Velocity oscillations at the head of the gravity current were investigated in experiments and numerical simulations of a locked-exchange flow.A comparison of the experimental and numerical simulations showed that the ...Velocity oscillations at the head of the gravity current were investigated in experiments and numerical simulations of a locked-exchange flow.A comparison of the experimental and numerical simulations showed that the depth and volume of the released fluid affected the oscillations in the velocity of the gravity current.At the initial stage,the head moved forward at a constant velocity,and velocity oscillations occurred.The head maximum thickness increased at the same time as the head,which did not have a round,and accumulated buoyant fluid due to the buoyancy effect intrusion force.The period of accumulation and release of the buoyant fluid was almost the same as that observed for the head movement velocity;the head movement velocity was faster when the buoyant fluid accumulated and slower when it was released.At the viscous stage,the forward velocity decreased proportionally to the power of 1/2 of time,since the head was not disturbed from behind.As the mass concentration at the head decreased,the gravity current was slowed by the viscous stage in its effect.At the viscous stage,the mass concentration at the head was no longer present,and the velocity oscillations also decreased.展开更多
The presence of a cavity changes the mean and fluctuating pressure distributions. Similarities are observed between a cylindrical cavity and a rectangular cavity for a compressible flow.The type of cavity flow field d...The presence of a cavity changes the mean and fluctuating pressure distributions. Similarities are observed between a cylindrical cavity and a rectangular cavity for a compressible flow.The type of cavity flow field depends on the diameter-to-depth ratio and the length-to-depth ratio.The feedback loop is responsible for the generation of discrete acoustic tones. In this study, the selfsustained oscillation for a compressible cylindrical cavity flow was investigated experimentally. For open-type cavities, the power spectra show that the strength of resonance depends on the diameterto-depth ratio(4.43–43.0) and the incoming boundary layer thickness-to-depth ratio(0.72–7.0). The effective streamwise length is used as the characteristic length to estimate the Strouhal number. At higher modes, there is a large deviation from Rossiter's formula for rectangular cavities. The gradient-based searching method was used to evaluate the values of the empirical parameters. Less phase lag and a lower convection velocity are observed.展开更多
In this paper, a Duffing oscillator model with delayed velocity feedback is considered. Applying the time delayed feedback control method and delayed differential equation theory, we establish some criteria which ensu...In this paper, a Duffing oscillator model with delayed velocity feedback is considered. Applying the time delayed feedback control method and delayed differential equation theory, we establish some criteria which ensure the stability and the existence of Hopf bifurcation of the model. By choosing the delay as bifurcation parameter and analyzing the associated characteristic equation,the existence of bifurcation parameter point is determined. We found that if the time delay is chosen as a bifurcation parameter,Hopf bifurcation occurs when the time delay is changed through a series of critical values. Some numerical simulations show that the designed feedback controllers not only delay the onset of Hopf bifurcation, but also enlarge the stability region for the model.展开更多
We examine MHD processes arising in melts placed in vessels of circular and rectangular cross-sections under the action of amplitude-and-frequency modulated rotating magnetic field.It is established that besides the m...We examine MHD processes arising in melts placed in vessels of circular and rectangular cross-sections under the action of amplitude-and-frequency modulated rotating magnetic field.It is established that besides the mean turbulent flow,seven oscillations arise in the melt,whose frequency and amplitude depend on modulation parameters.展开更多
文摘Velocity oscillations at the head of the gravity current were investigated in experiments and numerical simulations of a locked-exchange flow.A comparison of the experimental and numerical simulations showed that the depth and volume of the released fluid affected the oscillations in the velocity of the gravity current.At the initial stage,the head moved forward at a constant velocity,and velocity oscillations occurred.The head maximum thickness increased at the same time as the head,which did not have a round,and accumulated buoyant fluid due to the buoyancy effect intrusion force.The period of accumulation and release of the buoyant fluid was almost the same as that observed for the head movement velocity;the head movement velocity was faster when the buoyant fluid accumulated and slower when it was released.At the viscous stage,the forward velocity decreased proportionally to the power of 1/2 of time,since the head was not disturbed from behind.As the mass concentration at the head decreased,the gravity current was slowed by the viscous stage in its effect.At the viscous stage,the mass concentration at the head was no longer present,and the velocity oscillations also decreased.
基金support of the Ministry of Science and Technology (No. MOST 103-2923-E-006MY3)
文摘The presence of a cavity changes the mean and fluctuating pressure distributions. Similarities are observed between a cylindrical cavity and a rectangular cavity for a compressible flow.The type of cavity flow field depends on the diameter-to-depth ratio and the length-to-depth ratio.The feedback loop is responsible for the generation of discrete acoustic tones. In this study, the selfsustained oscillation for a compressible cylindrical cavity flow was investigated experimentally. For open-type cavities, the power spectra show that the strength of resonance depends on the diameterto-depth ratio(4.43–43.0) and the incoming boundary layer thickness-to-depth ratio(0.72–7.0). The effective streamwise length is used as the characteristic length to estimate the Strouhal number. At higher modes, there is a large deviation from Rossiter's formula for rectangular cavities. The gradient-based searching method was used to evaluate the values of the empirical parameters. Less phase lag and a lower convection velocity are observed.
基金supported by National Natural Science Foundation of China(Nos.11261010 and 11101126)Natural Science and Technology Foundation of Guizhou Province(No.J[2015]2025)+1 种基金125 Special Major Science and Technology of Department of Education of Guizhou Province(No.[2012]011)Natural Science Innovation Team Project of Guizhou Province(No.[2013]14)
文摘In this paper, a Duffing oscillator model with delayed velocity feedback is considered. Applying the time delayed feedback control method and delayed differential equation theory, we establish some criteria which ensure the stability and the existence of Hopf bifurcation of the model. By choosing the delay as bifurcation parameter and analyzing the associated characteristic equation,the existence of bifurcation parameter point is determined. We found that if the time delay is chosen as a bifurcation parameter,Hopf bifurcation occurs when the time delay is changed through a series of critical values. Some numerical simulations show that the designed feedback controllers not only delay the onset of Hopf bifurcation, but also enlarge the stability region for the model.
文摘We examine MHD processes arising in melts placed in vessels of circular and rectangular cross-sections under the action of amplitude-and-frequency modulated rotating magnetic field.It is established that besides the mean turbulent flow,seven oscillations arise in the melt,whose frequency and amplitude depend on modulation parameters.