聲學都卜勒流速儀系統研究

Study of the Acoustic Doppler Current Profiler System

陳俊宇(Jyun-Yu Chen)

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(2017年)

https://doi.org/10.6342/NTU201702212

摘要

台灣雖然擁有豐沛的雨量，但因地形關係以及常常為颱風暴雨，儲水相當困難，而水資源的永續發展卻相當重要，因此流量量測就扮演很重要的角色。要得知流量之前，就必須得知流速，但在台灣相關研究單位往往仰賴國外儀器，也就是聲學都卜勒剖面流速儀（Acoustic Doppler Current Profiler, ADCP），此儀器不但可以得知底床地形亦可以得知整體流場剖面流速，進而得知流量，因此本論文希望初步研究出整體儀器的架構系統。
ADCP是一種可以廣泛應用於海洋及內陸河川的測流領域。因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，所以非常適合運用於水中的流速量測。
本論文利用窄帶分析發法來計算出不同流速時的都卜勒頻移量，並運用國立臺灣大學工程科學及海洋工程學系的拖曳水槽做流速誤差的驗證，本實驗主要利用拖曳水槽之拖車移動使水流與拖車有著相對速度，利用此點來做流速分析及驗證。硬體方面，本實驗室自行自做25 mm及50 mm的1MHz超音波換能器及實驗機構，除此之外也自製限制隔離電路板隔離收發訊號外也可保護儀器受損，再搭配數位示波器、訊號產生器、功率放大器及脈衝收發器來進行量側。訊號端先將接收訊號利用帶通濾波器，再將訊號做正交解調，接著利用低通濾波器得到本實驗需要分析的訊號後，計算功率譜密度的權重進而得到都卜勒頻移量，最後帶入都卜勒原理可得知流速。得知實驗流速後在與拖車速度做驗證以及誤差分析。

關鍵字

超音波 ； 都卜勒 ； 聲學都卜勒剖面流速儀 ； 流速量測

並列摘要

Although Taiwan has abundant rainfall, there are lots of typhoons. And the relationship of the terrain is not ideal. It is important for sustainable development the water resources, so the flow measurement plays an important role. To know the flow before, we must know the flow rate. There are lots of research institutions to use foreign instruments in Taiwan. It called Acoustic Doppler Current Profiler (ADCP). It not only can measure the terrain of bottom, but the velocity of the flow. The hope of this paper is developing the system of the instrument initially.
Acoustic Doppler Current Profiler is widely used in the marine and inland rivers. Ultrasound is non-invasive, non-destroyed, high security, and attenuated lower than optical methods, so it is frequently applied to underwater measurement.
The experiment of this paper is using the narrow band method to calculate Doppler frequency shift, and to use the towing sink which is in the Department of Engineering Science and Ocean Engineering, NTU to verify the flow rate and error. The trailer of the towing tank moving will cause relative velocity to the water. It can analyze and verify flow rate. In terms of hardware, twenty-five millimeters and fifty millimeters of ultrasonic transducer and dock which is fitting the experiment are made in the laboratory. Protect the instrument from damage, and isolate received and emissive signal, this paper also used the limit isolation circuit board which is made in the laboratory. Digital oscilloscopes, function generator, power amplifier, and ultrasonic pulser/receiver are employed in the experiments. After bandpass filtering, quadrature demodulation, and low pass filtering, the Doppler frequency shift is calculated with power spectral density. Finally, using Doppler principle to get the flow velocities. Verify the results between experimental and actual values.

並列關鍵字

Ultrasound ； Acoustic Doppler Current Profiler ； measurement of flow rate

參考文獻

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