• 作者： 許榮均
• 作者服務機構： 台灣海洋大學造船工程學系
• 中文摘要： 由於不平衡及質心偏離之關係，軸系在轉動時會產生甩動，當轉動頻率與軸系彎曲振動之自然振頻接近時甩動幅度加大，而在某些狀況下轉動軸系可能會受到外力的作用，例如螺槳軸向的衝力，此軸向力可能會導致軸系甩動時彎曲振動；這衝力大小隨時間變化，而其頻率則由轉速及螺槳葉片的數目決定。而引起此彎曲振動之原因有來自於軸向力與彎曲振動之線性與非線性的耦合。本研究發現要激振起彎曲振動軸向力頻率隨轉速改變，而軸系之彎曲自然振頻隨著轉速改變，是造成此現象之原因。文中將理論部份做詳細描述，在實驗方面亦作了一模型實驗，證實了此現象之存在。
• 英文摘要： Due to initial imbalance or weight eccentricity, a shaft may whirl as it starts to rotate. The amplitudeof this whirling motion increases as the rotation speed approaches one of its bending natural frequencies. In some case, the shaft rotation may be excited by external dynamic axial forces, for example, thrustfluctuations induced by the propeller. This thrust fluctuation is time-varying, and its harmonics aredetermined by the rotation speed and the number of blades of the propeller. This axial excitation maycause additional bending vibrations on top of the whirling motion. The mechanisms that cause these bendingvibrations are the linear and nonlinear coupling between axial force and bending vibration. It is foundthat the excitation frequency needed to excite this additional bending vibration in large amplitude changeslinearly with respect to the rotational speed. The change of the bending natural frequencies of the rotatingshaft is responsible for this phenomeon. Equations of motion with respect to a rotating coordinate systemare given to describe the bifurcation of the bending frequencies and the linear and nonlinear couplingmechanisms Laboratory experiments on a rotating shaft excited by dynamic axial force were conductedand confirmed the existence of these phenomena.
• 中文關鍵字： bending natural frequency; rotating shaft; eccentricity; whirl; Axial force; linear coupling; parametric excitation
• 英文關鍵字： --