超音波都卜勒流速量測系統之開發與驗證

Development and Verification of The Ultrasonic Doppler Current Measurement System

張維剛(Wei-Kang Chang)

指導教授 ： 宋家驥

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02023

摘要

流速的量測可應用在海洋科技、水下技術、環境水流工程，甚至在高科技產業中，系統流速的大小也會對反應造成不同的結果。因此，在不同的工程領域範圍內，流速量測一直是重要的研究項目。而超音波本身具有非侵入、非破壞的特性，是安全性極高的科技，且超音波在水中的衰減量較電磁波與光波緩慢，非常適合水中的流速量測。依據量測系統對功率、靈敏度、解析度及中心頻率等方面的需求，自行製備超音波探頭。
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、都卜勒效應與壓電轉換特性為理論基礎。以背向散射回波訊號量測靜水與拖車的相對流速，並驗證流速量測的誤差。在硬體設備上使用自行製備的超音波換能器，配合訊號產生器、功率放大器、前置放大器、數位示波器、循環水槽及拖車等設備進行測試。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。將所接收的數位訊號輸入至Matlab作數位訊號處理取得都卜勒頻譜，並依都卜勒的頻移與速度公式推得Beam方向流速。最後把四個Beam方向流速轉為三維流速，並與定速拖車預設速度進行比較。
研究內容包括：流速計算方法、隔離限制電路、音鼓製備、數位訊號處理、系統可靠性及精確性之驗證等等。研究方法是利用四個方向的換能器組成音鼓，分別以逆壓電效應輸出聲束並接收背向散射回波訊號，經數位訊號處理及都卜勒頻移計算，取得量測系統與水流的相對速度，並驗證系統之可靠性與適用範圍。

關鍵字

超音波 ； 都卜勒 ； 流速量測

並列摘要

Measurement of flow velocity can apply to ocean technologies, underwater techniques, and fluid transportation systems in high-tech industries; thus, measurement of flow velocity is of great importance in engineering studies and research. Ultrasonic waves are noninvasive and nondestructive; moreover, the attenuation speed of ultrasonic waves under water is slower than that of electromagnetic waves, making the ultrasonic waves suitable to measure the velocity of water flows. This study draws on the acoustic Doppler effect theory and the characteristics of piezoelectric transition to establish a system to measure the pulsed Doppler flow velocity. The research contents include the designation of methods to measure flow velocity, the separation of limiting circuits, the piezoelectric ceramics, the processing of digital signals, the verification of system reliability and accuracy, etc. The study is conducted using transducers from four directions to output sound beams generated via converse piezoelectric effect, receiving backscatter echoes, and obtaining the relative speed of the measurement system and water flows by means of signal processing and calculation of Doppler shift. To verify the reliability and fields of application for the system, the study makes use of a constant-speed vehicle to control the speed of the measurement system in an actual flow field.

並列關鍵字

Ultrasonic ； Doppler ； Velocity Measurement

參考文獻

[29] 宋家驥、黃郁雅，超音波都卜勒系統應用於流速量測，台灣大學工程科學及海洋工程學系，2012。

[2] J. J. Campbell and W. R. Jones, IEEE Trans. Sonics and Ultrasonics, SU-15, 209, 1968.

[3] J. De Rosny and P. Roux, Multiple scattering in a reflecting cavity: application to fish counting in a tank, Journal of the Acoustical Society of America, 109: 2587–2597, 2001.

[4] J. De Rosny, P. Roux, M. Fink, J. H. Page, Field fluctuation spectroscopy in a reverberant cavity with moving scatterers, Physical Review Letters , 90: 9– 4302 , 2003.

[7] Wang Tiefeng, Wang Jinfu, Ren Fei, Jin Yong, Application of Doppler Ultrasound Velocimetry in Multiphase Flow, Chemical Engineering Journal, 92: 111-122, 2003.