消除存在於旋轉機械中的流體膜軸承的流體漩、流體颤及乾颤等不穩定，就安全和穩定操作而言是相當重要的。當平滑而圓柱狀的動壓軸承處在輕負載的狀況，由於轉子對重力作用之徑向負載，此時軸承中的軸頸可能移動到低偏心比，且軸承內部完全充滿潤滑油。當這種情況發生時，它可能觸發流體引發的不穩定問題。這個研究使用一個回授控制系統的電磁致動器去處理這類不穩定。此致動器可以被當作一個變動勁度的產生器。裝設在靠近旋轉機器的流體膜軸承處的致動器，用並聯結構結合流體膜軸承提供較高的勁度以消除流體引發的流體漩不穩定問題；裝設在靠近旋轉機器的軸中間處的致動器，用並聯結構結合軸勁度提供較高的勁度以消除流體引發的流體颤不穩定問題。致動器原是不動作的，直到遭遇流體引發的不穩定狀況時才動作。當不穩定發生，致動器將結合流體膜軸承或軸勁度去穩定旋轉機器。就致動器而言，藉由應用比例和微分控制當作控制演算法，改變致動器的控制電流利於提供合適的驅動力。比例增益導致力量增加，當作位移的函數，它的功用是模擬勁度。微分增益導致力量增加，當作速度的函數，它的功用是模擬阻尼。更進一步，使用彈簧模型以估算系統所需的勁度，進而增強系統和提升不穩定的門檻。在實驗轉子裝置模型基礎上，提議的方法結合根軌跡並以MATLAB®軟體去模擬轉子系統的勁度及阻尼之穩定狀態。實驗結果呈現旋轉機器的不穩定可以有效地被移除。所提出的技術也可以用來診斷配備有流體膜軸承的旋轉機器中所發生的摩擦和流體引發的不穩定問題。 Elimination of instabilities existing in rotating mechinery, including fluid whirl, fluid whip and dry whip, is imperative for safe and stable operation of rotating machines with journal bearings. When the plain cylindrical journal bearing in rotating machinery is lightly loaded, perhaps due to radial loads on the rotor that act against gravity, the shaft journal can move to low eccentricity ratios, and the bearing can become fully flooded. When this happens, it can trigger fluid-induced instability. This study develops an electromagnetic actuator with a feedback control system to tackle the kinds of instabilities. The actuator can be used as a generator of variable stiffness. The actuator mounted near the fluid-film bearing at a rotating machine incorporates the fluid-film bearing in parallel configuration to provide higher stiffness for eliminating fluid-induced whirl instability, and it mounted near mid-span at a rotating machine incorporates shaft in parallel configuration to provide higher stiffness for eliminating fluid-induced whip instability. The actuator does not act until the system encounters the fluid-induced instability. When instability occurs, the actuator will be actuated and combined with the fluid-film bearing or shaft stiffnesses to stabilize the rotating machine. For the actuator, favorable force of actuation is reached by changing the control current in the actuator applying the proportional and derivative controls as control algorithm. The proportional gain causes the force to increase as a function of displacements; its function simulates stiffness. The derivative gain causes the force to increase as a function of velocities; its function simulates damping. Moreover, a spring model is used to estimate the stiffness the system needs to stiffen the system and raise the threshold of instability. The proposed method combining the root locus plot is based on an experimental rotor rig model, as well as using MATLAB® for simulation. Experimental results demonstrate that the instability of the rotating machine can be removed effectively. The proposed technique can also be used to diagnose rub and fluid-induced instability existing in this kind of rotating machines.
