Numerical simulations are carried out to investigate the mechanism of the nonlinear evolution of two- dimensional （2-D） Tollmien-Schlichting （T-S） wave on a localized rough boundary layer. The three-dimensional （...Numerical simulations are carried out to investigate the mechanism of the nonlinear evolution of two- dimensional （2-D） Tollmien-Schlichting （T-S） wave on a localized rough boundary layer. The three-dimensional （3-D） numerical solution of a base flow on a boundary layer is obtained for the localized rough wall with the local- ized ejection, the localized suction and the combination of ejection and suction. Based on numerical simulations, the processes of stable and the most instable nonlinear evolution of the 2-D disturbance T-S wave are studied. The effects of the form on the localized roughness, the intensity, and the distribution structure on the nonlinear evolution of 2-D T-S wave and the growth rate are discussed. Results show that the basic flow induced by the lo- calized rough wall is a key factor causing the fast growth of the disturbance wave. Due to the change of the aver- age flow profile and the existence of the spanwise velocity, the localized rough wall enhances the instability of the flow. Consequently, the instable region of the neutral curve is enlargened, and the maximnum growth rate of the 2-D T-S wave is increased. In the process of the nonlinear evolution of 2-D disturbance T-S wave, with the in- crease of the nonlinear interaction, the most instable 2-D disturbance wave triggers the appearance of the 3-D dis- turbance wave and the high-frequency harmonic wave. Its streamwise wave number and the frequency are the same as those of 2-D disturbance wave. The spanwise velocity can excite the growth of the 2-D disturbance wave, the instability of 2-D wave, the formation of the streamwise vortex, and the generation of 3-D disturbance wave. Simulation results agree well with experimental results.展开更多
Combining vacuum preloading technology and electroosmosis can improve the treatment effect of soft soil foundation by utilizing the advantages of both methods.Many studies indicate that the soil electrical potential i...Combining vacuum preloading technology and electroosmosis can improve the treatment effect of soft soil foundation by utilizing the advantages of both methods.Many studies indicate that the soil electrical potential is non-linearly distributed in the treatment process by the combined method.However,in the previous theoretical study,the non-linear-distribution impacts of soil’s electrical potential on soft soil foundation treatment have not been considered.It is always assumed to be linear distribution,which is different from the experimental results.In this paper,the coupling consolidation model of this technology under the two-dimensional plane strain condition is initially established;and the well resistance effect,the vacuum load decreasing along the soil depth and the non-linear variation of electrical potential in the soil are considered.Then,the analytical solutions of the average excess pore water pressure and soil’s consolidation degree in the anode affected area are acquired based on the soil’s electrical potential distribution.Finally,the rationality of the analytical solution is testified by conducting an experimental model test,which proves the scientificity of the analytical solution.The analytical solution is adopted to better predict the dissipation of excess pore water pressure and soil consolidation degree when using the combined technology.This study can provide a reference with more accuracy for the engineering practices of this combined technology in the future.展开更多
Cold plasma techniques were used to treat the surface of Kevlar-49 fibers. The dynamic parameters of wetting, contact-angles and surface energy of the fiber before and alter the treatment were compared to see the chan...Cold plasma techniques were used to treat the surface of Kevlar-49 fibers. The dynamic parameters of wetting, contact-angles and surface energy of the fiber before and alter the treatment were compared to see the changes in the wetting property. ESCA and electron spin resonance were utilized to examine the chemical composition and the attached free radicals of the fiber surface. The results, together with changes in the magnitude of the contact-angle and the number of free radicals with time after the plasma treatment do not show any ageing effect. Single filament test revealed that the tensile strength was not impaired but even improved somewhat after the plasma treatment. The experiment shows that the interlaminar shear strength of Kevlar fiber reinforced epoxy resin compo- site is increased for more than 60％% after the treatment.展开更多
基金Supported by the National Natural Science Foundation of China(10872097)the Natural Science Foundation of Jiangsu Province(BK2007178)Science Foundation of Nanjing University Information Science & Technology(20080101)~~
文摘Numerical simulations are carried out to investigate the mechanism of the nonlinear evolution of two- dimensional （2-D） Tollmien-Schlichting （T-S） wave on a localized rough boundary layer. The three-dimensional （3-D） numerical solution of a base flow on a boundary layer is obtained for the localized rough wall with the local- ized ejection, the localized suction and the combination of ejection and suction. Based on numerical simulations, the processes of stable and the most instable nonlinear evolution of the 2-D disturbance T-S wave are studied. The effects of the form on the localized roughness, the intensity, and the distribution structure on the nonlinear evolution of 2-D T-S wave and the growth rate are discussed. Results show that the basic flow induced by the lo- calized rough wall is a key factor causing the fast growth of the disturbance wave. Due to the change of the aver- age flow profile and the existence of the spanwise velocity, the localized rough wall enhances the instability of the flow. Consequently, the instable region of the neutral curve is enlargened, and the maximnum growth rate of the 2-D T-S wave is increased. In the process of the nonlinear evolution of 2-D disturbance T-S wave, with the in- crease of the nonlinear interaction, the most instable 2-D disturbance wave triggers the appearance of the 3-D dis- turbance wave and the high-frequency harmonic wave. Its streamwise wave number and the frequency are the same as those of 2-D disturbance wave. The spanwise velocity can excite the growth of the 2-D disturbance wave, the instability of 2-D wave, the formation of the streamwise vortex, and the generation of 3-D disturbance wave. Simulation results agree well with experimental results.
基金Project(51979087)supported by the National Natural Science Foundation of ChinaProject(BK20180776)supported by the Jiangsu Natural Science Foundation,ChinaProject(202006710002)supported by the China Scholarship Council。
文摘Combining vacuum preloading technology and electroosmosis can improve the treatment effect of soft soil foundation by utilizing the advantages of both methods.Many studies indicate that the soil electrical potential is non-linearly distributed in the treatment process by the combined method.However,in the previous theoretical study,the non-linear-distribution impacts of soil’s electrical potential on soft soil foundation treatment have not been considered.It is always assumed to be linear distribution,which is different from the experimental results.In this paper,the coupling consolidation model of this technology under the two-dimensional plane strain condition is initially established;and the well resistance effect,the vacuum load decreasing along the soil depth and the non-linear variation of electrical potential in the soil are considered.Then,the analytical solutions of the average excess pore water pressure and soil’s consolidation degree in the anode affected area are acquired based on the soil’s electrical potential distribution.Finally,the rationality of the analytical solution is testified by conducting an experimental model test,which proves the scientificity of the analytical solution.The analytical solution is adopted to better predict the dissipation of excess pore water pressure and soil consolidation degree when using the combined technology.This study can provide a reference with more accuracy for the engineering practices of this combined technology in the future.
文摘Cold plasma techniques were used to treat the surface of Kevlar-49 fibers. The dynamic parameters of wetting, contact-angles and surface energy of the fiber before and alter the treatment were compared to see the changes in the wetting property. ESCA and electron spin resonance were utilized to examine the chemical composition and the attached free radicals of the fiber surface. The results, together with changes in the magnitude of the contact-angle and the number of free radicals with time after the plasma treatment do not show any ageing effect. Single filament test revealed that the tensile strength was not impaired but even improved somewhat after the plasma treatment. The experiment shows that the interlaminar shear strength of Kevlar fiber reinforced epoxy resin compo- site is increased for more than 60％% after the treatment.
