Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an...Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3~. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.展开更多
The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In th...The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.展开更多
Wind barriers have attracted significant attention as an effective measure to ensure train safety under crosswinds.However,in past decades,the influence of structural parameters such as the height and ventilation rati...Wind barriers have attracted significant attention as an effective measure to ensure train safety under crosswinds.However,in past decades,the influence of structural parameters such as the height and ventilation ratio of wind barriers on the difference of the average pressure coefficient between the train windward and leeward surface(ΔCp)has not been fully investigated.To determine the influence of the interaction among the three factors,namely the wind barrier height(H),ventilation ratio(R),and distance to the train(D),twenty five numerical simulation cases with different structural parameters were considered based on an orthogonal design.The shear stress transfer(SST)k-ωturbulent model was employed to calculate the wind pressure coefficients,and the calculation accuracy was validated by using wind tunnel experiments.The results indicated that with an increase in R,ΔCp first decreased and then increased,andΔCp decreased while D increased.Moreover,with the increase in H,ΔCp first increased and then decreased.Therefore,these three factors must be considered during the installation of wind barriers.Furthermore,according to a range analysis(judging the relative importance of the three factors intuitively),the three factors were ranked in the following order:R>H>D.Based on a variance analysis,R was found to be of high significance toΔCp,followed by H,which was significant,whereas D had relatively insignificant influence.Finally,the optimal values of R and H were determined to be 20%and 110 mm,respectively.And when R=40%,H=85 mm,the train was relatively unsafe under these such conditions.The findings of this study provide significant guidance for the structural design of wind barriers.展开更多
As computer simulation increasingly supports engine er ing design and manufacture, the requirement for a computer software environment providing an integration platform for computational engineering software increas e...As computer simulation increasingly supports engine er ing design and manufacture, the requirement for a computer software environment providing an integration platform for computational engineering software increas es. A key component of an integrated environment is the use of computational eng ineering to assist and support solutions for complex design. Computer methods fo r structural, flow and thermal analysis are well developed and have been used in design for many years. Many software packages are now available which provi de an advanced capability. However, they are not designed for modelling of powde r forming processes. This paper describes the powder compaction software (PCS_SU T), which is designed for pre- and post-processing for computational simulatio n of the process compaction of powder. In the PCS_SUT software, the adaptive analysis of transient metal powder forming process is simulated by the finite element method based on deformation theories . The error estimates and adaptive remeshing schemes are applied for updated co -ordinate analysis. A generalized Newmark scheme is used for the time domain di scretization and the final nonlinear equations are solved by a Newton-Raphson p rocedure. An incremental elasto-plastic material model is used to simulate the compaction process. To describe the constitutive model of nonlinear behaviour of powder materials, a combination of Mohr-Coulomb and elliptical yield cap model is applied. This model reflects the yielding, frictional and densification char acteristics of powder along with strain and geometrical hardening which occurs d uring the compaction process. A hardening rule is used to define the dependence of the yield surface on the degree of plastic straining. A plasticity theory for friction is employed in the treatment of the powder-tooling interface. The inv olvement of two different materials, which have contact and relative movement in relation to each other, must be considered. A special formulation for friction modelling is coupled with a material formulation. The interface behaviour betwee n the die and the powder is modelled by using an interface element mesh. In the present paper, we have demonstrated pre- and post-processor finite elem ent software, written in Visual Basic, to generate the graphical model and visua lly display the computed results. The software consist of three main part: · Pre-processor: It is used to create the model, generate an app ropriate finite element grid, apply the appropriate boundary conditions, and vie w the total model. The geometric model can be used to associate the mesh with th e physical attributes such as element properties, material properties, or loads and boundary conditions. · Analysis: It can deal with two-dimensional and axi-symmetric applications for linear and non-linear behaviour of material in static and dyna mic analyses. Both triangular and quadrilateral elements are available in the e lement library, including 3-noded, 6-noded and 7-noded (T6B1) triangles and 4 -noded, 8-noded and 9-noded quadrilaterals. The direct implicit algorithm bas ed on the generalized Newmark scheme is used for the time integration and an aut omatic time step control facility is provided. For non-linear iteration, choice s among fully or modified Newton-Raphson method and quasi-Newton method, using the initial stiffness method, Davidon inverse method or BFGS inverse method, ar e possible. · Post-processor: It provides visualization of the computed resu lts, when the finite element model and analysis have been completed. Post-proce ssing is vital to allow the appropriate interpretation of the completed results of the finite element analysis. It provides the visual means to interpret the va st amounts of computed results generated. Finally, the powder behaviour during the compaction of a multi-level component is numerically simulated by the PCS_SUT software, as shown in Fig.1. The predict ive compaction forces at different displacements are computed and compared with the available experimental展开更多
