We investigate the low-temperature statistical properties of a harmonic oscillator coupled to a heat bath, where the low-frequency spectrum vanishes. We obtain the exact result of the zero point energy. Due to the low...We investigate the low-temperature statistical properties of a harmonic oscillator coupled to a heat bath, where the low-frequency spectrum vanishes. We obtain the exact result of the zero point energy. Due to the low frequency shortage of environmental oscillators＇ spectral density, the coordinate and momentum correlation functions decay as T^-4 arid T^-6 respectively at zero temperature, where T is the correlation time. The low-temperature behavior of the mean energy does not violate the third law of thermodynamics, but differs largely from the Ohmic spectrum case.展开更多
The dynamics of an axially accelerating beam subjected to axial flow is studied.Based on the Floquet theory and the Runge-Kutta algorithm,the stability and nonlinear vibration of the beam are analyzed by considering t...The dynamics of an axially accelerating beam subjected to axial flow is studied.Based on the Floquet theory and the Runge-Kutta algorithm,the stability and nonlinear vibration of the beam are analyzed by considering the effects of several system parameters such as the mean speed,flow velocity,axial added mass coefficient,mass ratio,slenderness ratio,tension and viscosity coefficient.Numerical results show that when the pulsation frequency of the axial speed is close to the sum of first-and second-mode frequencies or twice the lowest two natural frequencies,instability with combination or subharmonic resonance would occur.It is found that the beam can undergo the periodic-1 motion under subharmonic resonance and the quasi-periodic motion under combination resonance.With the change of system parameters,the stability boundary may be widened,narrowed or drifted.In addition,the vibration amplitude of the beam under resonance can also be affected by changing the values of system parameters.展开更多
This paper introduces in detail the reactive power compensation technology and its characteristics, to reduce the loss of reactive power compensation technology 1N power distribution system and the electrical automati...This paper introduces in detail the reactive power compensation technology and its characteristics, to reduce the loss of reactive power compensation technology 1N power distribution system and the electrical automation, improve the utilization rate, and realize the control of the voltage amplitude in the system network, voltage stability of power distribution system, has carried on the system analysis to reduce failure of the harmonic current to the power supply system and other functions. And the paper in-depth study on the application of reactive power compensation technology in electrical automation from the reactive compensation technology, substation and distribution line reactive power compensation, power users of reactive power compensation and other aspects.展开更多
An unsteady Reynolds averaged Navier–Stokes(URANS) method combined with a rigid dynamic mesh technique was developed to simulate unsteady flows around complex configurations during pitching motion. First, a test case...An unsteady Reynolds averaged Navier–Stokes(URANS) method combined with a rigid dynamic mesh technique was developed to simulate unsteady flows around complex configurations during pitching motion. First, a test case with the NACA0012 airfoil was selected to validate the numerical methods and our in-house codes. Then, we evaluated the unsteady flows around an advanced aircraft model during harmonic pitching motion at high incidence. The effects of pitching motion on the hysteresis of aerodynamic force, the evolution of the leading-edge vortex, and the distribution of pressure on the model's surface were analyzed in detail. The roles of several significant parameters such as the reduced frequency and pitching amplitude were revealed. Several conclusions were found: pitching motion would delay the initiation of the leading-edge vortex, strengthen the vorticity, postpone the occurrence of vortex breakdown, and weaken the massively separated flows, thus causing additional aerodynamic force. Two categories of critical reduced frequency have been found, which divide the influence of reduced frequency on aerodynamic force into three stages, called the linear increasing range, slowly increasing range, and constant range. The first-order phase lag between the aerodynamic force and the incidence is a constant that is independent of the amplitude when the reduced frequency is sufficiently high. A scaled maximum value of C_L is proposed; it depends only on the reduced frequency(instead of the amplitude), and increases linearly when the reduced frequency is sufficiently low.展开更多
文摘We investigate the low-temperature statistical properties of a harmonic oscillator coupled to a heat bath, where the low-frequency spectrum vanishes. We obtain the exact result of the zero point energy. Due to the low frequency shortage of environmental oscillators＇ spectral density, the coordinate and momentum correlation functions decay as T^-4 arid T^-6 respectively at zero temperature, where T is the correlation time. The low-temperature behavior of the mean energy does not violate the third law of thermodynamics, but differs largely from the Ohmic spectrum case.
基金supported by the National Natural Science Foundation of China(Nos.11972167,12072119,12102139).
文摘The dynamics of an axially accelerating beam subjected to axial flow is studied.Based on the Floquet theory and the Runge-Kutta algorithm,the stability and nonlinear vibration of the beam are analyzed by considering the effects of several system parameters such as the mean speed,flow velocity,axial added mass coefficient,mass ratio,slenderness ratio,tension and viscosity coefficient.Numerical results show that when the pulsation frequency of the axial speed is close to the sum of first-and second-mode frequencies or twice the lowest two natural frequencies,instability with combination or subharmonic resonance would occur.It is found that the beam can undergo the periodic-1 motion under subharmonic resonance and the quasi-periodic motion under combination resonance.With the change of system parameters,the stability boundary may be widened,narrowed or drifted.In addition,the vibration amplitude of the beam under resonance can also be affected by changing the values of system parameters.
文摘This paper introduces in detail the reactive power compensation technology and its characteristics, to reduce the loss of reactive power compensation technology 1N power distribution system and the electrical automation, improve the utilization rate, and realize the control of the voltage amplitude in the system network, voltage stability of power distribution system, has carried on the system analysis to reduce failure of the harmonic current to the power supply system and other functions. And the paper in-depth study on the application of reactive power compensation technology in electrical automation from the reactive compensation technology, substation and distribution line reactive power compensation, power users of reactive power compensation and other aspects.
基金supported by the Innovation Foundation of CARDCthe Innovation Foundation of LSAI of CARDC
文摘An unsteady Reynolds averaged Navier–Stokes(URANS) method combined with a rigid dynamic mesh technique was developed to simulate unsteady flows around complex configurations during pitching motion. First, a test case with the NACA0012 airfoil was selected to validate the numerical methods and our in-house codes. Then, we evaluated the unsteady flows around an advanced aircraft model during harmonic pitching motion at high incidence. The effects of pitching motion on the hysteresis of aerodynamic force, the evolution of the leading-edge vortex, and the distribution of pressure on the model's surface were analyzed in detail. The roles of several significant parameters such as the reduced frequency and pitching amplitude were revealed. Several conclusions were found: pitching motion would delay the initiation of the leading-edge vortex, strengthen the vorticity, postpone the occurrence of vortex breakdown, and weaken the massively separated flows, thus causing additional aerodynamic force. Two categories of critical reduced frequency have been found, which divide the influence of reduced frequency on aerodynamic force into three stages, called the linear increasing range, slowly increasing range, and constant range. The first-order phase lag between the aerodynamic force and the incidence is a constant that is independent of the amplitude when the reduced frequency is sufficiently high. A scaled maximum value of C_L is proposed; it depends only on the reduced frequency(instead of the amplitude), and increases linearly when the reduced frequency is sufficiently low.
