The object of this paper is to analyze the coupling sensitivity ofunconventional responses of direct force control (DFC) aircraft with the closed-loopsystem dynamics and the aiming error dynamics, further, to venfy th...The object of this paper is to analyze the coupling sensitivity ofunconventional responses of direct force control (DFC) aircraft with the closed-loopsystem dynamics and the aiming error dynamics, further, to venfy the analytical resultsthrough numerical examples, and finally to obtain some important conclusions on thecoupling sensitivity, which can be referred to the system design and flying quality ratingfor DFC aircraft.展开更多
Conventional PID controllers are widely used in fin stabilizer control systems, but they have time-variations, nonlinearity, and uncertainty influencing their control effects. A lift feedback fuzzy-PID control method ...Conventional PID controllers are widely used in fin stabilizer control systems, but they have time-variations, nonlinearity, and uncertainty influencing their control effects. A lift feedback fuzzy-PID control method was developed to better deal with these problems, and this lift feedback fin stabilizer system was simulated under different sea condition. Test results showed the system has better anti-rolling performance than traditional fin-angle PID control systems.展开更多
In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54&#...In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54×106. The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes （URANS） equations with a k-ε turbulence model. The calculated results, produced flow structure drag and lift coefficients, as well as Strouhal numbers. The findings were in good agreement with previous published data, which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers. Meanwhile, an effective measure was presented to control the lift force on a cylinder, which points the way to decrease the vortex induced vibration of marine structure in future.展开更多
LES (Large-Eddy Simulation) computations were preformed to investigate the mechanisms of a kind of spanwisegroove for the passive control of laminar separation bubble on the suction surface of a low-speed highly loade...LES (Large-Eddy Simulation) computations were preformed to investigate the mechanisms of a kind of spanwisegroove for the passive control of laminar separation bubble on the suction surface of a low-speed highly loadedlow-pressure turbine blade at Re = 50,000 (Reynolds number, based on inlet velocity and axial chord length).Compared with the smooth suction surface, the numerical results indicate that: (1) the groove is effective toshorten and thin the separation bubble, which contributes the flow loss reduction on the groove surface, by thinningthe boundary layer behind the groove and promoting earlier transition inception in the separation bubble; (2)upstream movement of the transition inception location on the grooved surface is suggested being the result of thelower frequency at which the highest amplification rate of instability waves occurs, and the larger initial amplitudeof the disturbance at the most unstable frequency before transition; and (3) the viscous instability mode ispromoted on the grooved surface, due to the thinning of the boundary layer behind the groove.展开更多
文摘The object of this paper is to analyze the coupling sensitivity ofunconventional responses of direct force control (DFC) aircraft with the closed-loopsystem dynamics and the aiming error dynamics, further, to venfy the analytical resultsthrough numerical examples, and finally to obtain some important conclusions on thecoupling sensitivity, which can be referred to the system design and flying quality ratingfor DFC aircraft.
基金the "Ship Control Engineering" emphasis project of 211 Engineering in the tenth five-year plan.
文摘Conventional PID controllers are widely used in fin stabilizer control systems, but they have time-variations, nonlinearity, and uncertainty influencing their control effects. A lift feedback fuzzy-PID control method was developed to better deal with these problems, and this lift feedback fin stabilizer system was simulated under different sea condition. Test results showed the system has better anti-rolling performance than traditional fin-angle PID control systems.
基金Foundation item： Supported by Supported by the National Natural Science Foundation of China （Grant No. 51009070）.
文摘In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54×106. The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes （URANS） equations with a k-ε turbulence model. The calculated results, produced flow structure drag and lift coefficients, as well as Strouhal numbers. The findings were in good agreement with previous published data, which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers. Meanwhile, an effective measure was presented to control the lift force on a cylinder, which points the way to decrease the vortex induced vibration of marine structure in future.
文摘LES (Large-Eddy Simulation) computations were preformed to investigate the mechanisms of a kind of spanwisegroove for the passive control of laminar separation bubble on the suction surface of a low-speed highly loadedlow-pressure turbine blade at Re = 50,000 (Reynolds number, based on inlet velocity and axial chord length).Compared with the smooth suction surface, the numerical results indicate that: (1) the groove is effective toshorten and thin the separation bubble, which contributes the flow loss reduction on the groove surface, by thinningthe boundary layer behind the groove and promoting earlier transition inception in the separation bubble; (2)upstream movement of the transition inception location on the grooved surface is suggested being the result of thelower frequency at which the highest amplification rate of instability waves occurs, and the larger initial amplitudeof the disturbance at the most unstable frequency before transition; and (3) the viscous instability mode ispromoted on the grooved surface, due to the thinning of the boundary layer behind the groove.
