臺灣博碩士論文加值系統

傳統在計算消音器的傳輸損失中，只需要注意(0,1,0)模態被激發
的頻率即可，而在此頻率之前膨脹室內部的聲波皆可假設為一維平面
波，不管在理論解、數值解或是實驗值，所得到的結果皆相當吻合。
而在開口端相互靠近延伸管消音器中，傳統假設在(0,1,0)模態未發生之前，視管道中的聲波為一維平面波是不合理的，聲波自低頻開始即以三維的方式來傳遞，造成傳輸損失在低頻處約700 Hz 左右會有一個共振器的峰值產生，TL 值約60 dB ~ 80 dB。在開口端相互靠近延伸管消音器中，不管改變任何幾何的條件，只要延伸管開口端在相對距離不變的條件下，共振器的效應依然不變，使得傳輸損失在低頻處有峰值產生。而幾何的改變只會對峰值對應的頻率有所影響，因此可利用此現象來處理欲消除的噪音，幾何改變所造成峰值偏移的趨勢可由赫姆茲共振器的理論解加以說明。

Traditionally, the analytical solutions of the transmission loss (TL) of mufflers can be found if the acoustic mode of (0,1,0) is not excited. The acoustic waves in the expansion chamber before the cut-on frequency thus can be regarded as 1-D plane waves, and the results from theoretical, numerical and experimental solutions of the transmission loss agree well. For mufflers with extended tubes that in close propinquity, traditional research assumes a 1-D plane acoustic wave to occur, but this is an
irrational hypothesis due to the fact that acoustic waves propagate in 3-D form even at low frequencies. In this case, the peak of the transmission loss can occur at low frequencies around 700 Hz and the quantity of the TL is about 60 dB ~ 80 dB. When the extended tubes in mufflers are in close proximity and are the same distance apart, the effects of the resonators are identical regardless of any geometrical condition shifts. These effects also make a peak TL occur at low frequencies. The alteration of geometrical values only affects the peak frequency.
Therefore, engineers can use this phenomenon to attenuate sound energy at certain frequencies.

中文摘要…………………………………………………I
Abstract...……………………………………………II
目錄……………………………………………………III
圖目錄……………………………………………………V
表目錄……………………………………………………X
第一章 緒論……………………………………………1
1.1 研究動機……………………………………………1
1.2 文獻回顧……………………………………………3
1.3 研究方法……………………………………………4
第二章 理論基礎………………………………………7
2.1 一維聲波方程式…………………………………7
2.2 赫姆茲共振器理論解……………………………9
第三章 開口端相互靠近延伸管消音器傳輸損失探討………………11
3.1 短單膨脹室消音器傳輸損失……………………………………11
3.2 開口端相互靠近延伸管消音器傳輸損失………………………20
第四章 不同型式開口端相互靠近延伸管消音器模擬……………28
4.1 膨脹室長度固定下改變延伸管長度………………………………28
4.2 延伸管開口端相對位置及距離不變下改變膨脹室長度…………35
4.3 改變膨脹室及延伸管管徑…………………………………………38
4.4 入出口管徑方向垂直移動…………………………………………47
4.5 入出口管與膨脹室軸線相互垂直…………………………………49
第五章 結論與未來展望………………………………………………51
5.1 本文主要結論………………………………………………………51
5.2 未來研究方向……………………………………………………53
參考文獻………………………………………………………………54
附錄A 網格收斂測試…………………………………………………56
附錄B 一維聲波方程式………………………………………………59
附錄C 轉移矩陣法……………………………………………………61
附錄D 聲場模態標記方式……………………………………………70
附錄E 場點網格配置方式……………………………………………71
附錄F 開口端相互靠近延伸管消音器各模型峰值場點聲壓比較…72
附錄G 等效長度…………………………………………………………83
附錄H TMM Mathematica 計算程式………………………………84

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