2017 Vol. 37, No. 1
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2017, 37(1): 1-9.
doi: 10.11883/1001-1455(2017)01-0021-06
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Abstract:
Aiming at revealing the characteristics of premixed methane/air flame propagating in an obstructed duct.A 4 mm thick obstacle with a square hole of 50 mm×50 mm was equipped at 210 mm from the ignition source. In the experiment, the high-speed video photography was used to study the flame shape changes and flame front speed. In the numerical simulation, the large eddy simulation (LES) was applied to investigating the flow structure. The results demonstrate that the flame-tip successively takes on a spherical, finger and mushroom-like shape, and the flame begins to propagate in the backward direction after the mushroom-like flame appears. The mushroom-like flame can be explained by the interaction of the flame with two vortexes, and the reverse flow emerged in the flow field leads to the backward motion of the premixed flame. The flame speed is accelerated significantly due to the obstacle and the flame tip speed reaches the maximum value of 17 m/s when the flame passes through the square hole of the obstacle. The flame shape changes and the flow structure observed in the experiments can be well reproduced in the numerical simulations using the LES model. It is indicated that the LES model can be used to predict the premixed flame propagating in an obstructed duct.
Aiming at revealing the characteristics of premixed methane/air flame propagating in an obstructed duct.A 4 mm thick obstacle with a square hole of 50 mm×50 mm was equipped at 210 mm from the ignition source. In the experiment, the high-speed video photography was used to study the flame shape changes and flame front speed. In the numerical simulation, the large eddy simulation (LES) was applied to investigating the flow structure. The results demonstrate that the flame-tip successively takes on a spherical, finger and mushroom-like shape, and the flame begins to propagate in the backward direction after the mushroom-like flame appears. The mushroom-like flame can be explained by the interaction of the flame with two vortexes, and the reverse flow emerged in the flow field leads to the backward motion of the premixed flame. The flame speed is accelerated significantly due to the obstacle and the flame tip speed reaches the maximum value of 17 m/s when the flame passes through the square hole of the obstacle. The flame shape changes and the flow structure observed in the experiments can be well reproduced in the numerical simulations using the LES model. It is indicated that the LES model can be used to predict the premixed flame propagating in an obstructed duct.
2017, 37(1): 10-14.
doi: 10.11883/1001-1455(2017)01-0001-09
Abstract:
In simplifying large numbers of bolt connections in simulation to substitute the construction of the whole joint structure, it is essential to establish a joint constitutive model. In this paper, a shear constitutive model of the single lap bolt was established. Firstly, the curves of the load-displacement of the single lap shear bolt were obtained from experiments, and the corresponding physical mechanism was analyzed using the finite-element method. Then, the curve of the load-displacement was divided into several phases according to the physical mechanism. Based on the first three phases, the basic form of the shear constitutive model was proposed and the related parameters were determined in detail. In the second phase of the shear model, the support stiffness was solved by the strain energy method based on reasonable stress distribution hypothesis, which was a step most difficult to take. Finally, this constitutive model was verified by numerous examples. The results show that this shear model for the single lap bolt has the advantages of providing clear physical meaning, easy parameter estimation, and high accuracy.
In simplifying large numbers of bolt connections in simulation to substitute the construction of the whole joint structure, it is essential to establish a joint constitutive model. In this paper, a shear constitutive model of the single lap bolt was established. Firstly, the curves of the load-displacement of the single lap shear bolt were obtained from experiments, and the corresponding physical mechanism was analyzed using the finite-element method. Then, the curve of the load-displacement was divided into several phases according to the physical mechanism. Based on the first three phases, the basic form of the shear constitutive model was proposed and the related parameters were determined in detail. In the second phase of the shear model, the support stiffness was solved by the strain energy method based on reasonable stress distribution hypothesis, which was a step most difficult to take. Finally, this constitutive model was verified by numerous examples. The results show that this shear model for the single lap bolt has the advantages of providing clear physical meaning, easy parameter estimation, and high accuracy.
2017, 37(1): 15-20.
doi: 10.11883/1001-1455(2017)01-0015-06
Abstract:
In this work the digital image correlation (DIC) technique was used for the full field measurement of the dynamic tension strain in traditional split Hopkinson tension bar (SHTB) experiments using the commercial image correlation software and the digital ultra-high-speed camera. This system was used to study the dynamic tensile response of nylon and aluminum alloy. The dynamic tensile stress-strain curves of nylon and aluminum alloy were accurately obtained to verify the validity of the dynamic tensile strain measured by the DIC technique. The results show that the average strain thus determined agrees well with the strain measured with a strain gauge attached to the specimen, but the traditional SHTB experiment's analytic strain is larger than the strain measured from the DIC method, which can be rectified by using the effective gauge length in consideration of the effect of rounded fillets. The effective gauge length does not depend on the strain rate. Based on the full filed strain measurements of the specimen, the strain distribution within the gauge length is uniform for the brittle nylon specimen, but the strain distribution for the ductile aluminum alloy specimen is not uniform due to the effects of the necking.
