The effects of corrugation and wing planform （shape and aspect ratio） on the aerodynamic force production of model insect wings in sweeping （rotating after an initial start） motion at Reynolds number 200 and 3500 ...The effects of corrugation and wing planform （shape and aspect ratio） on the aerodynamic force production of model insect wings in sweeping （rotating after an initial start） motion at Reynolds number 200 and 3500 at angle of attack 40℃ are investigated, using the method of computational fluid dynamics. A representative wing corrugation is considered. Wing-shape and aspect ratio （AR） of ten representative insect wings are considered; they are the wings of fruit fly, cranefly, dronefly, hoverfly, ladybird, bumblebee, honeybee, lacewing （forewing）, hawkmoth and dragon- fly （forewing）, respectively （AR of these wings varies greatly, from 2.84 to 5.45）. The following facts are shown. （1） The corrugated and flat-plate wings produce approximately the same aerodynamic forces. This is because for a sweeping wing at large angle of attack, the length scale of the corrugation is much smaller than the size of the separated flow region or the size of the leading edge vortex （LEV）. （2） The variation in wing shape can have considerable effects on the aerodynamic force; but it has only minor effects on the force coefficients when the velocity at r2 （the radius of the second ：moment of wing area） is used as the reference velocity; i.e. the force coefficients are almost unaffected by the variation in wing shape. （3） The effects of AR are remarkably small： whenAR increases from 2.8 to 5.5, the force coefficients vary only slightly; flowfield results show that when AR is relatively large, the part of the LEV on the outer part of the wings sheds during the sweeping motion. As AR is increased, on one hand, the force coefficients will be increased due to the reduction of 3-dimensional flow effects; on the other hand, they will be decreased due to the shedding of part of the LEV; these two effects approximately cancel each other, resulting in only minor change of the force coefficients.展开更多
Both interchannel wetlands and multi-channels are crucial geomorphologic units in an anastomosing river system.Planform characteristics and development of interchannel wetlands and multi-channels control the character...Both interchannel wetlands and multi-channels are crucial geomorphologic units in an anastomosing river system.Planform characteristics and development of interchannel wetlands and multi-channels control the characteristics of anastomosing rivers.To under-stand the role that interchannel wetlands play in the development of anastomosing rivers,a study was conducted on the Maqu Reach of the Upper Yellow River(MRUYR),a gravel-bed anastomosing river characterized by highly developed interchannel wetlands and ana-branches.Geomorphologic units in the studied reach were extracted from high resolution satellite imagery in Google Earth.The size distributions of interchannel wetlands and inter-channel wetland clusters(IWCs),a special combination of interchannel wetlands and ana-branches,were investigated.Geomorphologic parameters,including the ratio of interchannel wetland area to IWC area(P),shoreline density(DL),and node density(Dn)were used to analyze planform characteristics of IWCs and the development of multi-channels in the stud-ied reach.The results suggest that small or middle sized interchannel wetlands and large or mega sized IWCs are more common at the study site.The area of IWC(Su)is highly cor-related with other geomorphologic parameters.P increases with increasing Su,and the upper limit is about 80%,which indicates that the development of interchannel wetlands and ana-branches in the IWC is in the equilibrium stage.In contrast,D~and D,show a tendency to decrease with increasing Su due to diverse evolution processes in IWCs with different sizes.There are three main reasons leading to the formation of IWCs:varying stream power due to the meandering principal channel;development of the river corridor due to the weakening of geologic structure control;and high stability of interchannel wetlands due to conservation by shoreline vegetation.展开更多
1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoratio...1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the展开更多
Meandering rivers of various scales are found globally and exhibit a high degree of regularity in their evolutionary processes.This study utilized remote sensing interpretation techniques to extract and analyze the pl...Meandering rivers of various scales are found globally and exhibit a high degree of regularity in their evolutionary processes.This study utilized remote sensing interpretation techniques to extract and analyze the planform migration characteristics of meandering rivers.Specifically,remote sensing images of three meandering rivers—the Black and White Rivers in the Tibetan Plateau and the Itui River in the Amazon Basin—were selected for this analysis.By comparing these observations with existing research data,this study quantitatively revealed the lag response patterns in the planform migration processes of meandering rivers.The findings of the study revealed several key insights.(1)The average migration rates for the three rivers were determined to be 1.74,3.84,and 2.34 m/a,respectively.The critical values of the relative curvature radius for the river channels ranged from 1.5 to 2.0,1.7 to 2.2,and 2.5 to 3.0,where local migration rate peaks were observed.These findings align with previous research that reported critical values between 2.0 and 4.0.(2)A significant lag is observed in the migration rate relative to curvature in spatial variation,with lag distances for the Black,White,and Itui Rivers measuring 227,281,and 324 m,corresponding to 2.02,2.39,and 3.15 times the river width,respectively.(3)A comparison with other meandering rivers indicates that,despite significant variations in climatic and hydrological conditions and river discharges differing by over 1,000times,the ratio of lag distance to river width(relative lag distance)for meandering rivers consistently falls within the range of 2.0to 4.0.This study suggests that the establishment of critical values for the relative curvature radius and the concentration of the relative lag distance reflects distinct quantitative relationships that emerge during the evolutionary processes of meandering rivers,aiming to minimize energy expenditure.These relationships appear to be applicable to various types of alluvial rivers.展开更多
