| Installing the diesel silencer in the diesel exhaust system is the main method to reduce exhaust noise. First, the mathematical model of inner acoustic FE equation is established and at the same time the calculation formulas about TL(Transmission loss) of muffler with two inlet are deduced .Finally,With the FE software SYSNOISE, the acoustic performance of the reactive and dissipative silencers is calculated by the 3-D FEM(Finite Element Method) in this thesis. In response to dissipative silencer with the different flow resistance, the different thickness of porous materials and the different expanding ratio of exhaust silencer, its transmission loss are discussed. The acoustic attenuation performance of two kinds of reactive and dissipative mufflers is discussed, and the four kinds of perforate tube structure are also investigated. The curve shows that the perforated tube influence greately on the silerncer's acoustic performance.The hole diameter of silencer is important at medium frequencies.The porosity is significant at medium and higher frequencies. Insertion loss reflect the muffler characteristic, insertion loss reflects practice noise elimination effect of the whole exhaust system, which inflect the integration impact of sound source, muffler and system bottom. The mathematical model of inner acoustic FE equation is established and the calculation formulas about IL of muffler are deduced in the end in this thesis. On this basis, with highly-precise acoustic elements FLUID30 and FLUID 130, the FE model of mufflers are developed under static state working condition.By means of acoustic transmission matrix, the muffler is simulated directly and indirectly. When the muffler is installed and not installed, the four—terminal network parameter is calculated, and IL (insert transmission) is calculated too. In the end, through comparing two kinds of simulation results, it shows that calculated values directly coincide well with calculated values indirectly.
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