Nonlinear dynamic modelling and testing of slack tether handling system

提出的研究目标是开发一种新的基于仿真的系绳处理技术，以提高用于航天、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负载路径。它通过调整其平衡几何形状以张力承载负载来响应外部负载。因此，当系绳张力接近零时，系绳变得不稳定，系绳系统变得不可控。除了传统的缆索张力反馈控制在低张力范围内效果不佳之外，新的操纵系统将基于计算机对缆索动力学的预测来控制缆索系统。现有的绳系模型大多存在一定的局限性，如零张力引起的奇异性、考虑弯曲刚度以减轻奇异性后膜模与弯曲模之间的刚度不匹配导致的高频振荡、传统有限元（FE）方法中较大的三维旋转导致的数值不准确以及欧拉角度下的数值奇异性。申请人将开发一个通用的缆绳模型，通过设计一个新的自适应缆绳有限元来解决这些缺点，该有限元使用(i)基于张力大小的变阶形状函数和（ii）一个新的全局位置矢量有限元公式。所得到的系索运动方程将采用改进的广义阿尔法方法进行处理，以达到较高的数值精度和稳定性。基于新的系绳模型和处理技术，申请人将开发一种使用电动系绳的纳米卫星任务末端脱轨器。将进行数值研究，使用新的元件和系绳处理技术，以及实验调查，使用仪器系绳，摄影测量和数字成像技术。这项工作将训练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，从而开发空间无推进剂推进、脱轨和重新定位装置以及航空航天空中系绳拾取和交付系统中的系绳系统。

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.