Contactless measurement of wind flow has been utilized in many fields, such as weather forecasting, hurricane tracking, and aeronautic alarm. In this paper, a novel multi-laser beams measuring system （MLBM） for high...Contactless measurement of wind flow has been utilized in many fields, such as weather forecasting, hurricane tracking, and aeronautic alarm. In this paper, a novel multi-laser beams measuring system （MLBM） for high precision detection of wind field based on optical scintillations and small perturbation theory was proposed and verified. According to the fluctuation intensity of laser backscatter received by two detectors, peak delay technique was adopted to determine the velocity of wind flow. Detailed procedure to deal with backscatter signals was also presented. Then, practical experiments and measurement results showed high precision of the proposed system for wind measurement with a relative error as 3.21%. Consequently, the MLBM system possesses obvious potential application in engineering project.展开更多
The stability for a class of linear neutral systems with time-varying delays is studied in this paper, where delay in neutral-type term includes a fast-varying case (i.e., the derivative of delay is more than one), wh...The stability for a class of linear neutral systems with time-varying delays is studied in this paper, where delay in neutral-type term includes a fast-varying case (i.e., the derivative of delay is more than one), which has never been considered in current literature. The less conservative delaydependent stability criteria for this system are proposed by applying new Lyapunov-Krasovskii functional and novel polynomials with time-varying delay (PTVD) compensation technique. The aim to deal with systems with fast-varying neutral-type delay can be achieved by using the new functional. The benefit brought by applying the PTVD compensation technique is that some useful elements can be included in criteria, which are generally ignored when estimating the upper bound of derivative of Lyapunov-Krasovskii functional. A numerical example is provided to verify the effectiveness of the proposed results.展开更多
In this paper, a modified averaging scheme is presented for a class of time-delayed vibration systems with slow variables. The new scheme is a combination of the averaging techniques proposed by Hale and by Lehman and...In this paper, a modified averaging scheme is presented for a class of time-delayed vibration systems with slow variables. The new scheme is a combination of the averaging techniques proposed by Hale and by Lehman and Weibel, respectively. The averaged equation obtained from the modified scheme is simple enough but it retains the required information for the local nonlinear dynamics around an equilibrium. As an application of the present method, the delay value for which a secondary Hopf bifurcation occurs is successfully located for a delayed van der Pol oscillator.展开更多
The Electro-optical sampling delay scanning technique can be used for electron beam bunch length measurement. A novel non-synchronous delay scanning technique based on the electro-optical sampling measurements is pres...The Electro-optical sampling delay scanning technique can be used for electron beam bunch length measurement. A novel non-synchronous delay scanning technique based on the electro-optical sampling measurements is presented. Based on Beijing Free Electron Laser （BFEL）, the electron beam bunch length was measured with the electro-optical sampling technique for the first time in China. The result shows that the electron beam bunch length at BFEL is about 5.6±1.2 ps.展开更多
基金supported by National Science Foundation of China (NSFC) under Grant No.60425101-1Foundation for Innovative Research Groups of NSFC under Grant No.60721001
文摘Contactless measurement of wind flow has been utilized in many fields, such as weather forecasting, hurricane tracking, and aeronautic alarm. In this paper, a novel multi-laser beams measuring system （MLBM） for high precision detection of wind field based on optical scintillations and small perturbation theory was proposed and verified. According to the fluctuation intensity of laser backscatter received by two detectors, peak delay technique was adopted to determine the velocity of wind flow. Detailed procedure to deal with backscatter signals was also presented. Then, practical experiments and measurement results showed high precision of the proposed system for wind measurement with a relative error as 3.21%. Consequently, the MLBM system possesses obvious potential application in engineering project.
基金Supported by National Basic Research Program of China(973 Program)(2009CB320601)National Natural Science Foundation of China(50977008,60774048)the Program for Cheung Kong Scholars
文摘The stability for a class of linear neutral systems with time-varying delays is studied in this paper, where delay in neutral-type term includes a fast-varying case (i.e., the derivative of delay is more than one), which has never been considered in current literature. The less conservative delaydependent stability criteria for this system are proposed by applying new Lyapunov-Krasovskii functional and novel polynomials with time-varying delay (PTVD) compensation technique. The aim to deal with systems with fast-varying neutral-type delay can be achieved by using the new functional. The benefit brought by applying the PTVD compensation technique is that some useful elements can be included in criteria, which are generally ignored when estimating the upper bound of derivative of Lyapunov-Krasovskii functional. A numerical example is provided to verify the effectiveness of the proposed results.
基金FANEDD of China (200430)the National Natural Science Foundation of China (10372116,10532050)
文摘In this paper, a modified averaging scheme is presented for a class of time-delayed vibration systems with slow variables. The new scheme is a combination of the averaging techniques proposed by Hale and by Lehman and Weibel, respectively. The averaged equation obtained from the modified scheme is simple enough but it retains the required information for the local nonlinear dynamics around an equilibrium. As an application of the present method, the delay value for which a secondary Hopf bifurcation occurs is successfully located for a delayed van der Pol oscillator.
基金Supported by National Natural Science Foundation of China (10575116)
文摘The Electro-optical sampling delay scanning technique can be used for electron beam bunch length measurement. A novel non-synchronous delay scanning technique based on the electro-optical sampling measurements is presented. Based on Beijing Free Electron Laser （BFEL）, the electron beam bunch length was measured with the electro-optical sampling technique for the first time in China. The result shows that the electron beam bunch length at BFEL is about 5.6±1.2 ps.
