Inverse Identification of Dynamic Wheel-rail Contact Forces

Abstract: Accurate evaluation of contact forces between wheel and rail is essential in the assessment of vehicle performance and to predict consequences of dynamic vehicle-track interaction. As the contact forces can not be measured directly in the field, one common approach is to measure the strain or acceleration at various positions on a wheel or wheel axle. 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, 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 sensitivity. In the third paper, 3D finite element model of the rotating wheel is introduced and the measured strains are combined using two Wheatstone bridges to estimate the contact force by static calibration technique. The inverse identification strategy is adopted for the designed measurement system. In the fourth paper, inverse identification using individual strains and inverse identification using the statically calibrated force are discussed. Furthermore, an economic approach for calculating the sensitivities is presented. Effects of centrifugal and gyroscopic terms in the equation of motion and consequences of noise in the measurement are evaluated. In the fifth paper, Three different identification strategies, static calibration, Kalman filter and inverse identification are compared on realistic load cases using DIFF to generate synthetic strains.