Select rotor geometry (shaft diameter, length, material) and bearing type (rolling element, hydrodynamic, or magnetic)
Input operating speed in RPM and unbalance mass eccentricity (grams at specified radius)
Run critical speed analysis to compare first and second bending mode frequencies against operating envelope
Review whirl orbits, bearing reaction forces, and damping ratios; adjust stiffness or add balance weights if needed

Worked Example

A steel rotor shaft (diameter 40 mm, length 800 mm, E = 210 GPa, density 7850 kg/m³) mounted on two cylindrical roller bearings spaced 700 mm apart operates at 6000 RPM with an unbalance of 15 grams at 50 mm radius. Simulation yields first critical speed ≈ 4200 RPM and second critical speed ≈ 11800 RPM. At steady state, peak radial vibration displacement is 0.35 mm and bearing load is 2.8 kN per support. Adding a 12-gram balance mass at the anti-node location reduces vibration to 0.18 mm.

Practical Notes

Run Campbell diagram sweeps to identify critical speeds and avoid operating near half-speed whirl instability in lightly damped systems
For turbomachinery (compressors, turbines), include gyroscopic effects if rotor length exceeds 3× diameter
Validate bearing stiffness coefficients experimentally; hydrodynamic bearing stiffness varies nonlinearly with speed and load
Use modal decomposition to isolate forward and backward whirl responses separately