Asymmetric sway panel design for noise reduction by modal radiation efficiency tuning approach

Abstract

Built-up panels are widely employed for noise reduction, with their effectiveness primarily dependent on transverse vibrations, as corroborated by numerous studies. Transverse vibrations occur perpendicular to the panel's surface and are known for their substantial sound radiation. This study introduces a novel technique for tuning modal radiation efficiency, designed to diminish sound radiation from a sway panel comprised of two vertical and one horizontal segment. Notably, when the primary vibration direction of a panel is parallel to its surface (i.e., sway vibration), both the level of transverse vibrations and the corresponding sound radiation efficiency are significantly reduced. A theoretical model was developed to investigate the interplay between transverse and longitudinal vibrations across adjacent components, shedding light on the sound radiation reduction mechanism. The sway structure exhibited a 43.5 % reduction in maximum transverse displacement compared to a simply supported beam, while the maximum longitudinal displacement was adjusted to align with the transverse displacement levels. Moreover, sway modes, in comparison to simply supported beams, demonstrate reduced radiation efficiency due to their dipole-like sound radiation patterns. Consequently, the maximum sound pressure level of the sway structure was lowered by 7 dB compared to that of the simply supported beam. This model also enables the creation of two sway modes with closely spaced frequencies through precise modifications of lengths and thicknesses, highlighting the significance of asymmetric geometry. Furthermore, comparisons of the proposed model with finite element methods and experimental results confirm a strong concordance, validating the effectiveness of the sway structure in achieving reduced sound radiation.