2016 Vol. 36, No. 3
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2016, 36(3): 289-296.
doi: 10.11883/1001-1455(2016)03-0289-08
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Abstract:
In this work we simulated the blasting excavation in a mine tunnel using a model test. Adopting the sound wave test method, we investigated the cumulative damage effects of young shotcrete under multiple blasting loads by analyzing variations of acoustic velocity and acoustic waveform during the model test. The results indicate that all the following factors, the times of blasting, the distance between the tunnel face and the test plane, and the dosage of the explosive used as are responsible for the cumulative damage of shotcrete. Their influences are shown both in the acoustic velocity and the acoustic waveform: the more times of blasting, the shorter distance, and the greater explosive dosage, then the greater the reduction value of the acoustic velocity and the more obvious the change of the acoustic waveform, and the greater the cumulative damage value. Specifically, there is a nonlinear relationship between the times of blasting and the cumulative damage. Between the distance and the cumulative damage there also exists a nonlinear relationship, which can be well fitted by a quadratic polynomial. Furthermore, it is found that the first time of blasting affects the acoustic velocity and the acoustic waveform the most, and causes the greatest damage. In general, when the explosive dosage is small, the maximum cumulative damage reaches 0.1268, which indicates that the shotcrete damage close to the blasting area should be the major concern.
In this work we simulated the blasting excavation in a mine tunnel using a model test. Adopting the sound wave test method, we investigated the cumulative damage effects of young shotcrete under multiple blasting loads by analyzing variations of acoustic velocity and acoustic waveform during the model test. The results indicate that all the following factors, the times of blasting, the distance between the tunnel face and the test plane, and the dosage of the explosive used as are responsible for the cumulative damage of shotcrete. Their influences are shown both in the acoustic velocity and the acoustic waveform: the more times of blasting, the shorter distance, and the greater explosive dosage, then the greater the reduction value of the acoustic velocity and the more obvious the change of the acoustic waveform, and the greater the cumulative damage value. Specifically, there is a nonlinear relationship between the times of blasting and the cumulative damage. Between the distance and the cumulative damage there also exists a nonlinear relationship, which can be well fitted by a quadratic polynomial. Furthermore, it is found that the first time of blasting affects the acoustic velocity and the acoustic waveform the most, and causes the greatest damage. In general, when the explosive dosage is small, the maximum cumulative damage reaches 0.1268, which indicates that the shotcrete damage close to the blasting area should be the major concern.
2016, 36(3): 297-304.
doi: 10.11883/1001-1455(2016)03-0297-08
Abstract:
To explore the mechanism of crack expansion in the adjacent tunnel under the influence of the combined stress field, a simulated experiment was carried out adopting the blast loading and static loading transmission of the dynamic caustics, and the result was analyzed combined with dynamic stress intensity factors and the energy release rate of the crack tip. The experimental results show that the region where cracks are located in the back-blast side of the adjacent model-tunnel is also the main disturbance zone of the tunnel and that the explosion load plays a leading role in inducing crack initiation in the combined stress field formed by the less vertical pressure and the explosion load. In the same combined stress field, with p=0.2 MPa, the prefabricated crack extension displacement is associated with the angle of the crack and, with θ=75°, the explosive stress wave cannot induce crack initiation. Under the effect of the same explosive stress wave, with θ=30°, the less vertical stress within a certain range has an inhibitory effect on the propagation of the crack, and this effect increases with the vertical pressure increase applied in the neighboring roadway. With p=0.4 MPa, the crack cannot induce crack initiation. Eventually the displacement of an extended crack occurred, which is positively correlated with the duration time of the dynamic stress intensity factor around its maximal value or with the accumulated value of the energy release rate in the stage of the crack propagation. The results of the present study will have a guiding significance for practical engineering in mining industry.
To explore the mechanism of crack expansion in the adjacent tunnel under the influence of the combined stress field, a simulated experiment was carried out adopting the blast loading and static loading transmission of the dynamic caustics, and the result was analyzed combined with dynamic stress intensity factors and the energy release rate of the crack tip. The experimental results show that the region where cracks are located in the back-blast side of the adjacent model-tunnel is also the main disturbance zone of the tunnel and that the explosion load plays a leading role in inducing crack initiation in the combined stress field formed by the less vertical pressure and the explosion load. In the same combined stress field, with p=0.2 MPa, the prefabricated crack extension displacement is associated with the angle of the crack and, with θ=75°, the explosive stress wave cannot induce crack initiation. Under the effect of the same explosive stress wave, with θ=30°, the less vertical stress within a certain range has an inhibitory effect on the propagation of the crack, and this effect increases with the vertical pressure increase applied in the neighboring roadway. With p=0.4 MPa, the crack cannot induce crack initiation. Eventually the displacement of an extended crack occurred, which is positively correlated with the duration time of the dynamic stress intensity factor around its maximal value or with the accumulated value of the energy release rate in the stage of the crack propagation. The results of the present study will have a guiding significance for practical engineering in mining industry.
