近年來國人對於生活品質的提升感到重視,而噪音就是一種降低生活品質的負面因素;對於工具機操作人員而言,噪音甚至導致職業傷害的發生,因此設計良好隔音結構,藉以降低噪音強度,進而提升操作人員的工作品質,是一件刻不容緩的議題。本文利用有限元素分析軟體COMSOL Multiphysics模擬一平面波於空氣中經過柱狀橡膠結構平板,觀察聲波通過不同柱高的平板前後的響度差異量。首先藉由柱狀橡膠結構平板的特徵頻率分析得知不同柱高的單元結構共振頻率與反共振頻率,進而利用頻率域分析探討柱狀平板單元結構諸多共振頻率與反共振頻率所對應的觀察面聲壓級大小。 本文以台灣大學校園中的吹葉機為研究對象,首先利用錄音機錄製吹葉機的工作聲量,接著將音訊檔匯入數值軟體,並藉由快速傅立葉轉換理論進行程式撰寫,可得頻率數列與其對應的傅立葉係數。 為了表示聽者於瞬間感受到的能量總和,首先將20~20000Hz每間隔1Hz所對應的觀察面平均壓力進行A加權函數濾波,然後將不同頻率加權後的平均壓力值之平方相加,最後取得柱狀平板於不同柱高之下所具有的觀察面數值分貝值。於本文發現對於hc值範圍為1mm~11mm,當單元結構柱高參數hc為11mm時,具有最多分貝減少量;而調整hc則可藉由改變反共振頻率,進而使平板阻隔介於4905Hz至5967Hz的特定頻率。最後發現單元結構hc=19.8425mm之反共振頻率為3370.17Hz,此結構對於重點頻率當中的3370Hz可使波源強度降低92.397dB。
The compatriots have paid attention to the promotion of life quality in recent years. And the noise is a type of negative factor reducing the quality of life. To the machine tool operator, the noise even induces the occurrence of the employment injuries. So designing a good soundproof structure to reduce the intensity of the noise and further enhancing the working quality of operator are urgent issues. The thesis utilizes the finite element analysis software ”COMSOL Multiphysics” to simulate a plane wave going through pillar rubber structural plate , and investigates the difference of loudness between the sound wave and the observation surface, for varied column heights. Conducting eigenfrequency analysis on the column plate can acquire the resonant and anti-resonant frequencies for some column heights. Then using the frequency analysis can learn the sound pressure levels for the observation surface corresponding to resonant and anti-resonant frequencies. The object of this study is the leaf blower in the campus of National Taiwan University. First, we take advantage of the sound recorder to record the sound coming from the leaf blower during operation. Then, by the program based on fast Fourier transform, we can acquire the Fourier coefficients corresponding to each frequency. To express the total energy the listener receives instantaneously, we conduct the ‘A’ frequency weighting function on the average pressure of the observation surface in frequency range 20~20kHz for the intervals of 1Hz. And then we sum the loudness corresponding to each frequency. Finally we acquire the numerical decibel of the observation surface for different height of the pillar plate. We can find that the case of hc=11mm has the best ability to reduce the decibel in the eleven cases. Adjusting the value of hc can change the anti-resonant frequency, and then block certain frequency in the range of 4905Hz-5967Hz. Finally we find that the case of hc=19.8425mm can reduce 92.397dB at 3370.17Hz.
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