Keywords: wheel flat identification, fibre optic rail pad sensor, steady state response, genetic algorithm, dynamic interaction, wayside monitoring.

Railways experience a significant set of problems associated with dynamic interaction of the train-track system. These problems mainly stem from existing wheel and track defects. In this paper, a possible way of vibration-based monitoring is investigated. The major component of the monitoring system is the fibre optic rail pad sensor (FORPS), which essentially serves as a rail pad as well as a load cell that can sense the load acting on it. To identify the wheel flat using the FORPS, two methods are proposed. One is by impact load estimation. After getting the force time history of the rail pad from the sensor, wheel-rail interaction force can be initially predicted by using the steady state response as a map to mapping the pad-force back into the impact force. Subsequent correction step is needed to take account of the impact effect caused by the wheel flat. Apart from directly geometric measurement devices which have to be used under low speed conditions, few methods can give the identification of wheel flat size under normal operation speed. The other method proposed here using genetic algorithm (GA) is capable of identifying the size of the wheel defect, i.e. length and depth of the wheel flat as well as the position where the impact happens.

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