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| 2. |
- Ekevid, Torbjörn, et al.
(author)
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Adaptive solid wave propagation : Influences of boundary conditions in high-speed train applications
- 2006
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In: Computer Methods in Applied Mechanics and Engineering. - : Elsevier. - 0045-7825. ; 195:4-6, s. 236-250
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Journal article (peer-reviewed)abstract
- Wave propagation in solid materials is of great interest in many engineering applications. The fact that the area of interest changes with time creates a number of computational problems such as the need for a mesh density varying in space and time. This means that the mesh must be continuously updated and controlled, rendering a large demand of computer effort. In certain applications like railway mechanics there are mobile loads. A load speed close to the natural speed in the underlying soil causes specific problems, shock waves being one of them. The transmitted waves have to leave the defined finite element domain without reflection, which imposes a need for certain modelling methods. The paper will deal with quality controlled FE-procedures for wave propagation including error estimation and mesh refinement/coarsening. As an application an important problem from railway mechanics is considered. When a high-speed train approaches an area with decreasing thickness of underlying soft soil on a stiff rock it is expected that the reflection of the wave will increase the total amplitude of the wave. We will study this problem with the procedures described above in full 3D with partly absorbing boundaries
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| 3. |
- Ekevid, Torbjörn, 1973, et al.
(author)
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Computational railway dynamics
- 2006
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In: Computational Mechanics (editors C A Mota Soares, J A C Martins, H C Rodrigues and J A C Ambrósio). ; , s. 577-598
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Journal article (peer-reviewed)
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| 4. |
- Ekevid, Torbjörn, 1973, et al.
(author)
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Reflection waves from high speed trains - adaptive FE solutions
- 2003
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In: Mekanikdagar 2003, Göteborg 13 - 15 Augusti.. ; , s. 66-
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Conference paper (other academic/artistic)abstract
- Wave propagation in solid materials is of great interest in many engineering applications. The fact that the area of interest changes with time gives a number of computational problems like the need of time and place dependent mesh density. This means that the mesh must be continuously updated and controlled, leading to a large demand of computer effort. In some applications like in railway mechanics loads are moving which gives rise to certain problems like shock waves when the speed of the moving load is close to the natural speed in the underlying soil material[1]. Related to such problems the wave has to leave the defined finite element domain without reflection, which demands certain methods.The paper will deal with quality controlled FE-procedures for wave propagation including error estimation[2] and mesh refinement/coarsening. As the problems are large (3D) and need many steps in time and iteration processes to handle nonlinearities direct solvers are out of question, and iterative techniques based on multigrid[3] have to be used. As an application an important problem from railway mechanics is considered. When a high speed train approaches an area with decreasing thickness of underlying soft soil on a stiff rock, a reflection of the wave will increase the total height of the wave, in a similar way as when sea waves approaches a shallow shore; it becomes much higher and brakes. We will study this problem with the procedures described above in 2D as well as in full 3D with partly absorbing boundaries.References:[1]T. Ekevid, Computational Solid Wave Propagation Numerical Techniques and Industrial Applications, Ph. D. thesis, Department of Structural Mechanics, Chalmers University of Technology, Publication 02:10, 2002.[2]K. Eriksson, D. Estep, P. Hansbo, C. Johnson, Computational Differential Equations, Studentlitteratur, Lund, Sweden, (1996).[3]U. Trottenberg, C. Oosterlee and A. Schüller, Multigrid, Academic Press, London (2001).
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| 5. |
- Kettil, Per, 1972, et al.
