The internal and external flow fields during vented explosions of methane were characterized through numerical simulation,and the capability of numerical simulation thereof was validated by previous experimental data ...The internal and external flow fields during vented explosions of methane were characterized through numerical simulation,and the capability of numerical simulation thereof was validated by previous experimental data at three ignition positions.The venting mechanism was revealed by the simulated concentration distribution,temperature profile,and airflow velocity.The results show rear ignition results in the external methane mass distribution taking the form of"mushroom"and columnar flames in the external space,which can be expressed as a third-order polynomial relationship with distance;central ignition forms a relationship of the form y=AxB.Front ignition causes the temperature to show a tendency to repeated oscillations(rising,falling,and rising).Central ignition generates the maximum vented airflow velocity(V_(max)=320 m/s)upon vent opening.The results indicate that it is acceptable to apply numerical simulation of methane explosions in practice.展开更多
Based on RNG k-ε turbulence model and sliding grid technique, solid-liquid two-phase three-dimensional(3-D) unsteady turbulence of full passage in slurry pump was simulated by means of Fluent software. The effects of...Based on RNG k-ε turbulence model and sliding grid technique, solid-liquid two-phase three-dimensional(3-D) unsteady turbulence of full passage in slurry pump was simulated by means of Fluent software. The effects of unsteady flow characteristics on solid-liquid two-phase flow and pump performance were researched under design condition. The results show that clocking effect has a significant influence on the flow in pump, and the fluctuation of flow velocity and pressure is obvious, particularly near the volute tongue, at the position of small sections of volute and within diffuser. Clocking effect has a more influence on liquid-phase than on solid-phase, and the wake-jet structure of relative velocity of solid-phase is less obvious than liquid-phase near the volute tongue and the impeller passage outlet. The fluctuation of relative velocity of solid-phase flow is 7.6% smaller than liquid-phase flow at the impeller outlet on circular path. Head and radial forces of the impeller are 8.1% and 85.7% of fluctuation, respectively. The results provide a theoretical basis for further research for turbulence, improving efficient, reducing the hydraulic losses and wear. Finally, field tests were carried out to verify the operation and wear of slurry pump.展开更多
The flowing behavior of liquid slag has an important effect on the heat efficiency, recovery ratio ofvaluable metals and life span of the electric cleaning furnace. The velocity procedure using "κ-ε" model...The flowing behavior of liquid slag has an important effect on the heat efficiency, recovery ratio ofvaluable metals and life span of the electric cleaning furnace. The velocity procedure using "κ-ε" model wasdeveloped under the cylindrical coordinate system. The procedure is used to calculate the velocity field ofmolten slag. The forces acting on molten slag were analyzed. The calculating method of electromagnetic forcewas described. The discrete equations, which were solved by using SIMPLE algorithm, were generated bymeans of interlace grids and control volume. The boundary layers near the solid wall were treated as wallfunction. The velocity distribution is obtained. The results show that the velocity of molten slag varies withdifferent horizontal sections. There are six eddies in the surface layer of molten slag. A large circle is formedin the sections below the electrodes, while the longitudinal section includes two large circles around the electrode. The influences of the features of the velocity field on the operation in the electric cleaning furnace arediscussed in detail.展开更多
We apply the forward modeling algorithm constituted by the convolutional Forsyte polynomial differentiator pro-posed by former worker to seismic wave simulation of complex heterogeneous media and compare the efficienc...We apply the forward modeling algorithm constituted by the convolutional Forsyte polynomial differentiator pro-posed by former worker to seismic wave simulation of complex heterogeneous media and compare the efficiency and accuracy between this method and other seismic simulation methods such as finite difference and pseudospec-tral method. Numerical experiments demonstrate that the algorithm constituted by convolutional Forsyte polyno-mial differentiator has high efficiency and accuracy and needs less computational resources, so it is a numerical modeling method with much potential.展开更多
In recent twenty years, much numerical simulation work has been done on the evolution of Qinghai-Xizang (Tibetan) plateau. In this paper some principal numerical models and results are reviewed and analyzed. The earli...In recent twenty years, much numerical simulation work has been done on the evolution of Qinghai-Xizang (Tibetan) plateau. In this paper some principal numerical models and results are reviewed and analyzed. The earlier plane stress or plane strain model has much discrepancy with the actual deformation of Qinghai-Xizang plateau, such as the thickening of Tibetan crust and the lateral extrusion of Tibet along strike-slip faults. The thin viscous sheet model and the thin-plate model may simulate the change of the crustal thickness and the deformation pro-duced by gravitational force. It is suitable for studying the large-scale and long-time deformation. The influence of faults on the deformation of Tibetan plateau should be further studied.展开更多
Pile foundation is widely used in the offshore engineering. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. The potentials of liquefaction and damages of pile foundation due to ...Pile foundation is widely used in the offshore engineering. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. The potentials of liquefaction and damages of pile foundation due to the liquefaction can be reduced by the implementation of the drainage in the liquefiable foundation. A patented pile technology, named rigidity-drain pile, was introduced. The partial section of the pile body was filled by materials with higher penetrability which forms some effective drainage channels in the pile. The principles and construction methods were presented. 3D models for both rigidity-drain pile and ordinary pile were built in FLAC3D code. The dynamic loadings were applied on the bottom of the model. According to the numerical results, in the case of the rigidity-drain pile, the water in the relevant distance range around the pile flows toward the pile drainage, the contour of the pore pressure shows a funnel form. Contrast to the ordinary pile, the rigidity-drain pile can dissipate the accumulated excess pore water, maintain effective stress and obviously reduce the possibility of surrounding soil liquefaction.展开更多
