Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct.The Reynolds number based on the entrance height was9.78×105.At f...Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct.The Reynolds number based on the entrance height was9.78×105.At first,the numerical model was validated with experimental data,and then,the interaction between the separated flow and the synthetic jets at different frequencies was discussed.The results demonstrate that the control effect is significantly dependent on the momentum mixing enhancement between inside of the separated boundary layer and the outer flow.There exists a narrow range of actuation frequency,in which effective separation control can be achieved using synthetic jets.A dimensionless frequency F+=1.0is identified as the optimal frequency,with a momentum coefficient of 1.62×10-3,the separation area is reduced about46%,and the aerodynamic performance of the S-duct is also greatly improved compared to uncontrolled case.Further analysis reveals that the choice of actuation frequency is mainly determined by the momentum flux produced by a single ejection and the spacing between adjacent ejections,the optimal frequency case can be understood as a balance between the two factors.In addition,it is found that the synthetic jets can also suppress the secondary flows while decreasing the separation.展开更多
Combining high-speed schlieren technology and infrared imaging technology,related research has been carried out on the influence of parameters such as actuation voltage,repetition frequency,and electrode size of an ac...Combining high-speed schlieren technology and infrared imaging technology,related research has been carried out on the influence of parameters such as actuation voltage,repetition frequency,and electrode size of an actuator on the discharge characteristics,induced flow field characteristics,and thermal characteristics of nanosecond pulsed dielectric barrier discharge.The results show that increasing the value of the actuation voltage can significantly increase the actuation intensity,and the plasma discharge area is significantly extended.Increasing the repetition frequency can increase the number of discharges per unit time.Both will cause more energy input and induce more changes in the flow field.The effect of temperature rise is more significant.The width of the covered electrode will affect the potential distribution during the discharge process,which in turn will affect the extension process of the plasma discharge filament.Under the same actuation intensity,the wider the covered electrode,the larger range the induced flow field and temperature rise is.Preliminary experimental analyses of high-frequency actuation characteristics,temperature field characteristics,flow field characteristics and actuation parameter settings provide support for the parameter selection and partial mechanism analysis of plasma anti-icing.展开更多
The flow induced by plasma synthetic jet actuator was simulated through solving the Reynolds-averaged Navier-Stokes equations augmented by body force phenomenological plasma model.The effect of actuation frequency on ...The flow induced by plasma synthetic jet actuator was simulated through solving the Reynolds-averaged Navier-Stokes equations augmented by body force phenomenological plasma model.The effect of actuation frequency on the plasma synthetic jet was examined by case study.The numerical results present that with the actuation frequency increasing,the stream-wise distance of the adjacent vortex pairs induced by the actuator decreases monotonically,which is the same as the situation of the velocity fluctuations field caused by the vortex pairs.When the actuation frequency is 60 Hz,the vortex pairs formed during the adjacent actuation periods merge together quickly,and the flow structure in the downstream region is more close to that of the steady case.The actuation frequency has no visible influence on the time-averaged flow field of plasma synthetic jet.However,when the actuation frequency is relatively low(f<40 Hz),the momentum flux close to the actuator increases with the actuation frequency increasing,which is contrary to the situation in the far field from the wall.展开更多
For general dynamic positioning systems,controllers are mainly based on the feedback of motions only in the horizontal plane.However,for marine structures with a small water plane area and low metacentric height,undes...For general dynamic positioning systems,controllers are mainly based on the feedback of motions only in the horizontal plane.However,for marine structures with a small water plane area and low metacentric height,undesirable surge and pitch oscillations may be induced by the thruster actions.In this paper,three control laws are investigated to suppress the induced pitch motion by adding pitch rate,pitch angle or pitch acceleration into the feedback control loop.Extensive numerical simulations are conducted with a semi-submersible platform for each control law.The influences of additional terms on surge−pitch coupled motions are analyzed in both frequency and time domain.The mechanical constraints of the thrust allocation and the frequency characters of external forces are simultaneously considered.It is concluded that adding pitch angle or pitch acceleration into the feedback loop changes the natural frequency in pitch,and its performance is highly dependent on the frequency distribution of external forces,while adding pitch rate into the feedback loop is always effective in mitigating surge−pitch coupled motions.展开更多
