| 1. |
- Aggestam, Emil, 1992, et al.
(författare)
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Numerical model reduction with error control in computational homogenization of transient heat flow
- 2017
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Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825. ; 326, s. 193-222
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Tidskriftsartikel (refereegranskat)abstract
- Numerical Model Reduction (NMR) is exploited for solving the finite element problem on a Representative Volume Element (RVE) that arises from the computational homogenization of a model problem of transient heat flow. Since the problem is linear, an orthogonal basis is obtained via the classical method of spectral decomposition. A symmetrized version of the space–time variational format is adopted for estimating the error from the model reduction in (i) energy norm and in (ii) given Quantities of Interest. This technique, which was recently developed in the context of the (non-selfadjoint) stationary diffusion–convection problem, is novel in the present context of NMR. By considering the discrete, unreduced, model as exact, we are able to obtain guaranteed bounds on the error while using only the reduced basis and with minor computational effort. The performance of the error estimates is demonstrated via numerical results, where the subscale is modeled in both one and three spatial dimensions.
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| 2. |
- Aggestam, Emil, 1992
(författare)
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Comparison of the dynamic response and environmental impact between traditional and innovative railway track systems
- 2023
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Ingår i: International Journal of Rail Transportation. - : Informa UK Limited. - 2324-8386 .- 2324-8378. ; 11:5, s. 685-704
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Tidskriftsartikel (refereegranskat)abstract
- Railways employ a range of different railway track forms. Here, a ballasted track design is compared to three different slab track solutions. The track designs are compared using both a life cycle analysis (LCA) and a methodology for simulation of three-dimensional vertical dynamic vehicle–track interaction, which has been verified versus field measurements. The interaction between vehicle and track is simulated in the time domain using an extended state-space vector approach. For the investigated load cases involving representative wheel and track irregularities, it is concluded that the maximum stress in the concrete parts is, for all designs, below the maximum flexural tensile strength. From the LCA, it is concluded that the production of steel and concrete cause most CO2 emissions, while the CO2 emissions due to maintenance activities such as tamping and rail grinding are only a small part of the overall emissions.
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| 3. |
- Aggestam, Emil, 1992, et al.
(författare)
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Dynamic interaction between vehicle and slab track – Influence of track design parameters
- 2018
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Ingår i: The Dynamics of Vehicles on Roads and Tracks. - 9781138035713 ; 2, s. 699-704
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Konferensbidrag (refereegranskat)abstract
- The vertical dynamic interaction between a high-speed railway vehicle and slab track is simulated in the time domain using a two-dimensional track model. The transient interaction problem is solved using an extended state-space vector approach in combination with a complex-valued modal superposition technique for the track model. The presented slab track model includes two layers of concrete beams, where the panels of the upper layer are described by possibly coupled beams of finite length, while the roadbed in the lower layer is a continuous beam. Both rail and concrete layers are modelled using Rayleigh-Timoshenko beam theory. The presented model is applied to calculate the influences of foundation stiffness gradient and track design parameters on various track responses. In particular, the influences of the thickness of the roadbed on the load distribution on the foundation, and of the stiffness of the rail pad on the bending moment in the concrete panels, are investigated in two demonstration examples.
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| 4. |
- Aggestam, Emil, 1992, et al.
(författare)
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Innovative requirements and evaluation methods for slab track design
- 2024
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - 0954-4097 .- 2041-3017. ; 238:6, s. 651-661
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Tidskriftsartikel (refereegranskat)abstract
- With increasing train speeds and reduced time windows for maintenance work, the interest in the application of slab track technology to increase the capacity of high-speed railways has grown. Slab track may still be considered a relatively young technology, but with several different designs available on the market. Current research on slab tracks commonly focuses on improved methods. In contrast, the formulation of requirements, and evaluation towards these, are seldom investigated. In this paper, state-of-the-art simulation models are employed to illustrate and address the needs for innovative requirements in terms of structural integrity and robustness, life cycle cost (LCC) and environmental footprint of new and existing slab track designs. Based on demonstration examples, it is argued that current standards may lead to overly conservative designs inducing higher LCC and environmental footprint than necessary. Extensions of the standards in terms of LCC and environmental footprint are suggested. The conflict of interest between structural integrity and robustness, LCC and environmental footprint is discussed, and suggestions for how to optimise slab track structures are proposed.
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| 5. |
- Aggestam, Emil, 1992, et al.
(författare)
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Multi-objective design optimisation of transition zones between different railway track forms
- 2018
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Ingår i: Proceedings of the 11th International Conference on Contact Mechanics and Wear of Rail/wheel Systems, CM 2018. - : TU Delft. - 2590-0609. - 9789461869630 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- The vertical dynamic interaction between vehicle and railway track is simulated in the time domain using an extended state space vector approach. The track model includes a transition zone between slab track on a bridge and ballasted track on an embankment. By considering a multi-objective optimisation problem, solved using a genetic algorithm, selected vehicle and track responses are simultaneously minimised by optimising the distributions of rail pad stiffness and sleeper spacing in the transition zone. It is shown that the magnitudes of the maximum dynamic loads in the optimised transition zone can be reduced to be similar as the magnitudes far away from the transition zone.
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| 6. |
- Aggestam, Emil, 1992, et al.
