Manoeuvrability is one of the essential keys in the development of improved autonomous underwater vehicles for challenging missions. In the last years, more researches were dedicated to the development of new hulls shapes and thrusters to assure more manoeuvrability. The present review explores various enabling technologies used to implement the vectorial thrusters (VT), based on water-jet or propellers. The proposals are analysed in terms of added degrees of freedom, mechanisms, number of necessary actuators, water-tightness, electromagnetomechanical complexity, feasibility, etc. The usage of magnetic coupling thrusters (conventional or reconfigurable) is analysed in details since they can assure the development of competitive full waterproof reconfigurable thrusters, which is a frictionless, flexible, safe, and low-maintenance solution. The current limitations (as for instance the use of non conductive hull) are discussed and ideas are proposed for the improvement of this new generation of underwater thrusters, as extending the magnetic coupling usage to obtain a fully contactless vector thrust transmission.

The concept of reconfigurable magnetic coupling thrusters (RMCT) applied to the vectorial thrust of autonomous underwater vehicles (AUV) has been recently developed and presented. This technology ensures greater robot watertightness with enhanced maneuvering capabilities, which are desired features in agile AUVs for marine renewable energy (MRE) system maintenance. It is possible since in RMCTs the driving torque is magnetically transmitted to the propeller, which has its orientation changed. This work is focused on the coupling and control torque calculation and further analysis of the latest prototype version (Flat-RMCT), in the static condition for the full thrust vector range. For this purpose, a numerical model is implemented and validated with experimental results. The numerical model is based on the finite volume integral method. The results indicate that the minimum magnetic reluctance propensity creates not only the expected magnetic spring effect but also an auto-driving torque due to the non-axial symmetry of coupling rotors, which exists only for reconfigurable couplings. Mathematical functions are proposed to model these effects and they are used to extend the understanding of the coupling. These models can be used to compose a full and accurate dynamic model for a better RMCT simulation, identification, and control.

Magnetic couplings play an essential role in designing fully waterproof mechanical transmission devices. These systems allow transmitting motions at a distance, therefore without complex and unreliable mechanical seals for rotating shafts. However, magnetic couplings naturally create less rigid joints when compared with mechanical ones. It means the driven rotor of a magnetic coupling can present a different movement of its motorised counterpart in transient conditions (while accelerating, for example). Usually, designers look for optimising the torque density. However, if we are looking for a fast response and position control accuracy (i.e. synchronisation), another approach must be carried out. The reason is that, for different magnetic couplings, the maximum transmissible torque can be achieved with widely different angles (according to device features), while we need high torques for tiny angles. Hence, our objective is to maximise the initial stiffness minimising the volume of magnets. Thus, this work aims to present a design method to find an optimal rigid axial magnetic coupling by maximising its initial stiffness density (defining the objective function) under geometric constraints. First, the stiffness analytical expression is obtained for a chosen axial magnetic coupling made with Halbach arrayed arched magnets. Secondly, an optimal magnetic coupling is sought for a given device. In conclusion, this stiffness density-based design is analysed and compared to the torque density-based one, finding the best number of poles-pairs.

Modélisation, optimisation et conception d'un propulseur magnéto-couplé reconfigurable pour la robotique sous-marine: Ce travail de recherche vise à développer un nouveau système de propulsion pour les véhicules sous-marins (robots), qui devrait garantir l'étanchéité totale, une plus grande maniabilité et une meilleure efficacité. L'étanchéité intégrale est assurée par des accouplements magnétiques, qui permettent la transmission du couple à l'extérieur du robot, sans trous ni joints mécaniques sur sa coque. Une meilleure manoeuvrabilité est obtenue grâce au système de propulsion reconfigurable, qui permet l'orientation de l'hélice, assurant ainsi plus de degrés de liberté pour chaque propulseur, ce qui réduit le nombre total de propulseurs requis pour propulser et diriger le véhicule, augmentant ainsi son efficacité. Ce système est appelé propulseur magnéto-couplé reconfigurable (PMCR) et n'avait pas encore été entièrement conçu et appliqué à un vrai robot sous-marin. Pour ce faire, un concept innovant doit être proposé avec des actionneurs appropriés, modélisés, optimisés, détaillés, fabriqués et testés. Pour une reconfiguration large de l'hélice, le nouveau PMCR doit avoir au moins plus deux degrés de liberté : un pour la transmission de puissance et un ou deux autres degrés agissant pour orienter l'hélice.Le nouveau design est modélisé paramétriquement avec ses actionneurs, compte tenu de son comportement mécanique et magnétique, aboutissant à un prototype numérique qui devrait être optimisé. Le modèle magnétique paramétrique utilise la méthode qui est évaluée (calculée) le plus rapidement parmi : la méthode des éléments finis ou la méthode d'intégration des volumes finis. Le processus d'optimisation est évolutif et utilise des algorithmes génétiques. Ainsi, un PMCR optimal est atteint pour les paramètres qui sont considérés. Le projet exécutif détaillé est réalisé, puis fabriqué et assemblé.