In this work the digital image correlation (DIC) technique was used for the full field measurement of the dynamic tension strain in traditional split Hopkinson tension bar (SHTB) experiments using the commercial image correlation software and the digital ultra-high-speed camera. This system was used to study the dynamic tensile response of nylon and aluminum alloy. The dynamic tensile stress-strain curves of nylon and aluminum alloy were accurately obtained to verify the validity of the dynamic tensile strain measured by the DIC technique. The results show that the average strain thus determined agrees well with the strain measured with a strain gauge attached to the specimen, but the traditional SHTB experiment's analytic strain is larger than the strain measured from the DIC method, which can be rectified by using the effective gauge length in consideration of the effect of rounded fillets. The effective gauge length does not depend on the strain rate. Based on the full filed strain measurements of the specimen, the strain distribution within the gauge length is uniform for the brittle nylon specimen, but the strain distribution for the ductile aluminum alloy specimen is not uniform due to the effects of the necking.
2017, 37(1): 21-26.
doi: 10.11883/1001-1455(2017)01-0010-05
Abstract:
Obtaining accurate waveforms is significant in impact mechanics numerical calculation. This paper is to analyze how the kernel functions and smooth length affect the result of stress wave simulation. The SPH (smoothed particle hydrodynamics) formulations with different kernel functions and smooth lengths of one dimensional wave equation was compared with the finite difference formulation, which was derived in this paper. One dimensional stress and strain waves were simulated using the SPH method with different kernel functions and smooth lengths, and waveforms were gained accurately by B-spline and Gaussian kernels when the smooth length was equal to or greater than the particle interval. The wave velocity obtained by the quadratic kernel is below the theoretical value, no matter what the smooth length is. A parameter was deduced in this paper as roughly equal to the dimensionless wave velocity. Several conclusions were drawn. Firstly, the smooth length is equal to or greater than the particle interval, which is the necessary prerequisite for accurate stress wave simulation with SPH. Then, the quadratic kernel is not suitable in impact mechanics numerical calculation. Finally, the parameter deduced in this paper is a significant index to evaluate the stress wave simulation result of SPH.
Obtaining accurate waveforms is significant in impact mechanics numerical calculation. This paper is to analyze how the kernel functions and smooth length affect the result of stress wave simulation. The SPH (smoothed particle hydrodynamics) formulations with different kernel functions and smooth lengths of one dimensional wave equation was compared with the finite difference formulation, which was derived in this paper. One dimensional stress and strain waves were simulated using the SPH method with different kernel functions and smooth lengths, and waveforms were gained accurately by B-spline and Gaussian kernels when the smooth length was equal to or greater than the particle interval. The wave velocity obtained by the quadratic kernel is below the theoretical value, no matter what the smooth length is. A parameter was deduced in this paper as roughly equal to the dimensionless wave velocity. Several conclusions were drawn. Firstly, the smooth length is equal to or greater than the particle interval, which is the necessary prerequisite for accurate stress wave simulation with SPH. Then, the quadratic kernel is not suitable in impact mechanics numerical calculation. Finally, the parameter deduced in this paper is a significant index to evaluate the stress wave simulation result of SPH.
2017, 37(1): 27-36.
doi: 10.11883/1001-1455(2017)01-0027-10
Abstract:
In order to understand the law of vibration propagation and the damage degree of the bedding rock slope during blasting excavation, we studied the bedding slope in Puli-Xuanwei Expressway in Yunnan Province as an example. By applying acoustic tests in combination with the monitoring vibration and sound velocities under different depths of the rock mass, we obtained the vibration velocities at different locations after blasting, and analyzed the damage range as well as the propagation and attenuation law of the vibration wave measured of different explosive doses. The results show that the vibration velocity at any point of the blasting area exhibits a corresponding relationship with the damage depth of the slope. It exhibits a linear relation for single explosion and a presents non-linear relation for repeated explosion. Assuming a decrease of 10% in the sound velocity as the damage limit and the control value of blasting, the critical velocity corresponding to single explosion is 11.54 cm/s, the damage radius is 5.57 m, and the critical velocity corresponding to repeated explosion is 24.20 cm/s, the damage radius is 7.56 m. The largest explosive dose is deduced by two ways mentioned above according to the Sadaovsk Formula.
In order to understand the law of vibration propagation and the damage degree of the bedding rock slope during blasting excavation, we studied the bedding slope in Puli-Xuanwei Expressway in Yunnan Province as an example. By applying acoustic tests in combination with the monitoring vibration and sound velocities under different depths of the rock mass, we obtained the vibration velocities at different locations after blasting, and analyzed the damage range as well as the propagation and attenuation law of the vibration wave measured of different explosive doses. The results show that the vibration velocity at any point of the blasting area exhibits a corresponding relationship with the damage depth of the slope. It exhibits a linear relation for single explosion and a presents non-linear relation for repeated explosion. Assuming a decrease of 10% in the sound velocity as the damage limit and the control value of blasting, the critical velocity corresponding to single explosion is 11.54 cm/s, the damage radius is 5.57 m, and the critical velocity corresponding to repeated explosion is 24.20 cm/s, the damage radius is 7.56 m. The largest explosive dose is deduced by two ways mentioned above according to the Sadaovsk Formula.
