Guillén Campaña-Alonso

Anthropogenic underwater noise from offshore wind turbines is a growing environmental concern, particularly with the large-scale deployment of bottom-fixed and floating devices. This study presents a physics-based vibroacoustic framework to predict operational underwater noise emissions from 10 MW offshore wind turbines, comparing monopile-supported and floating configurations. The methodology combines aero-hydro-servo-elastic simulations with a frequency-domain acoustic formulation based on equivalent dipole sources and Green’s function solutions accounting for confinement between the free surface and seabed. Results show that floating configurations exhibit enhanced low-frequency acoustic emissions, producing up to 15 dB higher OASPL than monopile structures below 10 Hz due to additional rigid-body motions, whereas monopiles radiate more efficiently at higher frequencies associated with drivetrain excitations. Floating platforms also display more complex three-dimensional directivity patterns, with direction-dependent variations reaching 10–15 dB in the 100–1000 Hz range. Water depth strongly influences propagation regimes and sound levels, with shallow-water floating configurations showing up to 9 dB OASPL variations compared to deep-water cases. The proposed framework provides a predictive tool for assessing underwater acoustic impacts during offshore wind turbine design.

This study examines how wave‐induced modulation affects the operational performance and structural dynamics of fixed‐bottom offshore wind turbines operating under a neutral atmospheric boundary layer profile. To capture these effects accurately while maintaining computational efficiency, unsteady RANS modelling techniques are employed. An actuator line method (ALM) is used to simulate the rotating blades, while a volume of fluid is used to generate the air–water interface and waves and to capture wake development. A 10‐MW wind turbine case study has been selected to study the impact of wave‐induced modulation on loads and wakes. Wake analysis reveals that wave modulation affects its development, resulting in a higher wake deficit and slower recovery. Specifically, four diameters downstream, the interaction leads to a 1.2% increase in wake deficit, with local increases up to 3.6% near the blade tips. These effects correspond to an average difference in wake deficit of 2.48% when wave modulation is taken into account and a consequent reduction in power of approximately 1%. In addition to wake effects, wave modulation leads to increased standard deviations across key aerodynamic variables, including blade loads and angle of attack, with the most pronounced changes occurring in the lower rotor area. The damage equivalent load (DEL) increases by 4% or up to 8% in the absence of the tower‐shadow effect. The ALM proves to be capable of capturing these interactions, suggesting its effectiveness in modelling realistic offshore conditions. These findings emphasise the importance of accounting for wave‐induced modulation in offshore wind turbine design and operation and suggest directions for future research, including wind‐wave misalignment and floating turbine configurations.

The numerical study of floating offshore wind turbines (FOWTs) requires accurate integrated simulations which consider the aerodynamic, hydrodynamic, servo and elastic responses of these systems. In addition, the floating system dynamics couplings need to be included to calculate the excitation over the ensemble accurately. In this paper, a new tool has been developed for coupling NREL's aero-servo-elastic tool OpenFAST with the computational fluid dynamics (CFD) toolbox OpenFOAM. OpenFAST is used to model the rotor aerodynamics along with the flexible response of the different components of the wind turbine and the controller at each time step considering the dynamic response of the platform. OpenFOAM is used to simulate the hydrodynamics and the platform's response considering the loads from the wind turbine. The whole simulation environment is called OF² (OpenFAST and OpenFOAM). The OC4 DeepCWind semi-submersible FOWT together with NREL's 5 MW wind turbine has been simulated using OF² under two load cases. The purpose of coupling these tools to simulate FOWT is to obtain high-fidelity results for design purposes, thereby reducing the computational time compared with the use of CFD simulations both for the rotor aerodynamics, which usually consider rigid blades, and for the platform's hydrodynamics. The OF² approach also allows us to include the aero-servo-elastic couplings that exist on the wind turbine along with the hydrodynamic system resolved by CFD. High-complexity situations of floating offshore wind turbines, like storms, yaw drifts, weather vanes or mooring line breaks, which imply high displacements and rotations of the floating platform or relevant non-linear effects, can be resolved using OF², overcoming the limitation of many state-of-the-art potential hydrodynamic codes that assume small displacements of the platform. In addition, all the necessary information for the FOWT calculation and design processes can be obtained simultaneously, such as the pressure distribution at the platform components and the loads at the tower base, fairleads tension, etc. Moreover, the effect of turbulent winds and/or elastic blades could be taken into account to resolve load cases from the design and certification standards.

This paper provides a summary of the work done within Phase III of the Offshore Code Comparison Collaboration, Continued, with Correlation and unCertainty (OC6) project, under the International Energy Agency Wind Technology Collaboration Programme Task 30. This phase focused on validating the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure. Numerical models of the Technical University of Denmark 10 MW reference wind turbine were validated using measurement data from a 1:75 scale test performed during the UNsteady Aerodynamics for FLOating Wind (UNAFLOW) project and a follow-on experimental campaign, both performed at the Politecnico di Milano wind tunnel. Validation of the models was performed by comparing the loads for steady (fixed platform) and unsteady (harmonic motion of the platform) wind conditions. For the unsteady wind conditions, the platform was forced to oscillate in the surge and pitch directions under several frequencies and amplitudes. These oscillations result in a wind variation that impacts the rotor loads (e.g., thrust and torque). For the conditions studied in these tests, the system aerodynamic response was almost steady. Only a small hysteresis in airfoil performance undergoing angle of attack variations in attached flow was observed. During the experiments, the rotor speed and blade pitch angle were held constant. However, in real wind turbine operating conditions, the surge and pitch variations would result in rotor speed variations and/or blade pitch actuations, depending on the wind turbine controller region that the system is operating. Additional simulations with these control parameters were conducted to verify the fidelity of different models. Participant results showed, in general, a good agreement with the experimental measurements and the need to account for dynamic inflow when there are changes in the flow conditions due to the rotor speed variations or blade pitch actuations in response to surge and pitch motion. Numerical models not accounting for dynamic inflow effects predicted rotor loads that were 9 % lower in amplitude during rotor speed variations and 18 % higher in amplitude during blade pitch actuations.

