Modal analysis for finite element updating

Finite element modeling is usually need for investigating the dynamic properties of a machine structure. In order to verify the validity of the finite element model, the simple and reliable way is modal testing. From modal testing, the frequency response functions (FRF) and the modal parameters (natural frequencies and mode shapes) of the structure can be found. The finite element models usually make some assumptions in order to simplify the problem. Dynamical parameters predicted by finite element method usually differ from those by modal analysis measurement. Thus, how to update finite element models to make the dynamical parameters approach those of the modal analysis is an important problem. Updating of the finite element model is a difficult problem, since it is an inverse process and is highly nonlinear. A method is developed to shift natural frequencies to approach the results of modal analysis by changing elements of the finite element model. The updating method is established at first. It can shift one or two natural frequencies to the desired or assigned frequencies. Finally a finite element model and real structure example are used to ii lustrate the procedure and to evaluate the effectiveness of the update method.