Optimization of Noise Transmission Loss of Damped Sandwich Structures

A numerical formulation to optimize the noise transmission loss (TL) of a damped sandwich structure is presented. It consists on considering the mass as an objective function to minimize, the TL as a constraint function and the thicknesses, the densities of each layer and the mechanical properties of the core as de sign variables. Unlike several methods developed since the sixties, the TL is calculated numerically using a finite element formulation for the sandwich plate coupled to a boundary element method for the acoustic medium. This has an advantage to have precisely the value of TL at each frequency and make it possible to consider a frequency dependent loss factor and shear modulus of the core. The considered sandwich structure makes it possible to obtain an interesting damping thanks to the properties of the viscoelastic material, while keeping a reasonable thickness and weight. The main result of this optimization study shows that one can get a law of the viscoelastic material behavior which increases the TL and thus improve the soundproofing of sandwich structures.