Cantilevered pipe conveying fluid may become unstable and flutter instability would occur when the velocity of the fluid flow in the pipe exceeds a critical value.In the present study,the theoretical model of a cantil...Cantilevered pipe conveying fluid may become unstable and flutter instability would occur when the velocity of the fluid flow in the pipe exceeds a critical value.In the present study,the theoretical model of a cantilevered fluid-conveying pipe attached by an inerter-based dynamic vibration absorber(IDVA)is proposed and the stability of this dynamical system is explored.Based on linear governing equations of the pipe and the IDVA,the effects of damping coefficient,weight,inerter,location and spring stiffness of the IDVAon the critical flow velocities of the pipe system is examined.It is shown that the stability of the pipe may be significantly affected by the IDVA.In many cases,the stability of the cantilevered pipe can be enhanced by designing the parameter values of the IDVA.By solving nonlinear governing equations of the dynamical system,the nonlinear oscillations of the pipe with IDVA for sufficiently high flow velocity beyond the critical value are determined,showing that the oscillation amplitudes of the pipe can also be suppressed to some extent with a suitable design of the IDVA.展开更多
The extended Brinkman Darcy model for momentum equations and an energy equation is used to calculate the unsteady natural convection Couette flow of a viscous incompressible heat generating/absorbing fluid in a vertic...The extended Brinkman Darcy model for momentum equations and an energy equation is used to calculate the unsteady natural convection Couette flow of a viscous incompressible heat generating/absorbing fluid in a vertical channel （formed by two infinite vertical and parallel plates） filled with the fluid-saturated porous medium. The flow is triggered by the asymmetric heating and the accelerated motion of one of the bounding plates. The governing equations are simplified by the reasonable dimensionless parameters and solved analytically by the Laplace transform techniques to obtain the closed form solutions of the velocity and temperature profiles. Then, the skin friction and the rate of heat transfer are consequently derived. It is noticed that, at different sections within the vertical channel, the fluid flow and the temperature profiles increase with time, which are both higher near the moving plate. In particular, increasing the gap between the plates increases the velocity and the temperature of the fluid, however, reduces the skin friction and the rate of heat transfer.展开更多
液滴的瞬态行为对强化水平管降膜吸收CO_(2)装置的性能至关重要。基于VOF(volume of fluid)方法建立了滴状流降膜吸收CO_(2)的二维模型,引入液滴下坠长度与无量纲时间来分析滴状流降膜吸收CO_(2)过程中的液滴脉动与管间距和雷诺数Re的...液滴的瞬态行为对强化水平管降膜吸收CO_(2)装置的性能至关重要。基于VOF(volume of fluid)方法建立了滴状流降膜吸收CO_(2)的二维模型,引入液滴下坠长度与无量纲时间来分析滴状流降膜吸收CO_(2)过程中的液滴脉动与管间距和雷诺数Re的关系。结果表明:液体在换热管下侧堆积直至形成液滴的过程中,受到重力、表面张力与惯性的相互作用,液滴的移动方向出现了多次反转;液滴脉动过程中,由于摩擦阻力的存在,随着无量纲时间的增加,液滴脉动幅度逐渐减小;由于管间距的增加提高了液滴在换热管底部交汇时的动能,导致随着管间距的增加,液滴的脉动次数与脉动幅度逐渐增加;在Re不断增加的情况下,液滴滴落速度的减小导致液滴的脉动次数与幅度也逐渐减小。展开更多
DVA (dynamic vibration absorber) is good for restrain of the resonance vibration in low frequency, especially under the condition that there are only one mode or two modes in a frequency band. It seems rather difficul...DVA (dynamic vibration absorber) is good for restrain of the resonance vibration in low frequency, especially under the condition that there are only one mode or two modes in a frequency band. It seems rather difficult to control the resonance vibration of elastic structures in high frequency, since usually there are so many modes in high frequency band. The broad band DVA is brought forward to reduce the resonance vibration of elastic structures. The broad band DVA is designed on the basis of the characteristic of power flow in structure in this paper. The broad band DVA is effective on absorbing the resonance vibration power flow of the most important modes. The ability of absorbing vibration for the broad band DVA is analyzed in detail. The results obtained in this paper provide a basis for the optimization design of the broad band DVA and the optimization positions on structures.展开更多
基金The authors gratefully acknowledge the support provided by the National Natural Science Foundation of China(Nos.11622216,11672115 and 11972167).
