Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Influence of Non-Gaussian Winds on the Performance of Floating Offshore Wind Turbines
Shu Dai1, 2, Bert Sweetman2, *1Shanghai Investigation, Design, and Research Institute Co. , Ltd.

Shanghai, China
2Department of Ocean Engineering, Texas A&M University

College Station, Texas, USA

ABSTRACT

Fatigue life of a medium scale horizontal axis wind turbine system wasestimated by using the well-known S–N damage equation with load
spectrum confirmed with at least 20-30 years’ operating life (Kong, et al,2006). Reliability-based calibration of a design code for wind-turbine
rotor blades is developed considering the fatigue failure in flapwise
bending (Ronold, et al, 2001). Hu use 10-min mean wind speed and 10min turbulence intensity based on long-term wind speed distribution tosimulate the random wind field and analyze the fatigue reliability of acomposite wind turbine blades considering wind load uncertainty (Hu, etal, 2012). A stochastic approach is employed to develop a computer codein order to simulate wind flow with randomness in its nature on the bladeand subsequently each load case is weighted by its rate of occurrence
using a Weibull wind speed distribution (Shokrieh and Rafiee, 2006).

Short-term wind process is normally assumed to be a Gaussian
distribution, such as TurbSim, the widely used 3D wind field tool.
Nowadays, newest researches indicate that non-Gaussian wind model isbelieved to be more accurate according to the field observation data. A
new numerical method is proposed to generate non-Gaussian wind filedusing translation process theory and spectral representation method. Thisstudy presents a comprehensive investigation on power production andblades fatigue damage of floating offshore wind turbines (FOWTs) to thenon-Gaussian wind field. The comparisons of Gaussian and nonGaussian simulation results indicate that the non-Gaussian wind fields
will cost obviously worse power performance and severe fatigue damageof FOWTs.

The analyze of field measurement data of wind speed find differentconclusion that natural short-term wind is not Gaussian distribution (Daiand Sweetman, 2020). Non-Gaussian wind inflow velocities to offshore
wind turbines could potentially affect the predicted power, load, torque,and blade fatigue life. This increased quantity of extreme events willcause alternating loads on the airfoil and on the main shaft in the form of
torque fluctuations, which may cause additional fatigue damage (Mücke,et al., 2011). Schottler et al. (2017) simulate non-Gaussian and Gaussian
wind inflow conditions in a wind tunnel and indicate that extreme loads
in non-Gaussian wind inflow conditions occur much more frequently
than predicted by a typical Gaussian wind model. Gong and Chen (2017)
investigate the extreme response of operational and parked wind turbines
in non-Gaussian wind conditions. Obviously larger extremes response of
blade root edgewise and tower base fore-aft bending moments are foundfor operational wind turbine in the non-Gaussian wind inflows. Similar
results of blade root flap wise bending moment are found for parked windturbine.

KEY WORDS: Turbine Blades; Offshore Wind Turbines; FatigueAnalysis; Power Performance

INTRODUCTION
Floating offshore wind turbines (FOWTs), which are deployed in thenature ocean environment, are working under huge number of cyclic
external loads. A typical wind turbine, during its 20 years life time, may
experience more than 108 cycles loads with an approximately 30 rpm
rotation speed and 4000 hours operation time per year (Manwell, et al,2010). Capital expenditures for offshore wind developments are
typically one and a half to two times more than for onshore developments(Watson, et al., 2005), and maintenance costs are likely to be 5–10 times
higher than onshore (Van Bussel, & Zaaijer, 2001, March). Accurate
estimation of fatigue damage is critical important to offshore windindustry.
Fatigue damage of FOWTs is the process in which an accumulation ofdamages is caused by a repeating environmental load of variablemagnitude applied on their structures. Once sufficient damage isaccumulated, fatigue fracture will initiate and propagate through theplasticized regions. Fatigue damage calculations and fatigue life
predictions of offshore wind turbines are quite complicated.

This paper proposes a detailed methodology to evaluate the fatigue
damage of blades of FOWTs which include short-term numericalsimulation and long-term wind speed distribution. This paper also
represents the comparison of blade fatigue damage with the windconditions of both Gaussian and non-Gaussian wind turbulence model.
Short-term numerical simulations with different wind conditions are175