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  • 1.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Enquist, Bertil
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Stiffness and damping evaluation of Elastomers in different setups2015In: Proceedings of the Internoise 2015 conference, Society of Experimental Mechanics (SEM) , 2015Conference paper (Refereed)
    Abstract [en]

    In timber buildings, elastomers are commonly used to decrease the sound transmission between apartments. Detailed properties of the elastomers are needed in order to model them in a correct yet computational efficient manner. In earlier studies, dynamic experiments have been made on elastomer strips half embedded. However, the sidewise effects need to be further evaluated. In this study, the elastomers are evaluated quasi-statically in different directions, having continuous as well as intermittent distributions, being plane supported or half embedded. An FE-model has been developed using data stemming from the quasi-static tests together with damping estimates stemming from vibrational tests.

  • 2.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Damping elastomers for wooden constructions: Dynamic properties2015In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, no 3, p. 245-255Article in journal (Refereed)
    Abstract [en]

    Elastomers are commonly used to decrease the sound transmission between apartments in timber framed houses. Inprevious studies, different types of connections have been evaluated. However, the frequency dependent dynamic propertiesin different directions of a connection including elastomers are not fully investigated yet. Previous studies have actuallyshown that elastomers cause the vibrations to increase in the direction perpendicular to the applied load within the lowfrequency span. The properties of the elastomers are needed in order to model the dynamic behaviour and thereby be ableto predict sound and vibration transmissions in wooden houses in the future. With known properties, the elastomerconnections can be modelled using springs and dashpots. In this study, dynamic experiments have been made on elastomerstrips half embedded. The test setup has been subjected to various loads using an electromagnetic shaker. The responseshave been measured and evaluated using modal analysis. With different loads, non-linear characteristics of the elastomers’behaviour have been obtained. The elastomers have also been tested quasi-statically, to obtain a load-deflection curve.Finally, the estimated properties of the elastomers have been included in an FE model using springs and the analyticalresults are compared with the experimental results.

  • 3.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Brandt, Anders
    University of Southern Denmark, Denmark.
    Ekevid, Torbjörn
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    FE Modelling of Light Weight Wooden Assemblies: parameter study and comparison between analyses and experiments2014In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 73, p. 125-142Article in journal (Refereed)
    Abstract [en]

    A finite element (FE) analysis of a model representing a mock-up structure previously investigated experimentally is investigated in this study. The aim is to make a correlation and calibration between test and analysis of the full scale wooden structure; both eigenmodes and acceleration levels are compared. Large scatter is found in material properties used for light weight wooden structures in literature. In this study, a parameter evaluation is therefore made to show how different properties influence the dynamic behaviour of the structure. It is shown that the wood beam material properties influence the behaviour of the light weight wooden structure FE model most.

    Two types of junctions are modelled and evaluated; a tied connection is used to simulate screwed junctions and spring/dashpot elements are used to represent elastomer junctions between the floor and the walls. The springs and dashpots used to model the elastomer in the junction work well in the bearing direction but need to be improved to obtain correct rotational stiffness, shear motion and friction. There are still many unknown parameters in a complex wooden structure that remain to be investigated. However, the results presented in this paper add data to be used for FE modelling of a complex wooden structure.

  • 4.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Linderholt, Andreas
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Jarnerö, Kirsi
    SP Wood Technology, SP Technical Research Institute of Sweden.
    FE modeling of a lightweight structure with different junctions2012In: Euronoise 2012-proceedings / [ed] Czech Acoustical Society, European Acoustics Association (EAA), 2012, p. 162-167Conference paper (Refereed)
    Abstract [en]

    In lightweight structures it is common to use damping material in junctions to decrease sound transmission. In field measurements, the damping properties of the structure are easily overestimated due to the omnipresent energy losses to the surroundings. Thus, reliable estimates of structural properties cannot be guaranteed.

    Vibrational tests were done on a full scale wooden construction, consisting of a floor and supporting beams, representing walls, to investigate the effect of different junctions. Totally seven different setups were made using the same building components. In one setup the floor and the walls were screwed together, in five setups different elastomers was positioned between the floor and the walls and in the last setup the floor was resting free on top of the walls. A shaker, with pseudorandom excitation, was used for the excitation of the structure and accelerometers were used for response measurements. The effect of the junction was investigated by studying the acceleration levels in the edge part of the floor-wall junction in different directions.

    Modal data, extracted from test data using experimental modal analysis, form input and validation data for the following finite element (FE) analysis. Two FE models; modeling one elastomer and the screwed setup, are used for the studies.

    The aim was to study if the eigenmodes rendering the acceleration levels are similar in test and in analysis, using common material properties.

    The results from correlation between test and analytical results show that the material properties of the wood need to be known better; more sophisticated models are needed to fully simulate the dynamic behavior of the structure. Anyhow, with the used properties the mode shapes are captured fairly well in the lower frequencies. Furthermore, the experiment shows that the damping properties of the junction material have a major influence on the behavior of the structure.

  • 5.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Olsson, Jörgen
    SP Trä.
    Model calibration of wooden structure assemblies: using EMA and FEA2014In: World Conference on Timber Engineering (WCTE), Quebec City, 10-14 August, 2014, 2014Conference paper (Refereed)
    Abstract [en]

    To predict and possibly, when needed to fulfil regularizations or other requirements, change the design to lower the impact sound transmission in light weight buildings prior to building, dynamically representative calculation models of assemblies are out most important. The quality of such models depends on the descriptions of the components themselves but also of the representation of the junction connecting the building components together. The material properties of commonly used components have a documented spread in literature. Therefore, to validate junction models, the dynamics of the assembly components at hand have to be known. Here, the dynamic properties of a number of component candidates are measured using hammer excited vibrational tests. Some of the components are selected to build up wooden assemblies which are evaluated both when they are screwed together and when they are screwed and glued together. The focus is here on achieving representative finite element models of the junctions between the building parts composing the assemblies.

  • 6.
    Bolmsvik, Åsa
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Ormarsson, Sigurdur
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vercruysse, Adrien
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Stenberg, Sarah
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Vibration Distribution Due to Continous, Intermittent or Half Embedded Elastomer Connections in Wooden Constructions2016In: Proceeding of the 2016 World Conference on Timber Engineering (WCTE), August 22-25, 2016 Vienna / [ed] Josef Eberhardsteiner, Wolfgang Winter, Alireza Fadai, Martina Pöll, Vienna: TU-MV Media Verlag , 2016, p. 2912-2920Conference paper (Refereed)
    Abstract [en]

    Elastomers are commonly used to decrease the sound transmission between apartments in timber framed houses. In previous studies, different types of elastomers have been evaluated experimentally. The wooden assemblies, in which elastomers were used in the connections, showed that elastomers cause the vibrations to increase in the direction perpendicular to the applied load within the low frequency span.

    In this study, the effects on acceleration, depending on how the elastomers are placed are studied. The cases having the elastomer continuous, placed as intermittent pieces or positioned half embedded in the junctions are evaluated.

