文档介绍：1
INTEGRATED FATIGUE LOADING FOR WIND TURBINES IN WIND FARMS
BINING AMBIENT TURBULENCE AND WAKES
Sten Frandsen  ∗ and Morten L. Thøgersen
Risø National Laboratory
DK-4000 Roskilde
Denmark
e-mail: sten.******@ and morten.******@
ABSTRACT
A study is presented of an offshore application of a fatigue model for wind turbines operating partly in ambient
turbulence and partly wakes. In order limit the number of aeroelelastic calculations in design verification, it is
necessary to reduce the measured distribution of turbulence intensities into specific design turbulence. In this
study, the observation that the fatigue loading is proportional to the turbulence is used. Thus, turbulence is used
as primary design parameter, substantially describing the fatigue effects. The design turbulence is defined as the
turbulence that gives an equal amount of fatigue damage as bination of true distribution of ambient
turbulence and turbulence generated from wake effects. The single most important parameter responsible for the
increase in fatigue loading is very short distances between turbines.
KEYWORDS
Turbulence, fatigue analysis, wakes, offshore, added turbulence, ambient turbulence.
NOMENCLATURE
a Slope parameter for the turbulence standard deviation model
a Constant in model for added turbulence “over” wind farm
b Constant in model for added turbulence “over” wind farm
b Constant in expression for “effective” width of wake
CT Thrust coefficient of wind turbine rotor
2
ct Drag coefficient for wind farm, corresponding to drag-per-m
e Equivalent stress range [N/m2]
f’ Coriolis parameter multiplied by e4
f(*) Normal distribution
f0 Probability as function of wind direction
h Hub-height [m]
iaddwf(y) Added turbulence intensity as function of downstream distance to wind turbine row
I Turbulence intensity
I’ Spatially averaged turbulence in wind farm
I15 Characteristic value of hub-height turbulence intensity at a wind speed