Real-Time Hybrid Model Testing of Moored Floating Structures Using Nonlinear Finite Element Simulations

The paper proposes an application of real-time hybrid model testing (abbreviated ReaTHM testing) for the study of moored offshore structures. The structure under study is a moored axisymmetric floater with various bilge configurations, whose hydrodynamic properties are of interest. The system is partitioned into a physical substructure, consisting of a scaled model of the floater, and a numerical substructure, consisting of 12 mooring lines. All mooring lines are described by a nonlinear finite element model, to capture important phenomena such as geometric stiffness and drag-induced damping. The paper describes the substructuring strategy, the architecture of the test setup, and provides details regarding its components, namely the sensors, kinematic observer, predictor, numerical model, control/allocation system, and actuators. Results from qualification tests in calm water are presented, the main sources of time delays (which are compensated for) are identified, and the presence of jitter induced by Newton-Raphson iterations is discussed.