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博碩士論文 etd-0809101-132337 詳細資訊
Title page for etd-0809101-132337
論文名稱
Title
平面聲波於不均勻海床沈積層上之反射問題研究
Coherent Reflection of Acoustic Plane Wave From a Random Sea floor
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
76
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2001-07-27
繳交日期
Date of Submission
2001-08-09
關鍵字
Keywords
水中聲學、體散射
underwater acoustics, volume scattering
統計
Statistics
本論文已被瀏覽 5702 次,被下載 1746
The thesis/dissertation has been browsed 5702 times, has been downloaded 1746 times.
中文摘要
本論文之研究目的在探討平面聲波入射不均勻海床之反射效應。由於海床沈積層之介質不均勻特性,會造成
聲速微小之隨機攝動,使得聲波在沈積層中傳播時,能量會散失於不均勻介質中,因而減少了入射聲波之能量,
此種能量削減之機制稱為聲波之體散射效應。而本文將引進聲波體散射效應之理論於海床環境上,探討
聲波入射海床之平均反射問題。吾人所研究之海床結構分別為隨機流體所組成之沈積層,
以及能夠支援剪力波傳播之彈性底層。

為了探討聲波於不均勻介質中之體散射效應,本論文的研究方法乃引用~Tang~與~Frisk~所發展之平面聲波
入射半無窮隨機流體之反射理論。此方法為應用攝動理論~(perturbation theory)~,以及導出層狀隨機流體層
之格林函數,進而推導出隨機流體層之聲波平均場,並藉由滿足環境之邊界條件,導出線性系統,最後應用數值程式解出
入射聲波之反射係數。

在探討本論文之聲波體散射問題時,本論文之先期研究以於國內學術研討會上發表了兩篇文章~[13]~[14]~,
其乃是由核心之體散射理論漸漸擴充發展,同時能夠深入探討聲波於海床之反射現象,使得本理論能夠更適切的運用
於複雜之海床環境。

由本論文研究結果顯示在隨機流體沈積層中,平均反射係數會因增加沈積層介質之隨機度大小、操作頻率、以及沈積層之厚度而減小,
除此之外,因為介質不均勻造成之體散射效應,入射聲波到達反射之臨界角時並不會發生全反射現象。
而在海洋底床為彈性體之狀況下時,由反射係數圖可看出彈性體之剪力波聲速對聲波反射造成的影響,也就是當彈性底床之
剪力波聲速增大時,底床提供了聲波能量外傳的機制,使的入射聲波之平均反射場減小。
Abstract
The problem of coherent reflecton of an acoustic plane wave from a random seabed consisting of a randomly
inhomogeneous sediment layer overlying a uniform elastic sea floor is considered in this analysis.
The random perturbation in the sediment layer is attributable to the sound-speed variations,
resulting in volume scattering due to medium inhomogenieties.

An approach based upon perturbation theory, combining with a derived Green's function for a slab bounded above and
below respectively by a fluid and an elastic half space ,is employed to obtain an analytic solution for the coherent field
in the sediment layer. A linear system is then constructed to facilitate the analysis of the coherent reflection field.

