A Robotic Actuation Approach for 6-DOF Force Control in Hydrodynamic Real-Time Hybrid Simulation^*

Hydrodynamic real-time hybrid simulation (hydro-RTHS) is a testing approach that couples physical and numerical sub-assemblies through actuators and sensors in real time, offering an enhanced-fidelity alternative to small-scale experiments; e.g., testing of a floating offshore wind turbine (FOWT) in a hydrodynamic laboratory. To address multi-degree-of-freedom (DOF) actuation in a unique, floating environment, a Franka Emika Panda robotic arm was integrated into the actuation approach for hydro-RTHS. The actuation system emulates the 6-DOF small-scale aerodynamic forces computed from a numerical model acting on a small-scale FOWT specimen in a wave basin. A task-prioritized control strategy was designed to apply forces with secondary "pose-keeping" control to limit the robot’s configuration drift. The system was experimentally validated for a 1:50-scale FOWT specimen for operational wind-only cases in still water at the O.H. Hinsdale Wave Research Laboratory. Results demonstrate consistent force tracking across all six DOFs and agreement between measured platform motions and OpenFAST numerical simulations of the complete FOWT. These results illustrate the feasibility of using an off-the-shelf robotic arm for 6-DOF force control in hydro-RTHS, expanding actuation options and enhancing force control capabilities.