Optimal Design Of Multi-modal Acoustic Absorbers And Their Application In Noise Control Of Enclosures

In the ship noise control, the implementation of noise reduction strategies is limited due to the narrow space of cabins. Although the active noise control approaches have shown a great potential in reducing the low-frequency noise, its control performance is lack of robust. Most of absorption materials and damping materials can well tackle the mid- and high-freque nc y noise. However, they become impossible for low-frequency noise since the requirement of large thickness. A long T-shaped acoustic resonator(TAR) has been developed for dealing with the low-frequency noise economically and conveniently. A TAR consists of two perpendicular tubes, one is a shorter circular tube, having two open ends, and another is a longer rectangular tube, having two closed ends. TAR has a large aspect ratio, which makes it easy to be installed on the structure surfaces or directly embedded into structures to save the space; The longer the pipe of the TARs is, the lower the control frequency of the TARs, and the more acoustic energy can be absorbed.The location of TARs needs to be calculated by optimization algorithms because of its great influence on the control results. In previous studies, single-objective optimization was used to predict the location, respectively, and the interaction between different TARs is ignored. This may result in an error between the predicted and the measured results. A multi-object i ve optimization method should be used.In this paper, the optimal design of TARs for low-frequency noise control in enclosures was theoretically and experimentally investigated. The following topics are systematica l ly studied: 1) Modelling the acoustic interaction among an enclosure and acoustic absorbers; 2) Based on the single- or multi-objective optimization, using Genetic and Hill Climb ing algorithms to study the optimal location of TARs in single- or multi-modal control; 3) Based on the multi- modal characteristic of TARs, proposing an innovative design methodology of a TAR which has dual working frequencies. The experimental results show that the models, optimal algorithms, and design method in this paper are effective, and the optimally designed TARs can significantly reduce the noise level in low frequency range in an enclosure.