| 1. |
- Larsson, Fredrik, 1975, et al.
(författare)
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Computational homogenization of uncoupled consolidation in micro-heterogeneous porous media
- 2010
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Ingår i: International Journal for Numerical and Analytical Methods in Geomechanics. - : Wiley. - 0363-9061 .- 1096-9853. ; 34:14, s. 1431-1458
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Tidskriftsartikel (refereegranskat)abstract
- Variationally consistent homogenization is exploited for the analysis of transient uncoupled consolidation in micro-heterogeneous porous solids, whereby the classical approach of first-order homogenization for stationary problems is extended to transient problems. Homogenization is then carried out in the spatial domain on representative volume elements (RVE), which are introduced in quadrature points in standard fashion. Along with the classical averages, a higher-order conservation quantity is obtained. An iterative FE2-algorithm is devised for the case of nonlinear permeability and storage coefficients, and it is applied to pore pressure changes in asphalt-concrete (particle composite). Various parametric studies are carried out, in particular, with respect to the influence of the 'substructure length scale' that is represented by the size of the RVE's.
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| 2. |
- Larsson, Fredrik, 1975, et al.
(författare)
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Variationally consistent computational homogenization of transient heat flow
- 2010
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 81:13, s. 1659-1686
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Tidskriftsartikel (refereegranskat)abstract
- A framework for variationally consistent homogenization, combined with a generalized macrohomogeneity condition, is exploited for the analysis of non-linear transient heat conduction. Within this framework the classical approach of (model-based) first-order homogenization for stationary problems is extended to transient problems. Homogenization is then carried out in the spatial domain on representative volume elements (RVE), which are (in practice) introduced in quadrature points in standard fashion. Along with the classical averages, a higher order conservation quantity is obtained. An iterative FE2-algorithm is devised for the case of non-linear diffusion and storage coefficients, and it is applied to transient heat conduction in a strongly heterogeneous particle composite. Parametric Studies are carried Out, in particular with respect to the influence of the 'internal length' associated with the second-order conservation quantity. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 3. |
- Liu, T., et al.
(författare)
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Heterodimer Nanostructures Induced Energy Focusing on Metal Film
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:14, s. 7778-7784
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Tidskriftsartikel (refereegranskat)abstract
- As a newly discovered surface plasmon resonance system, the nanoparticle dimer film structure provides a novel approach to enhance light power on a plane film due to the redistribution of the electromagnetic field. This structure has been widely applied in surface enhanced Raman scattering (SERS), solar cells, photocatalysis, etc., especially for the homodimer film case. However, the properties of heterodimers on film still remain unclear. In this work, the effect of particle size on electromagnetic field redistribution for a Ag nanoparticle dimer on Au film system is investigated first. The results obtained from the finite element method indicate that a smaller nanoparticle has much greater ability to focus light energy on Au film, and the corresponding energy can be 5 times stronger than that of the larger nanoparticle case. Further research indicates that this energy focusing ability has a strong relationship to the wavelength and the diameter ratio of the dimer. A similar focusing phenomenon has been found in the system of thick nanowire small nanoparticle on film. Then the SERS spectra collected in the small nanoparticle large nanowire system provide experimental evidence for this theoretical predication. Our results strengthen the understanding of surface plasmon on plane film and have potential applications in surface plasmon related fields.
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| 4. |
- Runesson, Kenneth, 1948, et al.
(författare)
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Assessment of homogenization errors in transient problems
- 2011
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Ingår i: Recent Developments and Innovtive Applications in Computational Mechanics, D. Mueller-Hoeppe, S. Loehnert and S. Reese (eds.). - 9783642174834 ; , s. 207-214
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Konferensbidrag (refereegranskat)
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| 5. |
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| 6. |
- Su, Fang, 1983, et al.
(författare)
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Computational homogenization of coupled consolidation problems in micro-heterogeneous porous media
- 2011
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 88:11, s. 1198-1218
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Tidskriftsartikel (refereegranskat)abstract
- Computational homogenization is exploited for the analysis of transient hydro-mechanically coupled problems subjected to quasistatic loading (consolidation) in micro-heterogeneous porous solids. The classical approach of first-order homogenization is adopted in the spatial domain on representative volume elements (RVE), which are introduced in quadrature points in standard fashion. Along with the classical averages, a higher order conservation quantity is obtained. An iterative FE 2-algorithm is devised for the case of nonlinear permeability and storage coefficients, and it is applied to pore pressure changes in asphalt-concrete (particle composite). Various parametric studies are carried out, in particular with respect to the influence of the characteristics (size, particle arrangement) of the RVE's.
