Reduction of Rotor-Bearing-Support Finite Element Model through Substructuring

Authors: Abdur Rosyid, Mohamed El-Madany, Mohanad Alata

Abstract:

Due to simplicity and low cost, rotordynamic system is often modeled by using lumped parameters. Recently, finite elements have been used to model rotordynamic system as it offers higher accuracy. However, it involves high degrees of freedom. In some applications such as control design, this requires higher cost. For this reason, various model reduction methods have been proposed. This work demonstrates the quality of model reduction of rotor-bearing-support system through substructuring. The quality of the model reduction is evaluated by comparing some first natural frequencies, modal damping ratio, critical speeds, and response of both the full system and the reduced system. The simulation shows that the substructuring is proven adequate to reduce finite element rotor model in the frequency range of interest as long as the number and the location of master nodes are determined appropriately. However, the reduction is less accurate in an unstable or nearly-unstable system.

Keywords: Finite element model, rotordynamic system, model reduction, substructuring.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1089269

References:

[1] Lund, J.W., Review of the Concept of Dynamic Coefficients for Fluid Film Journal Bearings. Journal of Tribology, 1987. 109(1): p. 37-41.
[2] Khonsari, M.M. and E.R. Booser, Applied Tribology: Bearing Design and Lubrication, 2001: John Wiley & Sons, Inc.
[3] Childs, D., Turbomachinery Rotordynamics: Phenomena, Modeling, Analysis, 1993: John Wiley & Sons, Inc.
[4] Wagner, M.B., et al., Model Reduction Methods for Rotor Dynamic Analysis: A Survey and Review. International Journal of Rotating Machinery, 2010. 2010: p. 1-17.
[5] Das, A.S. and J.K. Dutt, A reduced rotor model using modified SEREP approach for vibration control of rotors. Mechanical Systems and Signal Processing, 2012. 26: p. 167-180.
[6] Abduljabbar, Z.S., M.M. El-Madany, and A.A. Al-Abdulwahab, On the Dynamic Analysis of Rotor-Bearing Systems Using Finite Elements, 2005.
[7] Cook, R.D., Finite Element Modeling for Stress Analysis, 1995, USA: John Wiley & Sons.
[8] Jones, S., Finite Elements for the Analysis of Rotor-Dynamic Systems that Includes Gyroscopic Effects, in Mechanical Engineering Department, 2005, Brunel University.
[9] Logan, D.L., A First Course in the Finite Element Method. 4 ed, 2007, India: Thomson.
[10] Pilkey, W.D., Geometric Properties of Planes, in Formulas for Stress, Strain, and Structural Matrices, 2008, John Wiley & Sons: NJ, USA.
[11] Bethel, L.L., et al. Critical Speeds and the Importance of Stiffness - A Case Study in the Design and Testing of a Large Mechanical Drive Steam Turbine to API Standard 612 in Proceedings of the Twenty-Second Turbomachinery Simposium.