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- Ebenhag, Sven-Christian, 1976, et al.
(författare)
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Time transfer using an asynchronous computer network: Results from three weeks of measurements
- 2007
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Ingår i: European Frequency and Time Forum, 29/5 - 1/6, Geneva, CH.
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Konferensbidrag (refereegranskat)abstract
- We have performed a time transfer experimentbetween two atomic clocks, over a distance of approximately 75km using an 10 Gbit/s asynchronous fiber-optic computernetwork. The time transfer was accomplished through passivelistening on existing data traffic and a pilot sequence in the SDHbit stream. In order to assess the fiber-link clock comparison, wesimultaneously compared the clocks using a GPS carrier phaselink. The standard deviation of the difference between the twotime transfer links over the three-week time period was 243 ps.
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| 3. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a class of non-linear viscoelasticity models with adaptive error control
- 2007
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Ingår i: Computational Mechanics. - : Springer Science and Business Media LLC. - 1432-0924 .- 0178-7675. ; 41:1, s. 107-119
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of constitutive models is considered as an optimization problem where parameter values are sought to minimize the discrepancy between measured and simulated response. Since a finite element method is used to solve an underlying state equation, discretization errors arise, which induce errors in the calibrated parameter values. In this paper, adaptive mesh refinement based on the pertinent dual solution is used in order to reduce discretization errors in the calibrated material parameters. By a sensitivity assessment, the influence from uncertainties in experimental data is estimated, which serves as a threshold under which there is no need to further reduce the discretization error. The adaptive strategy is employed to calibrate a viscoelasticity model with observed data from uniaxial compression (i.e., homogeneous stress state), where the FE-discretization in time is studied. The a posteriori error estimations show an acceptable quality in terms of effectivity measures. © 2007 Springer Verlag.
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| 4. |
- Johansson, Håkan, 1979, et al.
(författare)
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Calibration of a class of non-linear viscoelasticity models with sensitivity assessment based on duality
- 2007
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 69:12, s. 2513-2537
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Tidskriftsartikel (refereegranskat)abstract
- The calibration of constitutive models is based on the solution of an optimization problem, whereby the sought parameter values minimize an objective function that measures the discrepancy between experimental observations and the corresponding simulated response. By the introduction of an appropriate adjoint problem, the resulting formulation becomes well suited for a gradient-based optimization scheme. A class of viscoelastic models is studied, where a discontinuous Galerkin method is used to integrate the governing evolution equation in time. A practical solution algorithm, which utilizes the time-flow structure of the underlying evolution equation, is presented. Based on the proposed formulation it is convenient to estimate the sensitivity of the calibrated parameters with respect to measurement noise. The sensitivity is computed using a dual method, which compares favourably with the conventional primal method. The strategy is applied to a viscoelasticity model using experimental data from a uniaxial compression test. Copyright © 2006 John Wiley & Sons, Ltd.
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| 6. |
- Johansson, Håkan, 1979, et al.
(författare)
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Error-Controlled Identification of Viscoelastic Relaxation Spectra
- 2007
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Ingår i: Proceedings of the 20th Nordic Seminar on Computational Mechanics NSCM 20 R. Larsson and K. Runesson (eds.). - 1652-8549. - 9788496736313 ; , s. 2p abstract-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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