Nonlinear dynamic modelling and testing of slack tether handling system

这项研究的目的是开发一种新的基于模拟的系绳操纵技术，以提高用于空间、航空、海洋工程等领域的低压系绳系统的稳定性和可控性。系绳是控制点和系统其余部分之间的单一加载路径。它通过调整其平衡几何结构来响应外部载荷，以通过张力来承载载荷。结果，系绳变得不稳定，因此当系绳张力接近零时，系绳系统变得无法控制。新的操纵系统将根据系绳动力学的计算机预测来控制系绳系统，除了传统的系绳张力反馈控制在低张力范围内不能很好地工作之外。现有的大多数系索模型都存在一定的局限性，如零张力引起的奇异性，在计入弯曲刚度以减轻奇异性后薄膜和弯曲模式之间的刚度失配引起的高频振荡，传统有限元方法中由于大的三维旋转而导致的数值不准确，以及欧拉角的数值奇异性。申请人将通过使用(I)基于张力值的可变阶形函数和(Ii)新的全局位置矢量有限元公式来设计新的自适应系绳有限元来开发通用系绳模型来解决这些缺点。所得到的系索运动方程将使用改进的广义阿尔法进行处理，以获得高的数值精度和稳定性。基于新的系绳模型和操作技术，申请者将使用电动系绳开发一种纳米卫星任务结束脱轨器。将使用新的单元和系绳处理技术进行数值研究，并使用仪表式系绳、摄影测量和数字成像技术进行实验研究。这项工作将培训HQP，为我们的知识增加一种新的有限元方法，并开发一种新的系绳处理技术，从而开发出空间无推进器推进、脱轨和重新定位装置中的系绳系统，以及航空航天中的航空系绳拾取和发射系统。

The objective of the proposed research is to develop a new simulation based tether handling technology to enhance the stability and controllability of low-tension tether systems used in the space, aeronautics, marine engineering, among others. The tether is the single load path between the control point and the rest of system. It responds to external loads by adapting its equilibrium geometry to carry the loads by tension. As a result, a tether becomes unstable and consequently the tether system becomes uncontrollable when tether tension approaches zero. The new handling system will control the tether system based on the computer prediction of tether dynamics in addition to the conventional tether tension feedback control that does not work well in the low-tension range. Most existing tether models suffer from certain limitations such as singularity arising from zero tension, high frequency oscillations due to stiffness mismatch between membrane and bending modes after the bending stiffness is included to alleviate the singularity, numerical inaccuracies resulting from large 3D rotations in the conventional finite element (FE) methods, and numerical singularity from Euler's angles. The applicant will develop a generic tether model to address these shortcomings by devising a new adaptive tether finite element using (i) variable order shape functions based on tension magnitude and (ii) a new global position vector finite element formulation. The resulting equations of motion of tethers will be treated using the modified generalized-alpha method to achieve high numerical accuracy and stability. Based on the new tether model and handling technology, the applicant will develop a nano-satellite end-of-mission deorbitor using an electrodynamic tether. Both numerical studies, using the new element and tether handling technology, and experimental investigations, using instrumented tethers, photogrammetry and digital imaging techniques, will be conducted. The work will train HQPs, add a new FE method to our knowledge, and develop a new tether handling technology leading to the development of tether systems in the space propellantless propulsion, deorbit and repositioning devices, and in the aerial-tether pickup and delivery system in aerospace.