The present study is devoted to researching the thermal security problems of large-scale solid rocket motor with Ammonium perchlorate/Hydroxyl-terminated polybutadiene(AP/HTPB). A two-dimensional axisymmetric model fo...The present study is devoted to researching the thermal security problems of large-scale solid rocket motor with Ammonium perchlorate/Hydroxyl-terminated polybutadiene(AP/HTPB). A two-dimensional axisymmetric model for the cook-off of solid rocket motor is established. The reaction kinetics for the cook-off process of AP/HTPB is described by the two-step global chemical mechanism. Numerical predictions of the cook-off behavior for the propellant are conducted at fast heating rate of 1.45-2.45 K/s,and slow heating rate of 0.001-0.003 K/s, respectively. The results show that in the fast cook-off condition. the initial ignition position of AP/HTPB occurs in the annular region of the outer wall of propellant without exception, and the center point in the region is(889.1,149.5). For the region, the axial width is1.8 mm and radial thickness is 0.8 mm. However, in the slow cook-off condition, the ignition center position is shifted along the axial direction toward the right end face of the propellant with the increase of heating rate. Therefore, the influence of heating rate on ignition temperature and ignition delay time is nonnegligible within a certain range.展开更多
On the basis of the two dimensional finite element analysis model, the pile foundations' mechanical effect of the rigid pile composite foundation under the dynamic load was researched. Through the research, the de...On the basis of the two dimensional finite element analysis model, the pile foundations' mechanical effect of the rigid pile composite foundation under the dynamic load was researched. Through the research, the development law and deformation property of axial force of pile body, shaft resistance of pile, and cumulative settlement of pile head under vertical cyclic dynamic loads were concluded. Through the comparison and analysis of the test results of dynamic models, the test results of Poulos(1989) and cumulative settlement model of the single pile under cyclic loads were confirmed. Based on the above research, Fortran language was adopted to introduce the soil attenuation factor, the secondary development of relevant modules of ABAQUS was carried out, and the effect of soil attenuation factor on dynamic property of pile-soil was discussed further.展开更多
Based on the engineering background of a soft rock roadway in Qinan Coal Mine 82 Area,Huaibei Mining Group,three creep models with different support patterns in soft rock roadway were established by using geotechnical...Based on the engineering background of a soft rock roadway in Qinan Coal Mine 82 Area,Huaibei Mining Group,three creep models with different support patterns in soft rock roadway were established by using geotechnical software of FLAC2D.According to the calculation results of different models,the change law of mechanical properties with the time of bolt-grouting support structure was obtained.Furthermore,for the test bolt-grouting support roadway,the deformation law of surrounding rock got by underground industrial experiment and field observation accords with the creep law got by numerical calculation.The results of numerical calculation and field observation show that,compared with other supports,the creep of bolt-grouting support roadway enters the steady-state creep stage from tertiary creep stage ahead,the deformations of roof,floor and two sides are decreased greatly,the plastically deforming area in surrounding rock is reduced obviously,and the distribution ranges of maximum and minimum principal stress are shrank obviously.All those fully show that the bolt-grouting support has its remarkable advantages in controlling surrounding rock creep and improving the whole strength of surrounding rock and self-bearing capacity.展开更多
Design of forming dies and whole process of simulation of cold rolling involutes spline can be realized by using of CAD software of PRO-E and CAE software of DEFORM-3D. Software DEFORM-3D provides an automatic and opt...Design of forming dies and whole process of simulation of cold rolling involutes spline can be realized by using of CAD software of PRO-E and CAE software of DEFORM-3D. Software DEFORM-3D provides an automatic and optimized remeshing function, especially for the large deformation. In order to use this function sufficiently, simulation of cold rolling involutes spline can be implemented indirectly. The relationship between die and workpiece, forming force and characteristic of deformation in the forming process of cold rolling involutes spline are analyzed and researched. Meanwhile, reliable proofs for the design of dies and deforming equipment are provided.展开更多
Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model a...Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model and the SIMPLE method were chosen to simulate the present model;the first order upwind difference scheme was utilized to perform a discrete solution for momentum equation.The distributing law of the velocity,pressure,turbulent kinetic energy of every section along the flow direction of air-bubble generator was analyzed.The results indicate that the bubbles are heavily broken up in the middle cross section of throat sect and the entrance of diffuser sect along the flow direction,and the turbulent kinetic energy of diffuser sect is larger than the entrance of throat sect and mixing chamber.展开更多
