Joint identification in structural waveguides using wave reflection and transmission coefficients

Abstract

The dynamic modelling of one-dimensional jointed structures is relevant to many engineering applications, such as pipe systems and beam networks in constructions. Currently available techniques are undermined by inadequate ability to model the joints and other discontinuities due to uncertainty in their properties. Measured modal data can be used to update joint models, but often with limited success. In this thesis a wave approach is employed to investigate the reflection and transmission coefficients of various joint models in structural waveguides. The reflection and transmission coefficients are potentially more sensitive to the parameters of the joint models. Numerical simulations and experiments have been performed on three types of jointed waveguides. Appropriate models have been identified for these cases and sensitivities of the scattering coefficients to joint parameters have been investigated. Accurate measurement of the reflection and transmission coefficients is desired in order to estimate joint parameters. A noise model is developed and a perturbation method is used to study the influence of measurement noise on the estimated reflection and transmission coefficients. An iterative method is examined to solve the non-linear problem of estimating the parameters of a joint from measured reflection and transmission coefficients, in a leastsquares sense. Issues concerning the iteration process, such as the selection of objective functions and frequency ranges, are examined in accordance with the sensitivity of the objective function to unknown parameters. The parameter identification method is validated by numerical simulation case studies and then verified by using measured data for mass discontinuities on beams, a supported straight pipe and a right-angled pipe bend. The case studies demonstrate that parameter identification of discontinuities in waveguides by using the wave approach is a success where modal methods are inappropriate.

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