    The frequency dependent properties of the elastomers are needed in order to model the dynamic behaviour and thereby be able to predict sound- and vibration transmission in wooden houses. Here, the properties of a wooden construction having different elastomers connections are studied to enable simulations of the behaviour of the elastomers in a FE model in the future.

  • 7.
    Brandt, Anders
    et al.
    University of Southern Denmark, Denmark.
    Linderholt, Andreas
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    A Periodogram-Based Method for Removing Harmonics in Operational Modal Analysis2012In: International Conference on Noise and Vibration Engineering 2012 (ISMA 2012): Proceedings of a meeting held 17-19 September 2012, Leuven, Belgium. Including USD 2012 / [ed] P. Sas, S. Jonckheere & D. Moens, Leuven: Katholieke Universiteit Leuven, Department of Mechanical Engineering , 2012, p. 2625-2634Conference paper (Refereed)
    Abstract [en]

    In many cases where operational modal analysis is of interest, harmonic components are disturbing the estimation of modal parameters. Sometimes the harmonics can be included in the parameter estimation process and subsequently removed (because the damping values become unrealistically low). However, this is difficult if a natural frequency is very close to, or coincides with, a harmonic. In this paper we investigate a recently proposed method for removing harmonics when estimating spectral densities for operational modal analysis. The method is essentially based on removing the harmonics in a periodogram, prior to estimating the spectral density by smoothing the same periodogram. This makes it a very time efficient method, as the harmonic removal is integrated into the spectral analysis process. To produce data for testing the method, a finite element dynamic model representing a wind turbine was created. The MATLAB-based finite element code CALFEM was used to achieve a flexible description of the tower. An aerodynamic force representation excited the rotating structure. An unbalance in one of the blades was introduced to produce a harmonic at the rotation speed of the turbine. To validate the efficiency of the harmonic removal, modal parameters were estimated using simulated data prior to, and after, removing the harmonics. The results show that the harmonic removal with the proposed method is efficient.

  • 8.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Ahlin, Kjell
    Xielalin Consulting, Sweden.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Bias errors of different simulation methods for linear and nonlinear systems2015In: Nonlinear Dynamics, Volume 1: Proceedings of the 33rd IMAC, A Conference and Exposition on Structural Dynamics, 2015 / [ed] Gaetan Kerschen, Springer, 2015, p. 505-520Conference paper (Other academic)
    Abstract [en]

    Responses of mechanical systems are often studied using numerical time-domain methods. Discrete excitation forces require a transformation of the dynamic system from continuous time into discrete time. Such a transformation introduces an aliasing error. To reduce the aliasing error, different discretization techniques are used. The bias errors introduced by some discretization techniques are studied in this paper.

    Algebraic expressions of the bias error obtained for some discretization methods are presented. The bias error depends on the assumption of the characteristics of the load between two subsequent time steps; here the zero-order, first-order and Lagrange second-order assumptions are studied. Different simulation methods are also studied for numerical evaluation of the derived theoretical bias errors. The discretization techniques are implemented for Runge-Kutta, the Digital Filter method and for the Pseudo Force in State Space method.

    The study is carried out for both a linear and a nonlinear system; two numerical examples assist in evaluating the theory. Perfect matches between the numerically estimated bias errors and the theoretical ones are shown. The results also show that, for the nonlinear example, the fourth order Runge-Kutta method is less accurate than the Digital Filter and the used single step Pseudo Force in State Space method.

  • 9.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    An Efficient Simulation Method for Large-Scale Systems with Local Nonlinearities2016In: Special topics in structural dynamics, 34th IMAC / [ed] DiMiao, D; Tarazaga, P; Castellini, P, Springer, 2016, Vol. 6Conference paper (Other academic)
    Abstract [en]

    In practice, most mechanical systems show nonlinear characteristics within the operational envelope. However, the nonlinearities are often caused by local phenomena and many mechanical systems can be well represented by a linear model enriched with local nonlinearities. Conventional nonlinear response simulations are often computationally intensive; the problem which becomes more severe when large-scale nonlinear systems are concerned. Thus, there is a need to further develop efficient simulation techniques. In this work, an efficient simulation method for large-scale systems with local nonlinearities is proposed. The method is formulated in a state-space form and the simulations are done in the Matlab environment. The nonlinear system is divided into a linearized system and a nonlinear part represented as external nonlinear forces acting on the linear system; thus taking advantage in the computationally superiority in the locally nonlinear system description compared to a generally nonlinear counterpart. The triangular-order hold exponential integrator is used to obtain a discrete state-space form. To shorten the simulation time additionally, auxiliary matrices, similarity transformation and compiled C-codes (mex) to be used for the time integration are studied. Comparisons of the efficiency and accuracy of the proposed method in relation to simulations using the ODE45 solver in Matlab and MSC Nastran are demonstrated on numerical examples of different model sizes.

  • 10.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Experimental Validation of a Nonlinear Model Calibration Method Based on Multiharmonic Frequency Responses2017In: Journal of Computational and Nonlinear Dynamics, ISSN 1555-1415, E-ISSN 1555-1423, Vol. 12, no 4, article id 041014Article in journal (Refereed)
    Abstract [en]

    Correlation and calibration using test data are natural ingredients in the process of validating computational models. Model calibration for the important subclass of nonlinear systems which consists of structures dominated by linear behavior with the presence of local nonlinear effects is studied in this work. The experimental validation of a nonlinear model calibration method is conducted using a replica of the École Centrale de Lyon (ECL) nonlinear benchmark test setup. The calibration method is based on the selection of uncertain model parameters and the data that form the calibration metric together with an efficient optimization routine. The parameterization is chosen so that the expected covariances of the parameter estimates are made small. To obtain informative data, the excitation force is designed to be multisinusoidal and the resulting steady-state multiharmonic frequency response data are measured. To shorten the optimization time, plausible starting seed candidates are selected using the Latin hypercube sampling method. The candidate parameter set giving the smallest deviation to the test data is used as a starting point for an iterative search for a calibration solution. The model calibration is conducted by minimizing the deviations between the measured steady-state multiharmonic frequency response data and the analytical counterparts that are calculated using the multiharmonic balance method. The resulting calibrated model's output corresponds well with the measured responses.

  • 11.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers tekniska högskola.
    Frequency Response Calculations of a Nonlinear Structure a Comparison of Numerical Methods2014In: Nonlinear Dynamics, Volume 2: Proceedings of the 32nd IMAC, A Conference and Exposition on Structural Dynamics, 2014 / [ed] Gaetan Kerschen, Springer, 2014, p. 35-44Conference paper (Refereed)
    Abstract [en]

    Mechanical systems having presence of nonlinearities are often represented by nonlinear ordinary differential 5 equations. For most of such equations, exact analytic solutions are not found; thus numerical techniques have to be used. 6 In many applications, among which model calibration can be one, steady-state frequency response functions are the desired 7 quantities to calculate. 8 The objective of this paper is to compare the performance of computations of nonlinear frequency response functions 9 (FRFs) calculated directly within the frequency domain, using the Multi-Harmonic Balance method, with the time-domain 10 methods Runge–Kutta, Newmark and Pseudo Force in State Space (PFSS). The PFSS method is a recently developed state- 11 space based force feedback method that is shown to give efficient solutions. 12 The accuracy and efficiency of the methods are studied and compared using a model of a cantilever beam connected to a 13 non-linear spring at its free end.

