We study the dynamics of the critical collapse of a spherically symmetric scalar field.Approximate analytic expressions for the metric functions and matter field in the large-radius region are obtained.In the central ...We study the dynamics of the critical collapse of a spherically symmetric scalar field.Approximate analytic expressions for the metric functions and matter field in the large-radius region are obtained.In the central region,owing to the boundary conditions,the equation of motion for the scalar field is reduced to the flat-spacetime form.展开更多
We study the energy issue in critical collapse.It is found that in critical collapse,the contribution from the material energy is greater than that from the gravitational energy.The quantity m/r plays an important rol...We study the energy issue in critical collapse.It is found that in critical collapse,the contribution from the material energy is greater than that from the gravitational energy.The quantity m/r plays an important role in identifying the formation of an apparent horizon in gravitational collapse,where m is the Misner-Sharp mass and r is the areal radius.We observe that in critical collapse,the maximum value of m/r fluctuates between 2/15 and 4/15.This denotes a large gap between critical collapse and black hole formation for which the criterion is m/r=1/2.展开更多
The complex behavior of granular material considering large deformation and post-failure is of great interest in the geotechnical field.Numerical prediction of these phenomena could provide useful insights for enginee...The complex behavior of granular material considering large deformation and post-failure is of great interest in the geotechnical field.Numerical prediction of these phenomena could provide useful insights for engineering design and practice.In this paper,we propose a novel numerical approach to study soil collapse involving large deformation.The approach combines a recently developed critical state-based sand model SIMSAND for describing complex sand mechanical behaviors,and the smoothed particle hydrodynamics(SPH)method for dealing with large deformation.To show the high efficiency and accuracy of the proposed approach,a series of column collapses using discrete element method(DEM)and considering the influence of particle shapes(i.e.spherical shape(SS),tetrahedral shape(TS),and elongated shape(ES))were adopted as benchmarks and simulated by the proposed method.The parameters of SIMSAND were calibrated from the results of DEM triaxial tests on the same samples.Compared with the results of DEM simulations and reference solutions derived by published collapse experiments,the runout distance and final height of specimens with different particle shapes simulated by SPH-SIMSAND were well characterized and incurred a lower computational cost.Comparisons showed that the novel SPH-SIMSAND approach is highly efficient and accurate for simulating collapse,and can be a useful numerical analytical tool for real scale engineering problems.展开更多
Many strip materials are coiled after rolling process. The stresses are imposed on the material wound on the automatically controlled collapse mandrel under the coiling tension. The coiling process can be described by...Many strip materials are coiled after rolling process. The stresses are imposed on the material wound on the automatically controlled collapse mandrel under the coiling tension. The coiling process can be described by three typical cases: winding without automatic adjustment, winding with automatic adjustment and after mandrel removal. A new model of equations for predicting the stresses during the strip coiling process is built by consideration of the three cases respectively. By solving the equations of different typical cases, the radial stresses and tangential stress of the layers of coil can be calculated. Also, the coiling parameters, such as strip thickness, coiling tension and necking critical pressure, affecting the coil performance are investigated. It is believed that the present model can be used for design and control of the automatically controlled collapse mandrel.展开更多
基金JQG is Supported by the Natural Science Foundation of Shandong Province,China(ZR2019MA068)YH,PPW and CGS are Supported by the National Natural Science Foundation of China(11925503)。
文摘We study the dynamics of the critical collapse of a spherically symmetric scalar field.Approximate analytic expressions for the metric functions and matter field in the large-radius region are obtained.In the central region,owing to the boundary conditions,the equation of motion for the scalar field is reduced to the flat-spacetime form.
基金supported by the National Natural Science Foundation of China(Grant No.11925503)supported by Shandong Province Natural Science Foundation under grant No.ZR2019MA068.
文摘We study the energy issue in critical collapse.It is found that in critical collapse,the contribution from the material energy is greater than that from the gravitational energy.The quantity m/r plays an important role in identifying the formation of an apparent horizon in gravitational collapse,where m is the Misner-Sharp mass and r is the areal radius.We observe that in critical collapse,the maximum value of m/r fluctuates between 2/15 and 4/15.This denotes a large gap between critical collapse and black hole formation for which the criterion is m/r=1/2.
基金the Shenzhen Research and Technology Fund(No.JSGG20180504170449754)the grant from the Research Grants Council of the Hong Kong Special Administrative Region(No.UGC/FDS13/E06/18),China。
文摘The complex behavior of granular material considering large deformation and post-failure is of great interest in the geotechnical field.Numerical prediction of these phenomena could provide useful insights for engineering design and practice.In this paper,we propose a novel numerical approach to study soil collapse involving large deformation.The approach combines a recently developed critical state-based sand model SIMSAND for describing complex sand mechanical behaviors,and the smoothed particle hydrodynamics(SPH)method for dealing with large deformation.To show the high efficiency and accuracy of the proposed approach,a series of column collapses using discrete element method(DEM)and considering the influence of particle shapes(i.e.spherical shape(SS),tetrahedral shape(TS),and elongated shape(ES))were adopted as benchmarks and simulated by the proposed method.The parameters of SIMSAND were calibrated from the results of DEM triaxial tests on the same samples.Compared with the results of DEM simulations and reference solutions derived by published collapse experiments,the runout distance and final height of specimens with different particle shapes simulated by SPH-SIMSAND were well characterized and incurred a lower computational cost.Comparisons showed that the novel SPH-SIMSAND approach is highly efficient and accurate for simulating collapse,and can be a useful numerical analytical tool for real scale engineering problems.
文摘Many strip materials are coiled after rolling process. The stresses are imposed on the material wound on the automatically controlled collapse mandrel under the coiling tension. The coiling process can be described by three typical cases: winding without automatic adjustment, winding with automatic adjustment and after mandrel removal. A new model of equations for predicting the stresses during the strip coiling process is built by consideration of the three cases respectively. By solving the equations of different typical cases, the radial stresses and tangential stress of the layers of coil can be calculated. Also, the coiling parameters, such as strip thickness, coiling tension and necking critical pressure, affecting the coil performance are investigated. It is believed that the present model can be used for design and control of the automatically controlled collapse mandrel.
