2021 Vol. 41, No. 9
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2021, 41(9): 092101.
doi: 10.11883/bzycj-2020-0239
Abstract:
In recent years, rotating detonation engine (RDE) has been wisely studied in the world due to its inherent advantages. In the process of the application of RDE, the stable and reliable performance of the engine is always what researchers pursue. In the process of the research on RDE, a phenomenon called Low Frequency Instability (LFI) has been widely found. But so far, the exact mechanism behind LFI hasn’t been really revealed yet. In this paper, a numerical investigation of LFI was performed. In the numerical study, Euler equation with source terms was chosen as the governing equation, ignoring viscosity, thermal conduction, and mass diffusion. The Strang’s operator splitting method, the fifth order weighted essentially non-oscillatory scheme (WENO) and the second order total variation diminishing (TVD) Runge-Kutta method were used. With the methods mentioned above, the mechanism behind LFI and the whole detailed process of shock waves causing this phenomenon were finally revealed. It is shown that near the inlet wall there exist some reverse shock waves (propagating in the opposite direction to the rotating detonation waves), which will interact with the inlet wall and therefore generate some injet blocking point (IBP) in the fresh gas layer which will make the fresh gas layer periodically irregularly distributed. The irregular fresh gas layer will cause the distribute of the pressure on the detonation front changes periodically. With the positions where the IBPs are generated moving slowly along the inlet wall, the distance between the sampling point and the last IBP will gradually changes, and this will lead to that every time the rotating detonation wave meet the sampling point, the pressure of the place where the detonation front contacts with the inlet wall (and so contacts with the sampling point) is different from the last time. Therefore, the peak pressure at the sampling point oscillates at a low frequency and in another word, a so called low frequency instability is formed.
In recent years, rotating detonation engine (RDE) has been wisely studied in the world due to its inherent advantages. In the process of the application of RDE, the stable and reliable performance of the engine is always what researchers pursue. In the process of the research on RDE, a phenomenon called Low Frequency Instability (LFI) has been widely found. But so far, the exact mechanism behind LFI hasn’t been really revealed yet. In this paper, a numerical investigation of LFI was performed. In the numerical study, Euler equation with source terms was chosen as the governing equation, ignoring viscosity, thermal conduction, and mass diffusion. The Strang’s operator splitting method, the fifth order weighted essentially non-oscillatory scheme (WENO) and the second order total variation diminishing (TVD) Runge-Kutta method were used. With the methods mentioned above, the mechanism behind LFI and the whole detailed process of shock waves causing this phenomenon were finally revealed. It is shown that near the inlet wall there exist some reverse shock waves (propagating in the opposite direction to the rotating detonation waves), which will interact with the inlet wall and therefore generate some injet blocking point (IBP) in the fresh gas layer which will make the fresh gas layer periodically irregularly distributed. The irregular fresh gas layer will cause the distribute of the pressure on the detonation front changes periodically. With the positions where the IBPs are generated moving slowly along the inlet wall, the distance between the sampling point and the last IBP will gradually changes, and this will lead to that every time the rotating detonation wave meet the sampling point, the pressure of the place where the detonation front contacts with the inlet wall (and so contacts with the sampling point) is different from the last time. Therefore, the peak pressure at the sampling point oscillates at a low frequency and in another word, a so called low frequency instability is formed.
2021, 41(9): 092102.
doi: 10.11883/bzycj-2021-0072
Abstract:
Aiming at the non-ideal properties of aluminized explosive, a local isentropic hypothesis of the expansion of aluminized explosive detonation product was proposed, and a nonlinear characteristic line model for aluminized explosive detonation was established, which provides a new theoretical analysis method for studying the non-isentropic flow and the expansion of detonation products. A lot of studies have shown that for micron aluminum powder, the reaction mainly occurs in the expansion zone of detonation products. The aluminum powder was treated as inert in the detonation reaction zone in the model. Considering the reaction rate of the aluminum powder is relatively slow, the expansion process of the detonation products of aluminized explosive was divided into finite time regions. The energy released from the reaction of aluminum powder has a relaxation effect on the state of the products. Based on the relaxation effect, it was assumed that the detonation products flow was approximately isentropic in each time region. Due to the reaction of aluminum powder, the entropy in each time region was different. Based on the theory of isentropic flow of ideal explosive and local isentropic hypothesis, the non-isentropic expansion process of the detonation products of aluminized explosives can be analyzed theoretically. To verify the correctness of the model, metal plate experiments were conducted. Experiments on aluminized explosives and LiF explosives with a particle diameter of 5μm and 50μm to drive 0.5 mm and 1 mm metal plates were designed. The velocity history of the metal plate was measured by a laser displacement interferometer, and then the reaction degree of aluminum powder in the detonation products was calculated from the experimental results. Combined with the nonlinear characteristic line model of the detonation products of aluminized explosives, the velocity of the metal plate driven by aluminized explosives was calculated theoretically. Compared with the experimental results, the non-isentropic model can well describe the contribution of the secondary reaction of aluminum powder to the work ability of explosives, which verifies the correctness of the model for aluminized explosives (micron aluminum powder).
