Investigation of local vibration phenomena of a jacket sub-structure caused by coupling with other components of an offshore wind turbine

This paper presents results from an in-depth investigation of local vibration phenomena and their impact on the fatigue loads of a jacket sub-structure. The analysis is performed in a coupled, aero-hydro-servoelastic tool ADCoS-Offshore that is based on the finite element method (FEM). Possible regions of resonance are identified from modal analysis studies and a Campbell diagram. Numerous high frequency vibrations in the range of 3.1 Hz - 5.0 Hz involving local eigenmodes coupled with higher order rotor modes are found. Time domain simulations are run for deterministic and stochastic load case categories, where local jacket dynamics is examined. Impact of marine growth on fatigue loads of the lowest braces is presented. Finally, recommendation on relative comparison of local vibration influence on the fatigue loads is given.