2016, 36(3): 305-312.
doi: 10.11883/1001-1455(2016)03-0305-08
Abstract:
A method is presented for conservatively transferring cell-centered physical quantities from one mesh to another with second-order accuracy, which is well-suited for finite-volume methods that rely on cell-centered variables. The proposed methodology implements the cell-intersection algorithm of 2D/3D mixed grid based on the local supermesh idea, and is able to accurately calculate the intersection of any two polygons or polyhedrons, thus providing a basis for accurate conservative interpolation. The accuracy and the efficacy of the new method are demonstrated with multiple 2D and 3D numerical experiments. The test results show that this method ensures strict conservation of physical quantities in the interpolation process, and achieves a higher accuracy than that achieved by conventional second-order interpolation methods.
A method is presented for conservatively transferring cell-centered physical quantities from one mesh to another with second-order accuracy, which is well-suited for finite-volume methods that rely on cell-centered variables. The proposed methodology implements the cell-intersection algorithm of 2D/3D mixed grid based on the local supermesh idea, and is able to accurately calculate the intersection of any two polygons or polyhedrons, thus providing a basis for accurate conservative interpolation. The accuracy and the efficacy of the new method are demonstrated with multiple 2D and 3D numerical experiments. The test results show that this method ensures strict conservation of physical quantities in the interpolation process, and achieves a higher accuracy than that achieved by conventional second-order interpolation methods.
2016, 36(3): 313-318.
doi: 10.11883/1001-1455(2016)03-0313-06
Abstract:
The effect of hydrodynamic impact on the amphibious seaplane is an important consideration in its structural designing and intensity checking. In addition, such impact is a major factor affecting its structural weight. By varying two parameters: drop height and drop weight in the experiment, the pressure and the change of the free surface of liquid for three different wedges are dynamically measured. In the present work, the local pressure distribution, the impact pressure changing with time and the variety of the free surface on several free-falling wedges have been investigated. These wedges have been chosen from the representative cross section of amphibious seaplanes commonly used worldwide. By comparing the experimental results, the conclusion is reached that the wedge with a flared cross section reduces the impact pressure effectively when the amphibious seaplanes land on intricate waves. This study is expected to offer valuable reference for the hull designing of the amphibious seaplane.
The effect of hydrodynamic impact on the amphibious seaplane is an important consideration in its structural designing and intensity checking. In addition, such impact is a major factor affecting its structural weight. By varying two parameters: drop height and drop weight in the experiment, the pressure and the change of the free surface of liquid for three different wedges are dynamically measured. In the present work, the local pressure distribution, the impact pressure changing with time and the variety of the free surface on several free-falling wedges have been investigated. These wedges have been chosen from the representative cross section of amphibious seaplanes commonly used worldwide. By comparing the experimental results, the conclusion is reached that the wedge with a flared cross section reduces the impact pressure effectively when the amphibious seaplanes land on intricate waves. This study is expected to offer valuable reference for the hull designing of the amphibious seaplane.
2016, 36(3): 319-325.
doi: 10.11883/1001-1455(2016)03-0319-07
Abstract:
This paper proposes that both macroscopic and mesoscopic flaws should be considered in the dynamic damage constitutive model for the jointed rock mass. Firstly, the calculation formula of the macroscopic damage variable (tensor) of the jointed rock mass is deduced based on the energy principle and the fracture mechanics theory so that the geometrical and mechanical parameters can be considered at the same time. Secondly, the compound damage variable (tensor) including both macroscopic and mesoscopic flaws and the Taylor-Chen-Kuszmaul model (TCK) for the intact rock are adopted to establish the corresponding dynamic damage constitutive model for the jointed rock mass under uniaxial compression. Finally, the effect law of the joint internal friction angle and the joint length on rock mass's dynamic mechanical property is examined with this model. The results show that the dynamic climax strength of the samples increases and decreases respectively with the increase of the joint internal friction and the joint length.
