A Contribution to the Dynamic Simulation of Nonlinear Rotating Machines with Fluid Dynamical Coupling Elements

Abstract

In this paper a simulation program for nonlinear rotordynamic analysis that allows to calculate the bending vibrations of systems with many degrees of freedom (DOF’s) is presented. The program is based on the Finite Element Method in combination with a modal substructure technique to reduce the system’s equations of motion. The solution of this nonlinear system is performed in time domain with a bimodal decoupling procedure in combination with a polygon method. The fluid dynamic coupling elements available in the program are seals (smooth and grooved) and journal bearings (circumferential, multi-lobe and tilting-pad). Whereas the seals may be modelled linearly, the journal bearings must be modelled nonlinearly, in the case of large excitation forces or of vertical machines. It is shown that the use of force tables to model the nonlinear bearing forces is a very fast method to realize parametric studies.