Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble v...Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble visualization and the Particle Image Velocimetry(PIV)techniques.There are three near-wall topological patterns with different Angles of Attack(AoAs):the separation bubble,the Leading-Edge Vortex(LEV)and the high Ao As flow.For the separation bubble pattern,two saddles and two foci form in the middle of the model.The features of the LEV pattern are the leading-edge separation lines.The topological characteristics of the separation lines are changed by the interaction between the LEV and the Wing-Tip Vortex(WTV).For the high Ao As flow pattern,four unstable foci are found at the forewing and the hindwing respectively.The angle between the trajectory of the WTV and the model increases with increasing Ao A even though the slope of the WTV angle versus Ao A curve declines at the moderate AoAs.展开更多
By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and...By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and by appling topology theory, the topological structures and vortex structure in the transverse section of a blade cascade were analyzed. Compared with conventional straight cascade, blade positive curving eliminates the separation line of the upper passage vortex, and leads the secondary vortex to change from close separation to open separation, while blade negative curving effects merely the positions of singular points and the intensities and scales of vortex.展开更多
Based on the concepts of fractal super fibers, the （3, 9＋2）-circle and （9＋2, 3）-circle binary fractal sets are abstracted form such prototypes as wool fibers and human hairs, with the （3）-circle and the （9＋2...Based on the concepts of fractal super fibers, the （3, 9＋2）-circle and （9＋2, 3）-circle binary fractal sets are abstracted form such prototypes as wool fibers and human hairs, with the （3）-circle and the （9＋2）-circle fractal sets as subsets. As far as the （9＋2） topological patterns are concerned, the following propositions are proved： The （9＋2） topological patterns accurately exist, but are not unique. Their total number is 9. Among them, only two are allotropes. In other words, among the nine topological patterns, only two are independent （or fundamental）. Besides, we demonstrate that the （3, 9＋2）-circle and （9＋2, 3）-circle fractal sets are golden ones with symmetry breaking.展开更多
ICM （Independent Continuous Mapping） method can solve topological optimization problems with the minimized weight as the objective and subjected to displacement constraints. To get a clearer topological configuratio...ICM （Independent Continuous Mapping） method can solve topological optimization problems with the minimized weight as the objective and subjected to displacement constraints. To get a clearer topological configuration, by introducing the discrete condition of topological variables and integrating with the original objective, an optimal model with multi-objectives is formulated to make the topological variables approach 0 or 1 as near as possible, and the model reduces the effect of deleting rate on the result. The image-filtering method is employed to eliminate the checkerboard patterns and mesh dependence that occurred in the topology optimization of a continuum structure. The computational efficiency is enhanced through selecting quasi-active displacement constraints and a design region. Numerical examples indicate that this algorithm is robust and practicable, though the number of iterations is slightly increased with respect to the original algorithm.展开更多
Wearable devices redefine the way people interact with machines.Despite the intensive effort in the design and fabrication of synthetic fibers to improve wearable device properties in terms of electronic and ionic con...Wearable devices redefine the way people interact with machines.Despite the intensive effort in the design and fabrication of synthetic fibers to improve wearable device properties in terms of electronic and ionic conductivity,stretchability,com-fort,and washability,challenges remain in fabricating single fiber materials that optimize all properties simultaneously.In this work,we demonstrate a highly stretchable,ionic,and electronic conductive fabric via(1)the natural nanoscale chan-nels in fibers for effective ion transportation,(2)confining the electronic conductive material with the cellulose fibers,and(3)decoupling the property degradation of the fiber from deformation using the knitted pattern.The hierarchical structure created by cotton fibers can serve as ionic conductive channels as well as a robust multiscale scaffold to host infiltrated elec-tronic conductive materials.Cotton strands with ionic and electronic conductivity can be knitted into fabrics that are highly stretchable(~300%).Moreover,high ionic and electronic conductivity are observed with 2 S/m and 5 S/m,respectively,even under a strain of 175%.With the inherent advantages of cotton fabrics such as moisture-wicking,washability,comfort,and light-weightiness for wearable applications,our approach of directly functionalized cellulose can potentially be a promising route towards highly stretchable and wearable mixed conductors.展开更多
基金funded by the National Natural Science Foundation of China (No. 11721202)。
文摘Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles.The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble visualization and the Particle Image Velocimetry(PIV)techniques.There are three near-wall topological patterns with different Angles of Attack(AoAs):the separation bubble,the Leading-Edge Vortex(LEV)and the high Ao As flow.For the separation bubble pattern,two saddles and two foci form in the middle of the model.The features of the LEV pattern are the leading-edge separation lines.The topological characteristics of the separation lines are changed by the interaction between the LEV and the Wing-Tip Vortex(WTV).For the high Ao As flow pattern,four unstable foci are found at the forewing and the hindwing respectively.The angle between the trajectory of the WTV and the model increases with increasing Ao A even though the slope of the WTV angle versus Ao A curve declines at the moderate AoAs.
