| Because noise pollution become a more and more serious problem,it is important to perform the research and analysis about noise control.This researches focus on the noise pollution in steel mill and the design for muffler structure which meet the demand of noise reduction for AY7-41N056A type centrifugal fan.This paper consists of four parts.First of all,the discrete Fourier transform(DFT)and the fast Fourier transform(FFT)were applied to calculate and treat with the same sound signal,and their advantages and disadvantages were analyzed,respectively.Secondly,there are two kinds of voice signal acquisition system.One is based on sound card and Matlab software,and the other is based on data collector and VA-Lab software.Both of them were applied in the same external environment and the same voice signal source.The related data analysis showed their own characteristics about time domain and frequency domain,and then gave the difference,accuracy and convenience between them.Thirdly,the noise in the mill was recorded,and the related data was analyzed to obtain the spectrum analysis,octave-band analysis and total sound level analysis and then indicated the noise distribution characteristics at different frequency.Finally,based on the characteristics of the sound-absorbing material and the theory about sound spread,reflection and interference,the muffler structure and sound-absorbing material were determined to meet the demand of noise reduction.Furthermore,the ANSYS finite element modal analysis was carried out to study the muffler structure and prompt the muffler performance.The results showed that:(1)The maximum of the relative error is less than 1.5%between DFT algorithm and FFT algorithm for the same frequency of the same sound signal.But FFT algorithm is two orders faster than DFT algorithm.(2)For the signal acquisition system based on sound card and Matlab software,the acoustic pressure of the sound wave should be less than 1Pa.Otherwise,signal distortion occurs.Thus,the signal acquisition system based on data collector and VA-Lab software is more credible.(3)The stronger noise appears in the cutting bed of steel-quality-testing workshop,RH furnace of steel-making workshop and straightening process of steel-rolling workshop,and the noise strength reach 98,46 dB(A),101.04 dB(A)and 100.44 dB(A),respectively.Further,their key noise frequency range focus on 250?8000 Hz,1000?16000 Hz and 250?8000 Hz,and their contribution to the total sound energy are 76.56%,64.68%and 76.67%respectively.The noise of the casting key-control room is the greatest in all lounge of the steel mill.The total sound level reaches 87.54 dB(A),the key noise frequency range is 63?2000 Hz,and the contribution to the total sound energy is 73.09%.Only noise intensity in the turning machine,sawing machine and grinding machine of steel-quality-testing workshop conforms to the noise standards prescribed by the state.(4)The key noise frequency ranges from 250 to 8000 Hz,and the sound energy in this frequency range accounts for about 66.2%of the total sound energy in the AY7-41N056A type centrifugal fan.The fifth muffler is the best muffler to reduce the noise caused by AY7-41N056A type centrifugal fan.The total sound level fall 12,07 dB(A)to 85.5 dB(A)if the measuring point is 2 meters from the muffler.Such a result can meet the demand of noise reduction.The modal analysis show that the maximum of the muffler inherent frequency is 20.577 Hz,which is far away from the peak frequency of the centrifugal fan.Thus,the muffler can't resonate during the work. |
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