基金The project supported by the National Natural Science Foundation of China(10232010 and 10472008)Ph.D.Student Foundation of Chinese Ministry of Education(20030006022)
文摘The effects of corrugation and wing planform （shape and aspect ratio） on the aerodynamic force production of model insect wings in sweeping （rotating after an initial start） motion at Reynolds number 200 and 3500 at angle of attack 40℃ are investigated, using the method of computational fluid dynamics. A representative wing corrugation is considered. Wing-shape and aspect ratio （AR） of ten representative insect wings are considered; they are the wings of fruit fly, cranefly, dronefly, hoverfly, ladybird, bumblebee, honeybee, lacewing （forewing）, hawkmoth and dragon- fly （forewing）, respectively （AR of these wings varies greatly, from 2.84 to 5.45）. The following facts are shown. （1） The corrugated and flat-plate wings produce approximately the same aerodynamic forces. This is because for a sweeping wing at large angle of attack, the length scale of the corrugation is much smaller than the size of the separated flow region or the size of the leading edge vortex （LEV）. （2） The variation in wing shape can have considerable effects on the aerodynamic force; but it has only minor effects on the force coefficients when the velocity at r2 （the radius of the second ：moment of wing area） is used as the reference velocity; i.e. the force coefficients are almost unaffected by the variation in wing shape. （3） The effects of AR are remarkably small： whenAR increases from 2.8 to 5.5, the force coefficients vary only slightly; flowfield results show that when AR is relatively large, the part of the LEV on the outer part of the wings sheds during the sweeping motion. As AR is increased, on one hand, the force coefficients will be increased due to the reduction of 3-dimensional flow effects; on the other hand, they will be decreased due to the shedding of part of the LEV; these two effects approximately cancel each other, resulting in only minor change of the force coefficients.
基金National Natural Science Foundation of China,No.41571005,No.41271027
文摘Both interchannel wetlands and multi-channels are crucial geomorphologic units in an anastomosing river system.Planform characteristics and development of interchannel wetlands and multi-channels control the characteristics of anastomosing rivers.To under-stand the role that interchannel wetlands play in the development of anastomosing rivers,a study was conducted on the Maqu Reach of the Upper Yellow River(MRUYR),a gravel-bed anastomosing river characterized by highly developed interchannel wetlands and ana-branches.Geomorphologic units in the studied reach were extracted from high resolution satellite imagery in Google Earth.The size distributions of interchannel wetlands and inter-channel wetland clusters(IWCs),a special combination of interchannel wetlands and ana-branches,were investigated.Geomorphologic parameters,including the ratio of interchannel wetland area to IWC area(P),shoreline density(DL),and node density(Dn)were used to analyze planform characteristics of IWCs and the development of multi-channels in the stud-ied reach.The results suggest that small or middle sized interchannel wetlands and large or mega sized IWCs are more common at the study site.The area of IWC(Su)is highly cor-related with other geomorphologic parameters.P increases with increasing Su,and the upper limit is about 80%,which indicates that the development of interchannel wetlands and ana-branches in the IWC is in the equilibrium stage.In contrast,D~and D,show a tendency to decrease with increasing Su due to diverse evolution processes in IWCs with different sizes.There are three main reasons leading to the formation of IWCs:varying stream power due to the meandering principal channel;development of the river corridor due to the weakening of geologic structure control;and high stability of interchannel wetlands due to conservation by shoreline vegetation.
基金supported by National Natural Sciences Fund (No. 41372125)Fund of Ministry of Education of Hubei Province (No. Q20121210)
文摘1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the
基金supported by the National Natural Science Foundation of China(Grant Nos.U2040215&52379079)。
文摘Meandering rivers of various scales are found globally and exhibit a high degree of regularity in their evolutionary processes.This study utilized remote sensing interpretation techniques to extract and analyze the planform migration characteristics of meandering rivers.Specifically,remote sensing images of three meandering rivers—the Black and White Rivers in the Tibetan Plateau and the Itui River in the Amazon Basin—were selected for this analysis.By comparing these observations with existing research data,this study quantitatively revealed the lag response patterns in the planform migration processes of meandering rivers.The findings of the study revealed several key insights.(1)The average migration rates for the three rivers were determined to be 1.74,3.84,and 2.34 m/a,respectively.The critical values of the relative curvature radius for the river channels ranged from 1.5 to 2.0,1.7 to 2.2,and 2.5 to 3.0,where local migration rate peaks were observed.These findings align with previous research that reported critical values between 2.0 and 4.0.(2)A significant lag is observed in the migration rate relative to curvature in spatial variation,with lag distances for the Black,White,and Itui Rivers measuring 227,281,and 324 m,corresponding to 2.02,2.39,and 3.15 times the river width,respectively.(3)A comparison with other meandering rivers indicates that,despite significant variations in climatic and hydrological conditions and river discharges differing by over 1,000times,the ratio of lag distance to river width(relative lag distance)for meandering rivers consistently falls within the range of 2.0to 4.0.This study suggests that the establishment of critical values for the relative curvature radius and the concentration of the relative lag distance reflects distinct quantitative relationships that emerge during the evolutionary processes of meandering rivers,aiming to minimize energy expenditure.These relationships appear to be applicable to various types of alluvial rivers.
