大型複材結構低頻聲場預測研究

Abstract

聲納罩通常安裝於船艏、龍骨或船體，主要用於安放導航、偵測系統或測距聲納，內部填充淡水或海水以維持形狀與內外壓力平衡。作為保護聲納的重要元件，採用橡膠或玻璃纖維強化塑膠(Fiber-reinforced plastic, FRP)，提供優化的結構與聲學性能以保證聲納系統效能，實現減重、耐腐蝕、降低製造與維護成本的優點。本研究使用複合材料聲納罩模型資料，及參考當前各國聲納護罩發展經驗，利用有限元素分析(Finite element analysis, FEA)軟體COMSOL Multiphysics建立聲固耦合(acoustic-structure coupling)數值模型進行聲納罩結構內部聲場響應分析。本文模擬從不同角度入射平面波所形成的聲納罩內部聲場。首先與參考文獻的數值計算結果比較，驗證本文數值模型之準確性，然後對低頻範圍進行模擬計算；分析結果發現結構共振頻率與聲壓響應頻率十分吻合，並影響了內部聲場模態；由不同頻率、不同聲波傳播方向的分析結果發現聲場模態的分佈、結構頻率響應、結構形狀與材料特性均會影響聲納系統的聲波接收效能。本研究以聲納罩內部聲壓與入射聲壓之比值做為指標探討聲納護罩的工作效能，將有助於後續聲納罩設計之參考。

Sonar domes are located at the bow or on the keel or hull of surface ships and filled with fresh or seawater to maintain their shape and design pressure. Their purpose is to house electronic equipment for navigating, detection or ranging. As an important part of protecting sonar system, sonar domes are made of rubber, steel or Fiber-reinforced plastic(FRP), providing optimized structural performance to protect the sonar array, optimized acoustic performance to enhance sonar reception, enabling weight reduction, corrosion resistance, and significantly reduced manufacturing and maintenance costs. We utilize Finite Element analysis tool, COMSOL Multiphysics, and dome data to build an acoustic-structure coupling model to analyze the response of inner sound field of sonar domes and simulate interior acoustic field formed by different incident plane waves from the current experience of the development of sonar domes in various countries. We compared numerical solutions with analytical solutions to verified the numerical accuracy and then, we used FEA to solve for low frequency domain. The results of frequency response show that structure vibration has a strong influence on interior acoustic field and we found that detecting efficiency of sonar system is influenced by sound field modes, frequency response of structure, structure shape and material properties. We use the ratio of interior pressure level and incident pressure level to evaluate the work efficiency of sonar domes, which we hope that it can contribute to the design of sonar domes.