Abstract
Conventional model updating methods are based on frequency response function (FRF) and/or modal parameter estimates obtained from freely suspended, or sometimes rigidly constrained, sub-structures. These idealised boundary conditions are, however, often difficult to realise in a practical scenario. Furthermore, they are in conflict with the requirement that the sub-structure should also be measured whilst under a representative mounting condition. This paper addresses the question whether model updating can be achieved in the presence of an arbitrary or unknown boundary condition using in-situ measurements, i.e. without removing the sub-structure from its assembly. It is shown that some measurable properties, dynamic transfer stiffness and generalised transmissibility, are invariant to sub-structural boundary conditions and can therefore be obtained in-situ. It is further shown that, with minor adaption, existing transmissibility-based updating methods can be applied more widely than previously thought; to sub-structures whose boundary conditions are non-ideal. The theory is verified by a numerical beam example. Application to a resilient isolator is then demonstrated where a finite element model is successfully updated without removing the isolator from its assembly.
Highlights
Model updating describes a class of methods that use experimental data to identify the uncertain parameters of a numerical model [1,2]
In the present paper we propose the application of in-situ experimental testing, and the extraction of invariant sub-structural properties, to update numerical sub-structure models
In summary of this section, we have shown that the dynamic stiffness elements, DAaa and DAac = DTAca, the force transmissibility TAf ca, and the displacement transmissibility TdAca, are invariant sub-structural properties of A, but are all available from measurements conducted in-situ, i.e. with an arbitrary boundary condition at c
Summary
Model updating describes a class of methods that use experimental data to identify the uncertain parameters of a numerical model [1,2]. What’s more, in realworld structures it is often difficult to measure acting forces directly, complicating the measurement of their FRF matrices This issue has led to an increased interest in output only methods for model updating. To successfully update a numerical model based on experimental measurements, the acquired data, whether modal, FRF or transmissibility-based, should characterise the target sub-structure independently; they should be invariant sub-structural properties.. To ensure invariant sub-structure data is acquired, measurements must be performed with precisely known boundary conditions. In the present paper we propose the application of in-situ experimental testing, and the extraction of invariant sub-structural properties, to update numerical sub-structure models. The key advantage of the proposed method is its potential to avoid the need to achieve an idealised boundary condition (i.e. free or constrained) when performing experimental tests for model updating purposes.
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