Mikael Mortensen

• Piterskaya, Anna; Miloch, Wojciech Jacek & Mortensen, Mikael (2023). A global spectral-Galerkin investigation of a Rayleigh-Taylor instability in plasma using an MHD-Boussinesq model. AIP Advances. ISSN 2158-3226. 13(10). doi: 10.1063/5.0155976. Fulltekst i vitenarkiv
• Vignon, Colin; Rabault, Jean; Vasanth, Joel; Alcántara-Ávila, Francisco; Mortensen, Mikael & Vinuesa, Ricardo (2023). Effective control of two-dimensional Rayleigh-Bénard convection: Invariant multi-agent reinforcement learning is all you need. Physics of Fluids. ISSN 1070-6631. 35(6). doi: 10.1063/5.0153181. Fulltekst i vitenarkiv
• Mortensen, Mikael (2023). A GENERIC AND STRICTLY BANDED SPECTRAL PETROV-GALERKIN METHOD FOR DIFFERENTIAL EQUATIONS WITH POLYNOMIAL COEFFICIENTS. SIAM Journal on Scientific Computing. ISSN 1064-8275. 45(1), s. A123–A146. doi: 10.1137/22M1492842. Fulltekst i vitenarkiv
• Friedemann, Christopher; Mortensen, Mikael & Nossen, Jan (2021). Two-phase co-current flow simulations using periodic boundary conditions in horizontal, 4, 10 and 90° inclined eccentric annulus, flow prediction using a modified interFoam solver and comparison with experimental results. International Journal of Heat and Fluid Flow. ISSN 0142-727X. 88, s. 1–20. doi: 10.1016/j.ijheatfluidflow.2020.108754. Fulltekst i vitenarkiv
• Marholm, Sigvald; Darian, Diako; Mortensen, Mikael; Miloch, Wojciech Jacek & Marchand, Richard (2020). A Novel Method for Circuits of Perfect Electric Conductors in Unstructured Particle-in-Cell Plasma–Object Interaction Simulations. IEEE Transactions on Plasma Science. ISSN 0093-3813. 48(8), s. 2856–2872. doi: 10.1109/TPS.2020.3010561. Fulltekst i vitenarkiv
• Friedemann, Christopher; Mortensen, Mikael & Nossen, Jan (2020). Two-phase flow simulations at 0 - 4° inclination in an eccentric annulus. International Journal of Heat and Fluid Flow. ISSN 0142-727X. 83. doi: 10.1016/j.ijheatfluidflow.2020.108586. Fulltekst i vitenarkiv
• Landet, Tormod; Mardal, Kent-Andre & Mortensen, Mikael (2020). Slope limiting the velocity field in a discontinuous Galerkin divergence-free two-phase flow solver. Computers & Fluids. ISSN 0045-7930. 196. doi: 10.1016/j.compfluid.2019.104322. Fulltekst i vitenarkiv
• Ketcheson, David I.; Mortensen, Mikael; Parsani, Matteo & Schilling, Nathanael (2019). More efficient time integration for Fourier pseudospectral DNS of incompressible turbulence. International Journal for Numerical Methods in Fluids. ISSN 0271-2091. doi: 10.1002/fld.4773. Fulltekst i vitenarkiv
• Friedemann, Christopher; Mortensen, Mikael & Nossen, Jan (2019). Gas-liquid slug flow in a horizontal concentric annulus, a comparison of numerical simulations and experimental data. International Journal of Heat and Fluid Flow. ISSN 0142-727X. 78. doi: 10.1016/j.ijheatfluidflow.2019.108437. Fulltekst i vitenarkiv Vis sammendrag

