Acoustical treatment of multi-tone broadband noise with hybrid side-branched mufflers using a simulated annealing method

Abstract

Presently, there existed in industrial plants broadband noise hybridized with pure tones. In order to overcome a pure tone noise with a high peak value that is harmful to human hearing, a traditional reactive muffler has been used. However, the traditional method for designing a reactive muffler has proven to be time-consuming and insufficient. Helmholtz mufflers that deal with a pure tone have been adequately researched. However, manufacturing costs for the Helmholtz resonator have been too expensive. Noise elimination of pure tones for side-branched resonators (SBRs) that are easily manufactured has also been addressed. Nevertheless, the shape optimization of multi-chamber side-branched mufflers that deal with a broadband noise hybridized with multiple tones has been mostly ignored. In order to efficiently reduce the peak noise level, interest in shape optimization of a side-branched muffler is coming to the forefront. That being so, an analysis of the sound transmission loss (STL) and the best optimized design for a hybrid side-branched muffler under a space-constrained situation will be considered, here.Concerning the plane wave effect, the theoretical acoustic performance of a multi-tone hybrid side-branched muffler will be established using a four-pole system matrix. A numerical case for eliminating broadband noise hybridized with two tones emitted from a machine room using eight kinds of mufflers (muffler B-I) will also be introduced. To find the best acoustical performance of a space-constrained muffler, a numerical assessment using a simulated annealing (SA) method is adopted. To verify the availability of the SA optimization, a numerical optimization of muffler A at a pure tone (600 Hz) is exemplified. Before the SA operation can be carried out, the accuracy of the mathematical model has been checked using the experimental data. Moreover, the influences of the sound transmission loss (STL) with respect to n-series SBRs and the STL with respect to m-parallel SBRs have also been assessed. Also, the influence of the STL with respect to the design parameters such as the section area (Sb) of the SBR, the height (ZH) of the SBR, and the section area (S) of the main duct has been analyzed. Results reveal that the peak values of the pure tones are efficiently reduced after the hybrid side-branched muffler is added. Moreover, the acoustical performance of the hybrid side-branched muffler will increase when the number (m) of the parallel SBRs increases.Consequently, a successful approach in eliminating a broadband noise hybridized with two pure tones using optimally shaped hybrid mufflers and a simulated annealing method within a constrained space has been demonstrated.