Proper room and pillar sizes are both critical factors for safe mining and high ore recovery rate in shrinkage stoping mining of underground metal mines.The rock masses of Tangdan copper mine of China are fractured,wh...Proper room and pillar sizes are both critical factors for safe mining and high ore recovery rate in shrinkage stoping mining of underground metal mines.The rock masses of Tangdan copper mine of China are fractured,which needs much reinforcement and support prior to mining.Cement-sodium silicate grout technology was selected,then its related parameters such as grout pressure,diffusion radius and time were calculated and proposed.In order to test the effect of the pressured grout in the fractured No.4 ore block,field experiments were conducted.To optimize stoping configuration,three-dimensional numerical simulation with ANSYS and FLAC 3 D softwares was proposed.The results show that the drilling porosity and mechanical properties of the rock masses are increased obviously.After grout,ore recovery rate is increased by 10.2%employing the newly designed stoping configuration compared with the previous.Last,analyzed from the surface movements,roof subsidence and the maximum principal stress of the pillars,the mining safety is probable of being ensured.展开更多
A dynamical moving pressure structural numerical calculation model using the internal ballistics calculation pressure-time results was constituted and the vicinity of the internal ballistics and quasiinternal ballisti...A dynamical moving pressure structural numerical calculation model using the internal ballistics calculation pressure-time results was constituted and the vicinity of the internal ballistics and quasiinternal ballistics structural model was checked. The Von Mises stresses obtained by the dynamical structural numerical model calculations and the Von Mises stresses calculated from the shot test strain measurements were compared. The difference for the worse case was 20% and for the best case was 0.1%.Furthermore, the model gave better agreement for the higher charge masses. The numerical structural quasi-internal ballistics computation model created was verified for the top charge mass which represents the highest stress condition and used in a gun barrel design.展开更多
This work provides a method to predict the three-dimensional equivalent elastic properties of the filament-wound composites based on the multi-scale homogenization principle.In the meso-scale,a representative volume e...This work provides a method to predict the three-dimensional equivalent elastic properties of the filament-wound composites based on the multi-scale homogenization principle.In the meso-scale,a representative volume element(RVE)is defined and the bridging model is adopted to establish a theoretical predictive model for its three-dimensional equivalent elastic constants.The results obtained through this method for the previous experimental model are compared with the ones gained respectively by experiments and classical laminate theory to verify the reliability of this model.In addition,the effects of some winding parameters,such as winding angle,on the equivalent elastic behavior of the filament-wound composites are analyzed.The rules gained can provide a theoretical reference for the optimum design of filament-wound composites.展开更多
Three-dimensional(3D) synthetic aperture radar(SAR)extends the conventional 2D images into 3D features by several acquisitions in different aspects. Compared with 3D techniques via multiple observations in elevation, ...Three-dimensional(3D) synthetic aperture radar(SAR)extends the conventional 2D images into 3D features by several acquisitions in different aspects. Compared with 3D techniques via multiple observations in elevation, e.g. SAR interferometry(InSAR) and SAR tomography(TomoSAR), holographic SAR can retrieve 3D structure by observations in azimuth. This paper focuses on designing a novel type of orbit to achieve SAR regional all-azimuth observation(AAO) for embedded targets detection and holographic 3D reconstruction. The ground tracks of the AAO orbit separate the earth surface into grids. Target in these grids can be accessed with an azimuth angle span of360°, which is similar to the flight path of airborne circular SAR(CSAR). Inspired from the successive coverage orbits of optical sensors, several optimizations are made in the proposed method to ensure favorable grazing angles, the performance of 3D reconstruction, and long-term supervision for SAR sensors. Simulation experiments show the regional AAO can be completed within five hours. In addition, a second AAO of the same area can be duplicated in two days. Finally, an airborne SAR data process result is presented to illustrate the significance of AAO in 3D reconstruction.展开更多
基金Projects(50934002,51074013,51104100)supported by the National Natural Science Foundation of ChinaProject(IRT0950)supported by the Program for Changjiang Scholars and Innovative Research Team in University of China
文摘Room and pillar sizes are key factors for safe mining and ore recovery in open-stope mining. To investigate the influence of room and pillar configurations on stope stability in highly fractured and weakened areas, an orthogonal design with two factors, three levels and nine runs was proposed, followed by three-dimensional numerical simulation using ANSYS and FLAC3~. Results show that surface settlement after excavation is concentrically ringed, and increases with the decrease of pillar width and distances to stope gobs. In the meantime, the ore-control fault at the ore-rock boundary and the fractured argillaceous dolomite with intercalated slate at the hanging wall deteriorate the roof settlement. Additionally, stope stability is challenged due to pillar rheological yield and stress concentration, and both are induced by redistribution of stress and plastic zones after mining. Following an objective function and a constraint function, room and pillar configuration with widths of 14 m and 16 m, respectively, is presented as the optimization for improving the ore recovery rate while maintaining a safe working environment.
