Coupled motion analysis of tether with time-varying length and rigid bodies

Abstract

In this paper, we discuss the motion of a tethered system during winding a tether in microgravity. When the tether is being wound, it comes into strong contact with the feeding section of the system. Accordingly, both are expected to undergo complex motion as they interact with each other. We have therefore carried out both a numerical and an experimental study to clarify the motion of such a system using a mobility device using the tether named TSMD proposed by us as an example. We first developed a numerical model composed of three rigid bodies and a flexible body that serves as the tether. To take into account the large deformation and displacement of the tether, the flexible body was modeled using the absolute nodal coordinate formulation. It is important for the tethered system to consider the motion of winding the tether. In this model, the flexible body which is pulled into the rigid bodies contacting with its feeding section is formulated. This numerical model allows the interaction between the rigid and flexible bodies to be investigated as the tether is being wound. To verify the numerical results obtained using the proposed model, experiments were performed for a tethered system in a microgravity environment, where the tether was being wound. Good agreement was found between the numerical and experimental results. The tension in the tether was shown to influence the motion of the rigid bodies when the tether was under strain, and the rigid bodies were moved by an inertial force when the tether had a deflection. It was also found that the tension in the tether could be controlled by the winding speed, so allowing rotation of the rigid bodies to be suppressed.