Environmental Engineering Reference
In-Depth Information
4.9.1
Fatigue-inducing actions on wind turbine support structures
4.9.1.1 Actions due to wind and turbine operation
Numerical simulations are performed in order to determine the extreme and operating
loads relevant for awind turbine structure. The representative environmental relationships
used in these calculations are based onDIN1055-4 and are regulated in theDIBt guideline
[9] or DIN EN 61400-1 [16] and DIN EN 61400-3 [10] (see Section 2.3). Besides the
steady inflow of the wind, the aerodynamic model also has to take into account the
turbulence and gust characteristics of the wind plus sudden changes in the wind direction,
and so on. The dynamic response behaviour of the total system - consisting of wind
turbine, tower and foundation - to the resultant loading plus the influences imposed by the
control and regulation of thewind turbine, for example rotor r.p.m., generator r.p.m., blade
pitch angle, also have to be included in the calculations [67], see also [68,69].
The numerical simulation does not cover the entire design working life of a wind
turbine because that would require an excessive amount of calculation. Instead,
individual periods are considered which, for example, include the design load cases
given in Table 4.1 or 4.4. Those design load cases include normal turbine operation,
gusts, oblique angle of attack, starting and stopping procedures, grid loss, plus
combinations of these (see Section 2.3.2). The design load cases specified depending
on the operating conditions are divided into groups N (normal and extreme), A
(accidental), F (fatigue) und T (transport/erection) (see Sections 4.5.3 and 4.6.4).
The loading time series thus obtained are combined using statistical methods and
taking into account the probability of occurrence of the individual events.
A time series for the design working life required can therefore be compiled for every
internal force component. In doing so, the time series must be determined for all the
design cross-sections of the support structure [70]. Figure 4.25 shows the course of a
numerical load simulation.
Fig. 4.25 Schematic presentation of a load simulation (after [70])
 
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