Comparison of nonlinear wave-loading models on rigid cylinders in regular waves

Mockute, Agota; Marino, Enzo; Lugni, Claudio; Borri, Claudio

Abstract

© 2019 by the authors. Monopiles able to support very large offshore wind turbines are slender structures susceptible to nonlinear resonant phenomena. With the aim to better understand and model the wave-loading on these structures in very steep waves where ringing occurs and the numerical wave-loading models tend to lose validity, this study investigates the distinct influences of nonlinearities in the wave kinematics and in the hydrodynamic loading models. Six wave kinematics from linear to fully nonlinear are modelled in combination with four hydrodynamic loading models from three theories, assessing the effects of both types of nonlinearities and the wave conditions where each type has stronger influence. The main findings include that the nonlinearities in the wave kinematics have stronger influence in the intermediate water depth, while the choice of the hydrodynamic loading model has larger influence in deep water. Moreover, finite-depth FNV theory captures the loading in the widest range of wave and cylinder conditions. The areas of worst prediction by the numerical models were found to be the largest steepness and wave numbers for second harmonic, as well as the vicinity of the wave-breaking limit, especially for the third harmonic. The main cause is the non-monotonic growth of the experimental loading with increasing steepness due to flow separation, which leads to increasing numerical overpredictions since the numerical wave-loading models increase monotonically.

Citation

Mockute, A., Marino, E., Lugni, C., & Borri, C. (2019). Comparison of nonlinear wave-loading models on rigid cylinders in regular waves. Energies, 12(21), 1-22. https://doi.org/10.3390/en12214022

• Journal Article Type: Article
• Acceptance Date: Oct 21, 2019
• Online Publication Date: Oct 23, 2019
• Publication Date: Oct 23, 2019
• Deposit Date: Dec 10, 2019
• Publicly Available Date: Dec 12, 2019
• Journal: Energies
• Electronic ISSN: 1996-1073
• Publisher: MDPI
• Peer Reviewed: Peer Reviewed
• Volume: 12
• Issue: 21
• Article Number: 4022
• Pages: 1-22
• DOI: https://doi.org/10.3390/en12214022
• Keywords: offshore wind turbines; monopile; ringing; secondary load cycle; nonlinear waves; hydrodynamic loading models; truncated surface-piercing cylinder; regular waves
• Public URL: https://hull-repository.worktribe.com/output/3307098
• Publisher URL: https://www.mdpi.com/1996-1073/12/21/4022