Publications

Linga, Gaute; Bolet, Asger & Mathiesen, Joachim (2020). Transient electrohydrodynamic flow with concentrationdependent fluid properties: Modelling and energystable numerical schemes. Journal of Computational Physics.
ISSN 00219991.
412 . doi:
10.1016/j.jcp.2020.109430
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Transport of electrolytic solutions under influence of electric fields occurs in phenomena ranging from biology to geophysics. Here, we present a continuum model for singlephase electrohydrodynamic flow, which can be derived from fundamental thermodynamic principles. This results in a generalized Navier–Stokes–Poisson–Nernst–Planck system, where fluid properties such as density and permittivity depend on the ion concentration fields. We propose strategies for constructing numerical schemes for this set of equations, where the electrochemical and the hydrodynamic subproblems are decoupled at each time step. We provide time discretizations of the model that suffice to satisfy the same energy dissipation law as the continuous model. In particular, we propose both linear and nonlinear discretizations of the electrochemical subproblem, along with a projection scheme for the fluid flow. The efficiency of the approach is demonstrated by numerical simulations using several of the proposed schemes.

Linga, Gaute; Møyner, Olav; Nilsen, Halvor Møll; Arthur, Moncorgé & Lie, KnutAndreas (2020). An implicit local timestepping method based on cell reordering for multiphase flow in porous media. Journal of Computational Physics: X.
ISSN 25900552.
6 . doi:
10.1016/j.jcpx.2020.100051
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We discuss how to introduce local timestep refinements in a sequential implicit method for multiphase flow in porous media. Our approach relies heavily on causalitybased optimal ordering, which implies that cells can be ordered according to total fluxes after the pressure field has been computed, leaving the transport problem as a sequence of ordinary differential equations, which can be solved cellbycell or blockbyblock. The method is suitable for arbitrary local time steps and grids, is massconservative, and reduces to the standard implicit upwind finitevolume method in the case of equal time steps in adjacent cells. The method is validated by a series of numerical simulations. We discuss various strategies for selecting local time steps and demonstrate the efficiency of the method and several of these strategies by through a series of numerical examples.

Nielsen, Bjarke Frost; Linga, Gaute; Christensen, Amalie & Mathiesen, Joachim (2020). Substrate curvature governs texture orientation in thin films of smectic block copolymers. Soft Matter.
ISSN 1744683X.
16(14), s 3395 3406 . doi:
10.1039/C9SM02389E
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Linga, Gaute; Bolet, Asger & Mathiesen, Joachim (2019). Bernaise: A flexible framework for simulating twophase electrohydrodynamic flows in complex domains. Frontiers in Physics.
ISSN 2296424X.
7 . doi:
10.3389/fphy.2019.00021

Linga, Gaute & Flåtten, Tore Halsne (2019). A Hierarchy of NonEquilibrium TwoPhase Flow Models. ESAIM: Proceedings and Surveys.
ISSN 22673059.
66, s 109 143 . doi:
10.1051/proc/201966006
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We review and extend a hierarchy of relaxation models for twophase flow. The models are derived from the nonequilibrium Baer–Nunziato model, which is endowed with relaxation source terms to drive it towards equilibrium. The source terms cause transfer of volume, heat, mass and momentum due to differences between the phases in pressure, temperature, chemical potential and velocity, respectively. In the context of twophase flow models, the subcharacteristic condition implies that the sound speed of an equilibrium system can never exceed that of the relaxation system. Here, previous work by Flåtten and Lund [Math. Models Methods Appl. Sci., 21 (12), 2011, 2379–2407] and Lund [SIAM J. Appl. Math. 72, 2012, 1713–1741] is extended to encompass twofluid models, i.e. models with separately governed velocities for the two phases. Each remaining model in the hierarchy is derived, and analytical expressions for the sound speeds are presented. Given only physically fundamental assumptions, the subcharacteristic condition is shown to be satisfied in the entire hierarchy, either in a weak or in a strong sense.

Bolet, Asger; Linga, Gaute & Mathiesen, Joachim (2018). Electrohydrodynamic channeling effects in narrow fractures and pores. Physical review. E.
ISSN 24700045.
97(4) . doi:
10.1103/PhysRevE.97.043114

Linga, Gaute; Bolet, Asger & Mathiesen, Joachim (2018). Controlling wetting with electrolytic solutions: Phasefield simulations of a dropletconductor system. Physical review. E.
ISSN 24700045.
98(1) . doi:
10.1103/PhysRevE.98.013101

