions of the artificial boundary area are more stringent than those of the internal domain due to the influence of the damping and stiffness of the viscoelastic artificial boundary. However, there is currently no clear and practical stability criterion for this problem, which affects the reasonable selection of the integral time step when using the viscoelastic artificial boundaries, and further restricts the application of viscoelastic artificial boundary in the explicit dynamic analysis. Aiming at the two-dimensional (2D) viscoelastic artificial boundary, two typical types of boundary subsystem that can represent the localized characteristics of the overall numerical model, namely the edge boundary subsystem and the corner boundary subsystem, were established and their motion equations as well as the transfer matrixes were obtained according to the stability analysis method based on the local subsystem. Then through the stability criteria based on the spectral radius of the transfer matrix, the analytical solutions of the stability conditions of different local subsystems were derived. Through the comparative analysis of the stability conditions of different calculation areas and their influencing factors, it is found that the stability of the overall model is controlled by the corner boundary subsystem. On that basis, a uniform stability criterion and a simplified practical calculation method of the stability condition for the overall model with 2D viscoelastic artificial boundary in explicit dynamic calculations were proposed. In practical applications, the dynamic calculation of the overall model can be successfully completed once the integral time step meets the proposed stability condition of the numerical system. This study provides theoretical guidance for the reasonable selection of the integral time step when applying 2D viscoelastic artificial boundaries in explicit dynamic calculations.
2022, 42(3): 035201.
doi: 10.11883/bzycj-2021-0126
Abstract:
The stability of anchored jointed rock slopes under dynamic disturbance of blasting excavation is a major concern for designers and constructors. For the left-bank slope at the valley bottom of the Baihetan hydropower station, the displacement characteristics and related energy mechanism of the anchored jointed rock slope under blasting excavation disturbance were investigated. The field monitoring data of the rock mass displacement and the anchor cable axial force were first presented to show their synchronous mutation characteristics under blasting excavation disturbance. A three-dimensional numerical simulation was then conducted by using FLAC3D to reveal the energy mechanism of the rock mass displacement mutation. The controlling effect of prestressed anchor cables on the rock mass displacement mutation was finally analyzed from the perspective of energy absorption and release. The results show that for the blasting excavation of the rock mass subjected to high in-situ stress at the valley bottom, the displacement mutation of the jointed rock slope is attributed to the rapid release of accumulated strain energy. The accumulated strain energy originates two actions, one is the blasting pressure, and the other one is the in-situ stress. The abrupt displacement of the jointed rock slope includes joint opening displacement and rock springback displacement. The total abrupt displacement will increase as the result of the in-situ stress level increases and the elastic modulus of the rock mass decreases. The prestressed anchor cable has a restraining effect on the displacement mutation of the jointed rock slope, and it mainly controls the joint opening displacement. The anchor cable with a higher prestress level corresponds to higher energy absorption and release rates, and thus has a stronger restraint on the displacement mutation of the jointed rock slope. However, when the prestress of the anchor cable is increased to a higher level, the displacement mutation of the jointed rock slope no longer decreases significantly with an increase in the prestress level.
The stability of anchored jointed rock slopes under dynamic disturbance of blasting excavation is a major concern for designers and constructors. For the left-bank slope at the valley bottom of the Baihetan hydropower station, the displacement characteristics and related energy mechanism of the anchored jointed rock slope under blasting excavation disturbance were investigated. The field monitoring data of the rock mass displacement and the anchor cable axial force were first presented to show their synchronous mutation characteristics under blasting excavation disturbance. A three-dimensional numerical simulation was then conducted by using FLAC3D to reveal the energy mechanism of the rock mass displacement mutation. The controlling effect of prestressed anchor cables on the rock mass displacement mutation was finally analyzed from the perspective of energy absorption and release. The results show that for the blasting excavation of the rock mass subjected to high in-situ stress at the valley bottom, the displacement mutation of the jointed rock slope is attributed to the rapid release of accumulated strain energy. The accumulated strain energy originates two actions, one is the blasting pressure, and the other one is the in-situ stress. The abrupt displacement of the jointed rock slope includes joint opening displacement and rock springback displacement. The total abrupt displacement will increase as the result of the in-situ stress level increases and the elastic modulus of the rock mass decreases. The prestressed anchor cable has a restraining effect on the displacement mutation of the jointed rock slope, and it mainly controls the joint opening displacement. The anchor cable with a higher prestress level corresponds to higher energy absorption and release rates, and thus has a stronger restraint on the displacement mutation of the jointed rock slope. However, when the prestress of the anchor cable is increased to a higher level, the displacement mutation of the jointed rock slope no longer decreases significantly with an increase in the prestress level.
