| 1. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
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Calibration and cross-validation of a car component using frequency response functions and a damping equalization technique
- 2014
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Ingår i: 26th International Conference on Noise and Vibration Engineering, ISMA 2014, Including the 5th International Conference on Uncertainty in Structural Dynamics, USD 2014. - 9789073802919 ; , s. 2625-2640
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Konferensbidrag (refereegranskat)abstract
- The calibration of an FE model of a car subframe is reported. In this calibration the minimum deviation between finite element model data and experimental data is searched for. The outcome of the calibrated model and cross-validation results are compared with results of testing being made on an ensemble of seemingly identical subframes. The subframe model has 250,440 degrees-of-freedom and the calibration is made for 16 uncertain model parameters. The efficiency of the calibration procedure under these conditions is reported. With model calibration being a cornerstone of the finite element validation procedure, the calibration problem is normally characterized as being a large scale optimization problem with many model parameters to solve for and with deviation metric that are nonlinear in these parameters. The calibrated parameters need to be found by iterative procedures, starting from initial estimates of parameter values. Sometimes these procedures get trapped in local deviation function minima and do not converge to the globally optimal calibration solution that is searched for. Here, a calibration formulation which gives a smooth deviation metric with a large radius of convergence to the global minimum is used. A method that utilizes damping equalization is used to avoid the mode correlation and mode pairing problem that need to be solved in various other model updating procedures. The method is combined with model reduction for increased speed and employs the Levenberg-Marquardt minimizer with randomized starts to achieve the calibration solution. The MATLAB-based open-domain software tool FEMcali has been used for calibration, validation and cross-validation.
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| 2. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
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Calibration and Validation of a Car Subframe Finite Element Model Using Frequency Responses
- 2015
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319152516 ; , s. 9-22
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Konferensbidrag (refereegranskat)abstract
- A finite element model of a car front subframe has been calibrated against test data. Stepped-sine testing has been used to give frequency response function estimates on an ensemble of seemingly identical subframes. Therefore, the deviation between test data and simulation results can be compared in a meaningful way by the outcome of model calibration and cross-validation. Emphasis has been put on the preparation of the test pieces for high fidelity testing and on bettering the chances of getting a calibration outcome that provides insight into the physical processes that govern the subframe dynamics. The front subframe model has more than 200,000 degrees-of-freedom and 17 model calibration parameters. The efficiency of the calibration procedure under these conditions is reported. To achieve efficiency, a calibration with a smooth deviation metric is used together with a damping equalization method that eliminates the need for matching of experimental and analytical eigenmodes. The method is combined with surrogate model frequency response evaluation based on model reduction for increased speed. The Matlab based open-domain software tool FEMcali that employs the Levenberg-Marquardt minimizer with randomized starts has been used for calibration and an unregularized Gauss-Newton minimizer has been used in the cross-validation.
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| 3. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
-
FEM calibration with FRF damping equalization
- 2014
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319007670 ; 3, s. 265-278
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Konferensbidrag (refereegranskat)abstract
- A finite element model calibration procedure that uses frequency response function data and relies on damping equalization is presented. In this, the dampings of the finite element model and the corresponding experimental model are set equal before calibration. The damping equalization is made to avoid the mode pairing problem that normally needs to be solved in other model updating procedures. It is demonstrated that one particular use of frequency response data gives a calibration deviation metric that is smooth in the variation of model parameters and give a large radius of convergence to the calibration minimum. The method is combined with model reduction for increased speed and employs a minimizing procedure that employs randomized multiple starting points in the parameter space to get to the calibration solution. The performance of the calibration procedure is demonstrated by two numerical examples. © The Society for Experimental Mechanics, Inc. 2014.
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| 4. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
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Finite element model calibration using frequency responses with damping equalization
- 2015
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Ingår i: Mechanical Systems and Signal Processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 62-63, s. 218-234
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Tidskriftsartikel (refereegranskat)abstract
- Model calibration is a cornerstone of the finite element verification and validation procedure, in which the credibility of the model is substantiated by positive comparison with test data. The calibration problem, in which the minimum deviation between finite element model data and experimental data is searched for, is normally characterized as being a large scale optimization problem with many model parameters to solve for and with deviation metrics that are nonlinear in these parameters. The calibrated parameters need to be found by iterative procedures, starting from initial estimates. Sometimes these procedures get trapped in local deviation function minima and do not converge to the globally optimal calibration solution that is searched for. The reason for such traps is often the multi-modality of the problem which causes eigenmode crossover problems in the iterative variation of parameter settings. This work presents a calibration formulation which gives a smooth deviation metric with a large radius of convergence to the global minimum. A damping equalization method is suggested to avoid the mode correlation and mode pairing problems that need to be solved in many other model updating procedures. By this method, the modal damping of a test data model and the finite element model is set to be the same fraction of critical modal damping. Mode pairing for mapping of experimentally found damping to the finite element model is thus not needed. The method is combined with model reduction for efficiency and employs the Levenberg-Marquardt minimizer with randomized starts to achieve the calibration solution. The performance of the calibration procedure, including a study of parameter bias and variance under noisy data conditions, is demonstrated by two numerical examples.
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| 5. |
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| 6. |
- Abrahamsson, Thomas, 1956, et al.
(författare)
-
What Is Normal About Normal Modes?
