Research on modeling and dynamic characteristics of complex coaxial rotor system

Abstract

Abstract. To make up deficiency of the finite element method in predicting nonlinear dynamic characteristics of coaxial rotor systems, nonlinear dynamic model of a coaxial rotor system was established with a method combining the finite element method and the fixed interface modal synthesis method. Then an implicit time domain method was presented to solve the nonlinear equations of motion thus dynamic characteristics of the rotor system can be obtained. The computational efficiency of this method largely depends on the number of degrees of freedom with nonlinear forces acting on. With nonlinear forces of squeeze film damper and intermediate bearing considered, nonlinear dynamic response characteristics of the coaxial rotor system under multiple unbalance forces were studied in this work. The results showed that the unbalance excitation frequencies are dominant in the responses of the rotor system. Besides, due to coupling effect of the intermediate bearing some combinations of the unbalance excitation frequencies were also observed in the spectrogram. Stability and periodicity of the rotor system was investigated with bifurcation diagram, Poincare map and phase diagram. It was found that the rotor system executes multiple periods orbital motion under relatively low rotational speeds. With the increasing of rotational speed, the rotor system would execute quasi-periodic motion, chaotic motion and periodic motion again. The quasi-periodic motion and chaotic motion are closely related with the SFD. Finally, under relatively low speed, the nonlinear model was validated by comparing the simulation results with the experimental data. The proposed modeling and solving method is expected to provide theoretical and engineering basis for improving prediction of nonlinear dynamic characteristics of complex rotor systems.

Instability threshold analysis and optimization of a rotor system considering the Alford force

“…The inertia matrix, damping matrix, gyrscopic matrix and stiffness matrix of the rotor system shown in Fig. 4 are established with Timoshenko beam theory [14]. At the same time, the effect of the cross stiffness caused by the Alford force at the impeller and the turbine are considered.…”

Coupling Vibration Analysis of Turbine Shared Support Rotor-Bearing System with Squeeze Film Dampers

“…The unbalanced force F e [19,20] established a dynamic model of a rotor-bearing system with intermediate bearings; they calculated the critical speeds and vibration modes of the system and verified them with a single-rotor test system, but the established analysis model did not consider nonlinear factors. Wang et al [21] established a rotor-bearing model that considered intermediate bearings and nonlinear SFD characteristics, and they carried out a rotor-bearing test to verify their proposed model-ing and analysis methods; their research results indicated that it is feasible to build a complex dual-rotor-bearing system with SFDs and bearings using Timoshenko beam elements. The FE modeling method using Timoshenko beam elements has now developed into an effective method for establishing dynamic models of complex rotor-bearing and whole-engine systems in aeroengines with nonlinear characteristics.…”

“…The mass matrix m e , stiffness matrix k e , and gyroscopic matrix g e of the shaft segment are given in Equations ( 2)-( 5), the derivations of which are given elsewhere [21].…”

Coupling vibration analysis of turbine shared support rotor-bearing system with squeeze film dampers

“…The mass matrix e m , stiffness matrix e k , and gyroscope matrix e g of the shaft segment are given in Eqs. ( 2)-( 5), the derivations of which are given elsewhere [21]:…”