  Multiphase flow simulations were run in OpenFOAM utilizing InterFoam, a volume of fluid type solver. A concentric annulus geometry was constructed and periodic boundary conditions were applied to alleviate the requirement for a longer domain. The simulations were run in 3, 5 and 7m long domains with the annulus dimensioned such that the outer and inner cylinder diameter were 0.1 and 0.05m respectively. The 4 individual mesh designs were constructed such that the coarsest mesh consists of 102k cells/m while the finest mesh was generated with 400k cells/m. Each mesh was significantly refined within 0.005m of both the inner and outer cylinder wall. The simulation data was compared with experimental pressure and holdup data collected at Institute for Energy Technology in Norway. The 3 and 7m domains reproduced slug frequencies to within 9% of the experiment results of 1.43 Hz for all mesh densities. Comparatively, the 5m domain has larger errors with respect to slugging frequency (22–27%). The 5m case performs poorly, probably due to an artificial restraint introduced by the limitation of available liquid which is set as oil = 0.53 for all cases. The αoil restriction combined with the domain length determines the amount of liquid in the system. This interaction of factors means that the domain length is an important parameter when preparing the simulation. The pressure data display a stronger dependence on the mesh quality in comparison to the slug frequency analysis. The 3m domain with a 400k cells/m mesh resulted in a maximum and minimum pressure gradient of 1783.5 and 803.9 Pa/m, compared to the experiment values of 1785 and 822 Pa/m, which are within 3% of the expected results.

• Darian, Diako; Marholm, Sigvald; Mortensen, Mikael & Miloch, Wojciech Jacek (2019). Theory and simulations of spherical and cylindrical Langmuir probes in non-Maxwellian plasmas. Plasma Physics and Controlled Fusion. ISSN 0741-3335. 61(8). doi: 10.1088/1361-6587/ab27ff. Fulltekst i vitenarkiv
• Marholm, Sigvald; Marchand, Richard; Darian, Diako; Miloch, Wojciech Jacek & Mortensen, Mikael (2019). Impact of Miniaturized Fixed-Bias Multineedle Langmuir Probes on CubeSats. IEEE Transactions on Plasma Science. ISSN 0093-3813. 47(8), s. 3658–3666. doi: 10.1109/TPS.2019.2915810. Fulltekst i vitenarkiv
• Darian, Diako; Miloch, Wojciech Jacek; Mortensen, Mikael; Miyake, Yohei & Usui, Hideyuki (2019). Numerical simulations of a dust grain in a flowing magnetized plasma. Physics of Plasmas. ISSN 1070-664X. 26(043701), s. 1–14. doi: 10.1063/1.5089631. Fulltekst i vitenarkiv
• Mortensen, Mikael; Dalcin, Lisandro & Keyes, David (2019). mpi4py-fft: Parallel Fast Fourier Transforms with MPI for Python. Journal of Open Source Software (JOSS). ISSN 2475-9066. 4(36). doi: 10.21105/joss.01340. Fulltekst i vitenarkiv
• Dalcin, Lisandro; Mortensen, Mikael & Keyes, David (2019). Fast parallel multidimensional FFT using advanced MPI. Journal of Parallel and Distributed Computing. ISSN 0743-7315. 128, s. 137–150. doi: 10.1016/j.jpdc.2019.02.006. Fulltekst i vitenarkiv
• Bergersen, Aslak Wigdahl; Mortensen, Mikael & Valen Sendstad, Kristian (2019). The FDA nozzle benchmark: “In theory there is no difference between theory and practice, but in practice there is”. International Journal for Numerical Methods in Biomedical Engineering. ISSN 2040-7939. 35(1). doi: 10.1002/cnm.3150. Fulltekst i vitenarkiv
• Kuchta, Miroslav; Mardal, Kent-Andre & Mortensen, Mikael (2019). On the singular Neumann problem in linear elasticity. Numerical Linear Algebra with Applications. ISSN 1070-5325. 26(1). doi: 10.1002/nla.2212. Fulltekst i vitenarkiv
• Kuchta, Miroslav; Mardal, Kent-Andre & Mortensen, Mikael (2019). Preconditioning trace coupled 3d-1d systems using fractional Laplacian . Numerical Methods for Partial Differential Equations. ISSN 0749-159X. 35(1), s. 375–393. doi: 10.1002/num.22304.
• Mortensen, Mikael (2018). Shenfun: High performance spectral Galerkin computing platform. Journal of Open Source Software (JOSS). ISSN 2475-9066. 3(31). doi: 10.21105/joss.01071. Fulltekst i vitenarkiv
• Miloch, Wojciech Jacek; Jung, Hendrik; Darian, Diako; Greiner, Franko; Mortensen, Mikael & Piel, A. (2018). Dynamic ion shadows behind finite-sized objects in collisionless magnetized plasma flows. New Journal of Physics. ISSN 1367-2630. 20(7), s. 1–6. doi: 10.1088/1367-2630/aad066. Fulltekst i vitenarkiv
• Miloch, Wojciech Jacek; Darian, Diako & Mortensen, Mikael (2017). Wake potential of a dust particle in magnetised plasmas. Physica Scripta. ISSN 0031-8949. 92(11). doi: 10.1088/1402-4896/aa90a5. Fulltekst i vitenarkiv
• Darian, Diako; Marholm, Sigvald; Paulsson, Joakim John Paul; Miyake, Y.; Usui, H. & Mortensen, Mikael [Vis alle 7 forfattere av denne artikkelen] (2017). Numerical simulations of a sounding rocket in ionospheric plasma: Effects of magnetic field on the wake formation and rocket potential. Journal of Geophysical Research (JGR): Biogeosciences. ISSN 2169-8953. 122(9), s. 9603–9621. doi: 10.1002/2017JA024284. Fulltekst i vitenarkiv
• Friedemann, Christopher; Mortensen, Mikael & Nossen, Jan (2017). Multiphase flow simulation in an annulus configuration. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), MekIT’17 - Ninth national conference on Computational Mechanics. International Center for Numerical Methods in Engineering (CIMNE). ISSN 978-84-947311-1-2. Fulltekst i vitenarkiv Vis sammendrag

