expected the two results are almost identical. This match again validates the correctness of the proposed VS algorithm and its implementation (as a MATLAB Program) in such a complex situation of a multiply-connected muffler. As both the approaches are based on one-dimensional analysis, their correctness has to be checked against some threedimensional analysis. Three-dimensional finite element (FE) analysis has been performed on the current muffler structure using SYSNOISE FEM software [12]. Modeling partitions inside the main chamber of the muffler (including tube walls) is a time consuming and tedious process. The method of node duplication with isolation of related elements has been used to create the tube walls inside the main chamber. Moreover, when perforated tubes are involved in the model, recognition of relevant surfaces for imposing the transfer admittance boundary condition is also an involved process. So, a typical automotive muffler of moderate complexity (as that of the present muffler) takes about 2 h of modeling and meshing time in a modeling software like I-DEAS Master Series 10. The symmetry about the major axis has been used and only one-half of the model has been meshed for analysis to reduce the CPU time. Results from this 3-D analysis have also been plotted on the same figure (Fig. 10) for comparison with the 1-D analysis results. 1-D analysis results deviate from the FEM results beyond 900 Hz due to the cut-on of the higher order modes in the chamber. This frequency is very low from the design point of view. However, the sonic velocity and the density of the air medium have been taken to be 340 m/s and 1.225 kg/m3. At this temperature (about 25 C), the first diametral mode would get cut-on at 1222 Hz. But, in practice, the exhaust gas temperature is always much higher than the ambient temperature. So, at those elevated temperatures, the sonic velocity of the medium will be much higher and the density of the medium will be very low. When the analysis is performed at an elevated temperature of 600 C, the sonic velocity would be 600 m/s and the medium density would be 0.5 kg/m3, and the 1-D results may be seen to match well with the 3-D results up to a frequency of around 1600 Hz (see Fig. 11). Incidentally, the cut-off frequency of the chamber at this temperature is 2157 Hz. Yet, it can be seen that the reso
Fig. 10. Comparison of TLa spectrum from 3-D FEM analysis, closed form analytical solution and that from the present volume synthesis algorithm.