Numerical Simulation Of Oscillation Characteristics Of Screwing Oscillators Built From Double-Walled Nanotubes

Carbon nanotubes(CNT),as an emerging special nanomaterial,provide the possibility for the next generation of finely-structured nanodevices.In this work,finite element method is used to study the vibration mode of the double-walled carbon nanotubes,and molecular dynamics method is used to study the coupling effect of screwing oscillator based on double-walled carbon nanotubes and the oscillation behavior of CNT@Mo S₂nanotubes(CNT@MST)screwing oscillators.The main research work is organized as follows:(1)A finite element model of double-walled carbon nanotubes is established,in which the interaction between the tubes is represented by non-linear springs.Based on the proposed finite element model,the effects of boundary conditions,aspect ratio and layer spacing on the vibration mode and natural frequency of the inner tube are investigated.The results show that the natural frequency of the inner tube increases with the strengthening of the boundary conditions,and decreases with the increase of the aspect ratio.The natural frequency of the inner tube is the highest when the layer spacing is the equilibrium distance.The molecular dynamics method and analytical solution are used to verify the non-linear spring model.The results show that the fundamental frequencies obtained by using the non-linear model,molecular dynamics method and analytical solution show a good agreement,which effectively verifies the reliability and accuracy of the proposed non-linear model.(2)Coupling effect of double-walled nanotubes is theoretically investigated.A certain pull-rotation coupling excitation is applied to the inner tube of the double-walled carbon nanotubes oscillator,and the inner tube will generate screwing motion.The Van der Waals force between two carbon nanotubes is expressed in a simple form of Fourier series so that the coupled nonlinear differential equations can be solved quickly.This novel method is thousands of times faster than the traditional method and saves a lot of calculation time,which makes it possible to fit the damping and coupling coefficient of the coupled equation of the double-walled carbon nanotubes screwing oscillator.As a result,expressions for the coefficients of the coupled equations are given.The results also show that a larger initial rotational frequency results in a higher amplitude dissipation rate and vice versa.The method can also be used to study the effects of temperature,carbon nanotube chirality,layer spacing and tube length on the oscillation behavior of double-walled carbon nanotubes oscillator.(3)A novel CNT@MST screwing oscillator based on a combination of heterogeneous materials is proposed.This crewing oscillator can simultaneously output translation and rotation signals.The friction mechanism of the CNT@MST screwing oscillator is studied using the molecular dynamics.It is found that the friction between the tubes is mainly affected by the layer spacing.The large tube spacing exacerbates the degree of swing of the inner tube,and the small layer spacing causes excessive Van der Waals forces.The above two situations will greatly enhance the friction effect and they are not suitable to serve as a stable and continuous,low loss oscillation device.A map between the excitation magnitude and the critical stable temperature is generated to show the maximum service temperature at which the inner tube can perform a stable screwing oscillation under different pull-rotation excitations.Increasing the initial rotation frequency will decrease the critical stable temperature,and increasing the initial pull-out distance will increase the critical stable temperature.Compared with the initial pull-out distance,the effect of the initial rotation frequency on the critical stable temperature of the inner tube is more significant.(4)The molecular dynamics method is used to study the effects of chiral combination,layer spacing,excitation amplitude(initial rotation frequency and initial pull-out distance)and temperature on the oscillation behavior of CNT@MST screwing oscillator.Compared with the CNT@CNT system,the CNT@MST screwing oscillator has better stability,lower dissipation rate,wider adjustable layer spacing range,higher axial oscillation frequency and critical stable temperature.The simulation shows that the CNT@MST screwing oscillators can maintain a stable and continuous,low-loss oscillation with a layer spacing in the range of 0.289-0.653 nm,and it will fail when the temperature reaches 600 K.The CNT@CNT screwing oscillators exhibits the same oscillation performance with a layer spacing only in the range of 0.340-0.376 nm,and it fails at a temperature of 400K.