轴承摩擦力作用下弹性支承轴系自激振动特性研究

Self-excited vibration of a flexibly supported shafting system under bearing friction

以重力式水洞中的弹性支承轴系为研究对象,研究其在水润滑橡胶轴承摩擦力作用下的自激振动特性及其机理。实验结果表明,系统于某一确定转速产生自激振动,并随转速下降维持不变直到一个较低转速由于驱动力不足而消失,各个转速下的自激振动均表现为转速调制下的单阶模态失稳。为了研究自激振动机理,建立了弹性支承轴系动力学模型。在建模时,将轴系分为弹性支承和转轴两个子结构,分别获取固有振动频率和模态振型,建立在轴承界面摩擦力作用下的支承-转轴耦合动力学模型,并采用模态叠加法对模型进行降阶处理。采用四阶Runge-Kutta方法求解动力学方程,分析主要物理参数对系统的影响。分析结果表明,失稳模态为支承的小阻尼扭转振动模态,支承振动与轴承摩擦耦合作用是系统失稳的主要原因。

Self-excited vibration characteristics and its mechanism of a flexibly supported shafting system placed in a gravity water tunnel and excited by a friction force from water-lubricated rubber bearings were investigated. Test results indicated that the system＇s self-excited vibration appears at a specific rotating speed and remains unchanged with decrease in the shaft rotating speed,it disappears at a lower rotating speed due to inadequate driving force; the system＇s selfexcited vibration under a certain rotating speed reveals a single mode to be unstable under rotating speed modulation. To study self-excited vibration mechanism,the dynamic model of the system was built. In modeling,the system was divided into two substructures including a flexible support and a shaft to get their natural frequencies and modal shapes,respectively. According to compatible conditions and boundary conditions,a support-shaft coupled dynamic model under the action of a friction force on bearing interface was built,the mode superposition method was adopted to reduce orders of the model. The fourth order Runge-Kutta method was used to numerically solve the dynamic equations. The influences of the main physical parameters on the system＇s vibration instability were analyzed. The test results agreed well with those of simulation. The results showed that the unstable mode is the support ＇s weakly damped torsional vibration one; the interaction between support vibration and bearing friction force is the main reason to cause the system unstable.