2022, 42(3): 035301.
doi: 10.11883/bzycj-2021-0198
Abstract:
The explosive welding process of large-area metal plates 304L/Q235B involves explosive detonation, high-speed collision and plastic deformation of two metal plates, etc. If the finite element method is used to simulate this problem, twist or distortion of the elements will lead to a decrease in the calculation accuracy, even negative volume elements will appear, resulting in the termination of the calculation. Moreover, it is difficult to use the finite element method to calculate and simulate the dispersion process of the gas products formed by explosive detonation. In order to simulate the whole process of explosive welding of large-area metal plates and obtain reasonable technical parameters, the material point method is used for three-dimensional numerical simulation analysis. As one of the meshless methods, the material point method mainly uses the explicit integral algorithm in the simulation of impact dynamics problems. By combining the Lagrangian particle elements with the fixed Euler background grid, this method can realize numerical simulations of the high-speed collision of clad and base plates, the explosive sliding detonation and the plastic deformation process of the metal plate surface, and obtain the results of deformation, effective plastic strain and collision velocity between the clad plate and the base plate. The deformation of the composite plate simulated by material point method is basically consistent with the experimental results of explosive welding. The collision velocity between the clad plate and the base plate is an important physical parameter. The relative error between the results of the material point method and Richter formula is less than 13%. Based on the numerical calculation by the material point method and the experimental results, it is shown that the material point method has advantages in numerical accuracy and computational efficiency, and it is also verified that the material point method is an effective numerical method to study metal explosive welding.
The explosive welding process of large-area metal plates 304L/Q235B involves explosive detonation, high-speed collision and plastic deformation of two metal plates, etc. If the finite element method is used to simulate this problem, twist or distortion of the elements will lead to a decrease in the calculation accuracy, even negative volume elements will appear, resulting in the termination of the calculation. Moreover, it is difficult to use the finite element method to calculate and simulate the dispersion process of the gas products formed by explosive detonation. In order to simulate the whole process of explosive welding of large-area metal plates and obtain reasonable technical parameters, the material point method is used for three-dimensional numerical simulation analysis. As one of the meshless methods, the material point method mainly uses the explicit integral algorithm in the simulation of impact dynamics problems. By combining the Lagrangian particle elements with the fixed Euler background grid, this method can realize numerical simulations of the high-speed collision of clad and base plates, the explosive sliding detonation and the plastic deformation process of the metal plate surface, and obtain the results of deformation, effective plastic strain and collision velocity between the clad plate and the base plate. The deformation of the composite plate simulated by material point method is basically consistent with the experimental results of explosive welding. The collision velocity between the clad plate and the base plate is an important physical parameter. The relative error between the results of the material point method and Richter formula is less than 13%. Based on the numerical calculation by the material point method and the experimental results, it is shown that the material point method has advantages in numerical accuracy and computational efficiency, and it is also verified that the material point method is an effective numerical method to study metal explosive welding.