  • 12.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Xia, Yuying
    University of the West of England, UK.
    Friswell, Michael I.
    Swansea University, UK.
    A Pretest Planning Method for Model Calibration for Nonlinear Systems2016In: Model Validation and Uncertainty Quantification, Volume 3: Proceedings of the 34th IMAC, A Conference and Exposition on Structural Dynamics 2016, Springer, 2016, Vol. 3, p. 371-379Conference paper (Other academic)
    Abstract [en]

    With increasing demands on more flexible and lighter engineering structures, it has been more common to take nonlinearity into account. Model calibration is an important procedure for nonlinear analysis in structural dynamics with many industrial applications. Pretest planning plays a key role in the previously proposed calibration method for nonlinear systems, which is based on multi-harmonic excitation and an effective optimization routine. This paper aims to improve the pretest planning strategy for the proposed calibration method. In this study, the Fisher information matrix (FIM), which is calculated from the gradients with respect to the chosen parameters with unknown values, is used for determining the locations, frequency range, and the amplitudes of the excitations as well as the sensor placements. This pretest planning based model calibration method is validated by a structure with clearance nonlinearity. Synthetic test data is used to simulate the test procedure. Model calibration and K-fold cross validation are conducted for the optimum configurations selected from the pretest planning as well as three other configurations. The calibration and cross validation results show that a more accurate estimation of parameters can be obtained by using test data from the optimum configuration.

  • 13.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Xia, Yuying
    University of the West of England, UK.
    Friswell, Michael I
    Swansea University, UK.
    Validation of a model calibration method through vibrational testing of a mechanical system with local clearance2016In: Proceedings of ISMA2016 International conference on noise and vibration engineering and USD2016 International conference on uncertainty in structural dynamics / [ed] Sas, P; Moens, D; VanDeWalle, A, Leuven, Belgium: Katholieke University Leuven , 2016, p. 2581-2595Conference paper (Refereed)
    Abstract [en]

    Nonlinear finite element models are often validated using experimental data. A previously proposed calibration method, which concerns pre-test planning, multi-sinusoidal excitation and an effective optimization routine, is improved with an extended version of the pre-test planning. The improved method is validated using a test structure with a clearance type nonlinearity. From the pretest planning, an optimal configuration for the data acquisition is determined. The multi-harmonic nonlinear frequency response functions (FRFs) of the structure under test are then generated by a multi-sinusoidal excitation. Model calibration is conducted by minimizing the difference between the experimental multi-harmonic nonlinear FRFs and their analytical counterparts. The uncertainties of the estimated parameters are assessed by a k-fold cross validation, which confirm that the uncertainties of the estimated parameters are small when the optimal configuration is applied.

  • 14.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Nasrabadi, Vahid
    Chalmers University of Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Informative Data for Model Calibration of Locally Nonlinear Structures Based on Multi-Harmonic Frequency Responses2016In: Journal of Computational and Nonlinear Dynamics, ISSN 1555-1415, E-ISSN 1555-1423, Vol. 11, no 5, article id 051023Article in journal (Refereed)
    Abstract [en]

    In industry, linear FE-models commonly serve as baseline models to represent the global structural dynamics behavior. However, available test data may show evidence of significant nonlinear dynamic characteristics. In such a case, the baseline linear model may be insufficient to represent the dynamics of the structure. The causes of the nonlinear characteristics may be local in nature and the remaining parts of the structure may be satisfactorily represented by linear descriptions. Although the baseline model can then serve as a good foundation, the physical phenomena needed to substantially increase the model's capability of representing the real structure are most likely not modelled in it. Therefore, a set of candidate nonlinear property parameters to control the nonlinear effects have to be added and subjected to calibration to form a credible model. The selection of the calibration parameters and the choice of data for a calibration metric form a coupled problem. An over-parameterized model for calibration may result in parameter value estimates that do not survive a validation test. The parameterization is coupled to the test data and should be chosen so that the expected co-variances of the chosen parameter's estimates are made small. Accurate test data, suitable for calibration, is often obtained from sinusoidal testing. Because a pure mono-sinusoidal excitation is difficult to achieve during a test of a nonlinear structure, the excitation is here designed to contain sub and super harmonics besides the fundamental harmonic. The steady-state responses at the side frequencies are shown to contain valuable information for the calibration process that can improve the accuracy of the parameter estimates. The nonlinear steady-state solutions can be found efficiently using the multi-harmonic balance method. In this paper, synthetic test data from a model of a nonlinear benchmark structure are used for illustration. The model calibration and an associated K-fold cross-validation are based on the Levenberg-Marquardt and the undamped Gauss-Newton algorithm, respectively. Starting seed candidates for calibration are found by the Latin hypercube sampling method. The realization that gives the smallest deviation to test data is selected as a starting point for the iterative search for a calibration solution. The calibration result shows good agreement with the true parameter setting, and the K-fold cross validation result shows that the variance of the estimated parameters shrinks when adding sub and super harmonics to the nonlinear frequency response functions.

  • 15.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Nasrabadi, Vahid
    Chalmers.
    Linderholt, Andreas
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Abrahamsson, Thomas
    Chalmers.
    Model calibration of locally nonlinear structures using information from sub and super harmonic responses2012In: International Conference on Noise and Vibration Engineering 2012 (ISMA 2012): Proceedings of a meeting held 17-19 September 2012, Leuven, Belgium. Including USD 2012 / [ed] P. Sas, S. Jonckheere & D. Moens, Leuven: Katholieke Universiteit Leuven, Department of Mechanical Engineering , 2012, p. 2451-2464Conference paper (Other academic)
    Abstract [en]

    Large linear finite element models are commonly used in industry to represent global structural behavior and such models are often validated by use of data from vibrational tests. The validated models serve to predict the structural responses due to dynamic loads. Hence, it is important to have models that are able to represent the structural dynamics within the given operating envelope. When test data show proof of non linear behavior, a linear model may not be able to represent the dynamics well enough and thus a modification of the model is required. The main part of the structure may have a linear characteristic whereas localized physical processes can be sources of the observed nonlinearities. Model calibration of such locally nonlinear structures is studied in this paper. Specifically, the calibration process including the selection of appropriate data to be used for calibration of the model parameters chosen is treated. Here, synthetic test data stemming from a model of the Ecole Centrale de Lyon (ECL) nonlinear benchmark are used.