This paper proposes that both macroscopic and mesoscopic flaws should be considered in the dynamic damage constitutive model for the jointed rock mass. Firstly, the calculation formula of the macroscopic damage variable (tensor) of the jointed rock mass is deduced based on the energy principle and the fracture mechanics theory so that the geometrical and mechanical parameters can be considered at the same time. Secondly, the compound damage variable (tensor) including both macroscopic and mesoscopic flaws and the Taylor-Chen-Kuszmaul model (TCK) for the intact rock are adopted to establish the corresponding dynamic damage constitutive model for the jointed rock mass under uniaxial compression. Finally, the effect law of the joint internal friction angle and the joint length on rock mass's dynamic mechanical property is examined with this model. The results show that the dynamic climax strength of the samples increases and decreases respectively with the increase of the joint internal friction and the joint length.
2016, 36(3): 326-332.
doi: 10.11883/1001-1455(2016)03-0326-07
Abstract:
In this work we investigated the dynamic behaviors of the projectile water entry using the SPH method. We developed our own SPH program based on the N-S equation of the Lagrange form and established a calculation model for the projectile water entry and, with corresponding material parameters and equation of state given, studied the influence of such factors as projectile shape, velocity and angle into the water on the process of the projectile water entry. The simulation results show that the formation and the development of the cavitation bubble are mainly determined by the projectile's state of motion: the more stable the projectile's trajectory, the smaller its drag coefficient, and the greater its sustained velocity. It is found that the SPH method has a high self-adaptability, for which it is applicable for studying the problems related with fluid-structure interaction occurring during the process of the projectile water entry.
In this work we investigated the dynamic behaviors of the projectile water entry using the SPH method. We developed our own SPH program based on the N-S equation of the Lagrange form and established a calculation model for the projectile water entry and, with corresponding material parameters and equation of state given, studied the influence of such factors as projectile shape, velocity and angle into the water on the process of the projectile water entry. The simulation results show that the formation and the development of the cavitation bubble are mainly determined by the projectile's state of motion: the more stable the projectile's trajectory, the smaller its drag coefficient, and the greater its sustained velocity. It is found that the SPH method has a high self-adaptability, for which it is applicable for studying the problems related with fluid-structure interaction occurring during the process of the projectile water entry.
2016, 36(3): 333-339.
doi: 10.11883/1001-1455(2016)03-0333-07
Abstract:
In this paper we report on the tests that investigate the blast resistance of graded sandwich plates. The deformation model, the back-face-sheet deflections and the core compressions have been compared with the test results obtained from tests done on structures with ungraded core layers. The stress transfer characteristics are analyzed based on the one dimensional stress wave theory, indicating that the stress wave transferred factor is smaller in the graded core layers and it is smallest in the relative density-tapered core arrangement specimen. By considering the deformation model, back-face-sheet deflections, core compressions and stress transfer characteristics, the blast resistance of the graded sandwich plates is found to be better than that of the ungraded ones, and in the present loading conditions, the relative density-tapered core arrangement from the front sheet to the back sheet is found to have the best blast resistance.
In this paper we report on the tests that investigate the blast resistance of graded sandwich plates. The deformation model, the back-face-sheet deflections and the core compressions have been compared with the test results obtained from tests done on structures with ungraded core layers. The stress transfer characteristics are analyzed based on the one dimensional stress wave theory, indicating that the stress wave transferred factor is smaller in the graded core layers and it is smallest in the relative density-tapered core arrangement specimen. By considering the deformation model, back-face-sheet deflections, core compressions and stress transfer characteristics, the blast resistance of the graded sandwich plates is found to be better than that of the ungraded ones, and in the present loading conditions, the relative density-tapered core arrangement from the front sheet to the back sheet is found to have the best blast resistance.
2016, 36(3): 340-346.
doi: 10.11883/1001-1455(2016)03-0340-07
Abstract:
According to the design specifications of national defense works and human defense works, a closed single rectangular cavity model was developed to obtain the explosion load distribution at the walls of typical cavities and the corresponding destruction forms resulted from the explosion inside the cavities. The developed cavity model was applied to carry out internal explosion experiments, in which the mass of the TNT charge was increased gradually until the cavity model could be damaged. Pressure and acceleration sensors were used to record the explosion pressure-time curves and the vibration acceleration-time curves at the cavity walls, respectively. And the explosion load distributions at the cavity walls and the destruction form of the model structure were analyzed. The first peaks of the measured data were compared with the results of theoretical calculation and numerical simulation to discuss the cause for the errors among the three methods.