  On the 20th of April 2010, explosion and fire killed 11 people on the Deepwater Horizon oil rig in the Gulf of Mexico. After two days in flames, the rig sank and left the riser (the pipe going up from the seabed) on the sea floor leaking oil and gas from the well through the gap between the drilling riser and the drill-string (rod holding the drillbit) inside it. The accident is known as the Macondo accident. Immediate concerns were raised regarding the amount of oil being released into the Gulf of Mexico killing fish and seabirds. The size of the oil spill has also played a significant role in the court proceedings where the operator BP at the end accepted to pay a fine of more than 18 bn US dollars. One of many techniques that were applied was based on using simulation software to match the observed frequency of plugs of oil flowing out of the sunken riser. There are, however, serious flaws to this approach. The most important is the lack of reliable models for multiphase flow in annuli, that is, flow of oil and gas in the ring shaped space between the drillstring and the outer pipe. Commercial simulation software packages for flow of oil and gas in pipes lack the ability to correctly predict pressure drop in annulus flow, even when the flow contains only gas or only liquid. When both gas and oil are flowing in the pipe at the same time, which is called multiphase flow, the models are even worse. Well design is thus based on crude formulas with large uncertainty and high error margins. This may lead to inefficient well design and high risk of production problems. ANNULUS will bring a step change in the scientific knowledge in this field and provide data and physical understanding that can be used as a basis for developing more usable and accurate commercial simulation software in the future. Improved models can be used by operators and contribute to significantly safer and more efficient and profitable well operations and production.

