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In-the-loop simulation Actual car Hardware Dynamic model Car 3 Dynamic model Car 1 Dynamic model Car 1 Dynamic model Car 3 Dynamic model Car 2

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To investigate and understand conditions of mutual contact and collision impact between a wheel-flat and a roller rig, we first did a bench test of a bogie with the wheel flat on the roller rig. In the bench test, the effect of the rotational speed of the wheel and the sprung mass on the vertical acceleration of an axlebox was observed. Based on the results of the bench test, we built a dynamic simulation model of the bogie composed of the rigid bodies. By comparing the vertical accelerations of the axlebox calculated by the model with those by the bench test, we could verify that the calculation results of the simulation model provided good agreement with the experimental ones. The model calculation made clear that the wheel rotated contacting the roller rig continuously up to the speed of 10 km/h, and at higher speed had a short period during which the wheel did not contact with the roller rig at the beginning of the flat. When there were any contactless periods, the maximum value of the vertical contact force occurred at the moment of the collision impact just after the contactless state. Particularly at 25 km/h, the impact spot was located around the area from the center to the end of the wheel-flat, and it was revealed by the result of the simulation that differences in the potential energy stored in a compressed axle spring result in differences in the collision velocity of the wheel to the roller rig in a higher speed range than 25 km/h according to the load on the bogie.