Linga, Gaute; Mathiesen, Joachim & Renard, Francois (2017). Selfsimilar distributions of fluid velocity and stress heterogeneity in a dissolving porous limestone. Journal of Geophysical Research (JGR): Solid Earth.
ISSN 21699313.
122(3), s 1726 1743 . doi:
10.1002/2016JB013536
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Wilhelmsen, Øivind; Aasen, Ailo; Skaugen, Geir; Aursand, Peder; Austegard, Anders; Aursand, Eskil; Gjennestad, Magnus Aashammer; Lund, Halvor; Linga, Gaute & Hammer, Morten (2017). Thermodynamic modeling with equations of state: present challenges with established methods. Industrial & Engineering Chemistry Research.
ISSN 08885885.
56(13), s 3503 3515 . doi:
10.1021/acs.iecr.7b00317
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Equations of state (EoS) are essential in the modeling of a wide range of industrial and natural processes. Desired qualities of EoS are accuracy, consistency, computational speed, robustness and predictive ability outside of the domain where they have been fitted. In this work, we review present challenges associated with established models, and give suggestions on how to overcome them in the future. The most accurate EoS available, multiparameter EoS, have a second artificial Maxwell loop in the twophase region that gives problems in phaseequilibrium calculations and exclude them from important applications such as treatment of interfacial phenomena with mass based density functional theory. Suggestions are provided on how this can be improved. Cubic EoS are among the most computationally efficient EoS, but they often lack sufficient accuracy. We show that extended corresponding state EoS are capable of providing significantly more accurate singlephase predictions than cubic EoS with only a doubling of the computational time. In comparison, the computational time of multiparameter EoS can be orders of magnitude larger. For mixtures in the twophase region, however, the accuracy of extended corresponding state EoS has a large potential for improvement. The molecularbased SAFT family of EoS are preferred when predictive ability is important, e.g. for systems with strongly associating fluids or polymers where few experimental data are available. We discuss some of their benefits and present challenges. A discussion is presented on why predictive thermodynamic models for reactive mixtures such as CO2NH3 and CO2H2OH2S must be developed in close combination with phase and reaction equilibrium theory, regardless of the choice of EoS. After overcoming present challenges, a nextgeneration thermodynamic modeling framework holds the potential to improve the accuracy and predictive ability in a wide range of applications such as process optimization, computational fluid dynamics, treatment of interfacial phenomena and processes with reactive mixtures.

Linga, Gaute & Lund, Halvor (2016). A TwoFluid Model for Vertical Flow Applied to CO2 Injection Wells. International Journal of Greenhouse Gas Control.
ISSN 17505836.
51, s 71 80 . doi:
10.1016/j.ijggc.2016.05.009
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Flow of CO2 in wells is associated with substantial variations in thermophysical properties downhole, due to the coupled transient processes involved: complex flow patterns, density changes, phase transitions, and heat transfer to and from surroundings. Large temperature variations can lead to thermal stresses and subsequent loss of well integrity, and it is therefore crucial to employ models that can predict this accurately. In this work, we present a model for vertical well flow that includes both twophase flow and heat conduction. The flow is described by a twofluid model, where mass transfer between the phases is modelled by relaxation source terms that drive the phases towards thermodynamic equilibrium. We suggest a new formulation of the mass transfer process that satisfies the second law of thermodynamics, and that is also continuous in the singlephase limit. This provides a more robust transition from twophase to singlephase flow than the previous formulation. The model predicts which flow regimes are present downhole, and calculates friction and heat transfer depending on this. Moreover, the flow model is coupled with a heat conduction model for the layers that comprise the well, including tubing, packer fluid, casing, cement or drilling mud, and rock formation. This enables prediction of the temperature in the well fluid and in each layer of the well. The model is applied to sudden shutin and blowout cases of a CO2 injection well, where we employ the highly accurate SpanWagner reference equationofstate to describe the thermodynamics of CO2. We predict pressure, temperature and flow regimes during these cases and discuss implications for well integrity. © 2016 Elsevier Ltd.

Linga, Gaute; Aursand, Peder & Flåtten, Tore (2015). Twophase nozzle flow and the subcharacteristic condition. Journal of Mathematical Analysis and Applications.
ISSN 0022247X.
426(2), s 917 934 . doi:
10.1016/j.jmaa.2015.01.065
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We consider nozzle flow models for twophase flow with phase transfer. Such models are based on energy considerations applied to the frozen and equilibrium limits of the underlying relaxation models. In this paper, we provide an explicit link between the mass flow rate predicted by these models and the classical subcharacteristic condition of Chen, Levermore and Liu. In particular, we demonstrate that for sufficiently small pressure differences, the equilibrium nozzle model will predict a lower mass flow rate than the frozen model when the subcharacteristic condition is satisfied. An application to tank leakage of CO2 is presented, indicating that the frozen and equilibrium models provide significantly different predictions. This difference is comparable in magnitude to the modeling error introduced by applying simple idealgas/incompressibleliquid equationsofstate for CO2.

Linga, Gaute; Ballone, Pietro & Hansen, Alex (2015). Creep rupture of fiber bundles: A molecular dynamics investigation. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics.
ISSN 15393755.
92(2) . doi:
10.1103/PhysRevE.92.022405
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Frost Nielsen, Bjarke; Linga, Gaute; Olsen, Kristian Stølevik & Simonsen, Lone (2020). Vejen til frihed. Weekendavisen.
ISSN 01064142.
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https://www.weekendavisen.dk/202019/ideer/vejentilfrihed

Linga, Gaute (2020). Stretching and mixing in twophase flow in porous media.

Linga, Gaute; Mathiesen, Joachim; Renard, Francois & Le Borgne, Tanguy (2020). Stretching and Folding in Intermittent TwoPhase Porous Media Flows.

Lie, KnutAndreas; Linga, Gaute; Møyner, Olav; Nilsen, Halvor Møll & Moncorge, A (2019). An implicit local timestepping method based on cell reordering for multiphase flow in porous media.

Linga, Gaute (2019). Influence of roughness, inertia and surface charge on fluid transport in fractures and pores: Insights from direct numerical simulations.

Linga, Gaute (2019). Twophase electrohydrodynamics in complex geometries – modelling and simulation.
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Published July 1, 2019 12:51 PM
 Last modified July 1, 2019 12:51 PM