According to the design specifications of national defense works and human defense works, a closed single rectangular cavity model was developed to obtain the explosion load distribution at the walls of typical cavities and the corresponding destruction forms resulted from the explosion inside the cavities. The developed cavity model was applied to carry out internal explosion experiments, in which the mass of the TNT charge was increased gradually until the cavity model could be damaged. Pressure and acceleration sensors were used to record the explosion pressure-time curves and the vibration acceleration-time curves at the cavity walls, respectively. And the explosion load distributions at the cavity walls and the destruction form of the model structure were analyzed. The first peaks of the measured data were compared with the results of theoretical calculation and numerical simulation to discuss the cause for the errors among the three methods.
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2016, 36(3): 347-352.
doi: 10.11883/1001-1455(2016)03-0347-06
Abstract:
We carried out experiments of suppressing the gasoline-air explosion by non-premixed nitrogen using the visualization experimental bench and a high-speed camera to take photos of the flame front extinction to capture the suppression process. Based on the analysis of the experimental data and high-speed taken photos, we examined the overpressure characteristics and the flame behavior of the suppression process. Results from our study show that the suppression by non-premixed nitrogen can significantly reduce the overpressure in the gasoline-air mixture explosion and its rise rate, and in the suppression process three phases are identified: sustained inertia, suppression/attenuation, and diffusion/extinction. The mechanism governing the suppression process is that nitrogen molecules participate in the chemical reaction as a third part and can then absorb energy from the high-energy free radicals so that the main reaction chains are changed to termination chains. The flame in the phase of the suppression/attenuation can be divided into the suppression/attenuation zone (where suppression and attenuation occur) and the core zone. In the phase of suppression and attenuation, the relationship between the flame speed and time can be described by a linear formula.
We carried out experiments of suppressing the gasoline-air explosion by non-premixed nitrogen using the visualization experimental bench and a high-speed camera to take photos of the flame front extinction to capture the suppression process. Based on the analysis of the experimental data and high-speed taken photos, we examined the overpressure characteristics and the flame behavior of the suppression process. Results from our study show that the suppression by non-premixed nitrogen can significantly reduce the overpressure in the gasoline-air mixture explosion and its rise rate, and in the suppression process three phases are identified: sustained inertia, suppression/attenuation, and diffusion/extinction. The mechanism governing the suppression process is that nitrogen molecules participate in the chemical reaction as a third part and can then absorb energy from the high-energy free radicals so that the main reaction chains are changed to termination chains. The flame in the phase of the suppression/attenuation can be divided into the suppression/attenuation zone (where suppression and attenuation occur) and the core zone. In the phase of suppression and attenuation, the relationship between the flame speed and time can be described by a linear formula.
2016, 36(3): 353-358.
doi: 10.11883/1001-1455(2016)03-0353-06
Abstract:
To obtain the characteristics and the mechanisms behind the penetration of steel ingot by linear shaped charge (LSC) with a cuniform cover, we built a three-dimensional numerical model using ANSYS/LS-DYNA program and performed a numerical simulation study. The actual cutting experiment was conducted on the basis of this numerical simulation and the following results were achieved: For a given standoff, the depth of LSC cutting steel ingot increases at first rapidly along with of time and then this increase gradually slows down; for different standoffs, the depth of LSC cutting steel ingot increases more slowly with the increase of the standoff. The penetration depth changes little at the standoffs ranging from 40 to 60 mm and from 70 to 120 mm, showing an insensitivity to the variation of the standoff. Different shapes of the cutting cross-sections of the steel ingot at different time were obtained under different conditions of the standoff. The results show that the penetration results of numerical simulation were consistent with those of the cutting experiment. Our three-dimensional numerical model can simulate the process of the penetration of the steel ingot by the real cutter. The characteristics and the mechanisms obtained can better reflect the actual cutting process.
