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
This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transfo...This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transformation （CST） is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight. The trim condition must be attainable. This paper considers rotor blade configuration for the hover flight condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.展开更多
Reconstructing meandering paleo-channels is attracting global research attention. We implemented a novel method by comprehensively integrating migration models and sedimentary structures. Firstly, the migration archit...Reconstructing meandering paleo-channels is attracting global research attention. We implemented a novel method by comprehensively integrating migration models and sedimentary structures. Firstly, the migration architectures of the corresponding characteristics in planform and cross-sectional models were summarised as expansion, translation, expansion and translation, expansion and downstream rotation, constriction and downstream rotation, and expansion and countercurrent rotation models. Secondly, full continuous core data from 270 dense drilling wells were collected from the Daqing Oil Field in the Songliao Basin, China, providing information on rock textures, sedimentary cycles, and boundary information for the two layers being studied. Through a comprehensive analysis of dense drill cores and logging data, the abandoned channels and the initial and final channel centrelines were identified. Consequently, four profiles, including one longitudinal and three transverse sections, were constructed to reveal the cross-sectional structures and planform migration architecture. Profile interpretation revealed the evolution from the initial channel centreline to the final centreline. Using a method of rational interpolation, we were able to reconstruct the migration architecture of the meandering channels. The results showed that the average ancient bankfull width(Wc) was approximately 100 m, a single meandering belt was800 m, the radius of the curvature was 250 m, the length of the channel bend was 700 m, the average meander wavelength was 1300 m, the sinuosity was 3.0, and the annual average discharge rate was 450 m3/s. Furthermore, we compared the results from empirical equations, which verified that our reconstruction is both feasible and potentially widely applicable.展开更多
Quantitative studies on river channel lateral erosion/accretion area changes over time can reveal the characteristics of channel evolution. Taking the 213-km-long Linhe reach braided channel of the Yellow River as an ...Quantitative studies on river channel lateral erosion/accretion area changes over time can reveal the characteristics of channel evolution. Taking the 213-km-long Linhe reach braided channel of the Yellow River as an example, area changes in channel bank ero- sion/accretion in four sub-reaches （S1, S2, S3 and S4） over 19 different periods were evalu- ated on the basis of remote sensing images captured since 1977. Mean channel shrinkage rate for the whole river reach was also obtained. Results show that the left and right banks of the Linhe reach were dominated by lateral net accretion between 1977 and 2014. The channel area of this section of the Yellow River was characterized by reduction between 1977 and 2001, while periods of alternate erosion and accretion occurred subsequent to 2001. Mean channel shrinkage rate in the Linhe reach braided channel was 6.15 km2/yr between 1977 and 2014, while the most remarkable changes in channel planform occurred in the 1990s. Compared to 1995, channel length and sinuosity increased by 5.8% and 6.6% by 2000, while channel area and mean width decreased by 39.4% and 42.8%, respectively. Significant changes in channel planform and shrinkage of the Linhe reach occurred in the 1990s, mainly as a result of the joint-operation of the Longyangxia and Liujiaxia reservoirs since 1986, which caused substantial reductions in runoff and sediment flux during the annual flooding season. In addition, bank erosion/accretion in the four sub-reaches was affected by the physical properties of local banks, engineering emplaced to protect channel banks, and hydrodynamic differences. However, since the implementation of integrated river manage- ment measures from 2000 onwards, these changes have been significantly mitigated and the health of the Linhe reach braided channel of the Yellow River has been restored.展开更多
When considering the practical engineering application of a waverider,the on-design and off-design aerodynamic characteristics of the design conditions,especially the lift-to-drag ratio and the stability,deserve atten...When considering the practical engineering application of a waverider,the on-design and off-design aerodynamic characteristics of the design conditions,especially the lift-to-drag ratio and the stability,deserve attention.According to recently studies,the planform and rear sight shape of a waverider are closely related to the above aerodynamic performance.Thus,the planform leading-edge profile curve used to design the planform shape of a vehicle is applied to designing an osculating cone waverider.Two key parameters concerned in planform and rear sight shape,namely the plan view sweep angle of the leading edge and the dihedral angle of the underside are introduced to the waverider design process.Each parameter is inserted in the control curve equation.Especially,a parameterization scheme is put forward for the free adjustment of the sweep angle along the leading edge.Finally,three examples are generated for verification and investigation.After the verification process based on the inviscid flow field of one case,the influences of the sweep and dihedral angles on the lift-to-drag ratio and the lateral static stability are evaluated,and meaningful results are obtained.Based on these results,we can conclude that,considering the maximum lift-to-drag ratio,the sweep angle plays a role on the lift-to-drag ratio only at subsonic and trans/supersonic speed as a negligible effect is observed at hypersonic speeds,whereas the dihedral angle is seem to produce a relevant difference at hypersonic speeds.Considering the lateral static stability,the dihedral angles have more influence on the waverider than the sweep angles.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.
