The Numerical and Experimental Characteristics of Multimode Dry-Friction Whip and Whirl

The nature of dry-friction whip and whirl is investigated through experimental and numerical methods. A test rig was designed and constructed to demonstrate and record the character of multimode dry-friction whip and whirl. These tests examined steady-state whip and whirl characteristics for a variety of rub materials and clearances. A simulation model was constructed using tapered Timoshenko beam finite elements to form multiple-degree-of-freedom rotor and stator models. These models were reduced by component mode synthesis to discard high-frequency modes while retaining physical coordinates at the rub location to model rotor-stator interaction using a nonlinear contact model with Coulomb friction. Simulations were performed for specific test cases, and compared against experimental data; these comparisons are favorable. Experimental data analysis showed multiple whirl and whip regions, despite claims of previous investigators that these regions are predicted analytically but not produced in simulations or experiments. Spectral analysis illustrates the presence of harmonic sidebands that accompany the fundamental whirl solution. These sidebands are more evident in whip, and can excite higher-frequency whirl solutions.