(author)
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Moving mesh domain adaptation technique - application to train induced wave propagation
- 2005
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In: Proceedings of the Second International Conference on Adaptive Modeling and Simulation held in Barcelona, Spain 8 - 10 September 2005. ; , s. 81-91
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Conference paper (other academic/artistic)abstract
- Railways are an important part of the infrastructure in the society and the cost for their construction and maintenance is significant. Hence, understanding, predication andimprovement of their performance is vital to utilize the resources in the best possible manner. Mathematical modeling and simulation of the railway mechanics provides a methodology to achieve this goal.In previous work, see e.g. [1]-[2], an integrated dynamic model of the entire 3D vehicle - track - underground system has been developed. The train has been modelled by rigid bodies, springs and dampers. The track and the underground have been modelled as elastic solids by FEM. This model has been successfully used to simulate and study the train induced wave propagation, see [1]-[2]. However, the size of the FE domain of the track and underground hasbeen limited to approximately 200 m due to high computational cost (time). Hence, it has onlybeen possible to follow the train running for about 200 metres.To be able to follow the train for many kilometres, something radical has to be done with the computational scheme. In this paper the following will be tested:1. Moving mesh domain adaptation technique2. Absorbing Boundary LayersThe idea of the moving mesh is that the FE mesh should follow the moving train or in other words, that in each time step only the domain in the vicinity of the train should be discretized by FEM. This scheme may be viewed as a special form of mesh adaptation where the mesh islocated, graded and updated based on error estimation [3] or as a change to the governing equations by using a moving (convective) coordinate system [4]. In addition, the exterior infinite domain will be represented by an absorbing boundary layer (cf. [5] for a general introduction)rather than by the previously tested SBFEM to reduce computational time and complexity.The paper gives the full details of the computational scheme and numerical testing.REFERENCES[1] T. Ekevid and N.-E. Wiberg: Wave propagation related to high-speed train - a scaled boundary FE-approach for unbounded domains, Comput. Mehods Appl. Mech. Engrg., Vol. 191, pp. 39473964, (2002).[2] H. Lane, T. Ekevid and N.-E. Wiberg: Towards Integrated Vehicle-track-underground Modelling of Train Induced Wave Propagation. 4th European Congress on Computational Methods in Applied Sciences and Engineering. July 24-28 2004, Jyväskylä, Finland.[3] M. J. Baines, M. E. Hubbard and P. K. Jimack: Moving Mesh Finite Element Algorithm for the Adaptive Solution of Time-Dependent Partial Differential Equations with MovingBoundaries. Preprint submitted to Elsevier, 23 January 2005.[4] S. Krenk, L. Kellezi, S.R.K. Nielsen and P.H. Kirkegaard: Finite Elements and TransmittingBoundary Conditions for Moving Loads, EURODYN conference, June 7-10, 1999, Prague, Czech Republic.[5] I. Harari and Z. Shohet: On non-reflecting boundaries in unbounded elastic solids. Comput. Mehods Appl. Mech. Engrg., Vol. 163, pp. 123-139, (1998).
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| 6. |
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| 7. |
- Lane, Håkan, 1975, et al.
(author)
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Adaptive Solid Wave Propagation - Influences of Boundary Conditions in High-Speed Train Applications
- 2003
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In: Proceedings of the First International Conference on Adaptive Modeling and Simulation held in Göteborg, Sweden 29 September - 1 October 2003. - 8495999307 ; , s. 93-94
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Conference paper (other academic/artistic)abstract
- Wave propagation in solid materials is of great interest in many engineering applications. The fact that the area of interest changes with time creates a number of computational problems such as the need for a mesh density varying in space and time. This means that the mesh must be continuously updated and controlled, rendering a large demand of computer effort. In certain applications like railway mechanics there are mobile loads. A load speed close to the natural speed in the underlying soil causes specific problems, shock waves being one of them. The mechanism behind high velocity wave propagation is described in Ekevid and Wibergi. Furthermore, the wave has to leave the defined finite element domain without reflection, which imposes a need for certain modeling methods. The paper will deal with quality controlled FE-procedures for wave propagation including error estimation and mesh refinement/coarsening. As the problems are large (3D) and need many steps in time and iteration processes to handle nonlinearities direct solvers are ruled out. Iterative techniques based on multigrid are preferred. As an application an important problem from railway mechanics is considered. When a high speed train approaches an area with decreasing thickness of underlying soft soil on a stiff rock, a reflection of the wave will increase the total height of the wave, in a way resembling to sea waves approaching a shallow shore; it becomes much higher and brakes. We will study this problem with the procedures described above in full 3D with partly absorbing boundaries.
