Session: 01-01-02 Offshore Platforms-II

Paper Number: 125160

125160 - Experimental Investigation of Nonlinear Forces on a Monopile Offshore Wind Turbine Foundation Under Directionally Spread Waves 

Wave loading significantly influences the structural design of marine and offshore installations, and accurately predicting the nonlinear high-order components of this loading has posed a persistent challenge. Previous research focused on unidirectional extreme sea states and examined the nonlinear harmonic components of hydrodynamic forces acting on a bottom-mounted vertical cylinder offshore wind turbine. The results unveiled that, for specific wave scenarios, linear loading accounted for less than 40% of the total wave loading, with high-order harmonics contributing more than 60%. This finding underscores the critical role of high-order nonlinear wave loading in the design of offshore wind turbine foundations.

 

This paper expands on this research by exploring a broader range of extreme wave interactions with the cylinder-type offshore wind turbine foundations, encompassing multidirectional and bidirectional focused wave groups. We introduce a phase-based harmonic separation method to isolate harmonic component groups from the total diffraction force by controlling the phase of incident focused waves. Remarkably, this method proves effective even in the presence of locally violent breaking waves and with multidirectional and bidirectional spreading. The clean separation of individual harmonics enables the estimation and prediction of high-order harmonic shapes and histories based solely on the linear component.

 

The new experimental data fits with previous findings, indicating a significant proportion of nonlinear wave loadings can be up to 50% as kA increases and kR decreases (where k is the incident wave number, A is the peak crest amplitude of the incident focused wave groups, and R is the cylinder radius). Additionally, wider spreading of incident waves results in scaled-down nonlinear high-order harmonics of the inline force on the cylinder. Notably, unidirectional waves are shown to generate the most severe nonlinear inline forces. This research underscores the necessity of considering high-order nonlinear wave loading in the design of offshore structures.

Presenting Author: Haoyu Ding University of Bath

Presenting Author Biography: Dr Haoyu Ding is a Research Associate at University of Bath, UK, working on a UK EPSRC project. He holds a Ph.D. in Civil Engineering from University of Bath, sponsored by Royal Academy of Engineering (RAE) PhD scholarship, and specialises in developing a hybrid WEC-Breakwater system. His publications primarily focus on the research areas of wave energy converters, numerical modelling, hydrodynamics, and gap resonance. His work has been presented at prestigious international conferences, including IWWWFB and OMAE conferences.

Authors:

Haoyu Ding University of Bath
Jun Zang University of Bath
Guangwei Zhao University of Strathclyde
Tianning Tang University of Oxford
Paul Taylor The University of Western Australia
Thomas Adcock University of Oxford
Saishuai Dai University of Strathclyde
Dezhi Ning Dalian University of Technology
Lifen Chen Dalian University of Technology
Jinxuan Li Dalian University of Technology
Rongquan Wang Dalian University of Technology