MODELING AND DESIGN METHODOLOGIES FOR SOUND ABSORBING POROUS MATERIALS WHEN USED AS LAYERED VIBRATION DAMPERS
thesisposted on 17.10.2019, 20:07 by Yutong Xue
Modeling methodologies based on state-of-the-art and classic theories of acoustics have been developed to provide a comprehensive toolbox, which can be used to model multilayer systems that involve acoustical and/or damping treatments, and to optimize these treatments' performance by designing their geometrical structures. The objective of this work was to understand, predict and optimize conventional sound absorbing porous media's near-field damping performance, so that automotive and aerospace industries can take full advantage of layered porous treatments' lightness and multi-functionality: i.e., absorption of airborne sound and reduction of structure-borne vibration, for noise control applications. First, acoustical models that include the Transfer Matrix Method and the Arbitrary Coefficient Method were developed to build connections between the bulk properties and acoustical properties of porous media when coupled into layered systems. Given a specified layered system consisting of a vibrating panel and a porous damping treatment, the acoustics models were then incorporated into the Near-field Damping model to predict the acoustical near-field and spatial response of the panel, based on which the near-field damping performance can be evaluated for a limp or an elastic porous layer when applied on different structures including an infinitely-extended panel, a partially-constrained panel, an aircraft fuselage-like structure and a vehicle floor pan-like structure. Furthermore, the relations between the material's microstructural details and bulk properties were established via an Air-Flow Resistivity model for porous media that are made of fibers, and the optimal fiber size that provides the largest damping for certain vibrating structures was identified. Relatively large fibers were found to be better at reducing lower frequency vibrations; fibers made of polymer were found to have manufacturing benefits over fibers made of glass to achieve equivalent optimal damping performance; and elastic fibers were found to have both manufacturing and damping advantages over limp fibers.