- 2016
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Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 10, s. 97-110
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Konferensbidrag (refereegranskat)abstract
- A normal mode of a vibrating system is a mode that is orthogonal to all other normal modes of that system. The orthogonality is in a weighted sense. For an undamped discretized linear mechanical system, the orthogonality is defined with respect to stiffness and mass such that normal modes are mutually stiffness and mass orthogonal. Another commonly used definition of an oscillating normal mode is that it is a pattern of motion in which all parts of the system vibrate harmonically with the same frequency and therefore with fixed relative phase relations between parts. The normality of a mode is thus not in a statistical sense. For lightly damped linear systems, a normal observation, i.e. one very common observation in the statistical sense, is that the phase relation between the motion of different parts of the system deviates very little from zero or pi. However, this normally occurring behavior should not lead us to think that that always has to be the case. Here it is shown by example that the normal modes of an undamped system may have arbitrary phase relations. One such mode of vibrationmay then possess the property of moving nodal lines, which is often attributed to non-proportionally damped or nonself-adjoint systems. The proper normalization of such modes is discussed and their relation to the well-known modal mass and MAC concepts and also to state-space based normalizations that are usually being used for complex-valued eigenmodes.
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| 7. |
- Allen, Matthew S., et al.
(författare)
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Experimental substructuring
- 2020
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Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; , s. 75-181
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter, we outline techniques to use measured dynamic characteristics of components to build an assembled model. Although the basic theory is pretty straightforward, the difficulty in experimental substructuring lies in the limitations in what can be measured and the special techniques needed to alleviate errors in the measured signals.—(Chapter Authors: Daniel Rixen, Maarten van der Seijs, Randall Mayes, Matt Allen & Thomas Abrahamsson).
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| 8. |
- Allen, Matthew S., et al.
(författare)
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Industrial applications & related concepts
- 2020
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Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; , s. 183-231
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This section highlights some specialized substructuring methods, such as methods for estimating the fixed-interface modes of a substructure from measurements of the free–free structure with a fixture attached at the interface, and also highlights some industrial examples. Transfer path analysis is reviewed, elaborating some of the similarities in the theoretical foundations. Most information about TPA has been obtained from van der Seijs et al. (2016), please refer to the original paper for a more elaborate discussion.
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| 9. |
- Allen, Matthew S., et al.
(författare)
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Introduction and Motivation
- 2020
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Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; , s. 1-4
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- “Divide and Conquer” is a paradigm that helped Julius Cesar to dominate on the wide Roman Empire. The power of dividing systems, then analyze them as parts before combining them in an assembly, is also an approach often followed in science and engineering. In this introductory chapter, we shortly discuss the main idea behind domain decomposition and substructuring applied to mechanical systems.
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| 10. |
- Allen, Matthew S., et al.
(författare)
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Model reduction concepts and substructuring approaches for linear systems
- 2020
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Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; , s. 25-73
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter, we give an overview of some of the most common reduction techniques based on substructuring. Although all techniques follow a similar approach, the main difference between the methods lies into the basis vectors used in the approximation subspace to represent the dynamics of each substructure and the manner in which the substructures are a couple.
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| 11. |
- Allen, Matthew S., et al.
(författare)
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Model reduction concepts and substructuring approaches for nonlinear systems
- 2020
-
Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; , s. 233-267
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter reviews common nonlinearities that are encountered in engineering structures, with a particular emphasis on geometric nonlinearity. Popular ways to construct reduced order models for geometrically nonlinear problems are discussed. The concept of nonlinear normal modes is presented to help understand the dynamics of these structures, and some recently presented substructuring methods are reviewed.
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| 12. |
- Allen, Matthew S., et al.
(författare)
-
Preface
- 2020
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Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - 2309-3706 .- 0254-1971. ; 594, s. v-vi
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 13. |
- Allen, Matthew S., et al.
(författare)
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Preliminaries: Primal and dual assembly of dynamic models
- 2020
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Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; , s. 5-24
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- There are several ways to formulate the dynamics of a substructure. The different domains in which the dynamics can be described will be reviewed since the manner in which substructures are characterized will later determine the substructuring methodology that can be applied. In addition to how the substructures are formulated, the way in which the coupling/decoupling problem is expressed will allow us in the subsequent chapters to develop different numerical and experimental techniques. Two conditions must be satisfied on the interface between substructures: a condition on the displacement field (compatibility) and on the interface stresses (force equilibrium). Those conditions can be accounted for following several different formulations, all mathematically equivalent, but each leading to different numerical methods, experimental approaches, and approximation techniques, as will be explained in the following chapters. In this chapter, we outline the basic concepts of the so-called three-field formulation, dual and primal assembly
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| 14. |
- Allen, Matthew S., et al.
(författare)
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Weakly nonlinear systems: Modeling and experimental methods
- 2020
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Ingår i: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; , s. 269-277
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The prior chapter presented rigorous theory and methods for nonlinear systems, which is necessary in general because many nonlinear systems exhibit strong modal coupling due to the nonlinearity; this is commonly the case for the geometrically nonlinear structures that were the focus of that chapter. However, one of the most common sources of nonlinearity in built-up structures is the joints, and in many cases, these introduce only a weak stiffness nonlinearity together with a significant damping nonlinearity. In this case, and in many others that are relevant to industry, one can obtain good estimates of the response of the structure using a weakly nonlinear model in which the linear modes of the structure are presumed to be preserved and coupling between modes is neglected. This chapter provides a brief introduction to these concepts.—Chapter Authors: Randall Mayes and Matt Allen.
