• 한국항공운항학회지
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• 제21권4호
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• pp.47-52
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• 2013

In this paper, limit cycle flutter induced by Hopf bifurcation is studied with nonlinear system analysis approach and observed for the critical slowing down phenomenon. Considering an attractor of the dynamics of a system, when a small perturbation is applied to the system, the dynamics converge toward the attractor at some rate. The critical slowing down means that this recovery rate approaches zero as a parameter of the system varies and the size of the basin of attraction shrinks to nil. Consequently, in the pre-bifurcation regime, the recovery rates decrease as the system approaches the bifurcation. This phenomenon is one of the features used to forecast bifurcation before they actually occur. Therefore, studying the critical slowing down for limit cycle flutter behavior would have potential applicability for forecasting those types of flutter. Herein, modeling and nonlinear system analysis of the 2D airfoil with torsional nonlinearity have been discussed, followed by observation of the critical slowing down phenomenon.

• 천문학회보
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• 제42권2호
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• pp.56.3-56.3
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• 2017

The Breakthrough Starshot initiative aims to launch gram-scale spacecraft to a speed of v~0.2c, capable of reaching Alpha Centauri and seeing the Earth-like exoplanet, Proxima b, from close distance, in about 20 years. However, a critical challenge for the initiative is the effects of interstellar matter and magnetic field to the relativistic spacecraft during the journey. In this talk, I will first present our evaluation for the damage to the spacecraft by interstellar gas and dust based on a detailed analysis of the interaction of a relativistic spacecraft with the ISM. Second, I will discuss the deflection and oscillation of spacecraft by interstellar magnetic fields. Third, I will discuss the gas drag fore at high energy regime and quantify its effect on the slowing down of the relativistic lightsails. Finally, we will discuss practical strategies to mitigate the damage by interstellar dust and to maintain the spacecraft aiming at the intended target.