Aiming at the non-ideal properties of aluminized explosive, a local isentropic hypothesis of the expansion of aluminized explosive detonation product was proposed, and a nonlinear characteristic line model for aluminized explosive detonation was established, which provides a new theoretical analysis method for studying the non-isentropic flow and the expansion of detonation products. A lot of studies have shown that for micron aluminum powder, the reaction mainly occurs in the expansion zone of detonation products. The aluminum powder was treated as inert in the detonation reaction zone in the model. Considering the reaction rate of the aluminum powder is relatively slow, the expansion process of the detonation products of aluminized explosive was divided into finite time regions. The energy released from the reaction of aluminum powder has a relaxation effect on the state of the products. Based on the relaxation effect, it was assumed that the detonation products flow was approximately isentropic in each time region. Due to the reaction of aluminum powder, the entropy in each time region was different. Based on the theory of isentropic flow of ideal explosive and local isentropic hypothesis, the non-isentropic expansion process of the detonation products of aluminized explosives can be analyzed theoretically. To verify the correctness of the model, metal plate experiments were conducted. Experiments on aluminized explosives and LiF explosives with a particle diameter of 5μm and 50μm to drive 0.5 mm and 1 mm metal plates were designed. The velocity history of the metal plate was measured by a laser displacement interferometer, and then the reaction degree of aluminum powder in the detonation products was calculated from the experimental results. Combined with the nonlinear characteristic line model of the detonation products of aluminized explosives, the velocity of the metal plate driven by aluminized explosives was calculated theoretically. Compared with the experimental results, the non-isentropic model can well describe the contribution of the secondary reaction of aluminum powder to the work ability of explosives, which verifies the correctness of the model for aluminized explosives (micron aluminum powder).
2021, 41(9): 093101.
doi: 10.11883/bzycj-2021-0097
Abstract:
The dynamic fracture of rock materials is a basic problem in the field of rock mechanics, while the dynamic fracture mechanism of shale is more complex due to its anisotropic characteristics. In order to study the effect of bedding angle on dynamic fracture process of shale, a split Hopkinson pressure bar (SHPB) system was used to carry out impact tests on notched semi-circular bend (NSCB) specimens of shale. Additionally, a crack propagation gauge (CPG) was set at the crack tip, and the whole fracture process of the shale NSCB specimen was studied with the help of a high-speed photography system and the digital image correlation (DIC) method. The loading rate and Mode-I dynamic fracture toughness of the shale NSCB samples were obtained by the method recommended by the International Society for Rock Mechanics (ISRM). And the crack initiation time and crack propagation speed of the shale NSCB samples can be accurately obtained by CPG. It is found from the experimental results that the Mode-I dynamic fracture toughness of the shale NSCB samples has significant anisotropy, and the loading angle has a positive correlation with the Mode-I dynamic fracture toughness. Although the crack propagation of the C-0sample is not affected by the bedding, its crack propagation needs to cut through the shale matrix, hence the C-0 and 90° shale specimens have a high Mode-I dynamic fracture toughness. When the impact velocity is low, the bending stress on the dangerous section affects the fracture direction of the shale specimen, but with less effect on the bedding. The crack propagation path finally closes to the notch direction. With the increase of impact velocity, stress concentration and micro cracks may exist along the weak plane of bedding due to its relatively low strength. With the increase of impact velocity, the cracks between the weak planes of bedding begin to extend, and the failure planes along the direction of bedding and notch occurred simultaneously.
The dynamic fracture of rock materials is a basic problem in the field of rock mechanics, while the dynamic fracture mechanism of shale is more complex due to its anisotropic characteristics. In order to study the effect of bedding angle on dynamic fracture process of shale, a split Hopkinson pressure bar (SHPB) system was used to carry out impact tests on notched semi-circular bend (NSCB) specimens of shale. Additionally, a crack propagation gauge (CPG) was set at the crack tip, and the whole fracture process of the shale NSCB specimen was studied with the help of a high-speed photography system and the digital image correlation (DIC) method. The loading rate and Mode-I dynamic fracture toughness of the shale NSCB samples were obtained by the method recommended by the International Society for Rock Mechanics (ISRM). And the crack initiation time and crack propagation speed of the shale NSCB samples can be accurately obtained by CPG. It is found from the experimental results that the Mode-I dynamic fracture toughness of the shale NSCB samples has significant anisotropy, and the loading angle has a positive correlation with the Mode-I dynamic fracture toughness. Although the crack propagation of the C-0sample is not affected by the bedding, its crack propagation needs to cut through the shale matrix, hence the C-0 and 90° shale specimens have a high Mode-I dynamic fracture toughness. When the impact velocity is low, the bending stress on the dangerous section affects the fracture direction of the shale specimen, but with less effect on the bedding. The crack propagation path finally closes to the notch direction. With the increase of impact velocity, stress concentration and micro cracks may exist along the weak plane of bedding due to its relatively low strength. With the increase of impact velocity, the cracks between the weak planes of bedding begin to extend, and the failure planes along the direction of bedding and notch occurred simultaneously.