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| 15. |
- Ander, Mats, 1964, et al.
(författare)
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Development, accomplishment and evaluation of a project course in applied mechanics---Lessons learnt
- 2009
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Ingår i: Svenska mekanikdagarna, Södertälje 2009, 15-17-juni, Session 7:4-Utbildning, sid 99 (1 page abstract). ; , s. 99-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Development, accomplishment and evaluation of a project course in applied mechanics---Lessons learnt M. Ander , T. Grönstedt, T. Abrahamsson and G. JohanssonThis presentation concerns teaching and learning from working in projects within the Chalmers Master programme in Solid and fluid mechanics. The academic tradition requires teaching solid and fluid mechanics as separated subjects of applied mechanics. The researchers/teachers and students belonging to either discipline do not meet on daily basis and thus two separate cultures develop; CFD for fluids and FEM for solids.However, in industry today fresh engineers will meet challenges in multidisciplinary problems and they are expected to be able to know how to treat them. As a remedy to better prepare for their engineering profession, a project course in applied mechanics has been developed. The outline of the course follows the CDIO[1] learning approach: Conceive, Design, Implement and Operate. Starting off from back of the envelope calculations, where all students are required to address all disciplines, the project proceeds towards distinct specializations. The students, divided into groups of six to seven members, focus on ‘student specialists’ roles in solid/structural mechanics-FEM, fluid dynamics, and experimental modal analysis EMA, simulating a true multidisciplinary working environment. The projects studied incorporate a fluid structure interaction core problem, but are required to pose challenges within each specialisation. The task is formulated as a competition to find better solutions or as an investigation of existing methods to solve a problem at hand. The examination is based on individual assignments, group work, presentation of a final report and opposition. As resources for analysing the problems, the students have access to wind tunnel testing, EMA-equipment, computer rooms with commercial software for CFD and FEM. This year we have introduced the ANSYS workbench as a common platform for fluid–structure interaction simulations, allowing the teams to work more closely together. The student perspective is dominated by the urge to approach real world problems with industrial tools. A better contact and understanding between students as well as between teachers/researchers in the different disciplines of applied mechanics are achieved by this approach. Some outstanding challenges are the limited time frame of the course, the time consuming communication required within the teachers team and the student frustration arising from having to address open end problems. [1]www.cdio.org
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| 16. |
- Andersson, Niclas, et al.
(författare)
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Comparison of Stimuli for Nonlinear System Response Classification
- 2020
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Ingår i: SAE International Journal of Vehicle Dynamics, Stability, and NVH. - : SAE International. - 2380-2162 .- 2380-2170. ; 4:3, s. 197-219
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Tidskriftsartikel (refereegranskat)abstract
- As part of the development of an automated virtual design classification approach for nonlinear structural dynamics, alternative excitation functions are evaluated with respect to their overall performance and efficiency in feature-based response analysis. Robust design of nonlinear structures requires analysis of extensive parameter variations. Both the character of the stimulus and feature metrics used are central to the performance of a response classification approach. The main purpose of this study is to compare stimulus candidates with respect to their efficiency in response classification. A deterministic multilevel, multifrequency stepped-sine periodic test function is used as a baseline. Order-wise differences between generalized and linearized system frequency response functions are evaluated by a selected feature metric to allow categorization into primary, sub and super harmonic responses, as well as odd and even order response distortions. An alternative excitation function type is the pseudorandom phase multi-sine. Its robust variant estimates the best linear approximation of the generalized frequency response function and related nonlinear and noise variances, which can be used for response classification. The fast variant of this method further detects and classifies occurring even and odd order nonlinear responses using a hypothesis test. This article describes the application of these three methods to a virtually running two-piece rotor shaft model. Time response signals from simulated test parameter variations are used to calculate selected nonlinear feature metric values. The total simulation and measurement time, as well as the predictive performance in a few typical nonlinear response cases are evaluated.
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| 17. |
- Andersson, N., et al.
(författare)
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Feature-based design analysis for automatic classification of simulated nonlinear responses using machine learning
- 2016
-
Ingår i: Proceedings of Isma2016 International Conference on Noise and Vibration Engineering and Usd2016 International Conference on Uncertainty in Structural Dynamics, ed. by Sas, P; Moens, D; VanDeWalle, A.. - 9789073802940 ; , s. 3259-3273
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Konferensbidrag (refereegranskat)abstract
- A practical concept design analysis approach for automatic processing and classification of simulated responses is presented. Deterministic and nonlinear dynamics are studied under ideal loading and low noise conditions to determine fundamental system properties, how they vary and possibly interact. Responses should be classified into characteristic types, such as periodic or nonperiodic, resonant or nonresonant, linear or nonlinear, and further into subcategories such as single or dual frequency responses, hardening or softening. For this, time-signals are evaluated using methods and metrics commonly used within structural dynamics and then possibly associated with qualitative features according to measures based on a set of rules-of-thumb criteria. A support vector machine is trained to determine whether a single feature, or combinations of features, applies or not. This paper describes elements of the analysis, report practical considerations and discuss the effectiveness of evaluated features using known few-degree-of-freedom examples.