In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step ...In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step for the dynamic response simulation of rock mass in a high in-situ stress field.In this paper,stress initialization methods,including their principles and operating procedures for reproducing steady in-situ stress state in LS-DYNA,are first introduced.Then the most popular four methods,i.e.,explicit dynamic relaxation(DR)method,implicit-explicit sequence method,Dynain file method and quasi-static method,are exemplified through a case analysis by using the RHT and plastic hardening rock material models to simulate rock blasting under in-situ stress condition.Based on the simulations,it is concluded that the stress initialization results obtained by implicit-explicit sequence method and dynain file method are closely related to the rock material model,and the explicit DR method has an obvious advantage in solution time when compared to other methods.Besides that,it is recommended to adopt two separate analyses for the whole numerical simulation of rock mass under the combined action of in-situ stress and dynamic disturbance.展开更多
High temperature air combustion (HTAC) is an attractive technology of saving energy and controlling environment. The mathematical models of turbulent jet flame under the highly preheated air combustion condition are c...High temperature air combustion (HTAC) is an attractive technology of saving energy and controlling environment. The mathematical models of turbulent jet flame under the highly preheated air combustion condition are conducted in the paper. The mixture fraction/probability density function model is employed. The results show that the maximum flame temperature is decreased, the temperature in the HTAC furnace is more uniform than that in the conventional furnace, and the NO x emission is low. The numerical results are partially validated by some experimental measurements.展开更多
The design of solid armature of railgun should take full account of its operating conditions and material properties because the armature is subjected to dynamic loading conditions and experiences a complicated electr...The design of solid armature of railgun should take full account of its operating conditions and material properties because the armature is subjected to dynamic loading conditions and experiences a complicated electrical,thermal and mechanical process in the interior ballistic cycle.In this paper present,we first introduced a multi-physical field model of railgun,followed by several examples to investigate the launching process.Especially,we used the explicit finite element method,in which material nonlinearity and geometric nonlinearity were accounted,to investigate the deform behaviors of solid armature.The results show that the dynamic mechanical process of armature is dependent on the armature geometry,material and exciting electric current.By the numerical simulation,the understanding of the fracture mechanism of solid armature was deepened.展开更多
Rockbursts were frequently encountered in the construction of deeply buried tunnels at the Jinping-II hydropower station, Southwest China. In those cases, the existence of large structural planes, such as faults, was ...Rockbursts were frequently encountered in the construction of deeply buried tunnels at the Jinping-II hydropower station, Southwest China. In those cases, the existence of large structural planes, such as faults, was usually observed near the excavation boundaries. The formation mechanism of the “11·28” rockburst, which was a typical rockburst and occurred in a drainage tunnel under a deep burial depth, high in-situ stress state and complex geological conditions, has been difficult to explain. Realistic failure process analysis(RFPA3D) software was adopted to numerically simulate the whole failure process of the surrounding rock mass around the tunnel subjected to excavation. The spatial distribution of acoustic emission derived from numerical simulation contributed to explaining the mechanical responses of the process. Analyses of the stress, safety reserve coefficient and damage degree were performed to reveal the effect of faults on the formation of rockbursts in the deep tunnel. The existence of faults results in the formation of stress anomaly areas between the tunnel and the fault. The surrounding rock mass failure propagates toward the fault from the initial failure, to different degrees. The relative positions and angles of faults play significant roles in the extent and development of surrounding rock mass failure, respectively. The increase in the lateral stress coefficient leads to the aggravation of the surrounding rock mass damage, especially in the roof and floor of the tunnel. Moreover, as the rock strength-stress ratio increases, the failure mode of the near-fault tunnel gradually changes from the stress-controlled type to the compound-controlled type. These findings were consistent with the microseismic monitoring results and field observations, which was helpful to understand the mechanical behavior of tunnel excavation affected by faults. The achievements of this study can provide some references for analysis of the failure mechanisms of similar deep tunnels.展开更多
High-speed train running in the sand environment is different from the general environment. In the former situation, there will be sand load applied on high-speed train(SLAHT) caused by sand particles hitting train su...High-speed train running in the sand environment is different from the general environment. In the former situation, there will be sand load applied on high-speed train(SLAHT) caused by sand particles hitting train surface. This will have a great impact on the train stability, running drag and surface corrosion. Numerical simulation method of SLAHT in sand environment is studied. The velocity and mass flow rate models of saltation and suspension sand particles and the calculation model of SLAHT caused by sand particles hitting train surface are established. The discrete phase method is adopted for numerical simulating the process of saltation and suspension sand particles moving to train surface and generating sand load. By comparison with the field tests, the numerical simulation reliability is analysed. The theoretical formula of SLAHT changing with cross-wind and train speed is proposed. SLAHT changing law is analyzed. Research results indicate that SLAHT changing with cross-wind and train speed is a quadratic relationship. When train speed is constant, SLAHT increases quadratically with cross-wind speed improvement. When cross-wind speed is constant, SLAHT increases quadratically with train speed improvement.展开更多