In the semiconductor manufacturing industry,the dynamic model of a controlled object is usually obtained from a frequency sweeping method before motion control.However,the existing isolators cannot properly isolate th...In the semiconductor manufacturing industry,the dynamic model of a controlled object is usually obtained from a frequency sweeping method before motion control.However,the existing isolators cannot properly isolate the disturbance of the inertial force on the platform base during frequency sweeping(the frequency is between 0 Hz and the natural frequency).In this paper,an adjustable anti-resonance frequency controller for a dual-stage actuation semi-active vibration isolation system(DSASAVIS)is proposed.This system has a significant anti-resonance characteristic;that is,the vibration amplitude can drop to nearly zero at a particular frequency,which is called the anti-resonance frequency.The proposed controller is designed to add an adjustable anti-resonance frequency to fully use this unique anti-resonance characteristic.Experimental results show that the closed-loop transmissibility is less than−15 dB from 0 Hz to the initial anti-resonance frequency.Furthermore,it is less than−30 dB around an added anti-resonance frequency which can be adjusted from 0 Hz to the initial anti-resonance frequency by changing the parameters of the proposed controller.With the proposed controller,the disturbance amplitude of the payload decays from 4 to 0.5 mm/s with a reduction of 87.5%for the impulse disturbance applied to the platform base.Simultaneously,the system can adjust the anti-resonance frequency point in real time by tracking the frequency sweeping disturbances,and a good vibration isolation performance is achieved.This indicates that the DSA-SAVIS and the proposed controller can be applied in the guarantee of an ultra-low vibration environment,especially at frequency sweeping in the semiconductor manufacturing industry.展开更多
文摘Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct.The Reynolds number based on the entrance height was9.78×105.At first,the numerical model was validated with experimental data,and then,the interaction between the separated flow and the synthetic jets at different frequencies was discussed.The results demonstrate that the control effect is significantly dependent on the momentum mixing enhancement between inside of the separated boundary layer and the outer flow.There exists a narrow range of actuation frequency,in which effective separation control can be achieved using synthetic jets.A dimensionless frequency F+=1.0is identified as the optimal frequency,with a momentum coefficient of 1.62×10-3,the separation area is reduced about46%,and the aerodynamic performance of the S-duct is also greatly improved compared to uncontrolled case.Further analysis reveals that the choice of actuation frequency is mainly determined by the momentum flux produced by a single ejection and the spacing between adjacent ejections,the optimal frequency case can be understood as a balance between the two factors.In addition,it is found that the synthetic jets can also suppress the secondary flows while decreasing the separation.
基金supported by the National Key R&D Program of China(No.2019YFA0405300)National Natural Science Foundation of China(Nos.51907205 and 12002363)。
文摘Combining high-speed schlieren technology and infrared imaging technology,related research has been carried out on the influence of parameters such as actuation voltage,repetition frequency,and electrode size of an actuator on the discharge characteristics,induced flow field characteristics,and thermal characteristics of nanosecond pulsed dielectric barrier discharge.The results show that increasing the value of the actuation voltage can significantly increase the actuation intensity,and the plasma discharge area is significantly extended.Increasing the repetition frequency can increase the number of discharges per unit time.Both will cause more energy input and induce more changes in the flow field.The effect of temperature rise is more significant.The width of the covered electrode will affect the potential distribution during the discharge process,which in turn will affect the extension process of the plasma discharge filament.Under the same actuation intensity,the wider the covered electrode,the larger range the induced flow field and temperature rise is.Preliminary experimental analyses of high-frequency actuation characteristics,temperature field characteristics,flow field characteristics and actuation parameter settings provide support for the parameter selection and partial mechanism analysis of plasma anti-icing.
