Modal testing for model validation of structures with discrete nonlinearities

Abstract

Model validation using data from modal tests is now widely practiced in many industries for advanced structural dynamic design analysis, especially where structural integrity is a primary requirement. These industries tend to demand highly efficient designs for their critical structures which, as a result, are increasingly operating in regimes where traditional linearity assumptions are no longer adequate. In particular, many modern structures are found to contain localized areas, often around joints or boundaries, where the actual mechanical behaviour is far from linear. Such structures need to have appropriate representation of these nonlinear features incorporated into the otherwise largely linear models that are used for design and operation. This paper proposes an approach to this task which is an extension of existing linear techniques, especially in the testing phase, involving only just as much nonlinear analysis as is necessary to construct a model which is good enough, or ‘valid’: i.e. capable of predicting the nonlinear response behaviour of the structure under all in-service operating and test conditions with a prescribed accuracy. A short-list of methods described in the recent literature categorized using our framework is given, which identifies those areas in which further development is most urgently required.

Extending modal testing technology for model validation of engineering structures with sparse nonlinearities: A first case study

“…upgrading) the model to include the necessary additional parameters, and then validating these by updating the coefficients for the additional model features. Full details can be found in ref [1] and will not be repeated here.…”

“…The procedure outlined in Ref [1] comprises a series of 10 steps grouped in 3 Phases, as can be seen in Figure 1: Phase I Preparation -preparation for a nonlinear model validation process, including derivation of a validated Underlying Linear Model (ULM); Phase II Test and Identification -of the primary nonlinear features in the test structure, also referred to as Modal Test+; and Phase III Verification and Validation extending (i.e. upgrading) the model to include the necessary additional parameters, and then validating these by updating the coefficients for the additional model features.…”

“…A methodology for such an extension to the modal testing that is undertaken for traditional linear model validation has recently been proposed and described in [1]. One constraint on this new procedure is that it should require the minimum of additional test equipment, practice and analysis software beyond that routinely available in today's high-technology industries.…”

“…One constraint on this new procedure is that it should require the minimum of additional test equipment, practice and analysis software beyond that routinely available in today's high-technology industries. Ref [1] includes mention of a range of algorithms that are currently available or under development to fill the gaps necessary for nonlinear identification, but does not extend to recommendation or critical comparison of any of these. The purpose of the current paper is to describe a specific worked example test case to explore the more advanced and more promising of these new techniques.…”

Model Upgrading T0 Augment Linear Model Capabilities into Nonlinear Regions

“…However an updated version of this process which incorporates modal testing into each step definition is presented in an opinion paper in [12]. This new updated process is tailored to answer industrial practical problems where structural integrity is of great concern.…”