船用消音器之聲學性能與背壓分析

Abstract

本研究針對大型船艦排氣系統中之消音器，進行聲學性能與背壓特性之綜合分析，並應用有限元素法建立模擬模型以探討其行為。首先，透過背壓理論所建立之經驗公式對第二代消音器進行背壓推估，並與實測數據進行趨勢比對後，進一步透過幾何調整中孔延伸管孔徑與長度，以降低背壓並設計出第三代消音器。 背壓分析結果顯示，主要背壓集中於膨脹管與中孔、入出口管之截面積變化處，故尺寸調整策略優先針對延伸管孔徑進行優化。 聲學性能方面，本研究亦探討噴灑水霧對消音性能之影響，發現其在高頻區段具有顯著提升傳輸損失之效果。為評估其潛在應用效益，分別針對不同霧化比例、水滴尺寸大小等條件進行模擬分析。 模擬結果顯示，第三代消音器在加入水霧後，於80Hz以上頻率範圍內皆可達10dB以上之傳輸損失，雖整體聲學性能略低於第二代設計，然其背壓控制表現更為優異，顯示第三代設計於兼顧聲學性能與流體性能方面更具實用性，適用於對低背壓與多頻段消音需求兼備之船用排氣系統。

This study focuses on the comprehensive analysis of acoustic performance and back pressure characteristics of mufflers used in large marine exhaust systems. A finite element model was developed to investigate the muffler’s behavior under various design and operating conditions. Initially, an empirical equation derived from back pressure theory was applied to estimate the pressure loss of the second-generation muffler. The estimated results were compared with experimental measurements, and based on this comparison, the geometry—specifically the diameter and length of the extended perforated pipe—was optimized to reduce back pressure, leading to the development of a third-generation muffler. Back pressure analysis revealed that the major pressure loss occurred near the abrupt changes in cross-sectional area between the expansion chamber and the perforated pipe, as well as at the inlet and outlet regions. Therefore, geometric optimization was primarily focused on the perforated pipe. In terms of acoustic performance, the study also investigated the effect of water droplets injection, which was found to significantly enhance sound attenuation, particularly in the high-frequency range. To evaluate its practical effectiveness, a series of simulations were conducted considering different scattering ratios, droplet sizes, and the pore diameter derived from measured back pressure. The results indicate that the third-generation muffler, when combined with water mist, achieves more than 10 dB of transmission loss across the frequency range above 80 Hz. Although its overall acoustic performance is slightly lower than that of the second-generation design, the improved back pressure characteristics make it more suitable for practical applications where both low back pressure and wideband noise attenuation are required in marine exhaust systems.