| A method for minimizing the radiated sound power from a vibrating structure with acoustic enclosures is presented here. The vibrating structure, which is difficult to modify structurally and acoustically due to its high mechanical impedance, is targeted especially in the low frequency range where resonance peaks dominate the frequency response. The enclosure is close-fitting, equipment-mounted and has a low mechanical impedance compared to the vibrating structure. It is installed on the structure and is optimized to give a broadband minimal sound radiation by tuning the mounting spring stiffness.; Structural dynamic analysis is performed by using a reduced eigenvalue re-analysis algorithm which modifies the structure/enclosure system during the optimization process. Acoustic analysis is performed in two places, inside of the enclosure cavity and on the external enclosure surface. The coupling acoustic interaction between the structure and the enclosure is analyzed using component modal synthesis (CMS). A new, compact, symmetric coupled finite element system is analyzed using the fluid displacement potential. The external sound radiation analysis is performed using a pre-stored modal radiation resistance matrix derived from the wave superposition method. The whole system is integrated and optimized using a non-gradient and population-based differential evolution (DE) algorithm.; Acoustic enclosures were optimized for two different cases, a plate problem and a cylindrical shell problem. In the plate enclosure problem, the sound power radiated from the enclosure is reduced by 4 dB with 1 spring, by 10 dB with 5 springs, and by 13 dB with 15 springs. Spring location and stiffness are considered as design variables in the optimization routine. Finally, a 15 dB reduction was obtained with 17 springs obtained from reducing a 25 spring optimization result where spring location is predefined. A more complicated cylindrical shell problem is also tested. After the cylindrical enclosure is installed on a vibrating cylindrical shell and the location and stiffness of springs are optimized, the sound power was reduced by 4∼5 dB. Design sensitivities obtained from CMS are presented, which are critical in the design of structures. |
