2022 Vol. 42, No. 12
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2022, 42(12): 121101.
doi: 10.11883/bzycj-2022-0434
Abstract:
The pulse wave constitutive relation determines propagation characteristics of pulse wave. How to determine it through experimental studies, and how to obtain it from the existing literature data through these methods, is one of the cores of the current research. Three feasible approaches were explored: (1) inverse analysis of the relationship C(p) (non-invasive method), (2) direct measurement of pulse wave p-V relationship (invasive method), and (3) Lagrange inverse analysis of a series of measured pulse wave (non-invasive method). By using the above methods and according to the existing literature data, it is found that the exponential p(V) constitutive relation can be deduced from the Rogers-Huang simplified formula of C(p) relation. The logarithmic p(V) constitutive relation can be deduced from the MK-Hughes equation. Pulse wave propagation characteristics vary significantly with nonlinear constitutive parameters. According to the viewpoint of body constitution classification in traditional Chinese medicine (TCM), the corresponding constitutive relation of pulse wave also has different types in principle, depending on people. In this sense, the Lagrange inverse analysis of pulse wave has a broad development prospect, but it puts forward higher requirements on the correct selection of measurement points and improving the sensitivity and accuracy of measurement.
The pulse wave constitutive relation determines propagation characteristics of pulse wave. How to determine it through experimental studies, and how to obtain it from the existing literature data through these methods, is one of the cores of the current research. Three feasible approaches were explored: (1) inverse analysis of the relationship C(p) (non-invasive method), (2) direct measurement of pulse wave p-V relationship (invasive method), and (3) Lagrange inverse analysis of a series of measured pulse wave (non-invasive method). By using the above methods and according to the existing literature data, it is found that the exponential p(V) constitutive relation can be deduced from the Rogers-Huang simplified formula of C(p) relation. The logarithmic p(V) constitutive relation can be deduced from the MK-Hughes equation. Pulse wave propagation characteristics vary significantly with nonlinear constitutive parameters. According to the viewpoint of body constitution classification in traditional Chinese medicine (TCM), the corresponding constitutive relation of pulse wave also has different types in principle, depending on people. In this sense, the Lagrange inverse analysis of pulse wave has a broad development prospect, but it puts forward higher requirements on the correct selection of measurement points and improving the sensitivity and accuracy of measurement.
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2022, 42(12): 122201.
doi: 10.11883/bzycj-2022-0173
Abstract:
In order to study the mechanism and the predictors of blast lung injuries, a finite element model including the human body and the explosion flow field was developed. The fluid-structure coupling algorithm of LS-DYNA was used to simulate the blast effect on the thorax. The developed model was validated using victims’ lung injury data in an explosion accident. A total of 39 simulation experiments were carried out. By changing the explosion equivalent and stand-off distance between the thorax and the explosive, the thorax was subjected to blast loads of different magnitudes, and the lung injuries ranged from no injury to extensive injuries. Base on the developed model, the pressure distribution in the explosion flow field, the dynamic response of the thorax and the stress distribution in the lung were investigated to clarify the mechanical mechanism of blast lung injuries. The thorax injuries and response of the human body model were analyzed, and the predictors of blast lung injuries were proposed. The results show that when subjected to the blast load, the anterior chest wall gains speed almost instantly and impacts the thoracic organs with a high velocity, causing the propagation of stress waves in the lung. Subsequently the anterior chest wall continuously compresses the thoracic organs and the ribs under inertia, which causes the thoracic deflection. The stress wave is the main cause of blast lung injuries, and the thoracic deflection is less likely to cause lung injuries. The damaged lung tissues are mainly in the area close to the anterior chest wall and heart. The peak sternum velocity and peak sternum acceleration have direct effects on the stress wave in the lung, and can be used as the predictors of blast lung injuries. The thoracic deflection and viscous criterion cannot reflect the damage to the lung caused by stress wave, and are not suitable for evaluating the blast lung injuries.
In order to study the mechanism and the predictors of blast lung injuries, a finite element model including the human body and the explosion flow field was developed. The fluid-structure coupling algorithm of LS-DYNA was used to simulate the blast effect on the thorax. The developed model was validated using victims’ lung injury data in an explosion accident. A total of 39 simulation experiments were carried out. By changing the explosion equivalent and stand-off distance between the thorax and the explosive, the thorax was subjected to blast loads of different magnitudes, and the lung injuries ranged from no injury to extensive injuries. Base on the developed model, the pressure distribution in the explosion flow field, the dynamic response of the thorax and the stress distribution in the lung were investigated to clarify the mechanical mechanism of blast lung injuries. The thorax injuries and response of the human body model were analyzed, and the predictors of blast lung injuries were proposed. The results show that when subjected to the blast load, the anterior chest wall gains speed almost instantly and impacts the thoracic organs with a high velocity, causing the propagation of stress waves in the lung. Subsequently the anterior chest wall continuously compresses the thoracic organs and the ribs under inertia, which causes the thoracic deflection. The stress wave is the main cause of blast lung injuries, and the thoracic deflection is less likely to cause lung injuries. The damaged lung tissues are mainly in the area close to the anterior chest wall and heart. The peak sternum velocity and peak sternum acceleration have direct effects on the stress wave in the lung, and can be used as the predictors of blast lung injuries. The thoracic deflection and viscous criterion cannot reflect the damage to the lung caused by stress wave, and are not suitable for evaluating the blast lung injuries.
