Paper A: Sandvin A, Nordbotten JM, Aavatsmark I. Multiscale Mass-Conservative Domain-Decomposition Preconditioners for Elliptic Problems on Irregular Grids. Computational Geosciences 2011 Jun;15(3):587-602. The article is available at: http://hdl.handle.net/1956/5207Paper B: Sandvin A, Nordbotten JM, Aavatsmark I. A Unified Multilevel Framework of Upscaling and Domain Decomposition. In: Carrera J, ed. Proceedings from the XVIII International Conference on Water Resources, Barcelona 2010. The article is available at: http://hdl.handle.net/1956/7417Paper C: Sandvin A, Keilegavlen E, Nordbotten JM. Auxiliary Variables for 3D Multiscale Simulations in Heterogeneous Porous Media. Journal of Computational Physics 2013 April; 238: 141–153. The article is available at: http://hdl.handle.net/1956/7429Supporting material: Nordbotten JM, Keilegavlen E, Sandvin A. Mass conservative domain decomposition for porous media flow. In: Petrova R, ed. Finite Volume Method: Powerful Means of Engineering Design. InTech; 2012. s. 235-256. The chapter is available at: http://hdl.handle.net/1956/7415