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| 18. |
- Andersson, Niclas S, 1971, et al.
(författare)
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Efficient Component Reductions in a Large-Scale Flexible Multibody Model
- 2018
-
Ingår i: SAE International Journal of Vehicle Dynamics, Stability, and NVH. - : SAE International. - 2380-2162 .- 2380-2170. ; 2:1, s. 5-26
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Tidskriftsartikel (refereegranskat)abstract
- To make better use of simulations in the automotive driveline design process there is a need for both improved predictive capabilities of typical system models and increased number of variant evaluations carried out during system concept design phase. A previously developed large-scale multibody rotor dynamical powertrain model that combines detailed linear-elastic finite element components and nonlinear joints is used to more accurately simulate system response modes and their variations across the operating-range. However, the total simulation time is too long to include extensive parameter evaluations during the rapid design iterations, which will have a negative influence on the total understanding of the designed system's behaviour. Therefore this paper is about reducing such a large-scale model to one that runs faster, but without losing the ability to predict the most fundamental system characteristics. Reduction methods considering defined stimuli-response relations are well established and used within the field of control systems, to balance prediction accuracy and evaluation effort, but are not yet commonly applied to large-scaled structural models and analysis of vibrations in continuous and lightly damped structures. Here, an implementation of two such state-space reduction methods into a common computational software workflow is described and their overall efficiency is compared to standard methods. Reductions are applied to two major structural components of the powertrain model. Steady-state simulations are performed for multiple engine speeds and responses related to vehicle noise and vibrations are compared using a quantitative error metric. The prediction accuracy, reduction and response simulation times of different model orders are evaluated, as well as the corresponding mode frequency spectra.
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| 19. |
- Andersson, Niclas S, 1971, et al.
(författare)
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Feature-Based Response Classification in Nonlinear Structural Design Simulations
- 2018
-
Ingår i: SAE International Journal of Vehicle Dynamics, Stability, and NVH. - : SAE International. - 2380-2162 .- 2380-2170. ; 2:3, s. 185-202
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Tidskriftsartikel (refereegranskat)abstract
- An applied system design analysis approach for automated processing and classification of simulated structural responses is presented. Deterministic and nonlinear dynamics are studied under ideal loading and low noise conditions to determine fundamental system properties, how they vary and possibly interact. Using powerful computer resources, large amounts of simulated raw data can be produced in a short period of time. Efficient tools for data processing and interpretation are then needed, but existing ones often require much manual preparation and direct human judgement. Thus, there is a need to develop techniques that help to treat more virtual prototype variants and efficiently extract useful information from them. For this, time signals are evaluated by methods commonly used within structural dynamics and statistical learning. A multi-level multi-frequency stimulus function is constructed and simulated response signals are combined into frequency domain functions. These are associated with qualitative system features, such as being periodic or aperiodic, linear or nonlinear and further into subcategories of nonlinear systems, such as fundamental, sub or super harmonic and even or odd order types. Appropriate classes are then determined from selected feature metrics and rules-of-thumb criteria. To automate the classification of large data sets, a support vector machine is trained on categorised responses to determine whether a single feature, or combinations of features, applies or not. The trained classifier can then efficiently process new sets of data and pick out cases that are associated with possible vibrational problems, which subsequently can be further analysed and understood. This article describes elements of the analysis, discuss the effectiveness of evaluated feature metrics, reports practical considerations and results from two separate training study examples.
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| 20. |
- Brewick, P., et al.
(författare)
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Hybrid Time/Frequency Domain Identification of Real Base-Isolated Structure
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. - 9783319297514 ; 2, s. 303-311
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Konferensbidrag (refereegranskat)abstract
- This paper presents a case study using hybrid time-and frequency-domain identifications in a synergistic manner to develop models of a full-scale experimental base-isolated structure. This four-story reinforced-concrete building on an isolation layer (of rubber bearings, elastic sliding bearings, passive metallic yielding dampers, and controllable oil dampers) was designed and constructed at the large-scale Japanese NIED E-Defense earthquake engineering laboratory. A variety of sensors, including accelerometers, were mounted within the structure to measure building response to shake table excitations. While the building was ultimately subjected to historical and synthetic ground motions, the recorded table and building accelerations during a number of random excitation tests are used to identify the structure's natural frequencies, damping ratios and mode shapes. The substantial damping provided by the isolation layer necessitates adopting a hybrid time-and frequency-domain approach for identification. The modes of the structure are separated by frequency content wherein lower frequency modes are identified using time domain approaches from the subspace identification family of methods and higher frequency modes are identified using frequency response functions. Individually, neither approach is able to successfully identify all of the desired modes but, through their combination, the modal properties of the structure are successfully characterized.
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| 21. |
- Bylin, Axel, et al.
(författare)
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Experimental-analytical state-space synthesis of passenger car components
- 2018
-
Ingår i: Proceedings of ISMA2018 International Conference on Noise and Vibration Engineering and USD2018 International Conference on Uncertainty in Structural Dynamics. - 9789073802995 ; 2018, s. 4021-4035
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Konferensbidrag (refereegranskat)abstract
- In this paper an experimental model of a Volvo XC90 body-in-white and a finite element model of a rear subframe are coupled for vibration assessment using a state-space synthesis method. This problem is challenging due to the complex structures considered. They are exhibiting high modal densities, high damping and the coupling is through four rubber bushings. The models are connected through four virtual points created at each coupling position. The state-space synthesis method relies on a system identification procedure for the experimental model, which in itself pose a significant challenge for the modally dense body-in-white. In this paper a newly proposed system identification technique focusing not to the least on direct accelerances, based on a subspace state-space method, is used. It also aims to fulfil physically motivated constraints. Results from the coupled system are shown to agree well with experimental data of the system assembly, and the method outperforms a finite element based coupling.
