Modal Analysis of Complex Structures Using the Finite Element Method

Cook, Graham (1986) Modal Analysis of Complex Structures Using the Finite Element Method. MSc(R) thesis, University of Glasgow.

Abstract

The subject dealt with concerns Finite Element analyses of complex structures. In particular the area studied is the determination of the natural frequencies and mode shapes of centrifugal-type impellers and the impact of this analysis on human and computer resources. This investigation was carried out during a Teaching company project between Glasgow University and James Howden and Company Ltd, involving optimisation of modal analysis of James Howden impeller products using the PAFEC FE package. The object was to maximise the accuracy of the analysis results whilst minimising both computer effort and man effort required for the analysis. As well as investigations of simple structures, several impeller structures were modelled and analysed, and some results verified experimentally. Different modelling techniques were used and several element types considered. The full analysis was considered, ie pre-modelling steps; modelling the structure; analysing the structure; and interpreting the results. The accumulation of specific results on good modelling practice allowed a Design Guide to be produced for James Howden which could lead an inexperienced FE analyst to produce an accurate model of a centrifugal impeller and from this produce natural frequency results in an accuracy band of +14% to -3.5%, utilising the minimum computer effort. The examples of good modelling practice and considerations required in complex FE analyses are transferable to many different types of analysis and many different types of FE package. The main conclusions of the investigation include the careful considerations necessary for different stages of an FE analysis, particularly when a complex structure is being analysed. Results from simple analyses are not transferrable to complex analyses and often methods and element types used do not produce the required results. However objective evaluations such as this one on a "family" of structures such as centrifugal impellers can produce guidelines which do not rely on the "art" or expertise of the FE analyst. As computing time becomes an increasingly precious resource in engineering companies, labour-saving aids and minimisation of computer effort required are actively sought. This investigation considers and advises on both of these.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Mechanical engineering
• Date of Award: 1986
• Depositing User: Enlighten Team
• Unique ID: glathesis:1986-76655
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 13:57
• Last Modified: 19 Nov 2019 13:57
• URI: https://theses.gla.ac.uk/id/eprint/76655