2022, 42(12): 123101.
doi: 10.11883/bzycj-2022-0045
Abstract:
In this paper, a finite element model of the granular slug launcher was constructed. Using the discrete element-finite element coupling method, the dynamic response and mechanism of mitigation and energy absorption of sandwich beams with reentrant honeycomb core of negative Poisson’s ratio subject to high velocity granular slugs were investigated. Effects of the load impulse, impact angle, core strengths and friction between the granular slug and face sheets on dynamic response of sandwich beams were analyzed. The results demonstrated that the active deformation mode of sandwich beam subject to the normal impact of the granular slug is combined local denting and overall bending. The deformation mode of the sandwich in-plane core is local denting mode due to the bending of cell walls, whilst the sandwich out-plane core is local folding mode due to buckling of the cell walls. Compared to the same areal density of the sandwich beam with the in-plane design of the soft core, the deflections of the sandwich beam with the out-of-plane design of the hard core are smaller but both its initial peak and level of impact force are higher and its response time is shorter. The mid-span maximum deflections of front and rear face sheets of the sandwich beam increase with the impact loading approximately log-linearly. Compared to the normal impact, the deformation mode of the sandwich beam subject to the oblique impact is asymmetrical and the local denting area reduced. The mid-span maximum deflections of the front and rear face sheets, the initial peak of impact force and the proportions of kinetic energy and momentum transferred to the sandwich beams subject to velocity granular slug with different impact angles decrease with the increase of the impact angles, while the friction between the granular slug and the face sheets has little effect on dynamic response of sandwich beams.
In this paper, a finite element model of the granular slug launcher was constructed. Using the discrete element-finite element coupling method, the dynamic response and mechanism of mitigation and energy absorption of sandwich beams with reentrant honeycomb core of negative Poisson’s ratio subject to high velocity granular slugs were investigated. Effects of the load impulse, impact angle, core strengths and friction between the granular slug and face sheets on dynamic response of sandwich beams were analyzed. The results demonstrated that the active deformation mode of sandwich beam subject to the normal impact of the granular slug is combined local denting and overall bending. The deformation mode of the sandwich in-plane core is local denting mode due to the bending of cell walls, whilst the sandwich out-plane core is local folding mode due to buckling of the cell walls. Compared to the same areal density of the sandwich beam with the in-plane design of the soft core, the deflections of the sandwich beam with the out-of-plane design of the hard core are smaller but both its initial peak and level of impact force are higher and its response time is shorter. The mid-span maximum deflections of front and rear face sheets of the sandwich beam increase with the impact loading approximately log-linearly. Compared to the normal impact, the deformation mode of the sandwich beam subject to the oblique impact is asymmetrical and the local denting area reduced. The mid-span maximum deflections of the front and rear face sheets, the initial peak of impact force and the proportions of kinetic energy and momentum transferred to the sandwich beams subject to velocity granular slug with different impact angles decrease with the increase of the impact angles, while the friction between the granular slug and the face sheets has little effect on dynamic response of sandwich beams.
2022, 42(12): 123102.
doi: 10.11883/bzycj-2022-0214
Abstract:
In order to study the damage of concrete structures which have relatively strict requirements on the formation and propagation of cracks, such as dam, pier and nuclear power plant containment, suffered by impact loads, numerical studies were conducted on the mechanical response of (reinforced) concrete slabs under two types of explosion loadings (contact explosion and closed explosion) by a three-dimensional meso-mechanical model together with a comprehensive computational dynamic constitutive model for concrete material, followed by a parametric discussion about the interfering factors of final crack morphologies in concrete targets. To generate the three-dimensional meso-mechanical model, regular hexahedral meshes were firstly applied to whole concrete specimens/structures and all the elements were assigned as mortar matrix, then the assemblies of elements as aggregate were randomly selected and the outer surfaces of each aggregate element assemblies were covered with shell elements as interfacial transition zone layers. The three-dimensional meso-mechanical model, in which taking the influence of internal meso-structures of concrete (e.g. volume fraction, size and gradation of coarse aggregate) and mechanical properties of three phase materials into consideration, succeeds in accurately predicting the crack patterns and crater sizes in the concrete slabs subjected to the two types of explosion loadings. It is shown that the numerical results are in good agreement with the experimental observations in terms of crater shapes and sizes in the contact explosion, as well as the number of main cracks in the closed explosion when compared with the predictions by the macroscopic homogeneous models. Parametric studies performed for further study on the influence factors of the explosion results indicate that both the global mesh size of the model and the relative mesh size of each component in the model produce effects on the accuracy of the numerical results, the balance between the computational accuracy and efficiency can be achieved by setting a similar mesh size for concrete material with air grids. In addition, the influence of the aggregate size can not be neglected in the response and failure of the concrete slabs subjected to explosion loadings. The three-dimensional meso-mechanical model plays an important role in understanding the meso-mechanism and influencing factors of the response and failure of the concrete structures subjected to impact loadings, which is of great theoretical and practical significance for engineering design and safety assessment.
In order to study the damage of concrete structures which have relatively strict requirements on the formation and propagation of cracks, such as dam, pier and nuclear power plant containment, suffered by impact loads, numerical studies were conducted on the mechanical response of (reinforced) concrete slabs under two types of explosion loadings (contact explosion and closed explosion) by a three-dimensional meso-mechanical model together with a comprehensive computational dynamic constitutive model for concrete material, followed by a parametric discussion about the interfering factors of final crack morphologies in concrete targets. To generate the three-dimensional meso-mechanical model, regular hexahedral meshes were firstly applied to whole concrete specimens/structures and all the elements were assigned as mortar matrix, then the assemblies of elements as aggregate were randomly selected and the outer surfaces of each aggregate element assemblies were covered with shell elements as interfacial transition zone layers. The three-dimensional meso-mechanical model, in which taking the influence of internal meso-structures of concrete (e.g. volume fraction, size and gradation of coarse aggregate) and mechanical properties of three phase materials into consideration, succeeds in accurately predicting the crack patterns and crater sizes in the concrete slabs subjected to the two types of explosion loadings. It is shown that the numerical results are in good agreement with the experimental observations in terms of crater shapes and sizes in the contact explosion, as well as the number of main cracks in the closed explosion when compared with the predictions by the macroscopic homogeneous models. Parametric studies performed for further study on the influence factors of the explosion results indicate that both the global mesh size of the model and the relative mesh size of each component in the model produce effects on the accuracy of the numerical results, the balance between the computational accuracy and efficiency can be achieved by setting a similar mesh size for concrete material with air grids. In addition, the influence of the aggregate size can not be neglected in the response and failure of the concrete slabs subjected to explosion loadings. The three-dimensional meso-mechanical model plays an important role in understanding the meso-mechanism and influencing factors of the response and failure of the concrete structures subjected to impact loadings, which is of great theoretical and practical significance for engineering design and safety assessment.
