Real time monitoring of structures is currently one of the leading research topics. The modal analysis of a structure subjected to operational conditions is called Operational Modal Analysis (OMA). This paper deals with the real time measurement on a 65 m high wind turbine located in Dortmund, Germany. The structural acceleration responses are recorded at five different elevations along the tower shaft. As one part of the project, a numerical wind turbine model has been created in ANSYS using an assembly of beam elements.
To validate the numerically determined modal characteristics, ambient response analysis has been undertaken. Modal parameters of significant modes are compared as results from three different analyses. In these analyses, the free vibration modal analysis and the transient analysis are carried out in ANSYS itself. The output only modal analysis is carried out using commercial software called ARTeMIS for both simulated and measured responses. To compare the mode shapes, Modal Assurance Criterion (MAC) analyses are conducted. The modal frequencies and mode shapes of the first six bending modes in X-Z and Y-Z planes from measured data match with the numerical results to within less than 10 % deviation. Thus, the results from in-situ-measured data validate the ones from the numerical model in the low frequency range. The high frequency modes could not be clearly recognized from the measured data. Potential future modifications in field measurements by introducing more measurement points in an organized way, however, will lead to higher order modes becoming recognizable.