Abstract: To address the resonance problem induced by the coupling between the structural modes of the tri-blade propeller quadrotor UAV and excitations at the propeller frequency (43-55 Hz) and its third harmonic (129-165 Hz), a resonance suppression method based on laminate parameter optimization is proposed. First, modal analysis was conducted to identify the roll mode of the entire UAV within the propeller frequency band and the bending-torsion mode of the middle frame within the third harmonic band, clarifying the resonance risk under multi-mode coupling. Subsequently, a sensitivity analysis of laminate parameters was performed to reveal that a higher proportion of 0° plies at the neutral surface results in a more significant enhancement of structural stiffness, and that the laminate parameters of the arms exert a coupled influence on multiple modes of different orders of the UAV. Therefore, with the constraints that the target modes (roll mode of the entire UAV and middle frame mode) are shifted out of the operating frequency band and no new resonance is induced in non-target modes, an optimization scheme was screened out, which adopts 45° plies at the neutral surface of the arms and reinforced 0° plies for the middle frame. Verification results from frequency response curves show that after optimization, the roll mode of the entire UAV is shifted to 59 Hz and the high-frequency mode of the middle frame is shifted to 188 Hz, both of which are moved away from the bandwidths of the propeller frequency and its third harmonic. In addition, the multi-directional frequency response curves at each measuring point exhibit no significant resonance peaks within the operating frequency band, no abrupt phase change of -90°, and the peak acceleration response of the arms is reduced by 20%, indicating that the resonance risk of the structure is effectively suppressed.

Key words: carbon fiber reinforced polymer composites, optimization of composite laminate lay-up, unmanned aerial vehicle, resonance suppression