  • 16.
    Chen, Yousheng
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Yaghoubi, Vahid
    Chalmers University of Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Model Calibration of a Locally Non-linear Structure Utilizing Multi Harmonic Response Data2014In: Nonlinear Dynamics, Volume 2: Proceedings of the 32nd IMAC, A Conference and Exposition on Structural Dynamics, 2014 / [ed] Gaetan Kerschen, Springer, 2014, p. 97-109Conference paper (Refereed)
    Abstract [en]

    Model correlation and model calibration using test data are natural ingredients in the process of validating computational models. Here, model calibration for the important sub-class of non-linear systems consisting of structures dominated by linear behavior having presence of local non-linear effects is studied. The focus is on the selection of uncertain model parameters together with the forming of the objective function to be used for calibration. To give precise estimation of parameters in the presence of measurement noise, the objective function data have to be informative with respect to the parameters chosen. Also, to get useful data the excitation force is here designed to be multi-harmonic since steady-state responses at the side frequencies are shown to contain valuable information for the calibration process. In this paper, test data from a replica of the Ecole Centrale de Lyon (ECL) nonlinear benchmark together with steady-state solutions stemming from calculations using the Multi-Harmonic Balancing method are used for illustration of the proposed model calibration procedure.

  • 17.
    Gustafsson, Pär
    et al.
    Saab Aeronautics.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    A Study of the Accuracy of Ground Vibration Test Data Using a Replica of the GARTEUR SM-AG19 Testbed Structure2016In: Proceedings of the 30th Congress of the International Council of the Aeronautical Sciences / [ed] The International Council of the Aeronautical Sciences, International Council of the Aeoronautical Sciences , 2016Conference paper (Other academic)
    Abstract [en]

    Ground Vibration Tests have been performed on a replica of the Group for Aeronautical Research and Technology in Europe (GARTEUR) testbed structure SM-AG19. The aim of the Ground Vibration Tests was to study the impact on modal data stemming from the test data, from the boundary conditions used to mimic a free-free condition. For the tests an air-spring support system was designed with the aim to give a behaviour that is in resemblance with the behaviour of real aircraft test conditions.

    To eliminate a potential, unwanted, impact on the test results generated by the wing to fuselage interface as it was designed for the original structure (SM-AG19), a deviation from the original interface has been made on the structure for this particular study.

  • 18.
    Johansson, Anders
    et al.
    Chalmers.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers.
    Model calibration and uncertainty of A600 wind turbine blades2014In: Model Validation and Uncertainty Quantification, Volume 3: Proceedings of the 32nd IMAC, A Conference and Exposition on Structural Dynamics, 2014, Springer, 2014, p. 215-227Conference paper (Refereed)
    Abstract [en]

    Recently, a lot of work has been made on modeling, testing and calibrating Ampair 600W wind turbine blades, owing to the use of that turbine as a test bed structure for the Dynamic Substructuring Focus Group within the Society of Experimental Mechanics. In Sweden alone, more than 20 blades have been tested for dynamical properties, geometrical differences and material properties as was presented in several papers at IMAC XXXI. The quantity of blades, originating from different manufacturing batches, makes them ideal for investigations of component variability.

    In this paper, measurement variability predominantly stemming from the difference between individual blades is propagated backwards to model parameters, using model calibration techniques, in an effort to quantify their uncertainties. The coupling between spread in structural properties such as mass, center of gravity together with blade twist angles and spread in the resulting blade dynamics is shown.

  • 19.
    Johansson, Marie
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Bolmsvik, Åsa
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Jarnerö, Kirsi
    SP Hållbar samhällsbyggnad.
    Olsson, Jörgen
    SP Hållbar samhällsbyggnad.
    Reynolds, Thomas
    University of Cambridge, UK.
    Building higher with light-weight timber structures: the effect of wind induced vibrations2015In: Proceedings of the Internoise 2015 conference, Society of Experimental Mechanics (SEM) , 2015Conference paper (Refereed)
  • 20.
    Johansson, Marie
    et al.
    Linnaeus University, Faculty of Technology, Department of Building Technology.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Jarnerö, Kirsi
    SP Sveriges tekniska forskningsinstitut.
    Landel, Pierre
    SP Sveriges tekniska forskningsinstitut.
    Tall timber buildings: a preliminary study of wind-induced vibrations of a 22-storey building2016In: Proceedings of the World Conference on Timber Engineering (WCTE 2016): August 22-25, 2016, Vienna, Austria / [ed] J. Eberhardsteiner, W. Winter, A. Fadai, M. Pöll, Vienna, Austria, 2016Conference paper (Other academic)
    Abstract [en]

    During the last years the interest in multi-storey timber buildings has increased and several medium-to-high-rise buildings with light-weight timber structures have been designed and built. Examples of such are the 8-storey building “Limnologen” in Växjö, Sweden, the 9-storey “Stadthouse” in London, UK and the 14-storey building “Treet” in Bergen, Norway. The structures are all light-weight and flexible timber structures which raise questions regarding wind induced vibrations. This paper will present a finite element-model of a 22 storey building with a glulam-CLT structure. The model will be used to study the effect of different structural properties such as damping, mass and stiffness on the peak acceleration and will be compared to the ISO 10137 vibration criteria for human comfort. The results show that it is crucial to take wind-induced vibrations into account in the design of tall timber buildings.

  • 21.
    Kodakadath Premachandran, Rammohan
    et al.
    Atlas Copco Rock Drills AB.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Håkansson, Lars
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Gothberg, Mattias
    Atlas Copco Rock Drills AB.
    An initial investigation of the correlation between a number of drilling related quantities measured during down the hole drilling2017In: Proceedings of the 24th International Congress on Sound and Vibration, Curran Associates, Inc., 2017Conference paper (Other academic)
    Abstract [en]

    Optimizing the performance for down the hole (DTH) drills is becoming increasingly important. This is due to that the industry is becoming highly competitive and therefore there is an ever-increasing demand for improving the efficiency of the drilling process. To do this, it is important to have a robust monitoring system in place that should be based on in-depth knowledge of the underlying physics of the drilling system and process. Such a system will assist drillers in improving the perfor-mance e.g. by providing recommendations concerning the settings of the drilling. To understand the performance of the system, it is very important to understand the information that can be extracted from different drilling related quantities. In this work, information obtained from the pressure signals from the feed/holdback line, impact pressure line and rotation line together with vibration signals measured with the aid of accelerometers mounted at specific locations on the drill rig are discussed. For instance, spectral properties of these quantities for good and bad drilling cases are investigated. The results indicate correlations, to some extent, between the spectral properties and the quality of the drilling.

  • 22.
    Kodakadath Premachandran, Rammohan
    et al.
    Atlas Copco Rock Drills AB.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Håkansson, Lars
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Gothberg, Mattias
    Atlas Copco Rock Drills AB.
    Numerical 1D and 3D models representing a DTH drilling system: A comparison of accuracy and computational speed2018In: Proceedings of the 25th International Congress on Sound and Vibration, The International Institute of Acoustics and Vibration , 2018 / [ed] The International Institute of Acoustics and Vibration , 2018., International Institute of Acoustics and Vibration (IIAV) , 2018Conference paper (Refereed)
    Abstract [en]

    The drilling industry is steadily moving towards automation. To have a better control over the drilling operation and to optimize the drilling performance, it is necessary to have a good understanding of the physics involved in the process. A good simulation model of the drilling process/system would be of great value in assisting this and in enabling the development of strategies to optimize it. A representative simulation model can provide insights into various phenomena that appear during drilling for different drilling conditions. Such a model is also likely to be of assistance in preparing various measurements. Issues such as choosing the type of sensors, their positions and which quantities to measure are supported by a model. A well calibrated model in combination with information extracted from measured data are hence likely to assist in selecting control strategies for optimized drilling performance. In this paper we present a MATLAB based 1D simulation model of a Down The Hole (DTH) drill and compare it with an existing 1D model in terms of computational speed and accuracy. The emphasis is to make a 3D model of a DTH system that is computationally efficient and accurate.

