To avoid the machine problems of excessive axial force, complex process flow and frequent tool changing during robotic drilling holes, a new hole-making technology (i.e., helical milling hole) was introduced for desig...To avoid the machine problems of excessive axial force, complex process flow and frequent tool changing during robotic drilling holes, a new hole-making technology (i.e., helical milling hole) was introduced for designing a new robotic helical milling hole system, which could further improve robotic hole-making ability in airplane digital assembly. After analysis on the characteristics of helical milling hole, advantages and limitations of two typical robotic helical milling hole systems were summarized. Then, vector model of helical milling hole movement was built on vector analysis method. Finally, surface roughness calculation formula was deduced according to the movement principle of helical milling hole, then the influence of main technological parameters on surface roughness was analyzed. Analysis shows that theoretical surface roughness of hole becomes poor with the increase of tool speed ratio and revolution radius. Meanwhile, the roughness decreases according to the increase of tool teeth number. The research contributes greatly to the construction of roughness prediction model in helical milling hole.展开更多
Vapor-liquid phase transition occurs via a nucleation process, and depending on the role of foreign objects, nucleation can be either homogeneous or heterogeneous. In this review, we focus on the recently developed co...Vapor-liquid phase transition occurs via a nucleation process, and depending on the role of foreign objects, nucleation can be either homogeneous or heterogeneous. In this review, we focus on the recently developed constrained lattice density functional theory （CLDFT） and its applications on vapor-liquid nucleation. We also review the recent theoretical advance on the stability of nanobubbles. Based on CLDFT, a pinning and supersaturation mechanism has proposed to interpret the surprising stability of surface nanobubbles. The mechanism can interpret most characteristics of nanobubbles. More importantly, the mechanism suggests that the critical nucleus can be stabilized under the condition of contact line pinning. Thus, CLDFT studies provide an alternative way to measure the critical nucleus that is difficult to measure experimentally in the bulk solution, through stabilizing it with surface roughness or heterogeneities.展开更多
Uncertainties in some key parameters in land surface models severely restrict the improvement of model capacity for successful simulation of surface-atmosphere interaction. These key parameters are related to soil moi...Uncertainties in some key parameters in land surface models severely restrict the improvement of model capacity for successful simulation of surface-atmosphere interaction. These key parameters are related to soil moisture and heat transfer and phy- sical processes in the vegetation canopy as well as other important aerodynamic processes. In the present study, measurements of surface-atmosphere interaction at two observation stations that are located in the typical semi-arid region of China, Tongyu Station in Jilin Province and Yuzhong Station in Gansu Province, are combined with the planetary boundary layer theory to estimate the value of two key aerodynamic parameters, i.e., surface roughness length zorn and excess resistance κB-1. Multiple parameterization schemes have been used in the study to obtain values for surface roughness length and excess resistance κB-1 at the two stations. Results indicate that Zorn has distinct seasonal and inter-annual variability. For the type of surface with low-height vegetation, there is a large difference between the default value of Zorn in the land surface model and that obtained from this study, κB-1 demonstrates a significant diurnal variation and seasonal variability. Using the modified scheme for the estimation of Zom and κB-1 in the land surface model, it is found that simulations of sensible heat flux over the semi-arid region have been greatly improved. These results suggest that it is necessary to further evaluate the default values of various parameters used in land surface models based on field measurements. The approach to combine field measurements with atmospheric boundary layer theory to retrieve realistic values for key parameters in land surface models presents a great potential in the improvement of modeling studies of surface-atmosphere interaction.展开更多
基金Foundation item： Projects（50975141, 51005118） supported by the National Natural Science Foundation of China Projects（20091652018, 2010352005） supported by Aviation Science Fund of China Project（YKJ11-001） supported by Key Program of Nanjing College of Information Technology Institute, China
文摘To avoid the machine problems of excessive axial force, complex process flow and frequent tool changing during robotic drilling holes, a new hole-making technology (i.e., helical milling hole) was introduced for designing a new robotic helical milling hole system, which could further improve robotic hole-making ability in airplane digital assembly. After analysis on the characteristics of helical milling hole, advantages and limitations of two typical robotic helical milling hole systems were summarized. Then, vector model of helical milling hole movement was built on vector analysis method. Finally, surface roughness calculation formula was deduced according to the movement principle of helical milling hole, then the influence of main technological parameters on surface roughness was analyzed. Analysis shows that theoretical surface roughness of hole becomes poor with the increase of tool speed ratio and revolution radius. Meanwhile, the roughness decreases according to the increase of tool teeth number. The research contributes greatly to the construction of roughness prediction model in helical milling hole.
基金supported by State Key Laboratory of Chemical Engineering (SKL-CHE-12B02)the National Natural Science Foundation of China (21276007)
文摘Vapor-liquid phase transition occurs via a nucleation process, and depending on the role of foreign objects, nucleation can be either homogeneous or heterogeneous. In this review, we focus on the recently developed constrained lattice density functional theory （CLDFT） and its applications on vapor-liquid nucleation. We also review the recent theoretical advance on the stability of nanobubbles. Based on CLDFT, a pinning and supersaturation mechanism has proposed to interpret the surprising stability of surface nanobubbles. The mechanism can interpret most characteristics of nanobubbles. More importantly, the mechanism suggests that the critical nucleus can be stabilized under the condition of contact line pinning. Thus, CLDFT studies provide an alternative way to measure the critical nucleus that is difficult to measure experimentally in the bulk solution, through stabilizing it with surface roughness or heterogeneities.
基金supported by the National Basic Research Program of China(Grant No.2011CB952002)the National Natural Science Foundation of China(Grant Nos.41475063+1 种基金41005047)Program for New Century Excellent Talents in University,and the Jiangsu Collaborative Innovation Center for Climate Change
文摘Uncertainties in some key parameters in land surface models severely restrict the improvement of model capacity for successful simulation of surface-atmosphere interaction. These key parameters are related to soil moisture and heat transfer and phy- sical processes in the vegetation canopy as well as other important aerodynamic processes. In the present study, measurements of surface-atmosphere interaction at two observation stations that are located in the typical semi-arid region of China, Tongyu Station in Jilin Province and Yuzhong Station in Gansu Province, are combined with the planetary boundary layer theory to estimate the value of two key aerodynamic parameters, i.e., surface roughness length zorn and excess resistance κB-1. Multiple parameterization schemes have been used in the study to obtain values for surface roughness length and excess resistance κB-1 at the two stations. Results indicate that Zorn has distinct seasonal and inter-annual variability. For the type of surface with low-height vegetation, there is a large difference between the default value of Zorn in the land surface model and that obtained from this study, κB-1 demonstrates a significant diurnal variation and seasonal variability. Using the modified scheme for the estimation of Zom and κB-1 in the land surface model, it is found that simulations of sensible heat flux over the semi-arid region have been greatly improved. These results suggest that it is necessary to further evaluate the default values of various parameters used in land surface models based on field measurements. The approach to combine field measurements with atmospheric boundary layer theory to retrieve realistic values for key parameters in land surface models presents a great potential in the improvement of modeling studies of surface-atmosphere interaction.
