The flutter characteristics of folding control fins with freeplay are investigated by numer- ical simulation and flutter wind tunnel tests. Based on the characteristics of the structures, fins with different freeplay ...The flutter characteristics of folding control fins with freeplay are investigated by numer- ical simulation and flutter wind tunnel tests. Based on the characteristics of the structures, fins with different freeplay angles are designed. For a 0° angle of attack, wind tunnel tests of these fins are conducted, and vibration is observed by accelerometers and a high-speed camera. By the expansion of the connected relationships, the governing equations of fit for the nonlinear aeroelastic analysis are established by the free-interface component mode synthesis method. Based on the results of the wind tunnel tests, the flutter characteristics of fins with different freeplay angles are analyzed. The results show that the vibration divergent speed is increased, and the divergent speed is higher than the flutter speed of the nominal linear system. The vibration divergent speed is increased along with an increase in the freeplay angle. The developed free-interface component mode synthesis method could be used to establish governing equations and to analyze the characteristics of nonlinear aeroe- lastic systems. The results of the numerical simulations and the wind tunnel tests indicate the same trends and critical velocities.展开更多
The dynamics character of a two degree-of-freedom aeroelastic airfoil with combined freeplay and cubic stiffness nonlinearities in pitch submitted to supersonic and hypersonic flow has been gaining significant attenti...The dynamics character of a two degree-of-freedom aeroelastic airfoil with combined freeplay and cubic stiffness nonlinearities in pitch submitted to supersonic and hypersonic flow has been gaining significant attention. The Poincare mapping method and Floquet theory are adopted to analyse the limit cycle oscillation flutter and chaotic motion of this system. The result shows that the limit cycle oscillation flutter can be accurately predicted by the Floquet multiplier. The phase trajectories of both the pitch and plunge motion are obtained and the results show that the plunge motion is much more complex than the pitch motion. It is also proved that initial conditions have important influences on the dynamics character of the airfoil system. In a certain range of airspeed and with the same system parameters, the stable limit cycle oscillation, chaotic and multi-periodic motions can be detected under different initial conditions. The figure of the Poincare section also approves the previous conclusion.展开更多
We investigate experimentally how controlled freeplay nonlinearity affects harvesting energy from a wing-based piezoaeroelastic energy harvesting system. This system consisits of a rigid airfoil which is supported by ...We investigate experimentally how controlled freeplay nonlinearity affects harvesting energy from a wing-based piezoaeroelastic energy harvesting system. This system consisits of a rigid airfoil which is supported by a nonlinear torsional spring （freeplay） in the pitch degree of freedom and a linear fiexural spring in the plunge degree of freedom. By attaching a piezoelectric material （PSI-5A4E） to the plunge degree of freedom, we can convert aeroelastic vibrations to electrical energy. The focus of this study is placed on the effects of the freeplay nonlinearity gap on the behavior of the harvester in terms of cut-in speed and level of harvested power. Although the freeplay nonlinearity may result in subcritical Hopf bifurcations （catastrophic for real aircrafts）, harvesting energy at low wind speeds is beneficial for designing piezoaeroelastic systems. It is demonstrated that increasing the freeplay nonlinearity gap can decrease the cut-in speed through a subcritical instability and gives the possibility to harvest energy at low wind speeds. The results also demonstrate that an optimum value of the load resistance exists, at which the level of the harvested power is maximized.展开更多
