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The yawing system in a wind turbine keeps the nacelle facing the incoming wind direction to obtain a better efficiency while it also induces the vibration and fatigue load to the structure. In this paper, the yawing system was discussed and an upgrade plan been provided to a real 2 MW wind turbine. The result has shown the significant improvement on the load output after the update.

The sandwich composites in this study are laminated structures with two outer thin glass fiber reinforced panels and one or more thick lightweight foam panels as the core material. Such sandwich composites are often used in wind turbine blade. The Impact-Echo method using a microphone as a receiver was used to test the sandwich composite panel specimens. The signals were analysed in the frequency domain and normalized by the Rayleigh wave amplitude. Preliminary results show that thicker plates generally have a lower maximum peak frequency (MPF) for specimens without defects, but MPFs are more unstable due to the higher number of layers of the inner foam plate. Internal defects generated by excavating the core material, with lateral dimensions as small as 20 mm, can be identified from lower MPF and higher maximum peak amplitude in the normalized amplitude spectrum.

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