Shimmy performance analysis and parameter optimization of a dual-wheel nose landing gear coupled with torsional nonlinear energy sink and considering structural nonlinear factor

Accurate shimmy prediction and effective oscillation suppression are essential for aircraft design as shimmy oscillation remains a significant concern in landing gear dynamics. In this paper, a torsional nonlinear energy sink (NES) based on the cam-roller mechanism is designed as a passive shimmy suppression device, the dynamical model of the dual-wheel nose landing gear (DW-NLG) coupled with torsional NES and considering structural nonlinear factor is established, including shock absorber, Coulomb friction and freeplay nonlinearities. The influence of shock absorber, Coulomb friction and freeplay as well as their interaction and simultaneous effects on the DW-NLG shimmy are studied in detail, which are mainly represented by the bifurcation analysis, together with corresponding time history, phase portrait and frequency spectrum for selected input parameters. The structural parameters of the torsional NES are also optimized to enhance its shimmy performance. The results show that considering the shock absorber could significantly increase the torsional shimmy area and limit cycle oscillation (LCO) amplitude, while its effect on lateral shimmy is opposite. The Coulomb friction is beneficial to decrease the torsional shimmy area and has trivial impact on the lateral shimmy, and it changes the criticality of torsional shimmy and leads to subcritical Hopf bifurcation. The torsional freeplay increases the torsional shimmy area while decreases the lateral shimmy area. The optimized torsional NES based on the genetic optimization algorithm further enhances the DW-NLG shimmy performance and shows its advantage in suppressing the DW-NLG shimmy.