sin αst

A
Basis for calculations
Wind turbines are subjected to environmental conditions that effect their loading, durabil-
ity and operation. To ensure an appropriate level of safety and reliability these conditions
are explicitly defined in this appendix and taken into account in the design.
The environmental conditions are divided into wind conditions and other environmental
conditions. Section A.1 contains the wind conditions that are the primary external consid-
erations for structural integrity and aerodynamic performance. Section A.2 defines other
relevant environmental data, such as air density and temperatures.
Load cases, which form the basis for structural calculations in accordance with IEC 61400-
2, are established in section A.3. Reference is made to the nomenclature in chapter 14 that
defines the symbols, subscripts, abbreviated terms and graphical representations used in
the present appendix.
A.1 Wind conditions
The environmental conditions that are to be considered during design of a wind turbine
depend on the specific site of installation. The wind turbine designed in this project thesis
is however intended to be used in a variety of different sites around the world. Therefore a
typical design site, which represents the characteristic values of many different sites, has
been established with input from EWB and their collaborative partners. The site character-
istics cause the wind turbine to be classified a class IV in accordance with the standard
SWT classes of IEC 61400-2 [5, p. 45]. This class defines basic external conditions in terms
of wind speeds at hub height, as indicated in table A.1.
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