Development of a Numerical Model for Dynamic Analysis of a Built-Up Structure by a Two-Step FEM-Test Correlation Approach

Abstract

A finite element method (FEM) model of a lightly damped built-up structure was developed based on a two-step approach. The approach utilizes the fact that damping changes natural frequencies very little but the resonance amplitudes significantly. In the first step, stiffness property of the model is refined by correlating natural frequencies obtained from test and FEM model while neglecting the effect of damping. In the second step, damping properties are identified by matching the resonance amplitudes of the system obtained from the FEM model with those obtained from measurement. As a demonstration, the approach was applied first to a simple cantilevered beam structure, then a simplified vane assembly structure clamped into a fixture. The two-step approach was applied to the vane assembly in the free-free configuration, then the assembly clamped in a cantilever form. It was shown that the proper boundary condition of the FEM model can be identified by adjusting the contact stiffness at the clamped edge. Various different damping models were adopted to identify the damping property of the model. It was shown that different models lead to slightly different forced responses of the system. Typical applications and limitations of the correlated model are discussed with some practical examples.