Finite element model updating for structural applications

A novel method for performing model updating on finite element models is presented. The approach is particularly tailored to modal analyses of buildings, by which the lowest frequencies, obtained by using sensors and system identification approaches, need to be matched to the numerical ones predicted by the model. This is done by optimizing some unknown material parameters (such as mass density and Young's modulus) of the materials and/or the boundary conditions, which are often known only approximately. In particular, this is the case when considering historical buildings. The straightforward application of a general-purpose optimizer can be impractical, given the large size of the model involved. In the paper, we show that, by slightly modifying the projection scheme used to compute the eigenvalues at the lowest end of the spectrum one can obtain local parametric reduced order models that, embedded in a trust-region scheme, form the basis for a reliable and efficient specialized algorithm. We describe an optimization strategy based on this approach, and we provide numerical experiments that confirm its effectiveness and accuracy

Criteria of evaluating initial model for effective dynamic model updating

Finite element model updating is an important research field in structural dynamics. Though a variety of updating methods have been proposed in the past decades, all the methods could be effective only on the assumption that the initial finite element model is updatable. The assumption has led to the fact that many researchers study on how to update the model while little attention is paid to studies on whether the model is updatable. This has become inevitable obstacle between research and engineering applications because the assumption is not a tenable hypothesis in practice. To circumvent this problem, the evaluation of model updatability is studied in this paper. Firstly, two conditional statements about mapping are proved as a theoretical basis. Then, two criteria for evaluation of initial models are deduced. A beam is employed in the numerical simulations. Two different initial models for the beam are constructed with different boundary conditions. The models are evaluated using the proposed criteria. The results indicate that the criteria are able to distinguish the model updatability

Latest Advances in Finite Element Modelling and Model Updating of Cable-Stayed Bridges

As important links in the transport infrastructure system, cable-stayed bridges are among the most popular candidates for implementing structural health monitoring (SHM) technology. The primary aim of SHM for these bridges is to ensure their structural integrity and satisfactory per-formance by monitoring their behaviour over time. Finite element (FE) model updating is a well-recognised approach for SHM purposes, as an accurate model serves as a baseline reference for damage detection and long-term monitoring efforts. One of the many challenges is the de-velopment of the initial FE model that can accurately reflect the dynamic characteristics and the overall behaviour of a bridge. Given the size, slenderness, use of long cables, and high levels of structural redundancy, precise initial models of long-span cable-stayed bridges are desirable to better facilitate the model updating process and to improve the accuracy of the final updated model. To date, very few studies offer in-depth discussions on the modelling approaches for ca-ble-stayed bridges and the methods used for model updating. As such, this article presents the latest advances in finite element modelling and model updating methods that have been widely adopted for cable-stayed bridges, through a critical literature review of existing research work. An overview of current SHM research is presented first, followed by a comprehensive review of finite element modelling of cable-stayed bridges, including modelling approaches of the deck girder and cables. A general overview of model updating methods is then given before reviewing the model updating applications to cable-stayed bridges. Finally, an evaluation of all available methods and assessment for future research outlook are presented to summarise the research achievements and current limitations in this field

Model updating of modal parameters from experimental data and applications in aerospace

The research in this thesis is associated with different aspects of experimental analyses of structural dynamic systems and the correction of the corresponding mathematical models using the results of experimental investigations as a reference. A comprehensive finite-element model updating software technology is assembled and various novel features are implemented. The software technology is integrated into an experimental test facility for structural dynamic identification and used in a number of real life aerospace applications which illustrate the advantages of the new features. To improve the quality of the experimental reference data a novel non-iterative method for the computation of optimised multi-point excitation force vectors for Phase Resonance Testing is introduced. The method is unique in that it is based entirely on experimental data, allows to determine both the locations and force components resulting in the highest phase purity, and enable to predict the corresponding mode indicator. A minimisation criterion for the real-part response of the test structure with respect to the total response is utilised and, unlike with the application of other methods, no further information such as a mass matrix from a finite-element model or assumptions on the structure's damping characteristics is required. Performance in comparison to existing methods is assessed in a numerical study using an analytical eleven-degrees-of-freedom model. Successful applications to a simple laboratory satellite structure and under realistic test conditions during the Ground Vibration Test on the European Space Agency's Polar Platform are described. Considerable improvements are achieved with respect to the phase purity of the identified mode shapes as compared to other methods or manual tuning strategies as well as the time and effort involved in the application during Ground Vibration Testing. Various aspects regarding the application of iterative model updating methods to aerospace-related test structures and live experimental data are discussed. A new iterative correction parameter selection technique enabling to create a physically correct updated analytical model and a novel approach for the correction of structural components with viscous material properties are proposed. A finite-element model of the GARTEUR SM-AG19 laboratory test structure is updated using experimental modal data from a Ground Vibration Test. In order to assess the accuracy and physical consistency of the updated model a novel approach is applied where only a fraction of the mode shapes and natural frequencies from the experimental data base is used in the model correction process and analytical and experimental modal data beyond the range utilised for updating are correlated. To evaluate the influence of experimental errors on the accuracy of finite-element model corrections a numerical simulation procedure is developed. The effects of measurement uncertainties on the substructure correction factors, natural frequency deviations, and mode shape correlation are investigated using simulated experimental modal data. Various numerical models are generated to study the effects of modelling error magnitudes and locations. As a result, the correction parameter uncertainty increases with the magnitude of the experimental errors and decreases with the number of modes involved in the updating process. Frequency errors, however, since they are not averaged during updating, must be measured with an adequately high precision. Next, the updating procedure is applied to an authentic industrial aerospace structure. The finite-element model of the EC 135 helicopter is utilised and a novel technique for the parameterisation of substructures with non-isotropic material properties is suggested. Experimental modal parameters are extracted from frequency responses recorded during a Shake Test on the EC 135-S01 prototype. In this test case, the correction process involves the handling of a high degree of modal and spatial incompleteness in the experimental reference data. Accordingly, new effective strategies for the selection of updating parameters are developed which are both physically significant and likewise have a sufficient sensitivity with respect to the analytical modal parameters. Finally, possible advantages of model updating in association with a model-based method for the identification and localisation of structural damage are investigated. A new technique for identifying and locating delamination damages in carbon fibre reinforced polymers is introduced. The method is based on a correlation of damage-induced modal damping variations from an elasto-mechanic structure to the corresponding data from a numerical model in order to derive information on the damage location. Using a numerical model enables the location of damages in a three-dimensional structure from experimental data obtained with only a single response sensor. To acquire sufficiently accurate experimental data a novel criterion for the determination of most appropriate actuator and sensor positions and a polynomial curve fitting technique are suggested. It will be shown that in order to achieve a good location precision the numerical model must retain a high degree of accuracy and physical consistency

Particle swarm optimization with sequential niche technique for dynamic finite element model updating

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Fuzzy finite element model updating of a laboratory wind turbine blade for structural modification detection

Peer reviewedPublisher PD

Correlating low energy impact damage with changes in modal parameters: diagnosis tools and FE validation

This paper presents a basic experimental technique and simplified FE based models for the detection, localization and quantification of impact damage in composite beams around the BVID level. Detection of damage is carried out by shift in modal parameters. Localization of damage is done by a topology optimization tool which showed that correct damage locations can be found rather efficiently for low-level damage. The novelty of this paper is that we develop an All In One (AIO) package dedicated to impact identification by modal analysis. The damaged zones in the FE models are updated by reducing the most sensitive material property in order to improve the experimental/numerical correlation of the frequency response functions. These approximate damage models(in term of equivalent rigidity) give us a simple degradation factor that can serve as a warning regarding structure safety