Tower design and analysis - Wind Power Generation and Wind Turbine Design - page 552

0.5

MDOF with TLCD
MDOF without TLCD

0.4

0.3

0.2

0.1

0

-0.1

-0.2

0 5 10 15 20 25 30 35 40 45 50

Time (s)

Figure 17: Time-history response of a rotating offshore turbine under wind and
'moderate' wave excitation with and without TLCD.

TLD or tuned liquid column damper (TLCD) can be useful to suppress undesirable
structural vibrations. The use of a TLCD for the vibration control of offshore
towers has been investigated by Colwell and Basu [65]. The simple model in the
previous section was used to analyse the dynamic response of the system under
joint wind and wave loading. The assumed wind velocity at a height of 10 m was
18 m/s. The blades were 60 m in length and individually weighed 9.5 tonnes.
The blades rotated at a frequency equal to the fundamental natural frequency
of the MDOF system. The system was subjected to joint wind and wave loading
with the wind turbulence simulated from Kaimal spectra and the wave excitation
simulated from JONSWAP spectra. The details on the damper parameters are avail-
able in [65]. Figure 17 compares the total displacement response at the top of the
tower with and without the TLCD. It has been concluded that the passive damper
has a signifi cant benefi cial impact in suppressing the structural vibrations by about
60%. The maximum design bending moment for the theoretical simulation at the
base of the structure is reduced from 6.2607

10 4 to 4.0101 10 4 kNm. × ×

7 Conclusions

Several aspects of dynamic analysis and design of wind turbine towers have been
discussed in this chapter. With the increase in rotor diameter and the height of the
towers, the analysis of wind turbine towers becomes crucial and needs special
attention particularly in the view of tower-rotor coupling. The important physi-
cal behaviour and phenomena to be accounted for are centrifugal stiffening of
blades, gravity effects, rotationally sampled turbulence and the tower-blade cou-
pled dynamic interaction. Numerical results have indicated that responses of the