Dynamic study of a structure with flexion-torsion coupling in the presenceof dry friction

In aero engines, blade vibrations are frequently reduced by centrifugal fly weights, which exert a dry friction force per unit length under blade platf orms. The response of this system to a periodic load has been analysed expe rimentally and theoretically. From a model having mode shapes similar to th ose of a blade, and a dry friction link per unit length, we show that the p resence of the dry friction link is very effective in reducing vibrations f or a range of excitation loads. The theoretical analysis is based on the Cr aig and Bampton mode synthesis, the rigid movement of the platform in its p lane and the replacing of the linear dry friction link by several discrete parallel systems. Direct integration of the equations of motion is carried out by using the Newmark method. The comparison with experimental results i s good. This method can easily be extended to more complex structures and s hows that the dry friction link is effective when stick-slip occurs in the contact zone by limiting the energy provided to the system.