2022, 42(12): 123201.
doi: 10.11883/bzycj-2022-0097
Abstract:
Chloroform was used to bond a polycarbonate (PC) plate and a polymethylmethacrylate (PMMA) plate to fabricate a model with a heterogeneous cemented interface. A cylinder blasthole was set in the PC plate with a certain angle to the interface. Base on the locations between the interface and the explosive initiation points, two kinds of initiation methods were used in the experiment. The one is the top initiation method, in which the initiation point is settled far away from the interface; and the other is the bottom initiation method, in which the initiation point is close to the interface. The digital image correlation (DIC) method was used to study the evolution of the strain field during the passage of the blast waves in the medium with the heterogeneous interface. The results show that the propagation pattern of the blast stress wave varies significantly after it passes through the interface. In the top initiation, a stress concentration zone is formed on the interface under blast loadings, and induce a crack initiate at the interface. The transverse tensile wave is the main reason for the cracking of the interface. Besides, it can be found that the initiation methods have different contributions to both the magnitude and the locations of the tensile/compressive strain in both the transverse and longitudinal directions. Moreover, in the bottom area of the borehole, the influence of the initiation method on the time-related characteristics of the strain field mainly has two aspects, namely, the duration time and the strain magnitude. And it is found that the transverse/longitudinal strain is of "short duration, high magnitude" variation characteristic for the top initiation. In terms of the strain magnitude, the influence of the initiation method on the transverse strain is much greater than it on the longitudinal strain. In addition, the initiation method can significantly influence the attenuation characteristics of the strain field, which is more obvious for the longitudinal strain field. In terms of the attenuation rate, the magnitude blast stress waves attenuated faster in the PC plate, whereas the blast stress waves attenuated slowly when it passed through the interface and propagated in the PMMA plate regardless of the initiation method.
Chloroform was used to bond a polycarbonate (PC) plate and a polymethylmethacrylate (PMMA) plate to fabricate a model with a heterogeneous cemented interface. A cylinder blasthole was set in the PC plate with a certain angle to the interface. Base on the locations between the interface and the explosive initiation points, two kinds of initiation methods were used in the experiment. The one is the top initiation method, in which the initiation point is settled far away from the interface; and the other is the bottom initiation method, in which the initiation point is close to the interface. The digital image correlation (DIC) method was used to study the evolution of the strain field during the passage of the blast waves in the medium with the heterogeneous interface. The results show that the propagation pattern of the blast stress wave varies significantly after it passes through the interface. In the top initiation, a stress concentration zone is formed on the interface under blast loadings, and induce a crack initiate at the interface. The transverse tensile wave is the main reason for the cracking of the interface. Besides, it can be found that the initiation methods have different contributions to both the magnitude and the locations of the tensile/compressive strain in both the transverse and longitudinal directions. Moreover, in the bottom area of the borehole, the influence of the initiation method on the time-related characteristics of the strain field mainly has two aspects, namely, the duration time and the strain magnitude. And it is found that the transverse/longitudinal strain is of "short duration, high magnitude" variation characteristic for the top initiation. In terms of the strain magnitude, the influence of the initiation method on the transverse strain is much greater than it on the longitudinal strain. In addition, the initiation method can significantly influence the attenuation characteristics of the strain field, which is more obvious for the longitudinal strain field. In terms of the attenuation rate, the magnitude blast stress waves attenuated faster in the PC plate, whereas the blast stress waves attenuated slowly when it passed through the interface and propagated in the PMMA plate regardless of the initiation method.
2022, 42(12): 123202.
doi: 10.11883/bzycj-2022-0041
Abstract:
Based on the Kong-Fang concrete material model and the multi-material arbitrary Lagrangian Eulerian (MMALE) algorithm available in LS-DYNA, the attenuation of stress wave in concrete subjected to explosion was numerically studied. On the basis of comparative analysis of different material models, numerical algorithms and selection of appropriate mesh size, the proposed numerical algorithm and material models along with the corresponding parameters were firstly validated by comparing the numerically simulated spherical charge detonated in a concrete target with the corresponding test data in terms of peak stress and stress-time history. Then the attenuation of stress wave subjected to spherical charge detonated in concrete was numerically investigated, in which the radial and circumferential stress-time histories at different scaled distances were analyzed in detail to reveal the mechanism of stress wave attenuation. The numerical results were fitted to develop an empirical formula for the peak stress of the free-field compression wave in concrete at the close zone with the aid of dimensional analysis. Besides, the applicability of the developed empirical formula was also discussed. The influence of charge buried depth on peak stress in concrete at different distances was also numerically studied to develop a quantitative relationship between charge buried depth, distance and the so-called coupling factor. Numerical results demonstrate that the Kong-Fang concrete material model can be used to simulate the attenuation of explosion stress wave in concrete with good accuracy. The influence of the charge buried depth and the distance from charge the center on the coupling factor of peak stress can be quantified by defining the mass coefficient and coupling constant. The empirical formula for peak stress of compression wave in concrete at the close zone is appropriate for varied charge buried depth, distance and concrete strength. The present numerical results are useful for blast-resistant design and can provide a reliable reference for estimating the damage degree of concrete caused by explosion.