The numerical simulation of a blast wave of a multilayer composite charge is investigated.A calculation model of the near-field explosion and far-field propagation of the shock wave of a composite charge is establishe...The numerical simulation of a blast wave of a multilayer composite charge is investigated.A calculation model of the near-field explosion and far-field propagation of the shock wave of a composite charge is established using the AUTODYN finite element program.Results of the near-field and far-field calculations of the shock wave respectively converge at cell sizes of 0.25-0.5 cm and 1-3 cm.The Euler--fluxcorrected transport solver is found to be suitable for the far-field calculation after mapping.A numerical simulation is conducted to study the formation,propagation,and interaction of the shock wave of the composite charge for different initiation modes.It is found that the initiation mode obviously affects the shock-wave waveform and pressure distribution of the composite charge.Additionally,it is found that the area of the overpressure distribution is greatest for internal and external simultaneous initiation,and the peak pressure of the shock wave exponentially decays,fitting the calculation formula of the peak overpressure attenuation under different initiation modes,which is obtained and verified by experiment.The difference between numerical and experimental results is less than 10%,and the peak overpressure of both internal and external initiation is 56.12% higher than that of central single-point initiation.展开更多
In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading ef...In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading effect of roof vibration on roadway surrounding rocks as well as the impact on stability. The results show that, on one hand, hard-thick roof will result in high stress concentration on mining surrounding rocks; on the other hand, the breaking of hard-thick roof will lead to mining seismicity, causing dynamic loading effect on coal and rock mass. High stress concentration and dynamic loading combination reaches to the mechanical conditions for the occurrence of rock burst, which will induce rock burst. The mining induced seismic events occurring in the roof breaking act on the mining surrounding rocks in the form of stress wave. The stress wave then has a reflection on the free surface of roadway and the tensile stress will be generated around the free surface. Horizontal vibration of roadway surrounding particles will cause instant changes of horizontal stress of roadway surrounding rocks; the horizontal displacement is directly related to the horizontal stress but is not significantly correlated with the vertical stress; the increase of horizontal stress of roadway near surface surrounding rocks and the release of elastic deformation energy of deep surrounding coal and rock mass are immanent causes that lead to the impact instability of roadway surrounding rocks. The most significant measures for rock burst prevention are controlling of horizontal stress and vibration strength.Key words展开更多
The calculation model was established by k-ε turbulence stress which reflects the change of indoor gas leak's volume fraction,and the CFD software was used to numerically simulate the volume fraction of gas after...The calculation model was established by k-ε turbulence stress which reflects the change of indoor gas leak's volume fraction,and the CFD software was used to numerically simulate the volume fraction of gas after the gas of continuity leakage,at the same time the changes of gas leak were studied. The results show that the process of gas leakage is different with the change of conditions of indoor and outdoor. Because of the different influencing factors,when the gas leak reaches a certain stable value,the volume fraction,velocity and the explosion of regional are different in the same state indoor. In some regions the gas will explode which meets the fire even if the mean volume fraction of the gas cannot achieve the explosion limit.展开更多
In order to control the dust pollution produced by air leg rock drill in the trolley area during the excavation of long-distance single ended tunnel,the full-scale physical model of working face was established by usi...In order to control the dust pollution produced by air leg rock drill in the trolley area during the excavation of long-distance single ended tunnel,the full-scale physical model of working face was established by using FLUENT software,and the numerical simulation analysis of tunnel drilling ventilation and dust removal parameters was carried out.The results show that it is difficult to control the dust pollution of the face by conventional ventilation,and the drilling dust is distributed in the range of 10 m from the face;after the introduction of the long pressure and short suction ventilation scheme,when the ratio of compressed air volume to exhaust air volume is 0.72,the height of the pressure fan is 2.5 m,the distance between the pressure fan and the palm face is 20 m,and the exhaust fan is 12 m away from the palm,the dust concentration control efficiency of the working face is increased by about 60%.Therefore,in the similar long-distance single head tunnel construction,it is appropriate to adopt the dust removal method of long-distance short suction and exhaust fan to ensure the working environment.展开更多
基金supported by the Young Scientists Fund of National Natural Science Foundation of China(Grant Nos.12202202 and 12202494)the National Key Research and Development Program of China(Grant No.2021YFC3100700)。
文摘The internal and external flow fields during vented explosions of methane were characterized through numerical simulation,and the capability of numerical simulation thereof was validated by previous experimental data at three ignition positions.The venting mechanism was revealed by the simulated concentration distribution,temperature profile,and airflow velocity.The results show rear ignition results in the external methane mass distribution taking the form of"mushroom"and columnar flames in the external space,which can be expressed as a third-order polynomial relationship with distance;central ignition forms a relationship of the form y=AxB.Front ignition causes the temperature to show a tendency to repeated oscillations(rising,falling,and rising).Central ignition generates the maximum vented airflow velocity(V_(max)=320 m/s)upon vent opening.The results indicate that it is acceptable to apply numerical simulation of methane explosions in practice.
