由於動壓軸承具有承載力強、構造簡單、成本低以及容易安裝等諸多優點，因此普遍被應用在大型轉動機械中，但是油漩與油顫這一類因動壓軸承中流體所引發之不穩定現象，卻經常困擾著工程人員。此不穩定現象主要發生在轉動機械剛啟動時，以及運轉中負載條件突然改變。油漩與油顫之處理方式有許多種，因動壓軸承中油膜的流體平均速度是引起不穩定的重要參數之一，在本研究中使用一氣壓回授裝置，當油漩發生時藉回授輸入改變流體平均速度，進而使系統穩定。通常運轉中的機械狀態改變時，系統狀態訊息會蘊藏在其振動信號中，經由分析油漩發生時的訊號得知;當油漩發生時，軸中心位置會偏離機器運轉位置，若將穩定位置設定一「可接受範圍」時，可做為適當之控制指標。此外，結合「線性二次調節器」演算法計算閉迴路系統之回授，此為一經過最佳化設計之控制回授，使用者可依其控制性能之需求，藉由調整演算法之權重來達成其設計規格;實驗結果除了展現轉動機械的不穩定可有效地被消除外，提議的「可接受範圍」方法，也可用來做為監測配備有流體膜軸承的機台在發生流體引發不穩定及摩擦時之依據。 Hydrodynamic bearings are often used in large rotating machinery because they have many advantages, such as high load capacities, simple structures, low cost and easily to be equipped etc. The fluid-induced instability, however, are usually vexing when rotating machinery, which is equipped with fluid-film bearings, are operating during start up or lightly loaded. There are several ways to cope with the fluid-induced instability. Since the fluid circumferential average velocity associated with journal speed generally is a key factor to cause the instability, therefore, in this study a method of anti-swirl injection is adopted to decrease the fluid circumferential average velocity and shift the instability to a higher operation speed. When the operation conditions of machinery are changed, the reasons can be figured out through the analysis of the machinery vibration signal. The study uses an acceptance region with a linear quadratic regulator to address the problem of fluid-induced instability. The former is applied as a control index and the latter is employed to obtain the optimal feedback gain. Appropriate setting of an acceptance region and adequate weightings can achiveve the desired control performance easily. The experimental results show that the instability is soothed and the proposed technique using acceptance region can also be used to monitor rub and fluid-induced instability existing in this kind of rotary machinery.