Based on the Kong-Fang concrete material model and the multi-material arbitrary Lagrangian Eulerian (MMALE) algorithm available in LS-DYNA, the attenuation of stress wave in concrete subjected to explosion was numerically studied. On the basis of comparative analysis of different material models, numerical algorithms and selection of appropriate mesh size, the proposed numerical algorithm and material models along with the corresponding parameters were firstly validated by comparing the numerically simulated spherical charge detonated in a concrete target with the corresponding test data in terms of peak stress and stress-time history. Then the attenuation of stress wave subjected to spherical charge detonated in concrete was numerically investigated, in which the radial and circumferential stress-time histories at different scaled distances were analyzed in detail to reveal the mechanism of stress wave attenuation. The numerical results were fitted to develop an empirical formula for the peak stress of the free-field compression wave in concrete at the close zone with the aid of dimensional analysis. Besides, the applicability of the developed empirical formula was also discussed. The influence of charge buried depth on peak stress in concrete at different distances was also numerically studied to develop a quantitative relationship between charge buried depth, distance and the so-called coupling factor. Numerical results demonstrate that the Kong-Fang concrete material model can be used to simulate the attenuation of explosion stress wave in concrete with good accuracy. The influence of the charge buried depth and the distance from charge the center on the coupling factor of peak stress can be quantified by defining the mass coefficient and coupling constant. The empirical formula for peak stress of compression wave in concrete at the close zone is appropriate for varied charge buried depth, distance and concrete strength. The present numerical results are useful for blast-resistant design and can provide a reliable reference for estimating the damage degree of concrete caused by explosion.
2022, 42(12): 123301.
doi: 10.11883/bzycj-2022-0249
Abstract:
By means of a 30-mm-caliber ballistic gun platform, a series of experiments were carried out on 2A12 aluminum targets subjected to normal penetration by three kinds of 30CrMnSi2A steel projectiles with different elliptical cross-section shapes in the striking velocity range from 200 m/s to 600 m/s. The residual velocities of the projectiles and the failure modes of the targets were experimentally obtained. Based on the experimental results, the corresponding numerical models were established and verified. And the influences of the major-to-minor axis length ratios of the projectile cross-sections on the failure modes and response characteristics of the targets were systematically analyzed. The results show as follows. The maximum cross-sectional areas of the projectiles are the main factor affecting the residual velocities of the projectiles, while the major-to-minor axis length ratios of the projectile cross-sections have little effect on the residual velocities. Therefore, in engineering applications, the engineering model for the circular cross-section projectile penetrating a target can be directly used to calculate the residual velocity of the elliptical cross-section projectile with the same maximum cross-sectional area. In addition, under normal penetration of the circular cross-section projectiles, the sizes, shapes and distribution of the petals induced at the back faces of the targets are uniform. However, under normal penetration of the elliptical cross-section projectiles, as the major-to-minor axis length ratios of the projectile cross-sections increase, the numbers of the petals induced at the back faces of the targets increase and the petal sizes decrease, and the petal numbers and the uplifted height in the minor axis direction are greater than those in the major axis direction. The radial displacement, radial stress and tangential stress of the targets under the normal penetration of the elliptical cross-section projectiles are obviously different from those of the targets under the normal penetration of the circular cross-section projectiles. Under normal penetrations of the circular cross-section projectiles, the above response characteristics of the targets change basically the same along the circumferential directions and the targets are under simple compression states with the tangential stress of zero. But, under normal penetrations of the elliptical cross-section projectiles, the stress states of different points of the targets are closely related to the major-to-minor axis length ratios and the circumferential angles of the projectiles, and the targets are subjected to the coupling effects of the compression and shear stresses.
By means of a 30-mm-caliber ballistic gun platform, a series of experiments were carried out on 2A12 aluminum targets subjected to normal penetration by three kinds of 30CrMnSi2A steel projectiles with different elliptical cross-section shapes in the striking velocity range from 200 m/s to 600 m/s. The residual velocities of the projectiles and the failure modes of the targets were experimentally obtained. Based on the experimental results, the corresponding numerical models were established and verified. And the influences of the major-to-minor axis length ratios of the projectile cross-sections on the failure modes and response characteristics of the targets were systematically analyzed. The results show as follows. The maximum cross-sectional areas of the projectiles are the main factor affecting the residual velocities of the projectiles, while the major-to-minor axis length ratios of the projectile cross-sections have little effect on the residual velocities. Therefore, in engineering applications, the engineering model for the circular cross-section projectile penetrating a target can be directly used to calculate the residual velocity of the elliptical cross-section projectile with the same maximum cross-sectional area. In addition, under normal penetration of the circular cross-section projectiles, the sizes, shapes and distribution of the petals induced at the back faces of the targets are uniform. However, under normal penetration of the elliptical cross-section projectiles, as the major-to-minor axis length ratios of the projectile cross-sections increase, the numbers of the petals induced at the back faces of the targets increase and the petal sizes decrease, and the petal numbers and the uplifted height in the minor axis direction are greater than those in the major axis direction. The radial displacement, radial stress and tangential stress of the targets under the normal penetration of the elliptical cross-section projectiles are obviously different from those of the targets under the normal penetration of the circular cross-section projectiles. Under normal penetrations of the circular cross-section projectiles, the above response characteristics of the targets change basically the same along the circumferential directions and the targets are under simple compression states with the tangential stress of zero. But, under normal penetrations of the elliptical cross-section projectiles, the stress states of different points of the targets are closely related to the major-to-minor axis length ratios and the circumferential angles of the projectiles, and the targets are subjected to the coupling effects of the compression and shear stresses.
