Hi Jason,
The reference is DS472, ‘Danish code of practise for loads and safety of wind turbine constructions’, july 1992 (in danish).
I enclose the relevant page in the annex.
When I wrote logd in percentage, it was just multiplying the real logd with 100, so:
zeta =0.02 to 0.03 equates to logd 0.125-0.188
or in percentage:
zeta =2-3% equates to logd = 12.5% to 18.8%.
DS472 suggests (see annex) 5%. I normally use 2% for glasfiber blades, 3% foor wood.
For the tower I normally use 1% in phatas and flex5. In these programs the damping is specified for the mode including RNA. For FAST I would then use 2% (see [url]Natural frequency and damping ratio calculation - #9 by Ruiliang.Wang]). Which then nicely corresponds to the value of DS472: 2%.
So in summary:
Blade: 12.5-18.8% (nrel), 5% (DS472)
Tower: 3.1-9.4% (nrel), 2% (DS472)
best regards,
Gerrit.