(författare)
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Multi-objective optimisation of transition zones between slab track and ballasted track using a genetic algorithm
- 2019
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 446, s. 91-112
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Tidskriftsartikel (refereegranskat)abstract
- The vertical dynamic vehicle–track interaction in a transition between ballasted track and slab track is simulated in the time domain using an extended state-space vector approach. A complex-valued modal superposition technique is applied for the linear, time-invariant and non-periodic finite element model of the railway track. By considering a multi-objective optimisation problem solved by a genetic algorithm, the maximum dynamic loads on the track structure are minimised with respect to the selected design variables. To reduce the risk of long-term degradation of track geometry due to ballast/subgrade settlement, the transition zone is designed to minimise the influence of the track stiffness gradient between the two different track forms. The methodology is demonstrated by minimising the maximum wheel–rail contact force and the maximum pressure between sleeper/panel and foundation, while the selected design variables are distributions of rail pad stiffness and sleeper spacing adjacent to the transition. From the solution of the optimisation problem, non-dominated fronts are obtained illustrating potential for a significant reduction of the dynamic loads. It is shown that the optimised design leads to a more uniform distribution of load on the foundation reducing the risk of differential track settlement. The influences of the length of the transition zone and direction of travel on the maximum dynamic loads are investigated. Prescribed irregularities in longitudinal level may be accounted for but have been neglected in the optimisation as the optimised design would be more influenced by the given irregularity than by the stiffness gradient.
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| 7. |
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| 8. |
- Aggestam, Emil, 1992, et al.
(författare)
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Optimisation of slab track design considering dynamic train–track interaction and environmental impact
- 2022
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Modern railway tracks for high-speed traffic are often built based on a slab track design. A major disadvantage of slab track compared to conventional ballasted track is that the environmental impact of the construction is higher due to the significant amount of concrete required. In this paper, the dimensions of the rectangular cross-sections and the types of concrete used in slab tracks are optimised with the objective to minimise greenhouse gas emissions, while considering the constraint that the design must pass the static dimensioning analysis described in the European standard 16432-2. The optimised track design is also analysed using a three-dimensional (3D) model of vertical dynamic vehicle–track interaction, where the rails are modelled as Rayleigh–Timoshenko beams and the concrete parts are represented by quadratic shell elements. Wheel–rail contact forces and the time-variant stress field of the concrete parts are calculated using a complex-valued modal superposition for the finite element model of the track. For the studied traffic scenario, it is concluded that the thickness of the panel can be reduced compared to the optimised design from the standard without the risk of crack initiation due to the dynamic vehicle load. In parallel, a model of reinforced concrete is developed to predict crack widths, the bending stiffness of a cracked panel section and to assess in which situations the amount of steel reinforcement can be reduced. To reduce the environmental impact even further, there is potential for an extended geometry optimisation by excluding much of the concrete between the rails.
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| 9. |
- Aggestam, Emil, 1992
(författare)
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Simulation of vertical dynamic interaction between railway vehicle and slab track
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The usage of slab track for high-speed railway lines has increased in recent decades. In Sweden, the building of new railway lines for higher speed and the selection of track design for such lines are currently being debated. Slab track has, so far, only been applied in small scale in Sweden, which implies that the knowledge and experience of such track are limited. This thesis aims to improve the understanding of the dynamic interaction between railway vehicle and slab track. The vertical dynamic vehicle–track interaction is simulated in the time domain using an extended state-space vector approach. By using a complex-valued modal superposition technique for the considered linear, time-invariant and two-dimensional track models, the computational cost of solving the associated initial-value problem is reduced. Two generic slab track models, including one or two layers of concrete slabs, are presented. The upper layer of the two-layer slab track model is described by decoupled beams of finite length, while the lower layer is a continuous beam. From the solution of the initial-value problem, wheel–rail contact forces, bending moments in the concrete panel and load distributions on the supporting foundation are evaluated. The presented models are applied to calculate the influences of track design parameters on various track responses. Furthermore, the influences of longitudinal track stiffness gradients and rail imperfections causing periodic and transient excitations are analysed. Transition zones between the one-layer slab track model and a ballasted track model are analysed. By considering a multi-objective optimisation problem solved by a genetic algorithm, the maximum dynamic loads on the track structure are minimised with respect to the selected design variables. From the solution of the optimisation problem, a non-dominated front of the objective functions is obtained illustrating potential for a significant reduction of the dynamic loads. Since the transition zones are optimised neglecting the influence of wheel and rail irregularities, a methodology is proposed to assess the robustness of the optimal design by evaluating its performance when periodic rail irregularities with different combinations of wavelength and phase, relative to the position of the transition, are applied in the model.
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| 10. |
- Aggestam, Emil, 1992, et al.
(författare)
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Simulation of vertical dynamic vehicle–track interaction – Comparison of two- and three-dimensional models
- 2020
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Ingår i: Lecture Notes in Mechanical Engineering. - Cham : Springer International Publishing. - 2195-4356 .- 2195-4364. ; , s. 415-422
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Konferensbidrag (refereegranskat)abstract
- By using an extended state-space vector approach, the vertical dynamic vehicle–track interaction between a railway vehicle and a slab track is simulated in the time domain. Both two- and three-dimensional track and vehicle models are considered. In the two-dimensional track model, the rail, panel and roadbed are modelled using Rayleigh‒Timoshenko beam elements. In the three-dimensional track model, the rails are modelled using Rayleigh–Timoshenko beam elements, whereas the panel and roadbed are modelled by 3D brick elements. Based on Python scripts, the parameterised three-dimensional track model is developed in Abaqus, from which the system matrices are exported to Matlab where the dynamic analysis is performed. In the presented numerical examples, similarities and differences between the two models are discussed, and it is highlighted in what scenarios the different models are feasible to employ.
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