A new finite/infinite scheme to model acoustic trim under realistic working conditions

Abstract

The paper presents a finite-element scheme modeling all aspects of the behavior of acoustic trim: insulation, absorption, and damping. The models can combine different materials (viscoelastic, poroelastic, incompressible), acoustic fluid, and include complex effects like visco-thermal dissipation in thin air layers. Unbounded acoustic regions are modeled using stabilized conjugated infinite elements that present exceptional convergence properties. The structure can be subjected to a number of different excitations: kinematical (fixed motion), dynamical (discrete or distributed forces) or acoustical. An incident diffuse sound field or distributed pressure fluctuations corresponding to aerodynamic boundary layers can also excite the structure. The presentation will be organized as follows: (1) a brief review of the techniques involved: finite-element method for the structure and the acoustic near field, infinite elements for the acoustic far field; (2) material models considered: viscoelastic, poroelastic, incompressible, acoustic (including viscothermal effects); (3) excitation models: kinematical, dynamical, acoustical, aerodynamic; (4) validation of the approach; (5) three application cases: comparison of the dynamic behavior of a treated and untreated shell, acoustic transparency of an insulating sandwich, evaluation of the acoustic impedance of a porous layer.