Finite Element Modelling and In Situ Modal Testing of an Offshore Wind Turbine

• Published in: Journal of Vibration Engineering & Technologies Vol. 6; no. 2; pp. 101 - 106
• Main Authors: Asnaashari, Erfan, Morris, Andy, Andrew, Ian, Hahn, Wolfgang, Sinha, Jyoti K.
• Format: Journal Article
• Language: English
• Published: Singapore Springer Singapore 01.04.2018
• Subjects: Acoustics; Control; Dynamical Systems; Engineering; Engineering Acoustics; Original Paper; Vibration; Structural dynamics; Finite element modelling; Offshore wind turbines; In situ modal testing
• ISSN: 2523-3920; 2523-3939
• DOI: 10.1007/s42417-018-0018-3

Purpose Generating electricity from wind turbines is currently a viable option to meet the electric power requirements in many countries. The structure of offshore wind turbines is constantly subjected to external dynamic loads due to wind, waves and rotor loads due to the rotation of blades. The frequency content of these dynamic loads is in the range of natural frequencies of the wind turbine. Therefore, determining the in situ dynamic characteristics of a wind turbine is very beneficial, as it can lead to further improvements in its design, performance and safety. Methods In this paper, the dynamics of the structure of an offshore wind turbine is investigated numerically and experimentally. The finite element (FE) model of structural components is developed based on design specifications. The model takes the effect of rotor–nacelle assembly into account by considering its mass and moment of inertias relative to the top centre of the tower. In situ modal tests using impulse excitations were carried out on the actual wind turbine when the rotor blades were not rotating to identify the modal parameters. Results This paper presents predicted natural frequencies from the FE model based on design conditions and those identified from the modal and ambient excitation tests. Conclusion It was observed that the first two bending modes are close to the natural frequencies identified experimentally by the in situ modal tests. It was also observed that the in situ modal tests were not able to excite other higher natural frequencies of the structure.