Session: 15-05-01 Mooring, Riser and Pipelines

Submission Number: 181953

A CFD Investigation of Wave-Current Coupling Effects on the Dynamic Response of a TLP FOWT 

Tension Leg Platforms (TLPs) are a promising floating foundation concept for deep-water offshore wind turbines, prized for their relatively shallow draft, compact structure, and favorable economics. Their design principle relies on vertical, pre-tensioned tendons tethered to the seabed, which restrain the buoyant platform, resulting in high global stiffness. This configuration gives TLP-based floating offshore wind turbines (FOWTs) characteristically high natural frequencies in heave (vertical motion) and pitch (fore-aft tilting). While this inherent rigidity effectively suppresses large, low-frequency motions common in other floating systems, it conversely makes TLPs more susceptible to high-frequency hydrodynamic excitations arising from nonlinear and viscous wave forces. Accurately predicting these complex fluid-structure interactions poses a challenge for conventional design tools based on potential flow theory, which often simplifies or neglects such effects. A particularly important yet underexplored phenomenon for TLPs is wave-current coupling. Research on other floating structures, such as semi-submersibles, has shown that the interaction between a steady current and waves can amplify high-frequency wave loads. However, in those systems, the motion response is typically moderate because their natural frequencies are lower and well-separated from the dominant wave energy and its higher harmonics. The situation is markedly different for TLPs. Their natural frequencies are inherently higher and lie closer to the frequency range of these excitations, meaning that wave-current interaction could potentially trigger more pronounced resonant-like responses. Despite this critical vulnerability, its specific impact on TLP dynamics remains inadequately quantified. To address this knowledge gap, this study employs high-fidelity Computational Fluid Dynamics (CFD) to investigate a TLP supporting the standard NREL 5 MW wind turbine. CFD simulations are uniquely capable of capturing the complex nonlinear interactions between waves, current, and the platform structure. The analysis focuses explicitly on isolating and quantifying the effect of combined wave-current conditions versus waves alone on the platform's motion responses. The results clearly demonstrate that wave-current interaction changes the characteristics of the motion responses of TLP FOWTs. This enhanced dynamic response directly leads to a substantial increase in the peak loads experienced by the critical tendon mooring system. These findings carry crucial implications for design practice. They indicate that wave-current interaction is not a minor secondary effect but a primary driver of extreme loads for TLPs. Neglecting this coupled environmental condition in dynamic analysis could lead to an underestimation of mooring system fatigue and ultimate loads, compromising the structure's long-term integrity and reliability. Therefore, integrating the effects of wave-current coupling is essential for the safe and optimized design of future TLP-based offshore wind energy systems.

Presenting Author: Yisheng Yao Shanghai Jiao Tong University

Presenting Author Biography: Mr Yisheng Yao is PhD student supervised by Prof. Decheng Wan of Shanghai Jiao Tong University.

Authors:

Yisheng Yao Shanghai Jiao Tong University
Maokun Ye Shanghai Jiao Tong University
Shiyuan Zhang Offshore Oil Engineering Co. Ltd
Decheng Wan Shanghai Jiao Tong University