| 1. |
- Danvind, Jonas, et al.
(författare)
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Calibration of a constitutive model for diffusive moisture transport in wood using data from X-ray CT-scanning and digital speckle photography
- 2004
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Ingår i: 5th Conference on Timber drying for value-added prducts, COST action E15 "advances in drying of wood". ; , s. 210-218
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An unsteady-state diffusion model is applied for studying wood drying below the fibre saturation point. The moisture diffusion coefficient in Fick's law for Norway spruce under isothermal drying conditions is determined. Using X-ray CT-scanning and Digital Speckle Photography, the wood density and moisture content are obtained in the radial direction of the wood samples. An optimization scheme is used to minimize the difference between observed and computed moisture content in order to calibrate the values of a set of parameters describing the diffusion coefficient. In this study the values of the parameters for a parameterization of Arrhenius' type are determined. The general idea discussed, however, is not limited to a specific model, butcan be used for a wide class of parameter identification problems. The results show a good agreement between observed and computed moisture content and it is concluded that the numerical realization of the optimization scheme works well. Nevertheless, the value of the diffusion coefficient is somewhat higher than expected. This is likely the consequence of a permeable coating of the samples.
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| 2. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a Nonlinear Elastic Composite with Goal-Oriented Error Control Using a Sub-Scale Modeling Approach
- 2004
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Ingår i: Proc. of Second International Conference on Multiscale Materials Modeling, MMM-2, October 11-15, 2004. ; 1:1, s. 466-468
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A recently proposed technique for the calibration of constitutive models is based on the optimization problem expressed such that the state equation is incorporated via an additional costate field. A distinct advantage is that error control is formally straightforward. This technique is applied to calibration of a nonlinear elastic composite using a meso-macro-transition approach, whereby the RVE is analyzed using (in this case) Dirichlet boundary conditions. The numerical results show the effectivity of the error prediction.
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| 3. |
- Johansson, Håkan, 1979, et al.
(författare)
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Computational Constitutive Calibration for Groundwater Flow
- 2003
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Ingår i: ADMOS 2003, Adaptive modeling and simulation, September 29-October 1, 2003, Göteborg, Sweden, P.Díez and N.-E.Wiberg (eds). - 8495999307 ; , s. 157-158
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Johansson, Håkan, 1979, et al.
(författare)
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Parameter identification for constitutive models with error control
- 2004
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Ingår i: ECCOMAS 2004, European Congress on Computational Methods in Applied Sciences and Engineering. - 9513918688
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A recently proposed technique for the calibration ofconstitutive models, that is based on optimization with built-in error control, is applied to Norton's viscoelasticity model. In order to focus on the characteristic features, only the constitutive response for uniaxial stress is considered; however, the extension to multiaxial states and spatially non-homogeneous situations is quite straightforward although technically more complex. Essentially, the optimization strategy is based onNewton's method and consists of solving three linear problems running forwards in time and one linear problem (for the costate) running backwards in time. It is interesting to note that the same problem character is pertinent to the solution of the dual problem, which is the basis for the a posteriori error computation.
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