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

To reduce lowfrequency noise of the water filled pipeline system,a compact Flexible Micro-Perforated Muffler with Flexible Back Cavity(FMPMFBC) is proposed The flexible pipe wall is made up of rubber-cord composite material.Numerical solution for the transmission loss is derived.Firstly,the Flexible Micro-Perforated Panel(FMPP) is equivalent to a flexible porous material based on Biot-Allard porous-elastic theory.Then,a periodic structural unit of the aramid fabric cloth is established with two-scale method,and the equivalent stiffness matrix is obtained.Using the lamination theory,a multi-layer composite model for the flexible pipe wall is established.Coupling with internal sound field,the transmission loss of the FMPMFBC is calculated.On a water filled impedance tube the transmission loss curves of the FMPMFBC prototypes are measured with the two source-location method,and compared with those of flexible micro-perforated muffler with rigid back cavity and expansion muffler.Theoretical results are experimentally verified.The FMPMFBC,with broadband low-frequency noise attenuation characteristics,is a hybrid muffler combined reflection with dissipation.The transmission loss of prototype B2 in the frequency bands of 40-300 Hz and 40-1200 Hz are 36 dB and 30 dB,respectively.While the transmission loss of the same size expansion muffler in the corresponding frequency band are 7 dB and 11 dB respectively