To obtain the characteristics and the mechanisms behind the penetration of steel ingot by linear shaped charge (LSC) with a cuniform cover, we built a three-dimensional numerical model using ANSYS/LS-DYNA program and performed a numerical simulation study. The actual cutting experiment was conducted on the basis of this numerical simulation and the following results were achieved: For a given standoff, the depth of LSC cutting steel ingot increases at first rapidly along with of time and then this increase gradually slows down; for different standoffs, the depth of LSC cutting steel ingot increases more slowly with the increase of the standoff. The penetration depth changes little at the standoffs ranging from 40 to 60 mm and from 70 to 120 mm, showing an insensitivity to the variation of the standoff. Different shapes of the cutting cross-sections of the steel ingot at different time were obtained under different conditions of the standoff. The results show that the penetration results of numerical simulation were consistent with those of the cutting experiment. Our three-dimensional numerical model can simulate the process of the penetration of the steel ingot by the real cutter. The characteristics and the mechanisms obtained can better reflect the actual cutting process.
2016, 36(3): 359-369.
doi: 10.11883/1001-1455(2016)03-0359-11
Abstract:
Treating the target as the incompressible material, by assuming that the cavity expansion produce plastic-elastic response region, the decay function for the back free-surface effect of target is constructed. The forcing function of metallic targets for perforation is obtained by multiplying the forcing function of compressible Strain-Harding targets with the decay function. Based on the three stage of elastic-decaying, plastic-decaying and cracking, the analytical model considering the compressibility, the back free-surface effect of target and cracking is established, and the analytical equation of instantaneous velocity of projectile is deduced. The deceleration, instantaneous and residual velocity of projectile is calculated by numerical methods. Through comparison with six sets of experimental data and other existing models, with the target thickness and impact velocity in a certain range, the free-effect should be considered.
Treating the target as the incompressible material, by assuming that the cavity expansion produce plastic-elastic response region, the decay function for the back free-surface effect of target is constructed. The forcing function of metallic targets for perforation is obtained by multiplying the forcing function of compressible Strain-Harding targets with the decay function. Based on the three stage of elastic-decaying, plastic-decaying and cracking, the analytical model considering the compressibility, the back free-surface effect of target and cracking is established, and the analytical equation of instantaneous velocity of projectile is deduced. The deceleration, instantaneous and residual velocity of projectile is calculated by numerical methods. Through comparison with six sets of experimental data and other existing models, with the target thickness and impact velocity in a certain range, the free-effect should be considered.
2016, 36(3): 370-378.
doi: 10.11883/1001-1455(2016)03-0370-09
Abstract:
To study cracks propagation rules on filled fissured rock about dynamic fracture, air, clay and water were used as fillings of organic glass prefabricated fissures, under the condition of different angles and distances from blasthole to prefabricated fissures, the explosion experiments on three kinds of different fillings models were carried out through single detonator loading. The results show that blasting cracks almost cannot surmount prefabricated fissures; total cracks and left end wing cracks of models with filling air all most are larger than models with filling clay and water; location and length of the longest cracks are related to propagation direction and energy of reflected stress wave; right end wing cracks of most models with filling air increase with the increase of angles, but right end wing cracks of models with filling clay are first increased and then decreased; blasting cracks propagation are sensitive to filling medium type.
To study cracks propagation rules on filled fissured rock about dynamic fracture, air, clay and water were used as fillings of organic glass prefabricated fissures, under the condition of different angles and distances from blasthole to prefabricated fissures, the explosion experiments on three kinds of different fillings models were carried out through single detonator loading. The results show that blasting cracks almost cannot surmount prefabricated fissures; total cracks and left end wing cracks of models with filling air all most are larger than models with filling clay and water; location and length of the longest cracks are related to propagation direction and energy of reflected stress wave; right end wing cracks of most models with filling air increase with the increase of angles, but right end wing cracks of models with filling clay are first increased and then decreased; blasting cracks propagation are sensitive to filling medium type.
2016, 36(3): 379-385.
doi: 10.11883/1001-1455(2016)03-0379-07
Abstract:
The reflection and focusing of the shock wave propagating into a convergent tube can create a high-temperature and high-pressure region, which is significant for the detonation engine to induce the mixed combustible gases to detonate in ignition. Based on the N-S equations and combined with the five order WENO scheme, the phenomena of the shock wave reflection and focusing in the triangular wedge have been numerically simulated with the Mach number as 6. The numerical results reveal that the modification of the vertex angles has an obvious influence on the kind of shock reflection and the shock wave focusing. With the vertex angle getting bigger, the shock wave transforms from the Mach reflection to the transitional-Mach and the double-Mach reflections, and the jetting on the ramp surface becomes more evident. The high-temperature and high-pressure region generated after the first collision of the triple points can then satisfy the ignition condition of the mixed combustible gases. The temperature and the pressure will rise with the vertex angle getting bigger, and approach the maximum as the shock wave reaches the critical point of the double-Mach reflection on the wedge. However, the shock wave turns to the regular reflection on the wedge when the vertex angle exceeds the angle of the critical double-Mach reflection, and the triple points will not collide. Therefore, no high-temperature and high-pressure region is generated under this condition.
