Using the IEC Simple Load Model for Small Wind Turbines - Small Wind Turbines: Analysis, Design, and Application - page 179

Table 9.5 Force coefficients for Load Case H from IEC 61400-2

Shape Circle Octagon Square Non-lifting body

or aerofoil at 90

Lifting aerofoil

Characteristic
length \ 0.1 m

1.3 1.3 1.5 1.5 2.0

Characteristic
length [ 0.1 m

0.7 1.2 1.5 1.5 2.0

9.2.9 Load Case I: Parked Wind Loading, Maximum Exposure

This load case considers the possibility of a failure in the yaw mechanism, such as
a seizure of the main yaw bearing. This could cause the turbine to be exposed to a
maximum wind velocity in the turbine's most unfavourable position (i.e. maxi-
mum projected area). For this reason, the lift and drag on tail fins at high a was
considered in Chap. 8 . These load calculations, which must include all affected
components, use U ref . The force on each individual component is found using 29 :
F ¼ 1

2 C f q U ref A proj

ð 9 : 28 Þ

The projected area for aerofoil shapes will be their planform area (C f may result
from either lift or drag effects). C f is again found from Table 9.5 .

9.2.10 Load Case J: Transportation, Assembly, Maintenance
and Repair

All loading conditions on the turbine from conditions outside the range of normal
operation fall into this Case. It includes:

• Gravitational loads during transportation
• Loads caused by special tools
• Wind loads during installation
• Loads associated with hoisting the turbine into position
• Loads on a tilt up tower during erection
• And loads associated with the support structure from climbing it.

A calculation for the bending moment at the base of the tower due to lifting the
turbine into position is given as 30 :
M tower ¼ 2 m tower top þ m over hang 2

gL lt

ð 9 : 29 Þ

29

(IEC 45).

30

(IEC 46).