Vibration analysis of mistuned damped blades with nonlinear friction and contact

In general, only in tangential direction, friction motion between blade dampers is concerned for vibration analysis of mistuned bladed disk. However, in practical, excitation acting on blades inevitably causes normal movement at friction interface due to the existence of angle between excitation force and contact surface. This fact leads to a variation of normal force or even a result of contact separation, which determine the maximum static friction for tangential frictional vibration. In order to assess the realistic nonlinear forced vibration of mistuned disk assemblies subjected to actual excitation with nonlinear friction and contact, an efficient method is developed by using large-scale finite element model and two-dimensional friction model. In the proposed paper, attentions are paid on the realistic coupled vibration and the impact of variable normal vibration on forced response to a traveling wave excitation. Three types of mistuned parameters, including tangential stiffness of friction surface, initial shroud gap (corresponding to preload normal force), and structural stiffness of blades are taken into account for analyzing the effect of mistuning on the coupling vibration, especially for cases of contact separation. Furthermore, by means of curve fitting of amplitude variation of normal forces, the dependence of friction motion of bladed disk studied at circumferential resonance on variation of axial displacement, even with contact separation involved, is addressed. The results show a complex nonlinear vibration with friction and contact, especially a complex multiple unstable vibration observed with repeated nonlinear snap at circumferential resonance for the cases of contact separation. With regard to a small initial normal force, a large amplitude value of force variation can greatly reduce the maximum response amplitude for mistuned blades, which is worth to pay attentions for the vibration analysis of bladed disk with nonlinear friction and contact.