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| 22. |
- Chen, Yousheng, 1985-, et al.
(författare)
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A Pretest Planning Method for Model Calibration for Nonlinear Systems
- 2016
-
Ingår i: Model Validation and Uncertainty Quantification, Volume 3. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319297538 - 9783319297545 ; , s. 371-379
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 23. |
- Chen, Yousheng, 1985-, et al.
(författare)
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An Efficient Simulation Method for Large-Scale Systems with Local Nonlinearities
- 2016
-
Ingår i: Special topics in structural dynamics, 34th IMAC. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319299105 - 9783319299099
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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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| 24. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Experimental Validation of a Nonlinear Model Calibration Method Based on Multiharmonic Frequency Responses
- 2017
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME Press. - 1555-1415 .- 1555-1423. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 25. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Frequency Response Calculations of a Nonlinear Structure a Comparison of Numerical Methods
- 2014
-
Ingår i: Nonlinear Dynamics, Volume 2. - Cham : Springer. - 9783319045221 - 9783319045221 ; 2, s. 35-44
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 26. |
- Chen, Yousheng, 1985-, et al.
(författare)
-
Informative Data for Model Calibration of Locally Nonlinear Structures Based on Multi-Harmonic Frequency Responses
- 2016
-
Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME Press. - 1555-1415 .- 1555-1423. ; 11:5
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 27. |
- Chen, Yousheng, 1985-, et al.
(författare)
-
Model Calibration of a Locally Non-linear Structure Utilizing Multi Harmonic Response Data
- 2014
-
Ingår i: Nonlinear Dynamics, Volume 2. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319045221 - 9783319045214 ; , s. 97-109
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 28. |
- Chen, Yousheng, 1985-, et al.
(författare)
-
Model calibration of locally nonlinear structures using information from sub and super harmonic responses
- 2012
-
Ingår i: International Conference on Noise and Vibration Engineering 2012 (ISMA 2012). - Leuven : Katholieke Universiteit Leuven, Department of Mechanical Engineering. - 9781622768257 ; , s. 2451-2464
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 29. |
- Chen, Yousheng, et al.
(författare)
-
Validation of a model calibration method through vibrational testing of a mechanical system with local clearance
- 2016
-
Ingår i: Proceedings of ISMA2016 International conference on noise and vibration engineering and USD2016 International conference on uncertainty in structural dynamics. - Leuven, Belgium : Katholieke University Leuven. - 9789073802940 ; , s. 2581-2595
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 30. |
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| 31. |
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| 32. |
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| 33. |
- Fagerlund, Jessica, 1978, et al.
(författare)
-
Passive Railway Car Secondary Suspension - Force, Power, Deflections, Roll and Comfort
- 2005
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Requirements on forces that need to be delivered by an active secondary railwaysuspension system are investigated, as well as the active system’s estimated powerconsumption. This is done by calculating the corresponding properties for a specifictrain with passive suspension system: the [. . . ] train from Bombardier.Quasi-static worst case conditions are studied in order to obtain the quasi-staticforces required by each actuator. The obtained quasi-static suspension forces areused to assess requirements on the actuators in three different, possible, activesystems. All active systems assume four actuators for each railway car. Whatdiffers is which passive components that are replaced with active.For the first scenario, the active suspension replaces the anti-roll bar and thesecondary vertical damper. Then the results show that each actuator must be ableto deliver quasi-static forces of roughly 32 kN.For the second scenario, the pneumatic pump system for the air-springs, whichadapts the air pressure to compensate for payload variations, is removed. Insteadthe active suspension will be used to keep the carbody at the same vertical positionregardless of the amount of payload. This requires a quasi-static force from eachactuator of about 13 kN, for the worst case.The third scenario combines the first two cases. The resulting quasi-staticforces that the actuators might need to deliver is the sum of the quasi-static forcesfrom the two different systems mentioned above, 46 kN.To get an indication of the peak force each actuator needs to deliver, and anestimate of the power it needs to deliver, dynamic simulations are carried out onthe passive train during several running conditions. For each running condition, thepeak (i.e. maximum) force, the mean power, and the peak (i.e. maximum) powerare calculated over the simulation time. Then, the largest of each of those threequantities are selected among all running conditions. The results are, that overthe running conditions the largest peak force is 42 kN, the largest mean power is0.64 kW, and the largest peak power is 4.6 kW, assuming the first scenario above.Additional to the required forces and powers, also deflections and roll in thepassive secondary suspension, as well as passenger comfort, are calculated for thedifferent running conditions. These results form requirements, and measures forcomparison, for future active suspension system.
