Improving the reliability of the frequency response function through semi-direct finite element model updating

In this work, a scheme to enhance the reliability of the frequency response function (FRF) for structural dynamics by semi-direct model updating is reported. The proposed semi-direct updating method is a combination of iterative model updating and direct model updating schemes, and comprises three updating steps. First, to match analysis results with test results, the finite element (FE) model is updated with the conventional iterative model updating within the reasonable tolerance limit of eigenfrequencies and mode shapes. Second, to enhance the reliability of the FRF typically showing lower correlation with test results despite the first step model updating, the eigenfrequencies are replaced by the measured ones without updating corresponding eigenvectors. Then, the stiffness matrix is updated by a direct model updating scheme: matrix mixing approach with the mass matrix preserved. Finally, the unmeasured modal damping ratios are obtained by the minimization of FRF error function. As a result, FRFs obtained by the proposed scheme show excellent agreement with test data without losing mass properties together with the updated stiffness matrix reproducing the test data exactly. To demonstrate the accuracy and efficiency of the proposed method, two examples are prepared.