• Mortensen, Mikael (2017). Shenfun - automating the spectral Galerkin method. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), MekIT’17 - Ninth national conference on Computational Mechanics. International Center for Numerical Methods in Engineering (CIMNE). ISSN 978-84-947311-1-2. s. 273–298. doi: 10.21105/joss.01071. Fulltekst i vitenarkiv
• Haga, Per Thomas; Pizzichelli, Giulia; Mortensen, Mikael; Kuchta, Miroslav; Pahlavian, Soroush Heidari & Sinibaldi, Edoardo [Vis alle 8 forfattere av denne artikkelen] (2017). A numerical investigation of intrathecal isobaric drug dispersion within the cervical subarachnoid space. PLOS ONE. ISSN 1932-6203. 12(3). doi: 10.1371/journal.pone.0173680. Fulltekst i vitenarkiv
• Kuchta, Miroslav; Nordaas, Magne; Verschaeve, Joris C. G.; Mortensen, Mikael & Mardal, Kent-Andre (2016). Preconditioners for saddle point systems with trace constraints coupling 2D and 1D domains. SIAM Journal on Scientific Computing. ISSN 1064-8275. 38(6), s. B962–B987. doi: 10.1137/15M1052822.
• Mortensen, Mikael & Langtangen, Hans Petter (2016). High performance Python for direct numerical simulations of turbulent flows. Computer Physics Communications. ISSN 0010-4655. 203, s. 53–65. doi: 10.1016/j.cpc.2016.02.005. Fulltekst i vitenarkiv
• Bø, Joakim; Bergersen, Aslak Wigdahl; Valen-Sendstad, Kristian & Mortensen, Mikael (2015). Implementation, verification and validation of large eddy simulation models in Oasis. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), Proceedings of MekIT'15 Eighth National Conference on Computational Mechanics. International Center for Numerical Methods in Engineering (CIMNE). ISSN 97884944244-96. s. 99–122.
• Darian, Diako & Mortensen, Mikael (2015). A pseudo-spectral study of Kelvin-Helmholtz instability. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), Proceedings of MekIT'15 Eighth National Conference on Computational Mechanics. International Center for Numerical Methods in Engineering (CIMNE). ISSN 97884944244-96. s. 133–148.
• Kuchta, Miroslav; Mardal, Kent-Andre & Mortensen, Mikael (2015). Characterization of the space of rigid motions in arbitrary domains. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), Proceedings of MekIT'15 Eighth National Conference on Computational Mechanics. International Center for Numerical Methods in Engineering (CIMNE). ISSN 97884944244-96. s. 259–274.
• Landet, Tormod; Mortensen, Mikael & Grue, John (2015). Towards a continuous and discontinuous Galerkin method for multi-phase flows. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), Proceedings of MekIT'15 Eighth National Conference on Computational Mechanics. International Center for Numerical Methods in Engineering (CIMNE). ISSN 97884944244-96. s. 275–294. Fulltekst i vitenarkiv
• Mortensen, Mikael; Kuchta, Miroslav; Mardal, Kent-Andre & Verschaeve, Joris C. G. (2015). BEND|P|Y: Python framework for computing bending of complex plate-beam systems. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), Proceedings of MekIT'15 Eighth National Conference on Computational Mechanics. International Center for Numerical Methods in Engineering (CIMNE). ISSN 97884944244-96. s. 307–320.
• Mortensen, Mikael & Valen-Sendstad, Kristian (2015). Oasis: A high-level/high-performance open source Navier-Stokes solver. Computer Physics Communications. ISSN 0010-4655. 188, s. 177–188. doi: 10.1016/j.cpc.2014.10.026.
• El Sayed, Ahmad; Mortensen, Mikael & Wen, John Z. (2014). Assessment of the presumed mapping function approach for the stationary laminar flamelet modelling of reacting double scalar mixing layers. Combustion theory and modelling. ISSN 1364-7830. 18, s. 552–581. doi: 10.1080/13647830.2014.939229.
• Mortensen, Mikael; Mardal, Kent-Andre; Martin, B & Pahlavian, S. (2013). Preliminary study of the impact of spinal cord nerve roots and denticulate ligaments on drug movement in the cervical spinal subarachnoid space. I Mardal, Kent-Andre; Logg, Anders Bernhard & Massing, Andre (Red.), Proceedings of the 26th Nordic Seminar on Computational Mechanics. Simula Research Laboratory. ISSN 978-82-92593-12-7. s. 213–216.
• Kuchta, Miroslav & Mortensen, Mikael (2013). A second order fast sweeping method for the Eikonal equation based on minimization. I Mardal, Kent-Andre; Logg, Anders Bernhard & Massing, Andre (Red.), Proceedings of the 26th Nordic Seminar on Computational Mechanics. Simula Research Laboratory. ISSN 978-82-92593-12-7. s. 145–148.
• Valen-Senstad, Kristian; Logg, Anders Bernhard; Mardal, Kent-Andre; Narayanan, Harish & Mortensen, Mikael (2012). A comparison of finite element schemes for the incompressible Navier–Stokes equations. I Logg, Anders; Mardal, Kent-Andre & Wells, Garth N. (Red.), Automated Solution of Differential Equations by the Finite Element Method. Springer. ISSN 9783642230981. s. 399–420.
• Mortensen, Mikael; Mardal, Kent-Andre & Langtangen, Hans Petter (2012). Simulation of transitional flows. I Logg, Anders; Mardal, Kent-Andre & Wells, Garth N. (Red.), Automated Solution of Differential Equations by the Finite Element Method. Springer. ISSN 9783642230981. s. 421–440.
• Mortensen, Mikael; Langtangen, Hans Petter & Myre, Jørgen (2011). CBC.RANS - a new flexible, programmable software framework for computational fluid dynamics. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), MekIT'11: Sixth National Conference on Computational Mechanics, Trondheim 23-24 May 2011. Tapir Akademisk Forlag. ISSN 978-82-519-2798-7.
• Valen-Senstad, Kristian; Mardal, Kent-Andre; Mortensen, Mikael; Reif, Bjørn Anders Pettersson & Langtangen, Hans Petter (2011). On The Complexity of Stationary Flow in Patient–Specific Aneurysms. I Skallerud, Bjørn Helge & Andersson, Helge Ingolf (Red.), MekIT'11: Sixth National Conference on Computational Mechanics, Trondheim 23-24 May 2011. Tapir Akademisk Forlag. ISSN 978-82-519-2798-7. Vis sammendrag

