Minimizing radiated sound power from vibrating shell structures: Theory and experiment

A new design methodology is presented here for finding optimal structural designs of shell structures for minimum sound power. Two optimization techniques are presented: the use of lumped masses and tuned absorbers.; Thin shell structures were targeted for noise reduction because of their ubiquity in industry. They are used to cover and protect noisy devices, such as gearboxes and electrical transformers, and also to keep dirt and other contaminants away from moving parts, as in the case of automotive valve covers.; The design strategy presented here involves three major computational tasks: predicting vibration of the structure, predicting the sound power created by the vibrating structure and finding optimal designs for minimum noise. A discrete Kirchhoff shell finite element is used to calculate vibration response, and a wave superposition boundary element method is used to calculate sound power. A combined gradient-based/stochastic optimization algorithm is used to find optimal lumped mass and absorber locations, as well as absorber design parameters (mass, stiffness and damping.); Three case studies are examined in this research: a flat plate, a half-cylindrical shell and a gearbox enclosure. Numerical and experimental results are presented for each study. It is shown that the optimization strategy presented here is capable of finding optimal designs which produce significant reductions in sound power in all three cases.