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Optimization of a Muffler
Comfort is one possible reason for choosing to buy a particular vehicle. However, not only the interior plays a role. The noise affects the overall driving experience and improves safety. To reduce the acoustic emission muffler were installed. Besides the reduction of the source of origin also the sound insulation of the interior can be improved. For example using acoustic optimization of ventilation systems or with a frequency analysis of the components can also effect the reduction of noise.
Among many other applications, with FEM-calculations it is possible to investigate the spread of sound waves by simulation. In the following case study we consider this for a muffler in a vehicle. By this study we want to identify starting points for geometry optimization.
Essentially two effects were used, to minimize exhaust noise: the averaging of sound pressure amplitudes by reflection and the conversion of sound energy into heat by absorption of porous materials. Hereafter, we have a more detailed look at the first option.
Exhaust gases leave the engine with a certain pressure and a certain frequency. By dividing the muffler into several chambers the principle of sound reflection can be used. So it is possible to minimize certain areas of the frequency spectrum. In Figure 1 we can see that by division into two chambers the level of sound pressure can be reduced by 30 dB between inlet and outlet. In Figure 2, the sound pressure level versus frequency is plotted; it can be seen that certain frequencies are drastically reduced at 400 and 600 Hz. Nesting into several chambers, introduction of impact walls, as well as the extension and narrowing of cross-section enables a specific adaptation of the frequency spectrum and thus a direct reduction of sound pressure level.
Advantages of FEM Simulation
- Calculation and presentation of items, which are experimentally difficult to reach
- geometry optimization concerning defined properties
- soon results