Nonlinear Modal Testing and Analysis of Multiple Degree of Freedom Engineering Structures using a Frequency Domain method

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Despite the combined improvements in computing power and modelling capabilities one major hindrance to optimal design is the present incapability to capture experimentally (identify) nonlinear dynamic behaviour which characterise many engineering structures. It can be argued that a step-change in the accuracy of structural dynamics prediction capability (i.e. the accuracy of the models used for simulations) can only occur if the nonlinear characteristics are opportunely captured and modelled. Currently, it is standard engineering practice to apply techniques that can provide an answer to whether or not the system being tested is nonlinear but do not help to identify the type and magnitude of nonlinearity. There is thus scope for implementing, within a standard dynamic experiment, a method for 'detection and quantification' of the nonlinear behaviour. Experimental Modal Analysis, or Modal Testing, is practiced on a daily basis in dynamics labs of universities and industries alike. The final goal is to transform a set of measured data into a set of modal parameters which eventually will allow the (re)construction (or validation) of a spatial model (most notably a Finite Element model). However, the theory developed to perform modal analysis so far ceases to be valid if the vibrating structure exhibits nonlinear behaviour. The work proposed in this project intends to initiate a more structured effort for the continuation and the expansion of theory and practice of modal analysis in nonlinear structural dynamics. This proposal responds to the need of introducing a novel modal analysis technique for nonlinear structures which aims, at least to a first degree of approximation, to extract type and magnitude of structural nonlinearity from measured frequency response functions. This is necessary in order to progress beyond the current boundaries of the well established linear techniques set decades ago and which no longer suffice to respond the expanding capabilities of simulation methods such as the finite elements.