Browsing by Author "Friswell, I. M."
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Item A Mass or Stiffness Addition Technique for Structural Parameter Updating(International Journal of Analytical and Experimental Modal Analysis, 1992-07) Nalitolela, Noel Gerald; Penny, J. E. T.; Friswell, I. M.Most methods used to update dynamic structural models use either frequency response data or both eigenvalues and mode shape data. This paper presents a technique to adjust the parameters using eigenvalues alone. Eigenvalues may be measured very accurately whereas mode shapes often contain substantial errors. The structure and its theoretical model are perturbed by adding mass of stiffness. The measured eigenvalues before and after each mass or stiffness addition are used to update the parameters by sensitivity analysis. It is shown that with error-free data and a proper choice of the perturbing coordinates, exact parameters can be identified from eigenvalues alone using unconstrained optimization. Due to measurement errors and possible inaccuracies in the structure of the model matrices, the parameters of a real structure are adjusted by incorporating a constraint of minimum changes from the initial estimates using a Bayesian estimator.Item Updating Model Parameters by Adding an Imagined Stiffness to the Structure(Academic Press, 1993-03-03) Nalitolela, Noel Gerald; Penny, J. E. T.; Friswell, I. M.A mass addition technique for structural parameters updating has recently been described by the authors. It uses eigenvalues of the structure, before and after it is perturbed by adding mass, to adjust selected parameters by sensitivity analysis. The technique avoids the use of noisy mode shape data and overcomes the problem of a non-unique set of parameters when eigenvalues alone are used. However, it is not suitable for a large structure because of the difficulty of adding the necessarily large perturbing mass to the existing structure. This paper presents an alternative technique. An "imagined" stiffness is added to the structure and the FRF of this perturbed structure is obtained from the measured FRF of the original structure by a simple structural modification technique. The eigenvalues of the original and perturbed structures are obtained from the measured and constructed FRFs respectively. These eigenvalues, together with the eigenvalues predicted from an analytical model of the structure, are used to adjust the structural parameters by sensitivity analysis. The technique is demonstrated by a simulated example and by an experiment on an H-frame.Item Updating Structural Parameters of a Finite Element Model by Adding Mass or Stiffness to the System(1993) Nalitolela, Noel Gerald; Penny, J. E. T.; Friswell, I. M.