Towards the Identification of Wheel-Rail Contact Forces
Licentiate thesis, 2010
The accurate determination of the contact forces between rail and wheel is essential in
the analysis of different kinds of rolling contact fatigue. As the contact forces cannot be
measured directly in the field, one approach is to measure the strain at certain positions
of an instrumented wheel. Upon employing signal processing techniques, the forces can be
estimated. However, such a scheme typically involves restrictions in terms of the choice of
spatial and temporal discretization of the underlying equations of motion or a neglect of
the inertia terms.
In this work, the vertical contact force is determined by the solution of an inverse problem.
A minimization problem is considered in which the time-history of the contact force
is sought such that the discrepancy between the predicted and the measured strains is
minimized. A particular feature of this formulation is that the discretization of the pertinent
state equations in space-time, the sampling instances of the measurements and the
parameterization of the sought contact force are all independent of each other. Additionally,
a well-established mathematical framework can be exploited to analyze the effect of
measurement noise as well as devise suitable strategies for regularization. Moreover, the
convergence of the spatial and temporal discretization of the model and the time parameterization
of the contact force history are investigated.
In the first paper of this work, the proposed strategy is evaluated for a simplified 2D disc
with focus on the temporal discretization. In addition, sensitivity to noise and improvements
due to proper regularization are investigated. In the second paper, the identification
strategy is modified by applying virtual calibration in order to compensate for spatial mesh