Modal shape identification of large structure exposed to wind excitation by operational modal analysis technique

• We achieve the dynamic characterisation of structure by Operational Modal Analysis.
• The Operational Modal Analysis was performed by Natural Excitation Technique.
• We achieve the characterisation of large structure by traditional modal analysis.
• The traditional modal analysis was performed by sine sweep phase resonance method.
• We compare successfully the results of experimental and operational modal analysis.

Research efforts during recent decades qualify Operational Modal Analysis (OMA) as an interesting tool that is able to identify the modal characteristic parameters of structures excited randomly by environmental loads, eliminating the problem of measuring the external exciting forces. In this paper, an existing OMA technique, the Natural Excitation Technique (NExT) was studied and implemented in order to achieve, from the wind force, the modal parameters of Vega Launcher, the new European launcher vehicle for small and medium satellites. Following a brief summary of the fundamental equations of the method, the modal parameters of Vega are calculated using the OMA technique; the results are then compared with those achieved using a traditional Experimental Modal Analysis under excitation induced by shakers.The comparison shows there is a very good agreement between the results obtained by the two different methods, OMA and the traditional experimental analysis, proving that OMA is a reliable tool to analyse the dynamic behaviour of large structures. Finally, this approach can be used for any type of large structure in civil and mechanical fields and the technique appears to be very promising for further applications.