| 1. |
- Allen, Matthew S., et al.
(author)
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Experimental substructuring
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 75-181
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Book chapter (other academic/artistic)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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| 2. |
- Allen, Matthew S., et al.
(author)
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Industrial applications & related concepts
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 183-231
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Book chapter (other academic/artistic)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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| 3. |
- Allen, Matthew S., et al.
(author)
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Introduction and Motivation
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 1-4
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Book chapter (other academic/artistic)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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| 4. |
- Allen, Matthew S., et al.
(author)
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Model reduction concepts and substructuring approaches for linear systems
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 25-73
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Book chapter (other academic/artistic)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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| 5. |
- Allen, Matthew S., et al.
(author)
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Model reduction concepts and substructuring approaches for nonlinear systems
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 233-267
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Book chapter (other academic/artistic)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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| 6. |
- Allen, Matthew S., et al.
(author)
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Preface
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - 2309-3706 .- 0254-1971. ; 594, s. v-vi
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Journal article (other academic/artistic)
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| 7. |
- Allen, Matthew S., et al.
(author)
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Preliminaries: Primal and dual assembly of dynamic models
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 5-24
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Book chapter (other academic/artistic)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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| 8. |
- Allen, Matthew S., et al.
(author)
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Weakly nonlinear systems: Modeling and experimental methods
- 2020
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In: CISM International Centre for Mechanical Sciences, Courses and Lectures. - Cham : Springer International Publishing. - 2309-3706 .- 0254-1971. ; 594, s. 269-277
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Book chapter (other academic/artistic)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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| 9. |
- Andersson, Niclas, et al.
(author)
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Comparison of Stimuli for Nonlinear System Response Classification
- 2020
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In: SAE International Journal of Vehicle Dynamics, Stability, and NVH. - : SAE International. - 2380-2162 .- 2380-2170. ; 4:3, s. 197-219
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Journal article (peer-reviewed)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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| 10. |
- Gibanica, Mladen, 1988, et al.
(author)
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Data-driven modal surrogate model for frequency response uncertainty propagation
- 2021
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In: Probabilistic Engineering Mechanics. - : Elsevier BV. - 0266-8920 .- 1878-4275. ; 66
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Journal article (peer-reviewed)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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| 11. |
- Gibanica, Mladen, 1988, et al.
(author)
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Identification of physically realistic state-space models for accurate component synthesis
- 2020
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In: Mechanical Systems and Signal Processing. - : Elsevier BV. - 0888-3270 .- 1096-1216. ; 145
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Journal article (peer-reviewed)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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| 12. |
- Gibanica, Mladen, 1988, et al.
(author)
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Model updating of multiple nominally identical car components
- 2020
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In: Experimental Techniques. - : Springer Science and Business Media LLC. - 0732-8818 .- 1747-1567. ; 44:4, s. 391-407
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Journal article (peer-reviewed)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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| 13. |
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| 14. |
- Lander, Sanna, et al.
(author)
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Controlling the rate of posolyte degradation in all-quinone aqueous organic redox flow batteries by sulfonated nanocellulose based membranes: The role of crossover and Michael addition
- 2024
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In: Journal of Energy Storage. - : Elsevier BV. - 2352-152X .- 2352-1538. ; 83
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Journal article (peer-reviewed)abstract
- Aqueous organic redox flow battery (AORFB) is a technological route towards the large-scale sustainable energy storage. However, several factors need to be controlled to maintain the AORFB performance. Prevention of posolyte and negolyte cross-contamination in asymmetric AORFBs, one of the main causes of capacity decay, relies on their membranes' ability to prevent migration of the redox-active species between the two electrolytes. The barrier properties are often traded for a reduction in ionic conductivity which is crucial to enable the device operation. Another factor greatly affecting quinone-based AORFBs is the Michael addition reaction (MAR) on the charged posolyte, quinone, which has been identified as a major reason for all-quinone AORFBs performance deterioration. Herein, we investigate deterioration scenarios of an all-quinone AORFB using both experimental and computational methods. The study includes a series of membranes based on sulfonated cellulose nanofibrils and different membrane modifications. The layer-by-layer (LbL) surface modifications, i.e. the incorporation of inorganic materials and the reduction of the pore size of the sulfonated cellulose membranes, were all viable routes to reduce the passive diffusion permeability of membranes which correlated to an increased cycling stability of the battery. The kinetics of MAR on quinone was detected using NMR and its impact on the performance fading was modeled computationally. The localization of MAR close to the membrane, which can be assigned to the surface reactivity, affects the diffusion of MAR reagent and the deterioration dynamics of the present all-quinone AORFB.
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| 15. |
- Nielsen, Jens, 1963, et al.
(author)
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Probability of instant rail break induced by wheel–rail impact loading using field test data
- 2022
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In: International Journal of Rail Transportation. - : Informa UK Limited. - 2324-8386 .- 2324-8378. ; 10:1, s. 1-23
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Journal article (peer-reviewed)abstract
- The probability of an instant rail break, initiated at a single pre-existing rail foot crack due to a severe wheel impact loading, is predicted using statistical methods and a time-domain model for the simulation of dynamic vehicle–track interaction. A linear elastic fracture mechanics approach is employed to calculate the stress intensity at the crack in a continuously welded rail subjected to combined bending and temperature loading. Based on long-term field measurements in a wayside wheel load detector, a three-parameter probability distribution of the dynamic wheel load is determined. For a faster numerical assessment of the probability of failure, a thin plate spline regression is implemented to develop a meta-model of the performance function quantifying the stress intensity at the crack. The methodology is demonstrated by investigating the influence of initial crack length, fracture toughness and rail temperature difference on the risk for an instant rail break.
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