Session: 09-09-01: Hybrid Energy I

Submission Number: 156719

Wave Power Extraction From Semi-Submersible Hybrid Platforms With Multi-Physics and High-Fidelity Simulations Powered by SPH 

“Hybridize-ing” wave energy seems a promising way forward to elevate wave energy converters’ (WEC) technology readiness and preparedness. As of now, hybrid systems consist of floating offshore wind turbine (FOWT) platforms that host WECs, which generally rely on purpose-built sub-structures that can accommodate WEC connections. This forms a promising scenario that sees synergistic interactions for mutual structural convenience, in which FOWTs and WECs can benefit from each other. First, WECs surely attain stronger waves by perching further offshore and can do so with relatively minor sub-structuring expenditure, as most of the station-keeping functionality and grid connection comes from the wind platform itself. Second, the hydrodynamic response of WECs can be broadened in frequency to achieve better energy capture characteristics by combining the modes of the WECs and the platform. Lastly, hybrid platforms can function as novel “power units” that supply rated power with higher quality, based on wind-to-wave combined generation capability. However, existing literature has provided sparse benchmark examples, for most of which low-fidelity modeling is used for the hydrodynamics [1,2]. Adequate physical testing has yet to yield substantial proof of concept.

We propose a high-fidelity performance estimation for a “power unit” comprising a semi-submersible platform for a 5-MW NREL wind turbine and three WaveStar WECs [3], which are radially deployed around each pontoon, for a theoretical additional power absorption of 500 kW. Here, we use the optimized and benchmarked layout presented in [1], from which only the conditions without wind are considered. The CFD numerical framework is based on DualSPHysics [4], owing to its multi-physics simulation support and great computational efficiency, enriched by integration of external libraries and powered by state-of-the-art CUDA parallelization. We first validate the response of the power unit by relying on individual model validations, specifically, validating a OC4 DeepCwind layout (i.e., with catenary lines) covering an operational range of frequencies from four to nine seconds. Across the same range, and after validation, a power matrix is constructed for the Wave Star device. During the last step of our research, the combined power ability of the three Wave Star systems is evaluated and critically likened to literature results. Our outcome suggests that estimating the power performance of a hybrid power unit can lead to inaccuracies to WEC’s disadvantage, indicating underestimation of power output and structural loads.

[1] Ghafari, H. R., Ghassemi, H., & He, G. (2021). Numerical study of the Wavestar wave energy converter with multi-point-absorber around DeepCwind semisubmersible floating platform. Ocean Engineering, 232, 109177. https://doi.org/10.1016/j.oceaneng.2021.109177

[2] Jin P. et al. (2023). Optimization and evaluation of a semi-submersible wind turbine and oscillating body wave energy

converters hybrid system. Energy, 282, 128889. https://doi.org/10.1016/j.energy.2023.128889

[3] Ransley, E. J. et al. (2017). RANS-VOF modelling of the Wavestar point absorber. Renewable Energy, 109, 49–65. https://doi.org/10.1016/j.renene.2017.02.079

[4] Crespo AJC et al. (2023). On the state-of-the-art of CFD simulations for WECs within the open-source numerical framework of DualSPHysics. In: Proceedings of the 15th European Wave and Tidal Energy Conference, Bilbao, Spain

Presenting Author: Bonaventura Tagliafierro Uppsala University

Presenting Author Biography: Bonaventura Tagliafierro is a Researcher in Renewable Energy Systems and Numerical Modeling. Now Marie Skłodowska-Curie Fellow at Uppsala University (Sweden) at the Dept. of Electrical Engineering, advised by Prof. Malin Göteman. Completed his doctoral program at the University of Salerno in Italy (2022), specializing in steel design and numerical methods for structural design. Has been collaborating with EPhysLab (University of Vigo, Spain) since 2019 as a researcher and has also joined the DualSPHysics code project, and since 2023 acts as Wiki Coordinator. Research interests include finite element analysis, computational fluid dynamics, dynamics of multibody systems, and coupling between fluid and solid mechanics. Computational methodologies include the Smoothed Particle Hydrodynamics (SPH) technique: a meshless method for developing Lagrangian frameworks. Code applications involve wave energy converters, floating offshore wind turbine platforms, and steel structures, aiming at investigating performance under extreme events. Formerly, post-doctoral researcher at the Universitat Politècnica de Catalunya (2022–2024, Spain); was awarded a Fulbright Schuman fellowship to research on the numerical implementation of control systems for offshore wind technology at Simulation Based Engineering Lab (SBEL, UW-Madison, US) using Project Chrono, supervised by Prof. Dan Negrut.