Static Orientation Control of AUVs - Conceptual Design and Control Architectures

To counteract the interaction forces between the vehicle and its manipulator arm, Underwater Vehicle-Manipulator Systems (UVMS) are usually equipped with a sufficient configuration of thrusters to allow for 6-DOF dynamic control. Another common design method is to place lightweight elements in the top part of the vehicle's hull and heavier components in its bottom part. By that, a large metacentric height is achieved, which results in a higher static stability of the vehicle. However, this also restricts the vehicle's orientation in the two DOF pitch and roll, since high thruster power would be required to orientate the vehicle arbitrarily. There are scenarios where the ability to align the vehicle to an arbitrary orientation appears to be beneficial. E.g., when manipulation tasks have to be conducted on the sea floor as well as overhead, orienting the usually limited working space of an UVMS to the object of interest would be advantageous. One way to enable a vehicle for this ability is to actively shift the center of gravity or the center of buoyancy or both of them and thereby modify the statically stable orientation. This can be realized by, e.g., moving mass inside the vehicle's hull or utilizing a buoyancy engine. The aim of this thesis is to examine and develop methods, that facilitate static orientation control of AUVs. After addressing conceptual design aspects and feasibility, a control algorithm shall be designed and evaluated on a demonstrator.