Application of the modal expansion method in the prediction of dynamic responses in a reciprocating compressor interstage piping system

Abstract

Structures and equipment subject to dynamic loading are prone to a shortened life span due to excessive vibration levels, which can lead to fatigue failure of its components. Continuous monitoring of those systems can be a complicated and expensive task, due to the complexity and little or no accessibility to some locations, which makes it difficult to assess the structural integrity. One way to deal with this issue is to use finite element model, output-only modal analysis and the modal expansion method to predict dynamic responses in locations that have not been measured. In this work, three case studies are analyzed. The first two case studies are developed using an aluminum rectangular beam, each one with its respective boundary condition and the third case study was of a real industry system. The experimental modal matrix was obtained through output-only modal analysis and a mixed reduction process using Guyan and the System Equivalent Reduction Expansion Method (SEREP) technique was used to reduce the Finite Element model for each case studied, thus ensuring the compatibility between numerical and experimental degrees of freedom. Model smoothing was carried out using the local correspondence for modes and coordinates, an extension of the LC method. Finally, by using the modal expansion method, the smoothed modal model was used to predict dynamic responses. Results showed high accuracy between the measured and the predicted acceleration signals for all three cases presented.