Vibration Based Damage Detection for Structures of Offshore Wind Energy Plants

The offshore wind industry has been growing significantly in the last years. Consequently, a need of structural health monitoring (SHM) methodologies arises to monitor the expensive structures of offshore wind plants (OWEP) which are often difficult to access. Using the vibration of the plants to extract damage sensitive features is often accompanied by problems due to variations of the dynamical properties with the changing environmental and operational conditions (EOC). So it could happen that the EOCs have the same effect on the features variation as a damage. In order to design adequate SHM algorithms for OWEP monitoring, the paper starts with a discussion of the basic characteristics of excitation sources, vibration and environmental conditions of OWEPs. Subsequently, the theoretical backgrounds of the null space-based damage detection algorithm (NSFD) and one approach for compensation of EOC effects by means of fuzzy-classification techniques are presented. Finally the theory and the algorithms are successfully tested with time series from the OWEP M5000 and with data from a OWEP laboratory model.