2021, 41(9): 093102.
doi: 10.11883/bzycj-2020-0288
Abstract:
In order to study the failure characteristics and damage evolution law of sandstone type uranium ore by blasting, the SHPB experimental system with strain control loop is used to conduct dynamic impact experiment on sandstone samples under controlled strain conditions. Combined with the wave velocity experiment and CT scanning experiments, the whole failure process, crack distribution and strain damage evolution law of sandstone samples are analyzed and studied. The experimental results show that the sandstone sample will suddenly appear obvious overall failure when the strain value exceeds 0.008 3 under impact load, and that the overall failure form is approximately biconical and its failure mode is shear-tension mixed failure. With the increase of strain, the generation and propagation of cracks can be roughly divided into crack free stage (0−0.003 3), microcrack initiation stage (0.003 3−0.008 3) and crack through stage (0.008 3−0.009 9). The quantitative relationship between strain and damage is established from macroscopic and microscopic aspects. The growth trend of damage variable with strain can be roughly divided into two stages, i.e. the smooth development area (0−0.008 3) and the rapid growth area (0.008 3−0.011 5). The damage variable does not increase linearly with the increase of strain, but the damage degree increases sharply when the strain value exceeds the strain damage threshold (0.008 3).
In order to study the failure characteristics and damage evolution law of sandstone type uranium ore by blasting, the SHPB experimental system with strain control loop is used to conduct dynamic impact experiment on sandstone samples under controlled strain conditions. Combined with the wave velocity experiment and CT scanning experiments, the whole failure process, crack distribution and strain damage evolution law of sandstone samples are analyzed and studied. The experimental results show that the sandstone sample will suddenly appear obvious overall failure when the strain value exceeds 0.008 3 under impact load, and that the overall failure form is approximately biconical and its failure mode is shear-tension mixed failure. With the increase of strain, the generation and propagation of cracks can be roughly divided into crack free stage (0−0.003 3), microcrack initiation stage (0.003 3−0.008 3) and crack through stage (0.008 3−0.009 9). The quantitative relationship between strain and damage is established from macroscopic and microscopic aspects. The growth trend of damage variable with strain can be roughly divided into two stages, i.e. the smooth development area (0−0.008 3) and the rapid growth area (0.008 3−0.011 5). The damage variable does not increase linearly with the increase of strain, but the damage degree increases sharply when the strain value exceeds the strain damage threshold (0.008 3).
2021, 41(9): 093201.
doi: 10.11883/bzycj-2021-0058
Abstract:
The energy coupling between the underground explosion and the medium and the wave propagation mechanism in the medium are important bases for understanding the physics of the underground explosion source. In order to study the law of the propagation and attenuation for the seismic wave energy of underground explosion, the composition of the radiated energy of underground explosion in viscoelastic medium was analyzed, and the formulas for calculating inflow energy, outflow energy, radiated kinetic energy, potential energy and dissipation energy in a limited observation region were given. Based on the theory of viscoelastic spherical wave in infinite medium, the theoretical solutions of velocity, displacement, stress and strain in the Laplace domain were given by using the exponential attenuation pressure model and the generalized Maxwell viscoelastic model. The numerical solutions of velocity, displacement, stress and strain were given by using the Laplace numerical inverse method, and the inflow energy, outflow energy, radiated kinetic energy, potential energy and dissipation energy were calculated by these numerical results. The numerical results of different components of seismic wave energy are consistent with the theoretical results, and the correctness of this method is proved. Using the dry loess as typical viscoelastic material, the radial stress and particle velocity at different radii were calculated, and the relationship between the inflow energy at different radii and the wave propagation distance was obtained. The spatial distributions of the radiated kinetic energy of seismic wave were calculated by using the spatial distributions of the radial particle velocity at different times, and the propagation law of the radiated kinetic energy was obtained. The changes of the inflow energy and the radiated kinetic energy with the propagation distance in the limited observation area were analyzed, and the results show as follows: (1) In a viscoelastic medium, the energy flowing into a sphere surface decreases gradually with the increase of radius. In an ideal elastic medium, the energy flowing into a sphere surface at the elastic radius of about several times can be stabilized to a constant value. (2) The potential energy and the dissipative energy tend to constant values when the observation time is long enough in a fixed limited observation region, and the radiated kinetic energy tends to zero. (3) When a limited observation area can hold the seismic waves with complete wave length, the steady-state value of the radiated kinetic energy of seismic waves decreases with the increase of the wave propagation distance. In general, exponential function and power function can be used for piecewise fitting of the attenuation law for the steady-state value of the radiated kinetic energy of the seismic wave.
The energy coupling between the underground explosion and the medium and the wave propagation mechanism in the medium are important bases for understanding the physics of the underground explosion source. In order to study the law of the propagation and attenuation for the seismic wave energy of underground explosion, the composition of the radiated energy of underground explosion in viscoelastic medium was analyzed, and the formulas for calculating inflow energy, outflow energy, radiated kinetic energy, potential energy and dissipation energy in a limited observation region were given. Based on the theory of viscoelastic spherical wave in infinite medium, the theoretical solutions of velocity, displacement, stress and strain in the Laplace domain were given by using the exponential attenuation pressure model and the generalized Maxwell viscoelastic model. The numerical solutions of velocity, displacement, stress and strain were given by using the Laplace numerical inverse method, and the inflow energy, outflow energy, radiated kinetic energy, potential energy and dissipation energy were calculated by these numerical results. The numerical results of different components of seismic wave energy are consistent with the theoretical results, and the correctness of this method is proved. Using the dry loess as typical viscoelastic material, the radial stress and particle velocity at different radii were calculated, and the relationship between the inflow energy at different radii and the wave propagation distance was obtained. The spatial distributions of the radiated kinetic energy of seismic wave were calculated by using the spatial distributions of the radial particle velocity at different times, and the propagation law of the radiated kinetic energy was obtained. The changes of the inflow energy and the radiated kinetic energy with the propagation distance in the limited observation area were analyzed, and the results show as follows: (1) In a viscoelastic medium, the energy flowing into a sphere surface decreases gradually with the increase of radius. In an ideal elastic medium, the energy flowing into a sphere surface at the elastic radius of about several times can be stabilized to a constant value. (2) The potential energy and the dissipative energy tend to constant values when the observation time is long enough in a fixed limited observation region, and the radiated kinetic energy tends to zero. (3) When a limited observation area can hold the seismic waves with complete wave length, the steady-state value of the radiated kinetic energy of seismic waves decreases with the increase of the wave propagation distance. In general, exponential function and power function can be used for piecewise fitting of the attenuation law for the steady-state value of the radiated kinetic energy of the seismic wave.