基金Project(2020YFA0710901)supported by the National Key Research and Development Program of ChinaProject(2023JJ30643)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(12372204)supported by the National Natural Science Foundation of ChinaProject(2022ZZTS0725)supported by the Self-exploration and Innovation Project for Postgraduates of Central South University,China。
文摘The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.
基金Project(51822803)supported by the National Natural Science Foundation of ChinaProject(2019JJ50688)supported by Hunan Provincial Natural Science Foundation,China+1 种基金Project(kq1905005)supported by Training Program for Excellent Young Innovators of Changsha,ChinaProject(CX20210775)supported by Hunan Provincial Innovative Foundation for Postgraduates,China。
文摘Wind barriers have attracted significant attention as an effective measure to ensure train safety under crosswinds.However,in past decades,the influence of structural parameters such as the height and ventilation ratio of wind barriers on the difference of the average pressure coefficient between the train windward and leeward surface(ΔCp)has not been fully investigated.To determine the influence of the interaction among the three factors,namely the wind barrier height(H),ventilation ratio(R),and distance to the train(D),twenty five numerical simulation cases with different structural parameters were considered based on an orthogonal design.The shear stress transfer(SST)k-ωturbulent model was employed to calculate the wind pressure coefficients,and the calculation accuracy was validated by using wind tunnel experiments.The results indicated that with an increase in R,ΔCp first decreased and then increased,andΔCp decreased while D increased.Moreover,with the increase in H,ΔCp first increased and then decreased.Therefore,these three factors must be considered during the installation of wind barriers.Furthermore,according to a range analysis(judging the relative importance of the three factors intuitively),the three factors were ranked in the following order:R>H>D.Based on a variance analysis,R was found to be of high significance toΔCp,followed by H,which was significant,whereas D had relatively insignificant influence.Finally,the optimal values of R and H were determined to be 20%and 110 mm,respectively.And when R=40%,H=85 mm,the train was relatively unsafe under these such conditions.The findings of this study provide significant guidance for the structural design of wind barriers.
文摘As computer simulation increasingly supports engine er ing design and manufacture, the requirement for a computer software environment providing an integration platform for computational engineering software increas es. A key component of an integrated environment is the use of computational eng ineering to assist and support solutions for complex design. Computer methods fo r structural, flow and thermal analysis are well developed and have been used in design for many years. Many software packages are now available which provi de an advanced capability. However, they are not designed for modelling of powde r forming processes. This paper describes the powder compaction software (PCS_SU T), which is designed for pre- and post-processing for computational simulatio n of the process compaction of powder. In the PCS_SUT software, the adaptive analysis of transient metal powder forming process is simulated by the finite element method based on deformation theories . The error estimates and adaptive remeshing schemes are applied for updated co -ordinate analysis. A generalized Newmark scheme is used for the time domain di scretization and the final nonlinear equations are solved by a Newton-Raphson p rocedure. An incremental elasto-plastic material model is used to simulate the compaction process. To describe the constitutive model of nonlinear behaviour of powder materials, a combination of Mohr-Coulomb and elliptical yield cap model is applied. This model reflects the yielding, frictional and densification char acteristics of powder along with strain and geometrical hardening which occurs d uring the compaction process. A hardening rule is used to define the dependence of the yield surface on the degree of plastic straining. A plasticity theory for friction is employed in the treatment of the powder-tooling interface. The inv olvement of two different materials, which have contact and relative movement in relation to each other, must be considered. A special formulation for friction modelling is coupled with a material formulation. The interface behaviour betwee n the die and the powder is modelled by using an interface element mesh. In the present paper, we have demonstrated pre- and post-processor finite elem ent software, written in Visual Basic, to generate the graphical model and visua lly display the computed results. The software consist of three main part: · Pre-processor: It is used to create the model, generate an app ropriate finite element grid, apply the appropriate boundary conditions, and vie w the total model. The geometric model can be used to associate the mesh with th e physical attributes such as element properties, material properties, or loads and boundary conditions. · Analysis: It can deal with two-dimensional and axi-symmetric applications for linear and non-linear behaviour of material in static and dyna mic analyses. Both triangular and quadrilateral elements are available in the e lement library, including 3-noded, 