Performance of micro-perforated muffler with flexible back cavity for water filled pipelines

In order to reduce the low frequency noise of water filled pipelines, a micro-perforated muffler with composite structure flexible back cavity is proposed. The sound pressure and the displacement are expanded into three or two-dimensional Chebyshev series forms respectively. A numerical model, based on Hamilton’s principle of minimum potential energy and Rayley-Ritz method, is proposed for the accurate prediction of sound pressure and transmission loss. The results show that the noise attenuation bandwidth can be widened by selecting the proper length of internal intubation. In a certain range, the peak frequency of transmission loss moves to low frequency by increasing the perforation diameter and the thickness of the MPP or reducing the perforation rate. By reducing the laying angle or the number of layers of the flexible wall, the lower peak frequency and lowest muffling frequency of transmission loss can be obtained. The transmission loss has a sudden change at the axial mode frequency, which results in peaks and dips. Finally, the experimental research is carried out to verify the theory of this paper.