2021, 41(9): 093901.
doi: 10.11883/bzycj-2020-0240
Abstract:
Supercavitation projectile is one of the research hotspots of underwater defence technology. The cost of underwater damage test is so high that equivalent test on land is considered as a possible alternative. Therefore, it is necessary to obtain the equivalent relationship between the target and related materials under the condition of supercavitating projectile underwater penetration. Taking MK48-5 torpedo as the object, a typical torpedo structure model composed of shell and 14 key components is constructed. Considering the influence of aqueous medium on penetration, the process of underwater supercavitating projectile penetrated torpedo could be divided into two stages: (1) the projectile penetrated the aqueous medium and the torpedo shell, (2) the projectile penetrated key parts of the torpedo. The energy consumption model of aqueous medium and target plate are established. According to the principle of limit penetration velocity equivalence and energy equivalence, the relationship between target and equivalent target in two stages is obtained respectively. In order to obtain the damage effect of projectiles hitting torpedoes vertically in different directions and under different working conditions, it is necessary to study the four typical sections of torpedoe: warhead, control section, fuel tank and torpedo afterbody. Therefore, the multi-layer equivalent target models of underwater penetration and torpedo penetration under different conditions are established.
Supercavitation projectile is one of the research hotspots of underwater defence technology. The cost of underwater damage test is so high that equivalent test on land is considered as a possible alternative. Therefore, it is necessary to obtain the equivalent relationship between the target and related materials under the condition of supercavitating projectile underwater penetration. Taking MK48-5 torpedo as the object, a typical torpedo structure model composed of shell and 14 key components is constructed. Considering the influence of aqueous medium on penetration, the process of underwater supercavitating projectile penetrated torpedo could be divided into two stages: (1) the projectile penetrated the aqueous medium and the torpedo shell, (2) the projectile penetrated key parts of the torpedo. The energy consumption model of aqueous medium and target plate are established. According to the principle of limit penetration velocity equivalence and energy equivalence, the relationship between target and equivalent target in two stages is obtained respectively. In order to obtain the damage effect of projectiles hitting torpedoes vertically in different directions and under different working conditions, it is necessary to study the four typical sections of torpedoe: warhead, control section, fuel tank and torpedo afterbody. Therefore, the multi-layer equivalent target models of underwater penetration and torpedo penetration under different conditions are established.
2021, 41(9): 094101.
doi: 10.11883/bzycj-2021-0124
Abstract:
Responses of materials and structures to intense pulsed X-ray radiation, such as thermal shock wave propagation and blowoff impulse generation are referred to collectively as X-ray thermomechanical effects, which have been applied to radiation hardening, astrophysics, and planetary science. Preliminary experiments for thermomechanical effects have been performed utilizing wire array Z-pinch X-ray sources on a pulsed power facility with a drive current of about 10 MA. A total X-ray radiation energy of about 230 kJ was produced by a nested aluminum wire array of 20 mm in outer diameter, and theK-shell yield of about 30 kJ for aluminum was measured. An X-ray energy fluence up to 732 J/cm2 was produced on an irradiated target which was positioned at 5 cm away from the X-ray source center. The irradiated target was an aluminum disk 2 mm in thickness and 10 mm in diameter, backed by an aluminum liner. The total weight of the disk and liner was 585 mg. An all-fiber photonic Doppler velocimeter (PDV) was used to monitor the motion of the rear surface of the irradiated target. The velocity history measured by PDV suggested a free-face velocity of 2.12 km/s when the shock wave arrived at the rear surface of the target, and the final velocity of the target is 180 m/s. Based on the Hugoniot relationships and the law of momentum conservation, a stress of the thermal shock wave of 19.2 GPa and a blowoff impulse per unit target area of 1341 Pa·s were deduced. Furthermore, a consequent coupling coefficient of 1.83 Pa·s·cm2/J was estimated from the measurements of blowoff impulse and the X-ray energy fluence. Finally, discussions on the reliability and uncertainty of the measurement were presented. These experimental results described here preliminarily validated the feasibility of the application of PDV to the research of X-ray thermomechanical effect.
