In this paper,according to the cantilever beam of fetching carton mechanism in square packaging machine, considering the impact of motion of air cylinder on it,its dynamics model and finite element model are built by ...In this paper,according to the cantilever beam of fetching carton mechanism in square packaging machine, considering the impact of motion of air cylinder on it,its dynamics model and finite element model are built by using ANSYS. This paper not only acquires the deformation distribution,stress distribution and natural frequency of the cantilever beam in the static state; but also gets the dynamic response curve in the maximum deformation and the dynamic stress response curve in the near of the maximum stress during the motion of air cylinder. Result shows that no matter static state or dynamic state,deformation of the cantilever in the fetching carton mechanism is acceptable. The design of mechanism is reliable and its motion is also stable; no resonance can occur on the cantilever beam.展开更多
Web pre-fetching is one of the most popular strategies,which are proposed for reducing the perceived access delay and improving the service quality of web server. In this paper, we present a pre-fetching model based o...Web pre-fetching is one of the most popular strategies,which are proposed for reducing the perceived access delay and improving the service quality of web server. In this paper, we present a pre-fetching model based on the hidden Markov model, which mines the latent information requirement concepts that the user's access path contains and makes semantic-based pre-fetching decisions.Experimental results show that our scheme has better predictive pre-fetching precision.展开更多
Tibetans in Kamba (referring to Qamdo and Tibetan areas in Sichuan, Yunnan and Qinghai) have developed many habits and customs unique to themselves. Fetching the First Bucket of Water in a New Year is a case in point.
As the sand mass flux increases from zero at the leading edge of a saltating surface to the equilibrium mass flux at the critical fetch length,the wind flow is modified and then the relative contribution of aerodynami...As the sand mass flux increases from zero at the leading edge of a saltating surface to the equilibrium mass flux at the critical fetch length,the wind flow is modified and then the relative contribution of aerodynamic and bombardment entrainment is changed.In the end the velocity,trajectory and mass flux profile will vary simultaneously.But how the transportation of different sand size groups varies with fetch distance is still unclear.Wind tunnel experiments were conducted to investigate the fetch effect on mass flux and its distribution with height of the total sand and each size group in transportation.The mass flux was measured at six fetch length locations(0.5,1.2,1.9,2.6,3.4 and 4.1 m)and at three free-stream wind velocities(8.8,12.2 and 14.5 m/s).The results reveal that the total mass flux and the mass flux of each size group with height can be expressed by q=aexp(–bh),where q is the sand mass flux at height h,and a and b are regression coefficients.The coefficient b represents the relative decay rate.Both the relative decay rates of total mass flux and each size group are independent of fetch length after a quick decay over a short fetch.This is much shorter than that of mass flux.The equilibrium of the relative decay rate cannot be regarded as an equilibrium mass flux profile for aeolian sand transport.The mass fluxes of 176.0,209.3 and 148.0μm size groups increase more quickly than that of other size groups,which indicates strong size-selection of grains exists along the fetch length.The maximal size group in mass flux(176.0μm)is smaller than the maximal size group of the bed grains(209.3μm).The relative contribution of each size group to the total mass flux is not monotonically decreasing with grain size due to the lift-off of some small grains being reduced due to the protection by large grains.The results indicate that there are complex interactions among different size groups in the developmental process of aeolian sand transport and more attention should be focused on the fetch effect because it has different influences on the total mass flux,the mass flux profile and its relative decay rate.展开更多
Combining the 3/2 power law proposed by Toba with the significant wave energy balance equation for wind waves, wave growth in deep water for short fetch is investigated. It is found that the variations of wave height ...Combining the 3/2 power law proposed by Toba with the significant wave energy balance equation for wind waves, wave growth in deep water for short fetch is investigated. It is found that the variations of wave height and period with fetch have the form of power function with fractional exponents 3/8 and 1/4 respectively. Using these exponents in the power functions and through data fitting, the concise wind wave growth relations for short fetch are obtained.展开更多
