پيش بيني جذب صوت منسوجات بي بافت با استفاده از روش ميكروپرتونگاري مقطعي رايانه اي (μCT) و مدل ميكي

چكيده انگليسي :

AbstractIn the last two decades worldwide economic development has resulted in phenomenal growth ofindustrialization and urbanization and consequently numerous environmental issues such as noisepollution Noise pollution has become a very threatening issue to urbanized societies Publicawareness in regard to noise pollution has forced governments to introduce mandatory legislationeither to limit or eliminate noise pollution Reduction in sound level or elimination of noise can beachieved using acoustic absorbers Nonwoven textiles are considered to be one of the most effectiveand advantageous acoustic absorbers Ease of formability bulkiness microstructural engineeringability complex internal structure and relatively low production cost has made nonwoven textiles asa very viable material for use in acoustic engineering In this study the effect of in plane fiberorientation needling density and thermal calendering on needled nonwoven samples micro structure and acoustic behavior were investigated 3D images of micro structure of the samples wereobtained using X ray micro computed tomography CT The micro structure image of samples wasanalyzed using image analysis and the effect of production parameters on the internal structure ofthe samples was investigated Using computational fluid dynamics CFD and by solving Navier Stokes equations in the micro structure od samples the flow resistivity of the nonwoven sampleswas calculated Miki model was used to predict sound absorption at different frequencies A twomicrophone impedance tube was used to measure the sound absorption coefficient of the samples Comparison of experimental and predicted results showed that for the same amount of porosity samples with moderately aligned fiber orientation had the largest pore diameter 342 m and thelowest flow resistivity It was also found that samples with random in plane fiber orientation incomparison to parallel oriented samples had the smallest pore diameter 196 m and higher flowresistivity It was found that increase in the fiber alignment along the flow direction due to decreasein resistance to flow leads to increase in permeability of the samples Additionally it was found thatsubject to constant pore diameter in plane orientation of fibers has no significant effect on the flowresistivity and permeability of the samples Results also showed that 19 mm thickness samples withmoderately aligned fiber orientation had a lower sound absorption coefficient in comparison tosamples with random fiber orientation It was established that sound absorption coefficient insamples with 31 mm thickness was not affected by in plane fiber orientation at frequencies above2200 Hz Results showed that peak of absorption coefficient of the samples shifts from 4000 Hz to2000 Hz when sample thickness increases from 19 mm to 31 mm It was found that the absorptioncoefficient of the samples at frequencies below 3000 Hz decreases due to the decrease in samplethickness despite the increased resistance to flow due to the increased needling density Resultsshowed that at frequencies below 3000 Hz the acoustic behavior of the samples is more affected bythe thickness of the sample rather than by the flow resistivity Results showed that increase in thepunching density from 52 to 387 needles cm2 causes the maximum sound absorption coefficientshifts from the frequency of 2000 Hz to the frequency of 5000 Hz It was concluded that thermalcalender finishing process adversly affects the sound absorption coefficient of the samples Finallyexcellent compatibility was found to exist between the experimental data and the results of theproposed model Key words Nonwoven fabric sound absorption Miki model computational flow dynamics X raymicro computed tomography

رفيعي فروشاني، زهرا

پيش بيني جذب صوت منسوجات بي بافت با استفاده از روش ميكروپرتونگاري مقطعي رايانه اي (μCT) و مدل ميكي

جذب صوت , مدل ميكي , منسوج بي بافت , ديناميك سيالات محاسباتي , ميكرو پرتونگار مقطعي رايانه اي