The numerical study of floating offshore wind turbines requires accurate integrated simulations, considering aerodynamics, hydrodynamics, servo and elastic response of these systems. In addition, the floating system dynamics couplings need to be included to calculate precisely the excitation over the ensemble. In this paper, a new tool has been developed coupling the NREL´s aero-servo-elastic tool OpenFAST with the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. OpenFAST is used to model the rotor aerodynamics alongside with the flexible response of the different components of the wind turbine and the controller at each time step considering the dynamic response of the platform. OpenFOAM is used to simulate the hydrodynamics and the platform's response considering the loads from the wind turbine. The whole simulation environment is called OF² (OpenFOAM & OpenFAST). The OC4 DeepCWind semi-submersible FOWT together with the NREL´s 5MW wind turbine has been simulated using OF² under two load cases. The purpose of coupling these tools to simulate FOWT is to obtain high-fidelity results for design purposes reducing the computational time compared with the use of CFD simulations both for the rotor aerodynamics, that usually consider rigid blades, and the platform's hydrodynamics. The OF² approach allows also to include the aero-servo-elastic couplings that exist on the wind turbine alongside with the hydrodynamic system resolved by CFD. High complexity situations of floating offshore wind turbines, like storms, yaw drifts, weather-vane, or mooring line breaks, that implies high displacements and rotations of the floating platform or relevant non-linear effects can be resolved using OF², overcoming the limitation of many state of the art potential hydrodynamic codes that assume small displacements of the platform. In addition, all the necessary information for the FOWT calculation and design processes can be obtained simultaneously, such as the pressure distribution at the platform components and the loads at the tower base, fairleads tension, etc. Moreover, the effect of turbulent winds and/or elastic blades could be taken in account to resolve load cases from the design and certification standards.

This paper provides a summary of the work done within Phase III of the Offshore Code Comparison, Collaboration, Continued, with Correlation and unCertainty project (OC6), under International Energy Agency Wind Task 30. This phase focused on validating the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure. Numerical models of the Danish Technical University 10-MW reference wind turbine were validated using measurement data from a 1:75 scale test performed during the UNsteady Aerodynamics for FLOating Wind (UNAFLOW) project and a follow-on experimental campaign, both performed at the Politecnico di Milano wind tunnel. Validation of the models was performed by comparing the loads for steady (fixed platform) and unsteady wind conditions (harmonic motion of the platform). For the unsteady wind conditions, the platform was forced to oscillate in the surge and pitch directions under several frequencies and amplitudes. These oscillations result in a wind variation that impacts the rotor loads (e.g., thrust and torque). For the conditions studied in these tests, the system mainly described a quasi-steady aerodynamic behavior. Only a small hysteresis in airfoil performance undergoing angle of attack variations in attached flow was observed. During the experiments, the rotor speed and blade pitch angle were held constant. However, in real wind turbine operating conditions, the surge and pitch variations would result in rotor speed variations and/or blade pitch actuations depending on the wind turbine controller region that the system is operating. Additional simulations with these control parameters were conducted to verify the fidelity between different models. Participant results showed in general a good agreement with the experimental measurements and the need to account for dynamic inflow when there are changes in the flow conditions due to the rotor speed variations or blade pitch actuations in response to surge and pitch motion. Numerical models not accounting for dynamic inflow effects predicted rotor loads that were 9 % lower in amplitude during rotor speed variations and 18 % higher in amplitude during blade pitch actuations.

Currently, the design of floating offshore wind systems is primarily based on mid-fidelity models with empirical drag forces. The tuning of the model coefficients requires data from either experiments or high-fidelity simulations. As part of the OC6 (Offshore Code Comparison Collaboration, Continued, with Correlation, and unCertainty (OC6) is a project under the International Energy Agency Wind Task 30 framework) project, the present investigation explores the latter option. A verification and validation study of computational fluid dynamics (CFD) models of the DeepCwind semisubmersible undergoing free-decay motion is performed. Several institutions provided CFD results for validation against the OC6 experimental campaign. The objective is to evaluate whether the CFD setups of the participants can provide valid estimates of the hydrodynamic damping coefficients needed by mid-fidelity models. The linear and quadratic damping coefficients and the equivalent damping ratio are chosen as metrics for validation. Large numerical uncertainties are estimated for the linear and quadratic damping coefficients; however, the equivalent damping ratios are more consistently predicted with lower uncertainty. Some difference is observed between the experimental and CFD surge-decay motion, which is caused by mechanical damping not considered in the simulations that likely originated from the mooring setup, including a Coulomb-friction-type force. Overall, the simulations and the experiment show reasonable agreement, thus demonstrating the feasibility of using CFD simulations to tune mid-fidelity models.