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Abstract

The attenuation effects of a number of sheathing materials on pipe flow noise are assessed by numerical simulations of the sound pressure field around pipe wall and the transfer mobility function of pipe wall vibration. The simulation model is established by using the finite element method (FEM) and the boundary element method (BEM), in which solid elements are used for the pipe wall and the sheathing material. Between pipe wall and sheathing material , contact elements are adopted. The frequency dependent loss factors of the sheathing material are determined by the experimental modal analysis (EMA) based on the half power method in the peak frequency bands and are expressed in terms of equivalent Rayleigh’s damping form. Also, the EMA has conducted to validate the simulation model of pipe flow induced sound level and pipe wall vibration. Six types of sheathing material, i.e., (1) rock wool (2) glass wool (3) PE (polyethylene) (4) PU (polyurethane) (5) PE + lead sheet (6) glass wool + aluminum, are considered to compare their effectiveness in attenuating pipe flow noise. Both the analysis and experiment results show that the sandwich damping materials can further reduce the radiated pipe flow noise by an amount of 12 ~ 15 dB than that using pure sound absorptive material for pipe sheathing.

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