Responses of materials and structures to intense pulsed X-ray radiation, such as thermal shock wave propagation and blowoff impulse generation are referred to collectively as X-ray thermomechanical effects, which have been applied to radiation hardening, astrophysics, and planetary science. Preliminary experiments for thermomechanical effects have been performed utilizing wire array Z-pinch X-ray sources on a pulsed power facility with a drive current of about 10 MA. A total X-ray radiation energy of about 230 kJ was produced by a nested aluminum wire array of 20 mm in outer diameter, and theK-shell yield of about 30 kJ for aluminum was measured. An X-ray energy fluence up to 732 J/cm2 was produced on an irradiated target which was positioned at 5 cm away from the X-ray source center. The irradiated target was an aluminum disk 2 mm in thickness and 10 mm in diameter, backed by an aluminum liner. The total weight of the disk and liner was 585 mg. An all-fiber photonic Doppler velocimeter (PDV) was used to monitor the motion of the rear surface of the irradiated target. The velocity history measured by PDV suggested a free-face velocity of 2.12 km/s when the shock wave arrived at the rear surface of the target, and the final velocity of the target is 180 m/s. Based on the Hugoniot relationships and the law of momentum conservation, a stress of the thermal shock wave of 19.2 GPa and a blowoff impulse per unit target area of 1341 Pa·s were deduced. Furthermore, a consequent coupling coefficient of 1.83 Pa·s·cm2/J was estimated from the measurements of blowoff impulse and the X-ray energy fluence. Finally, discussions on the reliability and uncertainty of the measurement were presented. These experimental results described here preliminarily validated the feasibility of the application of PDV to the research of X-ray thermomechanical effect.
2021, 41(9): 094201.
doi: 10.11883/bzycj-2021-0129
Abstract:
In the traditional immersed boundary methods for solving compressible fluid-structure interaction problems, conservation is one of the problems that must be considered. When the coupling boundary moves on the fixed grid, the structure coverage will change, resulting in many dead elements and emerging elements on the fluid grid. In the ghost-cell immersed boundary method, the reconstructed grid can not maintain the strict mass conservation when the dead elements and emerging elements appear. In order to overcome the shortcomings of traditional methods, a strong coupling prediction-correction immersed boundary method for compressible fluid-structure interaction problems was proposed. Firstly, the matrix representation of a general fluid-structure coupling system was described, and a strong coupling Gauss-Seidel iterative scheme of fluid-structure coupling system was derived. Furthermore, a prediction-correction scheme was derived, and a prediction-correction immersed boundary method was proposed. The fluid-structure coupling boundary was regarded as a free surface, and the space originally occupied by the solid was initialized as zero mass elements, allowing the fluid to pass through the coupling boundary freely. For the calculation of fluid, the second-order MUSCL finite volume scheme with the minmod limiter and the AUSM+-up flux based on Zha-Bilgen splitting were used to advance the time step with the third-order Runge-Kutta scheme. In the correction step, the transport process was realized by a set of mass conservation transport rules. The transport algorithm could be summarized as marking the fluid inside the boundary, dividing and moving the fluid in a uniform way according to the marking order, generating a flow pointing to the outside of the boundary, and finally applying a velocity correction near the boundary to ensure the no-slip condition. The marking and transport algorithm avoided the tedious geometric treatment of the cut-cells, and ensured the easy implementation of the algorithm. For the calculation of solids, the first-order difference scheme and the implicit dynamic finite element scheme were used to solve the rigid body and linear elastic body respectively, and the Gauss quadrature was used to obtain the coupling force on the solid surface. The one-dimensional and two-dimensional problems were calculated by the prediction-correction immersed boundary method. In the one-dimensional piston problem, the accuracy, conservation and convergence of the method were investigated by comparing the results with those in the literature. In the two-dimensional shock wave impact problem, the experimental optical schlieren images were compared with those obtained by the numerical simulation, and the deflection history of the plate structure was investigated. The study shows that this method can accurately maintain the mass conservation of the flow field and has the advantage of easy implementation, which is different from the traditional ghost-cell method and the cut-cell method. This method has the first-order convergence accuracy, and can accurately predict the flow field after shock diffraction and the deflection of plate under shock waves. It provides a new idea for the development of fluid-structure coupling algorithms.
In the traditional immersed boundary methods for solving compressible fluid-structure interaction problems, conservation is one of the problems that must be considered. When the coupling boundary moves on the fixed grid, the structure coverage will change, resulting in many dead elements and emerging elements on the fluid grid. In the ghost-cell immersed boundary method, the reconstructed grid can not maintain the strict mass conservation when the dead elements and emerging elements appear. In order to overcome the shortcomings of traditional methods, a strong coupling prediction-correction immersed boundary method for compressible fluid-structure interaction problems was proposed. Firstly, the matrix representation of a general fluid-structure coupling system was described, and a strong coupling Gauss-Seidel iterative scheme of fluid-structure coupling system was derived. Furthermore, a prediction-correction scheme was derived, and a prediction-correction immersed boundary method was proposed. The fluid-structure coupling boundary was regarded as a free surface, and the space originally occupied by the solid was initialized as zero mass elements, allowing the fluid to pass through the coupling boundary freely. For the calculation of fluid, the second-order MUSCL finite volume scheme with the minmod limiter and the AUSM+-up flux based on Zha-Bilgen splitting were used to advance the time step with the third-order Runge-Kutta scheme. In the correction step, the transport process was realized by a set of mass conservation transport rules. The transport algorithm could be summarized as marking the fluid inside the boundary, dividing and moving the fluid in a uniform way according to the marking order, generating a flow pointing to the outside of the boundary, and finally applying a velocity correction near the boundary to ensure the no-slip condition. The marking and transport algorithm avoided the tedious geometric treatment of the cut-cells, and ensured the easy implementation of the algorithm. For the calculation of solids, the first-order difference scheme and the implicit dynamic finite element scheme were used to solve the rigid body and linear elastic body respectively, and the Gauss quadrature was used to obtain the coupling force on the solid surface. The one-dimensional and two-dimensional problems were calculated by the prediction-correction immersed boundary method. In the one-dimensional piston problem, the accuracy, conservation and convergence of the method were investigated by comparing the results with those in the literature. In the two-dimensional shock wave impact problem, the experimental optical schlieren images were compared with those obtained by the numerical simulation, and the deflection history of the plate structure was investigated. The study shows that this method can accurately maintain the mass conservation of the flow field and has the advantage of easy implementation, which is different from the traditional ghost-cell method and the cut-cell method. This method has the first-order convergence accuracy, and can accurately predict the flow field after shock diffraction and the deflection of plate under shock waves. It provides a new idea for the development of fluid-structure coupling algorithms.