基金supported by the National Natural Science Foundation of China (Grant No. 10872021)the Fundamental Research Funds for the Central Universities (Grant No. YWF-10-01-A05)
文摘The flow induced by plasma synthetic jet actuator was simulated through solving the Reynolds-averaged Navier-Stokes equations augmented by body force phenomenological plasma model.The effect of actuation frequency on the plasma synthetic jet was examined by case study.The numerical results present that with the actuation frequency increasing,the stream-wise distance of the adjacent vortex pairs induced by the actuator decreases monotonically,which is the same as the situation of the velocity fluctuations field caused by the vortex pairs.When the actuation frequency is 60 Hz,the vortex pairs formed during the adjacent actuation periods merge together quickly,and the flow structure in the downstream region is more close to that of the steady case.The actuation frequency has no visible influence on the time-averaged flow field of plasma synthetic jet.However,when the actuation frequency is relatively low(f<40 Hz),the momentum flux close to the actuator increases with the actuation frequency increasing,which is contrary to the situation in the far field from the wall.
基金the National Natural Science Foundation of China(Grant Nos.51179103 and 51979167)the Ministry of Industry and Information Technology(Grant No.[2016]22)the Hainan Provincial Joint Project of Sanya Bay Science and Technology City(Grant No.520LH051).
文摘For general dynamic positioning systems,controllers are mainly based on the feedback of motions only in the horizontal plane.However,for marine structures with a small water plane area and low metacentric height,undesirable surge and pitch oscillations may be induced by the thruster actions.In this paper,three control laws are investigated to suppress the induced pitch motion by adding pitch rate,pitch angle or pitch acceleration into the feedback control loop.Extensive numerical simulations are conducted with a semi-submersible platform for each control law.The influences of additional terms on surge−pitch coupled motions are analyzed in both frequency and time domain.The mechanical constraints of the thrust allocation and the frequency characters of external forces are simultaneously considered.It is concluded that adding pitch angle or pitch acceleration into the feedback loop changes the natural frequency in pitch,and its performance is highly dependent on the frequency distribution of external forces,while adding pitch rate into the feedback loop is always effective in mitigating surge−pitch coupled motions.
基金Project supported by the National Natural Science Foundation of China(No.51975160)。
文摘In the semiconductor manufacturing industry,the dynamic model of a controlled object is usually obtained from a frequency sweeping method before motion control.However,the existing isolators cannot properly isolate the disturbance of the inertial force on the platform base during frequency sweeping(the frequency is between 0 Hz and the natural frequency).In this paper,an adjustable anti-resonance frequency controller for a dual-stage actuation semi-active vibration isolation system(DSASAVIS)is proposed.This system has a significant anti-resonance characteristic;that is,the vibration amplitude can drop to nearly zero at a particular frequency,which is called the anti-resonance frequency.The proposed controller is designed to add an adjustable anti-resonance frequency to fully use this unique anti-resonance characteristic.Experimental results show that the closed-loop transmissibility is less than−15 dB from 0 Hz to the initial anti-resonance frequency.Furthermore,it is less than−30 dB around an added anti-resonance frequency which can be adjusted from 0 Hz to the initial anti-resonance frequency by changing the parameters of the proposed controller.With the proposed controller,the disturbance amplitude of the payload decays from 4 to 0.5 mm/s with a reduction of 87.5%for the impulse disturbance applied to the platform base.Simultaneously,the system can adjust the anti-resonance frequency point in real time by tracking the frequency sweeping disturbances,and a good vibration isolation performance is achieved.This indicates that the DSA-SAVIS and the proposed controller can be applied in the guarantee of an ultra-low vibration environment,especially at frequency sweeping in the semiconductor manufacturing industry.
