| 21. |
|
|
| 22. |
|
|
| 23. |
|
|
| 24. |
|
|
| 25. |
- Johansson, Håkan, 1979, et al.
(författare)
-
Parameter identification for constitutive models with error control
- 2004
-
Ingår i: ECCOMAS 2004, European Congress on Computational Methods in Applied Sciences and Engineering. - 9513918688
-
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.
|
|
| 26. |
|
|
| 27. |
- Johansson, Håkan, 1979, et al.
(författare)
-
Parameter identification in constitutive models via optimization with a posteriori error control
- 2005
-
Ingår i: International Journal for Numerical Methods in Engineering. ; 62:10, s. 1315-1340
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we outline a computational technique for the calibration of macroscopic constitutive lawswith automatic error control. In the most general situation the state variables of the constitutive law,as well as the material parameters, are spatially non-homogeneous. The experimental observations aregiven in spacetime. Based on an appropriate dual problem, we compute a posteriori the discretizationerror contributions from approximations of the parameter, state and costate fields in spacetime foran arbitrarily chosen goal-oriented error measure of engineering significance. Such a measure can beused in an adaptive strategy (not discussed in this paper) to meet a predefined error tolerance. Animportant observation is that the Jacobian matrix associated with the resulting Newton method is used(in principle) in solving the dual problem. Rather than treating the Jacobian in a monolithic fashion,we utilize a sequential solution strategy, whereby the FE-topology of the discretized state problem isused repeatedly. Moreover, the proposed solution strategy lends itself naturally to the computation offirst and second order sensitivities, which are obtained with little extra computational effort. Numericalresults are given for the prototype model of confined aquifer flow with spatially non-homogeneouspermeability. The efficiency of the optimization strategy and the effectivity of the error computationare assessed.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
|
|
