Figure 10 Normalized PSD of edgewise blade vibration for measurement 1 Blade 2. Figure 11 Normalized PSD of flapwise blade vibration for measurement 3 Blade 3. As can be seen from Figure 11, flapwise vibration data enables more frequencies to be identified. The integer multiples of rotation frequency up to 4P can be detected from the corresponding PSD graph. The contribution of these P components in the overall motion is consistent with those reported by several researchers (35). Besides these P components, first flapwise mode can also be seen in Figure 11. Since the response is mainly dominated by the 272
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