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| 34. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
A reduced interface component mode synthesis method using coarse meshes
- 2017
-
Ingår i: Procedia Engineering. - : Elsevier BV. - 1877-7058 .- 1877-7058. ; 199, s. 348-353
-
Konferensbidrag (refereegranskat)abstract
- Component mode synthesis is a technique to simplify the analysis of complicated finite element models. A structure is split into substructures from which reduced order models can be generated and subsequently assembled. A model reduction performance gain can be limited if the component interfaces contain many degrees of freedom, which is often the case for high resolution models. In this paper a substructuring framework with interface reduction is presented. The method first splits a detailed model into substructures. The substructures’ fine mesh is then coarsened on the internal region, while keeping the boundary mesh intact. Thereafter a Guyan reduction is performed on each coarse mesh substructure. The Guyan computations are cheap due to the reduced size of the linear equation system necessary to solve for the coarse mesh system. After synthesis of the statically reduced systems, a reduction basis for the interface degrees of freedom is computed. Thereafter a Craig-Bampton reduction is performed on each fine mesh substructure using projections with the reduced interface degrees of freedom and fixed interface modes. The method is verified on a dense mesh plate model consisting of two substructures.
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| 35. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Calibration, Validation and Uncertainty Quantification of Nominally Identical Car Subframes
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 3, s. 315-326
-
Konferensbidrag (refereegranskat)abstract
- In this paper a finite element model, with over half a million degrees-of-freedom, of a car front subframe has been calibrated and validated against experimental MIMO data of several nominally identical components. The spread between the individual components has been investigated and is reported. Sensor positioning was performed with an extended effective independence method, using system gramians to reject sensors with redundant information. The Fisher information matrix was used in the identification of the most significant model calibration parameters. Validation of the calibrated model was performed to evaluated the difference between the nominal and calibrated model, and bootstrapping used to investigate the validity of the calibrated parameters. The parameter identification, calibration, validation and bootstrapping have been performed using the open-source MATLAB tool FEMcali.
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| 36. |
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| 37. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Data-driven modal surrogate model for frequency response uncertainty propagation
- 2021
-
Ingår i: Probabilistic Engineering Mechanics. - : Elsevier BV. - 0266-8920 .- 1878-4275. ; 66
-
Tidskriftsartikel (refereegranskat)abstract
- A method is developed for propagation of model parameter uncertainties into frequency response functions based on a modal representation of the equations of motion. Individual local surrogate models of the eigenfrequencies and residue matrix elements for each mode are trained to build a global surrogate model. The computational cost of the global surrogate model is reduced in three steps. First, modes outside the range of interest, necessary to describe the in-band frequency response, are approximated with few residual modes. Secondly, the dimension of the residue matrices for each mode is reduced using principal component analysis. Lastly, multiple surrogate model structures are employed in a mixture. Cheap second-order multivariate polynomial models and more expensive Gaussian process models with different kernels are used to model the modal data. Leave-one-out cross-validation is used for model selection of the local surrogate models. The approximations introduced allow the method to be used for modally dense models at a small computational cost, without sacrificing the global surrogate model's ability to capture mode veering and crossing phenomena. The method is compared to a Monte Carlo based approach and verified on one industrial-sized component and on one assembly of two car components.
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| 38. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Experimental-Analytical Dynamic Substructuring of Ampair Testbed: A State-Space Approach
- 2014
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 1, s. 1-14
-
Konferensbidrag (refereegranskat)abstract
- The Society for Experimental Mechanics (SEM) Substructuring Focus Group has initiated a research project in experimental dynamic substructuring using the Ampair 600W wind turbine as a testbed. In this paper, experimental as well as analytical models of the blades of said wind turbine are coupled to analytical models of its brackets. The focus is on a state-space based substructuring method designed specifically for experimental-analytical dynamic substructuring. It is shown a) theoretically that the state-space method gives equivalent results to the second order methods under certain conditions, b) that the state-space method numerically produces results equivalent to those of a well-known frequency-based substructuring technique when the same experimental models are used for the two methods and c) that the state-space synthesis procedure can be translated to the general framework given by De Klerk et al.
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| 39. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Identification of physically realistic state-space models for accurate component synthesis
- 2020
-
Ingår i: Mechanical Systems and Signal Processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 145
-
Tidskriftsartikel (refereegranskat)abstract
- For components that are difficult to model with conventional analytical or numerical tools, experimentally derived state-space models can instead be used in system synthesis. For successful state-space synthesis, a physically realistic model must be identified. For this purpose, a hybrid first- and second-order system description is used here as the basis for identification. In the identification procedure, a physically motivated rigid body rank constraint is imposed together with a reciprocity constraint. The two constraints are enforced during a re-estimation phase of the state-space matrices following after a traditional state-space subspace identification phase. In this paper, two complex and modally dense industrial components are combined into a dynamical system. An experimental model of a car body-in-white structure is identified. The identified subsystem model is coupled with a finite element model of a rear subframe in a system synthesis. The two subsystems are attached through four rubber bushings modelled by finite element procedures. It is shown that the experimental-analytical assembly successfully predicts the reference measured system, with higher accuracy than what could be achieved with a model based solely on finite elements. It is also shown that synthesis with individually calibrated rear subframe models can capture the variability in the coupled system.
