Investigation of steady-state harmonic axial and torsional vibrations of linear rotors under arbitrarily distributed loading using the Numerical Assembly Technique

Most rotor dynamic investigations focus on lateral vibrations, because they are dominant in most rotor-bearing
systems, but torsional as well as axial vibrations are not negligible in a variety of cases. Geared rotor-bearing
systems, for example, often tend to torsional vibrations, axial vibrations can occur in all rotor systems with axial
bearings. Although with today’s computational power, resonance frequencies and other dynamic characteristics
can be calculated even for complex rotor geometries, these calculations can get computationally very expensive.
Therefore, a numerical method called Numerical Assembly Technique (NAT) is used in this paper to investigate
axial and torsional vibrations of rotor-bearing systems. NAT is a quasi-analytical method and therefore no discretisation
of the rotor is required. Consequently, the calculation time is significantly lower. An existing framework,
which is using NAT to calculate the steady-state harmonic response of linear elastic rotor-bearing systems with
discontinuous shaft and arbitrarily distributed mass unbalance is altered to consider axial and torsional vibrations
instead of bending vibrations. The capacity of this NAT framework to take arbitrarily distributed loading conditions
into account is also modified to axial and torsional loading. A numerical example with general load conditions is
presented and a comparison with a FEM result is shown to validate the method.