ESTIMATION OF IN-PLANE ELASTIC PARAMETERS AND STIFFENER GEOMETRY OF STIFFENED PLATES

An investigation on stiffened plates has been conducted for the first time to determine the elastic parameters as well as the cross-sectional dimensions of rectangular stiffeners from experimental modal data and finite element predictions, using model-updating technique. The problem is formulated as a global minimization of the error function, defined by the difference in modal properties as predicted from the finite element modelling to that obtained “experimentally”. The parameter estimation problem is solved using an iterative-gradient-based minimization algorithm and can start from different randomly selected set of initial parameters. The Levenberg–Marquardt algorithm has been implemented to minimize the error function. Proper bounds are realistically chosen for the selection of the initial values of the parameters. The position, physical properties and orientation of stiffeners create considerable variations in the modal properties as compared with the bare plates of similar construction. This makes each of the stiffened plate identification problem rather unique. The position of stiffeners as well as its orientation makes certain measurement points more suitable for comparing analytical and experimental mode shapes. The optimum measurement set of co-ordinates, which can be used for the purpose of identification, is thus case specific. The geometrical properties of stiffener cross-section also affect the modes. Inclusion of different sets of modes in noisy environment and the differences in the estimated parameters are studied. A few simulated examples are presented to investigate the uniqueness and convergence of results. The methodology is found to be very accurate and robust.