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The performance of improved initial estimates and ‘heuristic’ and ‘adaptive’ techniques for time step control in the iterative solution of Richards equation is evaluated. The so-called heuristic technique uses the convergence behaviour of the iterative scheme to estimate the next time step whereas the adaptive technique regulates the time step on the basis of an approximation of the local time truncation error. The sample problems used to assess these various schemes are characterized by nonuniform (in time) boundary conditions, sharp gradients in the infiltration fronts, and discontinuous derivatives in the soil hydraulic properties. It is found that higher order initial solution estimates improve the convergence of the iterative scheme for both the heuristic and adaptive techniques, with greater overall performance gains for the heuristic scheme, as could be expected. It is also found that the heuristic technique outperforms the adaptive method under strongly nonlinear conditions. Previously reported observations suggesting that adaptive techniques perform best when accuracy requirements on the numerical solution are very stringent are confirmed. Overall both heuristic and adaptive techniques have their limitations, and a more general or mixed time stepping strategy combining truncation error and convergence criteria is recommended for complex problems.
| Type de document: | Article |
|---|---|
| Mots-clés libres: | adaptive time stepping; nonlinear processes; numerical modelling; Richards' equation; subsurface hydrology; time truncation error; unsaturated zone |
| Centre: | Centre Eau Terre Environnement |
| Date de dépôt: | 11 janv. 2021 16:29 |
| Dernière modification: | 11 janv. 2021 16:29 |
| URI: | https://espace.inrs.ca/id/eprint/10919 |
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