  Summary Sound or bruits in the vasculatory system at the range of 1Hz-1kHz is known to occur, and frequency peaks at high frequencies are associated with sick blood vessels. The exact reason for these sounds are not known, but the sound may be generated by turbulence. Turbulence generated sound is typically associated with high frequencies but also with low energy levels. Unfortunately, most blood flow simulations are performed with space and time resolutions where rapid fluctuations typ- ically associated with non-laminar flow cannot be captured. Complex non-laminar flow and the subsequent oscillatory wall stresses can po- tentially be of importance in understanding aneurysm rupture through the local arterial wall response. To investigate the possible presence of complex non-laminar blood flow in intracranial aneurysms, we per- formed high resolution computational fluid dynamics (CFD) simulations for patient specific middle cerebral artery (MCA) aneurysms with sta- tionary inflow conditions. The current study confirms, through high resolution simulations, that complex oscillatory flow may occur in in- tracranial aneurysms. CFD practitioners should therefore be aware of the potentially strong demands to space-time computational resolution in blood flow simulations.

• Valen-Senstad, Kristian; Mardal, Kent-Andre; Mortensen, Mikael; Reif, Bjørn Anders Pettersson & Langtangen, Hans Petter (2011). Direct numerical simulation of transitional flow in a patient-specific intracranial aneurysm. Journal of Biomechanics. ISSN 0021-9290. 44(16), s. 2826–2832. doi: 10.1016/j.jbiomech.2011.08.015.
• Mortensen, Mikael; Langtangen, Hans Petter & Wells, Garth N. (2011). A FEniCS-based programming framework for modeling turbulent flow by the Reynolds-averaged Navier-Stokes equations. Advances in Water Resources. ISSN 0309-1708. 34(9), s. 1082–1101. doi: 10.1016/j.advwatres.2011.02.013.
• Reif, Bjørn Anders Pettersson & Mortensen, Mikael (2011). A Nonlinear Eddy-Viscosity Model for Near-Wall Turbulence. ERCOFTAC Series. ISSN 1382-4309. 14, s. 269–276. doi: 10.1007/978-90-481-9603-6_28.
• Mortensen, Mikael; Reif, Bjørn Anders Pettersson & Wasberg, Carl Erik (2010). Assessment of the finite volume method applied to the nu(2)-f model. International Journal for Numerical Methods in Fluids. ISSN 0271-2091. 63(4), s. 495–516. doi: 10.1002/fld.2091. Vis sammendrag

