Windblown sand transport is a leading factor in the geophysical evolution of arid and semi-arid regions.The evolution speed is usually indicated by the sand transport rate that is a function of launch velocity of sand...Windblown sand transport is a leading factor in the geophysical evolution of arid and semi-arid regions.The evolution speed is usually indicated by the sand transport rate that is a function of launch velocity of sand particle,which has been investigated by the experimental measurement and numerical simulation.However,the obtained results in literatures are inconsistent.Some researchers have discovered a relation between average launch velocity and wind shear velocity,while some other researchers have suggested that average launch velocity is independent of wind shear velocity.The inconsistence of launch velocity leads to a controversy in the scaling law of the sand transport rate in the windblown case.On the contrary,in subaqueous case,the scaling law of the sand transport rate has been widely accepted as a cubic function of fluid shear velocity.In order to explain the debates surrounding the windblown case and the difference between windblown and subaquatic cases,this study reinvestigates the scaling law of the vertical launch velocity of windblown transported sand particles by using a dimensional analysis in consideration of the compatibility of the characteristic time of sand particle motion and that of air flow.Then a wind tunnel experiment is conducted to confirm the revisited scaling law,where the sand particle motion pictures are recorded by a high-speed camera and then the launch velocity is solved by the particle tracking velocimetry.By incorporating the results of dimensional analysis and wind tunnel experiment,it can be concluded that,the ratio of saltons number to reptons number determines the scaling law of sand particle launch velocity and that of sand transport rate,and using this ratio is able to explain the discrepancies among the classical models of steady sand transport.Moreover,the resulting scaling law can explain the sand sieving phenomenon:a greater fraction of large grains is observed as the distance to the wind tunnel entrance becomes larger.展开更多
It is very necessary for investigation on mechanism of windblown sand movement to understand and find out effective measures of preventing and reducing windblown sand. This also deals with some general features and ho...It is very necessary for investigation on mechanism of windblown sand movement to understand and find out effective measures of preventing and reducing windblown sand. This also deals with some general features and hot spots in the scientific forelands, such as multi-scale problems, interactions among multi-physical-fields, randomness and non-linearity as well as complex systems. In recent years, a series of experiments in wind tunnels and theoretical modeling as well as computer simulation have been taken by our research group (the Laboratory of Environmental Mechanics on Windblown Sand Movement in Lanzhou University) in a cross-disciplinary (mechanics and geography) viewpoint. Several original and essential studies were explored such as the main regularities of charges on sand particles, the mechanisms of electric field in windblown sand flux, the effects induced by the electric field on the flux, the microwave propagations, the evolution process of windblown sand flux under mutual couple interactions among several physical fields, and the simulation of the main features of Aeolian sand ripples.展开更多
It is very necessary for the investigation on mechanism of windblown sand movement to under- stand and find out effective measures of preventing and reducing danger of windblown sands,which al- so deals with some gene...It is very necessary for the investigation on mechanism of windblown sand movement to under- stand and find out effective measures of preventing and reducing danger of windblown sands,which al- so deals with some general characters and hot spots in the scientific forelands,such as multi-scale prob- lems,interactions among multi-physical-fields,ran- domness and nonlinearity as well as complex sys- tems.In recent years,a series of experiments in wind tunnels and theoretical modeling as well as computer simulation have been undertaken in the re- search group of environmental mechanics on wind- blown sand movement in Lanzhou University with the point of mechanical and geography intersecting view.Some original and essential progress has been achieved, which includes that the main regu- larities of charges on sand particles and the electric field in windblown sand flux and the effect of the electric field on the flux and the microwave propaga- tion are revealed,and the evolution process of windblown sand flux under the mutual couple inter- actions among several physical fields are predicted as well as the main features of Aeolian sand ripples are simulated.展开更多
基金funded by the National Natural Science Foundation of China(11402190)the China Postdoctoral Science foundation(2014M552443)the Shaanxi Province Natural Science Foundation Research Project(2018JM1021)
文摘Windblown sand transport is a leading factor in the geophysical evolution of arid and semi-arid regions.The evolution speed is usually indicated by the sand transport rate that is a function of launch velocity of sand particle,which has been investigated by the experimental measurement and numerical simulation.However,the obtained results in literatures are inconsistent.Some researchers have discovered a relation between average launch velocity and wind shear velocity,while some other researchers have suggested that average launch velocity is independent of wind shear velocity.The inconsistence of launch velocity leads to a controversy in the scaling law of the sand transport rate in the windblown case.On the contrary,in subaqueous case,the scaling law of the sand transport rate has been widely accepted as a cubic function of fluid shear velocity.In order to explain the debates surrounding the windblown case and the difference between windblown and subaquatic cases,this study reinvestigates the scaling law of the vertical launch velocity of windblown transported sand particles by using a dimensional analysis in consideration of the compatibility of the characteristic time of sand particle motion and that of air flow.Then a wind tunnel experiment is conducted to confirm the revisited scaling law,where the sand particle motion pictures are recorded by a high-speed camera and then the launch velocity is solved by the particle tracking velocimetry.By incorporating the results of dimensional analysis and wind tunnel experiment,it can be concluded that,the ratio of saltons number to reptons number determines the scaling law of sand particle launch velocity and that of sand transport rate,and using this ratio is able to explain the discrepancies among the classical models of steady sand transport.Moreover,the resulting scaling law can explain the sand sieving phenomenon:a greater fraction of large grains is observed as the distance to the wind tunnel entrance becomes larger.
文摘It is very necessary for investigation on mechanism of windblown sand movement to understand and find out effective measures of preventing and reducing windblown sand. This also deals with some general features and hot spots in the scientific forelands, such as multi-scale problems, interactions among multi-physical-fields, randomness and non-linearity as well as complex systems. In recent years, a series of experiments in wind tunnels and theoretical modeling as well as computer simulation have been taken by our research group (the Laboratory of Environmental Mechanics on Windblown Sand Movement in Lanzhou University) in a cross-disciplinary (mechanics and geography) viewpoint. Several original and essential studies were explored such as the main regularities of charges on sand particles, the mechanisms of electric field in windblown sand flux, the effects induced by the electric field on the flux, the microwave propagations, the evolution process of windblown sand flux under mutual couple interactions among several physical fields, and the simulation of the main features of Aeolian sand ripples.
基金the Key Project of the National Natural Science Foundation of China(No.10532040)
文摘It is very necessary for the investigation on mechanism of windblown sand movement to under- stand and find out effective measures of preventing and reducing danger of windblown sands,which al- so deals with some general characters and hot spots in the scientific forelands,such as multi-scale prob- lems,interactions among multi-physical-fields,ran- domness and nonlinearity as well as complex sys- tems.In recent years,a series of experiments in wind tunnels and theoretical modeling as well as computer simulation have been undertaken in the re- search group of environmental mechanics on wind- blown sand movement in Lanzhou University with the point of mechanical and geography intersecting view.Some original and essential progress has been achieved, which includes that the main regu- larities of charges on sand particles and the electric field in windblown sand flux and the effect of the electric field on the flux and the microwave propaga- tion are revealed,and the evolution process of windblown sand flux under the mutual couple inter- actions among several physical fields are predicted as well as the main features of Aeolian sand ripples are simulated.