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Experimental and Numerical Study of Single Chamber Muffler
|關鍵字:||消音器;muffler;傳輸損失;頻譜儀;雙麥克風轉移函數;有限元素;transmission loss;single spectrum analyzer;dual-microphone transfer function;finite element||出版社:||機械工程學系所||引用:|| D. D. Davis, J. M. Stokes, D. Moorse, L. Steven,"Theoretical and experimental investigation of mufflers with components on engine muffler design", NACA Report 1192, 1954.  A. F. Seybert and D. F. Ross, "Experimental determination of acoustic properties using a two-microphone random-excitation technique ", Acoustical society of America, Vol.61, No.5, 1977: pp. 1362-1370  J. Y. Chung and D. A. Blaser, "Transfer function method of measuring in-duct acoustic properties. I. Theory", Acoustical society of America Vol.68, No.3, 1980: pp. 907-913. M. L. Munjal and A. G. Doige, "Theory of a two source-location method for direct experimental evaluation of the four-pole parameters of an aero acoustic element", Journal of Sound and Vibration, Vol.141, No.2, 1990: pp. 323-333  Cheng-I. J. Young, M. J. Crocker,"Prediction of transmission loss in mufflers by the finite-element method", Acoustical Society of American , Vol.57, No.1, 1975, pp. 144-148  D. F. Ross, "A finite element analysis of perforated component acoustic systems", Journal of Sound and Vibration, Vol.79, No.1, 1981: pp. 133-143  A. Craggs, "A finite element method for damped acoustic systems: an application to evaluate the performance of reactive mufflers", Journal of sound and vibration, vol.48, No.3, 1976: pp. 377-392  "Numerical Acoustics Theoretical Manual", lms international.  M. L. Munjal, "Acoustics of ducts and mufflers", JOHN WILEY & SONS 1987. A. Craggs, "The use of simple three-dimensional acoustic finite elements for determing the natural modes and frequencies of complex shaped enclosures ", Journal of Sound and Vibration, Vol.23, No.3, 1972: pp. 331-339 Z. Tao and A. F. Seybert, "A review of current techniques for measuring muffler transmission loss", Society of Automotive Engineers, Inc, 03NVC-38, 2003 A. Craggs, "The application of the transfer matrix and matrix condensation methods with finite elements to duct acoustic", Journal of Sound and Vibration, Vol.132, No.2, 1989: pp. 393-402  S. Bilawchuk, K. R. Fyfe, "Comparison and implementation of the various numerical methods used for calculating transmission loss in silencer systems", Applied Acoustic, 64, 2003: pp. 903-916  S. N. Y. Gerges, R. Jordan, F. A. Thieme, J. L. Bento Coelho and J.P. Arenas, "Muffler modeling by transfer matrix method and experiental verification", Journal of the Brazilian Society of Mechanical Sciences and Engineering, Vol.XXVII, No.2,2005: pp. 132-140 Byrne, K., Skeen, M. and Kessissoglou, N.," Measurement of the sound transmission loss of a smallexpansion chamber muffler to consider the effects of mean flow and wall compliance, "Proceedings of ACOUSTICS 2006, 20-22 November 2006 M J. Crocker, "Handbook of noise and vibration control", JOHN WILEY & SONS  R. Matas, J. Knourek, J. Voldrich, "Influence of the muffler geometry with three chambers and two tailpipes topology on its attenuation characteristics", Applied Acoustic, 3,2009: pp. 121-132 Munjal, M. L. and L. J. Eriksson, "An analytical, one-dimensional, standing-wave model of a linear active noise control system in a duct ", Journal of Acoustical Society of America, 84, 1988: pp. 1086-1093  R. Matas, J. Knourek, J. Voldrich, "Influence of the terminal muffler geometry with three chambers and two tailpipes topology on its attenuation characteristics", Applied and Computational Mechanics, 3 , 2009: pp.121-132  A. Selamet, V. Easwaran, A. G. Falkowski, "Three-pass mufflers with uniform perforations", Journal of Acoustical Society of America, Vol. 105, No. 3, March 1999: pp. 1548-1562  A. Selamet, M. B. Xu, I.-J. Lee, N. T. Huff, "Analytical approach for sound attenuation in perforated dissipative silencers", Journal of Acoustical Society of America, Vol. 115, No. 5, May 2004 : pp. 2091-2099||摘要:||
消音器是機械中常見的動力附屬設備。消音器的傳輸損失(Trans- mission Loss)以及聲壓分佈是改良消音器內部結構以及提昇消音器性能之關鍵資料。
實驗時，除了先製作一根實際比例的實驗用單室消音管以外，量測儀器設備主要包括了全音域喇叭、擴大機、阻抗管、頻譜儀、兩組麥克風等等。實驗過程中，我們經由頻譜儀訊號處理器，可以得到管路上下游測量點的聲壓值，然後我們使用雙點函數轉換法 (Dipole Transfer Function) 把量測點的聲壓值換算為消音器的傳輸損失。實驗完成後，我們另外建構一個與實驗消音器相同的三維實體有限元素氣流模式 (Acoustic Finite Element Model)，置入適當的邊界以及負載條件，使用鄔老師所開發的FEAST聲學有限元素分析FORTRAN模組，進行數值模擬分析並求出消音器的傳輸損失。再將有限元素分析得到的傳輸損失結果與實驗得到的結果相比較。這個比較過程，除了能了解實驗過程的缺失以外，還可以從有限元素分析的眾多數據中，得到許多實驗所無法得到的資訊。在設計高效能消音器的時候，這些資訊能提供設計人員一些有價值的參考資料。
Muffler is a common ancillary equipment in power machines. Transmission loss and the sound pressure distribution are key points of the improvement of the muffler performance and it’s structures.
The experiment of estimating muffler performance is mature. It has numerous studies published related to the muffler design in the past two decades. In this study, we made a group of single-chamber muffler system and use the measuring instruments to read some basic experimental information first. Next, we build up a acoustic finite element model of the experimental muffler and use the self-developed FEAST acoustic finite element module to solve for a set of results. Finally, we compare the previous two sets of data to investigate the demerits of experiments and appropriate modification for the numerical simulation.
In experiment, in addition to make a real object of single-chamber muffler pipe, the measurement equipments include full-range speakers, amplifiers, impedance tube, signal spectrum analyzer and two sets of microphones.
During the experiment we can read the sound pressures from the spectrum signal analyzer in up and down pipes at the measuring locations. Then we use the Dipole Transfer Function to calculate the transmission loss of the muffler by such recorded sound pressures. Having completed with experiment, we build up a three-dimensional acoustic finite element model similar to the experimental muffler accompanied with appropriate boundary and loading conditions. After then, we use FEAST acoustic finite element FORTRAN module developed by Professor Wu to perform the numerical simulation analysis and to obtain the transmission loss of the muffler. Finally, results of transmission loss obtained from finite element analysis are compared with those from the experiments. Thus, we can not only understand the demerits of experiments, but also derive more information from the finite element models for purpose of design. In manufacturing high-performance mufflers, the study may provide powerful information to the engineer designers.
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