  The objective of this paper is to assess the accuracy of low-order finite volume (FV) methods applied to the nu(2)-f turbulence model of Durbin (Theoret. Comput. Fluid Dyn. 1991; 3:1-13) in the near vicinity of solid walls. We are not (like many others) concerned with the stability of solvers - the topic at hand is simply whether the mathematical properties of the nu(2)-f model can be captured by the given, widespread, numerical method. The nu(2)-f model is integrated all the way up to solid walls, where steep gradients in turbulence parameters are observed. The full resolution of wall gradients imposes quite high demands on the numerical schemes and it is not evident that common (second order) FV codes can fully cope with such demands. The nu(2)-f model is studied in a statistically one-dimensional, fully developed channel flow where we compare FV schemes with a highly accurate spectral element reference implementation. For the FV method a higher-order face interpolation scheme, using Lagrange interpolation polynomials up to arbitrary order, is described. It is concluded that a regular second-order FV scheme cannot give an accurate representation of all model parameters, independent of mesh density. To match the spectral element solution an extended source treatment (we use three-point Gauss-Lobatto quadrature), as well as a higher-order discretization of diffusion is required. Furthermore, it is found that the location of the first internal node need to be well within y(+) = 1. Copyright (C) 2009 John Wiley & Sons, Ltd.

• Reif, Bjørn Anders Pettersson; Mortensen, Mikael & Langer, Carlos A. (2009). Towards Sensitizing the Nonlinear v(2)-f Model to Turbulence Structures. Flow Turbulence and Combustion. ISSN 1386-6184. 83(2), s. 185–203. doi: 10.1007/s10494-008-9194-7. Vis sammendrag

  In this paper a one-way coupling between the nonlinear v (2) -aEuro parts per thousand f model by Pettersson Reif (Flow Turbul Combust 76:241-256, 2006) and an algebraic structure-based model have been investigated. Comparisons with available experimental and numerical data indicate that the compatibility between the two models is good and that their joint performance is satisfactory in the cases considered here. A full coupling between the models seems therefore a potentially viable route towards a significant advancement of engineering turbulence models and their predictive capabilities.

• Mortensen, Mikael & Bilger, Robert W. (2008). Derivation of the conditional moment closure equations for spray combustion. Combustion and Flame. ISSN 0010-2180. 155(3), s. 369–369. doi: 10.1016/j.combustflame.2008.10.013. Vis sammendrag

  In this work we derive the fundamental equations for conditional moment closure (CMC) modelling of individual phases set in a two-phase flow. The derivation is based on the instantaneous transport equations for the single phase that involve a level set/indicator function technique for accounting for interfaces. Special emphasis is put on spray combustion with the CMC equations formulated for the gas phase. The CIVIC equations are to be viewed as an adjunct to existing methods for the modelling of the dynamics of sprays: they provide a refinement of the modelling of chemical reactions in the gas phase. The resulting CIVIC equations differ significantly from those already in use in the literature. They contain, of course, unclosed terms that need to be modelled. Investigation of the unclosed terms associated with evaporation at the droplet surface is well beyond the capabilities of laboratory measurement or direct numerical simulation. it is proposed that modelling of these terms be based on the well-established 'laws' of similarity between heat and mass transfer: an example is detailed for one example of the general modelling of the spray dynamics. other unclosed terms are important throughout the gas phase. Models used for these terms in single-phase flows are reviewed and it is proposed that any modifications needed for these models be investigated by DNS of suitable model problems having good resolution of the flow and mixing in the inter-droplet space. It is proposed that a spray analogue of the scalar mixing layer that has been widely studied in single-phase flows be used as the model problem for such DNS studies and also for LES and RANS modelling. (c) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

• Mortensen, Mikael; de Bruyn Kops, Stephen M & Cha, Chong M. (2007). Direct numerical simulations of the double scalar mixing layer Part II: Reactive scalars. Combustion and Flame. ISSN 0010-2180. 149(4), s. 392–408. doi: 10.1016/j.combustflame.2007.03.001. Vis sammendrag