基金Project(51375498)supported by the National Natural Science Foundation of China
文摘Based on RNG k-ε turbulence model and sliding grid technique, solid-liquid two-phase three-dimensional(3-D) unsteady turbulence of full passage in slurry pump was simulated by means of Fluent software. The effects of unsteady flow characteristics on solid-liquid two-phase flow and pump performance were researched under design condition. The results show that clocking effect has a significant influence on the flow in pump, and the fluctuation of flow velocity and pressure is obvious, particularly near the volute tongue, at the position of small sections of volute and within diffuser. Clocking effect has a more influence on liquid-phase than on solid-phase, and the wake-jet structure of relative velocity of solid-phase is less obvious than liquid-phase near the volute tongue and the impeller passage outlet. The fluctuation of relative velocity of solid-phase flow is 7.6% smaller than liquid-phase flow at the impeller outlet on circular path. Head and radial forces of the impeller are 8.1% and 85.7% of fluctuation, respectively. The results provide a theoretical basis for further research for turbulence, improving efficient, reducing the hydraulic losses and wear. Finally, field tests were carried out to verify the operation and wear of slurry pump.
文摘The flowing behavior of liquid slag has an important effect on the heat efficiency, recovery ratio ofvaluable metals and life span of the electric cleaning furnace. The velocity procedure using "κ-ε" model wasdeveloped under the cylindrical coordinate system. The procedure is used to calculate the velocity field ofmolten slag. The forces acting on molten slag were analyzed. The calculating method of electromagnetic forcewas described. The discrete equations, which were solved by using SIMPLE algorithm, were generated bymeans of interlace grids and control volume. The boundary layers near the solid wall were treated as wallfunction. The velocity distribution is obtained. The results show that the velocity of molten slag varies withdifferent horizontal sections. There are six eddies in the surface layer of molten slag. A large circle is formedin the sections below the electrodes, while the longitudinal section includes two large circles around the electrode. The influences of the features of the velocity field on the operation in the electric cleaning furnace arediscussed in detail.
基金Open Fund of State Key Laboratory of Geological Processes and Mineral Resources, China University of Geo-sciences (GPMR0750)National Natural Science Foundation of China (40437018)
文摘We apply the forward modeling algorithm constituted by the convolutional Forsyte polynomial differentiator pro-posed by former worker to seismic wave simulation of complex heterogeneous media and compare the efficiency and accuracy between this method and other seismic simulation methods such as finite difference and pseudospec-tral method. Numerical experiments demonstrate that the algorithm constituted by convolutional Forsyte polyno-mial differentiator has high efficiency and accuracy and needs less computational resources, so it is a numerical modeling method with much potential.
文摘In recent twenty years, much numerical simulation work has been done on the evolution of Qinghai-Xizang (Tibetan) plateau. In this paper some principal numerical models and results are reviewed and analyzed. The earlier plane stress or plane strain model has much discrepancy with the actual deformation of Qinghai-Xizang plateau, such as the thickening of Tibetan crust and the lateral extrusion of Tibet along strike-slip faults. The thin viscous sheet model and the thin-plate model may simulate the change of the crustal thickness and the deformation pro-duced by gravitational force. It is suitable for studying the large-scale and long-time deformation. The influence of faults on the deformation of Tibetan plateau should be further studied.
