The following references were consulted when creating this example problem:
Nelson, H.D. & McVaugh, J. M. (May, 1976). The dynamics of rotor-bearing
                    systems using finite elements. ASME Journal of Engineering for
                        Industry.
Beley, A., Rajakumar, C., & Thieffry, P. (2009). Computational methods for
                    rotordynamics simulation. NAFEMS World Congress.