  • 23.
    Landel, Pierre
    et al.
    RISE Research Institutes of Sweden.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Johansson, Marie
    RISE Research Institutes of Sweden.
    Dynamical properties of a large glulam truss for a tall timber building2018Conference paper (Refereed)
    Abstract [en]

    When designing a tall timber building, the accelerations due to wind loads are in many cases decisive. The parameters governing the dynamic behaviour of the building are the structure’s stiffness, damping and mass together with the loads. The first two parameters are not well-known during the serviceability limit state of timber structures generally and of timber connections specifically.

    In this study, dynamical properties of a large glulam truss, a part of the vertical and horizontal structural system in a residential six-storey timber building, are estimated from measurements made in the manufacturing plant. The timber members of the truss are joined with slotted-in steel plates and dowels. Forced vibrational test data are used to extract the dynamical properties. Finite element (FE) models, supported by the experimental results, were developed and simulations, to study the influence of the connection stiffnesses on the total behaviour, were performed. The vibration test results of measurements made on separate structural parts give valuable input to model timber structures and better possibilities to simulate the dynamic behaviour of tall timber buildings as well as the load distribution in wooden structures in the serviceability limit state.

  • 24.
    Larsson, Andreas
    Chalmers.
    Localization of Finite Element Model Errors: Error Criteria and Identifiability1999Licentiate thesis, monograph (Other academic)
  • 25.
    Larsson, Andreas
    et al.
    Chalmers University of Technology.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    A Comparison of Finite Element Model Error Localization Methods1999In: 1999 IMAC XVII - 17th International Modal Analysis Conference, Orlando, Florida, 1999, p. 929-935Conference paper (Refereed)
    Abstract [en]

    The aim of this study is to compare a new and some existing finite element model error localization methods. The methods are applied to two problems. First, fundamental properties of the error localization methods are studied on a simple sprung mass  system.  In  the second  problem  a  three-bay  frame structure is studied. Here the analytical results of a finite element analysis is taken as substitute for measured data. The model differences between this model and a perturbed model are then found by use of error localization methods.

    When data from a known finite element model take place as substitute for test data, the cause of the differences between the data sets are known. A so-called consistent para- meterization, i.e. a parameterization of the quantities known to be in error, is then possible. The error localization method are  compared for both consistent and inconsistent parameterization.

    A pre-error localization is made. It is based on the finite element model’s properties. Candidate model parameters, possibly in error, for which the experimental data are not informative,  are  rejected.  Non-identifiable  parameters  are also rejected. Quantification of data information richness and identifiability with newly developed index numbers support the pre-error localization.

    Four error localization methods are compared. Two of these are developed by Lallement and Piranda. These are the so- called Balancing of Eigenvalue Equation and Best Subspace Methods. The third is developed by Link and Santiago and is the Substructure Energy Function Method. A new localization method, using gradient and Hessian information of the error criterion function, constitute the fourth method.

  • 26.
    Larsson, Andreas
    et al.
    Chalmers University of Technology.
    Abrahamsson, Thomas
    Chalmers.
    On the Parameter Identifiability and Test Data Informativeness in Finite Element Model Error Localization2000In: Proceedings of IMAC XVIII, San Antonio, TX, 2000, p. 1520-1527Conference paper (Refereed)
    Abstract [en]

    Two fundamental questions that arise in finite ele- ment model updating and error localization prob- lems are addressed. These are whether available test data are informative enough with respect to the quantification of possible model errors and whether sufficient identifiability of such errors is at hand for a given test data set. We advocate the use of informativeness and identifiability based indices in a preparatory process to increase the likelihood of a successful error localization. Based on model properties, such informativeness and identifiability indices may be used in the pre-test planning for the determination of frequency, time and spatial resolution to be used in a vibratory test.

     

    First, the test data informativeness with respect to model parameters which might be in error is quan- tified. Here a dual assumption is made such that if model parameter perturbations could be detected by data from the planned test, then the test data could be used to detect such perturbations, i.e. the test is informative. A Data Information Richness (DIR) index has been developed to assess the level od Data Informativeness with respect to model parameters. Secondly, the identifiability of the model parame- ters are studied. The dynamic properties of a struc- ture, as recorded by a measurement system, may under certain conditions change similarly by changing one parameter or a set of other parame

    ters. Should that be the case, there is no identifi- ability and before a meaningful error localization may take place, either complementary test data have to be added or a re-parameterization of the model has to be made. To assess the identifiability, identifiability based criteria are further developed, based on earlier work by the authors. A newly developed orthogonality/co-linearity index ocI assist in the re-parameterization of systems with low identifiability.

     

    The methods of preparatory error localisation are applied to a six-degree-of-freedom system in a numerical example in which the analytical results of a finite element analysis are taken as substitute for measured data.

  • 27.
    Linderholt, Andreas
    Chalmers University of Technology.
    Localization of Finite Element Model Errors: Error Criteria and Identifiability1999Licentiate thesis, monograph (Other academic)
  • 28.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Model Calibration of an A600 Wind Turbine Blade2013In: Proceedings of the International Modal Analysis Conference (IMAC XXXI), Orange County, CA, 2013Conference paper (Refereed)
  • 29.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Revealing the Hidden Properties of the Non-linear Structural Identification Benchmark Properties2014In: International Modal Analysis Conference (IMAC XXXII), 3-6 February, 2014, 2014Conference paper (Refereed)
  • 30.
    Linderholt, Andreas
    Chalmers tekniska högskola.
    Test Design for Finite Element Model Updating: Identifiable Parameters and Informative Test Data2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    It is important to predict structural phenomena, such as noise and fatigue, stemming from vibra- tions. To do this, reliable structural dynamic models are needed. To be useful the models have to compare well with reality in the validation against test data; if not, the models should be mod- ified. The thesis research is in the field of computational model updating, which is, more often than not, the updating of uncertain parameters of a finite element model to better correlate to test data. This is a specialization that started to grow in the 1970s, and since then much research has been done. The work presented here concerns the design of tests for model updating, which is one of several model updating sub-tasks.