基金Project (50639010) supported by the National Natural Science Foundation of China
文摘Pile foundation is widely used in the offshore engineering. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. The potentials of liquefaction and damages of pile foundation due to the liquefaction can be reduced by the implementation of the drainage in the liquefiable foundation. A patented pile technology, named rigidity-drain pile, was introduced. The partial section of the pile body was filled by materials with higher penetrability which forms some effective drainage channels in the pile. The principles and construction methods were presented. 3D models for both rigidity-drain pile and ordinary pile were built in FLAC3D code. The dynamic loadings were applied on the bottom of the model. According to the numerical results, in the case of the rigidity-drain pile, the water in the relevant distance range around the pile flows toward the pile drainage, the contour of the pore pressure shows a funnel form. Contrast to the ordinary pile, the rigidity-drain pile can dissipate the accumulated excess pore water, maintain effective stress and obviously reduce the possibility of surrounding soil liquefaction.
文摘The present study is devoted to researching the thermal security problems of large-scale solid rocket motor with Ammonium perchlorate/Hydroxyl-terminated polybutadiene(AP/HTPB). A two-dimensional axisymmetric model for the cook-off of solid rocket motor is established. The reaction kinetics for the cook-off process of AP/HTPB is described by the two-step global chemical mechanism. Numerical predictions of the cook-off behavior for the propellant are conducted at fast heating rate of 1.45-2.45 K/s,and slow heating rate of 0.001-0.003 K/s, respectively. The results show that in the fast cook-off condition. the initial ignition position of AP/HTPB occurs in the annular region of the outer wall of propellant without exception, and the center point in the region is(889.1,149.5). For the region, the axial width is1.8 mm and radial thickness is 0.8 mm. However, in the slow cook-off condition, the ignition center position is shifted along the axial direction toward the right end face of the propellant with the increase of heating rate. Therefore, the influence of heating rate on ignition temperature and ignition delay time is nonnegligible within a certain range.
基金Projects(51478178,51508181) supported by the National Natural Science Foundation of China
文摘On the basis of the two dimensional finite element analysis model, the pile foundations' mechanical effect of the rigid pile composite foundation under the dynamic load was researched. Through the research, the development law and deformation property of axial force of pile body, shaft resistance of pile, and cumulative settlement of pile head under vertical cyclic dynamic loads were concluded. Through the comparison and analysis of the test results of dynamic models, the test results of Poulos(1989) and cumulative settlement model of the single pile under cyclic loads were confirmed. Based on the above research, Fortran language was adopted to introduce the soil attenuation factor, the secondary development of relevant modules of ABAQUS was carried out, and the effect of soil attenuation factor on dynamic property of pile-soil was discussed further.
基金Project(106084) supported by the Scientific and Technological Research of the Ministry of EducationProject(BK2007701) supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(2006CB2022010) supported by the National Basic Research Program of China and the Qing-lan Project of Jiangsu Province,China
文摘Based on the engineering background of a soft rock roadway in Qinan Coal Mine 82 Area,Huaibei Mining Group,three creep models with different support patterns in soft rock roadway were established by using geotechnical software of FLAC2D.According to the calculation results of different models,the change law of mechanical properties with the time of bolt-grouting support structure was obtained.Furthermore,for the test bolt-grouting support roadway,the deformation law of surrounding rock got by underground industrial experiment and field observation accords with the creep law got by numerical calculation.The results of numerical calculation and field observation show that,compared with other supports,the creep of bolt-grouting support roadway enters the steady-state creep stage from tertiary creep stage ahead,the deformations of roof,floor and two sides are decreased greatly,the plastically deforming area in surrounding rock is reduced obviously,and the distribution ranges of maximum and minimum principal stress are shrank obviously.All those fully show that the bolt-grouting support has its remarkable advantages in controlling surrounding rock creep and improving the whole strength of surrounding rock and self-bearing capacity.
文摘Design of forming dies and whole process of simulation of cold rolling involutes spline can be realized by using of CAD software of PRO-E and CAE software of DEFORM-3D. Software DEFORM-3D provides an automatic and optimized remeshing function, especially for the large deformation. In order to use this function sufficiently, simulation of cold rolling involutes spline can be implemented indirectly. The relationship between die and workpiece, forming force and characteristic of deformation in the forming process of cold rolling involutes spline are analyzed and researched. Meanwhile, reliable proofs for the design of dies and deforming equipment are provided.