2017, 37(1): 37-45.
doi: 10.11883/1001-1455(2017)01-0037-09
Abstract:
The dynamic response of sandwich plates with identical face sheets separated by compressible PVC (polyvinyl chloride) core subjected to shock loading was investigated. Combined with the three-dimensional digital image correlation technology, the deflection-time history of the back face sheet was measured. Deformation and failure modes of the sheets and core were exhibited to examine the effects of the projectile impulse and the core density. It was found that the fracture and failure occurred mainly at the center of the sandwich plates, and the deflection of the back sheets decreased gradually from the center to the outside, and finally the deformation turned into a corn-like shape. The results indicate that there is a good linear relationship between the projectile impulse and the permanent deflection of the central point of the back face sheets. Reducing the density of the core and raising the thickness of the core can effectively decrease the deflection of the back face sheets while maintaining the quality. The experimental results can provide help for the optimum design of polymer sandwich structures.
The dynamic response of sandwich plates with identical face sheets separated by compressible PVC (polyvinyl chloride) core subjected to shock loading was investigated. Combined with the three-dimensional digital image correlation technology, the deflection-time history of the back face sheet was measured. Deformation and failure modes of the sheets and core were exhibited to examine the effects of the projectile impulse and the core density. It was found that the fracture and failure occurred mainly at the center of the sandwich plates, and the deflection of the back sheets decreased gradually from the center to the outside, and finally the deformation turned into a corn-like shape. The results indicate that there is a good linear relationship between the projectile impulse and the permanent deflection of the central point of the back face sheets. Reducing the density of the core and raising the thickness of the core can effectively decrease the deflection of the back face sheets while maintaining the quality. The experimental results can provide help for the optimum design of polymer sandwich structures.
2017, 37(1): 46-52.
doi: 10.11883/1001-1455(2017)01-0046-07
Abstract:
To investigate the characteristics of the AP/HTPB composition propellant at different heating rates in the slow cook-off, we constructed a a model consisting of two-dimensional unsteady-state heat transfer and two-step chemical reaction kinetics. The characteristics of the composition propellant at the heating rates of 3.3, 4.7 and 6 K/h were analyzed respectively. The results show that the ignition position occurs in the left side of the interface between the propellant and the gas. The heating rate has a great effect on the ignition time and the position for the composition propellant. As the heating rate increases, the ignition delay time decreases and the ignition position moves to the right. The change of the heating rate has limited impact on the ignition delay temperature.
To investigate the characteristics of the AP/HTPB composition propellant at different heating rates in the slow cook-off, we constructed a a model consisting of two-dimensional unsteady-state heat transfer and two-step chemical reaction kinetics. The characteristics of the composition propellant at the heating rates of 3.3, 4.7 and 6 K/h were analyzed respectively. The results show that the ignition position occurs in the left side of the interface between the propellant and the gas. The heating rate has a great effect on the ignition time and the position for the composition propellant. As the heating rate increases, the ignition delay time decreases and the ignition position moves to the right. The change of the heating rate has limited impact on the ignition delay temperature.
2017, 37(1): 53-60.
doi: 10.11883/1001-1455(2017)01-0053-08
Abstract:
An experimental system of a confined space with a weakly constrained structure at the top was established. A series of gasoline/air mixture explosion experiments were conducted, and overpressure characteristics as well as flame behaviors were obtained. The results show that the internal overpressure exhibited a phenomenon of multi-peaks and pressure oscillations, induced by such factors as venting, external explosion, flame extension, etc. The value of the external overpressure decreased obviously with the increase of the distance from the weakly constrained structure, and the value along the vertical direction was larger than that along the horizontal direction. The impact of the weakly constrained structure was mainly reflected in the enhancement effect on the overpressure value and the lagging effect on the development rate of the explosion. The overpressure value showed the tendency to increase at first and then to decrease with the increase of the volume fraction of the gasoline/air vapor volume corresponding to the maximum overpressure, which is 1.79%. The flame propagation process involves three stages, i.e. stages of primary combustion, transitional combustion and secondary combustion. Affected by the Rayleigh instability, the Helmholtz instability and the baroclinic effect, the flame front was twisted and wrinkled, and the maximum height and maximum diameter were 0.80 and 0.55 m, respectively.
An experimental system of a confined space with a weakly constrained structure at the top was established. A series of gasoline/air mixture explosion experiments were conducted, and overpressure characteristics as well as flame behaviors were obtained. The results show that the internal overpressure exhibited a phenomenon of multi-peaks and pressure oscillations, induced by such factors as venting, external explosion, flame extension, etc. The value of the external overpressure decreased obviously with the increase of the distance from the weakly constrained structure, and the value along the vertical direction was larger than that along the horizontal direction. The impact of the weakly constrained structure was mainly reflected in the enhancement effect on the overpressure value and the lagging effect on the development rate of the explosion. The overpressure value showed the tendency to increase at first and then to decrease with the increase of the volume fraction of the gasoline/air vapor volume corresponding to the maximum overpressure, which is 1.79%. The flame propagation process involves three stages, i.e. stages of primary combustion, transitional combustion and secondary combustion. Affected by the Rayleigh instability, the Helmholtz instability and the baroclinic effect, the flame front was twisted and wrinkled, and the maximum height and maximum diameter were 0.80 and 0.55 m, respectively.
