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研究生:林昆鴻
研究生(外文):Kung-Hung Lin
論文名稱:楔形體導波在流體負載下的頻散行為量測
論文名稱(外文):Measurement of the dispersion behaviors of wedge waves with fluid loading
指導教授:楊哲化
指導教授(外文):Che-Hua Yang
學位類別:碩士
校院名稱:長庚大學
系所名稱:機械工程研究所
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2001
畢業學年度:89
語文別:中文
論文頁數:122
中文關鍵詞:截平楔形體頻散無頻散
外文關鍵詞:truncationwedgedispersiondispersion-free
相關次數:
  • 被引用被引用:2
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所謂楔形體導波是能量局限於楔形體頂端,並沿著楔形體頂端傳遞的波導。而過去的研究中曾對直線形及圓盤形楔形體在不同的截平下進行量測,探討其頻散行為。對於直線形楔形體,本研究結果與Mckenna以不等厚的平板理論模型相比較時,發現在高頻時或是較大的頂角時有相當大的誤差。對於圓盤形楔形體的量測,則發現在低頻時其頻散關係圖上呈現負斜率現象。而文獻上對於楔形體導波受流體負載下的頻散行為,均局限於無頻散行為的探討,本研究將利用雷射超音波量測技術及有限元素法來探討直線形及圓盤形楔形體受流體負載後其導波之頻散現象。利用海軍黃銅以及鋁塊兩種材料當做試片,當受流體負載後量測其楔形體導波頻散關係現象之變化,並隨楔形體頂端之截平改變時,探討其導波在水面下傳播頻散行為與在空氣中傳播頻散行為之差異。
楔形體受水負載後,其導波波傳速度會比在空氣中導波波傳速度來的慢,但因受水作用其波傳速度並無法超過水波波速。當無截平楔形體受水作用後,會出現頻散現象,這與空氣中無截平楔形體並不相同,若將楔形體頂端之截平逐漸加大時,其導波波傳速度也會逐漸變大。
當Cw小於流體波速時,圓盤形楔形體Cw/Ca比值與頻率改變有關係,呈一正斜率現象。但直線形楔形體的Cw/Ca比值則與頻率改變無關。
對於有截平的楔形體,當Cw到達流體波速時,其反對稱波波速並無法超過流體波速,因此Cw/Ca比值會下降。
本研究的量測及分析結果,主要對於未來以楔形體導波為原理的液體感測器研發做準備工作。
Wedge waves are guided acoustics waves propagating along the tip of a wedge with energy tightly confined wear the wedge tip. In the previous research, that studied the dispersion behavior of linear and circular wedges with variable truncation. For the linear wedge, the thin plate theory was proposed by Mckenna is limited only for the wedge of very small apex angle or very narrow bandwidth. For circular wedge, that discovered the dispersion curve with a negative slope for the wedge waves.
For the dispersion curve behavior of wedge waves with fluid loading, the literature reports are limited the dispersion —free case. The dispersion curve behavior of linear and circular wedges with fluid loading will be studied both with laser ultrasonic technique and finite element method.
This research showed the A1 mode wave velocity of straight wedge with fluid loading was lower than the A1 mode wave velocity of straight wedge in air. And experiment results pointed out the A1 mode wave velocity of linear and truncation wedge with fluid loading hadn’t overstepped water’s wave velocity.
