Dynamic positioning concepts and strategies for the mobile offshore base

The Mobile Offshore Base (MOB) is a large, self-propelled, floating, pre-positioned ocean structure formed of three to five modules and reaching up to 1,500 meters in length. In most concepts, the structure is made of several modules, which have to be kept tightly aligned under large environmental loads. The alignment is maintained through the use of thrusters, connectors, or a combination of both. We will address the general Dynamic Positioning (DP) problem for the MOB using an interdisciplinary approach that draws from ocean, electrical, civil and mechanical engineering. The system requirements are quite complex since the roles, relative positions and dependencies of the modules may change during operation, and the system is hybrid (it contains both continuous activities and discrete event features). A hierarchical control architecture has been designed and implemented, both in simulation and on a scaled model of the MOB. A simulation framework has been used to provide low-cost, fast and efficient evaluation of different control strategies and techniques. We are conducting experiments in which three 1:150 scale modules are kept aligned by pivoting thrusters and form a miniature runway. The paper addresses the control architecture and its implementation, both in simulation and in the real-time environment.