基金Project supported by the Scientific Research Foundation of Hebei University of Technology of China
文摘Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model and the SIMPLE method were chosen to simulate the present model;the first order upwind difference scheme was utilized to perform a discrete solution for momentum equation.The distributing law of the velocity,pressure,turbulent kinetic energy of every section along the flow direction of air-bubble generator was analyzed.The results indicate that the bubbles are heavily broken up in the middle cross section of throat sect and the entrance of diffuser sect along the flow direction,and the turbulent kinetic energy of diffuser sect is larger than the entrance of throat sect and mixing chamber.
基金Project(41630642)supported by the Key Project of National Natural Science Foundation of ChinaProject(51974360)supported by the National Natural Science Foundation of ChinaProject(2018JJ3656)supported by the Natural Science Foundation of Hunan Province,China。
文摘In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step for the dynamic response simulation of rock mass in a high in-situ stress field.In this paper,stress initialization methods,including their principles and operating procedures for reproducing steady in-situ stress state in LS-DYNA,are first introduced.Then the most popular four methods,i.e.,explicit dynamic relaxation(DR)method,implicit-explicit sequence method,Dynain file method and quasi-static method,are exemplified through a case analysis by using the RHT and plastic hardening rock material models to simulate rock blasting under in-situ stress condition.Based on the simulations,it is concluded that the stress initialization results obtained by implicit-explicit sequence method and dynain file method are closely related to the rock material model,and the explicit DR method has an obvious advantage in solution time when compared to other methods.Besides that,it is recommended to adopt two separate analyses for the whole numerical simulation of rock mass under the combined action of in-situ stress and dynamic disturbance.
文摘High temperature air combustion (HTAC) is an attractive technology of saving energy and controlling environment. The mathematical models of turbulent jet flame under the highly preheated air combustion condition are conducted in the paper. The mixture fraction/probability density function model is employed. The results show that the maximum flame temperature is decreased, the temperature in the HTAC furnace is more uniform than that in the conventional furnace, and the NO x emission is low. The numerical results are partially validated by some experimental measurements.
文摘The design of solid armature of railgun should take full account of its operating conditions and material properties because the armature is subjected to dynamic loading conditions and experiences a complicated electrical,thermal and mechanical process in the interior ballistic cycle.In this paper present,we first introduced a multi-physical field model of railgun,followed by several examples to investigate the launching process.Especially,we used the explicit finite element method,in which material nonlinearity and geometric nonlinearity were accounted,to investigate the deform behaviors of solid armature.The results show that the dynamic mechanical process of armature is dependent on the armature geometry,material and exciting electric current.By the numerical simulation,the understanding of the fracture mechanism of solid armature was deepened.
基金Project(42177143) supported by the National Natural Science Foundation of ChinaProject(2020JDJQ0011) supported by the Science Foundation for Distinguished Young Scholars of Sichuan Province,China。
文摘Rockbursts were frequently encountered in the construction of deeply buried tunnels at the Jinping-II hydropower station, Southwest China. In those cases, the existence of large structural planes, such as faults, was usually observed near the excavation boundaries. The formation mechanism of the “11·28” rockburst, which was a typical rockburst and occurred in a drainage tunnel under a deep burial depth, high in-situ stress state and complex geological conditions, has been difficult to explain. Realistic failure process analysis(RFPA3D) software was adopted to numerically simulate the whole failure process of the surrounding rock mass around the tunnel subjected to excavation. The spatial distribution of acoustic emission derived from numerical simulation contributed to explaining the mechanical responses of the process. Analyses of the stress, safety reserve coefficient and damage degree were performed to reveal the effect of faults on the formation of rockbursts in the deep tunnel. The existence of faults results in the formation of stress anomaly areas between the tunnel and the fault. The surrounding rock mass failure propagates toward the fault from the initial failure, to different degrees. The relative positions and angles of faults play significant roles in the extent and development of surrounding rock mass failure, respectively. The increase in the lateral stress coefficient leads to the aggravation of the surrounding rock mass damage, especially in the roof and floor of the tunnel. Moreover, as the rock strength-stress ratio increases, the failure mode of the near-fault tunnel gradually changes from the stress-controlled type to the compound-controlled type. These findings were consistent with the microseismic monitoring results and field observations, which was helpful to understand the mechanical behavior of tunnel excavation affected by faults. The achievements of this study can provide some references for analysis of the failure mechanisms of similar deep tunnels.
文摘High-speed train running in the sand environment is different from the general environment. In the former situation, there will be sand load applied on high-speed train(SLAHT) caused by sand particles hitting train surface. This will have a great impact on the train stability, running drag and surface corrosion. Numerical simulation method of SLAHT in sand environment is studied. The velocity and mass flow rate models of saltation and suspension sand particles and the calculation model of SLAHT caused by sand particles hitting train surface are established. The discrete phase method is adopted for numerical simulating the process of saltation and suspension sand particles moving to train surface and generating sand load. By comparison with the field tests, the numerical simulation reliability is analysed. The theoretical formula of SLAHT changing with cross-wind and train speed is proposed. SLAHT changing law is analyzed. Research results indicate that SLAHT changing with cross-wind and train speed is a quadratic relationship. When train speed is constant, SLAHT increases quadratically with cross-wind speed improvement. When cross-wind speed is constant, SLAHT increases quadratically with train speed improvement.
