Xiao XIE Thesis Defense

Slender swimming robots, inspired by aquatic snakes or eels, are gaining popularity in academia. They are maneuverable and energy efficient compared to autonomous surface ships. However, they suffer from surface instability under extreme conditions (swell, wind and surface debris). The stabilization process for these multibody swimmers remains an open question. The SSSNAEQ project seeks to solve this problem by taking inspiration from snakes to actively stabilize these robots. Through this objective, a new serpentiform robot prototype, named NATRIX, was developed, equipped with bio-inspired ``organs'' located in the neck and along the body to achieve active stabilization. In this context, this thesis reports the exploration of the static and dynamic stability of the robot on the surface from a numerical aspect. It focuses at first on the geometric, kinematic and dynamic modeling of the robot. Based on these models, two new open-loop and closed-loop strategies on postural control were proposed. These control laws make it possible to calculate the joint trajectories which stabilize the robot's posture on the water surface for static poses or when swimming. Then, we report a self-excited parametric resonance during cyclic swimming, causing the robot to capsize through an unrestricted rolling motion. The physical process of this instability is associated with the internal movements of the robot, which are different from those of monobody vessels \cite{thompson1992mechanics}. A stability template, different from that for bipedal locomotors \cite{full1999templates}, was developed to predict this instability. In the end, it was confirmed that, by exploiting the additional organs, this instability is considerably reduced. This work represents the first methodological blocks, paving the way for the development of active control for the stabilization of swimming snake robots on the water surface.