基金co-supported by National Foundation for Science and Technology Development(NAFOSTED) of Vietnam (Project No. 107.04-2012.25)the Agency for Defense Development in the Republic of Korea under contract UD100048JDthe project KARI-University Partnership Program 2009-09-2
文摘This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transformation （CST） is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight. The trim condition must be attainable. This paper considers rotor blade configuration for the hover flight condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.
基金supported by the National Natural Science Foundation of China (No. 41372125)National Science and Technology Major Project (No. 2016ZX05063002-006)
文摘Reconstructing meandering paleo-channels is attracting global research attention. We implemented a novel method by comprehensively integrating migration models and sedimentary structures. Firstly, the migration architectures of the corresponding characteristics in planform and cross-sectional models were summarised as expansion, translation, expansion and translation, expansion and downstream rotation, constriction and downstream rotation, and expansion and countercurrent rotation models. Secondly, full continuous core data from 270 dense drilling wells were collected from the Daqing Oil Field in the Songliao Basin, China, providing information on rock textures, sedimentary cycles, and boundary information for the two layers being studied. Through a comprehensive analysis of dense drill cores and logging data, the abandoned channels and the initial and final channel centrelines were identified. Consequently, four profiles, including one longitudinal and three transverse sections, were constructed to reveal the cross-sectional structures and planform migration architecture. Profile interpretation revealed the evolution from the initial channel centreline to the final centreline. Using a method of rational interpolation, we were able to reconstruct the migration architecture of the meandering channels. The results showed that the average ancient bankfull width(Wc) was approximately 100 m, a single meandering belt was800 m, the radius of the curvature was 250 m, the length of the channel bend was 700 m, the average meander wavelength was 1300 m, the sinuosity was 3.0, and the annual average discharge rate was 450 m3/s. Furthermore, we compared the results from empirical equations, which verified that our reconstruction is both feasible and potentially widely applicable.
基金National Natural Science Foundation of China,No.41271027,No.41571005National Basic Research Program of China,No.2011CB403305
文摘Quantitative studies on river channel lateral erosion/accretion area changes over time can reveal the characteristics of channel evolution. Taking the 213-km-long Linhe reach braided channel of the Yellow River as an example, area changes in channel bank ero- sion/accretion in four sub-reaches （S1, S2, S3 and S4） over 19 different periods were evalu- ated on the basis of remote sensing images captured since 1977. Mean channel shrinkage rate for the whole river reach was also obtained. Results show that the left and right banks of the Linhe reach were dominated by lateral net accretion between 1977 and 2014. The channel area of this section of the Yellow River was characterized by reduction between 1977 and 2001, while periods of alternate erosion and accretion occurred subsequent to 2001. Mean channel shrinkage rate in the Linhe reach braided channel was 6.15 km2/yr between 1977 and 2014, while the most remarkable changes in channel planform occurred in the 1990s. Compared to 1995, channel length and sinuosity increased by 5.8% and 6.6% by 2000, while channel area and mean width decreased by 39.4% and 42.8%, respectively. Significant changes in channel planform and shrinkage of the Linhe reach occurred in the 1990s, mainly as a result of the joint-operation of the Longyangxia and Liujiaxia reservoirs since 1986, which caused substantial reductions in runoff and sediment flux during the annual flooding season. In addition, bank erosion/accretion in the four sub-reaches was affected by the physical properties of local banks, engineering emplaced to protect channel banks, and hydrodynamic differences. However, since the implementation of integrated river manage- ment measures from 2000 onwards, these changes have been significantly mitigated and the health of the Linhe reach braided channel of the Yellow River has been restored.
基金Project supported by the National Natural Science Foundation of China(No.11702322)the Natural Science Foundation of Hunan Province,China(No.2018JJ3589)。
文摘When considering the practical engineering application of a waverider,the on-design and off-design aerodynamic characteristics of the design conditions,especially the lift-to-drag ratio and the stability,deserve attention.According to recently studies,the planform and rear sight shape of a waverider are closely related to the above aerodynamic performance.Thus,the planform leading-edge profile curve used to design the planform shape of a vehicle is applied to designing an osculating cone waverider.Two key parameters concerned in planform and rear sight shape,namely the plan view sweep angle of the leading edge and the dihedral angle of the underside are introduced to the waverider design process.Each parameter is inserted in the control curve equation.Especially,a parameterization scheme is put forward for the free adjustment of the sweep angle along the leading edge.Finally,three examples are generated for verification and investigation.After the verification process based on the inviscid flow field of one case,the influences of the sweep and dihedral angles on the lift-to-drag ratio and the lateral static stability are evaluated,and meaningful results are obtained.Based on these results,we can conclude that,considering the maximum lift-to-drag ratio,the sweep angle plays a role on the lift-to-drag ratio only at subsonic and trans/supersonic speed as a negligible effect is observed at hypersonic speeds,whereas the dihedral angle is seem to produce a relevant difference at hypersonic speeds.Considering the lateral static stability,the dihedral angles have more influence on the waverider than the sweep angles.
