It has recently been demonstrated that layers of fibrous, "acoustical" material can effectively damp structural vibration in the sub-critical frequency range. In that frequency range, the acoustical near-field of a panel consists of oscillatory flow oriented primarily parallel with the panel surface. When a fibrous layer occupies that region, energy is dissipated by the viscous interaction of the near-field and the fibrous medium, and the result is a damping of the panel motion. Previously, the damping effect has been demonstrated to occur for line-driven, infinite panels and panels with isolated constraints. In this article, the focus is instead on periodically-constrained panels driven into motion by a convective pressure distribution. The constraints are allowed to have translational and rotational inertias and stiffnesses. This arrangement is intended to represent a very simple model of an aircraft fuselage structure. By considering the power flows in this system, it is possible to compute an equivalent loss factor, and then to identify the fibrous layer macroscopic parameters that result in optimal damping at a given mass per unit area. Finally, given that information, it is possible to identify the microstructural details, e.g., fiber size, that would be required to achieve that damping in practice.
Structural dynamics, Damping, Fibrous material, Periodic structures, Nearfield damping
Acoustics and Noise Control
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