Nested Control Co-design of a Spar Buoy Horizontal-axis Floating Offshore Wind Turbine

TL;DR

This paper introduces a nested control co-design approach for floating offshore wind turbines, demonstrating over 11% improvement in energy production by optimizing plant and control decisions simultaneously.

Contribution

It presents a novel nested CCD methodology using open-loop optimal control for simplified FOWT models, highlighting the benefits of integrated design optimization.

Findings

Over 11% increase in annual energy production compared to baseline.

Simplified models effectively capture key physics and coupling effects.

Provides a template for future high-fidelity FOWT co-design studies.

Abstract

Floating offshore wind turbine (FOWT) systems involve several coupled physical analysis disciplines, including aeroelasticity, multi-body structural dynamics, hydrodynamics, and controls. Conventionally, physical structure (plant) and control design decisions are treated as two separate problems, and generally, control design is performed after the plant design is complete. However, this sequential design approach cannot fully capitalize upon the synergy between plant and control design decisions. These conventional design practices produce suboptimal designs, especially in cases with strong coupling between plant and control design decisions. Control co-design (CCD) is a holistic design approach that accounts fully for plant-control design coupling by optimizing these decisions simultaneously. CCD is especially advantageous for system design problems with complex interactions between physics disciplines, which is the case for FOWT systems. This paper presents and demonstrates a nested CCD approach using open-loop optimal control (OLOC) for a simplified reduced-order model that simulates FOWT dynamic behavior. This simplified model is helpful for optimization studies due to its computational efficiency, but is still sufficiently rich enough to capture important multidisciplinary physics couplings and plant-control design coupling associated with a horizontal-axis FOWT system with a spar buoy floating platform. The CCD result shows an improvement in the objective function, annual energy production (AEP), compared to the baseline design by more than eleven percent. Optimization studies at this fidelity level can provide system design engineers with insights into design directions that leverage design coupling to improve performance. These studies also provide a template for future more detailed turbine CCD optimization studies that utilize higher fidelity models and design representations.