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
This paper presents examples of field data of extreme seiche waves measured at Coffs Harbour by MHL and describes the generation and measuring methodology to detect and reduce seiche agitation in the Coifs Harbour boa...This paper presents examples of field data of extreme seiche waves measured at Coffs Harbour by MHL and describes the generation and measuring methodology to detect and reduce seiche agitation in the Coifs Harbour boat ramp using a 3D physical model. The paper also discusses the techniques in investigating a short wave problem of stability in the same model where a long wave is simulated. Waves offshore of Coffs Harbour at 80 m depth have been recorded by MHL for a period of over 30 years. Long waves have been simultaneously measured in the harbour over a period of a decade. These data enabled the model to be verified on two dates （4/6/12, 5/9/14） when high long waves were recorded at the boat ramp harbour under storm and non-storm conditions. Long waves are generated in harbours due to group bounded long wave and surf beat or edge waves. The paper presents methodologies of generating long waves both numerically and by using physical models, and discusses the advantages and disadvantages of these generation techniques. Numerical modelling carried out using long period regular waves in a previous investigation predicted reductions up to 50% due to change of planform of the boat ramp harbour where an area next to the boat ramp was excavated and roughness elements introduced to dampen long periods. The 3D physical model simulated a 25% decrease in the long wave energy in the boat ramp when a suitable change in the planform was made. A 3D undistorted model of scale 1：58 was used in the investigation.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
文摘This paper presents examples of field data of extreme seiche waves measured at Coffs Harbour by MHL and describes the generation and measuring methodology to detect and reduce seiche agitation in the Coifs Harbour boat ramp using a 3D physical model. The paper also discusses the techniques in investigating a short wave problem of stability in the same model where a long wave is simulated. Waves offshore of Coffs Harbour at 80 m depth have been recorded by MHL for a period of over 30 years. Long waves have been simultaneously measured in the harbour over a period of a decade. These data enabled the model to be verified on two dates （4/6/12, 5/9/14） when high long waves were recorded at the boat ramp harbour under storm and non-storm conditions. Long waves are generated in harbours due to group bounded long wave and surf beat or edge waves. The paper presents methodologies of generating long waves both numerically and by using physical models, and discusses the advantages and disadvantages of these generation techniques. Numerical modelling carried out using long period regular waves in a previous investigation predicted reductions up to 50% due to change of planform of the boat ramp harbour where an area next to the boat ramp was excavated and roughness elements introduced to dampen long periods. The 3D physical model simulated a 25% decrease in the long wave energy in the boat ramp when a suitable change in the planform was made. A 3D undistorted model of scale 1：58 was used in the investigation.
