高斯聲柱對於液體耦合層板及薄殼之穿透與反射聲場分析

Abstract

本文探討浸沒於流體之圓殼層板結構凹側受到高斯聲柱傾斜照射，所產生的非幾何反射與穿透聲場分析。有限聲柱之建立係以complex-source- point方法配合聲學的角頻譜法，藉點波源格林函數的解模擬出具有高斯分佈特性之聲柱，有別於傳統分析假設入射聲柱的所有入射波向量均平行於中心軸線，後者無法適切模擬發散波柱。極座標在圓周方向具有週期性，聲場的角頻譜表示將以一傅立葉級數取代直角座標之傅立葉積分式。圓殼層板的聲波反射與穿透係數係以Thomson-Haskel法推導其正解。所考慮的圓殼材料為短纖玻璃環氧樹脂，或於兩側增設聲阻匹配層，均視為積層等向性之複材結構。本文並探討多項設計參數對於反射與穿透聲場非幾何效應的影響。

This thesis presents an analysis of acoustic wave propagation across layered cylindrical structures that are immersed in fluids and obliquely insonified by acoustic Gaussian beams from the concave side. The acoustic nonspecular reflection is due to the interference of geometric reflection and leaky guided waves. Contrast to the ealier studies assuming that incident rays are all parallel to the central beam axis. The acoustic Gaussian beam is modeled by the complex source point (CSP) method and angular spectrum. In the present method the beam is not limited with well collimation. Spectral integral representation of the reflected and transmitted acoustic fields are replaced by a Fourier series due to circumferential period in polar coordinates. The exact forms of reflection and transmission coefficients of a layered cylindrical structure are derived using Thomson-Haskell method. The cylindrical structure made of chopped-fiber glass/epoxy is assumed to be isotropic. Two acoustic impedance matching layers added on both sides of the structure to construct a laminated acoustic window is also studied. Influences of various design parameters on nonspecular reflected and transmitted acoustic fields are well-disscussed.