2022, 42(3): 035401.
doi: 10.11883/bzycj-2021-0176
Abstract:
An oil-gas deflagration simulation experimental condition system in the large-scale unconfined space was independently designed and built against the theoretical requirements for safety monitoring and controlling of oil-gas mixture explosions in large-scale unconfined spaces. To begin with, pressure and flame signals, variations in global temperature and radiation indicators in various areas of the system were accurately collected through sensors, thermal imagers and radiometers. Also, high-speed cameras were adopted to capture the dynamic development of flames during deflagration, acquiring specific behavior characteristics of flame shape. The results show that the oil-gas combustion modes in the unconfined space can be divided into fireless gas cloud firing, oil-gas combustion with open flame, and oil-gas deflagration with compression wave, according to the differences in initial oil-gas concentration. To be specific, the flame generated from oil-gas deflagration is in the mirror-image shape of “L”, which can be found in the infield of the bench as well as behind and right above the ignition surface. Moreover, several peaks can be found in the dynamic overpressure sequence development curve. Based on the peak type, the whole deflagration process can be partitioned into stable spread, flame bleeding, and burning collapse. Specifically, the high-intensity area of deflagration flame could be primarily observed at the 1/3 to 2/3 of the bench, with the peak reaching up to 4816.03 mV. It can be observed that the flame is principally presented in blue and orange, and the flame speed is downward in fluctuation along with the deflagration process. It can also be coupled with the overpressure development stage. After that, the overpressure peak is presented in a trend of first decreasing and then increasing along with the increase in the initial oil-gas concentration, whereas time consumed in peak forming is displayed in an opposite law. Note that both can fitted using the cubic polynomial. Besides, temperature gradient of deflagration flames is associated with the flame heading, and the temperature gradient of the flame front surface is typically smaller than that of the tail flame. What’s more, the formation time of radiation peak of deflagration has a certain delay in comparison to the flame intensity, causing that high-intensity radiation can be easily formed at the end of deflagration spreading. To sum up, key parameter supports and theoretical bases are provided for the online monitoring and explosion suppression of oil gas cloud deflagration in the large-scale unconfined space, presenting a significance in guiding the research and development of explosion suppression equipment.
An oil-gas deflagration simulation experimental condition system in the large-scale unconfined space was independently designed and built against the theoretical requirements for safety monitoring and controlling of oil-gas mixture explosions in large-scale unconfined spaces. To begin with, pressure and flame signals, variations in global temperature and radiation indicators in various areas of the system were accurately collected through sensors, thermal imagers and radiometers. Also, high-speed cameras were adopted to capture the dynamic development of flames during deflagration, acquiring specific behavior characteristics of flame shape. The results show that the oil-gas combustion modes in the unconfined space can be divided into fireless gas cloud firing, oil-gas combustion with open flame, and oil-gas deflagration with compression wave, according to the differences in initial oil-gas concentration. To be specific, the flame generated from oil-gas deflagration is in the mirror-image shape of “L”, which can be found in the infield of the bench as well as behind and right above the ignition surface. Moreover, several peaks can be found in the dynamic overpressure sequence development curve. Based on the peak type, the whole deflagration process can be partitioned into stable spread, flame bleeding, and burning collapse. Specifically, the high-intensity area of deflagration flame could be primarily observed at the 1/3 to 2/3 of the bench, with the peak reaching up to 4816.03 mV. It can be observed that the flame is principally presented in blue and orange, and the flame speed is downward in fluctuation along with the deflagration process. It can also be coupled with the overpressure development stage. After that, the overpressure peak is presented in a trend of first decreasing and then increasing along with the increase in the initial oil-gas concentration, whereas time consumed in peak forming is displayed in an opposite law. Note that both can fitted using the cubic polynomial. Besides, temperature gradient of deflagration flames is associated with the flame heading, and the temperature gradient of the flame front surface is typically smaller than that of the tail flame. What’s more, the formation time of radiation peak of deflagration has a certain delay in comparison to the flame intensity, causing that high-intensity radiation can be easily formed at the end of deflagration spreading. To sum up, key parameter supports and theoretical bases are provided for the online monitoring and explosion suppression of oil gas cloud deflagration in the large-scale unconfined space, presenting a significance in guiding the research and development of explosion suppression equipment.
