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Sökning: WFRF:(Johansson Kenneth) > Chalmers tekniska högskola > (2010-2013)

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  • Johansson, Håkan, 1979, et al. (författare)
  • Application-specific error control for parameter identification problems
  • 2011
  • Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : Wiley. - 2040-7939 .- 2040-7947. ; 27:4, s. 608-618
  • Tidskriftsartikel (refereegranskat)abstract
    • An often occurring scenario in the mathematical modeling of physical phenomena is that of a two-step computation consisting of, first, identifying a relevant parameter set from experiments (such as material parameters) and, second, carrying out a subsequent simulation using these parameters. In order to ensure the quality of the results from the simulation, the different sources of errors, for example, from discretization and inexact solution, must be traced and properly reduced. In this paper, a previously developed method for goal-oriented a posteriori error estimation for identification problems is extended to accommodate the combined identification and subsequent simulation. © 2009 John Wiley & Sons, Ltd.
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  • Rieck, Carsten, 1972, et al. (författare)
  • VLBI time-transfer using CONT08 data
  • 2010
  • Ingår i: Proceedings of the 24th European Frequency and Time Forum ESA/ESTEC Noordwijk (NL) 13-16 April 2010. - 9781467359702
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • One important prerequisite for geodetic Very Long Baseline Interferometry (VLBI) is the use of frequency standards with excellent short term stability, i.e. hydrogen masers. This makes VLBI stations, which are often co-located with Global Navigation Satellite System (GNSS) receiving stations, interesting for studies of time- and frequency-transfer techniques. In this paper we present an assessment of VLBI time-transfer based on the data of the two week long consecutive IVS Cont08 VLBI-campaign by using GPS Carrier Phase (GPSCP). Cont08 was a 15 days long campaign in August 2008 that involved eleven VLBI stations on five continents. For Cont08 we estimated the worst case VLBI time link stability between the station clocks of ONSALA and WETTZELL to about 1.5e-15 at one day. Comparisons with clock differences estimated with GPSCP confirm the VLBI results. The paper also indicates time-transfer related problems of the VLBI technique as used today. © 2010 IEEE.
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  • Sandström, Carl, 1978, et al. (författare)
  • A two-scale finite element formulation of Stokes flow in porous media
  • 2013
  • Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825. ; 261, s. 96-104
  • Tidskriftsartikel (refereegranskat)abstract
    • Seepage through saturated porous material with an open pore system is modeled as a non-linear Stokes flow through a rigid matrix. Based on variationally consistent homogenization, the resulting macroscale problem becomes a Darcy-type flow. The prolongation of the Darcy flow fulfills a macrohomogeneity condition, which in a Galerkin context implies a symmetric macroscale problem. The homogenization is of 1st order and periodic boundary conditions are adopted on a Representative Volume Element. A nonlinear nested multiscale technique, in which the subscale problem is used as a constitutive model, is devised. In the presented numerical investigation, the effects of varying physical parameters as well as of the discretization are considered. In particular, it is shown that the two-scale results agree well with those of the fully resolved fine-scale problem.
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  • Sandström, Carl, 1978, et al. (författare)
  • Homogenization of Stokes Flow in Porous Media
  • 2012
  • Ingår i: ECCOMAS 2012, European Congress on Computational Methods in Science and Engineering, (1 p. abstract).
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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  • Sandström, Carl, 1978, et al. (författare)
  • Multiscale modeling of porous media
  • 2011
  • Ingår i: Proceedings of NSCM-24, the 24th Nordic Seminar on Computational Mechanics. ; , s. 111-114
  • Konferensbidrag (refereegranskat)
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  • Sandström, Carl, 1978, et al. (författare)
  • MULTISCALE MODELING OF POROUS MEDIA
  • 2010
  • Ingår i: Proceedings of NSCM-23, Anders Eriksson och Gunnar Tibert, Nordic Seminar on Computational Mechanics, Sockholm, 21-22 October 2010. - 0348-467X. ; 2010, s. 177-180
  • Konferensbidrag (refereegranskat)abstract
    • Homogenization of flow in porous media is studied. The continuity equation in conjunction with Darcy’s law as a constitutive relation on the macroscale, where the permeability is a function of the pressure gradient, is applied to a macroscopic domain. On the heterogenousmesoscale, a Stokes flow problem is formulated on a Representative Volume Element with a prescribed pressure gradient and suitable boundary condition. The numerical procedure for finite element simulations of the two-scale problem is outlined and illustrated by a few exampleproblems.
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  • Resultat 1-10 av 12

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