Sensitivity-Based Robust NMPC for Close-Proximity Offshore Wind Turbine Inspection with a Tilted Multirotor
TLDR
A sensitivity-based robust NMPC is proposed for close-proximity offshore wind turbine inspection, preventing safety violations under uncertainties.
Key contributions
- Introduces a sensitivity-based robust NMPC for tilted multirotors inspecting wind turbines.
- Robustifies tower-clearance constraints via online tightening using first-order state sensitivities.
- Incorporates a stage-dependent additive margin to handle bounded wind gusts effectively.
- Eliminates safety violations seen in nominal NMPC, confirmed by Monte-Carlo simulations.
Why it matters
Close-proximity inspection of offshore wind turbines is critical but challenging due to environmental uncertainties and model mismatch. Nominal NMPC often fails to maintain safety clearances. This paper introduces a robust NMPC that ensures safety by preventing constraint violations, making autonomous inspection safer and more reliable.
Original Abstract
Close-proximity offshore wind turbine inspection requires strict clearance control around large cylindrical structures under wind and model mismatch. Nominal Nonlinear Model Predictive Control (NMPC) may violate safety constraints when mass, inertia, thrust effectiveness, drag, or wind conditions differ from nominal assumptions. We propose a sensitivity-based robust NMPC for a tilted multirotor that robustifies the tower-clearance constraint via online constraint tightening. First-order parametric state sensitivities provide a structured-uncertainty margin, while bounded gusts are handled by a stage-dependent additive margin. The formulation augments the nominal NMPC with sensitivity propagation and margin evaluation only, leaving the receding-horizon optimization structure unchanged. Monte-Carlo evaluation over 500 uncertainty realizations on a boundary-critical helical inspection trajectory shows that the proposed controller eliminates the clearance violations observed under nominal NMPC at the cost of a moderate increase in solve time.
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