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| 8. |
- Lane, Håkan, 1975
(author)
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Computational Railway Dynamics - Integrated Train - Track - Subgrade Modeling and Simulations
- 2007
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Doctoral thesis (other academic/artistic)abstract
- The primary objective of the thesis has been to extend the capabilities for computational modeling, prediction and simulation of the elastic response of the train, track structure and soil in railway systems. The industrial background is the high level of ground borne vibrations reported from citizens as a consequence of train traffic (in particular from high speed trains) in several Swedish locations. Computational analysis is a tool for enhanced understanding of the governing phenomena, preliminary tests of different countermeasures and for visualization of the behaviour of the system.An advanced application encompassing finite element analysis, a large variety of solvers for large systems of equations and generation of output for graphical visualisaton was developed prior to this project. During the course of the work described in this thesis, it has been enhanced by three main features:The integration of three-dimensional rigid body dynamics with finite elements for analysis of vehicle / solid interaction problemsThe insertion of a fictitious layer of viscoelastic elements of a viscoelastic material to reduce unphysical reflections in the solutionMoving mesh calculations allowing for analysis over long distancesThe outcome is an advanced application for vehicle – solid interaction problems over long distances. The inclusion of rigid body equations incorporates the dynamic behaviour of the train components, allows for tests of various passive or semi active suspension strategies and makes it possible to analyse the results in the carbody, bogies and wheels. Wheel – rail interface modelling accounts for contact stiffness theory and opens up for simulations of the effect of various types of imperfections. Usage of a moving mesh extends the capacity to selectively relocate a predefined mesh so that the track / ground geometries and track design can be modified as a function of the traveled distance.The high level of detail leads to a system with many degrees of freedom. It is of great importance to consider the relationship between the range of problems that can be solved, the computational resources and efficiency of the numerical procedures and the chosen model. This is one of the main themes of the appended articles.Simulations of real world problems confirm that passage at certain critical train speeds leads to strongly magnified vibrations in the track and soil. In another study, mitigation techniques show that lime cement columns can provide very good protection against ground borne vibrations. Finally, it has been shown that rail head irregularities beyond allowed levels can induce vibrations threatening the comfort of the people in the coach.
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| 9. |
- Lane, Håkan, 1975, et al.
(author)
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Finite element calculations of rail vibration countermeasures
- 2007
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In: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 45:6, s. 565-581
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Journal article (peer-reviewed)abstract
- Elastic waves may constitute a nuisance for people living close to high- speed lines. In order to decrease the spread of vibrations, it is common to reinforce the ground with lime cement columns. This article presents the results of simulations of three different ways to install the columns. The calculations have been done with an integrated rigid body - finite element model. Equations from various physical domains are merged into one big system. The results indicate that the straight configuration works best to protect the track. When attention is focused on preventing vibrations from the soil, the leaning column method is more effective. The chosen technique would depend on the aims of the countermeasure.
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| 10. |
- Lane, Håkan, 1975, et al.
(author)
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Modelling train passage in curves with isoparametric differntial constraint equations.
- 2004
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In: Proceedings of the 17th Nordic Seminar on Computational Mechanics. ; , s. 141-144
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Conference paper (other academic/artistic)abstract
- A high speed train traveling at or above the wave velocity of the top layer of soil will inevitablycause shock waves to spread to the surroundings. The previous model [1] where the rigid body dynamics of the train was connected to the soil finite element domain will be extended to allow passage through portions of curved track. The constraint equations representing the rail guiding the wheel are inserted into a monolithic system based on Lagrange multipliers solved in the time domain with a Newmark scheme.Reference[1] H. Lane, T. Ekevid and N.-E. Wiberg: Towards Fully Integrated Vehicle-Track-Underground Modelling of Train Induced Wave Propagation. Presented at the 4th European Congress on Computational Methods in Applied Sciences and Engineering, Jyväskylä 2004.
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