Investigation of nonlinear difference-frequency wave excitation on a semisubmersible offshore-wind platform with bichromatic-wave CFD simulations

Lu Wang, Amy Robertson, Jason Jonkman, Yi-Hsiang Yu, Arjen Koop, Adrià Borràs Nadal, Haoran Li, Wei Shi, Romain Pinguet, Yang Zhou, Qing Xiao, Rupesh Kumar, Hamid Sarlak

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

Abstract

The natural surge and pitch frequencies of semisubmersible offshore wind platforms are typically designed to be below the wave frequencies to avoid direct excitation. However, surge or pitch resonance can be excited by the nonlinear low-frequency loads generated by irregular incident waves. Second-order potential-flow models with added Morison drag have been found to underpredict this low-frequency excitation and response. As part of the OC6 project1, the authors performed computational fluid dynamics (CFD) simulations to enable a better understanding of the low-frequency loads and the limitations of lower-fidelity models. The focus of this paper is to set up a computationally cost-effective CFD simulation of a fixed semisubmersible platform to investigate nonlinear differencefrequency loads and establish the corresponding uncertainty in the results. Because of the high computing cost, CFD simulations of irregular waves can be challenging. Instead, simulations were performed with bichromatic waves having a shorter repeat period. A preliminary comparison with quadratic transfer functions from second-order potential-flow theory shows that CFD models consistently predict higher nonlinear wave loads at the difference frequency, likely because of flow separation and viscous drag not accounted for in potential-flow theory.
Original languageEnglish
Title of host publicationProceedings of the Asme 2021 3rd International Offshore Wind Technical Conference, Iowtc 2021
Number of pages14
PublisherAmerican Society of Mechanical Engineers
Publication date2021
Article numberIOWTC2021-3537
ISBN (Electronic)978-0-7918-8476-8
DOIs
Publication statusPublished - 2021
EventASME 2021 3rd International Offshore Wind Technical Conference - Online event
Duration: 16 Feb 202117 Feb 2021

Conference

ConferenceASME 2021 3rd International Offshore Wind Technical Conference
CityOnline event
Period16/02/202117/02/2021

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