2022, 42(12): 123901.
doi: 10.11883/bzycj-2021-0426
Abstract:
In order to solve the problems of structural damage and ballistic runaway caused by huge impact loads suffered by air-drop vehicles and rocket-assisted vehicles during high-speed water-entry, a slotted wrapping buffer head cap was proposed to guarantee the structural safety of the vehicles during water entry. Firstly, the structural composition and detailed parameters of the head cap were given, and a numerical model for the high-speed water-entry of the vehicles was established based on the arbitrary Lagrangian-Eulerian (ALE) algorithm. The Lagrangian viewpoint was used to solve the small deformation of the vehicle and the head cap, and the Eulerian viewpoint was used to capture the large deformation of the free surface such as water and air, thereby overcoming the problems that the Eulerian mesh was not accurate enough to solve the structural deformation and the numerical oscillation caused by mesh distortion in solving large deformation problems by the Lagrangian mesh. On this basis, the evolution processes of the cavity and flow field around the vehicle entering the water with the head cap at different angles were studied by numerical simulation, and the interaction process between the head cap and the water was given. Furthermore, the distribution of effective stress of the buffer was analyzed when it entering the water vertically and obliquely. Finally, the load reduction performances of the head cap when the vehicle entered the water at different velocities and angles were investigated. The results show that the cavities obtained by the simulation are basically consistent with the experimental images, and the change trends of impact acceleration are basically consistent with the experimental results. The relative error of the axial peak acceleration between the numerical simulation and experiment is 6.72%, and the relative error of the radial peak acceleration is 7.52%. The ratio of axial load reduction is 22.17% when the vehicle enters the water vertically with a head cap at 300 m/s. At the same time, the ratio of axial load reduction is 31.83% and the ratio of radial load reduction is 66.80% when the vehicle with a head cap enters the water at 100 m/s and 60°. So this research has a certain guiding role in the design of new load-reduction structure.
In order to solve the problems of structural damage and ballistic runaway caused by huge impact loads suffered by air-drop vehicles and rocket-assisted vehicles during high-speed water-entry, a slotted wrapping buffer head cap was proposed to guarantee the structural safety of the vehicles during water entry. Firstly, the structural composition and detailed parameters of the head cap were given, and a numerical model for the high-speed water-entry of the vehicles was established based on the arbitrary Lagrangian-Eulerian (ALE) algorithm. The Lagrangian viewpoint was used to solve the small deformation of the vehicle and the head cap, and the Eulerian viewpoint was used to capture the large deformation of the free surface such as water and air, thereby overcoming the problems that the Eulerian mesh was not accurate enough to solve the structural deformation and the numerical oscillation caused by mesh distortion in solving large deformation problems by the Lagrangian mesh. On this basis, the evolution processes of the cavity and flow field around the vehicle entering the water with the head cap at different angles were studied by numerical simulation, and the interaction process between the head cap and the water was given. Furthermore, the distribution of effective stress of the buffer was analyzed when it entering the water vertically and obliquely. Finally, the load reduction performances of the head cap when the vehicle entered the water at different velocities and angles were investigated. The results show that the cavities obtained by the simulation are basically consistent with the experimental images, and the change trends of impact acceleration are basically consistent with the experimental results. The relative error of the axial peak acceleration between the numerical simulation and experiment is 6.72%, and the relative error of the radial peak acceleration is 7.52%. The ratio of axial load reduction is 22.17% when the vehicle enters the water vertically with a head cap at 300 m/s. At the same time, the ratio of axial load reduction is 31.83% and the ratio of radial load reduction is 66.80% when the vehicle with a head cap enters the water at 100 m/s and 60°. So this research has a certain guiding role in the design of new load-reduction structure.
2022, 42(12): 124101.
doi: 10.11883/bzycj-2021-0484
Abstract:
One-dimensional cylindrical load was imposed on the middle part and half height of the metal cylinders which have the initial height of 160 mm, the wall thickness of 4 mm and the external diameter of 48 mm, by the way of an electric exploding wire initiating explosives, and then drove the nylon lining to expand the metal cylinder. At the same time, a validity criterion of the one-dimensional cylindrical load was proposed based on the load or radial velocity monitoring on the outside surface of the cylinder along its axis and circumference. Compared with the load of sliding detonation, the one-dimensional cylindrical load has the advantages of simple stress state and easy analysis as a problem on a simplified two-dimensional axial symmetrical structure, and can provide an explicit analysis on the stress components related to the fracture of the cylinder. Based on the radial velocities of the test points distributed at the outside surface of the cylinder, a method was proposed to diagnose the initial fracture over the periphery of the cylinder. The principle of the proposed diagnosis method is that the fracture of the cylinder under homogeneous load can result in the bifurcation (or change of the evolution trend) in the uniform velocity-curve cluster. And the initial fracture time and position will be the same as the bifurcating time of the velocity curves and the position of bifurcated velocity curve, respectively, when the bifurcation angle of the velocity curves exceeds the normal scope corresponding to structure strength of the tested cylinder. Compared with the high-speed framing photography which can obtain the exact fracture information over part of the periphery of the cylinder, the distributed velocity monitoring can obtain the exact initial fracture information over the whole periphery of the cylinder. The initial fracture parameters of the 304 steel and 45 steel cylinders under one-dimensional dynamic expanding load were obtained by using the established loading and diagnosis technologies for expanding cylinder experiment with linear initiation explosives. These parameters include the fracture strain and the average strain rate. The fracture strain or ductility of the 45 steel cylinder is lower than that of the 304 steel cylinder.
One-dimensional cylindrical load was imposed on the middle part and half height of the metal cylinders which have the initial height of 160 mm, the wall thickness of 4 mm and the external diameter of 48 mm, by the way of an electric exploding wire initiating explosives, and then drove the nylon lining to expand the metal cylinder. At the same time, a validity criterion of the one-dimensional cylindrical load was proposed based on the load or radial velocity monitoring on the outside surface of the cylinder along its axis and circumference. Compared with the load of sliding detonation, the one-dimensional cylindrical load has the advantages of simple stress state and easy analysis as a problem on a simplified two-dimensional axial symmetrical structure, and can provide an explicit analysis on the stress components related to the fracture of the cylinder. Based on the radial velocities of the test points distributed at the outside surface of the cylinder, a method was proposed to diagnose the initial fracture over the periphery of the cylinder. The principle of the proposed diagnosis method is that the fracture of the cylinder under homogeneous load can result in the bifurcation (or change of the evolution trend) in the uniform velocity-curve cluster. And the initial fracture time and position will be the same as the bifurcating time of the velocity curves and the position of bifurcated velocity curve, respectively, when the bifurcation angle of the velocity curves exceeds the normal scope corresponding to structure strength of the tested cylinder. Compared with the high-speed framing photography which can obtain the exact fracture information over part of the periphery of the cylinder, the distributed velocity monitoring can obtain the exact initial fracture information over the whole periphery of the cylinder. The initial fracture parameters of the 304 steel and 45 steel cylinders under one-dimensional dynamic expanding load were obtained by using the established loading and diagnosis technologies for expanding cylinder experiment with linear initiation explosives. These parameters include the fracture strain and the average strain rate. The fracture strain or ductility of the 45 steel cylinder is lower than that of the 304 steel cylinder.
