Full-Field Strain Prediction Applied to an Offshore Wind Turbine
Fatigue life is a design driver for the foundations of offshore wind turbines (OWT’s). A full-scope structural health monitoring strategy for OWT’s needs to consider the continuous monitoring of the consumption of fatigue life as an essential part. To do so, the actual stress distribution along the entire length of the structure and predominantly at the fatigue hotspots needs to be known. However installation of strain sensors at these hotspots is not always feasible since these hotspots are mainly situated beneath the water level (e.g., mudline). In practice this implies the installation of strain gauges on the monopile prior to pile driving and difficulty in maintaining these submerged sensors throughout the operational life of the turbine. Therefore, an effective and robust implemented technique using the more reliable accelerometers and very limited strain sensors at few easily accessible locations integrated within a new analytical structural dynamic approach is preferred. In this paper, a novel multi-band implementation of the well-known modal expansion approach, a.k.a. full-field strain prediction, is introduced. This technique utilizes the limited set of response data derived during a monitoring campaign and a calibrated Finite Element Model (FEM) to reconstruct the full field response of the structure. The obtained virtual responses are compared with measurements from an ongoing measurement campaign on an offshore wind turbine.
KeywordsModal expansion Full-field strain prediction Offshore wind turbines Fatigue assessment Structural health monitoring
This research has been performed in the framework of the Offshore Wind Infrastructure Project (http://www.owi-lab.be) and the O&O Parkwind project. The authors also acknowledge the financial support by the Agency for innovation by Science and Technology (IWT). The authors gratefully thank the people of Parkwind and Belwind and the colleagues in OWI-lab for their continuous support within this project.
- 5.Maes, K., Smyth, A., De Roeck, G., Lombaert, G.: Joint input-state estimation in structural dynamics. J. Mech. Syst. Signal Process. 70–71, 445–466 (2016)Google Scholar
- 6.Maes, K., De Roeck, G., Lombaert, G., Iliopoulos, A., Van Hemelrijck, D., Devriendt, C., Guillaume, P.: Continuous strain prediction for fatigue assessment of an offshore wind turbine using Kalman filtering techniques. In: Proceedings of the Environmental, Energy and Structural Monitoring Systems (EESMS), IEEE Workshop, pp. 44–49. Trento, 9–10 July 2015. doi: 10.1109/EESMS.2015.7175850
- 8.Baqersad, J., Poozesh, P., Niezrecki, C., Avitabile, P.: Predicting full-field strain on a wind turbine for arbitrary excitation using displacements of optical targets measured with photogrammetry. In: Proceedings of the IMAC 33 Conference on Structural Dynamics, Orlando, FL (2015)Google Scholar
- 11.Iliopoulos, A., Shirzadeh, R., Weijtjens, W., Guillaume, P., Van Hemelrijck, D., Devriendt, C.: A modal decomposition and expansion approach for prediction of dynamic responses on a monopile offshore wind turbine using a limited number of vibration sensors. J. Mech. Syst. Signal Process. 68, 84–104 (2016). doi: 10.1016/j.ymssp.2015.07.016
- 12.Maes, K., Iliopoulos, A., Weijtjens, W., Devriendt, C., Lombaert, G.: Dynamic strain estimation for fatigue assessment of an offshore monopile wind turbine using filtering and modal expansion algorithms. J. Mech. Syst. Signal Process. Available online 15 February 2016, ISSN 0888-3270, doi:http://dx.doi.org/10.1016/j.ymssp.2016.01.004
- 13.Weijtjens, W., Iliopoulos, A., Helsen, J., Devriendt, C.: Monitoring the consumed fatigue life of wind turbines on monopile foundations. In: Proceedings of the EWEA Offshore, Copenhagen (2015)Google Scholar
- 14.Weijtjens, W., Shirzadeh, R., De Sitter, G., Devriendt, C.: Classifying resonant frequencies and damping values of an offshore wind turbine on a monopile foundation. In: Proceedings of the EWEA, Barcelona (2014)Google Scholar
- 15.Heylen, W., Lammens, S., Sas, P.: Modal Analysis: Theory and Testing. Katholieke Universiteit Leuven, Leuven (1997)Google Scholar
- 16.Maia, N., Silva, J., He, J., Lieven, N., Lin, R-M., Skingle, G., To, W., Urgueira, A.: Theoretical and Experimental Modal Analysis. Research Studies Press Ltd, Somerset (1997)Google Scholar
- 17.Ewins, D.: Modal Testing 2, Theory, Practice and Application, 2nd edn. Research Studies Press Ltd, Baldock (2000)Google Scholar
- 18.Iliopoulos, A., Weijtjens, W., Van Hemelrijck, D., Devriendt, C.: Long-term prediction of dynamic responses on an offshore wind turbine using a virtual sensor approach. In: Proceedings of the 10th International Workshop on Structural Health Monitoring 2015: System Reliability for Verification and Implementation, pp. 2793–2800. Stanford, CA, 1–3 September 2015Google Scholar