Advances in Sandwich Structural Optimization for Noise Transmission Reduction

The sandwich structures in aerospace industry experience high noise transmissions since they are often stiff and light, and have low damping. Optimization studies of sandwich structures for noise transmission are relatively fewer. Most optimization studies in composite sandwich community seek for high stiffness with minimal weight. Advanced sandwiches must meet not only stiffness to weight ratio demands, but also have improved acoustic transmission performance. This paper presents recent advances in optimization of sandwich structures for minimum sound transmission. The finite element models of sandwich beams and plates are presented in this paper. The acoustic radiation of the structure is computed by using the Rayleigh integral. Sensitivity plays an important role in optimization studies. Analytical expressions of sensitivity can improve computational efficiency dramatically and accuracy at the same time. The explicit sensitivity functions of power and natural frequencies with respect to design parameters are derived in this work. In the optimization studies, we have considered structural parameters that can influence the transverse propagation of sound from the sandwich to the acoustic medium. These parameters include core topology and coupling stiffiness between in- and out-of-plane strains. We also study the optimization of the structure with respect to the structural boundary conditions to minimize the sound transmission. Numerical examples of single tone and broadband applications are presented in the paper. The results show that significant reduction of sound transmission across sandwich structures can be obtained. Finally, it should be noted that the novel optimized sandwich structures can meet not only stiffness to weight ratio demands, but also have significantly improved acoustic performance.