文摘By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and by appling topology theory, the topological structures and vortex structure in the transverse section of a blade cascade were analyzed. Compared with conventional straight cascade, blade positive curving eliminates the separation line of the upper passage vortex, and leads the secondary vortex to change from close separation to open separation, while blade negative curving effects merely the positions of singular points and the intensities and scales of vortex.
基金supported by the National Natural Science Foundation of China (Nos. 10572076 and10872114)the Natural Science Foundation of Jiangsu Province (No. BK2008370)
文摘Based on the concepts of fractal super fibers, the （3, 9＋2）-circle and （9＋2, 3）-circle binary fractal sets are abstracted form such prototypes as wool fibers and human hairs, with the （3）-circle and the （9＋2）-circle fractal sets as subsets. As far as the （9＋2） topological patterns are concerned, the following propositions are proved： The （9＋2） topological patterns accurately exist, but are not unique. Their total number is 9. Among them, only two are allotropes. In other words, among the nine topological patterns, only two are independent （or fundamental）. Besides, we demonstrate that the （3, 9＋2）-circle and （9＋2, 3）-circle fractal sets are golden ones with symmetry breaking.
基金supported by the National Natural Science Foundation of China(10472003)Beijing Natural Science(3002002)+1 种基金Beijing Educational Committee Foundations(KM200410005019)Suspensofled by American MSC Company.
文摘ICM （Independent Continuous Mapping） method can solve topological optimization problems with the minimized weight as the objective and subjected to displacement constraints. To get a clearer topological configuration, by introducing the discrete condition of topological variables and integrating with the original objective, an optimal model with multi-objectives is formulated to make the topological variables approach 0 or 1 as near as possible, and the model reduces the effect of deleting rate on the result. The image-filtering method is employed to eliminate the checkerboard patterns and mesh dependence that occurred in the topology optimization of a continuum structure. The computational efficiency is enhanced through selecting quasi-active displacement constraints and a design region. Numerical examples indicate that this algorithm is robust and practicable, though the number of iterations is slightly increased with respect to the original algorithm.
文摘Wearable devices redefine the way people interact with machines.Despite the intensive effort in the design and fabrication of synthetic fibers to improve wearable device properties in terms of electronic and ionic conductivity,stretchability,com-fort,and washability,challenges remain in fabricating single fiber materials that optimize all properties simultaneously.In this work,we demonstrate a highly stretchable,ionic,and electronic conductive fabric via(1)the natural nanoscale chan-nels in fibers for effective ion transportation,(2)confining the electronic conductive material with the cellulose fibers,and(3)decoupling the property degradation of the fiber from deformation using the knitted pattern.The hierarchical structure created by cotton fibers can serve as ionic conductive channels as well as a robust multiscale scaffold to host infiltrated elec-tronic conductive materials.Cotton strands with ionic and electronic conductivity can be knitted into fabrics that are highly stretchable(~300%).Moreover,high ionic and electronic conductivity are observed with 2 S/m and 5 S/m,respectively,even under a strain of 175%.With the inherent advantages of cotton fabrics such as moisture-wicking,washability,comfort,and light-weightiness for wearable applications,our approach of directly functionalized cellulose can potentially be a promising route towards highly stretchable and wearable mixed conductors.