  The reacting double scalar mixing layer (RDSML) is investigated as a canonical multistream flow and a model problem for simple piloted diffusion flames. In piloted diffusion flames, the reacting fuel and oxidizer streams are initially separated by a central pilot stream at stoichiometric composition. The primary purpose of this pilot is to delay the mixing of the pure streams until a stable flame base can develop. In such multistrearn systems, the modeling of turbulent scalar mixing is complicated by the multiple feed streams, leading to more complex fine-scale statistics, which remain as yet an unmet modeling challenge compared to the simpler two-feed system. In Part I we described how multimodal mixture fraction probability density functions (PDFs) and conditional scalar dissipation rates can be modeled with a presumed mapping function approach. In this work we present an efficient and robust extension of the modeling to a general multistrearn reacting flow and compare predictions to three-dimensional direct numerical simulations (DNS) of the RDSML with a single-step reversible chemistry model and varying levels of extinction. With high extinction levels, the interaction with the pilot stream is described. Additionally, state-of-the-art combustion modeling calculations including conditional moment closure (CMC) and stationary laminar flamelet modeling (SLFM) are performed with the newly developed mixing model. Excellent agreement is found between the DNS and modeling predictions, even where the PDF is essentially a triple-delta shape near the flame base, so long as extinction levels are moderate to low. The suggested approach outlined in this paper is strictly valid only for flows that can be described by a single mixture fraction. For these flows the approach should provide engineers with fine-scale models that are of accuracy comparable to those already available for binary mixing, at only marginally higher complexity and cost. (C) 2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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• Miloch, Wojciech Jacek; Usui, Hideyuki; Miyake, Yohei; Mortensen, Mikael; Chernyshov, A.A. & Baddeley, Lisa [Vis alle 11 forfattere av denne artikkelen] (2021). Long-term and sustainable research- based student mobility projects within space weather.
• Friedemann, Christopher; Mortensen, Mikael & Nossen, Jan (2017). Multiphase flow simulation in an annulus configuration. Vis sammendrag

  On the 20th of April 2010, explosion and fire killed 11 people on the Deepwater Horizon oil rig in the Gulf of Mexico. After two days in flames, the rig sank and left the riser (the pipe going up from the seabed) on the sea floor leaking oil and gas from the well through the gap between the drilling riser and the drill-string (rod holding the drillbit) inside it. The accident is known as the Macondo accident. Immediate concerns were raised regarding the amount of oil being released into the Gulf of Mexico killing fish and seabirds. The size of the oil spill has also played a significant role in the court proceedings where the operator BP at the end accepted to pay a fine of more than 18 bn US dollars. One of many techniques that were applied was based on using simulation software to match the observed frequency of plugs of oil flowing out of the sunken riser. There are, however, serious flaws to this approach. The most important is the lack of reliable models for multiphase flow in annuli, that is, flow of oil and gas in the ring shaped space between the drillstring and the outer pipe. Commercial simulation software packages for flow of oil and gas in pipes lack the ability to correctly predict pressure drop in annulus flow, even when the flow contains only gas or only liquid. When both gas and oil are flowing in the pipe at the same time, which is called multiphase flow, the models are even worse. Well design is thus based on crude formulas with large uncertainty and high error margins. This may lead to inefficient well design and high risk of production problems. ANNULUS will bring a step change in the scientific knowledge in this field and provide data and physical understanding that can be used as a basis for developing more usable and accurate commercial simulation software in the future. Improved models can be used by operators and contribute to significantly safer and more efficient and profitable well operations and production.

• Mortensen, Mikael (2015). Massively parallel implementation in Python of a pseudo-spectral DNS code for turbulent flows. Vis sammendrag

  https://www.euroscipy.org/2015/schedule/presentation/6/

• Mardal, Kent-Andre; Støverud, Karen-Helene; Mortensen, Mikael; Jain, Kartik; Martin, Bryn & Pahlavian, Soroush (2014). Cerebrospinal fluid flow in association with the central nervous system -- Chiari and drug delivery.

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