Using pattern search algorithm and finite element method to detect rotor cracks

Abstract

The vibration pattern of a rotor system reflects the mechanical parameter changes in the
system. Hence, the use of vibration monitoring is considered as a possible means of detecting the
presence and growth of the cracks. In this paper, a pattern search based method for shaft crack
detection is proposed and described which formulates the shaft crack detection as an optimization
problem by means of finite element method and the utilizes the pattern search algorithm to search the
solution. Using a direct search method avoids some of the weaknesses of the traditional gradient
based analytical search method, including the difficulty in constructing well-defined mathematical
models directly from practical inverse problems. First, a finite element code was developed for
analyzing a rotor system with open cracks. To extract the flexibility matrix of an element containing
cracks an exact integration scheme was adopted which is more accurate than the conventional
methods. Then, the crack detection method was formulated as an inverse problem which can be
solved by optimization algorithms. The numerical simulations suggest that good predictions of shaft
crack location and depth are possible and the proposed method is feasible.

Keywords

Crack Detection, Rotor Dynamics, Pattern Search Algorithm, FEM