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- Lenhof, Bernd, 1975, et al.
(författare)
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A comparison of variational formats for porous media subjected to dynamic loading
- 2011
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Ingår i: International Journal for Numerical and Analytical Methods in Geomechanics. - : Wiley. - 0363-9061 .- 1096-9853. ; 35:7, s. 807-823
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comparison of two variational formats for fully saturated porous media subjected to dynamic loading, whereby the general situation of relative fluid acceleration is considered: (1) the classical three-field (u, p, w)-format and (2) a novel two-field (u, p)-format, where the seepage velocity w is a spatially 'local' field whose treatment resembles that of internal variables in material models. The limited numerical comparison shows that the (u, p)-format competes well with the (u, p, w)-format. Indeed, it is consistent with the general acceleration modeling in the full range of permeabilities. Moreover, in the low permeability regime (where the magnitude of w is insignificant), the new format reflects the situation pertinent to 'added-mass' and is more efficient than the classical (u, p, w)-format. Finally, the (u, p)-format can conveniently be implemented in existing FE-codes based on the 'added mass' formulation.
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| 3. |
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| 4. |
- Kettil, Per, 1972, et al.
(författare)
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Coupled simulation of wave propagation and water flow in soil induced by high-speed trains
- 2008
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Ingår i: International Journal for Numerical and Analytical Methods in Geomechanics. - 0363-9061 .- 1096-9853. ; 32:11, s. 1311-1319
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to simulate the coupled dynamic deformation and water flow that occur in saturated soils when subjected to traffic loads, which is a problem with several practical applications. The wave propagation causes vibrations leading to discomfort for passengers and people in the surroundings and increase wear on both the vehicle and road structure. The water flow may cause internal erosion and material transport in the soil. Further, the increased pore water pressure could reduce the bearing capacity of embankments. The saturated soil is modelled as a water-saturated porous medium. The traffic is modelled as a number of moving wheel contact loads. Dynamic effects are accounted for, which lead to a coupled problem with solid displacements, water velocity and pressure as primary unknowns. A finite element program has been developed to perform simulations. The simulations clearly demonstrate the induced wave propagation and water flow in the soil. The simulation technique is applicable to railway as well as road traffic.
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| 5. |
- Kettil, Per, 1972, et al.
(författare)
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Simulation of inelastic deformation in road structures due to cyclic mechanical and thermal loads
- 2007
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Ingår i: Computers & Structures. ; 85, s. 59-70
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents modeling and simulation of inelastic deformation in road structures leading to rutting. Two material models, one for asphalt-concrete and another for unbound materials, have been calibrated to laboratory test data. The models account for the time and temperature dependent deformation of the asphalt-concrete as well as the friction and cyclic compaction of the unbound layers. The models have been used in simulations of a complete road structure exposed to cyclic mechanical and thermal loads. The simulation results are qualitatively similar to the rutting observed in reality. The simulations can either trace the complete history of the individual load cycles, or can be performed to directly obtain the accumulated effect after a certain number of load cycles. This makes it possible to get quickly the result due to a large number of loadings as desired in engineering design practice.
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| 6. |
- Lenhof, Bernd, 1975, et al.
(författare)
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Assessment of acceleration modelling for fluid-filled porous media subjected to dynamic loading
- 2008
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Ingår i: International Journal for Numerical and Analytical Methods in Geomechanics. - : Wiley. - 0363-9061 .- 1096-9853. ; 32:2, s. 109-119
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to examine the importance of different possible simplifying approximations when performing numerical simulations of fluid-filled porous media subjected to dynamic loading. In particular, the relative importance of the various acceleration terms for both the solid and the fluid, especially the convective contribution, is assessed. The porous medium is modelled as a binary mixture of a solid phase, in the sense of a porous skeleton, and a fluid phase that represents both liquid and air in the pores. The solid particles are assumed to be intrinsically incompressible, whereas the fluid is assigned a finite intrinsic compressibility. Finite element (FE) simulations are carried out while assuming material properties and loading conditions representative for a road structure. The results show that, for the range of the material data used in the simulations, omitting the relative acceleration gives differences in the solution of the seepage velocity field, whereas omitting only the convective term does not lead to significant differences.