2017, 37(1): 61-67.
doi: 10.11883/1001-1455(2017)01-0061-07
Abstract:
Spallation process of melted metal on release or shock attracts considerable attention for basic weapon physics studies and engineering applications. In the present study, numerous cavitations within the shocked metal were initiated to induce the liquid fragments, defined as the micro-spall, revealing discrete and quasi-continuous spatial distributions, validated by proton radiography experiments. Here we improved the traditional Asay-window technique by attaching a thin LiF layer on the impacted plate of the LiF window and contriving a diffuse reflection interface. With these two optimized design, we successfully detected high-quality signals of micro-spalling fragments. Combining the medium-energy X-ray with the DPS diagnostic technique, we obtained clear volume-density distributions and evolution character for micro-spalling productions of melting Sn at different moments. We found the semiquantitative findings among the two tools are in good agreement. These clear images provide convinced experimental evidences for understanding the mechanism of the micro-spalling phenomenon and also offer useful data for theoretical modeling.
Spallation process of melted metal on release or shock attracts considerable attention for basic weapon physics studies and engineering applications. In the present study, numerous cavitations within the shocked metal were initiated to induce the liquid fragments, defined as the micro-spall, revealing discrete and quasi-continuous spatial distributions, validated by proton radiography experiments. Here we improved the traditional Asay-window technique by attaching a thin LiF layer on the impacted plate of the LiF window and contriving a diffuse reflection interface. With these two optimized design, we successfully detected high-quality signals of micro-spalling fragments. Combining the medium-energy X-ray with the DPS diagnostic technique, we obtained clear volume-density distributions and evolution character for micro-spalling productions of melting Sn at different moments. We found the semiquantitative findings among the two tools are in good agreement. These clear images provide convinced experimental evidences for understanding the mechanism of the micro-spalling phenomenon and also offer useful data for theoretical modeling.
2017, 37(1): 68-76.
doi: 10.11883/1001-1455(2017)01-0068-09
Abstract:
In the process of the premixed gas flame propagation, obstacles have vital influence on the flame's structure and propagation, and will enhance the flame acceleration and the DDT process. Through the methane/air premixed flame propagation experiment with obstacles in the visual pipe, the flame microstructure changes and the propagation characteristics were captured. By means of the three-dimensional physical model, a large eddy simulation mode (LES) with the WALE sub-grid scale models, and the thickened flame model (TFM) were used to repeat experiment process. The complex changes of the flow field were obtained when the premixed flame climbed over the obstacle, and the characteristics of the flow turbulence transition were analyzed. Finally, the direct cause of the premixed flame disturbance instability under the influence of the obstacles was revealed. It was induced by the coupling effect of the Kelvin-Helmholtz instability and the Rayleigh-Taylor instability, which in turn was affected by three vortexes as a result of the obstacle.
In the process of the premixed gas flame propagation, obstacles have vital influence on the flame's structure and propagation, and will enhance the flame acceleration and the DDT process. Through the methane/air premixed flame propagation experiment with obstacles in the visual pipe, the flame microstructure changes and the propagation characteristics were captured. By means of the three-dimensional physical model, a large eddy simulation mode (LES) with the WALE sub-grid scale models, and the thickened flame model (TFM) were used to repeat experiment process. The complex changes of the flow field were obtained when the premixed flame climbed over the obstacle, and the characteristics of the flow turbulence transition were analyzed. Finally, the direct cause of the premixed flame disturbance instability under the influence of the obstacles was revealed. It was induced by the coupling effect of the Kelvin-Helmholtz instability and the Rayleigh-Taylor instability, which in turn was affected by three vortexes as a result of the obstacle.
2017, 37(1): 77-83.
doi: 10.11883/1001-1455(2017)01-0077-07
Abstract:
In this work, based on the blasting vibration live data collected, the energy distributions at different frequency bands for the blasting vibration signals were obtained by the wavelet packet analysis technology. By comparing the results of each point analysis it was found that the tunnel excavation blasting seismic wave energy mainly concentrated in the tangential and radial directions; along the direction of the tunnelling, with the increase of the distance between the tunnel faces, the main frequency of the seismic wave decreased and the energy concentration frequency band became narrower and developed to the low frequency band; however, along the vertical direction of the tunnel, the main frequency decreases with the decrease of the depth and, at the same time, the wave energy concentration frequency band became narrower and developed to the low frequency band. The results show that wavelet packet analysis is an effective approach to estimating the structure safety under blasting vibration conditions.
In this work, based on the blasting vibration live data collected, the energy distributions at different frequency bands for the blasting vibration signals were obtained by the wavelet packet analysis technology. By comparing the results of each point analysis it was found that the tunnel excavation blasting seismic wave energy mainly concentrated in the tangential and radial directions; along the direction of the tunnelling, with the increase of the distance between the tunnel faces, the main frequency of the seismic wave decreased and the energy concentration frequency band became narrower and developed to the low frequency band; however, along the vertical direction of the tunnel, the main frequency decreases with the decrease of the depth and, at the same time, the wave energy concentration frequency band became narrower and developed to the low frequency band. The results show that wavelet packet analysis is an effective approach to estimating the structure safety under blasting vibration conditions.