2022, 42(12): 124201.
doi: 10.11883/bzycj-2022-0054
Abstract:
A two-stage light gas gun is a common hypervelocity launcher. Over the years, most researchers adopted simplified one-dimensional models and rarely used three-dimensional finite element models. This paper used the coupled Eulerian-Lagrangian algorithm to calculate the gas-driven hydrodynamic field in a 14-mm-caliber two-stage light gas gun. The two-stage light gas gun was decoupled into two three-dimensional numerical models according to whether the diaphragm was broken. A three-factor four-level orthogonal test was carried out to get the material friction coefficient and the broken diaphragm pressure, which were difficult to measure in experiments. The ordinary least square method was used to calculate the orthogonal test data. The friction coefficient between the piston and the pump tube was 0.82, the friction coefficient between the projectile and the launch tube was 0.30, and the broken diaphragm pressure was 11.73 MPa. The orthogonal test showed that the friction coefficient and the broken diaphragm pressure significantly influenced the calculation results. The friction could not be ignored in calculating the launch process of the two-stage light gas gun. So keeping the gun body clean was necessary to improve the projectile velocity. The numerical model for the two-stage light gas gun was established based on the method mentioned above, which completely reproduced the launch process of the gas gun, and visually represented the change of the flow field. The velocities of the projectile were numerically obtained by the established model, which were highly consistent with the experimental results. In addition, the verification condition was selected to analyze the change of the flow field, and the pressure nephograms at the critical moments were given. It should be noted that the velocity range of the projectile was 3－5 km/s. The method is fully applicable for the projectile velocity below 3 km/s and is generalizable for the higher projectile velocity. The gas gun simplification method, grading idea and key parameter confirmation method can be extended to other two/multi-stage light-gas guns, such as solid propellant driven and detonation driven.
A two-stage light gas gun is a common hypervelocity launcher. Over the years, most researchers adopted simplified one-dimensional models and rarely used three-dimensional finite element models. This paper used the coupled Eulerian-Lagrangian algorithm to calculate the gas-driven hydrodynamic field in a 14-mm-caliber two-stage light gas gun. The two-stage light gas gun was decoupled into two three-dimensional numerical models according to whether the diaphragm was broken. A three-factor four-level orthogonal test was carried out to get the material friction coefficient and the broken diaphragm pressure, which were difficult to measure in experiments. The ordinary least square method was used to calculate the orthogonal test data. The friction coefficient between the piston and the pump tube was 0.82, the friction coefficient between the projectile and the launch tube was 0.30, and the broken diaphragm pressure was 11.73 MPa. The orthogonal test showed that the friction coefficient and the broken diaphragm pressure significantly influenced the calculation results. The friction could not be ignored in calculating the launch process of the two-stage light gas gun. So keeping the gun body clean was necessary to improve the projectile velocity. The numerical model for the two-stage light gas gun was established based on the method mentioned above, which completely reproduced the launch process of the gas gun, and visually represented the change of the flow field. The velocities of the projectile were numerically obtained by the established model, which were highly consistent with the experimental results. In addition, the verification condition was selected to analyze the change of the flow field, and the pressure nephograms at the critical moments were given. It should be noted that the velocity range of the projectile was 3－5 km/s. The method is fully applicable for the projectile velocity below 3 km/s and is generalizable for the higher projectile velocity. The gas gun simplification method, grading idea and key parameter confirmation method can be extended to other two/multi-stage light-gas guns, such as solid propellant driven and detonation driven.
2022, 42(12): 125101.
doi: 10.11883/bzycj-2021-0492
Abstract:
Pipelines with a gasketed bell and spigot joint are more vulnerable to external load damage, leading to pipeline failure. To ensure the safe operation of adjacent high-density polyethylene (HDPE) bellows during blasting excavation, control of the influence of blasting vibration load on the pipeline is the main focus. The vibration velocity and dynamic strain response data of the pipeline were collected from the field test of a full-scale embedded single-segment HDPE bellow. The HDPE bellow models without socket contact and with an elastic sealing ring were established using the LS-DYNA numerical simulation software. The reliability of the model parameters of the HDPE bellows without a joint was verified by the field test data, and the response laws and failure mechanisms of the structural displacement, vibration velocity, and effective stress of the HDPE bellows with a gasketed bell and spigot joint were compared and analyzed. The safe vibration velocity of the pipe was determined using the pipeline response law and the allowable rotation angle of the interface in conjunction with the current specification. The research results show that the resultant vibration velocity, resultant displacement, and effective stress of the bellow with a gasketed bell and spigot joint are greater than those of the bellow without a joint. At the same cross-section, the resultant vibration velocity and effective stress on the explosion side of the bellow with a gasketed bell and spigot joint are higher, and the maximum resultant displacement occurs on the back of the explosion side of the cross-section. Along the axis direction of the pipeline, the resultant displacement and the resultant vibration velocity of the pipeline decrease continuously from the center to both ends of the pipeline, and the resultant displacement of the pipeline with a gasketed bell and spigot joint is larger. The safe vibration velocity of the pipeline with a gasketed bell and spigot joint under such working conditions is 24.77 cm/s, according to the allowable rotation angle of the interface.
