Truck hunting of rail freight vehicles is investigated on a tangent (i.e., straight) track with the carbody moving at a certain constant forward velocity. The truck has three degrees of freedom in the lateral, yaw, and parallelogramming directions. The method of describing functions is employed for the investigation of hunting. The three nonlinear differential equations of motion are thus converted to a set of six coupled nonlinear algebraic equations which are solved to obtain the values of the frequency, three amplitudes and two phase angles when hunting exists. It is shown that when hunting begins to occur at the critical speed, the amplitudes are small enough that the flanges do not contact the rails. Flange contact occurs when the speed is increased to a value beyond the critical speed. It is shown that when hunting exists, the values of the frequency, amplitudes and phase angles are such that the energy input per cycle is exactly balanced by the energy dissipated. The orbital stability of limit cycles is investigated by employing the energy balance. The effects of the various parameters on hunting are investigated by parametric studies.

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