2017, 37(1): 84-91.
doi: 10.11883/1001-1455(2017)01-0084-08
Abstract:
The sheet explosive can be used to simulate the space structure response caused by the high-power pulse X-rays, and the impulse coupling of the sheet explosive and the target is the basis for designing the simulated load. Based on the numerical results by the nonlinear finite element code, the computational modeling for the impulse coupling of the sheet explosive and the target is formulated in consideration of the effect on the specific impulse of the sheet explosive caused by the rarefaction of the border of the sheet explosive and the reflection of the support for connecting the mild detonating fuse and the sheet explosive. The analytic results reveal that the increment of the specific impulse caused by the rarefaction of the border is approximately in inverse relation to the diameter of the sheet explosive, and that caused by the reflection of the support is approximately in inverse relation to the square of the diameter of the sheet explosive. The specific impulse for the sheet explosive converges to the limit specific impulse related to the depth of the sheet explosive as the diameter of the sheet explosive reaches infinity. Both the rarefaction for the border of the sheet explosive and the reflection of the support are negligible with the diameter of the sheet explosive increasing. There exists a critical diameter and when it is equaled by the diameter of the sheet explosive, the specific impulse for the sheet explosive equals the limit specific impulse as the diameter of the sheet explosive reaches infinity.
The sheet explosive can be used to simulate the space structure response caused by the high-power pulse X-rays, and the impulse coupling of the sheet explosive and the target is the basis for designing the simulated load. Based on the numerical results by the nonlinear finite element code, the computational modeling for the impulse coupling of the sheet explosive and the target is formulated in consideration of the effect on the specific impulse of the sheet explosive caused by the rarefaction of the border of the sheet explosive and the reflection of the support for connecting the mild detonating fuse and the sheet explosive. The analytic results reveal that the increment of the specific impulse caused by the rarefaction of the border is approximately in inverse relation to the diameter of the sheet explosive, and that caused by the reflection of the support is approximately in inverse relation to the square of the diameter of the sheet explosive. The specific impulse for the sheet explosive converges to the limit specific impulse related to the depth of the sheet explosive as the diameter of the sheet explosive reaches infinity. Both the rarefaction for the border of the sheet explosive and the reflection of the support are negligible with the diameter of the sheet explosive increasing. There exists a critical diameter and when it is equaled by the diameter of the sheet explosive, the specific impulse for the sheet explosive equals the limit specific impulse as the diameter of the sheet explosive reaches infinity.
2017, 37(1): 92-98.
doi: 10.11883/1001-1455(2017)01-0092-07
Abstract:
In order to analyze the anti-blast properties of the RC superimposed slab's shear wall, comparative experimental studies of two RC superimposed slab shear walls and two in-situ cast shear walls under explosion were conducted. The structural failure feature, deformation capability, bearing capacity and crack distribution pattern were analyzed systematically. The result shows that the failure mode of the RC superimposed slab shear wall is similar to that of the in-situ cast shear wall. The stiffness of two kinds of specimen are basically identical within the elastic stage. But the post-cracking stiffness' descending speed of the in-situ cast shear wall is greater than that of the RC superimposed slab shear wall. The RC superimposed slab effectively restrained the crack extension and there were no shear failure throughout the loading procedure, which proves its high integrity. The blasting-resistance performance of the RC superimposed slab shear wall is superior to that of the in-situ cast shear wall.
In order to analyze the anti-blast properties of the RC superimposed slab's shear wall, comparative experimental studies of two RC superimposed slab shear walls and two in-situ cast shear walls under explosion were conducted. The structural failure feature, deformation capability, bearing capacity and crack distribution pattern were analyzed systematically. The result shows that the failure mode of the RC superimposed slab shear wall is similar to that of the in-situ cast shear wall. The stiffness of two kinds of specimen are basically identical within the elastic stage. But the post-cracking stiffness' descending speed of the in-situ cast shear wall is greater than that of the RC superimposed slab shear wall. The RC superimposed slab effectively restrained the crack extension and there were no shear failure throughout the loading procedure, which proves its high integrity. The blasting-resistance performance of the RC superimposed slab shear wall is superior to that of the in-situ cast shear wall.
2017, 37(1): 99-106.
doi: 10.11883/1001-1455(2017)01-0099-08
Abstract:
With a view to obtaining the characterisstic of shock response of the hull to underwater explosion, based on the experimental impact vibration data subjected to underwater explosion trial of ship, the time-frequency characteristics of the monitored impact vibration signals were studied by wavelet analysis. By using these signals, the acceleration-time curves and the energy distributions in different blasting frequency bands were obtained. The result show that the time-frequency characteristics of impact vibration can be obtained by the wavelet analysis, it is easy to get the time-frequency information details of the impact vibration signal intensity, frequency and duration, including the peak values and attenuation and vibration energy of impact vibration signals. Based on the analysis of the energy statistics and impact strength of the wavelet frequency band, found that has a wide distribution of shock response spectrum energy, more than 80% of vibration energy distributed above 312.5Hz at the main deck and below deck, and more vibration energy in low frequency at superstructure deck platform.
With a view to obtaining the characterisstic of shock response of the hull to underwater explosion, based on the experimental impact vibration data subjected to underwater explosion trial of ship, the time-frequency characteristics of the monitored impact vibration signals were studied by wavelet analysis. By using these signals, the acceleration-time curves and the energy distributions in different blasting frequency bands were obtained. The result show that the time-frequency characteristics of impact vibration can be obtained by the wavelet analysis, it is easy to get the time-frequency information details of the impact vibration signal intensity, frequency and duration, including the peak values and attenuation and vibration energy of impact vibration signals. Based on the analysis of the energy statistics and impact strength of the wavelet frequency band, found that has a wide distribution of shock response spectrum energy, more than 80% of vibration energy distributed above 312.5Hz at the main deck and below deck, and more vibration energy in low frequency at superstructure deck platform.