Pipelines with a gasketed bell and spigot joint are more vulnerable to external load damage, leading to pipeline failure. To ensure the safe operation of adjacent high-density polyethylene (HDPE) bellows during blasting excavation, control of the influence of blasting vibration load on the pipeline is the main focus. The vibration velocity and dynamic strain response data of the pipeline were collected from the field test of a full-scale embedded single-segment HDPE bellow. The HDPE bellow models without socket contact and with an elastic sealing ring were established using the LS-DYNA numerical simulation software. The reliability of the model parameters of the HDPE bellows without a joint was verified by the field test data, and the response laws and failure mechanisms of the structural displacement, vibration velocity, and effective stress of the HDPE bellows with a gasketed bell and spigot joint were compared and analyzed. The safe vibration velocity of the pipe was determined using the pipeline response law and the allowable rotation angle of the interface in conjunction with the current specification. The research results show that the resultant vibration velocity, resultant displacement, and effective stress of the bellow with a gasketed bell and spigot joint are greater than those of the bellow without a joint. At the same cross-section, the resultant vibration velocity and effective stress on the explosion side of the bellow with a gasketed bell and spigot joint are higher, and the maximum resultant displacement occurs on the back of the explosion side of the cross-section. Along the axis direction of the pipeline, the resultant displacement and the resultant vibration velocity of the pipeline decrease continuously from the center to both ends of the pipeline, and the resultant displacement of the pipeline with a gasketed bell and spigot joint is larger. The safe vibration velocity of the pipeline with a gasketed bell and spigot joint under such working conditions is 24.77 cm/s, according to the allowable rotation angle of the interface.
2022, 42(12): 125102.
doi: 10.11883/bzycj-2021-0437
Abstract:
Semi-armor-piercing warhead is likely to penetrate into the inner space of warship to induce severe damage. Published research indicated that the corner part of ship cabin tended to fail first. In present study, the novel design of corner structure aims to improve the capability of explosion-proof of ship cabin. Motivated by this idea, six kinds of typical corner connection structures were designed using the concept of weakening converged shock wave, improving the structure stress and strain state, coordinating deformation and transforming failure modes. The LS-DYNA software was employed to investigate the dynamic response of cabin structure subjected internal blast loading. Lagrange shell element and solid element based on multi-material ALE algorithm are used to simulate steel structure and air region, respectively. The interaction between shock wave and structure was fulfilled using fluid-structure interaction algorithm. The accuracy of the numerical model proposed in present paper was validated by comparing the published experimental results. Main attention of present study focuses on the effects of corner connection structure on the maximum deflection, corner pressure and deformation/failure mode of cabin structure. It attempts to explore the failure mechanisms of cabin structure. Simulation results confirm that the corner position of cabin structure is susceptive to fail under internal blast loading. Compared with the original structure without corner connection, the existence of corner connection structure can obviously reduce the plastic deformation of cabin structure. To be specific, the corner connection in the flat-plate form could reduce the maximum deflection by up to 31.9% relative to the original structure. In addition, the application of the corner connection in the arc shape could decrease the equivalent plastic strain by about 60%. Moreover, the existence of corner connection structure could ameliorate the position of high plastic strain and the failure modes of cabin structure. In present study, the corner connections in flat-plate form, concave form and arc shape could effectively avoid the failure behavior of cabin corner.
Semi-armor-piercing warhead is likely to penetrate into the inner space of warship to induce severe damage. Published research indicated that the corner part of ship cabin tended to fail first. In present study, the novel design of corner structure aims to improve the capability of explosion-proof of ship cabin. Motivated by this idea, six kinds of typical corner connection structures were designed using the concept of weakening converged shock wave, improving the structure stress and strain state, coordinating deformation and transforming failure modes. The LS-DYNA software was employed to investigate the dynamic response of cabin structure subjected internal blast loading. Lagrange shell element and solid element based on multi-material ALE algorithm are used to simulate steel structure and air region, respectively. The interaction between shock wave and structure was fulfilled using fluid-structure interaction algorithm. The accuracy of the numerical model proposed in present paper was validated by comparing the published experimental results. Main attention of present study focuses on the effects of corner connection structure on the maximum deflection, corner pressure and deformation/failure mode of cabin structure. It attempts to explore the failure mechanisms of cabin structure. Simulation results confirm that the corner position of cabin structure is susceptive to fail under internal blast loading. Compared with the original structure without corner connection, the existence of corner connection structure can obviously reduce the plastic deformation of cabin structure. To be specific, the corner connection in the flat-plate form could reduce the maximum deflection by up to 31.9% relative to the original structure. In addition, the application of the corner connection in the arc shape could decrease the equivalent plastic strain by about 60%. Moreover, the existence of corner connection structure could ameliorate the position of high plastic strain and the failure modes of cabin structure. In present study, the corner connections in flat-plate form, concave form and arc shape could effectively avoid the failure behavior of cabin corner.
2022, 42(12): 125401.
doi: 10.11883/bzycj-2022-0100
Abstract:
Study on propagation characteristics of detonation in bifurcated tubes is of great significance to the safety protection of gas explosion in pipelines and engineering application. The propagation states of detonation vary with the geometrical structure when passing through the bifurcated tee. Based on the detonation circular test tube, the stoichiometric hydrogen-air mixture gas with 29.5% H2 in the volume fraction under different initial pressures was ignited by a 10-kV double high-voltage electrode to be detonated before entering the 30°, 45° and 90° bifurcation tees, respectively. The propagation characteristics of the detonation in the bifurcated tubes were analyzed based on the propagation velocity and cellular structure evolution characteristics obtained from the feedback signals of flame sensors and smoke-foils records. The results show that the H2/air detonation will decay when it passes through a bifurcated tee which is affected by rarefaction wave, but it is only a local phenomenon. The detonation re-initiation is gradually completed from regular reflection to Mach reflection after collision of incident shock wave and wall. In the straight branch tube, the detonation decay is mainly affected by the inlet area of the collateral branch tube. With the increase of the bifurcation angle, the inlet area decreases, and the detonation decay and re-initiation distance decrease as well. In the collateral branch tube, the detonation decay is affected by both the inlet area of the collateral branch tube and the gradual expansion of the section. When the bifurcated angle exceeds the critical value, the inlet area becomes the main influence factor. In addition, it is proved that increasing the experimental initial pressure of premixed gas can significantly improve the detonation stability and weaken the influence of bifurcation geometry. The mechanism of detonation decay and re-initiation in the bifurcated tubes is clarified by this study, which enriches the study of detonation diffraction and contributes to provide a scientific reference for engineering application and taking proper measures of explosion safety protection of gas pipelines as well.