The results of the coherent reflection coefficient for various sediment randomness, frequency , sediment thickness, and
sea floor elasticity have been numerically generated and analyzed. It was found that the higher/larger size of randomness
, frequency, thickness, and shear-wave speed, the lower the coherent reflection. Physical interpretation for the
characteristics of various results were provided.
目次 Table of Contents
目錄
頁次
第一章 緒論.……….……..……….….…….……..…………….………1
1.1 研究動機與目的….…………….….…….….………………..1
1.2研究環境簡介…...……………………..………………………..2
1.3 文獻回顧與先期研究……………………………....………..3
1.4 研究方法…………….…………………………………………..3
第二章 理論模式.……….…..……….….…….…...…..………….….…5
2.1簡介……………………………………………………………5
2.2 聲波方程式….…………………………………………….......6
2.3 隨機流體沈積層中之波動方程式……….……….…………….8
2.4格林定理………………………..………..………………………9
2.5 沈積層中聲波平均場之控制方程式………………………….12
2.6 滿足沈積層解之格林函數與邊界條件……………………….13
2.6.1 隨機流體沈積層之底床……………………………….13
2.6.2 均勻彈性之底床……………………………………….14
2.7 相關函數………………………………………………………15
第三章 平面聲波於層狀隨機流體層之反射………………17
3.1相關函數……………………………………………… .17
3.2求解聲波之平均場….………………………………….………18
3.3 線性系統……………………….………………………………20
3.4 結果與討論………………….…………………………..….….22
第四章 平面聲波於彈性海床上之反射效應………….26
4.1相關函數…..………………………………………… .26
4.2求解聲波之平均場….……………………………….………..27
4.3 線性系統…………………….………………………………..29
4.4 結果與討論………………….………………………..….…...31
第五章 結論與建議…….…………...…………………….35
5.1結論………………………………………………..…..……….35
5.2建議…..…………….…………………………………………..36
參考書目……………………………………………………...37
附錄A 平面聲波在半無窮隨機流體介質之粗糙界面上反射問題之研究…………………………….…………………A-1
附錄B 平面聲波於隨機流體介質之層狀海床上反射問題之研究………………….……………………………………B-1
附錄C Coherent reflection of acoustic plane wave from a random sediment layer over an elastic sea floor…….………………………………………C-1










圖目錄
圖1.1:研究之海洋環境示意圖………………………………………..2
圖2.1:有限介質中由分佈聲源所產生聲場的問題…………………..10
圖3.1: 海洋環境示意圖…………………………….…………………18
圖3.2: 不同隨機參數之反射係數曲線.…..………………………....22
圖3.3: 不同頻率下之反射係數曲線…………………...……………..23
圖3.4: 改變沈積層厚度之反射係數曲線………………………….....24
圖3.5: 底層沈積層介質隨機度較上層大………………………...…..25
圖3.7: 上層沈積層介質隨機度較底層大………………………...…..25
圖4.1: 海洋環境示意圖…………………………………….….….…..27
圖4.2: 改變隨機參數下之反射係數曲線………….….……………....31
圖4.3: 改變操作頻率下之反射係數曲線…….….………..………..…32
圖4.4: 改變沈積層厚度下之反射係數曲線.….………..………….….33
圖4.5: 改變底層剪力波聲速下之反射係數曲線……..……………....33

參考文獻 References
1.Frisk, G.V.,“Inhomogeneous waves and the plane wave reflection coefficient, ’’ J. Acoust. Soc. Am., 66, 219-234, 1979.
2.Goff, J.A. and T. Jordan, “Stochastic modeling of seafloor morphology: Inversion of Sea Beam data for second-order statistics, ’’ J. Geophys. Res., 93, 13,589-13,608, 1988.
3.Ivakin, A.N and Yu. P. Lysanov,“Theory of underwater sound scattering by random inhomogenieties of the bottom,’’ Sov. Phys. Acoust, 27, 61-64, 1981.
4.Kuperman, W.A. and H. Schmidt, “Self-consistent perturbation approach to rough surface scattering in stratified elastic media, ' J. Acoust. Soc. Am. 86, 1511-1522, 1986.
5.Liu, Jin-Yuan and Chau-Chang Wang, “Coherent reflection from a rough interface over an inhomogeneous transition fluid layer,’’ (To appear in J. Comput. Acoust.)
6.Schmidt, H., OASES: Application and Upgrade Notes, version 1.6, MIT, 1993.
7.Tang, Dajun and George V. Frisk, “Plane-wave reflection from a random fluid half-space,’’ J. Acoust. Soc. Am., 90, 2751-2756, 1991.
8.Wenzel, A.,“A method for distinguishing between the attenuation due to absorption for waves propagating in a dissipative, randomly inhomogeneous medium,’’ J. Acoust. Soc. Am., Supp1.1, 80, S90, 1986.
9.Yamamoto, T.,“Geoacoustic properties of the seabed sediment critical to acoustic reverberation at 50 to 500 Hz: a preliminary data set,’’ J. Acoust. Soc. Am., Suppl.1 85, S86, 1989.
10. Liu, J.-Y. and C.-F. Huang, “Coheren Reflection of Acoustic Plane Wave From Rough Interfaces in a Stratified Random Fluid Medium” J. Marine Sci. technology.

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