针对间隙非线性机翼颤振系统的亚临界问题,引入了非线性能量阱(nonlinear energy sink,NES)技术来提高系统发生极限环振荡的临界速度。建立了具有NES控制的间隙非线性机翼颤振系统动力学模型,并分析了质量比、频率比、阻尼比、相对位置...针对间隙非线性机翼颤振系统的亚临界问题,引入了非线性能量阱(nonlinear energy sink,NES)技术来提高系统发生极限环振荡的临界速度。建立了具有NES控制的间隙非线性机翼颤振系统动力学模型,并分析了质量比、频率比、阻尼比、相对位置等NES参数对颤振系统极限环振荡的抑制效果,以及NES参数对颤振系统极限环振荡临界速度的影响规律。结果表明,阻尼比越大,可以在越小的自振频率比情况下使系统进入稳定区,但需要更苛刻的NES位置要求,即越靠近机翼前缘;而阻尼比越小,则使颤振系统极限环振荡响应进入稳定区所需的NES质量越小。在NES位置靠近机翼前缘时,增大自振频率比会使极限环振荡抑制效果有明显的提升,而增大质量比可以显著提高极限环振荡的抑制效果和临界速度。此外,NES的阻尼比越小,其颤振系统的极限环振荡抑制效果越好。展开更多
文摘The flutter characteristics of folding control fins with freeplay are investigated by numer- ical simulation and flutter wind tunnel tests. Based on the characteristics of the structures, fins with different freeplay angles are designed. For a 0° angle of attack, wind tunnel tests of these fins are conducted, and vibration is observed by accelerometers and a high-speed camera. By the expansion of the connected relationships, the governing equations of fit for the nonlinear aeroelastic analysis are established by the free-interface component mode synthesis method. Based on the results of the wind tunnel tests, the flutter characteristics of fins with different freeplay angles are analyzed. The results show that the vibration divergent speed is increased, and the divergent speed is higher than the flutter speed of the nominal linear system. The vibration divergent speed is increased along with an increase in the freeplay angle. The developed free-interface component mode synthesis method could be used to establish governing equations and to analyze the characteristics of nonlinear aeroe- lastic systems. The results of the numerical simulations and the wind tunnel tests indicate the same trends and critical velocities.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10872141)the Research Fund for the Doctoral Program of Higher Education (Grant No. 20060056005)the National Basic Research Program of China (GrantNo. 007CB714000)
文摘The dynamics character of a two degree-of-freedom aeroelastic airfoil with combined freeplay and cubic stiffness nonlinearities in pitch submitted to supersonic and hypersonic flow has been gaining significant attention. The Poincare mapping method and Floquet theory are adopted to analyse the limit cycle oscillation flutter and chaotic motion of this system. The result shows that the limit cycle oscillation flutter can be accurately predicted by the Floquet multiplier. The phase trajectories of both the pitch and plunge motion are obtained and the results show that the plunge motion is much more complex than the pitch motion. It is also proved that initial conditions have important influences on the dynamics character of the airfoil system. In a certain range of airspeed and with the same system parameters, the stable limit cycle oscillation, chaotic and multi-periodic motions can be detected under different initial conditions. The figure of the Poincare section also approves the previous conclusion.
文摘We investigate experimentally how controlled freeplay nonlinearity affects harvesting energy from a wing-based piezoaeroelastic energy harvesting system. This system consisits of a rigid airfoil which is supported by a nonlinear torsional spring （freeplay） in the pitch degree of freedom and a linear fiexural spring in the plunge degree of freedom. By attaching a piezoelectric material （PSI-5A4E） to the plunge degree of freedom, we can convert aeroelastic vibrations to electrical energy. The focus of this study is placed on the effects of the freeplay nonlinearity gap on the behavior of the harvester in terms of cut-in speed and level of harvested power. Although the freeplay nonlinearity may result in subcritical Hopf bifurcations （catastrophic for real aircrafts）, harvesting energy at low wind speeds is beneficial for designing piezoaeroelastic systems. It is demonstrated that increasing the freeplay nonlinearity gap can decrease the cut-in speed through a subcritical instability and gives the possibility to harvest energy at low wind speeds. The results also demonstrate that an optimum value of the load resistance exists, at which the level of the harvested power is maximized.
文摘针对间隙非线性机翼颤振系统的亚临界问题,引入了非线性能量阱(nonlinear energy sink,NES)技术来提高系统发生极限环振荡的临界速度。建立了具有NES控制的间隙非线性机翼颤振系统动力学模型,并分析了质量比、频率比、阻尼比、相对位置等NES参数对颤振系统极限环振荡的抑制效果,以及NES参数对颤振系统极限环振荡临界速度的影响规律。结果表明,阻尼比越大,可以在越小的自振频率比情况下使系统进入稳定区,但需要更苛刻的NES位置要求,即越靠近机翼前缘;而阻尼比越小,则使颤振系统极限环振荡响应进入稳定区所需的NES质量越小。在NES位置靠近机翼前缘时,增大自振频率比会使极限环振荡抑制效果有明显的提升,而增大质量比可以显著提高极限环振荡的抑制效果和临界速度。此外,NES的阻尼比越小,其颤振系统的极限环振荡抑制效果越好。