Study on propagation characteristics of detonation in bifurcated tubes is of great significance to the safety protection of gas explosion in pipelines and engineering application. The propagation states of detonation vary with the geometrical structure when passing through the bifurcated tee. Based on the detonation circular test tube, the stoichiometric hydrogen-air mixture gas with 29.5% H2 in the volume fraction under different initial pressures was ignited by a 10-kV double high-voltage electrode to be detonated before entering the 30°, 45° and 90° bifurcation tees, respectively. The propagation characteristics of the detonation in the bifurcated tubes were analyzed based on the propagation velocity and cellular structure evolution characteristics obtained from the feedback signals of flame sensors and smoke-foils records. The results show that the H2/air detonation will decay when it passes through a bifurcated tee which is affected by rarefaction wave, but it is only a local phenomenon. The detonation re-initiation is gradually completed from regular reflection to Mach reflection after collision of incident shock wave and wall. In the straight branch tube, the detonation decay is mainly affected by the inlet area of the collateral branch tube. With the increase of the bifurcation angle, the inlet area decreases, and the detonation decay and re-initiation distance decrease as well. In the collateral branch tube, the detonation decay is affected by both the inlet area of the collateral branch tube and the gradual expansion of the section. When the bifurcated angle exceeds the critical value, the inlet area becomes the main influence factor. In addition, it is proved that increasing the experimental initial pressure of premixed gas can significantly improve the detonation stability and weaken the influence of bifurcation geometry. The mechanism of detonation decay and re-initiation in the bifurcated tubes is clarified by this study, which enriches the study of detonation diffraction and contributes to provide a scientific reference for engineering application and taking proper measures of explosion safety protection of gas pipelines as well.
2022, 42(12): 125402.
doi: 10.11883/bzycj-2021-0459
Abstract:
Explosion venting and inerting are two commonly used explosion protective measures in hydrogen-based industries, both of them are effective in reducing the maximum explosion overpressure when used alone. However, the coupling effects of venting and inerting on hydrogen deflagrations have not been well understood. To this end, experiments were carried out in a 1 m high top-vented vessel with a cross-section area of 0.3 m×0.3 m to investigate the effects of nitrogen volume fraction (φ) in the range of 0 to 50% by volume on vented hydrogen-air explosions with a fixed equivalence ratio. The premixed hydrogen-nitrogen-air mixtures obtained according to Dolton’s law of partial pressure were ignited in the center of the vented container by an electric spark with an energy of about 500 mJ. A 0.75-m long transparent window was installed in the center of the vented container, through which the flame images in the container were recorded by a high-speed camera at 2 000 frames per second. The pressure-time histories within and outside the vented container were measured by four piezoresistive pressure sensors with a measuring range of 0–150 kPa. The experimental results reveal that φ significantly affects the vented deflagration of hydrogen-air mixtures. The pressure peak owing to the external explosion dominates the internal pressure-time histories when φ≤40% and that resulting from the rupture of vent cover becomes dominant for higher values of φ. Under the current experimental conditions, Helmholtz-type oscillations with a frequency decreasing with φ are always observed, and acoustic oscillations appear in the tests only for φ=25%, 30%. The maximum internal explosion overpressures (pmax) near the vent, at the center of the vessel, and near the bottom of the vessel decrease with increasing φ. Moreover, the highest overall pmax is obtained always near the bottom of the vessel. However, the difference of pmax between the three measuring points is negligible when φ is larger than 40%. The maximum external explosion overpressure decreases with increasing φ. In addition, significant effects of the external explosion on the internal pressure-time histories are observed in all tests, regardless of its explosion overpressure.
Explosion venting and inerting are two commonly used explosion protective measures in hydrogen-based industries, both of them are effective in reducing the maximum explosion overpressure when used alone. However, the coupling effects of venting and inerting on hydrogen deflagrations have not been well understood. To this end, experiments were carried out in a 1 m high top-vented vessel with a cross-section area of 0.3 m×0.3 m to investigate the effects of nitrogen volume fraction (φ) in the range of 0 to 50% by volume on vented hydrogen-air explosions with a fixed equivalence ratio. The premixed hydrogen-nitrogen-air mixtures obtained according to Dolton’s law of partial pressure were ignited in the center of the vented container by an electric spark with an energy of about 500 mJ. A 0.75-m long transparent window was installed in the center of the vented container, through which the flame images in the container were recorded by a high-speed camera at 2 000 frames per second. The pressure-time histories within and outside the vented container were measured by four piezoresistive pressure sensors with a measuring range of 0–150 kPa. The experimental results reveal that φ significantly affects the vented deflagration of hydrogen-air mixtures. The pressure peak owing to the external explosion dominates the internal pressure-time histories when φ≤40% and that resulting from the rupture of vent cover becomes dominant for higher values of φ. Under the current experimental conditions, Helmholtz-type oscillations with a frequency decreasing with φ are always observed, and acoustic oscillations appear in the tests only for φ=25%, 30%. The maximum internal explosion overpressures (pmax) near the vent, at the center of the vessel, and near the bottom of the vessel decrease with increasing φ. Moreover, the highest overall pmax is obtained always near the bottom of the vessel. However, the difference of pmax between the three measuring points is negligible when φ is larger than 40%. The maximum external explosion overpressure decreases with increasing φ. In addition, significant effects of the external explosion on the internal pressure-time histories are observed in all tests, regardless of its explosion overpressure.