基金funded by the National Natural Science Foundation of China under NO.11202103Qing-lan Project of Jiangsu Province。
文摘The numerical simulation of a blast wave of a multilayer composite charge is investigated.A calculation model of the near-field explosion and far-field propagation of the shock wave of a composite charge is established using the AUTODYN finite element program.Results of the near-field and far-field calculations of the shock wave respectively converge at cell sizes of 0.25-0.5 cm and 1-3 cm.The Euler--fluxcorrected transport solver is found to be suitable for the far-field calculation after mapping.A numerical simulation is conducted to study the formation,propagation,and interaction of the shock wave of the composite charge for different initiation modes.It is found that the initiation mode obviously affects the shock-wave waveform and pressure distribution of the composite charge.Additionally,it is found that the area of the overpressure distribution is greatest for internal and external simultaneous initiation,and the peak pressure of the shock wave exponentially decays,fitting the calculation formula of the peak overpressure attenuation under different initiation modes,which is obtained and verified by experiment.The difference between numerical and experimental results is less than 10%,and the peak overpressure of both internal and external initiation is 56.12% higher than that of central single-point initiation.
基金Project(51404243)supported by the National Natural Science Foundation of ChinaProject(2014QNB26)supported by the Fundamental Research Funds for the Central Universities,China
文摘In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading effect of roof vibration on roadway surrounding rocks as well as the impact on stability. The results show that, on one hand, hard-thick roof will result in high stress concentration on mining surrounding rocks; on the other hand, the breaking of hard-thick roof will lead to mining seismicity, causing dynamic loading effect on coal and rock mass. High stress concentration and dynamic loading combination reaches to the mechanical conditions for the occurrence of rock burst, which will induce rock burst. The mining induced seismic events occurring in the roof breaking act on the mining surrounding rocks in the form of stress wave. The stress wave then has a reflection on the free surface of roadway and the tensile stress will be generated around the free surface. Horizontal vibration of roadway surrounding particles will cause instant changes of horizontal stress of roadway surrounding rocks; the horizontal displacement is directly related to the horizontal stress but is not significantly correlated with the vertical stress; the increase of horizontal stress of roadway near surface surrounding rocks and the release of elastic deformation energy of deep surrounding coal and rock mass are immanent causes that lead to the impact instability of roadway surrounding rocks. The most significant measures for rock burst prevention are controlling of horizontal stress and vibration strength.Key words
基金Projects(50704041, 50838009, 50678179) supported by the National Natural Science Foundation of ChinaProjects(2006BAJ02A09, 2006BAJ02A13-4) supported by the National Key Technologies R & D Program of China+1 种基金Project(CSTC2008BB6347) supported by the Natural Science Foundation Project of ChongqingProject(20080430752) supported by the Postdoctoral Science Foundation of China
文摘The calculation model was established by k-ε turbulence stress which reflects the change of indoor gas leak's volume fraction,and the CFD software was used to numerically simulate the volume fraction of gas after the gas of continuity leakage,at the same time the changes of gas leak were studied. The results show that the process of gas leakage is different with the change of conditions of indoor and outdoor. Because of the different influencing factors,when the gas leak reaches a certain stable value,the volume fraction,velocity and the explosion of regional are different in the same state indoor. In some regions the gas will explode which meets the fire even if the mean volume fraction of the gas cannot achieve the explosion limit.
基金Project(51874016)supported by the National Natural Science Foundation of China。
文摘In order to control the dust pollution produced by air leg rock drill in the trolley area during the excavation of long-distance single ended tunnel,the full-scale physical model of working face was established by using FLUENT software,and the numerical simulation analysis of tunnel drilling ventilation and dust removal parameters was carried out.The results show that it is difficult to control the dust pollution of the face by conventional ventilation,and the drilling dust is distributed in the range of 10 m from the face;after the introduction of the long pressure and short suction ventilation scheme,when the ratio of compressed air volume to exhaust air volume is 0.72,the height of the pressure fan is 2.5 m,the distance between the pressure fan and the palm face is 20 m,and the exhaust fan is 12 m away from the palm,the dust concentration control efficiency of the working face is increased by about 60%.Therefore,in the similar long-distance single head tunnel construction,it is appropriate to adopt the dust removal method of long-distance short suction and exhaust fan to ensure the working environment.
