EXPERIMENTALLY OBTAINED BIFURCATION PHENOMENON IN CHAOTIC TRACTOR VIBRATING IN TIME AND FREQUENCY DOMAIN.

This paper investigates through experimental methods the dynamic characteristics of a farm tractor by changing the forward velocity from 0.63 m/s to 4.50 m/s. Nonlinear time series, frequency spectrum and continuous wavelet transform were used in the analysis. From the nonlinear time series analysis, a nonlinear resonance of the tractor vibration occurred at forward velocity of 2.15 m/s. The existence of a subharmonic frequency at 4.32 m/s indicated chaotic dynamics that was confirmed by the trend of the Lyapunov exponent analysis with a positive exponent indicating chaos. Continuous wavelet transform analysis results, presented graphically, called coefficient plots showed patterns composed of large and fine feature distribution in both time and scale. Quasi-periodic velocities of 1.95 m/s and 2.15 m/s were estimated by these coefficient plots. At forward velocity of 2.88 m/s, the coefficient plots showed dominant features that varied periodically and were estimated to be a period-doubling vibration. The coefficient plots during chaotic vibration at 3.52 m/s, 4.02 m/s and 4.32 m/s showed various feature distributions. At forward velocities of 0.95 m/s and 1.42 m/s, the existence of features with scale values of almost equal and half of the dominant feature was due to the influence of the gravel road surface and not to the artificial test track profile. Experimentally obtained bifurcation was observed clearly from the coefficient plots that showed three different patterns from quasi-periodic vibration at 2.15 m/s, period-doubling at 2.88 m/s and chaos at 3.52 m/s. [ABSTRACT FROM AUTHOR]