The genetic algorithm method has been utilized with a thermomechanical model to determine an optimum welding sequence. The thermomechanical model developed for this purpose predicts residual stress and distortion in thin plates. The thermal history of the plate is computed using a transient two-dimensional ®nite element model which serves as an input to the mechanical analysis. The mechanical response of the plate is estimated through a thermoelastic-viscoplastic ®nite element model. The proposed model is veri®ed by comparison with the experimental data where available. By choosing the appropriate objective function for the considered case, an optimum welding sequence is determined by a genetic algorithm.

In this research, an empty freight wagon with Y25 bogies have been modelled. Non-linear creep forces with spin moment between wheel and rail have been used, and also all impacts and friction forces have been modelled. Non-linear equations of motion and kinematical constraints have been solved in time domain, and limit cycles, saddle nodes, and critical speeds have been shown. Both primary and secondary hunting can be seen in the responses of the wagons. The relation between frequency of oscillations and speed can be seen, also, there are chaotic oscillations. Results show that stiffness in impacts affects calculation time and limit cycles.

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In the current research an empty freight wagon with BA652 and an old BA661 bogies have been modelled. Non-linear creep forces with spin moment between wheel and rail have been used and also all impacts and friction forces have been modelled. The characteristics of primary suspension systems for BA652 and an old BA661 have been evaluated by means of test. Non-linear equations of motions and kinematical constraints have been solved in time domain and limit cycles have been showed. Both primary and secondary hunting can be seen in responses of wagon. For BA652 there are non-linear and linear critical speeds and also saddle nodes but for old BA661 the situation is too critical and the system can oscillate in very low speeds.

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