Second-order difference-frequency effects on floating wind turbine responses: full-QTF modelling and experimental comparison
Abstract
Accurate prediction of low-frequency responses is important for the dynamic assessment of floating offshore wind turbines (FOWTs), as second-order difference-frequency wave loads can contribute substantially to platform motions and mooring loads. Their relative importance, however, remains less well established when aerodynamic and hydrodynamic low-frequency excitations coexist under operating conditions. This study develops an efficient time-domain formulation for full difference-frequency quadratic transfer function (QTF) loading using bandwidth truncation and integrates it into a fully coupled model of the IEA 15 MW turbine on the VolturnUS-S semi-submersible platform. Numerical predictions are compared with 1:70-scale real-time hybrid wave-basin experiments covering both irregular wave-only and combined turbulent wind-wave conditions. Three hydrodynamic formulations are compared: linear wave excitation, Newman's approximation, and the full-QTF model. Under wave-only conditions, second-order difference-frequency loading substantially improves the prediction of surge and the associated mooring response, particularly in energetic sea states, with the full-QTF model generally providing the closest agreement with measured low-frequency spectra and peak-amplitude distributions. Under combined wind-wave conditions, low-frequency thrust fluctuations dominate near rated wind speed, reducing the relative importance of difference-frequency wave excitation, whereas its contribution becomes more apparent at higher wind speeds as thrust fluctuations diminish. Overall, the full-QTF model provides the most consistent improvement over the linear and Newman models, with maximum surge standard deviation discrepancy from measurement under the most energetic wave conditions less than 18%, with smaller discrepancies for heave, pitch, and mooring tensions.
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BibTeX
@misc{zhang2026secondorder,
title = {{Second-order difference-frequency effects on floating wind turbine responses: full-QTF modelling and experimental comparison}},
author = {Yi Zhang and Tom Tosdevin and Tianning Tang and Peter Stansby},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27940},
eprint = {2610.27940},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27940},
}
RIS
TY - UNPB
TI - Second-order difference-frequency effects on floating wind turbine responses: full-QTF modelling and experimental comparison
AU - Yi Zhang
AU - Tom Tosdevin
AU - Tianning Tang
AU - Peter Stansby
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.27940
UR - https://arxiv.org/abs/2610.27940
AB - Accurate prediction of low-frequency responses is important for the dynamic assessment of floating offshore wind turbines (FOWTs), as second-order difference-frequency wave loads can contribute substantially to platform motions and mooring loads. Their relative importance, however, remains less well established when aerodynamic and hydrodynamic low-frequency excitations coexist under operating conditions. This study develops an efficient time-domain formulation for full difference-frequency quadratic transfer function (QTF) loading using bandwidth truncation and integrates it into a fully coupled model of the IEA 15 MW turbine on the VolturnUS-S semi-submersible platform. Numerical predictions are compared with 1:70-scale real-time hybrid wave-basin experiments covering both irregular wave-only and combined turbulent wind-wave conditions. Three hydrodynamic formulations are compared: linear wave excitation, Newman's approximation, and the full-QTF model. Under wave-only conditions, second-order difference-frequency loading substantially improves the prediction of surge and the associated mooring response, particularly in energetic sea states, with the full-QTF model generally providing the closest agreement with measured low-frequency spectra and peak-amplitude distributions. Under combined wind-wave conditions, low-frequency thrust fluctuations dominate near rated wind speed, reducing the relative importance of difference-frequency wave excitation, whereas its contribution becomes more apparent at higher wind speeds as thrust fluctuations diminish. Overall, the full-QTF model provides the most consistent improvement over the linear and Newman models, with maximum surge standard deviation discrepancy from measurement under the most energetic wave conditions less than 18%, with smaller discrepancies for heave, pitch, and mooring tensions.
ER -