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- Jørg E. Aarnes, Stein Krogstad, Knut-Andreas Lie
- Multiscale Modeling & Simulation
- 2006

We analyse and further develop a hierarchical multiscale method for the numerical simulation of two-phase flow in highly heterogeneous porous media. The method is based upon a mixed finite-element formulation, where fine-scale features are incorporated into a set of coarse-grid basis functions for the flow velocities. By using the multiscale basis… (More)

- Knut–Andreas Lie, Stein Krogstad, Ingeborg S. Ligaarden, Jostein R. Natvig, Halvor Møll Nilsen, B̊ard Skaflestad
- 2011

Accurate geological modelling of features such as faults, fractures or erosion requires grids that are flexible with respect to geometry. Such grids generally contain polyhedral cells and complex grid cell connectivities. The grid representation for polyhedral grids in turn affects the efficient implementation of numerical methods for subsurface flow… (More)

Multiscale simulation is a promising approach to facilitate direct simulation of large and complex grid-models for highly heterogeneous petroleum reservoirs. Unlike traditional simulation approaches based on upscaling/downscaling, multiscale methods seek to solve the full flow problem by incorporating subscale heterogeneities into local discrete… (More)

- J R Ebright, K E Smith, L Drexler, R Ivsin, S Krogstad, S G Farmer
- Sexually transmitted diseases
- 1982

A prospective study compared rates of isolation of Neisseria Gonorrhoeae after immediate plating of clinical specimens onto Thayer-Martin medium with isolation rates after initial transport in modified Stuart's medium (MST) contained in Culturettes. Of 75 specimens positive for Neisseria gonorrhoeae after immediate plating onto Thayer-Martin medium, 65… (More)

- Stein Krogstad
- 2001

A low complexity Lie group method for numerical integration of ordinary differential equations on the orthogonal Stiefel manifold is presented. Based on the quotient space representation of the Stiefel manifold we provide a representation of the tangent space suitable for Lie group methods. According to this representation a special type of generalized… (More)

- Hans Z. Munthe-Kaas, Stein Krogstad
- Future Generation Comp. Syst.
- 2003

The algebraic structure underlying non-commutative Lie-Butcher series is the free Lie algebra over ordered trees. In this paper we present a characterization of this algebra in terms of balanced Lyndon words over a binary alphabet. This yields a systematic manner of enumerating terms in non-commutative Lie-Butcher series.

We present MRST-AD, a free, open-source framework written as part of the Matlab Reservoir Simulation Toolbox and designed to provide researchers with the means for rapid prototyping and experimentation for problems in reservoir simulation. The article outlines the design principles and programming techniques used and explains in detail the implementation of… (More)

- Stein Krogstad, Hans Z. Munthe-Kaas, Antonella Zanna
- Numerische Mathematik
- 2009

Motivated by recent developments in numerical Lie group integrators, we introduce a family of local coordinates on Lie groups denoted generalized polar coordinates. Fast algorithms are derived for the computation of the coordinate maps, their tangent maps and the inverse tangent maps. In particular we discuss algorithms for all the classical matrix Lie… (More)

Previous research has shown that multiscale methods are robust and capable of providing more accurate solutions than traditional upscaling methods. Multiscale methods solve the pressure equation on a coarse grid, but capture the effects from fine-scale heterogeneities through basis functions computed numerically from local single-phase problems on the… (More)

- Eka Suwartadi, Stein Krogstad, Bjarne Foss
- CDC
- 2010