由振動流管決定其質量流量之方法

Abstract

本研究旨於建立一個用於分析模擬單直管科氏質量流量計的解析模型。首先根據尤拉樑和均速流的假設，推導出具流動流體之振動管的解析模型，該解析模型並考慮了驅動器和感測器的集中質量效應。接著採用模態展開法求解該解析模型，推導出位於量測管之二個對稱位置的感測器之振動信號，及該二個感測器之振動訊號的相位差與質量流量之間的轉換關係。將該振動訊號的相位差與質量流量之間的轉換關係導入流量計的質量流量演算法，便可由流量計的輸出信號得知管中的質量流量。本論文完整呈現了單直管科氏質量流量計的模擬分析過程，並且以實驗驗證了解析模型和相位差計算演算法的可行性，進而作為單直管科氏質量流量計產品原型的設計依據。

This thesis aims at developing an analytical model of straight-tube Coriolis mass flowmeter. Based on Euler-Bernoulli beam theory and the assumption of uniform flow, an analytical model considering the concentrated masses of a driver, which is mounted on the middle point of the tube, and two motion sensors, which are mounted on two symmetrical positions with respect to the driver, is derived. The driver, mounted on the middle point of the flow tube, actuates the flow tube at its first natural frequency. The two motion sensors, mounted at symmetrical positions on both sides of the driver, sense the vibration of flow tube. The analytical model is solved by means of modal expansion method. The phase difference of the signals output by the motion sensors is dependent on the mass flow rate. In summary, this thesis use an algorithm based on the Nelder-Mead Simplex algorithm and least square fitting for calculating the mass flow rate from the signals output by the motion sensors. The algorithm is validated by experiment. A reference to design the prototype of straight-tube Coriolis mass flowmeter is established.