Dynamic modeling and flutter analysis of a fin-actuator system

Dynamics of an actuator has a direct impact on the flutter characteristics of a fin structure. Thus it is important to build the dynamic model of the fin-actuator system precisely before a flutter analysis. A typical fin-actuator system is investigated by constructing its motor model, reducer model and controller model, respectively. Based on the characteristics of the ground vibration test (GVT) data, two nonlinear factors are considered including the contact stiffness between the screw and the balls, as well as the freeplay. Simulation results reproduce what were seen in the test. It is found that the contact stiffness and freeplay dominate the dynamic characteristics of the fin-actuator system. In the flutter analysis, the angular responses of the actuator stimulated by different angular step commands under both contact stiffness assumption and constant stiffness assumption are compared. The results show that a limit cycle ossllation (LCO) domain and an unstable domain exist under the constant stiffness. Its critical velocities do not vary with the freeplays. However, besides the LCO and unstable domains, a stable domain appears under the contact stiffness. At a specific flow velocity, its critical command angle is higher than the one under constant stiffness. But its critical velocity decreases as the freeplay increases, and even reaches a lower level than the critical velocity under constant stiffness. Enough attention should be paid to this issue.