     For a test to be useful for model updating, the test data set must be such that the model param- eters are sufficiently well identifiable. The dynamic properties of a structure to be compared with test data may under certain conditions change similarly when one parameter or a set of other parameters is changed. When this happens, there is lack of identifiability and, before a meaningful model updating can take place, either complementary test data have to be added or a re-parameterization of the model must be made. An index was developed, the Orthogonality- Co-linearity Index (OCI), that helps to find the best way to reduce the number of parameters when there is low identifiability. For the model updating, test data also need to be informative with respect to the parameters to be tuned. The data informativeness depends on the test design, i.e. the choice of stimuli and the placement of the actuators and sensors. A data informativeness index that supports the design of an informative test is proposed. Procedures were also worked out to make the test design robust with respect to parameter uncertainties. The study is limited to linear and time-invariant systems.

  • 31.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Transmission Simulator Mass Loading Effects in Experimental Substructuring: A Study of the Ampair 600 Benchmark System2018In: Dynamics of Coupled Structures, Volume 4: Proceedings of the 36th IMAC, A Conference and Exposition on Structural Dynamics 2018 / [ed] Linderholt, A., Allen, M.S., Mayes, R.L., Rixen, D., Springer, 2018, Vol. 4, p. 15p. 127-141Conference paper (Other academic)
    Abstract [en]

    During the last years, a lot of research focusing on appropriate interfaces between substructures has been made; the transmission simulator method has become a tool in that strive. In this paper, possible sensitivity, related to ill-conditioning, of the end effects on assembled structures consisting of finite element substructure models representing experimental setups with different levels of transmission simulator mass loadings at their interfaces are studied. Here, components of the Society of Experimental Mechanics, SEM, substructuring focus group's benchmark; the Ampair A600 wind turbine, constitute the structure studied. Models of an A600 blade and bracket system attached to dummy masses of different sizes are coupled to models representing an A600 hub together with two blades attached to dummy masses of different sizes after numerical subtraction of the dummy masses on each of the substructures. The results are compared to data stemming from a model of the assembled system.

  • 32.
    Linderholt, Andreas
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Wind turbine blade modeling: setting out from experimental data2014In: LMS Nordic User Conference For Automotive And Mechanical Industry, Gothenburg, 27-28 Mars, 2014, 2014Conference paper (Other (popular science, discussion, etc.))
  • 33.
    Linderholt, Andreas
    et al.
    Chalmers University of Technology, Sweden.
    Abrahamsson, Thomas
    Chalmers University of Technology, Sweden.
    A Comparison of Finite Element Model ErrorLocalization Methods1999In: International Modal Analysis Conference (IMAC) XVII, Orlando, Florida, 1999., 1999, p. 929-935Conference paper (Other academic)
    Abstract [en]

    The aim of this study is to compare a new and some existing finite elementmodel error localization methods. The methods are applied to two problems. First,fundamental properties of the error localization methodsare studied on asimple sprung mass system. Inthe second problem a three-bay frame structure is studied.Here the analytical results of a finite element analysisis taken as substitute for measured  data. The model differences between  thismodel and a perturbed model are then found by use of error localization methods. When data from a known finite element model take place as substitute for test data, the cause of the differences between the data sets are known. A so-calledconsistent para­ meterization, i.e. a parameterization of the quantities known to be in error, is then possible. The error localization methods are compared for both consistent and inconsistent parameterization. A pre-error  localization  is  made. It is based  on  the  finiteelement model's properties. Candidatemodel parameters, possibly in error, for which the experimental data are not informative, are rejected. Non-identifiable parameters are also rejected. Quantification of data information richness and identifiability with newly  developed index numbers support the pre-error localization.

    Four error localization methods are compared. Two of these are developed by Lallement and Piranda. These are the so­ called Balancing of Eigenvalue Equation and Best Subspace Methods. The third is developed by Link and Santiago and is the Substructure Energy Function Method. A new localization method, using gradient and Hessian information of the error criterion function, constitute the fourth method.

  • 34.
    Linderholt, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Computational Model Updating of a Fan Blade Using Optimal Robust Test Data2014In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216Article in journal (Refereed)
  • 35.
    Linderholt, Andreas
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Engineering.
    Abrahamsson, Thomas
    Chalmers.
    Finding Local Non-Linearities Using Error Localization from Model Updating Theory: Proceedings of the 30th IMAC, A Conference on Structural Dynamics, 20122012In: Topic in Nonlinear Dynamics: Vol. 3 / [ed] D. Adams, G. Kerschen, A. Carrella, New York: Springer, 2012, p. 323-334Chapter in book (Refereed)
    Abstract [en]

    Within the aerospace industry, linear finite element models are traditionally used to describe the global structural dynamics of an aircraft. Ground vibration test data serve to facilitate the validation of models which are then used to characterize the aeroelastic behavior of the aircraft and to predict the responses due to dynamic loads. Thus, it is vital that the models contain the essential dynamics of the aircraft. Observed nonlinearities are judged to be local in nature whereas the main part of the structure behaves linearly under normal loading. In this work we focus on the identification of nonlinear effects and do that based on model updating theory. That includes methods for error localization with proper selection of candidate error parameters. The nonlinearities are treated as local modeling errors not considered in the linear system model. The error localization behavior is studied using synthetic test data from a simple system, known as the ECL Benchmark, with known nonlinear properties.

  • 36.
    Linderholt, Andreas
    et al.
    Chalmers University of Technology, Sweden.
    Abrahamsson, Thomas
    Chalmers University of Technology, Sweden.
    On the Parameter Identifiability and Test Data Informativeness in Finite Element Model Error Localization2000In: Proceedings of IMAC XVIII - 18th International Modal Analysis Conference, 2000, p. 1520-1527Conference paper (Other academic)
    Abstract [en]

    Two fundamental questions that arise in finite ele­ment model updating and error localization prob­ lems are addressed. These are whether available test data are informative enough with respect to the quantification of possible model errors and whether sufficient identifiability of such errors is at hand for a given test data set. We advocate the use of informativeness and identifiability based indices in a preparatory process to increase the likelihood of a successful error localization. Based on model properties, such informativeness and identifiability indices may be used in the pre-test planning for the determination of frequency, time and spatial resolution to be used in a vibratory test. First, the test data informativeness with respect to model parameters which might be in error is quan­ tified. Here a dual assumption is made such that if model parameter perturbations could be detected by data from the planned test, then the test data could be used to detect such perturbations, i.e. the test is informative. A Data Information Richness (DIR) index has been developed to assess the level of data informativeness with respect to model parameters. Secondly, the identifiability of the model parame­ ters are studied. The dynamic properties of a struc­  ters. Should that be the case, there is no identifi­ ability and before a meaningful error localization may  take place, either  complementary  test data have to be added or a re-parameterization of the model has to be made. To assess the identifiability, identifiability based criteria are further developed, based on earlier work by the authors. A newly developed orthogonality/co-linearity index OCI assist in the re-parameterization of systems with low identifiability. The methods of preparatory error localisation are applied to a six-degree-of-freedom system in a numerical example in which the analytical results of a finite element analysis are taken as substitute for measured data.

  • 37.
    Linderholt, Andreas
    et al.
    Chalmers University of Technology.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    On the Requirements of Physical Parameters to be used in Model Updating2001In: Proceedings of International Conference on Structural System Identification, Kassel, Germany, 2001Conference paper (Refereed)
    Abstract [en]

    A fundamental question that arises in finite element model updating and error localization problems is which requirements that have to be fulfilled by the physical parameters to be used in the procedures.