目錄
第1章 前言..................................................1
1.1 研究背景..............................................1
1.2 研究目的..............................................3
1.3 研究進行方法..........................................4
第2章 理論基礎..............................................6
2.1 楔形體在空氣中的波傳速度..............................6
2.2 楔形體在受水作用下的波傳速度..........................6
第3章 研究方法.............................................11
3.1 實驗量測部份.........................................11
3.1.1 雷射超音波之信號激發部份.........................12
3.1.2 雷射超音波之信號量測部份.........................12
3.2 試片準備.............................................14
第4章 有限元素法...........................................16
4.1 直線形楔形體導波於空氣中之有限元素分析...............16
4.1.1 直線形楔形體之有限元素網格分割(mesh size)......17
4.1.2 直線形楔形體之邊界條件(Boundary Condition).....18
4.1.3 海軍黃銅直線形楔形體導波於空氣中之有限元素分析結果...........................................................18
4.1.4 鋁直線形楔形體導波於空氣中之有限元素分析結果.....19
4.2 直線形楔形體導波受水負載後之有限元素分析.............19
4.2.1 直線形楔形體受水負載後之有限元素網格分割(mesh size)........................................................20
4.2.3 海軍黃銅直線形楔形體導波受水負載後之有限元素分析結果...........................................................21
4.2.4 鋁直線形楔形體導波受水負載後之有限元素分析結果....22
第5章 結果與討論...........................................23
5.1 30度海軍黃銅直線形楔形體導波於空氣中及水作用下的訊號量測結果.........................................................23
5.2 15度海軍黃銅直線形楔形體導波於空氣中及水作用下的訊號量測結果.........................................................28
5.3 30度鋁直線形楔形體導波於空氣中及水作用下的訊號量測結果 ..........................................................29
5.4 15度鋁直線形楔形體導波於空氣中及水作用下的訊號量測結果...........................................................31
5.5 直徑40mm圓盤形楔形體導波於空氣中及水作用下的訊號量測結果
.............................................................32
5.6 直徑20mm圓盤形楔形體導波於空氣中及水作用下的訊號量測結果
................. ..........................................34
第6章 結論.................................................37
參考文獻....................................................121
1. P.E Lagasse ,I.M. Mason and E.A.,1973, ’’Microwave Theory and Techniques’’,Ash IEEE Trans,MIT21,225
2. James Mckenna, Garyd. Boyd, 1974 ,’’Plate Theory Solution for Guided Flexural Acoustic Wave along the Tip of a Wedge’’,IEEE Transactions on Sonics and Ultrasonics,Vol.Su-21,No.3,P.178-1864
3. Victor V. Krylov, 1999 ,”Propagation of Localized Vibration Modes along Edges of Immersed Wedge-Like Structures: Geometrical-
Acoustics Approach”,Journal of Computational Acoustics,Vol.7,
No.1,P.59-70
4. X. Jia and M. de Billy, 1992 ,’’Observation of the Dispersion Behavior of Surface Acoustic Waves in Wedge Waveguide by Laser Ultrasonics’’,Appl.Phys.Lett,P.2970-2972
5. Jacques R. Chamuel, 1993 ,”Edge Waves along Immersed Elastic Elliptical Wedge with Range Dependent Apex Angle”,Process IEEE Ultrasonics Symposium,P.313-317
6. Victor V. Krylov, 1994 ,”Propagation of Wedge Acoustic Waves along Wedges Imbedded in water”,IEEE,P.793-796
7. A.C.Hladky-Hennion, 1997 ,’’Finite Element Analysis of The Propagation of Acoustic Waves along Waveguides Immersed in Water’’,IEMN,Department ISDN,P.519-530
8. Jacques R. Chamuel, 1997 ,”Flexural Edge Waves along Free and Immersed Elastic Waveguides’’,Review of progress in QNDE,Vol.16,
P.129-136
9. C.H.Yang and J.S.Liaw, 1997 ,’’Measurement and Finite Element Simulations of Guided Waves Propagation along Linear and Circular Wedges’’,IEEE,P.1139-1142
10. M. de Billy, 1996 ,”On the Influence of Loading on the Velocity of Guided Acoustic Waves Propagating in Linear Elastic Wedges”,
Acoustical Society of America,Vol.100,No.1,P.659-662
11. 尤國男, 2000 ,”楔形體導波頻散現象之探討”,長庚大學機械工程研究所碩士論文
12. K. Kawashima, 1998 ,”Finite Element Simulation of Propagation of Leaky Surface Waves Excited By a Line-Focused Transducer”,
Review of Progress in Quantitative Nondestructive Evaluation,
Vol.17,P.995-1002
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