Microwave Structural Health Monitoring of the Grouted Connection of a Monopile-Based Offshore Wind Turbine: Fatigue Testing Using a Scaled Laboratory Demonstrator

Table 4

Evaluation of the modal analysis of damage mode.

Date	Associated load level	Frequency (Hz)	Diff. to previous (Hz)	Damping (%)	Diff. to previous (%)
October 31	Reference	260.41	—	0.5	—
November 03	Initial commissioning 10%	258.46	−1.95	0.52	0.02
November 16 08:36 UTC	5 hours 10%	254.43	−4.03	1.02	0.5
November 18 07:36 UTC	5 hours 20%	251.72	−2.71	1.37	0.35
November 22 07:36 UTC	5 hours 40%	247.59	−4.13	2.93	1.56