Development And Application Of Simulative Software For Duct Acoustics

The simulative software,which is named as MAP(Muffler Acoustic Prediction)is developed for the rapid calculation and analysis of acoustic attenuation performance of duct muffling systems.Not a plenty of classic mufflers but many typical acoustic elements which are presented in this article are also contained in MAP.Based on the one dimensional plane wave theory,the transfer matrixes of the typical acoustic elements in different boundary conditions are presented.Then,the Graphic User Interface(GUI)of MAP is designed by the Visual Basic 6.0 platform and the computational code of MAP is written using FORTRAN.MAP has a friendly GUI for input of the geometrical and physical parameters to build and modify duct muffling systems expediently,then examine the effects of design changes on the acoustic attenuation characteristics quickly.Normally,the duct systems are composed of various basic duct and acoustic elements,for which the sound propagation characteristics may be expressed in terms of the transfer matrix.The relations among the acoustic elements are established by using the transfer matrix method,the transmission loss(TL)and insertion loss(IL)may be calculated for the given frequencies,and then the results are plotted in terms of curves.The developed software may reduce the R&D time of duct muffling systems significantly compared to the three-dimensional numerical methods,especially in the preliminary design phase.In order to validate the presented transfer matrixes and computational program,use MAP to calculate the transmission loss of all the acoustic elements,and then compare the transmission loss from MAP and FEM.The result shows that the 1-D analytical solution agrees reasonable well with the FEM predictions in the plane wave region,therefore illustrates the presented transfer matrixes and computational program are correct.MAP is then used to investigate the effects of parameters changes on the acoustic attenuation performance of the two-pass and three-pass perforated tube mufflers.For the two-pass tube muffler,the resonant frequencies in the middle range move to higher frequency as increasing the porosity of perforated tube,while the transmission loss is greater for the muffler with lower duct porosities.Increasing the length of the end cavities shifts the peaks in the transmission loss to lower frequencies.The perforated bulkheads have significant influence on the resonant frequency of the end-cavity and contribute it to be higher.The resonance frequency contributed by end cavity with perforated bulkhead shifts to higher frequency as increasing the porosity of perforate.For the three-pass tube reactive and hybrid muffler with perforated bulkheads,perforates on the bulkhead may change the resonant frequency of the three-pass perforated tube reactive muffler,and the resonance frequency is shifted to higher frequency as increasing the porosity of perforation.The sound-absorbing material filling in the middle chamber may improve the acoustic attenuation performance of the mufflers in middle to high frequencies,while the acoustic attenuation performance around the resonance frequencies is lowered somewhat,therefore a flatter acoustic response may be formed for the hybrid muffler than the reactive muffler.For the three-pass tube muffler with perforated inlet or(and)outlet tubes,acoustic attenuation behavior around the resonance frequency which is contributed by the end cavity with perforated tube is decreased and the acoustic attenuation improves in middle range frequencies.In the middle frequency range,the transmission loss decreases as increasing the perforated area of the perforated inlet tube,and increasing the perforated area of the perforated outlet tube leads to a higher resonance frequency.