2021, 41(9): 095101.
doi: 10.11883/bzycj-2020-0320
Abstract:
In the process of blasting and excavation of urban subways, controlling the impact of blasting vibration on adjacent pipelines is critical. Based on the characteristics of directly buried gas pipelines in Wuhan and the full-scale direct-buried gas pipeline blasting seismicexperiment, the dynamic finite element numerical calculation software LS-DYNA was used to establish gas pipeline without joints and flange gas pipeline models under different blasting source distances. The effects of blasting seismic wave’s dynamic response characteristics of flanged gas pipeline were analyzed. The research results show that the strain of pipeline section is mainly axial tensile strain, supplemented by circumferential strain. The peak particle velocity of pipeline without joints and flange pipes and the ground surface increase with the decrease of the distance from the blasting source under different blasting conditions. Along the pipeline axis, the peak vibration velocity of the pipeline without joints and the ground surface decreases along the two ends with the central section of the pipe as the symmetry plane. The peak particle velocity of the flange pipeline gradually increases from two sides to the middle but suddenly decreases at the flange joint. There is an obvious stress concentration at the flange interface. The flange joint is the key point of pipeline under blasting earthquake. The peak effective stress of the bolt, the axial pressure of the gasket, the peak effective stress of the flange, and the flange deflection angle decrease with the increase of the explosion source distance. The deflection angle of the flanged pipeline has a corresponding relationship with the peak vibration velocity of the ground surface. The control vibration speed of 13.82 cm/s on the surface directly above the center of the flanged gas pipeline is used as the safety control value of the adjacent gas pipeline under blasting engineering.
In the process of blasting and excavation of urban subways, controlling the impact of blasting vibration on adjacent pipelines is critical. Based on the characteristics of directly buried gas pipelines in Wuhan and the full-scale direct-buried gas pipeline blasting seismicexperiment, the dynamic finite element numerical calculation software LS-DYNA was used to establish gas pipeline without joints and flange gas pipeline models under different blasting source distances. The effects of blasting seismic wave’s dynamic response characteristics of flanged gas pipeline were analyzed. The research results show that the strain of pipeline section is mainly axial tensile strain, supplemented by circumferential strain. The peak particle velocity of pipeline without joints and flange pipes and the ground surface increase with the decrease of the distance from the blasting source under different blasting conditions. Along the pipeline axis, the peak vibration velocity of the pipeline without joints and the ground surface decreases along the two ends with the central section of the pipe as the symmetry plane. The peak particle velocity of the flange pipeline gradually increases from two sides to the middle but suddenly decreases at the flange joint. There is an obvious stress concentration at the flange interface. The flange joint is the key point of pipeline under blasting earthquake. The peak effective stress of the bolt, the axial pressure of the gasket, the peak effective stress of the flange, and the flange deflection angle decrease with the increase of the explosion source distance. The deflection angle of the flanged pipeline has a corresponding relationship with the peak vibration velocity of the ground surface. The control vibration speed of 13.82 cm/s on the surface directly above the center of the flanged gas pipeline is used as the safety control value of the adjacent gas pipeline under blasting engineering.
2021, 41(9): 095102.
doi: 10.11883/bzycj-2020-0291
Abstract:
Steel concrete steel composite slab is a new type of composite structure. It has the characteristics of high shear strength, high ductility and strong energy consumption compared with the traditional reinforced concrete slab. The new type composite slab has been widely used in nuclear reactor containment, offshore platform and oil storage tank. Two scaled reinforced concrete slabs (RCS) and steel-concrete-steel (SCS) composite slabs were designed and manufactured, and the experimental study was carried out under the contact explosion load. The anti-blast performance of different slabs was analyzed by damage analysis and displacement. Based on ANSYS/LS-DYNA nonlinear finite element program, the damage modes and the maximum deflection of the mid-span of the steel-concrete composite slab are numerically investigated, and the numerical damage modes and maximum deflection of the steel-concrete composite slabs are compared with the test results of the components, which verifies the accuracy and applicability of the finite element analysis model. In this study, the influences of parameters, such as explosive quantity, concrete strength and steel plate thickness on the anti-blast performance of steel-concrete composite plate are numerically analyzed by parametric analysis. Then, the prediction formula of mid-span deflection of SCS slab is proposed by using the method of multi parameter regression analysis. The results show that the plastic damage of the structure can be reduced by increasing the strength of concrete, and the maximum deflection of SCS can be effectively reduced by increasing the thickness of steel plate. It is indicated that the SCS maintains good integrity and owns the ability to continue to carry load compared with the RCS. Finally, the fitting formula can well predict the relationship between the mid span deflection of SCS plate and the charge amount and the thickness of steel plate.
