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Title: Nonlinear dynamics and rolling-sliding wear in a free floating cam follower with seven degrees-of-freedom
Author: Stewart, Donald
ISNI:       0000 0001 3483 903X
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2006
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This thesis considers the dynamics of a free floating cam follower in a hydraulic motor.  The follower consists of a rod which forms a metal-to-metal seal against a rotor and is subject to rolling-sliding wear. A mathematical model was constructed to study the nonlinear dynamics and wear of the rod.  In particular, two wear phenomena frequently observed in the field were of interest, namely a barrelling type of wear in which the rods would suffer significantly higher wear towards the ends than in the middle, and a polygonisation type of wear in which the rod would be worn to a generally hexagonal, pentagonal or square profile. Initially a 3 degree-of-freedom planar model was constructed.  An analysis of the friction coefficients of the rotor and stator was carried out, and revealed the importance of maintaining a lower coefficient of friction on the stator than on the rotor in order to ensure that the rod continued to roll on the rotor. This was followed by a 7-degree-of-freedom modelling 3 dimensions.  In this model the rod is modelled as two shorter rods connected at a pivot point with rotational stiffness located at the centre of mass of the real rod.  CFD analysis was used to model the fluid forces acting on the rod. A wear rig was constructed to carry out wear experiments with differing rolling:sliding ratios.  The outputs from these experiments were used to calibrate an Archard-type wear model in the mathematical model.  Wear patterns could then be iteratively fed back in to the mathematical model and the evolution of the wear pattern studied.  The results of this approach are contrasted with models where wear is only calculated at the end of a simulation, and demonstrate that it is necessary to iteratively feed back wear into the geometry of the model to correctly model wear over a long period.  Mechanisms for both polygonisation and barrelling wear are shown to exist from the dynamics of the 7 degree-of-freedom model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available