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首页> 外文期刊>International journal of non-linear mechanics >Interaction of torque link freeplay and Coulomb friction nonlinearities in nose landing gear shimmy scenarios
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Interaction of torque link freeplay and Coulomb friction nonlinearities in nose landing gear shimmy scenarios

机译：前起落架摆振场景中扭矩连杆自由游隙和库仑摩擦非线性的相互作用

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摘要

Aircraft nose landing gears are known to be prone to shimmy oscillations, rooted mainly in inadequate design and maintenance. Being a highly nonlinear dynamical system, stable limit-cycles can arise for certain values of input parameters, which are both a nuisance to the occupants and a threat to the safety and integrity of the aircraft. Influence of different landing gear nonlinearities are discussed in differing depth in the literature, leaving the interaction and simultaneous effect of these nonlinearities mostly unexplored. In particular, Coulomb friction in the shock absorber is largely neglected or oversimplified, while it was shown in the authors' previous work to have a substantial effect on the stability boundaries. In the present novel investigation, we further explore the significance of state-dependent Coulomb friction in the shock absorber in presence of rotational freeplay, which is another key nonlinearity of the landing gear systems. Using a representative high-fidelity Multi-Body Dynamic model and numerical solution scheme in the time domain, 3D shimmy maps and 2D stability boundaries are obtained and employed to understand the nonlinear phenomena of interest, contributing to more realistic performance estimation of nose landing gears in early design stages. Together with time histories of the limit-cycles, phase portraits, and frequency spectra for selected inputs, the stability maps showed that presence of freeplay leads to emergence of a new area in the stability map, characterized with low-amplitude rotational oscillations and zero steady-state lateral amplitude. Furthermore, with Coulomb friction and freeplay both being part of the model, the freeplay-induced area of the stability map vanishes, while the freeplay effect is still manifested in the frequency spectra and expansion of the rotational-dominant area. The sensitivity of the freeplay-induced changes to the magnitude of the torque link freeplay is also depicted and discussed, for cases with and without Coulomb friction.
机译：众所周知，飞机前起落架容易产生颤动的振动，这主要是由于设计和维护不当造成的。作为高度非线性的动力系统，对于某些输入参数值，可能会出现稳定的极限环，这既给乘员带来麻烦，又对飞机的安全性和完整性造成威胁。在文献中以不同的深度讨论了不同的起落架非线性的影响，而这些非线性的相互作用和同时影响大多未得到探讨。尤其是，减震器中的库仑摩擦在很大程度上被忽略或简化了，而作者的先前工作表明这对稳定性边界具有实质性影响。在当前的新颖研究中，我们进一步探讨了在存在旋转自由游隙的情况下减震器中状态相关的库仑摩擦的重要性，这是起落架系统的另一个关键非线性。使用时域中具有代表性的高保真多体动力学模型和数值解方案，获得了3D摆振图和2D稳定边界，并将其用于理解感兴趣的非线性现象，从而有助于更准确地估计前起落架的性能。早期设计阶段。连同选定输入的极限周期，相画像和频谱的时间历史记录，稳定性图显示，自由游动的存在会导致稳定性图中出现一个新区域，其特征在于低振幅旋转振荡和零稳态状态的横向振幅。此外，由于库仑摩擦和自由运动都是模型的一部分，稳定性图的自由运动引起的区域消失了，而自由运动效果仍在频谱和旋转主导区域的扩展中表现出来。对于具有和不具有库仑摩擦的情况，还描绘和讨论了由自由运动引起的转矩链接自由度大小变化的敏感性。

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