Transonic rudder buzz responses based on the computational fluid dynamics or computational structural dynamics(CFD/CSD)loosely method are analyzed for a tailless flying wing unmanned aerial vehicle(UAV).The Reynolds-a...Transonic rudder buzz responses based on the computational fluid dynamics or computational structural dynamics(CFD/CSD)loosely method are analyzed for a tailless flying wing unmanned aerial vehicle(UAV).The Reynolds-averaged Navier-Stokes(RANS)equations and finite element methods based on the detailed aerodynamic and structural model are established,in which the aerodynamic dynamic meshes adopt the unstructured dynamic meshes based on the combination of spring-based smoothing and local remeshing methods,and the lower-upper symmetric-Gauss-Seidel(LU-SGS)iteration and Harten-Lax-van Leer-Einfeldt-Wada(HLLEW)space discrete methods based on the shear stress transport(SST)turbulence model are used to calculate the aerodynamic force.The constraints of the rudder motions are fixed at the end of structural model of the flying wing UAV,and the structural geometric nonlinearities are also considered in the flying wing UAV with a high aspect ratio.The interfaces between structural and aerodynamic models are built with an exact match surface where load transferring is performed based on 3Dinterpolation.The flying wing UAV transonic buzz responses based on the aerodynamic structural coupling method are studied,and the rudder buzz responses and aileron,elevator and flap vibration responses caused by rudder motion are also investigated.The effects of attack,height,rotating angular frequency and Mach number under transonic conditions on the flying wing UAV rudder buzz responses are discussed.The results can be regarded as a reference for the flying wing UAV engineering vibration analysis.展开更多
Youngsters learn that with the right approach,museums can rhyme with fun Desp Ite her childish looks,eight-year-old Meng Ziyu isn’t like other girls her age-infatuated with Barbie dolls or the latest Disney film.What...Youngsters learn that with the right approach,museums can rhyme with fun Desp Ite her childish looks,eight-year-old Meng Ziyu isn’t like other girls her age-infatuated with Barbie dolls or the latest Disney film.What she really gets a kick out of is visiting a museum with her mother on weekends.展开更多
同学们,你们喜欢吃奶酪吗?本期,Abby和Jack围绕着奶酪展开了一段有趣的小故事,一起来看看吧!Real Cheese真正的奶酪Abby:I wish my parents would take me to Europe.Jack:Why do you want to go there?Abby:I loveEuropeanfood,especia...同学们,你们喜欢吃奶酪吗?本期,Abby和Jack围绕着奶酪展开了一段有趣的小故事,一起来看看吧!Real Cheese真正的奶酪Abby:I wish my parents would take me to Europe.Jack:Why do you want to go there?Abby:I loveEuropeanfood,especiallypizza.Jack:You don't need to go to Italy to eat pizza;you can eat it here.Abby:But I want to eat real Italian pizza with authentic(正宗的)European cheese on top!展开更多
Over 50 genera of bees release pollen from flower anthers using thoracic vibrations,a phenomenon known as buzz-pollination.The efficiency of this process is directly affected by the mechanical properties of the buzzes...Over 50 genera of bees release pollen from flower anthers using thoracic vibrations,a phenomenon known as buzz-pollination.The efficiency of this process is directly affected by the mechanical properties of the buzzes,namely the duration,amplitude,and frequency.Nonetheless,although the effects of the former two properties are well described,the role of buzz frequency on pollen release remains unclear.Furthermore,nearly all of the existing studies describing vibrational properties of natural buzz-pollination are limited to bumblebees(Bombus)and carpenter bees(Xvlocopa)constraining our current understanding of this behavior and its evolution.Therefore,we attempted to minimize this shortcoming by testing whether flower anthers exhibit optimal frequency for pollen release and whether bees tune their buzzes to match these(optimal)frequencies.If true,certain frequencies will trigger more pollen release and lighter bees will reach buzz frequencies closer to this optimum to compensate their smaller buzz amplitudes.Two strategies were used to test these hypotheses:(i)the use of(artificial)vibrational playbacks in a broad range of buzz frequencies and amplitudes to assess pollen release by tomato plants(Solarium Ivcopersicum L.)and(ii)the recording of natural buzzes of Neotropical bees visiting tomato plants during pollination.The playback experiment indicates that although buzz frequency does affect pollen release,no optimal frequency exists for that.In addition,the recorded results of natural buzz-pollination reveal that buzz frequencies vary with bee genera and are not correlated with body size.Therefore,neither bees nor plants are tuned to optimal pollen release frequencies.Bee frequency of buzz-pollination is a likely consequence of the insect flight machinery adapted to reach higher accelerations,while flower plant response to buzz-pollination is the likely result of its pollen granular properties.展开更多
Socialism With Chinese Characteristics Socialism with Chinese Characteristics refers to building a socialist system under the leadership of the Communist Party of China(CPC) and in light of China’s basic condition.It...Socialism With Chinese Characteristics Socialism with Chinese Characteristics refers to building a socialist system under the leadership of the Communist Party of China(CPC) and in light of China’s basic condition.It contains five basic components:a peo- ple-oriented approach,a market econo- my,common prosperity,Chinese culture and socialist democracy.展开更多
