Dynamics of a rotor-structure-soil system: transient response by iterative coupling

Abstract

In this paper, the transient dynamics of a rotor-foundation-structure-soil system is studied to obtain unbalance response of the rotor considering the influence of the structure and the unbounded soil. Transient responses are obtained through iterative coupling between the rotor subsystem and the frame-soil subsystem. The non-linear rotor subsystem is represented by a Laval rotor with rigid bearings and external and internal damping. These equations of motion are solved with the fourth-order Runge-Kutta method. The frame is modeled by the Finite Element Method, while the homogeneous half-space is modeled by the 3D Direct Boundary Element Method in the frequency domain. To derive time-domain equivalent equations of motion, a methodology is proposed based on extracting modal parameters from Frequency Response Functions of the coupled soil-foundation system, using the Rational Fraction Polynomial Method. The methodology renders transient response for the rotor and structure with small time steps, allowing an accurate simulation of the rotor runup phase and the dynamics of the system going through resonance frequencies.