چكيده به لاتين
Nowadays, in order to reduce noise and increase passenger comfort, acoustical materialsare used as barriers, or sound-absorbers. Acoustic metamaterials are artificial materials made from single unit cells smaller than the length of the sound wave they encounter, which can reduce the amplitudeof sound waves efficiently in the specific frequency range.Researchersare interested in the applications of this phenomenon in the fields of aerospace, automotive and control sound pollution. Since so far no research has been done on the use of these materials in cars, hence, in this thesis, first of all acoustic metamaterial baffle with a local resonator in the form of a circle containing unit cellswith mass and springs are designed. This baffles are placed in the exhaust pipeand the effect of these materials in terms of noise cancelation is investigated.By tuning its geometry we found the appropriate stop band and transmission loss in the desired frequency range. At the end of this section, with eliminating of the muffler from the exhaust system and with using baffle in whole exhaust pipes, their effects and their behavior have been investigated. After extracting the results for verification of the method,an experimental study of the acoustic matematerial was performed; first a cube of acoustic metamaterial with local resonators was constructed by a 3D printer and compared with cubes of MDF and Plexiglas, and it was shown that this metamaterial has behaved much better than conventional materials in terms of Transmission Loss. The methodology is achieved by modeling in the Solidworks software, and simulation has done for obtaining the transmission loss of the exhaust and the complete modeling of the exhaust system in Comsol software, as well as simulating the cubes in Abaqus software with finite element method. The result of the transmission loss at the specified frequency range is acceptable. For example,an empty exhaust with the 10 dB transmission loss compared to an exhaust which contains baffles in three frequency ranges (low, medium and high) increased up to the 65 to 85 dB. In the end, the results of the experimental test were good for validationin a way that we had reduction of weight and noise simultaneously.
