On the vibro-acoustical operational modal analysis of a helicopter cabin

• Published in: Mechanical systems and signal processing Vol. 23; no. 4; pp. 1205 - 1217
• Main Authors: Pierro, E., Mucchi, E., Soria, L., Vecchio, A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-05-2009; Elsevier
• Subjects: Acoustical measurements and instrumentation; Acoustics; EMA; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Helicopter; OMA; Physics; PU-probes; Structural acoustics and vibration; Vibro-acoustics; EMA; OMA; Helicopter; PU-probes; Vibro-acoustics; Microphone; Acoustic measurement; Modal analysis; Enclosure; Fluid structure interaction; Experimental study; Modeling; Transducer position; Position sensor; Position measurement; Pressure measurement; Sensor array; Mobile antenna; Structural acoustics; Power spectrum
• ISSN: 0888-3270; 1096-1216
• DOI: 10.1016/j.ymssp.2008.10.009

This paper aims to present a modal decomposition formulation for a vibro-acoustical operational modal analysis (OMA). In literature many works can be found on this topic, but until now no attention has been focused on the analytical form of the cross-power spectra (CPs) between the system outputs when a fluid–structure coupling is present. In this work it is shown that the CPs modal decomposition depends on the choice of the references, i.e. acoustical or structural. At first it is theoretically pointed out that the CP formulation for the acoustical and structural case is formally identical if appropriately pre-processed. Then, this theoretical result is verified through the results of an extensive experimental testing on the helicopter EUROCOPTER EC-135. The CPs between the structural output velocities and the acoustical response of the microphone inside the helicopter cabin are considered as inputs of an OMA. In order to verify the effectiveness of the modal model so obtained a classical modal analysis is also performed. The acoustical reference choice reveals to be suitable for a vibro-acoustical OMA. It is highlighted, indeed, that the acoustical pressure measurement inside the enclosure can be used as reference instead of the commonly used structural sensors, both from the theoretical and practical point of view. This is useful for high scale structures where the structural responses are usually measured by means of moving sensor arrays and additional fixed reference sensors should be positioned on the surface.