臺灣博碩士論文加值系統

一般在探討導波環境中的聲波傳遞問題時，都將密度視為常數。但是在1980 年 Hamilton[1] 建立一系列的海床地質聲學模式 (geoacoustic modeling)指出，在海洋環境的沉積層中，壓力波聲速與密度均呈現梯度的分佈。因此，在本文裡我們將傳統的海洋導波環境中，沉積層中的聲速與密度假設成深度的函數，並藉此探討沉積層，對反射係數與波傳機制的影響。首先，本文由連續方程式 (continuity equation) 、動量方程式 (momentum equation) 、以及狀態方程式 (equation of state) ，配合微量攝動 (small perturbation) 法的使用，推導出沉積層中的波動方程式。並經由傅立葉轉換 (Fourier transform) 將時間與水平的因素去除，得到僅與深度相關的二維格林函數 (Green's function)並求出聲波方程式的解；配合邊界條件、數值方法及波數積分法的使用，求出反射係數與波數頻譜。接著，本文以改變參數的方式，針對由過渡層所產生的反射，就反射與波傳的機制進行分析。最後，選擇臺灣西部的淺海海域，將相關的環境參數輸入 OASES 軟體進行模擬，以了解其音傳損失的情形。並就臺灣西部大陸棚的淺海海域，在反潛作戰上所必需考量的聲學問題上，做一概括性的探討。

Generally speaking, when treating wave propagation in an ocean waveguide, the density is assumed to be constant in the media. However, the study report of Hamilton[1] shows that there exists a transition layer in the water-sediment interface, in which the density varies continuously and gradually with depth. The objective of this thesis project is to study the effects of such transition layer on the reflection coefficient and wave propagation in an waveguide environment.The first part of this thesis is to derive the wave equation from the governing equation for compressible fluid using small perturbation method. Then, the wave equation has been solved using the wavenumber integration method. Many results relevant to the problem such as reflection coefficient, wavenumber spectrum are obtained analyzed.The second part is to investigate the effects of the transition layer for reflection coefficient and wave number spectrum for various parameters, followed by the calculation of the transmission loss for the shallow water environment in the simulation of Taiwan strait using existing software OASES.Finally, a general discussion for the acoustic problem encountered in the shallow water ASW (anti-submarine warfare)are provided.-1 aWaveguide Propagation in an Ocean With a Sediment Layer of Continuous Sound-Speed and Density Variations