By numerically solving the unforced and inviscid nonlinear barotropic vorticity equation through the quasi-Newton method, the steady free modes are obtained, which are very similar to the real flow fields, and their s...By numerically solving the unforced and inviscid nonlinear barotropic vorticity equation through the quasi-Newton method, the steady free modes are obtained, which are very similar to the real flow fields, and their scatter diagram of (ψ, q) display segmented linear or nonlinear relations. From this scheme a range of free modes have been achieved, each corresponding to one of the atmospheric flow fields. In the study of changes in the western Pacific subtropical high (WPSH) as revealed by free modes it is discovered that the west-extension/northward jump and east-movement/southward withdrawal of WPSH for the free mode occur 5-10 days ahead of the changes in the high as shown in the 500 hPa geopotential height field. Besides, a standard mode technique is adopted to investigate the stability of the free modes, indicating that the faster the instable mode grows, the closer it comes to a quasi-steady state. Especially, the instable mode with its quasi-steady state growing the fastest bears a correspondence with the high in steady intensification, leading to the fact that the persistent strengthening of the high is likely to be caused by the instable free modes with the fastest growth that are of quasi-steady state, or experience long-period low-frequency variation.展开更多
We have numerically and experimentally investigated the flow modes of Taylor-Couette system consisting of coaxial two cylinders with vertical axes. The inner cylinder rotates and the outer cylinder and the bottom end ...We have numerically and experimentally investigated the flow modes of Taylor-Couette system consisting of coaxial two cylinders with vertical axes. The inner cylinder rotates and the outer cylinder and the bottom end of the cylinders remain stationary. The upper top boundary is the free surface of the working liquid between the inner and outer cylinders and it contacts with the air. While this flow appears in fluid machinery and chemical reactors and includes industrial interests, it also contains problems of fluid mechanics, which is about the behavior of the free surface in the rotating field. In this paper, we concretely show the developments of the one cell mode flow and the three cell mode flow at a small aspect ratio. We also represent the bifurcation diagram of the flow at the moderate aspect ratio about 5.5. In the numerical simulation, the flow is rest in the initial state, and the inner cylinder is linearly or suddenly accelerated to attain a flow with a prescribed Reynolds number. When the acceleration of the inner cylinder is high, an imperfect bifurcation occurs and the flows of the secondary modes emerge. At high Reynolds numbers, the flow first has many vortices and then some of the vortices collapse and the final stable flow arises. The loci of the normal five cell mode, the anomalous six cell mode and the secondary seven cell mode are determined.展开更多
Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom c...Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom can be recovered back to its original position without any defects introduced. Based on surface hydroxylation and chemisorption theory, material removal mechanism of quartz glass in the elastic mode is analyzed to obtain defect-free surface. Elastic contact condition between nanoparticle and quartz glass surface is confirmed from the Hertz contact theory model. Atoms on the quartz glass surface are removed by chemical bond generated by impact reaction in the elastic mode, so no defects are generated without mechanical process. Experiment was conducted on a numerically controlled system for nanoparticle jet polishing, and one flat quartz glass was polished in the elastic mode. Results show that scratches on the sample surface are completely removed away with no mechanical defects introduced, and microroughness(Ra) is decreased from 1.23 nm to 0.47 nm. Functional group Ce — O — Si on ceria nanoparticles after polishing was detected directly and indirectly by FTIR, XRD and XPS spectra analysis from which the chemical impact reaction is validated.展开更多
The kinetic characteristics of the ion confined in a MMFM operation point of a combined trap were compared with that in a non_MMFM point by numerical simulation both for the ion produced within a combined trap or inje...The kinetic characteristics of the ion confined in a MMFM operation point of a combined trap were compared with that in a non_MMFM point by numerical simulation both for the ion produced within a combined trap or injected from an external source into the trap. It turns out that the MMFM working point can provide better trapping condition for the ions with stronger localization and higher stability.展开更多
基金The work is supported by the National Natural Science Foundation of China under Grant No. 40275016.
文摘By numerically solving the unforced and inviscid nonlinear barotropic vorticity equation through the quasi-Newton method, the steady free modes are obtained, which are very similar to the real flow fields, and their scatter diagram of (ψ, q) display segmented linear or nonlinear relations. From this scheme a range of free modes have been achieved, each corresponding to one of the atmospheric flow fields. In the study of changes in the western Pacific subtropical high (WPSH) as revealed by free modes it is discovered that the west-extension/northward jump and east-movement/southward withdrawal of WPSH for the free mode occur 5-10 days ahead of the changes in the high as shown in the 500 hPa geopotential height field. Besides, a standard mode technique is adopted to investigate the stability of the free modes, indicating that the faster the instable mode grows, the closer it comes to a quasi-steady state. Especially, the instable mode with its quasi-steady state growing the fastest bears a correspondence with the high in steady intensification, leading to the fact that the persistent strengthening of the high is likely to be caused by the instable free modes with the fastest growth that are of quasi-steady state, or experience long-period low-frequency variation.
文摘We have numerically and experimentally investigated the flow modes of Taylor-Couette system consisting of coaxial two cylinders with vertical axes. The inner cylinder rotates and the outer cylinder and the bottom end of the cylinders remain stationary. The upper top boundary is the free surface of the working liquid between the inner and outer cylinders and it contacts with the air. While this flow appears in fluid machinery and chemical reactors and includes industrial interests, it also contains problems of fluid mechanics, which is about the behavior of the free surface in the rotating field. In this paper, we concretely show the developments of the one cell mode flow and the three cell mode flow at a small aspect ratio. We also represent the bifurcation diagram of the flow at the moderate aspect ratio about 5.5. In the numerical simulation, the flow is rest in the initial state, and the inner cylinder is linearly or suddenly accelerated to attain a flow with a prescribed Reynolds number. When the acceleration of the inner cylinder is high, an imperfect bifurcation occurs and the flows of the secondary modes emerge. At high Reynolds numbers, the flow first has many vortices and then some of the vortices collapse and the final stable flow arises. The loci of the normal five cell mode, the anomalous six cell mode and the secondary seven cell mode are determined.
基金Projects(51305450,51275521)supported by the National Natural Science Foundation of China
文摘Removal of brittle materials in the brittle or ductile mode inevitably causes damaged or strained surface layers containing cracks, scratches or dislocations. Within elastic deformation, the arrangement of each atom can be recovered back to its original position without any defects introduced. Based on surface hydroxylation and chemisorption theory, material removal mechanism of quartz glass in the elastic mode is analyzed to obtain defect-free surface. Elastic contact condition between nanoparticle and quartz glass surface is confirmed from the Hertz contact theory model. Atoms on the quartz glass surface are removed by chemical bond generated by impact reaction in the elastic mode, so no defects are generated without mechanical process. Experiment was conducted on a numerically controlled system for nanoparticle jet polishing, and one flat quartz glass was polished in the elastic mode. Results show that scratches on the sample surface are completely removed away with no mechanical defects introduced, and microroughness(Ra) is decreased from 1.23 nm to 0.47 nm. Functional group Ce — O — Si on ceria nanoparticles after polishing was detected directly and indirectly by FTIR, XRD and XPS spectra analysis from which the chemical impact reaction is validated.
文摘The kinetic characteristics of the ion confined in a MMFM operation point of a combined trap were compared with that in a non_MMFM point by numerical simulation both for the ion produced within a combined trap or injected from an external source into the trap. It turns out that the MMFM working point can provide better trapping condition for the ions with stronger localization and higher stability.