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| 40. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Model updating of multiple nominally identical car components
- 2020
-
Ingår i: Experimental Techniques. - : Springer Science and Business Media LLC. - 0732-8818 .- 1747-1567. ; 44:4, s. 391-407
-
Tidskriftsartikel (refereegranskat)abstract
- A method for estimation of rubber bushing stiffness parameters is presented. Four individual rubber bushings, mounted in a car rear subframe are considered. A traditional model of the bushing elements using a generalised spring model, known as a CBUSH element in Nastran, is compared to a geometrically more realistic approach where the bushing is modelled with solid elements and a linear elastic material model. Each bushing is mass loaded to better reveal the bushing's dynamic behaviour in a lower frequency range of interest. In an initial step, the overall subframe model is updated towards test data. In a second step, the bushing parameters are updated. Three nominally identical components are used to investigate the spread between the identified parameters. The model updating procedure is based on frequency responses and equalised damping. The undamped behaviour at frequencies below 300~Hz are considered. To quantify the parameter uncertainty, with respect to measurement noise for each individual, an uncertainty quantification procedure is proposed, using a linear-in-parameters surrogate model with bootstrapping.
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| 41. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Multifidelity component interface reduction and modal truncation augmentation
- 2019
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 120:1, s. 105-124
-
Tidskriftsartikel (refereegranskat)abstract
- A Hurty‐Craig‐Bampton reduced order component can have unnecessarily large dimension if it contains many interface degrees‐of‐freedom. This is often the case for high spatial resolution models. Furthermore, for such high fidelity models their static constraint modes can be expensive to compute. To overcome these problems, a component mode synthesis method with interface reduction is developed using multifidelity models. The interface reduction basis is computed from the assembled system by coarsening each substructure's mesh, but keeping the model resolution at the interface intact. It is shown that such a mesh coarsening has a small effect on the interface reduction basis quality. Using this reduction basis the dimension of the static constraint modes problem can be reduced and the modes computed at a low cost. When few interface modes can be used without significant loss of accuracy, it is possible to enrich the Hurty‐Craig‐Bampton basis with modal truncation augmentation vectors to increase accuracy at a small extra cost. The accuracy of a procedure that utilises modal truncation augmentation vectors together with the multifidelity interface reduction is investigated. The method's performance and accuracy are illustrated on a planar problem and a more complex problem from industry.
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| 42. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Parameter Estimation and Uncertainty Quantification of a Subframe with Mass Loaded Bushings
- 2017
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 3, s. 61-76
-
Konferensbidrag (refereegranskat)abstract
- In the automotive industry components are often connected through rubber bushings. The bushingsʼ material properties are usually not well known. In computational models these properties are parametrised and their spread can be considerable. A good estimate of these parameters is important in various applications, including substructuring, and for uncertainty quantification of systems with connected components. This paper deals with the calibration of an industrial size finite element model of a car subframe with parametrised bushing models. Mass loading is used on the bushings to bring local bushing modes to a lower frequency region and impose a more realistic boundary condition in component testing. The model parameters can be calibrated in different ways. In this paper two approaches are considered. They are based on two test configurations, one with and one without mass loaded boundaries. In the first case only the bushing parameters are considered for the mass loaded boundary configuration. In the second case, consisting of two steps, the configuration without mass loaded boundaries is considered in which the bushing parameters are first fixed and other model parameters considered, and in the last step a subset of all parameters is considered. The calibration, validation and uncertainty quantification, using bootstrapping, have been performed using the open-source MATLAB tool FEMcali.
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| 43. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Physically motivated rank constraint on direct throughput of state-space models
- 2018
-
Ingår i: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 51:15, s. 329-334
-
Konferensbidrag (refereegranskat)abstract
- In frequency range vibration testing a few outside band eigenmodes are often included in the system identification to compensate for residual mass and stiffness influences. It has been observed that, in particular, energy conjugate input-output pair transfer functions with strong outside band modes tend to render models with poor fit even after inclusion of mass and stiffness residuals. For such problems the inclusion of another complementary residual term has been found to improve the fit to data. In this paper, modal models identified from acceleration data with a subspace state-space method are considered. The residual mass influence is modelled with a state-space direct throughput while the stiffness and complementary residuals are modelled with extra states. Furthermore, for state-space models on accelerance form it is shown that the direct throughput matrix can be partitioned into a flexible and rigid motion partition. For systems with more inputs and outputs than rigid body modes it is shown that the rigid body motion partition has a bounded rank. The upper bound is equal to the number of rigid body modes. Therefore, for identified models on accelerance form this constraint must be enforced for physical consistency. The proposed method is applied on simulated finite element test data from an automotive component.
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| 44. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Redundant Information Rejection in Sensor Localisation Using System Gramians
- 2016
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 10, s. 325-333
-
Konferensbidrag (refereegranskat)abstract
- Sensors placement is important in vibration testing. The method of effective independence, recently extended to account for triaxial sensors, is widely used for this purpose in case a finite element model of the structure is available. In this paper a criteria is added to reject redundant information that usually arises in symmetric structures or finite element models with high candidate sensor density. A sensor placement strategy is proposed in which, initially, the method of effective independence is used to select the best sensors from a candidate set by maximising the Fisher information matrix determinant. Next, the gramians of a balanced realisation is used to compare the information between systems consisting of only previously added sensors to the final set with systems of the previous and candidate sensors. Sensors with redundant information will have negligible effect on the gramian and can be rejected. The method is fast, as gramians of systems with only one or two outputs are evaluated. It is sub-optimal in the sense that all possible sensor placement combinations are not evaluated for optimality. A test case, consisting of a rectangular plate, is presented, but the method has been used on a large scale industrial model with good results.