2017, 37(1): 107-113.
doi: 10.11883/1001-1455(2017)01-0107-07
Abstract:
In order to reveal the mechanism of the interference vibration reduction of the short millisecond blasting of a high-precision detonator, on-site measured single-stage blasting vibration signals were selected to study the time frequency characteristics of the superposed signals in different millisecond intervals using the Matlab program. Comprehensively considering the three elements of the blasting vibration, energy reduction ratio and amplitude ratio were defined based on the HHT energy spectrum to study the influence of the segments, explosive charge ratio and vibration velocity proportion on the vibration reduction effect of the short millisecond blasting. The results show that an extremely big explosive charge ratio nearby should be avoided in the design of the millisecond blasting, and it would be better for a segment with a bigger explosive charge to have a posterior ignition. The research also shows that the energy reduction ratio increases with that of the segments in the same millisecond interval; the energy reduction ratio exhibits little obvious increases with that of the segments after the segments increase to a certain degree; the more similar the vibration characteristics of the two signals are to each other, the more evident the energy reduction effect; the energy reduction ratio of the superposed signals with a posterior vibration velocity proportion is more than the other orders.
In order to reveal the mechanism of the interference vibration reduction of the short millisecond blasting of a high-precision detonator, on-site measured single-stage blasting vibration signals were selected to study the time frequency characteristics of the superposed signals in different millisecond intervals using the Matlab program. Comprehensively considering the three elements of the blasting vibration, energy reduction ratio and amplitude ratio were defined based on the HHT energy spectrum to study the influence of the segments, explosive charge ratio and vibration velocity proportion on the vibration reduction effect of the short millisecond blasting. The results show that an extremely big explosive charge ratio nearby should be avoided in the design of the millisecond blasting, and it would be better for a segment with a bigger explosive charge to have a posterior ignition. The research also shows that the energy reduction ratio increases with that of the segments in the same millisecond interval; the energy reduction ratio exhibits little obvious increases with that of the segments after the segments increase to a certain degree; the more similar the vibration characteristics of the two signals are to each other, the more evident the energy reduction effect; the energy reduction ratio of the superposed signals with a posterior vibration velocity proportion is more than the other orders.
2017, 37(1): 114-119.
doi: 10.11883/1001-1455(2017)01-0114-06
Abstract:
Numerical simulation of multi-material flows has been an important issues in CFD, and most CFD production codes used for multi-material flow simulation is of either first or second order accuracy, too inefficient and costly with its grid refinement for high accuracy required problems. In this paper, a high-order, efficient, compact method, called the spectral volume method, was developed for the simulation of the multi-material flow as an extension of the spectral volume method for the conservation laws. It has been pointed out that the conservative spectral volume method for the multi-material flow will cause oscillation, and the reason for this has been analyzed. So the idea of quasi-conservative scheme was borrowed to prevent the spurious oscillations in the vicinity of a material contact discontinuity. Several numerical experiments proved that there is no oscillation near the material interface and the result also demonstrates the accuracy, the efficiency and the high performance of the scheme for the multi-material flow simulation.
Numerical simulation of multi-material flows has been an important issues in CFD, and most CFD production codes used for multi-material flow simulation is of either first or second order accuracy, too inefficient and costly with its grid refinement for high accuracy required problems. In this paper, a high-order, efficient, compact method, called the spectral volume method, was developed for the simulation of the multi-material flow as an extension of the spectral volume method for the conservation laws. It has been pointed out that the conservative spectral volume method for the multi-material flow will cause oscillation, and the reason for this has been analyzed. So the idea of quasi-conservative scheme was borrowed to prevent the spurious oscillations in the vicinity of a material contact discontinuity. Several numerical experiments proved that there is no oscillation near the material interface and the result also demonstrates the accuracy, the efficiency and the high performance of the scheme for the multi-material flow simulation.
2017, 37(1): 120-125.
doi: 10.11883/1001-1455(2017)01-0120-06
Abstract:
In the uniaxial compression, deformation with damage and temperature-rise of two types of plastic-bonded explosives were recorded by means of a high-speed camera and a high-speed infrared radio camera. The results show that the damage evolution and the temperature-rise of the two PBXs are obviously different. As for the PBX with a low content of the binder, the brittleness of the material is characteristically obvious, the strain softening of the stress-strain curve is accompanied with a damage evolution, and the crack formation is due to the failure of the sample, where there existed a local temperature band. As for the PBX with a high content of the binder, the toughness of the material is observed, the strain softening in the stress-strain curve is absent, and the damage is distributed evenly, with a network temperature-rise in the direction of shear.
In the uniaxial compression, deformation with damage and temperature-rise of two types of plastic-bonded explosives were recorded by means of a high-speed camera and a high-speed infrared radio camera. The results show that the damage evolution and the temperature-rise of the two PBXs are obviously different. As for the PBX with a low content of the binder, the brittleness of the material is characteristically obvious, the strain softening of the stress-strain curve is accompanied with a damage evolution, and the crack formation is due to the failure of the sample, where there existed a local temperature band. As for the PBX with a high content of the binder, the toughness of the material is observed, the strain softening in the stress-strain curve is absent, and the damage is distributed evenly, with a network temperature-rise in the direction of shear.