The reflection and focusing of the shock wave propagating into a convergent tube can create a high-temperature and high-pressure region, which is significant for the detonation engine to induce the mixed combustible gases to detonate in ignition. Based on the N-S equations and combined with the five order WENO scheme, the phenomena of the shock wave reflection and focusing in the triangular wedge have been numerically simulated with the Mach number as 6. The numerical results reveal that the modification of the vertex angles has an obvious influence on the kind of shock reflection and the shock wave focusing. With the vertex angle getting bigger, the shock wave transforms from the Mach reflection to the transitional-Mach and the double-Mach reflections, and the jetting on the ramp surface becomes more evident. The high-temperature and high-pressure region generated after the first collision of the triple points can then satisfy the ignition condition of the mixed combustible gases. The temperature and the pressure will rise with the vertex angle getting bigger, and approach the maximum as the shock wave reaches the critical point of the double-Mach reflection on the wedge. However, the shock wave turns to the regular reflection on the wedge when the vertex angle exceeds the angle of the critical double-Mach reflection, and the triple points will not collide. Therefore, no high-temperature and high-pressure region is generated under this condition.
2016, 36(3): 386-390.
doi: 10.11883/1001-1455(2016)03-0386-05
Abstract:
As the increasing quantity of space debris has become a great hazard to the high-voltage solar array of the spacecraft in orbit, there is a more urgent need to evaluate the discharge effect of hypervelocity on the solar array as a result of the impact by space debris. In this paper, using projectiles loaded by a two-stage light gas gun, and employing the Langmuir triple probe and the probes of the current and the voltage, we explored the discharge effect on the space solar array at different impact velocities. Results showed that the impact may give rise to solar array discharge, which is induced by high density plasma generated by the impact, and that the increasing impact velocities can lead to more serious damage to the solar array.
As the increasing quantity of space debris has become a great hazard to the high-voltage solar array of the spacecraft in orbit, there is a more urgent need to evaluate the discharge effect of hypervelocity on the solar array as a result of the impact by space debris. In this paper, using projectiles loaded by a two-stage light gas gun, and employing the Langmuir triple probe and the probes of the current and the voltage, we explored the discharge effect on the space solar array at different impact velocities. Results showed that the impact may give rise to solar array discharge, which is induced by high density plasma generated by the impact, and that the increasing impact velocities can lead to more serious damage to the solar array.
2016, 36(3): 391-399.
doi: 10.11883/1001-1455(2016)03-0391-09
Abstract:
To study damage characteristics of the shield building for nuclear power plant subjected to a large commercial aircraft impact, finite element models for Boeing 767 commercial aircraft impacting on a shield building made of steel-concrete-steel sandwich panels are established to simulate the impact process. The following results were achieved: the aircraft's axial mesh size greatly influences the impact force; some parts of the shield building hit by the aircraft undergo significant deformations while the deformation is smaller in the other parts; the impact velocity has little effect on the impact duration but a great effect on the structural response displacement, and the total impact force rapidly declines with the impact velocity decreasing. The impact force arising from different parts of the aircraft hitting the shield building are given, the simplified curve and the load area of different impact forces are obtained, which will contribute to the determination of the impact force distribution form, thus providing a positive help to the engineering design of shield buildings.
To study damage characteristics of the shield building for nuclear power plant subjected to a large commercial aircraft impact, finite element models for Boeing 767 commercial aircraft impacting on a shield building made of steel-concrete-steel sandwich panels are established to simulate the impact process. The following results were achieved: the aircraft's axial mesh size greatly influences the impact force; some parts of the shield building hit by the aircraft undergo significant deformations while the deformation is smaller in the other parts; the impact velocity has little effect on the impact duration but a great effect on the structural response displacement, and the total impact force rapidly declines with the impact velocity decreasing. The impact force arising from different parts of the aircraft hitting the shield building are given, the simplified curve and the load area of different impact forces are obtained, which will contribute to the determination of the impact force distribution form, thus providing a positive help to the engineering design of shield buildings.
