臺灣博碩士論文加值系統

流速的量測可應用在海洋科技與水下技術，以及環境上的水流工程，甚至在高科技產業中其系統流速的大小亦對反應造成不同的結果表現；因此，在不同的工程領域範圍下，流速量測一直是一重要的研究項目。而超音波本身為非侵入性、非破壞性，安全性極高的科技，且其在水中的衰減量較電磁波與光波緩慢，適合水中的流速量測。本研究建立一脈衝超音波都卜勒流速量測系統，其以超音波能量散射與都卜勒效應為理論基礎，並由訊號產生器、功率放大器、超音波換能器、前置放大器、示波器等儀器架構，並另外製作隔離發射訊號與接收訊號的電路，以避免發射與接收兩端的訊號互相干擾，與應用工程分析軟體Matlab作數位訊號處理，包含:解調、濾波、取樣保持，頻譜分析等硬體架構與軟體運算所構成，並以可產生穩態流速的空蝕水槽為實驗對象進行實作量測，為避免量測時種種的不確定因素，在每個流速皆量測10次；最後將量測的流速平均值對照壓力計量測水槽兩斷面的壓力差所推得的流速，以作為系統量測結果的準確性之依據與驗證。另外搭配統計分析，如:相對誤差與標準差，評估本研究系統的穩定性與可信度。由實驗分析結果顯示本系統可以成功的分析三個不同角度的超音波探頭其所量測的六個流速值其訊號處理後所得的都卜勒頻率偏移，以進一步推得實驗水槽的流速值並在壓力計上得到驗證，而從誤差與標準差的分析顯示本系統有良好的穩定性與一定的可信度。

The velocity measurement is an important item in various engineering field. Ultrasound is non-invasive, non- destroyed, high security, and attenuated lower than optical methods, so it is frequently applied to underwater measurement. This work establishes a pulsed ultrasonic Doppler system, which is based on scattering and Doppler-effect, consists of burst signal generator, power amplifier, transducer, pre- amplifier, oscilloscope, and digital signal processing software, Matlab. The measurement was conducted in a cavitation tank of uniform velocity distribution and the measured velocities were compared with a calibrated Pitot probe. By extracting the Doppler frequency shift, six flow velocities with three ultrasound projection angles were measured and the results of both velocities and flow directions matched very well with those of Pittot probe.

摘要 I
Abstract II
目錄 III
圖目錄 VI
表目錄 X
第一章 緒論 1
1.1 研究動機與目的 1
1.2 研究背景 2
1.3 文獻回顧 5
1.4 論文架構與介紹 6
第二章 理論基礎 7
2.1 超音波理論 7
2.1.1 聲波方程式 8
2.1.2 介質的聲阻抗 10
2.1.3 水中聲速 12
2.2 散射理論 12
2.2.1 單體散射理論 13
2.2.2 多體散射理論 17
2.2.3 散射體大小對背散射訊號中心頻率的影響 18
2.3 超音波都卜勒 19
2.3.1 都卜勒效應 20
2.3.2 脈衝式超音波與單一散射子 21
第三章 量測系統與實驗架構 27
3.1 超音波換能器 27
3.1.2 壓電換能器結構 28
3.2 其他實驗裝置 30
3.3 實驗架構 40
3.3.1 脈衝式超音波都卜勒流速系統架構 40
3.3.2 訊號處理流程 41
3.3.3 實驗流程 43
第四章 實驗結果與討論 46
4.1 都卜勒頻譜分析 46
4.2 都卜勒流速分析 58
4.2.1 不同流速分析 59
4.2.2 不同量測角分析 60
第五章 結論與未來展望 66
5.1 結論 66
5.2 未來展望 67
參考文獻 68

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