ACTIVE ISOLATION OF MULTIPLE STRUCTURAL WAVES ON A HELICOPTER GEARBOX SUPPORT STRUT

✍ Scribed by T.J. Sutton; S.J. Elliott; M.J. Brennan; K.H. Heron; D.A.C. Jessop

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 308 KB
• Volume: 205
• Category: Article
• ISSN: 0022-460X
• DOI: 10.1006/jsvi.1997.0972

✦ Synopsis

A helicopter gearbox support strut has been set up in the laboratory under realistic loading conditions to investigate the active control of longitudinal and lateral vibration transmission to a connected receiving structure. Three magnetostrictive actuators were clamped to the strut to introduce secondary vibration in the frequency range 250-1250 Hz, the control objective being to minimize the kinetic energy of vibration of the receiving structure. Using an extensive set of frequency response measurements, it was possible to predict on a linear basis the attenuation in the kinetic energy of the receiving structure at any discrete frequency in the measurement range for a wide range of conditions. Calculations based on frequency response measurements showed that with the installed steel bearings on the strut, attenuations in the kinetic energy of the receiving structure of 30-40 dB were possible over a range of frequencies between 250 and 1250 Hz. At some frequencies in this range, notably around 500 Hz and 800 Hz, the control was less effective. This was due to torsional motion of the strut which was amplified by the secondary actuators. Good control was also predicted when the primary excitation to the strut was applied laterally rather than longitudinally.

Real-time active control has been implemented at discrete frequencies on the test strut and has generally confirmed the linear predictions. Attenuations in excess of 40 dB were measured in a number of cases. The tests confirmed that the active control of vibration transmission through a helicopter strut is practical at frequencies up to at least 1250 Hz.