Steel concrete steel composite slab is a new type of composite structure. It has the characteristics of high shear strength, high ductility and strong energy consumption compared with the traditional reinforced concrete slab. The new type composite slab has been widely used in nuclear reactor containment, offshore platform and oil storage tank. Two scaled reinforced concrete slabs (RCS) and steel-concrete-steel (SCS) composite slabs were designed and manufactured, and the experimental study was carried out under the contact explosion load. The anti-blast performance of different slabs was analyzed by damage analysis and displacement. Based on ANSYS/LS-DYNA nonlinear finite element program, the damage modes and the maximum deflection of the mid-span of the steel-concrete composite slab are numerically investigated, and the numerical damage modes and maximum deflection of the steel-concrete composite slabs are compared with the test results of the components, which verifies the accuracy and applicability of the finite element analysis model. In this study, the influences of parameters, such as explosive quantity, concrete strength and steel plate thickness on the anti-blast performance of steel-concrete composite plate are numerically analyzed by parametric analysis. Then, the prediction formula of mid-span deflection of SCS slab is proposed by using the method of multi parameter regression analysis. The results show that the plastic damage of the structure can be reduced by increasing the strength of concrete, and the maximum deflection of SCS can be effectively reduced by increasing the thickness of steel plate. It is indicated that the SCS maintains good integrity and owns the ability to continue to carry load compared with the RCS. Finally, the fitting formula can well predict the relationship between the mid span deflection of SCS plate and the charge amount and the thickness of steel plate.
2021, 41(9): 095201.
doi: 10.11883/bzycj-2020-0363
Abstract:
Drilling and blasting is the most economical rock fracture technology in water conservancy, transportation, mining and tunnel engineering. And the application of nonel detonator network in rock blasting is still the most widely used initiation method in engineering blasting practice. Due to the detonator delay error, there is a deviation between the actual initiation time and designed initiation time in the Nonel detonation network, which will cause the change of blasting time sequence and the overlapping of blast-holes. There are detonator dispersion phenomenon with the same delay time and superposition effect for seismic waves with different delay time, which brings great trouble to the value of charge weight per delay and the prediction of particle peak vibration velocity. In order to the predict particle peak vibration velocity more accurately and efficiently, the millisecond delay blasting test was conducted, and the calculation model of vibration velocity for group blast-hole simultaneous blasting with dispersed charge was established. The influence of the blast-hole number on the equivalent charge weight for simultaneous blasting and its value selection method were studied and constructed. The modified particle peak vibration velocity scaled distance formula and the particle peak vibration velocity prediction method were proposed based on the results of regression analysis of single-hole blasting. The results show that the equivalent charge weight of group blast-hole simultaneous blasting is smaller than the nominal charge weight per delay, and the equivalent charge weight of simultaneous blasting can be calculated by converting through the reduction coefficient, which decreases exponentially with the increase of the blast-hole number. The superposition effect of seismic waves with different delay time can be considered by introducing vibration wave superposition factor into the modified particle peak vibration velocity scaled distance formula. The average absolute error, average relative error and root mean square error between the actual and the predicted particle peak vibration velocity values are 0.05 cm/s, 9.52% and 0.059 cm/s, respectively. It is feasible to apply the modified particle peak vibration velocity proportional distance regression analysis method to the prediction and control of blasting vibration velocity in the field.
Drilling and blasting is the most economical rock fracture technology in water conservancy, transportation, mining and tunnel engineering. And the application of nonel detonator network in rock blasting is still the most widely used initiation method in engineering blasting practice. Due to the detonator delay error, there is a deviation between the actual initiation time and designed initiation time in the Nonel detonation network, which will cause the change of blasting time sequence and the overlapping of blast-holes. There are detonator dispersion phenomenon with the same delay time and superposition effect for seismic waves with different delay time, which brings great trouble to the value of charge weight per delay and the prediction of particle peak vibration velocity. In order to the predict particle peak vibration velocity more accurately and efficiently, the millisecond delay blasting test was conducted, and the calculation model of vibration velocity for group blast-hole simultaneous blasting with dispersed charge was established. The influence of the blast-hole number on the equivalent charge weight for simultaneous blasting and its value selection method were studied and constructed. The modified particle peak vibration velocity scaled distance formula and the particle peak vibration velocity prediction method were proposed based on the results of regression analysis of single-hole blasting. The results show that the equivalent charge weight of group blast-hole simultaneous blasting is smaller than the nominal charge weight per delay, and the equivalent charge weight of simultaneous blasting can be calculated by converting through the reduction coefficient, which decreases exponentially with the increase of the blast-hole number. The superposition effect of seismic waves with different delay time can be considered by introducing vibration wave superposition factor into the modified particle peak vibration velocity scaled distance formula. The average absolute error, average relative error and root mean square error between the actual and the predicted particle peak vibration velocity values are 0.05 cm/s, 9.52% and 0.059 cm/s, respectively. It is feasible to apply the modified particle peak vibration velocity proportional distance regression analysis method to the prediction and control of blasting vibration velocity in the field.