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| 7. |
- Su, Fang, 1983, et al.
(författare)
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Computational Homogenization of Transient Heat Conduction
- 2008
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Ingår i: 21st Nordic Seminar on Compuational Mechanics (T. Kvamsdal, K.M. Mathisen and B. Pettersen Eds.). - 9788496736566 ; , s. 156-158
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A Variational Multiscale Modeling framework, combined with a generalized macro-homogeneity condition, is exploited for the analysis of nonlinear transient heat conduction in a strongly heterogeneous particle composite. For the special case of a linear problem, a model-adaptive approach is adopted based on duality arguments which devises a low cost ’work model' wherever appropriate in order to reduce the computational cost.
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| 8. |
- Su, Fang, 1983
(författare)
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Computational Homogenization of Transient Problems - Application to Porous Media
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to the development and analysis of a homogenization-basedcomputational strategy for simulating the transient and nonlinear coupled consolidationproblem in micro-heterogeneous porous media. A variational framework and the pertinentfinite element (FE) strategy, based on a generalized macro-homogeneity condition,are proposed for the spatial homogenization of a class of transient problems, wherebythe classical assumption of first order homogenization is adopted. The homogenizationis carried out on Representative Volume Elements (RVEs), which in the discrete settingare introduced in quadrature points of the macroscale elements in the spatial domain.The corresponding algorithm is thus of a nested character, often referred to as a ”FiniteElement Square” (FE2) implementation. Along with the classical averages, a higher orderconservation quantity is obtained. Dirichlet and Neumann boundary conditions areimposed on the RVEs as prolongation conditions that connect the macro- and subscales.The corresponding algorithmic tangent tensors for fully nonlinear material response arederived. The accuracy of homogenization relies on various features of the RVEs, includingsize, geometrical structure, subscale constitutive models, prolongation conditions and FEdiscretization.In particular, it is important to choose the proper prolongation conditionsin order to keep the RVE size small and the computation efficient. From the saddle-pointproperties of an appropriately defined RVE-potential it is possible to establish bounds onthe homogenized response within a given time increment, and the bounds are obtained forcombinations of Dirichlet and Neumann boundary conditions on the coupled fields. Thetheoretical bounds are verified numerically for the special cases of drained and undrainedresponse. For the case of very stiff and low-permeable particles in a soft and permeablematrix, which is pertinent to asphalt concrete, it was observed numerically that the mostfavourable choice is Neumann condition on the displacement and Dirichlet condition onthe pore pressure field. The target application of the proposed computational strategy is the transient responseof water-saturated asphalt concrete, which has a random substructure and viscousmaterial behaviour. However, the numerical results in the thesis are obtained for asimplified micro-structure and elastic response of both ballast and mastic.
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| 9. |
- Su, Fang, 1983, et al.
(författare)
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Computational homogenization of uncoupled consolidation in micro-heterogeneous porous media
- 2011
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Ingår i: Proceedings för Svenska Mekanikdagar SMD2011. ; , s. 29-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A Variational Multiscale Modeling framework, combined with a generalized macro-homogeneity condition, is exploited for the analysis of uncoupled quasistatic poromechanics problem in a strongly heterogeneous particle/matrix composite. Within this framework the classical approach of 1st order homogenization for stationary diffusion problems is extended to transient problems in a consistent manner. Homogenization is then carried out on representative volume elements (RVE’s), which are in practice introduced in quadrature points of the macroscale elements in the spatial domain.The modeling and computational strategy are applied to the transient problem of consolidation of geological materials which are strongly heterogeneous on the microscale. A typical example is asphalt-concrete consisting of a porous bitumen matrix and aggregates which are nearly impermeable. We consider a nearly-periodic micro-structure of particles embedded in a matrix. Without loss of generality but with considerable savings in computational effort, we restrict the analysis to 2D. Results obtained by solving the full-fledged micro-macroscale FE2 problem for the initial/boundary value problem will be discussed. In particular, we are interested in assessing the influence of the RVE size, the particle arrangement and local boundary conditions (Dirichlet/Neumann), on the subscale transient character.
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| 10. |
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