Final report for WP4.3: Enhancement of design methods ... - Upwind

UPWIND WP4: Offshore Support Structures and Foundations
The third test case considered a complete wind turbine structure consisting of a three blade rotor supported by
a tubular steel tower. Again, the lowest mode shapes were calculated and compared with respect to frequency
and shape. Full results are given in [98], and indicate an excellent agreement between the modes calculated by
ANSYS and Bladed v4.0.
1
DISPLACEMENT
STEP=1
SUB =3
FREQ=.377211
DMX =.003682
Y
Z
X
SEP 3 2010
16:09:59
Figure 7.1: Mode shape 2 of the complete wind turbine
structure calculated by ANSYS (above) and Bladed v4.0
(below)
86
1
DISPLACEMENT
STEP=1
SUB =15
FREQ=4.146
DMX =.044085
Z
X Y
SEP 3 2010
15:54:37
Figure 7.2: Mode shape 14 of the complete wind turbine
structure calculated by Ansys (above) and Bladed v4.0
(below).
In the third level of testing a code-to-code comparison was performed using test cases from phase I of the OC3
project [15], modelling a 5MW offshore turbine mounted on a monopile support structure. Figure 7.3 presents
the natural frequencies of the complete system calculated by GH Bladed Multibody, together with the average
over all the participant codes. The error bars show the standard deviation in frequency between the different
codes. Two series are shown for the natural frequencies because the results differ substantially depending on
whether the yaw degree of freedom of the support structure has been included in the calculation, especially for
the 2 nd blade asymmetric flapwise yaw mode. Good agreement is seen for the both cases, with or without the
tower torsion mode included. Figure 7.4 presents time histories of the tower base bending moment due to wave
loads. Differences in higher frequency may be due to differences in damping of transient structural vibrations.
Overall the results for the complete wind turbine show good agreement with other simulation codes, which include
modal, multibody and finite element structural models.