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Stable and efficient time integration of a dynamic pore network model for two-phase flow in porous media
We study three different time integration methods for a dynamic pore network
model for immiscible two-phase flow in porous media. Considered are two
explicit methods, the forward Euler and midpoint methods, and a new
semi-implicit method developed herein. The explicit methods are known to suffer
from numerical instabilities at low capillary numbers. A new time-step
criterion is suggested in order to stabilize them. Numerical experiments,
including a Haines jump case, are performed and these demonstrate that
stabilization is achieved. Further, the results from the Haines jump case are
consistent with experimental observations. A performance analysis reveals that
the semi-implicit method is able to perform stable simulations with much less
computational effort than the explicit methods at low capillary numbers. The
relative benefit of using the semi-implicit method increases with decreasing
capillary number , and at the
computational time needed is reduced by three orders of magnitude. This
increased efficiency enables simulations in the low-capillary number regime
that are unfeasible with explicit methods and the range of capillary numbers
for which the pore network model is a tractable modeling alternative is thus
greatly extended by the semi-implicit method.Comment: 33 pages, 12 figure
PREPARE: guidelines for planning animal research and testing
There is widespread concern about the quality, reproducibility and translatability of studies involving research animals. Although there are a number of reporting guidelines available, there is very little overarching guidance on how to plan animal experiments, despite the fact that this is the logical place to start ensuring quality. In this paper we present the PREPARE guidelines: Planning Research and Experimental Procedures on Animals: Recommendations for Excellence. PREPARE covers the three broad areas which determine the quality of the preparation for animal studies: formulation, dialogue between scientists and the animal facility, and quality control of the various components in the study. Some topics overlap and the PREPARE checklist should be adapted to suit specific needs, for example in field research. Advice on use of the checklist is available on the Norecopa website, with links to guidelines for animal research and testing, at https://norecopa.no/PREPARE
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