2016, 36(3): 400-406.
doi: 10.11883/1001-1455(2016)03-0400-07
Abstract:
To explore a method for control over the boulders splitting morphology, cylindrical concrete specimens were penetrated by a linear-shaped charge, the splitting cracks' propagation and development were photographed and the splitting development process of their 3D deformation characteristics were analyzed using high-speed 3D DIC. The results show that the velocity of the crack propagation within the data analysis region exhibits a tendency for a step-by-step increase. The peak velocity and the average velocity are respectively 235.52 m/s and 140.89 m/s. The impact of the linear shaped-charge jet plays a significant role in determining the splitting of the target so that the cracks of the target propagated symmetrically downward in an s-shape along the axis, and on its path the crack showed three obvious inflection points, where branch cracks were produced whose propagation distance was below 5 cm. The shape and location of the main strain concentration determines the crack propagation trend and path, and the tensile strain concentration occurs before the crack appears. The specimen exhibits a quasi-static splitting and the cracks have a fairly even distribution.
To explore a method for control over the boulders splitting morphology, cylindrical concrete specimens were penetrated by a linear-shaped charge, the splitting cracks' propagation and development were photographed and the splitting development process of their 3D deformation characteristics were analyzed using high-speed 3D DIC. The results show that the velocity of the crack propagation within the data analysis region exhibits a tendency for a step-by-step increase. The peak velocity and the average velocity are respectively 235.52 m/s and 140.89 m/s. The impact of the linear shaped-charge jet plays a significant role in determining the splitting of the target so that the cracks of the target propagated symmetrically downward in an s-shape along the axis, and on its path the crack showed three obvious inflection points, where branch cracks were produced whose propagation distance was below 5 cm. The shape and location of the main strain concentration determines the crack propagation trend and path, and the tensile strain concentration occurs before the crack appears. The specimen exhibits a quasi-static splitting and the cracks have a fairly even distribution.
2016, 36(3): 407-415.
doi: 10.11883/1001-1455(2016)03-0407-09
Abstract:
In internal combustion engines, different combustion technologiescan result in different knocks, such as the conventional knock of gasoline engines, the super knock and the knock of HCCI engines.Though they are all caused by the auto-ignition of unburned mixture which leads to the oscillation burning, the rising rate and the oscillation amplitude of their pressure are totally different. In order to explore the inner mechanism working behind them, three kinds of auto-ignition modes were built up to illustrate the different phenomena of pressure oscillations under different combustion technologies. The differences of these three kinds of auto-ignition modes in engines were clarified. In the method of "Energy Injected", the heat source term of the energy equation can be changed based on the heat release rate obtained from experiments, and then a series of numerical simulations were conducted to realize these three kinds of auto-ignition modes. The numerical simulation shows that different auto-ignition modes will lead to different pressure waves, which can explain the different pressure rising rate and pressure oscillation amplitude. The method of "Energy Injection" based on the experiment measured heat release rate can accurately and rapidly identify the formation and propagation of pressure waves in the engine combustion chamber.
In internal combustion engines, different combustion technologiescan result in different knocks, such as the conventional knock of gasoline engines, the super knock and the knock of HCCI engines.Though they are all caused by the auto-ignition of unburned mixture which leads to the oscillation burning, the rising rate and the oscillation amplitude of their pressure are totally different. In order to explore the inner mechanism working behind them, three kinds of auto-ignition modes were built up to illustrate the different phenomena of pressure oscillations under different combustion technologies. The differences of these three kinds of auto-ignition modes in engines were clarified. In the method of "Energy Injected", the heat source term of the energy equation can be changed based on the heat release rate obtained from experiments, and then a series of numerical simulations were conducted to realize these three kinds of auto-ignition modes. The numerical simulation shows that different auto-ignition modes will lead to different pressure waves, which can explain the different pressure rising rate and pressure oscillation amplitude. The method of "Energy Injection" based on the experiment measured heat release rate can accurately and rapidly identify the formation and propagation of pressure waves in the engine combustion chamber.