     

    One requirement is that the test data are informative with respect to the chosen parameters. That implies that a change of a certain parameter should give a detectable change in the model’s dynamic behaviour. Another requirement is that the chosen parameters should be identifiable. The dynamic properties of a structure, as recorded by a measurement system, may under certain conditions change similarly by changing one parameter or a set of other parameters. Should that be the case, there is no identifiability.

     

    This article shows that parameters of which test data have low informativeness and parame- ters that are lacking identifiability, are of no use for error localization or model updating and should therefore not be used for these purposes. Thus, before a meaningful error localization may take place either complementary test data have to be added or a re-parameterization of the model has to be made.

     

    Before an error localization is to be carried out a preparatory error localization, using only data from an FE-analysis, is justified. The purpose of such preparatory work is both to decide which parameters to use to quantify model errors and to design the tests for the error localiza- tion in order to meet the parameter requirements.

  • 38.
    Linderholt, Andreas
    et al.
    Chalmers University.
    Abrahamsson, Thomas
    Chalmers University.
    Optimizing the informativeness of test data used for computational model updating2005In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 19, no 4, p. 736-750Article in journal (Refereed)
    Abstract [en]

    In advance of a computational model updating or an error localisation, it can be advantageous to make a preparatory error localisation using data from a nominal analytical model. The purpose is then to select parameters for quantifying model errors and also to design effective tests for determining the best parameter setting. For successful subsequent error localisation, the test data must be informative with respect to the model parameters chosen when such data become available after test. The demand for test data informativeness puts requirements on the experiment with regard to spatial resolution of sensors, bandwidth of excitation, signal-to-noise ratios, etc.

    Optimising a test design is a huge task, sometimes impossible in practice, due to its combinatorial nature. The number of possible sensor/actuator placement combinations grows rapidly as the number of sensor and actuator candidates increases. For industrial sized problems, finding a sub-optimal solution may be a more realistic target. Such solutions are sought in this work.

    The aim of this study is to quantify data informativeness, shown to relate to the Fisher information matrix, with respect to physical parameters that are used in error localisation and model updating. Deterministic finite-element models in combination with stochastic noise models are used for assessing data informativeness, and a procedure for test design optimisation with respect to this is devised.

  • 39.
    Linderholt, Andreas
    et al.
    Chalmers University.
    Abrahamsson, Thomas
    Chalmers University.
    Parameter Identifiability in Finite Element Model Error Localization1999In: Svenska Mekanikdagarna, Stockholm, 1999Conference paper (Refereed)
  • 40.
    Linderholt, Andreas
    et al.
    Chalmers University.
    Abrahamsson, Thomas
    Chalmers.
    Parameter Identifiability in Finite Element Model Error Localization2003In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 17, no 3, p. 579-588Article in journal (Refereed)
    Abstract [en]

    A fundamental question in finite element model updating and error localisation is whether sufficient identifiability of model parameters is at hand for a given set of test data. Under certain conditions, the dynamic properties (to be compared with test data) of a structural model, may change similarly when a certain model parameter or a combination of other parameters are modified. Since low confidence in identified parameters can also be expected for marginally identifiable systems, due to the omnipresent noise when real test data are used, one should seek such states so as to avoid them. Should the problem lack identifiability, then before a meaningful error localisation can be made; either complementary test data have to be added or new parameters chosen for the model. The latter is studied in this paper. An index, the orthogonality/colinearity index, was developed to facilitate finding the best way to reduce the number of parameters when there is low identifiability The use of the index is demonstrated on a six-degree-of-freedom system in a numerical example. The example shows that error localisation or model updating using a parameterisation which has insufficient parameter identifiability is pointless.

  • 41.
    Linderholt, Andreas
    et al.
    Chalmers University.
    Abrahamsson, Thomas
    Chalmers.
    Parameter Requirements in Model Updating2001In: Nordic Vibration Research, Stockholm, 2001Conference paper (Refereed)
  • 42.
    Linderholt, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers.
    Robust Optimal Sensor Placement for Computational Model UpdatingIn: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216Article in journal (Refereed)
  • 43.
    Linderholt, Andreas
    et al.
    Chalmers tekniska högskola, Sweden.
    Abrahamsson, Thomas
    Chalmers tekniska högskola, Sweden.
    Test Data Informativeness Assessment for Finite Element Model Updating2002Report (Other academic)
    Abstract [en]

    Before a computational model updating or an error localization is to be carried out, a prepara­ tory error localization using only analytical data is justified. The purpose of such preparation should be to select the parameters for quantifying model errors and also to design optimal tests for determining the correct parameter setting. For a successful error localization, it is required that the test data should be informative with respect to the parameters chosen. The demand for test data informativeness limits the experiment with regard to the spatial resolution of sensors, bandwidth of excitation, signal-to-noise ratios, etc. On the other hand, for a given test condition and test data, the omnipresent noise may make parameter estimates useless because of estima­ tion covariances that are too large. This is often caused by over parameterized models; these should be identified by the preparatory error localization and remedied by are-parameterization before model updating take place.

     

    The aim of this study is to quantify data informativeness with respect to physical parameters that are used in error localization and model updating. The data informativeness  is shown to relate to the Fisher information matrix. Deterministic finite-element related state-space models in combination with stochastic noise models are used for evaluating data informativeness.  A nu­ merical study utilizing a finite-element model validated by test data from a scanning laser vi­ brometer is used to substantiate the theory.

  • 44.
    Linderholt, Andreas
    et al.
    Chalmers University of Technology.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Test Data Informativeness Assessment for Finite Element Model Updating2003In: Proceedings of IMAC XXI, Orlando, Florida, 2003Conference paper (Refereed)
    Abstract [en]

    In advance of a computational model updating or an er- ror localization, it can be advantageous to make a pre- paratory error localization using a nominal analytical model. The purpose is then to select parameters for quantifying model errors and also to design effective tests for determining the best parameter setting. For suc- cessful error localization, the test data must be informa- tive with respect to the model parameters chosen. For dynamic  computational  models,  the  demand  for  test data informativeness puts limitations on the experiment with regard to spatial resolution of sensors, bandwidth of excitation, signal-to-noise ratios, etc.

     

    Solving a full test design optimization problem is a huge task, sometimes impossible in practice, due to its com- binatorial nature. The number of possible sensor/actua- tor  placement  combinations  grows  rapidly  as  the number of sensor and actuator candidates increases. For industrial sized problems, finding a sub-optimal solu- tion may be a more realistic target.

     

    The aim of this study is to quantify data informative- ness, shown to relate to the Fisher information matrix, with respect to physical parameters that are used in error localization and model updating. Deterministic finite- element models in combination with stochastic noise models are used for evaluating data informativeness, and a procedure for test design optimization with re- spect to this is devised.

