Nonlinear modelling and parameter influence of supercritical transmission shaft with dry friction damper

Supercritical transmission shafts, which have one or more critical speeds below their working speeds, are becoming more popular in new rotorcraft designs. To attenuate the excessive transcritical vibration, dry friction damper is a prevailing choice. In this paper, we focus on the basic working mechanism and parameter influence of the dry friction damper for supercritical transmission shaft. Mathematical model of the dry friction damper, which fully considers the nonlinear rub-impact and side-dry-friction effects, is proposed and integrated with finite element model of the transmission shaft to investigate nonlinear interactions between the shaft and damper. It is demonstrated through systematic numerical simulations that a typical transcritical response with dry friction damper can be divided into 4 sub-regions and the dry friction damper takes effect only within region II and III respectively through hard-stopping and side-dry-friction effects. In addition, effects of nonlinear bearing force, transcritical acceleration and initial location of the damper are discussed in detail. Moreover, influences of 3 key damper parameters, that is the rub-impact clearance, the critical slip force and the circumferential friction coefficient, are further investigated, which provides a guidance for designs of the dry friction damper. Finally, prototypes of the dry friction damper are designed, manufactured and tested on a rotor dynamics test rig. For the first time, the theoretical analysis and numerical simulation results are quantitatively verified by an experiment.