On the validation of nonlinear dynamic models for structures with frictional joints
File(s)
Author(s)
Pesaresi, Luca
Type
Thesis
Abstract
High cycle fatigue caused by dynamic stresses is one of the main threats for aeroengine components. Friction damping is regularly being used as a passive system
to dissipate the vibrational energy of these components. Due to the presence of
friction contacts, the dynamic behaviour of engine components becomes nonlinear,
making an analysis much more challenging. Various modelling approaches have
been proposed, however due to the complexity of the systems, a standard fully validated approach is still not available. This research introduces a detailed explicit
modelling approach, based on Imperial College long standing experience with nonlinear dynamic modelling, which has been extended, refined and fully validated for the predictions of the dynamic behaviour of structures with frictional joints. The main focus of this research is on the modelling of underplatform dampers, due to their importance to reduce the vibration amplitudes of turbine blades. A new underplatform damper test rig was designed for this scope, and the tests performed
highlighted its ability to reproduce the nonlinear effects caused by the dampers on
the blades dynamics often observed in real engines. The explicit modelling approach
was then validated against the experimental results of the new rig, providing
new insights and guidelines for a state of art damper model. A successful application of the explicit modelling approach to a beam with a frictional bolted
joint further demonstrated the versatility of the approach. Nonlinear model validation
was then further extended to the local contact behaviour by developing suitable
techniques which allow to monitor the stick-slip-separation. Two techniques,
one based on high speed camera and digital image correlation, and the other one
based on ultrasounds, were proposed and tested, showing a promising potential to
provide additional understanding of the contact mechanism at work.
to dissipate the vibrational energy of these components. Due to the presence of
friction contacts, the dynamic behaviour of engine components becomes nonlinear,
making an analysis much more challenging. Various modelling approaches have
been proposed, however due to the complexity of the systems, a standard fully validated approach is still not available. This research introduces a detailed explicit
modelling approach, based on Imperial College long standing experience with nonlinear dynamic modelling, which has been extended, refined and fully validated for the predictions of the dynamic behaviour of structures with frictional joints. The main focus of this research is on the modelling of underplatform dampers, due to their importance to reduce the vibration amplitudes of turbine blades. A new underplatform damper test rig was designed for this scope, and the tests performed
highlighted its ability to reproduce the nonlinear effects caused by the dampers on
the blades dynamics often observed in real engines. The explicit modelling approach
was then validated against the experimental results of the new rig, providing
new insights and guidelines for a state of art damper model. A successful application of the explicit modelling approach to a beam with a frictional bolted
joint further demonstrated the versatility of the approach. Nonlinear model validation
was then further extended to the local contact behaviour by developing suitable
techniques which allow to monitor the stick-slip-separation. Two techniques,
one based on high speed camera and digital image correlation, and the other one
based on ultrasounds, were proposed and tested, showing a promising potential to
provide additional understanding of the contact mechanism at work.
Version
Open Access
Date Issued
2017-05
Date Awarded
2017-08
Advisor
Schwingshackl, Christoph
Hoffman, Norbert
Sponsor
Rolls-Royce Group plc
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)