The atmospheric boundaly layer over sea surface is simplified as mixed convection of turbulent boundary lay er flow over a horizontal plate, and the momentum exchange between wind and waves is also included in the mod...The atmospheric boundaly layer over sea surface is simplified as mixed convection of turbulent boundary lay er flow over a horizontal plate, and the momentum exchange between wind and waves is also included in the model. Ef fects of wind speed, air-sea temperature difference and fetch on the momentum exchange between air and sea are re vealed. The turbulence model used in calculating boundary layer is an extended version of the Van Driest mixing lengthmodel, and a combined theoretical and semi-empirical approach is employed in estimating the effect of ocean waves. Forfetch-limited cases, i. e. wind blows off sea shore for a limited distance. fetch plays a fundamental role in the air-sea mo mentum exchange under different air-sea temperature conditions, which is not discussed in previous studies.展开更多
关于 bring、fetch、take、carry 这四个动词的区别,无论是老教材,还是新教材,讲述得都很详细,也很清楚。可是,新教材高一（上）的练习册第80—81页却出现了这样两道题:2.The boy CalTle to fetch the ball.They said that it was<su...关于 bring、fetch、take、carry 这四个动词的区别,无论是老教材,还是新教材,讲述得都很详细,也很清楚。可是,新教材高一（上）的练习册第80—81页却出现了这样两道题:2.The boy CalTle to fetch the ball.They said that it was<sub><sub><sub><sub>their,theirs. （Exercise 3,p,80）展开更多
In this paper, it is held that the universal relationships of wave growth in fetch-limited conditions , i. e., (f|~) p=A(x|~)-Band (m|~)0= C(x|~) Dshould satisfy the Toba 3/2 power law and the wave energy balance equa...In this paper, it is held that the universal relationships of wave growth in fetch-limited conditions , i. e., (f|~) p=A(x|~)-Band (m|~)0= C(x|~) Dshould satisfy the Toba 3/2 power law and the wave energy balance equation. In the ideal generation situation, theoretically it can be derived that the ideal fetch-limited wave growth relationship should have D=3B and D+B =1, (i.e., B = 0.25, D = 0.75 ) and A3C=2. 1×l(T4C^(1/2)_d , where Cd is the drag coefficient. The 3/2 power law, the wave energy balance equation and the decrease of wave steepness with increasing fetch have became three requirements which should be satisfied by fetch-limited wave growth algorithms. A semi-empirical and semi-theoretical model for fetch-limited wave growth is presented. In the application to the slanting wind situation an un(?)ersal relationship of dimensionless wave energy vs dimensionless peak frequency is presented and the comparisons show that the model is in good agreement with observations.展开更多
在机器人搬运场景中,经常会出现货物实际姿态与预期不一致的情况,这时往往需要人工协作进行调整,工作效率和节拍因此受到影响。为解决以上问题,设计了一种自主移动运输机器人,可全向移动且具有新型摩擦轮-夹爪复合式取物结构及货物姿态...在机器人搬运场景中,经常会出现货物实际姿态与预期不一致的情况,这时往往需要人工协作进行调整,工作效率和节拍因此受到影响。为解决以上问题,设计了一种自主移动运输机器人,可全向移动且具有新型摩擦轮-夹爪复合式取物结构及货物姿态调整结构,其控制系统采用同步定位与建图(Simultaneous Localization And Mapping,SLAM)等技术。通过pitch轴和yaw轴货物姿态调整实验确定了关键工作参数的最优值。最后进行了自主导航实验,结果表明该机器人在室内环境可实现自主导航。展开更多
基金Program for Changjiang Scholars and Innovative Research Team in University,China(No.IRT1220)Donghua University Thesis Innovation Fund,China(No.EG2014028)
文摘In this paper,according to the cantilever beam of fetching carton mechanism in square packaging machine, considering the impact of motion of air cylinder on it,its dynamics model and finite element model are built by using ANSYS. This paper not only acquires the deformation distribution,stress distribution and natural frequency of the cantilever beam in the static state; but also gets the dynamic response curve in the maximum deformation and the dynamic stress response curve in the near of the maximum stress during the motion of air cylinder. Result shows that no matter static state or dynamic state,deformation of the cantilever in the fetching carton mechanism is acceptable. The design of mechanism is reliable and its motion is also stable; no resonance can occur on the cantilever beam.
基金The research is supported by the National Natural Science Foundation of China(No. 60082003)
文摘Web pre-fetching is one of the most popular strategies,which are proposed for reducing the perceived access delay and improving the service quality of web server. In this paper, we present a pre-fetching model based on the hidden Markov model, which mines the latent information requirement concepts that the user's access path contains and makes semantic-based pre-fetching decisions.Experimental results show that our scheme has better predictive pre-fetching precision.
文摘Tibetans in Kamba (referring to Qamdo and Tibetan areas in Sichuan, Yunnan and Qinghai) have developed many habits and customs unique to themselves. Fetching the First Bucket of Water in a New Year is a case in point.
