| 摘要: | 本研究執行纖維吸音材料動態流阻與聲響性質之模擬分析與量測；研究中使用多孔彈性理論模擬動態流阻產生之吸音係數，並與雙麥克風阻抗管量測之吸音係數進行比較探討。
本文首先運用Navier-Stokes流體運動方程式於拉普拉斯域及邊界條件設定下進行動態平行流阻之推導，其次使用透氣試驗法、雙厚度法及無響室法量測玻璃纖維與岩棉纖維吸音材料的流阻，並與Tarnow之動態平行與垂直流阻模擬結果進行比較。續而應用雙麥克風阻抗管量測兩種纖維吸音材料之聲響性質，並探討於材料厚度及密度改變下對聲響性質如音響阻抗、複數動態勁度、吸音係數等之影響。之後再藉由Biot多孔彈性理論推導上表面可穿透之吸音平板之複數動態勁度、音響阻抗及吸音係數。並據以探討應用材料厚度、密度及動態流阻量測值所模擬之吸音係數與量測吸音係數之差異。
由研究結果顯示纖維材料之間距、排列方式、密度、厚度等皆是影響動態流阻與聲響性質之重要因素。本文推導之平行流阻與三種不同方式量測之流阻皆落於Tarnow推導之平行與垂直流阻預估值之間，三種量測法中以雙厚度法較適合一般實驗室量測使用。由流阻量測值及材料參數所衍生之吸音係數預估值，於中低頻域與雙麥克風阻抗管量測之吸音係數結果相符，而於中高頻域時則與阻抗管吸音係數量測結果互有差異但趨勢相符，其中以無響室法所模擬之吸音係數結果較接近於量測結果。
In this thesis, dynamic flow resistance and acoustic properties of fibrous sound absorbing materials are simulated and measured. In the study, the poroelastic theory is used to simulate the dynamic flow resistance extending sound absorption coefficient, and carries two-microphone impedance tube measurement on the comparison.
During the study, the dynamic parallel flow resistance is first derived from using Navier-Stokes equation in Laplace domain with specified boundary conditions. Secondary, flow resistances of fiberglass and rock wool sound absorbing materials are measured using air permeability test method, two-thickness method, and anechoic chamber method, then, the measured results are compared with that resulted from Tarnow’s parallel and perpendicular dynamic flow resistance simulations. Thereafter, acoustic properties of two kind of fibrous absorbing materials are measured by two-microphone impedance tube method, and the influences of material thickness and density on the acoustic properties such as acoustical impedance, complex dynamic stiffness, and sound absorption coefficient are also discussed. Afterward, complex dynamic stiffness, acoustical impedance, and sound absorption coefficient for the fibrous absorbing material with a permeable upper surface are derived using Biot’s poroelastic theory. Accordingly, the differences between the sound absorption coefficient simulated with the use of thickness, density, dynamic flow resistance, and that measured are discussed.
It is learned that the spacing of fiber, fiber arrangement, density, and thickness are key factors for affecting the dynamic flow resistance and acoustical properties. In the study, it is found the simulated parallel flow resistance and the flow resistances measured by three measuring ways fall in between the values predicted by Tarnow’s parallel and perpendicular dynamic flow resistance simulations. Two-thickness method is superior to the other two kinds of measuring ways in Labs. The sound absorption coefficients simulated by applying the measured flow resistance and material properties are agree with that measured by two-microphone impedance tube method, in the low frequency region. And in the high frequency region, the simulated values have the differences with the measuring results but both have the same tendency. The sound absorption coefficients predicted by the results of the anechoic chamber method is proved much closer to the measured results. |
