Papers by sedigheh basirjafari
International Journal of Engineering, 2022
International Journal of NanoScience and Nanotechnology, 2018
In this paper, numerical results obtained and explained from an exact formula in relation to soun... more In this paper, numerical results obtained and explained from an exact formula in relation to sound pressure load due to the presence of liquid inside the finite-length non-rigid carbon nanotubes (CNTs), which is coupled with the dynamic equations of motion for the CNT. To demonstrate the accuracy of this work, the obtained formula has been compared to what has been used by other researchers. For this purpose, the solution of the modified complex Helmholtz equation was derived by considering the non-rigidity of the CNT and the wave reflections at the open ends of the CNT for three different liquids with or without considering the relaxation time. The results showed that neglecting the non-rigidity of CNT would cause a decrease on the pressure fluctuations and the pressure associated with the viscosity force of the liquid in the liquid-filled CNT, at both axi-symmetric, and asymmetric cases. Also, it is showed that the viscous liquid in a CNT is a dispersive medium for sound wave prop...
Original Research Paper Received 24 November 2015 Accepted 01 January 2016 Available Online 14 Fe... more Original Research Paper Received 24 November 2015 Accepted 01 January 2016 Available Online 14 February 2016 In an anechoic chamber, the flat multi-layer sound absorber is cheaper, easier to install and less complicated in manufacturing than conventional wedge and pyramid absorbers. Therefore, design of the optimum flat multi-layer absorber which has minimum thickness is desirable. In this paper, the genetic algorithm has been employed as an effective optimization tool to determine flat triple layer porous absorber. To obtain a broader range of porous materials, a combination of foam and fiber types is used. Theoretical and numerical method (finite element method specifically COMSOL Multi-physics version 4.4) have been used to investigate the operation of sound absorption corresponding to the multi-layer structure. In the first step, mathematical model is verified and finite element method, theoretical and experimental results are compared together for two different samples of struc...
Journal of Environmental Health Science and Engineering, 2020
Sound absorbing elements commonly used to make quieter spaces are very desirable for high-frequen... more Sound absorbing elements commonly used to make quieter spaces are very desirable for high-frequency noise control. It is more attractive if it is possible to produce sound absorbing structures that perform well for a wide frequency range, especially in low-frequencies. In this regard, Helmholtz resonator array is a well-known structure but the maximum performance of each resonator unit in an array panel can only be achieved at resonance frequency that is dependent on its size. Therefore, a resonator array panel with equal size units has insufficient performance in a wide frequency range. Hence, the consideration of suitable sizes for each resonator in an array panel consisting of unequal size units is a key point to widen the frequency range of sound absorption. On the other hand, it seems that engineering science can be developed by nature inspiration. In addition, Fibonacci sequence is a famous mathematical model which describes the shape/ratio of different phenomena which exist i...
BioResources
Applying acoustic panels made of natural fibers, due to their high biodegradable characteristics,... more Applying acoustic panels made of natural fibers, due to their high biodegradable characteristics, light weight, low density, cheap price and non-toxicity, are proper alternatives to acoustic absorbers made of synthetic fibers. Considering their stance and vast applicability in industry, the possibility of producing them of natural palm fibers with sodium silicate adhesive of 10 and 20% in two 16 and 32 mm thicknesses, 350 and 450 kg/m3 densities, 50 and 100 mm particles length (strands), as variable factors in 16 types of matched panels with 3 repetitions is proposed in this article. The palm-trunk discs constituted the control sample. The effect of variables on sound absorption coefficient was assessed. The effect of variable thickness and adhesive percentage on all frequencies was significant and the effect of density variable on all frequencies except 250 and 2000 Hz was also significant. The effect of particle length was significant except at the 500 Hz frequency. The effects of...
Micro & Nano Letters
Efforts have been made to investigate the role of adding carbon nanotubes (CNTs) as the sound ene... more Efforts have been made to investigate the role of adding carbon nanotubes (CNTs) as the sound energy decaying fillers on the physical and mechanical properties of polyurethane (PU) foam and thus to correlate them with its directly measured sound absorption coefficient. For this aim, the microstructures of PU/CNT nanocomposite foams were investigated and analysed through field emission scanning electron microscopy. Owing to the different microstructures of the samples, large differences were observed in their morphological and physical properties such as density, porosity, pore diameter, closed pore content and thus on their acoustic damping performance.
Journal of Applied Physics, 2013
In this paper, an exact formula is obtained for the inner diameter of double-walled carbon nanotu... more In this paper, an exact formula is obtained for the inner diameter of double-walled carbon nanotube (DWCNT) as a function of its higher radial breathing mode (RBM) frequency, using the symbolic package of maple software. Its outer diameter is obtained from the inner diameter formula by considering the constant interlayer spacing between two tubes of DWCNT. For this purpose, DWCNT is considered as double concentric elastic thin cylindrical shells, which are coupled through the van der Waals (vdW) forces between two tubes. Lennard-Jones potential is used to calculate the vdW forces between tubes. The advantage of this analytical approach is that in the double concentric elastic shell model all degrees of freedom in the vibrational analysis of DWCNTs are considered. To demonstrate the accuracy of this work, the relationship between RBM frequency of a single-walled carbon nanotube and its radius is deduced from the DWCNT formula that is well consistent with other publications. To illustrate the application of...
Journal of Applied Physics, 2012
The aim of this paper is to fabricate a sound absorber flexible semi-open cell polymeric foam bas... more The aim of this paper is to fabricate a sound absorber flexible semi-open cell polymeric foam based on polyether urethane (PEU) with carboxylic functionalized multi-walled carbon nanotubes (COOH-MWCNTs) as an energy decaying filler at low loadings up to 0.20 wt. %. This paper provides the relationship between the mentioned foam microstructure via field emission scanning electron microscopy and different acoustical and non-acoustical properties of PEU/COOH-MWCNT composites. Addition of just 0.05 wt. % COOH-MWCNTs enhanced the sound absorption coefficient of the mentioned nanocomposite foam over the entire frequency range. Raman spectra revealed the better dispersion of COOH-MWCNTs in the PEU matrix leading to more stress transfer between them to cause a significant dissipation of energy.
Current Applied Physics, 2013
Abstract In this paper, exact formulas are obtained for the radial breathing mode (RBM) frequenci... more Abstract In this paper, exact formulas are obtained for the radial breathing mode (RBM) frequencies of triple-walled carbon nanotubes (TWCNTs) using symbolic package in MAPLE software. For this purpose, TWCNT is considered as triple concentric elastic thin cylindrical shells, which are coupled through van der Waals (vdW) forces between two adjacent tubes. Lennard–Jones potential is used to calculate the vdW forces between adjacent tubes. Then, explicit formulas for RBM frequencies of single-walled (SW), and double-walled (DW) CNTs have been deduced from TWCNT formulas that show an excellent agreement with the available experimental results and the other theoretical model results. The advantage of this analytical approach is that the elastic shell model considers all degrees of freedom in the vibrational analysis of CNTs. To demonstrate the accuracy of this work, the RBM frequencies of different multi-walled carbon nanotubes (MWCNTs) are compared with the available experimental or atomistic results with relative errors of less than 1.5%. To illustrate the application of this approach, the diameters of DWCNTs are obtained from their RBM frequencies which show an excellent agreement with the available experimental results. Also, this approach can be used to determine the diameters of the TWCNTs and MWCNTs. The influence of changing the geometrical and mechanical parameters of a TWCNT on its RBM frequencies has been investigated, too.
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Papers by sedigheh basirjafari