Voluntary research organizations are becoming more significant forces in the study of ‘lights in the sky’ something unusual was happening on the quiet, clear night in Hangzhou, Zhejiang Province, on July 7 this year...Voluntary research organizations are becoming more significant forces in the study of ‘lights in the sky’ something unusual was happening on the quiet, clear night in Hangzhou, Zhejiang Province, on July 7 this year. Because of sightings of an Unidentified Flying Object (UFO), more than 20 flights were postponed for 56 minutes at the city’s Xiaoshan International Airport. Immediately the event was connected with alien spacecraft. Speculations and rumors were everywhere.展开更多
基金supported by the Natural Science Foundation of China(No.61074155)the Shaanxi Provincial Natural Science Foundation of China(No.2013JM015)
文摘Transonic rudder buzz responses based on the computational fluid dynamics or computational structural dynamics(CFD/CSD)loosely method are analyzed for a tailless flying wing unmanned aerial vehicle(UAV).The Reynolds-averaged Navier-Stokes(RANS)equations and finite element methods based on the detailed aerodynamic and structural model are established,in which the aerodynamic dynamic meshes adopt the unstructured dynamic meshes based on the combination of spring-based smoothing and local remeshing methods,and the lower-upper symmetric-Gauss-Seidel(LU-SGS)iteration and Harten-Lax-van Leer-Einfeldt-Wada(HLLEW)space discrete methods based on the shear stress transport(SST)turbulence model are used to calculate the aerodynamic force.The constraints of the rudder motions are fixed at the end of structural model of the flying wing UAV,and the structural geometric nonlinearities are also considered in the flying wing UAV with a high aspect ratio.The interfaces between structural and aerodynamic models are built with an exact match surface where load transferring is performed based on 3Dinterpolation.The flying wing UAV transonic buzz responses based on the aerodynamic structural coupling method are studied,and the rudder buzz responses and aileron,elevator and flap vibration responses caused by rudder motion are also investigated.The effects of attack,height,rotating angular frequency and Mach number under transonic conditions on the flying wing UAV rudder buzz responses are discussed.The results can be regarded as a reference for the flying wing UAV engineering vibration analysis.
文摘Youngsters learn that with the right approach,museums can rhyme with fun Desp Ite her childish looks,eight-year-old Meng Ziyu isn’t like other girls her age-infatuated with Barbie dolls or the latest Disney film.What she really gets a kick out of is visiting a museum with her mother on weekends.
文摘同学们,你们喜欢吃奶酪吗?本期,Abby和Jack围绕着奶酪展开了一段有趣的小故事,一起来看看吧!Real Cheese真正的奶酪Abby:I wish my parents would take me to Europe.Jack:Why do you want to go there?Abby:I loveEuropeanfood,especiallypizza.Jack:You don't need to go to Italy to eat pizza;you can eat it here.Abby:But I want to eat real Italian pizza with authentic(正宗的)European cheese on top!
基金support provided by the CAPES Foundation(Brazilian Ministry of Education)the National Council of Scientific and Technological Development(CNPq+1 种基金Brazilian Ministry of Science and Technology)the Minas Gerais State Foundation for Research Aid(FAPEMIG)were also greatly appreciated.
文摘Over 50 genera of bees release pollen from flower anthers using thoracic vibrations,a phenomenon known as buzz-pollination.The efficiency of this process is directly affected by the mechanical properties of the buzzes,namely the duration,amplitude,and frequency.Nonetheless,although the effects of the former two properties are well described,the role of buzz frequency on pollen release remains unclear.Furthermore,nearly all of the existing studies describing vibrational properties of natural buzz-pollination are limited to bumblebees(Bombus)and carpenter bees(Xvlocopa)constraining our current understanding of this behavior and its evolution.Therefore,we attempted to minimize this shortcoming by testing whether flower anthers exhibit optimal frequency for pollen release and whether bees tune their buzzes to match these(optimal)frequencies.If true,certain frequencies will trigger more pollen release and lighter bees will reach buzz frequencies closer to this optimum to compensate their smaller buzz amplitudes.Two strategies were used to test these hypotheses:(i)the use of(artificial)vibrational playbacks in a broad range of buzz frequencies and amplitudes to assess pollen release by tomato plants(Solarium Ivcopersicum L.)and(ii)the recording of natural buzzes of Neotropical bees visiting tomato plants during pollination.The playback experiment indicates that although buzz frequency does affect pollen release,no optimal frequency exists for that.In addition,the recorded results of natural buzz-pollination reveal that buzz frequencies vary with bee genera and are not correlated with body size.Therefore,neither bees nor plants are tuned to optimal pollen release frequencies.Bee frequency of buzz-pollination is a likely consequence of the insect flight machinery adapted to reach higher accelerations,while flower plant response to buzz-pollination is the likely result of its pollen granular properties.
文摘Socialism With Chinese Characteristics Socialism with Chinese Characteristics refers to building a socialist system under the leadership of the Communist Party of China(CPC) and in light of China’s basic condition.It contains five basic components:a peo- ple-oriented approach,a market econo- my,common prosperity,Chinese culture and socialist democracy.
文摘Voluntary research organizations are becoming more significant forces in the study of ‘lights in the sky’ something unusual was happening on the quiet, clear night in Hangzhou, Zhejiang Province, on July 7 this year. Because of sightings of an Unidentified Flying Object (UFO), more than 20 flights were postponed for 56 minutes at the city’s Xiaoshan International Airport. Immediately the event was connected with alien spacecraft. Speculations and rumors were everywhere.
