Understanding Complexities in Underplatform Damper Mechanics

All numerical models of friction damped bladed arrays require knowledge or information of contact-friction parameters, which are established either through direct frictional measurements, done with the help of single contact test arrangements, or by fine tuning the parameters in the numerical model and comparing the experimental response of damped blade against its computed response. Some critical assumptions are necessary to the purpose, such as the position and extension of the real contact areas and the values of local friction coefficients.In the light of recent results from direct measurements on under-platform dampers [1–3] it became evident that a dedicated routine for the damper mechanics is a much more effective tool to capture those finer details which are essential to an appropriate description of damper behaviour. This was made possible by the successful effort of the present authors to accurately measure the forces transmitted between the platforms through the damper and to relate them with the relative platform movement [2].Simulations, and the matching experiments which are here not described, are performed under so called out-of-phase (O-O-P) and in-phase (I-P) condition simulating the two basically important motion types. Damper forces and damper kinematics are discussed for two highly representative cases in the low frequency range. Diagrams are then used to show the sensitivity to contact parameters, input motion and initial conditions on damper behaviour, casting heavy doubts on the validity of oversimplified practices.Copyright © 2014 by ASME