Stationary shoulder friction stir lap welding （SSFSLW） was successfully used to weld 6005A-T6 aluminum alloy in this paper. Effect of pin rotating speed on cross section morphologies and lap shear strength of the SS...Stationary shoulder friction stir lap welding （SSFSLW） was successfully used to weld 6005A-T6 aluminum alloy in this paper. Effect of pin rotating speed on cross section morphologies and lap shear strength of the SSFSLW joints were mainly discussed. Results show that joints without flash and shoulder marks can be obtained by the stationary shoulder. Cross section of the SSFSLW joint presents a basin-like morphology and little material loss. By increasing the rotating speed from 1 000 rpm to 1 600 rpm, both effective sheet thickness and lap width increase, while lap shear failure load firstly decreases and then increases. The maximum failure load of 14. 05 kN /s attained when 1 000 rpm is used. All SSFSLW joints present shear fracture mode.展开更多
Abstract With low-lifting capability taken into account, a robust guidance law for Mars entry vehicles with low lift-l：o-drag ratios, such as Mars Science Laboratory （MSL）, is presented. Consider the nonlinear term...Abstract With low-lifting capability taken into account, a robust guidance law for Mars entry vehicles with low lift-l：o-drag ratios, such as Mars Science Laboratory （MSL）, is presented. Consider the nonlinear term in the drag dynamic equation and bounded disturbances as a lumped disturbance, and design a linear disturbance observer （DOB） to estimate it. With the consideration of the control input saturation, an innovative sliding surface and a virtual system are introduced to design the guidance law. Analyses of disturbance observer performance and Lyapunov-based transient performance are also presented. It is shown explicit choices of design parameters. Simulation guidance law. that the drag tracking error can be adjustable by results confirm the effectiveness of the proposed展开更多
The attitude maneuver control of spacecraft under bounded disturbance and input saturation is investigated in this paper.Using the Lyapunov stability theory,an anti-saturation sliding mode control algorithm is given b...The attitude maneuver control of spacecraft under bounded disturbance and input saturation is investigated in this paper.Using the Lyapunov stability theory,an anti-saturation sliding mode control algorithm is given by designing a time-varying sliding mode to solve the input saturated attitude control problem without disturbance.Then combining the merit in anti-saturation of time-varying sliding mode controller with the merit in anti-disturbance of time-invariant sliding mode controller,a switching strategy between the two controllers is designed to solve the attitude maneuver control problem under input saturation and bounded disturbance.However,double value of quaternions makes the attitude slewing unwinding.To solve the problem,an attitude error vector is designed.Based on the error vector,a modified sliding mode control algorithm is proposed which simultaneously has the ability of anti-saturation,anti-disturbance and anti-unwinding.Simulation results show that the algorithm in this paper is feasible and effective.展开更多
文摘Stationary shoulder friction stir lap welding （SSFSLW） was successfully used to weld 6005A-T6 aluminum alloy in this paper. Effect of pin rotating speed on cross section morphologies and lap shear strength of the SSFSLW joints were mainly discussed. Results show that joints without flash and shoulder marks can be obtained by the stationary shoulder. Cross section of the SSFSLW joint presents a basin-like morphology and little material loss. By increasing the rotating speed from 1 000 rpm to 1 600 rpm, both effective sheet thickness and lap width increase, while lap shear failure load firstly decreases and then increases. The maximum failure load of 14. 05 kN /s attained when 1 000 rpm is used. All SSFSLW joints present shear fracture mode.
基金co-supported by the National Basic Research Program of China(No.2012CB720000)the National Natural Science Foundation of China(No.61174201)
文摘Abstract With low-lifting capability taken into account, a robust guidance law for Mars entry vehicles with low lift-l：o-drag ratios, such as Mars Science Laboratory （MSL）, is presented. Consider the nonlinear term in the drag dynamic equation and bounded disturbances as a lumped disturbance, and design a linear disturbance observer （DOB） to estimate it. With the consideration of the control input saturation, an innovative sliding surface and a virtual system are introduced to design the guidance law. Analyses of disturbance observer performance and Lyapunov-based transient performance are also presented. It is shown explicit choices of design parameters. Simulation guidance law. that the drag tracking error can be adjustable by results confirm the effectiveness of the proposed
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2012CB720000)the National Naturalm Science Foundation of China (Grant No. 61174201)
文摘The attitude maneuver control of spacecraft under bounded disturbance and input saturation is investigated in this paper.Using the Lyapunov stability theory,an anti-saturation sliding mode control algorithm is given by designing a time-varying sliding mode to solve the input saturated attitude control problem without disturbance.Then combining the merit in anti-saturation of time-varying sliding mode controller with the merit in anti-disturbance of time-invariant sliding mode controller,a switching strategy between the two controllers is designed to solve the attitude maneuver control problem under input saturation and bounded disturbance.However,double value of quaternions makes the attitude slewing unwinding.To solve the problem,an attitude error vector is designed.Based on the error vector,a modified sliding mode control algorithm is proposed which simultaneously has the ability of anti-saturation,anti-disturbance and anti-unwinding.Simulation results show that the algorithm in this paper is feasible and effective.