2017, 37(1): 126-133.
doi: 10.11883/1001-1455(2017)01-0126-08
Abstract:
The experiment of the single shot impacting the 316L stainless steel surface was carried out using a surface nano-crystallization testing machine. Three-dimensional morphology of the dimple was observed with a laser scanning confocal microscope, and the dimple's diameter and off-plane displacement in different vibration frequencies were also measured. The in-plane strain around the dimple was measured by moiré interferometry. The effect of the vibration frequency and the way of impacting on the dimple size, the plastic strain size and the plastic strain zone were also analyzed. In comparison with the experimental result, the strain field was simulated using the finite element method, and the distribution of the residual stress around the dimple was also analyzed. The result showed that the crater diameter and the off-plane displacement increases with the increase of the vibration frequency. When the frequency is from 50 to 55 Hz, the crater diameter experiences mutations. When the shot impacts the surface vertically, the greater the vibration frequency, the greater the plastic strain and plastic strain zone, and the plastic strain zone are two times larger than the crater diameter. The plastic strain by the vertical impact is slightly greater than the plastic strain by the oblique impact, but it has little effect on the plastic strain zone. The experimental U field strain is in fairly good agreement with the numerical simulation result, and the maximum error is less than 10%.
The experiment of the single shot impacting the 316L stainless steel surface was carried out using a surface nano-crystallization testing machine. Three-dimensional morphology of the dimple was observed with a laser scanning confocal microscope, and the dimple's diameter and off-plane displacement in different vibration frequencies were also measured. The in-plane strain around the dimple was measured by moiré interferometry. The effect of the vibration frequency and the way of impacting on the dimple size, the plastic strain size and the plastic strain zone were also analyzed. In comparison with the experimental result, the strain field was simulated using the finite element method, and the distribution of the residual stress around the dimple was also analyzed. The result showed that the crater diameter and the off-plane displacement increases with the increase of the vibration frequency. When the frequency is from 50 to 55 Hz, the crater diameter experiences mutations. When the shot impacts the surface vertically, the greater the vibration frequency, the greater the plastic strain and plastic strain zone, and the plastic strain zone are two times larger than the crater diameter. The plastic strain by the vertical impact is slightly greater than the plastic strain by the oblique impact, but it has little effect on the plastic strain zone. The experimental U field strain is in fairly good agreement with the numerical simulation result, and the maximum error is less than 10%.
2017, 37(1): 134-139.
doi: 10.11883/1001-1455(2017)01-0134-06
Abstract:
In this work we performed experimental tests using the dynamic strain test and high speed photography system to study the mechanism of the air-deck slotted charging structure blasting, with four axial air-deck structures adopted. The results show that the highest strain ratio reached 2.1 as the axial decoupling coefficient 1.5, and the corresponding function time of pressure was 9 μs. The best result of directional fracture was achieved. The crack propagation process was recorded by high-speed photography, which show that the propagation speed of the crack was not a constant. The expansion speed of the crack fluctuated with time, and illustrated the phenomenon. Finally, the field tests were performed in the underground tunneling and open slope projects with 1.50 and 1.66 as the axial decoupling coefficient respectively, and with good results achieved.
In this work we performed experimental tests using the dynamic strain test and high speed photography system to study the mechanism of the air-deck slotted charging structure blasting, with four axial air-deck structures adopted. The results show that the highest strain ratio reached 2.1 as the axial decoupling coefficient 1.5, and the corresponding function time of pressure was 9 μs. The best result of directional fracture was achieved. The crack propagation process was recorded by high-speed photography, which show that the propagation speed of the crack was not a constant. The expansion speed of the crack fluctuated with time, and illustrated the phenomenon. Finally, the field tests were performed in the underground tunneling and open slope projects with 1.50 and 1.66 as the axial decoupling coefficient respectively, and with good results achieved.
2017, 37(1): 140-149.
doi: 10.11883/1001-1455(2017)01-0140-10
Abstract:
In this work, by using the ANSYS and LS-DYNA softwares, we established the three-dimensional finite element model of the refuge chamber, the gas/gas and grime and the laneway. The ultimate strength and deformation of the refuge chamber were simulated under the action of three kinds of loads, mainly including the fluid-solid interaction numerical analysis of the real gas/gas and grime explosion effect, the equivalent triangle wave explosion numerical dynamic simulation and the hydrostatic pressure load calculations. Through the above three forms of numerical simulations of loading, we determined the dynamic/static load capacities of the refuge chamber as well as the deformation rules with the given gas/gas and coal dust explosion overpressure variation. The simulation results indicate that the limit overpressure of the refuge chamber under the equivalent triangle wave explosion is bigger than the fluid-solid interaction numerical analysis results, which approaches more closely to the experimental results. If the refuge chamber can meet the demand of transformation under explosion loading, it can also satisfy the transformation requirement under hydrostatic pressure load.
In this work, by using the ANSYS and LS-DYNA softwares, we established the three-dimensional finite element model of the refuge chamber, the gas/gas and grime and the laneway. The ultimate strength and deformation of the refuge chamber were simulated under the action of three kinds of loads, mainly including the fluid-solid interaction numerical analysis of the real gas/gas and grime explosion effect, the equivalent triangle wave explosion numerical dynamic simulation and the hydrostatic pressure load calculations. Through the above three forms of numerical simulations of loading, we determined the dynamic/static load capacities of the refuge chamber as well as the deformation rules with the given gas/gas and coal dust explosion overpressure variation. The simulation results indicate that the limit overpressure of the refuge chamber under the equivalent triangle wave explosion is bigger than the fluid-solid interaction numerical analysis results, which approaches more closely to the experimental results. If the refuge chamber can meet the demand of transformation under explosion loading, it can also satisfy the transformation requirement under hydrostatic pressure load.
