Multiple response levels of structures with wedge friction dampers

Wedge dampers are widely used in turbomachines to reduce the amplitude of blade vibrations. Computation of the forced response of turbine blades in the presence of these dampers will give non-unique solutions due to the possibility of having different contact forces that still satisfy the equilibrium. In the paper, the response variability, in terms of upper and lower limit, is investigated for a lumped-parameter system simulating multiple wedge dampers pressed between adjacent vibrating blades. An optimization algorithm is developed by considering, as further dofs of the system, a series of coefficients representing the ratio between the tangential force and the Coulomb limit, assumed as initial hypothesis in the construction of the hysteresis loop within the contact model. This algorithm maximizes or minimizes the loss factor of the system, allowing the response limits to be identified. Several combinations of preload and geometry of the dampers are considered, and the evolution of the variability of the dynamic response of the blades is then investigated.