Many factors,such as deck motion and air wave,influence the determination of the approach speed which has an important effect on landing safety. Until recently,there are no design criteria about approach speed of carr...Many factors,such as deck motion and air wave,influence the determination of the approach speed which has an important effect on landing safety. Until recently,there are no design criteria about approach speed of carrier aircraft in the current standards and available publications. Therefore,the requirements of stall margin, longitudinal acceleration ability,altitude correction and field-of-view on approach speed were researched. Based on the flight dynamics model,the flight simulations were conducted to study the effect of the response time of engine,wave off requirements,elevator efficiency and deflection rate on the approach speed. The results presented that the approach longitudinal acceleration and altitude correction ability had crucial influence on the approach speed envelope of the aircraft. The limitations of the control requirements,field- of- view requirements and gear were also given through the simulation and analysis. Based on the above results,the approach speed envelope were determined.展开更多
Characteristic measurement of contact discharge currents are made through a hand-held metal rod from charged human body. Correlation coefficients are obtained, through Statistic Package for Social Science (SPSS), for ...Characteristic measurement of contact discharge currents are made through a hand-held metal rod from charged human body. Correlation coefficients are obtained, through Statistic Package for Social Science (SPSS), for various charge voltages, which is based on the effect test of electrode contact approach speeds on discharge current parameters of current peaks, maximum rising slope and spark lengths. Discharge parameters at charge voltage 300V are independent on approach speed. For charge voltages equal to and higher than 500V, the contact approach speed has strong positive cor- relation with discharge parameters of the peak current and the maximum rising slope, whereas has strong negative correlation with the spark length.展开更多
The problem of collinear periodic cracks in an infinite piezoelectric body is studied. Effect of saturation strips at the crack-tips is taken into account. By means of the Stroh formalism and the conformal mapping tec...The problem of collinear periodic cracks in an infinite piezoelectric body is studied. Effect of saturation strips at the crack-tips is taken into account. By means of the Stroh formalism and the conformal mapping technique, the general periodic solutions for collinear cracks are obtained. The stress intensity factors and the size of saturation strips are derived analytically, and their dependencies on the ratio of the periodicity on the half-length of the crack are analyzed in detail. Numerical results show the following two facts. （1） When h/l 〉 4.0, the stress intensity factors become almost identical to those of a single crack in an infinite piezoelectric body. This indicates that the interaction between cracks can be ignored in establishing the criterion for the crack initiation in this case. （2） The speed of the saturation strip size of periodic cracks approaching that of a single crack depends on the electric load applied at infinity. In general, a large electric load at infinity is associated with a slow approaching speed.展开更多
Purpose-This article proposes a chattering-free sliding mode control scheme with unidirectional auxiliary surfaces(UAS-SMC)for small miniature autonomous helicopters(Trex 250).Design/methodology/approach-The proposed ...Purpose-This article proposes a chattering-free sliding mode control scheme with unidirectional auxiliary surfaces(UAS-SMC)for small miniature autonomous helicopters(Trex 250).Design/methodology/approach-The proposed UAS-SMC scheme consists of a nested sequence of rotor dynamics,angular rate,Euler angle,velocity and position loops.Findings-It is demonstrated that the UAS-SMC strategy can eliminate the chattering phenomenon exhibiting in the convenient SMC method and achieve a better approaching speed.Originality/value-The proposed control strategy is implemented on the helicopter and flight tests clearly demonstrate that a much better performance could be achieved,compared with convenient SMC schemes.展开更多
Discharge parameters are measured and calculated in electrostatic discharge （ESD） from charged human body through a small moving handheld metal rod. Correlation study has been performed on discharge parameters with ...Discharge parameters are measured and calculated in electrostatic discharge （ESD） from charged human body through a small moving handheld metal rod. Correlation study has been performed on discharge parameters with charge voltage as well as approach speed. At charge voltage 800 V, difference of discharge parameters caused by fast and slow approach speed of electrode is found to reach extreme values. To explore the reason for this special case, an analysis with a short-gap ESD model is carried out.展开更多
文摘Many factors,such as deck motion and air wave,influence the determination of the approach speed which has an important effect on landing safety. Until recently,there are no design criteria about approach speed of carrier aircraft in the current standards and available publications. Therefore,the requirements of stall margin, longitudinal acceleration ability,altitude correction and field-of-view on approach speed were researched. Based on the flight dynamics model,the flight simulations were conducted to study the effect of the response time of engine,wave off requirements,elevator efficiency and deflection rate on the approach speed. The results presented that the approach longitudinal acceleration and altitude correction ability had crucial influence on the approach speed envelope of the aircraft. The limitations of the control requirements,field- of- view requirements and gear were also given through the simulation and analysis. Based on the above results,the approach speed envelope were determined.
基金Supported by the National Natural Science Foundation of China (No.60473021)
文摘Characteristic measurement of contact discharge currents are made through a hand-held metal rod from charged human body. Correlation coefficients are obtained, through Statistic Package for Social Science (SPSS), for various charge voltages, which is based on the effect test of electrode contact approach speeds on discharge current parameters of current peaks, maximum rising slope and spark lengths. Discharge parameters at charge voltage 300V are independent on approach speed. For charge voltages equal to and higher than 500V, the contact approach speed has strong positive cor- relation with discharge parameters of the peak current and the maximum rising slope, whereas has strong negative correlation with the spark length.
基金Project supported by the Postdoctoral Science Foundation of China (No.20070410944)
文摘The problem of collinear periodic cracks in an infinite piezoelectric body is studied. Effect of saturation strips at the crack-tips is taken into account. By means of the Stroh formalism and the conformal mapping technique, the general periodic solutions for collinear cracks are obtained. The stress intensity factors and the size of saturation strips are derived analytically, and their dependencies on the ratio of the periodicity on the half-length of the crack are analyzed in detail. Numerical results show the following two facts. （1） When h/l 〉 4.0, the stress intensity factors become almost identical to those of a single crack in an infinite piezoelectric body. This indicates that the interaction between cracks can be ignored in establishing the criterion for the crack initiation in this case. （2） The speed of the saturation strip size of periodic cracks approaching that of a single crack depends on the electric load applied at infinity. In general, a large electric load at infinity is associated with a slow approaching speed.
文摘Purpose-This article proposes a chattering-free sliding mode control scheme with unidirectional auxiliary surfaces(UAS-SMC)for small miniature autonomous helicopters(Trex 250).Design/methodology/approach-The proposed UAS-SMC scheme consists of a nested sequence of rotor dynamics,angular rate,Euler angle,velocity and position loops.Findings-It is demonstrated that the UAS-SMC strategy can eliminate the chattering phenomenon exhibiting in the convenient SMC method and achieve a better approaching speed.Originality/value-The proposed control strategy is implemented on the helicopter and flight tests clearly demonstrate that a much better performance could be achieved,compared with convenient SMC schemes.
基金Guizhou Provincial Foundation for Natural Science and Technology (20072211)the National Natural Science Foundation of China (50237040)the Hi-Tech Research and Development Program of China (2007AA01Z281)
文摘Discharge parameters are measured and calculated in electrostatic discharge （ESD） from charged human body through a small moving handheld metal rod. Correlation study has been performed on discharge parameters with charge voltage as well as approach speed. At charge voltage 800 V, difference of discharge parameters caused by fast and slow approach speed of electrode is found to reach extreme values. To explore the reason for this special case, an analysis with a short-gap ESD model is carried out.
