加勁複合材料板的揚聲特性研究

Abstract

複合材料板因質輕強度大，在航太與民生工業中常被用來製作高性能系統的構件。當複合材料板件受激震時會因振動而發出聲音，對靜音需求高的系統言，若板件中某些自然頻率及模態被激震起來時，一些不悅耳的噪音便會產生，影響系統的功能。一種解決這種噪音產生的問題是在板件上貼上加勁條，藉改變板件的振形來抑制噪音的發生，另一方面，對將板件用做揚聲用的系統言，增加加勁條可因改變板件的振形而消除某些頻段的音谷或尖銳的聲音。本計劃將應用理論和實驗的方法來研究具加勁條複合材料板的揚聲特性，其中理論部分將應用Ritz方法來建立分析加勁複合材料板振動的數學模式，並用Rayleigh的聲壓計算公式來分析複合材料板具不同加勁方式的揚聲行為，最後利用最佳化方法設計特定複合材料板的最佳加勁方式。實驗方面，製作不同加勁複合材料板，藉量測這些板的自然頻率及聲壓曲線來探討其揚聲特性，並藉所得結果驗証理論分析方法的正確性。本計畫所獲得的結果將有助於加勁複合材料板的設計，而所建立的分析方法亦具學術參考價值。

Because of their many superior properties, composite plates have been widely used in making parts/components in many high performance systems such as aircrafts and flat panel speakers. When a composite plate is subjected to excitation, it will vibrate and radiate sounds. If certain natural frequencies and mode shapes of the plate are excited, some unpleasant noise may be generated. For systems requiring noiselessness, such noise may be unbearable. One mean to tackle this problem is to add stiffeners on the plate. By doing this, the natural frequencies and mode shapes of the plate will be altered so that the noise can be suppressed. On the other hand, if the plate is used for sound radiation, the addition of the stiffeners can help suppress sharp sound pressure levels and eliminate sound pressure dips in the audio frequency range. In this proposal, the sound radiation characteristics of stiffened composite plates are investigated via both theoretical and experimental approaches. In the theoretical approach, Ritz method is used to construct the mathematical model of the stiffened plate subjected to vibration. The first Rayleigh integral is used to calculate the sound pressure level of the vibrating plate. The sound radiation characteristics of several composite plates stiffened by different techniques are investigated using the proposed method. The optimal stiffening patterns for some specific composite plates are determined using an optimal design technique. In the experimental approach, several stiffened composite plates are fabricated for vibration and sound radiation tests. The experimental natural frequencies and sound pressure level curves are used to validate the proposed theoretical method and study the sound radiation characteristics of the plates. The results and method presented in this project will have both academic values and practical applications.