6-noded and 7-noded (T6B1) triangles and 4 -noded, 8-noded and 9-noded quadrilaterals. The direct implicit algorithm bas ed on the generalized Newmark scheme is used for the time integration and an aut omatic time step control facility is provided. For non-linear iteration, choice s among fully or modified Newton-Raphson method and quasi-Newton method, using the initial stiffness method, Davidon inverse method or BFGS inverse method, ar e possible. · Post-processor: It provides visualization of the computed resu lts, when the finite element model and analysis have been completed. Post-proce ssing is vital to allow the appropriate interpretation of the completed results of the finite element analysis. It provides the visual means to interpret the va st amounts of computed results generated. Finally, the powder behaviour during the compaction of a multi-level component is numerically simulated by the PCS_SUT software, as shown in Fig.1. The predict ive compaction forces at different displacements are computed and compared with the available experimental
基金Projects(51374034,51674012)supported by the National Natural Science Foundation of ChinaProject(2013BAB02B05)supported by the China National Science and Technology Support Program during the 12th Five-Year Plan Period
文摘Proper room and pillar sizes are both critical factors for safe mining and high ore recovery rate in shrinkage stoping mining of underground metal mines.The rock masses of Tangdan copper mine of China are fractured,which needs much reinforcement and support prior to mining.Cement-sodium silicate grout technology was selected,then its related parameters such as grout pressure,diffusion radius and time were calculated and proposed.In order to test the effect of the pressured grout in the fractured No.4 ore block,field experiments were conducted.To optimize stoping configuration,three-dimensional numerical simulation with ANSYS and FLAC 3 D softwares was proposed.The results show that the drilling porosity and mechanical properties of the rock masses are increased obviously.After grout,ore recovery rate is increased by 10.2%employing the newly designed stoping configuration compared with the previous.Last,analyzed from the surface movements,roof subsidence and the maximum principal stress of the pillars,the mining safety is probable of being ensured.
基金Ministry of Science, Industry, and Technology which supported this project under the Industrial Thesis Support Program
文摘A dynamical moving pressure structural numerical calculation model using the internal ballistics calculation pressure-time results was constituted and the vicinity of the internal ballistics and quasiinternal ballistics structural model was checked. The Von Mises stresses obtained by the dynamical structural numerical model calculations and the Von Mises stresses calculated from the shot test strain measurements were compared. The difference for the worse case was 20% and for the best case was 0.1%.Furthermore, the model gave better agreement for the higher charge masses. The numerical structural quasi-internal ballistics computation model created was verified for the top charge mass which represents the highest stress condition and used in a gun barrel design.
文摘This work provides a method to predict the three-dimensional equivalent elastic properties of the filament-wound composites based on the multi-scale homogenization principle.In the meso-scale,a representative volume element(RVE)is defined and the bridging model is adopted to establish a theoretical predictive model for its three-dimensional equivalent elastic constants.The results obtained through this method for the previous experimental model are compared with the ones gained respectively by experiments and classical laminate theory to verify the reliability of this model.In addition,the effects of some winding parameters,such as winding angle,on the equivalent elastic behavior of the filament-wound composites are analyzed.The rules gained can provide a theoretical reference for the optimum design of filament-wound composites.
基金supported by the National Natural Science Foundation of China (62001436)the Natural Science Foundation of Jiangsu Province under (BK 20190143,JSGG20190823094603691)。
文摘Three-dimensional(3D) synthetic aperture radar(SAR)extends the conventional 2D images into 3D features by several acquisitions in different aspects. Compared with 3D techniques via multiple observations in elevation, e.g. SAR interferometry(InSAR) and SAR tomography(TomoSAR), holographic SAR can retrieve 3D structure by observations in azimuth. This paper focuses on designing a novel type of orbit to achieve SAR regional all-azimuth observation(AAO) for embedded targets detection and holographic 3D reconstruction. The ground tracks of the AAO orbit separate the earth surface into grids. Target in these grids can be accessed with an azimuth angle span of360°, which is similar to the flight path of airborne circular SAR(CSAR). Inspired from the successive coverage orbits of optical sensors, several optimizations are made in the proposed method to ensure favorable grazing angles, the performance of 3D reconstruction, and long-term supervision for SAR sensors. Simulation experiments show the regional AAO can be completed within five hours. In addition, a second AAO of the same area can be duplicated in two days. Finally, an airborne SAR data process result is presented to illustrate the significance of AAO in 3D reconstruction.
