@misc{KupkaLoschZaussingeretal., author = {Kupka, Friedrich and Losch, Martin and Zaussinger, Florian and Zweigle, Thomas}, title = {Semi-convection in the ocean and in stars: A multi-scale analysis}, series = {Meteorologische zeitschrift}, volume = {24}, journal = {Meteorologische zeitschrift}, number = {3}, issn = {0941-2948}, doi = {10.1127/metz/2015/0643}, pages = {343 -- 358}, abstract = {Fluid stratified by gravitation can be subject to a number of instabilities which eventually lead to a flow that causes enhanced mixing and transport of heat. The special case where a destabilizing temperature gradient counteracts the action of a stabilizing gradient in molecular weight is of interest to astrophysics (inside stars and giant planets) and geophysics (lakes, oceans) as well as to some engineering applications. The detailed dynamics of such a system depend on the molecular diffusivities of heat, momentum, and solute as well as system parameters including the ratio of the two gradients to each other. Further important properties are the formation and merging of well-defined layers in the fluid which cannot be derived from linear stability analysis. Moreover, the physical processes operate on a vast range of length and time scales. This has made the case of semi-convection, where a mean temperature gradient destabilizes the stratification while at the same time the mean molecular gradient tends to stabilize it, a challenge to physical modelling and to numerical hydrodynamical simulation. During the MetStr{\"o}m project the simulation codes ANTARES and MITgcm have been extended such that they can be used for the simulations of such flows. We present a comparison of effective diffusivities derived from direct numerical simulations. For both stars and the oceanic regimes, the Nusselt numbers (scaled diffusivities) follow similar relationships. Semi-convection quickly becomes inefficient, because the formation of layers limits vertical mixing. In contrast to the complementary saltfingering, these layers tend to damp instabilities so that effective diffusivities of salinity (concentration) are up to two orders of magnitudes smaller than in the former case.}, language = {en} } @misc{ZaussingerKupkaEgbersetal., author = {Zaussinger, Florian and Kupka, Friedrich and Egbers, Christoph and Neben, Matthias and H{\"u}cker, S. and Bahr, C. and Schmitt, M.}, title = {Semi-convective layer formation}, series = {Journal of Physics: Conference Series}, volume = {837}, journal = {Journal of Physics: Conference Series}, number = {1}, doi = {10.1088/1742-6596/837/1/012012}, pages = {7}, language = {en} } @misc{ZaussingerKupkaMontgomeryetal., author = {Zaussinger, Florian and Kupka, Friedrich and Montgomery, M. and Egbers, Christoph}, title = {Numerical simulation of DA white dwarf surface convection}, series = {Journal of physics / Conference Series}, volume = {1031}, journal = {Journal of physics / Conference Series}, number = {1}, issn = {1742-6596}, doi = {10.1088/1742-6596/1031/1/012013}, pages = {7}, language = {en} } @misc{KupkaZaussingerMontgomery, author = {Kupka, Friedrich and Zaussinger, Florian and Montgomery, M. H.}, title = {Mixing and overshooting in surface convection zones of DA white dwarfs: First results from ANTARES}, series = {Monthly Notices of the Royal Astronomical Society}, volume = {474}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, issn = {1365-2966}, pages = {4660 -- 4671}, language = {en} } @misc{GrimmStreleKupkaLoewBasellietal., author = {Grimm-Strele, Hannes and Kupka, Friedrich and L{\"o}w-Baselli, Bernhard and Mundprecht, Eva and Zaussinger, Florian and Schiansky, Peter}, title = {Realistic simulations of stellar surface convection with ANTARES: I. Boundary conditions and model relaxation}, series = {New Astronomy}, volume = {34}, journal = {New Astronomy}, issn = {1384-1076}, doi = {10.1016/j.newast.2013.11.005}, pages = {278 -- 293}, language = {en} }