基金supported by the National Natural Science Foundation of China (41601002, 41871011)the China Postdoctoral Science Foundation (2017M623115)+1 种基金the Science Foundation of Shaanxi Province (2018JQ4010)the Fundamental Research Funds for the Central Universities (GK201903077)
文摘As the sand mass flux increases from zero at the leading edge of a saltating surface to the equilibrium mass flux at the critical fetch length,the wind flow is modified and then the relative contribution of aerodynamic and bombardment entrainment is changed.In the end the velocity,trajectory and mass flux profile will vary simultaneously.But how the transportation of different sand size groups varies with fetch distance is still unclear.Wind tunnel experiments were conducted to investigate the fetch effect on mass flux and its distribution with height of the total sand and each size group in transportation.The mass flux was measured at six fetch length locations(0.5,1.2,1.9,2.6,3.4 and 4.1 m)and at three free-stream wind velocities(8.8,12.2 and 14.5 m/s).The results reveal that the total mass flux and the mass flux of each size group with height can be expressed by q=aexp(–bh),where q is the sand mass flux at height h,and a and b are regression coefficients.The coefficient b represents the relative decay rate.Both the relative decay rates of total mass flux and each size group are independent of fetch length after a quick decay over a short fetch.This is much shorter than that of mass flux.The equilibrium of the relative decay rate cannot be regarded as an equilibrium mass flux profile for aeolian sand transport.The mass fluxes of 176.0,209.3 and 148.0μm size groups increase more quickly than that of other size groups,which indicates strong size-selection of grains exists along the fetch length.The maximal size group in mass flux(176.0μm)is smaller than the maximal size group of the bed grains(209.3μm).The relative contribution of each size group to the total mass flux is not monotonically decreasing with grain size due to the lift-off of some small grains being reduced due to the protection by large grains.The results indicate that there are complex interactions among different size groups in the developmental process of aeolian sand transport and more attention should be focused on the fetch effect because it has different influences on the total mass flux,the mass flux profile and its relative decay rate.
基金supports from the Major State Basic Research Program(No.G1999043809)the National Natural Science Foundation(No.40076003)+1 种基金the EYTP of MOE(No.200139)support by Visiting Scholar Foundation of Key Lab.in the University.
文摘Combining the 3/2 power law proposed by Toba with the significant wave energy balance equation for wind waves, wave growth in deep water for short fetch is investigated. It is found that the variations of wave height and period with fetch have the form of power function with fractional exponents 3/8 and 1/4 respectively. Using these exponents in the power functions and through data fitting, the concise wind wave growth relations for short fetch are obtained.
文摘The atmospheric boundaly layer over sea surface is simplified as mixed convection of turbulent boundary lay er flow over a horizontal plate, and the momentum exchange between wind and waves is also included in the model. Ef fects of wind speed, air-sea temperature difference and fetch on the momentum exchange between air and sea are re vealed. The turbulence model used in calculating boundary layer is an extended version of the Van Driest mixing lengthmodel, and a combined theoretical and semi-empirical approach is employed in estimating the effect of ocean waves. Forfetch-limited cases, i. e. wind blows off sea shore for a limited distance. fetch plays a fundamental role in the air-sea mo mentum exchange under different air-sea temperature conditions, which is not discussed in previous studies.
文摘关于 bring、fetch、take、carry 这四个动词的区别,无论是老教材,还是新教材,讲述得都很详细,也很清楚。可是,新教材高一（上）的练习册第80—81页却出现了这样两道题:2.The boy CalTle to fetch the ball.They said that it was<sub><sub><sub><sub>their,theirs. （Exercise 3,p,80）
文摘In this paper, it is held that the universal relationships of wave growth in fetch-limited conditions , i. e., (f|~) p=A(x|~)-Band (m|~)0= C(x|~) Dshould satisfy the Toba 3/2 power law and the wave energy balance equation. In the ideal generation situation, theoretically it can be derived that the ideal fetch-limited wave growth relationship should have D=3B and D+B =1, (i.e., B = 0.25, D = 0.75 ) and A3C=2. 1×l(T4C^(1/2)_d , where Cd is the drag coefficient. The 3/2 power law, the wave energy balance equation and the decrease of wave steepness with increasing fetch have became three requirements which should be satisfied by fetch-limited wave growth algorithms. A semi-empirical and semi-theoretical model for fetch-limited wave growth is presented. In the application to the slanting wind situation an un(?)ersal relationship of dimensionless wave energy vs dimensionless peak frequency is presented and the comparisons show that the model is in good agreement with observations.
文摘在机器人搬运场景中,经常会出现货物实际姿态与预期不一致的情况,这时往往需要人工协作进行调整,工作效率和节拍因此受到影响。为解决以上问题,设计了一种自主移动运输机器人,可全向移动且具有新型摩擦轮-夹爪复合式取物结构及货物姿态调整结构,其控制系统采用同步定位与建图(Simultaneous Localization And Mapping,SLAM)等技术。通过pitch轴和yaw轴货物姿态调整实验确定了关键工作参数的最优值。最后进行了自主导航实验,结果表明该机器人在室内环境可实现自主导航。
