Space-time adaptive hierarchical model reduction for parabolic equations.
BACKGROUND
Surrogate solutions and surrogate models for complex problems in many fields of science and engineering represent an important recent research line towards the construction of the best trade-off between modeling reliability and computational efficiency. Among surrogate models, hierarchical model (HiMod) reduction provides an effective approach for phenomena characterized by a dominant direction in their dynamics. HiMod approach obtains 1D models naturally enhanced by the inclusion of the effect of the transverse dynamics.


METHODS
HiMod reduction couples a finite element approximation along the mainstream with a locally tunable modal representation of the transverse dynamics. In particular, we focus on the pointwise HiMod reduction strategy, where the modal tuning is performed on each finite element node. We formalize the pointwise HiMod approach in an unsteady setting, by resorting to a model discontinuous in time, continuous and hierarchically reduced in space (c[M([Formula: see text])G(s)]-dG(q) approximation). The selection of the modal distribution and of the space-time discretization is automatically performed via an adaptive procedure based on ana posteriorianalysis of the global error. The final outcome of this procedure is a table, namedHiMod lookup diagram, that sets the time partition and, for each time interval, the corresponding 1D finite element mesh together with the associated modal distribution.


RESULTS
The results of the numerical verification confirm the robustness of the proposed adaptive procedure in terms of accuracy, sensitivity with respect to the goal quantity and the boundary conditions, and the computational saving. Finally, the validation results in the groundwater experimental setting are promising.


CONCLUSIONS
The extension of the HiMod reduction to an unsteady framework represents a crucial step with a view to practical engineering applications. Moreover, the results of the validation phase confirm that HiMod approximation is a viable approach.
MOX, Department of Mathematics, Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milan, Italy.
Simona
S
Perotto
Centre d'Analyse et de Mathématique Sociales, École des Hautes Études en Sciences Sociales, 190-198 Avenue de France, 75244 Paris Cedex 13, France.
Alessandro
A
Zilio
Goal-oriented a posteriori error analysis; Hierarchical model reduction; Model adaptation; Space–time adaptation; Unsteady advection–diffusion–reaction problems