Active periodic struts for a gearbox support system

Abstract

Active periodic structures exhibit unique dynamic characteristics that make them act as tunable mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called the ‘pass bands’ and wave propagation is completely blocked within other frequency bands called the ‘stop bands’. The spectral width of these bands can be tuned according to the nature of the external excitation. In this paper, the emphasis is placed on developing a new class of these periodic structures called active periodic struts (APS) which can be used to support gearbox systems on the airframes of helicopters. When designed properly the APS can stop the propagation of vibration from the gearbox to the airframe within critical frequency bands and consequently minimize the effects of transmission of undesirable vibration and sound radiation to the helicopter cabin. The theory governing the operation of this class of APS is presented and their tunable filtering characteristics are demonstrated experimentally as a function of their design parameters. The presented concept of the APS can be easily employed in many applications to control the wave propagation and the force transmission in an attempt to stop/confine the propagation of undesirable disturbances.

Analysis of Longitudinal Waves in Rod-Type Piezoelectric Phononic Crystals

“…The proposed MTMM combines the Love rod theory [27,28], [29] (pp. 139-142), [30], the method of reverberation-ray matrix (MRRM) [5] and the transfer matrix method (TMM) [14][15][16][17][18][19]21,22,25] to analyze the dispersion curves by considering the Floquet-Bloch theorem [31,32] and to calculate the transmission spectra. The Love rod theory is adopted to model the longitudinal wave motions in the piezoelectric, elastic and electrode constituent rods of the unit cell.…”

“…After Baz [9] proposed the seminal concept about active control of periodic structures, Singh et al [14] illustrated the effectiveness of the periodic rod with piezoelectric actuators by analyzing the frequency bands and responses with the TMM. Asiri et al [15] and Asiri [16,17] predicted the attenuation of longitudinal waves in periodic binary piezoelectric-elastic composite rods using the combination of spectral element method and TMM, and validated their analysis by experiment. Using the same TMM, Li et al [18] and Wang et al [19] analyzed the localization of frequency bands in randomly disordered periodic binary piezoelectric-elastic rods without and with initial stress, respectively.…”

“…Therefore, rod-type phononic crystals containing smart material components have been presented in order to control the longitudinal waves in an active mode. Their frequency bands can be adjusted by tuning the temperature [6,7], magnetic [8] or electric [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] field to suit the external excitations.…”

“…Among these smart periodic rods, the periodic piezoelectric rods [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] have particularly been paid more attention, because the piezoelectric materials are widely used and the electric field is comparatively easier to control. Thus far, two kinds of rod-type piezoelectric phononic crystals have been presented to actively control longitudinal-wave bands via electromechanical coupling.…”

“…The influence of the elastic rod inserts on the band structures is not clear enough. (3) Two electrical control manners in general have been proposed, i.e., setting the external voltage through the feedback control gain [14][15][16][17] and tuning the external electric capacity [18][19][20][21][22][23][24][25][26], since the electric-open and electric-short conditions correspond to zero and infinity electric capacities, respectively. The connection and difference of the influences of the applied feedback control and of the applied electric capacity on the frequency bands are not known.…”