Design optimization of a noise insulation panel to reduce the noise generated in a mechanical system

Abstract

Great attention in the noise insulation structure to reduce an unwanted sound generated in a mechanical system has been grown. The various mechanical systems excited by the motor/engine vibrate with the harmonic component corresponding to the frequency characteristics of the power source. As a result, the vibration of the mechanical system excite ambient air and sound radiation occurs. This radiated noise exacerbates the operating environment and causes the user’s anxiety. Also, vibration caused by the power source can lead to system failure. Thus, reducing noise/vibration from the mechanical system is closely dependent on consumer satisfaction and system stability. Methods for reducing noise generated by the mechanical system are divided into active control and passive control. However, in the case of active control, the cost of operation and maintenance is incurred because it also requires a relatively precise instrumentation system and additional power. Therefore, the design of a noise reduction system based on passive control was performed in this thesis. In this regards, structural designs were performed to reduce the noise generated by the mechanical system. Considering a computational efficiency, this thesis focuses on the design optimization to improve the noise insulation performance calculated from only structural analysis, not coupled with an acoustic domain. In Section 2, topometry optimization of cellular-type noise insulation panel was implemented to improve the sound transmission loss calculated by a structural finite element analysis. The finite element model was formulated to calculate a sound transmission loss between incident/transmitted acoustic pressures for noise insulation panel based on the Reissener-Mindlin plate theory. At the practical viewpoint, in Section 3, the design optimization of noise insulation performance calculated by structural analysis was applied to the industrial application. The target frequency band which shows the high radiated sound power was defined using the in-situ experiment. The finite element model to calculate the equivalent radiated power of the air conditioning system in the operating condition was developed. Also, a topography optimization to improve the equivalent radiated power was implemented and the optimization result was experimentally validated. In Section 4, the topography optimization of the washing machine cabinet was implemented to minimize the equivalent radiated power during a dehydration process. In order to reduce the computation time, a framework for efficient topography optimization was proposed using the model-order reduction based on Craig-Bampton method.