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| 7. |
- Lenhof, Bernd, 1975
(författare)
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Computational Modeling of the Dynamics of Fluid-Filled Porous Media with Application to Road and Railway Structures
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dynamics of fluid-saturated porous media is a challenging topic with applications in many engineering fields like, e.g., road and railway mechanics. The complexity of the problem requires high computational effort when performing simulations of the coupled dynamic deformation and fluid flow in a saturated porous medium. Different possibilities for reducing the computational costare discussed in the thesis. The porous medium is modeled as a binary mixture of a solid matrix phase and a fluid phase, whereby the thermodynamically consistent so-called Porous Media Theory is adopted. Reduction of the computational effort is achieved through simplifications of the continuum (physical) model as well as a novel reformulation of the variational format.As to the adopted modeling, different simplifying approximations for the relative fluid acceleration are compared. From the numerical examples, it is concluded that the contribution from the convective part of the relative fluid acceleration may be neglected without significant loss of accuracy; however, neglecting the complete relative fluid acceleration may lead to detrimental loss of accuracy. A problem of significant engineering importance, to which the developed model has been applied, is the coupled dynamic deformation and water flow in soils subjected to over-rolling of a high-speed train.As to the choice of computational method for the fully dynamic response, a novel two-field variational format, with the seepage velocity treated as a "local" field, was developed and compared to the more commonly used three-field format. This leads to a substantial reduction of the computational effort for given accuracy. A pressure gradient dependent permeability coefficient was introduced in the constitutive model for the seepage velocity. This was done essentially to illustrate the effectiveness of algorithmic structure for a nonlinear model.
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| 8. |
- Lenhof, Bernd, 1975
(författare)
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On the Dynamics of Porous Media - Application to Road and Railway Structures
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Load-bearing road and railway structures normally consist of layers of particulate porous materials, often with bitumen-based binders. The layered system is subjected to dynamic loading from traffic, which inevitably causes material deterioration that enhances permanent surface deformation. For example, internal erosion of fines from the solid skeleton is brought about by high seepage rates in the open pore system. The interplay between deformation, pore-water flow and material degradation is a highly complex problem that poses significant challenges from both the modeling and computational viewpoints. The thesis is, therefore, concerned also with means of reducing the computational cost without jeopardizing the predictive capability.The so-called Porous Media Theory (a mixture theory with phase volume fractions) is adopted as the modeling paradigm. In order to model the coupling between deformationand pore-water flow in the presence of internal erosion, a triphasic erosion system is considered in terms of the solid skeleton and an ideal mixture of pore-water and eroded fines (the abrasive phase). Small strain kinematics is assumed, and the pertinent model is obtained from consistent linearization of finite strain kinematics. Linear elastic response is assumed in the absence of erosion (for fixed porosity); however, strong nonlinearity in stiffness and permeability arise due to the finite change of porosity from erosion. The developed simulationtool is used to analyze a simplified road structure subjected to dynamic loading.As part of the effort to reduce the model complexity and computational cost, different simplifying approximations for the relative fluid acceleration are assessed. From the numerical examples, it is concluded that the convective part of the relative fluid acceleration may be neglected without significant loss of accuracy; however, simply using the ”added mass” approximation is normally unacceptable. A novel space-variational format with reduced number of global fields was developed based on the time-discretized balance equations. For the adopted triphasic system, three global fields (displacement, pore-pressure and abrasive volume fraction) and two local fields (seepage velocity and total porosity) constitute the coupled problem. The local fields can be eliminated similarly to internal variables in constitutive models. A comparison with the ”classical” format carried out for a biphasic model (without erosion) showed that the novel format competes well in terms of convergence behavior.
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