A New Identification Method for Bolt Looseness in Wind Turbine Towers

Table 4

Natural frequencies of the wind turbine towers.

Tower ID	Test results before tightening (Hz)				Test results after tightening (Hz)
	Working condition 1	Working condition 2	Working condition 3	Working condition 4	Working condition 5	Working condition 6
1	0.391	0.391	0.391	0.391	0.391	0.391
2	0.391	0.391	0.391	0.391	0.391	0.391
3	0.322	0.322	0.322	0.322	0.322	0.322
4	0.322	0.322	0.322	0.322	0.322	0.322
5	0.322	0.322	0.322	0.322	0.322	0.322
6	0.322	0.322	0.322	0.322	0.322	0.322