Roohalah Hajizadeh, Ali Khavanin, Ahmad Jonidi Jafari, Mohammad Barmar, Somayeh Farhang Dehghan,
Volume 9, Issue 4 (12-2019)
Abstract
Introduction: Nowadays multiple techniques have been developed to noise control. One the most important way is the control based on sound absorption and insulation. The purpose of current study was to improve the acoustic properties of soft polyurethane foam regarding combined sound absorption and insulation characteristics.
Materials and Methods: Polyacrylonitrile and polyvinylidine fluoride nanofibers are fabricated using solution electrospinning technique. Nano-clay particles (montmorillonite, 1-2 nm in diameter) were purchased from Sigma-Aldrich, Inc. Experimental design was prepared using Design-Expert ver.7 software. The 50 samples of nanocomposites were fabricated on the basis of experimental run. The measurement of sound transmission loss and the absorption coefficient was conducted using BSWA SW477 550005 Impedance Tubes according to the standard ASTM E2611-09 and ISO10534-2, techniques. Response surface methodology (RSM) with central composite design (CCD) was applied to optimize the conditions to produce nanocomposites for each frequency range.
Results: The polymer nanocomposites had the higher combined sound transmission loss and the absorption coefficient than pure polyurethane foam. Their combined transmission loss and the absorption coefficient in the low, middle and high frequency range was 02.02, 1.91 and 2.53 times higher than the pure polymer. The combined transmission loss and the absorption coefficient in all frequency ranges have been increased by increasing the thickness of the composites and air gap. At a thickness of 2 cm, the combined composites, sound transmission loss and the absorption coefficient increased with the increase of content of both nanofibers. The highest combined transmission loss and the absorption coefficient was observed when mass fraction of nanofibers was in at its maximum level.
Conclusion: This study showed that the adding nano-clay particles, polyacrylonitrile and polyvinylidine fluoride nanofibers to polyurethane foam can lead to increased sound transmission loss and the absorption coefficient. The obtained optimized nanocomposite can be applied to noise control where requiring the absorption as well as reduction of sound transmission.
Iraj Alimohammadi, Mahdi Farrokhi, Sevda Javadi, Mozhgan Nouraei, Leila Hosseini Shafeie,
Volume 15, Issue 1 (3-2025)
Abstract
Introduction: A significant contributor to noise pollution in urban areas is automobile exhaust systems, wherein mufflers, as passive devices, are designed to mitigate the noise produced. The dimensions, shape, and configuration of the muffler, along with its associated components and pipes, influence its effectiveness in sound transmission loss. This study investigates the impact of varying the length of the muffler’s connecting pipes and their associated holes on sound transmission loss in reactive mufflers, utilizing software simulation for analysis.
Material and Methods: The research utilized COMSOL 5.5 to simulate the effects of different geometric factors on sound transmission loss in mufflers. Modifying factors such as the length of connecting pipes and the existence of holes led to the development of various designs. Analysis of the results was conducted to assess the impact of each parameter on sound attenuation, enabling a straightforward comparison of acoustic efficiency.
Results: Studies demonstrate that changing the form of pipes at different frequencies produces diverse outcomes. Introducing a perforation prior to the tube and utilizing elongated connecting tubes with expansion chambers can enhance transmission attenuation. On the other hand, transmission loss decreases with longer pipes that lack holes. Lower pitches experience minimal attenuation, whereas higher pitches undergo more loss. Reactive mufflers work best at certain frequencies, where the length of the connecting pipe affects both the acoustic mass and the effectiveness of the muffler.
Conclusion: The results obtained from this study can inform the optimal design of mufflers aimed at enhancing their efficacy in sound transmission loss. Furthermore, it is essential to consider the synergistic impact of the geometrical configurations of the internal pipes within the muffler to minimize sound emissions from the exhaust outlet.