2016, 36(3): 416-421.
doi: 10.11883/1001-1455(2016)03-0416-06
Abstract:
In this work we conducted numerical simulations of semi-circular bending (SCB) test of steel with cracks respectively in a static condition and under impact loading, using ANSYS/LS-DYNA, a finite element software. According to the results achieved from the simulation of the static test, we have put forward the formula for the calculation of Steel Ⅰ's fitted stress intensity factor which, when applied to the calculation of the factor under the mixed-mode loading, can keep the maximum error below 10%. The simulation result of dynamic test shows that: for semi-circular bending (SCB) test of pure Steel Ⅰ under impact loading, the dynamic stress intensity factor exhibits regular variation with the change in the specimen's radius, the distance between the supports, and the relative crack length: When the specimen's radius is less than 60 mm, the distance between two supports is 1.2 and the relative crack length is in the range of 0.1 to 0.4, the inertial effect is relatively small and the error of the dynamic stress intensity factor calculated with the above formula is about 10%; when the relative crack length is 0.2 to 0.4 and the crack angle is in the range of 10° to 40°, the error of KId which is calculated with this formula is less than 10% for semi-circular bending (SCB) test under mixed-mode loading.
In this work we conducted numerical simulations of semi-circular bending (SCB) test of steel with cracks respectively in a static condition and under impact loading, using ANSYS/LS-DYNA, a finite element software. According to the results achieved from the simulation of the static test, we have put forward the formula for the calculation of Steel Ⅰ's fitted stress intensity factor which, when applied to the calculation of the factor under the mixed-mode loading, can keep the maximum error below 10%. The simulation result of dynamic test shows that: for semi-circular bending (SCB) test of pure Steel Ⅰ under impact loading, the dynamic stress intensity factor exhibits regular variation with the change in the specimen's radius, the distance between the supports, and the relative crack length: When the specimen's radius is less than 60 mm, the distance between two supports is 1.2 and the relative crack length is in the range of 0.1 to 0.4, the inertial effect is relatively small and the error of the dynamic stress intensity factor calculated with the above formula is about 10%; when the relative crack length is 0.2 to 0.4 and the crack angle is in the range of 10° to 40°, the error of KId which is calculated with this formula is less than 10% for semi-circular bending (SCB) test under mixed-mode loading.
2016, 36(3): 422-428.
doi: 10.11883/1001-1455(2016)03-0422-07
Abstract:
The rate sensitivity of concrete-like brittle materials results mainly from their inhomogeneity, which leads to their different paths of crack development at different load rates and accounts for their different dynamic flexural strengths. On the basis of the above theoretical analysis, this paper presents the algebraic expression of the dynamic flexural strength, which consists of the weighted average of the flexural strength of mortar and aggregate and the inertia term, predicts the limit flexural intensity of concrete materials under different impact loads and, finally, investigates their crack paths and intensity variations at different loading rates by the three-point bending beam test with a special rhombus aggregate.
The rate sensitivity of concrete-like brittle materials results mainly from their inhomogeneity, which leads to their different paths of crack development at different load rates and accounts for their different dynamic flexural strengths. On the basis of the above theoretical analysis, this paper presents the algebraic expression of the dynamic flexural strength, which consists of the weighted average of the flexural strength of mortar and aggregate and the inertia term, predicts the limit flexural intensity of concrete materials under different impact loads and, finally, investigates their crack paths and intensity variations at different loading rates by the three-point bending beam test with a special rhombus aggregate.
2016, 36(3): 429-432.
doi: 10.11883/1001-1455(2016)03-0429-04
Abstract:
In this work we studied the effect of CO2 on explosion suppression for multi-component mixed gas at different initial temperatures by igniting the gas obtained from adding CO2 to the mixture of LPG and air. Our study indicates that when the volume fraction of CO2 reaches 36% at the initial temperature of 15℃, the mixed gas is beyond the explosive range and the critical volume fraction of oxygen is 12.8%; when the volume fraction of CO2 reaches 39% at the initial temperature of 50℃, the mixed gas is beyond the explosive range, and the critical volume fraction oxygen is 12.2%. The result shows that the effect of CO2 on the LPG suppression explosion is influenced by temperature to a certain extent.
In this work we studied the effect of CO2 on explosion suppression for multi-component mixed gas at different initial temperatures by igniting the gas obtained from adding CO2 to the mixture of LPG and air. Our study indicates that when the volume fraction of CO2 reaches 36% at the initial temperature of 15℃, the mixed gas is beyond the explosive range and the critical volume fraction of oxygen is 12.8%; when the volume fraction of CO2 reaches 39% at the initial temperature of 50℃, the mixed gas is beyond the explosive range, and the critical volume fraction oxygen is 12.2%. The result shows that the effect of CO2 on the LPG suppression explosion is influenced by temperature to a certain extent.