2021, 41(9): 095401.
doi: 10.11883/bzycj-2020-0295
Abstract:
Based on the lack of systematic research on flame propagation in large-diameter and long-distance pipelines in the tank area of petrochemical plants, an experimental device for flame propagation in DN50-DN500 industrial-scale pipelines was designed and built. In this paper, effects of concentration of gas mixture for propagation characteristics of steady gaseous detonation waves in ethylene-air mixtures with DN50 pipeline were studied experimentally. The volume concentration of gas mixture was 5.6%, 5.93%, 6.6%, 7.15%, 8.0% ethylene in air. Homogeneous C2H4/air (6.6%) and C3H8/air (4.2%) mixtures were used with 9 kinds of pipelines which were from DN50 to DN500 to study the effects of pipeline diameter for propagation characteristics of steady gaseous detonation. The experimental results show that the concentration of combustible gas has an effect on flame propagation and detonation. The detonation runup distance is short and steady detonation is more likely to be formed when it is close to chemical equivalent concentration, when the combustible mixture is poorer or richer, the steady detonation will need more runup distance. The detonation flame speed and pressure are more affected by the type of combustible gas instead of pipe diameter. The detonation pressure of the mixture of 6.6% C2H4/air and the mixture of 4.2% C3H8/air is 15.17 and 14.47 times of the initial pressure, respectively, which is different from the reference value given by the ISO16852 standard where the ratio pm/p0 (the average value of the detonation pressure to initial pressure) increases with pipe diameter. The detonation pressure of pipeline below DN150 is far higher than the reference value which is 10 and 12. It’s suggested that in the design of pipelines and selection and installation of flame arresters for connecting pipelines in the tank areas, detonation pressure requires careful consideration and appropriate arresters should be selected in combination with the installation position.
Based on the lack of systematic research on flame propagation in large-diameter and long-distance pipelines in the tank area of petrochemical plants, an experimental device for flame propagation in DN50-DN500 industrial-scale pipelines was designed and built. In this paper, effects of concentration of gas mixture for propagation characteristics of steady gaseous detonation waves in ethylene-air mixtures with DN50 pipeline were studied experimentally. The volume concentration of gas mixture was 5.6%, 5.93%, 6.6%, 7.15%, 8.0% ethylene in air. Homogeneous C2H4/air (6.6%) and C3H8/air (4.2%) mixtures were used with 9 kinds of pipelines which were from DN50 to DN500 to study the effects of pipeline diameter for propagation characteristics of steady gaseous detonation. The experimental results show that the concentration of combustible gas has an effect on flame propagation and detonation. The detonation runup distance is short and steady detonation is more likely to be formed when it is close to chemical equivalent concentration, when the combustible mixture is poorer or richer, the steady detonation will need more runup distance. The detonation flame speed and pressure are more affected by the type of combustible gas instead of pipe diameter. The detonation pressure of the mixture of 6.6% C2H4/air and the mixture of 4.2% C3H8/air is 15.17 and 14.47 times of the initial pressure, respectively, which is different from the reference value given by the ISO16852 standard where the ratio pm/p0 (the average value of the detonation pressure to initial pressure) increases with pipe diameter. The detonation pressure of pipeline below DN150 is far higher than the reference value which is 10 and 12. It’s suggested that in the design of pipelines and selection and installation of flame arresters for connecting pipelines in the tank areas, detonation pressure requires careful consideration and appropriate arresters should be selected in combination with the installation position.
2021, 41(9): 095402.
doi: 10.11883/bzycj-2021-0016
Abstract:
In order to explore the coupling of flame propagation velocity and pressure in butane gas explosion under the action of hydrophobic SiO2 powder as flame retardant and flow-enhancing additive, experiments were carried out on a self-designed and constructed\begin{document}$\varnothing $\end{document} ![]()
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In order to explore the coupling of flame propagation velocity and pressure in butane gas explosion under the action of hydrophobic SiO2 powder as flame retardant and flow-enhancing additive, experiments were carried out on a self-designed and constructed
2021, 41(9): 095403.
doi: 10.11883/bzycj-2020-0437
Abstract:
To investigate the effect of sodium bicarbonate on the process of ducted venting, an experimental study was performed to suppress the methane-air explosions in a 5 L vessel connected with different duct length (250, 500, 750 mm) under NaHCO3 dry powder with the mass concentration C=0, 40, 80, 120, 160, 200, 240 g/m3. The flame front propagation and explosion overpressure waveform were analyzed. The results show that NaHCO3 powder greatly weakened the secondary explosion in the discharge duct, and the appropriate mass concentration of NaHCO3 powder eliminated the secondary explosion. As the NaHCO3 powder mass concentration increased, the flame structure in the vessel was gradually irregular, and the flame in the discharge duct went through the process of weakening to extinguishing. Moreover, the time for the flame to reach the end of the vessel was prolonged with the increase of powder mass concentration. Different mass concentration of NaHCO3 dry powder led to three development modes of flame velocity. The mechanism for the pressure rise in the vessel depended on the NaHCO3 powder mass concentration. The maximum pressure in the vessel was mainly dominated by the second pressure peak for the low powder mass concentration, but by the first pressure peak for the high powder mass concentration. The drop rate of overpressure increased at first and then leveled off with the increase of NaHCO3 powder mass concentration, which indicates that the mass concentration effect gradually weaken. Finally, the relationship between flame propagation velocity and explosion overpressure in the ducted vented vessel was quantitatively analyzed.
