Optimization and co-design of the IEA 15MW VolturnUS-S semi-submersible floating offshore wind turbine using the WEIS-HAWC2 framework

Optimization presents a promising route to cost reductions and performance enhancements of floating offshore wind turbines (FOWTs) and the National Laboratory of the Rockies (NLR)’s Wind Energy with Integrated Servo-controls (WEIS) is the leading open-source multi-disciplinary FOWT optimization toolset. An objective of the EU’s FloatFarm project was to expand WEIS by enabling the use of DTU Wind and Energy Systems’ HAWC2 aero-elastic-servo-hydro solver within the framework as an alternative to NLR’s OpenFAST. This work demonstrates the capabilities of the coupled framework, which includes attractive features such as control co-design (CCD) and parallel design load case (DLC) generation, execution and analysis. An optimization and CCD case study is presented, which serves to demonstrate the functioning WEIS-HAWC2 framework, showcasing the ability for a HAWC2 model to be updated according to iterative changes in a FOWT design, and whose simulation outputs can be used to guide optimization problems to convergence. The case study performed modifications to the blades, tower, moorings and floating platform of the IEA 15 MW VolturnUS-S FOWT with the aim of minimizing the total structural mass, which was ultimately reduced by 3.2%, relative to the initial design, while adhering to prescribed constraints, when simulated under normal operating conditions. The implemented CCD algorithm was also applied to ensure that controller gains were suitable to iteration-specific structural designs. The coupled WEIS-HAWC2 framework provides HAWC2’s established and expanding user-base with opportunities to perform multi-disciplinary optimization of FOWTs, and is intended to be a valuable tool for the FOWT research community.