文摘Cantilevered pipe conveying fluid may become unstable and flutter instability would occur when the velocity of the fluid flow in the pipe exceeds a critical value.In the present study,the theoretical model of a cantilevered fluid-conveying pipe attached by an inerter-based dynamic vibration absorber(IDVA)is proposed and the stability of this dynamical system is explored.Based on linear governing equations of the pipe and the IDVA,the effects of damping coefficient,weight,inerter,location and spring stiffness of the IDVAon the critical flow velocities of the pipe system is examined.It is shown that the stability of the pipe may be significantly affected by the IDVA.In many cases,the stability of the cantilevered pipe can be enhanced by designing the parameter values of the IDVA.By solving nonlinear governing equations of the dynamical system,the nonlinear oscillations of the pipe with IDVA for sufficiently high flow velocity beyond the critical value are determined,showing that the oscillation amplitudes of the pipe can also be suppressed to some extent with a suitable design of the IDVA.
文摘The extended Brinkman Darcy model for momentum equations and an energy equation is used to calculate the unsteady natural convection Couette flow of a viscous incompressible heat generating/absorbing fluid in a vertical channel （formed by two infinite vertical and parallel plates） filled with the fluid-saturated porous medium. The flow is triggered by the asymmetric heating and the accelerated motion of one of the bounding plates. The governing equations are simplified by the reasonable dimensionless parameters and solved analytically by the Laplace transform techniques to obtain the closed form solutions of the velocity and temperature profiles. Then, the skin friction and the rate of heat transfer are consequently derived. It is noticed that, at different sections within the vertical channel, the fluid flow and the temperature profiles increase with time, which are both higher near the moving plate. In particular, increasing the gap between the plates increases the velocity and the temperature of the fluid, however, reduces the skin friction and the rate of heat transfer.
文摘液滴的瞬态行为对强化水平管降膜吸收CO_(2)装置的性能至关重要。基于VOF(volume of fluid)方法建立了滴状流降膜吸收CO_(2)的二维模型,引入液滴下坠长度与无量纲时间来分析滴状流降膜吸收CO_(2)过程中的液滴脉动与管间距和雷诺数Re的关系。结果表明:液体在换热管下侧堆积直至形成液滴的过程中,受到重力、表面张力与惯性的相互作用,液滴的移动方向出现了多次反转;液滴脉动过程中,由于摩擦阻力的存在,随着无量纲时间的增加,液滴脉动幅度逐渐减小;由于管间距的增加提高了液滴在换热管底部交汇时的动能,导致随着管间距的增加,液滴的脉动次数与脉动幅度逐渐增加;在Re不断增加的情况下,液滴滴落速度的减小导致液滴的脉动次数与幅度也逐渐减小。
基金This work was supported by the National Natural Science Foundation of Chinaby Post-Doctoral ScienceFoundation ofChina and by Excellent DoctoralFoundation ofChina.
文摘DVA (dynamic vibration absorber) is good for restrain of the resonance vibration in low frequency, especially under the condition that there are only one mode or two modes in a frequency band. It seems rather difficult to control the resonance vibration of elastic structures in high frequency, since usually there are so many modes in high frequency band. The broad band DVA is brought forward to reduce the resonance vibration of elastic structures. The broad band DVA is designed on the basis of the characteristic of power flow in structure in this paper. The broad band DVA is effective on absorbing the resonance vibration power flow of the most important modes. The ability of absorbing vibration for the broad band DVA is analyzed in detail. The results obtained in this paper provide a basis for the optimization design of the broad band DVA and the optimization positions on structures.