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| 45. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Residual States for Modal Models Identified from Accelerance Data
- 2019
-
Ingår i: Conference Proceedings of the Society for Experimental Mechanics Series. - Cham : Springer International Publishing. - 2191-5644 .- 2191-5652. ; 9, s. 195-206
-
Konferensbidrag (refereegranskat)abstract
- Residual stiffness and mass terms are often employed in frequency response synthesis to compensate for outside band eigenmodes in the identification of modal models from test data. For structures that have strongly participating modes above the test frequency band, it has been observed that in particular direct accelerances with strong outside-band modal contribution tend to render modal models that give poor fit to test data. For such problems it may be insufficient to just add residual mass and stiffness terms to the accelerance modal series to get a sufficiently improved fit. For accelerance, such residual terms are constant and quadratic in frequency. Another, residual term that is quasi-linear over the frequency range of interest has been found to augment the identified model. In this paper that complementary term is added to the constant and quadratic terms in a state-space model identification with a subspace state-space identification method. A comparison is performed to an alternative residualisation method. The methods' results are compared on simulated finite element test data from of an automotive component.
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| 46. |
- Gibanica, Mladen, 1988, et al.
(författare)
-
Spread in Modal Data Obtained From Wind Turbine Blade Testing
- 2014
-
Ingår i: Topics in Experimental Dynamic Substructuring, Conference Proceedings of the Society for Experimental Mechanics Series. - New York, NY : Springer New York. - 9781461465409 ; 2, s. 207-215
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a pre-study for an on-going research project in experimental dynamic substructuring, initiated by the SEM Substructures Focus Group. The focus group has selected a small wind turbine, the Ampair 600W, to serve as test bed for the studies. The turbine blades are considered in this study. A total of twelve blades have been tested for modal properties in a free-free configuration. The data has been acquired and analysed by students participating in the undergraduate course ”Structural Dynamics - Model Validation” at Chalmers University of Technology. Each blade was tested by different students as part of their required course work to account for spread in modal properties between the blades. A subset of the blades weretested independently multiple times to account for variability in the test setup. Furthermore, correlation analysis of test data was made with Finite Element model eigensolution data of the blade.
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| 47. |
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| 48. |
- Herlitz, Johan, 1949, et al.
(författare)
-
Long-term survival after development of acute myocardial infarction has improved after a more widespread use of thrombolysis and aspirin.
- 1999
-
Ingår i: Cardiology. - : S. Karger AG. - 0008-6312 .- 1421-9751. ; 91:4, s. 250-5
-
Tidskriftsartikel (refereegranskat)abstract
- We describe the mortality during the subsequent 5 years after development of acute myocardial infarction prior to and after the introduction of a more widespread use of thrombolytic agents and aspirin in the community of Göteborg. During period I, 4% received thrombolysis as compared with 32% during period II (p < 0.0001). The corresponding figures for prescription of aspirin at discharge were 14 and 84%, respectively (p < 0.0001). The overall 5-year mortality was 48% during period I and 46% during period II (p = 0.09). However, the age-adjusted mortality during period II was significantly reduced (risk ratio 0.86; 95% confidence interval 0.78-0.95; p = 0. 004). There was no significant interaction between improvement in survival and sex or any other parameter reflecting patients' clinical history.
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| 49. |
- Johansson, Anders, 1982, et al.
(författare)
-
A method for improving test rig performance using passive components
- 2015
-
Ingår i: Mechanical Systems and Signal Processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 52-53:1, s. 614-627
-
Tidskriftsartikel (refereegranskat)abstract
- The time waveform replication (TWR) algorithm is presently used in industry for calculating the actuation force needed to replicate a certain reference sensor output in a test rig. Power and force rate limitations restrict the feasible range of that actuation force. If the input force distribution of the reference test cannot be replicated in the test rig, the required test rig input force magnitudes may be large or the replication properties poor due to lack of controllability. To circumvent this, a theory of passive components to improve replication and limit the input force demands of dynamic test rigs is developed. The theory fits within the framework of the TWR algorithm.
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| 50. |
- Johansson, Anders, 1982, et al.
(författare)
-
An experimental approach to improve controllability in test rigs using passive components
- 2012
-
Ingår i: Proceedings, International Conference on Noise and Vibration Engineering, ISMA2012; International Conference on Uncertainty in Structural Dynamics, USD2012. Editors : P. Sas, D. Moens, S. Jonckheere. KU Leuven (Belgium), 17 - 19 September 2012. - 9789073802896 ; , s. 2367-2381
-
Konferensbidrag (refereegranskat)abstract
- The first step in successful vibration testing is to calculate input signals such that the test rig accuratelyreplicates the reference signal. The Time Waveform Replication (TWR) method, or augmentations of it, isoften used to this end. TWR and similar methods most often result in a test output which closely replicates,or tracks, the reference signal; however, if there are eigenmodes of the test specimen in the desired frequencyrange of the test which are uncontrollable, it can be shown that the output error cannot be removed beyond theuncontrollable state’s contribution to the reference trajectory. For those specific cases, a method to improvetracking by the use of passive control components designed using a validated finite element (FE) model of thetest specimen has been previously proposed by the authors. In this article we propose instead an experimentalapproach, based on state-space substructure synthesis, to passive control components design for improvedtracking in controllability-lacking test rigs.
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