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

Abstract

Modal testing is widely used today as a means of validating theoretical (Finite Element) models for the dynamic analysis of engineering structures, prior to these models being used for optimisation of product design. Current model validation methodology is confined to linear models and is primarily concerned with (i) correcting inaccurate model parameters and (ii) ensuring that sufficient elements are included for these cases, using measured data. Basic experience is that this works quite well, largely because the weaknesses in the models are relatively sparse and, as a result, are usually identifiable and correctable. The current state-of-the-art in linear model validation has contributed to an awareness that residual errors in FE models are increasingly the consequence of some unrepresented nonlinearity in the structure. In these cases, additional, higher order parameters are required to improve the model so that it can represent the nonlinear behaviour. This is opposed to the current practice of simply refining the mesh. Again, these nonlinear features are generally localised, and are often associated with joints. We seek to provide a procedure for extending existing modal testing to enable these nonlinear elements to be addressed using current nonlinear identification methods directed at detection, characterisation, location and then quantification -in order to enhance the elements in an FE model as necessary to describe nonlinear dynamic behaviour. Emphasis is placed on the outcome of these extended methods to relate specifically to the physical behaviour of the relevant components of the structure, rather than to the nonlinear response characteristics that are the result of their presence.

Metodología para la detección de fallas en una estructura entramada metálica empleando las técnicas de análisis modal y PSO

“…Desde el punto de vista experimental, llamado Análisis Modal Experimental (EMA), la técnica busca relacionar la respuesta vibratoria del sistema con las fuerzas de excitación que las genera, y ha sido ampliamente utilizada para la caracterización modal de elementos de máquinas, placas, etc. [7][8] [9]. En este caso, tanto las amplitudes de vibración como las características de la fuerza aplicada son conocidas.…”

Exciting vibrations: the role of testing in an era of supercomputers and uncertainties

“…This introduces an epistemic uncertainty which must be resolved before model updating can be applied. The process of ensuring that a model is capable of being updated has recently been re-enforced and termed model upgrading [6].…”

“…However, we must now be looking ahead to the next level of modelling and validation, to situations where nonlinearities cannot be ignored. One recent publication has set out a proposed procedure for managing this situation [5] and another provides a first example application [6]. The proposed approach builds on current (linear) methodology by seeking to use test data to enhance, or upgrade, the underlying linear model by identifying which parts of the structure are exhibiting non-linear characteristics.…”

A laser triangulation sensor for vibrational structural analysis and diagnostics

“…Modal testing has been practiced for over 60 years; in fact, the first documented method, with the aim to predict the behavior of a structure under dynamic loads, dated back to the 1940s. 1 An enormous literature regarding the EMA has been published, and among them, a special mention must be given to the works of Ewins 2 and Delli Carri et al 3 and Heylen et al 4…”