2017, 37(1): 150-156.
doi: 10.11883/1001-1455(2017)01-0150-07
Abstract:
Adiabatic shear band (ASB) is a typical failure mode of material during high speed deformation. In order to better understand its formation and expansion process, two-dimensional numerical simulation with the Johnson-Cook constitutive model was conducted to reveal shear behaviors of hat-shaped high manganese steel specimens under high-speed impact using the ANSYS/LS-DYNA software. The results show that across the shear band, the strain distributions are the highest in the shear zone center, and are then gradually reduced to the sides, which is similar to a Gaussian distribution, and in the direction parallel to the shear zone, its distributions are characterized by that they are high at both ends and low in the middle. The formation and propagation direction of ASB are determined according to the simulated strain distributions. It is observed that ASBs are formed from both ends of the shear zone and extend to the middle of the samples. Finally, the temperature distributions inside and outside the ASB interior and exterior are obtained directly by editing the k file of the software and they are similar to those of the strain. Simulation and experimental results are shown in good agreement.
Adiabatic shear band (ASB) is a typical failure mode of material during high speed deformation. In order to better understand its formation and expansion process, two-dimensional numerical simulation with the Johnson-Cook constitutive model was conducted to reveal shear behaviors of hat-shaped high manganese steel specimens under high-speed impact using the ANSYS/LS-DYNA software. The results show that across the shear band, the strain distributions are the highest in the shear zone center, and are then gradually reduced to the sides, which is similar to a Gaussian distribution, and in the direction parallel to the shear zone, its distributions are characterized by that they are high at both ends and low in the middle. The formation and propagation direction of ASB are determined according to the simulated strain distributions. It is observed that ASBs are formed from both ends of the shear zone and extend to the middle of the samples. Finally, the temperature distributions inside and outside the ASB interior and exterior are obtained directly by editing the k file of the software and they are similar to those of the strain. Simulation and experimental results are shown in good agreement.
2017, 37(1): 157-161.
doi: 10.11883/1001-1455(2017)01-0157-05
Abstract:
In the present work, the parameters of shock wave and secondary pressure wave with different aluminum powder content and particle size of CL-20-based aluminized explosives were measured by underwater explosion testing, the shock wave energy and bubble energy were calculated, and the explosion reaction mechanism of CL-20-based aluminized explosives was analyzed. The results show that the shock wave energy and the bubble energy of the underwater explosion represent the energy distribution in the early detonation period and the secondary reaction period, with only a minor portion of the aluminum powder participating in the early detonation period. The secondary pressure wave formed by the bubble pulsation can describe the effect of the aluminum and detonation products on the secondary reaction. The amount of the aluminum content has a significant influence on the process of the secondary reaction and, while the aluminum particle size has little effect on the initial shock wave parameters, shock wave energy and bubble energy, its effect is great on the secondary reaction rate of the aluminum power and detonation products.
In the present work, the parameters of shock wave and secondary pressure wave with different aluminum powder content and particle size of CL-20-based aluminized explosives were measured by underwater explosion testing, the shock wave energy and bubble energy were calculated, and the explosion reaction mechanism of CL-20-based aluminized explosives was analyzed. The results show that the shock wave energy and the bubble energy of the underwater explosion represent the energy distribution in the early detonation period and the secondary reaction period, with only a minor portion of the aluminum powder participating in the early detonation period. The secondary pressure wave formed by the bubble pulsation can describe the effect of the aluminum and detonation products on the secondary reaction. The amount of the aluminum content has a significant influence on the process of the secondary reaction and, while the aluminum particle size has little effect on the initial shock wave parameters, shock wave energy and bubble energy, its effect is great on the secondary reaction rate of the aluminum power and detonation products.
2017, 37(1): 162-168.
doi: 10.11883/1001-1455(2017)01-0162-07
Abstract:
Using the digital-laser dynamic caustic system, the impact tests of the three-point bending beam were performed to investigate the interaction mechanism between a pre-existing crack defect with different angles and a running crack. The experimental results show that the secondary cracks were initiated at the tips of the middle pre-existing cracks under impact loading; the secondary cracks at the tip of the pre-existing cracks would not initiate until they have accumulated more energy in 0-10 μs; both the peak value of the dynamic stress intensity factor of the main cracks and the secondary cracks would rise with the increase of the pre-existing cracks angle in the central part of the specimen.
Using the digital-laser dynamic caustic system, the impact tests of the three-point bending beam were performed to investigate the interaction mechanism between a pre-existing crack defect with different angles and a running crack. The experimental results show that the secondary cracks were initiated at the tips of the middle pre-existing cracks under impact loading; the secondary cracks at the tip of the pre-existing cracks would not initiate until they have accumulated more energy in 0-10 μs; both the peak value of the dynamic stress intensity factor of the main cracks and the secondary cracks would rise with the increase of the pre-existing cracks angle in the central part of the specimen.