  • 45.
    Linderholt, Andreas
    et al.
    Chalmers University.
    Abrahamsson, Thomas
    Chalmers.
    Test Design aiming at Informative Test Data with Respect to Model Parameters2002In: Proceedings of The International Conference on Structural Dynamics Modelling, 2002Conference paper (Refereed)
  • 46.
    Linderholt, Andreas
    et al.
    Chalmers University of Technology.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Hoang, Nam
    Structural Engineering Program, School of Civil Engineering, Asian Institute of Technology.
    Information in Data Used for Finite Element Model Updating: Theory and Experiment2001In: Proceedings of SEM Annual Conference on Experimental Mechanics, Portland, Oregon, 2001Conference paper (Refereed)
    Abstract [en]

    To discriminate bad parameter settings from good, in finite element modelling, experimental data is usually required. Such experimental data should be informative with respect to the parameters in ques- tion. The demand for informativeness put require- ments on the experiment with regards to spatial resolution of sensors, bandwidth of shaker excita- tion, ambient noise levels, etc. In this paper, in- formativeness is studied by means of the Fisher information matrix and parameter accuracy is relat- ed to the adjoint statistical Cramer-Rao lower bound. The evaluation of information content in data used for model updating is discussed. Deter- ministic state-space models and stochastic noise models are used for informativeness evaluation. A numerical study together with Scanning laser vi- brometer measurements, on a system with well known mass perturbations, are used to substantiate the theory.

  • 47.
    Linderholt, Andreas
    et al.
    Chalmers University of Technology.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Hoang, Nam
    Structural Engineering Program, School of Civil Engineering, Asian Institute of Technology.
    Informative Data for Model Parameter Updating2001In: Proceedings of IMAC XIX, Orlando, Florida, 2001, p. 581-586Conference paper (Refereed)
    Abstract [en]

    Before an error localization is to be carried out a preparatory error localization, using only data from an FE-analysis, is justified. The purpose of such preparatory work is both to decide what parameters to use to quantify model errors and to design opti- mal tests for the error localization. A reasonable re- quirement on the parameterization is that the test data are informative with respect to the parameters. That implies that a change of a certain parameter should give a detectable change in the model’s dy- namic behaviour.

     

    The aim of this study is to examine data informa- tivity with respect to physical parameters, used in error localization and model updating. The data in- formativity is here quantified by the use of the Fisher information matrix. It is shown that the in- formativity depends on both excitation and meas- urements. It is reasonable to believe that parameters of which test data have low informativ- ity, are of no use for error localization and should not be used for model updating purposes. Such pa- rameters should be excluded from the parameters set or the test aimed for its determination should be re-designed.

  • 48.
    Linderholt, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Johansson, Anders
    Chalmers University of Technology.
    Mahdiabadi, Morteza Karamooz
    Technical University of Munich, Germany.
    Rixen, Daniel
    Technical University of Munich, Germany.
    The Dynamic Behavior of Three Sets of the Ampair 600 Wind Turbine2016In: Proceedings of the International Modal Analysis Conference (IMAC XXXIV), 2016 / [ed] Society of Experimental Mechanics, SEM Society of Experimental Mechanics , 2016Conference paper (Other academic)
    Abstract [en]

    A modified version of the Ampair 600 wind turbine was defined by the SEM substructuring focus group to be a benchmark for use in the pursuit of developing methods for high precision experimental substructuring. Today, seven such, intended to be identical, systems have been assembled at test laboratories within Europe and the USA. This paper reports the experimentally found dynamic behavior of five out of the seven systems. The aim of the study is to provide high fidelity data to support future component synthesis and model validation activities. Comparisons are made by evaluating deviations of measured frequency response functions and identified structural eigenfrequencies together with the correlation between eigenvector estimates. The testing is made in two parts. First, partly assembled systems, not including the rotors or the blades, are tested. This constitutes one possible and logical subsystem splitting that is likely to appear in future substructure synthesis efforts. In the second part, the fully assembled benchmark systems are tested. The test procedure, the test setup, the obtained test data and test data statistics are presented.

  • 49.
    Linderholt, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers, Sweden.
    Johansson, Anders
    Chalmers, Sweden.
    Steinepreis, Daniel
    University of Stuttgart, Germany.
    Reuss, Pascal
    University of Stuttgart, Germany.
    A Comparison of the Dynamic Behavior of Three Sets of the Ampair 600 Wind Turbine2015In: Dynamics of Coupled Structures: Proceedings of the 33rd IMAC, A Conference and Exposition on Structural Dynamics, 2015 / [ed] Matt Allen, Randall L. Mayes, Daniel J. Rixen, Springer Publishing Company, 2015, Vol. 4, p. 99-110Conference paper (Other academic)
    Abstract [en]

    The Ampair 600  wind turbine assembly has been modified to suit as a benchmark structure in the pursuit of finding best practices for experimental substructure coupling of structural dynamic systems. Seven such systems have been assembled in test laboratories in Europe and in the USA. We scrutinize the dynamic behavior of the total assembly of three of those by vibration testing and compare the test outcome from seemingly identical assemblies. The aim is to support future component synthesis activities with high fidelity data and support future model validation. Comparisons are made by evaluating deviations of measured frequency response functions, the differences of identified structural eigenfrequencies and the correlation between eigenvector estimates. The testing is made in two parts. First, a partly assembled system, not including the hub and blades, is tested. This constitutes one possible and logical subsystem splitting that is likely to appear in future substructure synthesis efforts. In the second part, the full system assembly is tested. The test procedure, the test setup, the obtained test data and test data statistics are presented.

  • 50.
    Linderholt, Andreas
    et al.
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Chen, Yousheng
    Linnaeus University, Faculty of Technology, Department of Mechanical Engineering.
    Abrahamsson, Thomas
    Chalmers University of Technology.
    Time Domain Dynamic Simulations of Locally Nonlinear Large-Scale Systems2016In: Presented at Aerospace technology congress: The Swedish Aeronautics Congress in a Globaised world, October 11-12, 2016, 2016Conference paper (Other academic)
    Abstract [en]

    In practice, most mechanical systems show nonlinear characteristics within the operational envelope. However, the nonlinearities are often caused by local phenomena and many mechanical systems can be well represented by a linear model enriched with local nonlinearities. Conventional nonlinear response simulations are often computationally intensive; the problem which becomes more severe when large-scale nonlinear systems are concerned. Thus, there is a need to further develop efficient simulation techniques. In this work, an efficient simulation method for large-scale systems with local nonlinearities is proposed. The method is formulated in a state-space form and the simulations are done in the Matlab environment. The nonlinear system is divided into a linearized system and a nonlinear part represented as external nonlinear forces acting on the linear system; thus taking advantage in the computationally superiority in the locally nonlinear system description compared to a generally nonlinear counterpart. The triangular-order hold exponential integrator is used to obtain a discrete state-space form. To shorten the simulation time additionally, auxiliary matrices, similarity transformation and compiled C-codes (mex) to be used for the time integration are studied. Comparisons of the efficiency and accuracy of the proposed method in relation to simulations using the ODE45 solver in Matlab and MSC Nastran are demonstrated on numerical examples of different model sizes.

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