## Contact

Gaute Linga, PhD

Postdoctoral researcher

The Njord Centre,

University of Oslo,

Norway

**E-mail:** gaute [dot] linga [at] mn [dot] uio [dot] no or linga [at] nbi [dot] dk (public key)

**Phone:** (+47) 41 22 77 10

## About me

I am a physicist from Bergen, Norway, with a PhD in Physics from the Niels Bohr Institute, University of Copenhagen. I hold a MSc degree (siv. ing.) in Applied Physics from the Norwegian University of Science and Technology, Trondheim (with an exchange stay at Université Pierre et Marie Curie in Paris). I am currently a postdoc at The Njord Centre, at the intersection between the Departments of Physics and Geoscience, at the University of Oslo. The fellowship is funded jointly by Equinor through the Akademia project (Modiflow) and by the PoreLab Center of Excellence through the Research Council of Norway. Before my PhD studies, I was a researcher in the Flow phenomena group at SINTEF Energy Research, Trondheim, and I have worked as a Research Scientist at SINTEF Digital in Oslo.

My research revolves around *modelling* and *numerical simulation* of *fluid flow in* and *deformation of* disordered multiphase systems.
Such systems typically arise in fluid-saturated fractures and porous rock, but also has applications to microfluidic devices and biological systems.
As a concrete example, my research may lead to an improved understanding of the physical aspects of carbon capture, transport and storage.
My PhD thesis advisor was Assoc. Prof. Joachim Mathiesen, and my PhD project was a part of the NanoHeal network.

## Research

My scientific interests are located at the intersection between statistical physics, continuum mechanics and scientific computing. Currently, I am mostly interested in fluid flow phenomena in the presence of complex fluid-fluid or fluid-solid interfaces. I try to gain insight into these by combining high-performance numerical simulations and methods from statistical physics. Here follows more information on the overarching themes:

### Flow, fracture and stress in geophysical systems

The application of stress to heterogeneous disordered solid-liquid systems leads to a feedback loop between flow and deformation. Regions of high stress are prone to dissolution and/or crack formation, while regions of low stress are generally more prone to mineral precipitation. This changes the geometry, and subsequently the fluid flow paths which control the distribution of precipitate - closing the feedback loop between flow and deformation. We have studied the fracture and creep of idealized materials on the microscopic scale (using molecular dynamics). Further, using data from real rock samples, we studied the stress formation in evolving porous microstructures. We have also studied the channeling effects in charged model microfractures.

Current research is focused the role of inertia for flow through self-affine fractures, and the role of roughness on the laminar-turbulent transition in wall-bounded shear flows.

*Collaborators: Joachim Mathiesen, François Renard, Luiza Angheluta*.

### Computational microfluidics

Micro- and nanofluidics are areas of rapid growth which are expected to continue to yield technological progress. At such small scales, electrokinetic effects may be essential. Such flow of ion-laden fluids under influence of electric fields is called electrohydrodynamics. For example, electrohydrodynamic effects alter the wetting properties of two-phase systems, which also may have consequences in geophysical systems.

Reliable computational methods are necessary to complement physical experiments, to validate theoretical models, and to enable rapid prototyping of devices. As much of computational microfluidics (especially with electrohydrodynamics) relies on black-box software, we have developed the open-source phase-field solver Bernaise (built on top of the finite-element framework FEniCS). Current research efforts include developing new, stable schemes for the strongly coupled problem of electrohydrodynamics.

### Models for (non-equilibrium) multiphase flow

We have used and developed phase-field models for direct numerical simulation of multiphase fluid flows.
At the scale of pipelines (meters to kilometers), it is, however, unfeasible to resolve the entire flow field.
For such applications, which are highly relevant with regard to CO_{2} transport, the multiphase flow is represented as a system of (hyperbolic) first-order partial differential equations, wherein the complicated fluid-fluid and fluid-solid interactions are represented by effective relaxation source terms.
Building on results from the literature, we have completed a hierarchy of simplified models.
In particular (*at least* in the limit of equal phase velocities) every equilibrium assumption reduces the wave velocities of the relaxation system.

*Collaborator: Tore Flåtten*

### General interests

- Physics of complex systems
- Statistical mechanics
- Interface dynamics
- Instabilities in fluid mechanics
- Multiscale simulation
- CO
_{2}transport and storage (CCS)

## Publications

### Articles in preparation

**Transitional flow in self-affine rough channels**

GL, L. Angheluta, J. Mathiesen (2019).

### Submitted articles

**Transient electrohydrodynamic flow with concentration-dependent fluid properties: modelling and energy-stable schemes**

GL, A. Bolet, J. Mathiesen (2019) [arXiv].

### Articles published in peer-reviewed journals

**Creep rupture of fiber bundles: A molecular dynamics investigation**

GL, Pietro Ballone, Alex Hansen,*Physical Review E***92**, 022405 (2015).**Two-phase nozzle flow and the subcharacteristic condition**

GL, Peder Aursand, Tore Flåtten,*Journal of Mathematical Analysis and Applications***426**, 917-934 (2015).**A two-fluid model for vertical flow applied to CO**_{2}injection wells

GL, Halvor Lund,*International Journal of Greenhouse Gas Control***51**, 71-80 (2016).**Self-similar distributions of fluid velocity and stress heterogeneity in a dissolving porous limestone**

GL, François Renard, and Joachim Mathiesen,*Journal of Geophysical Research: Solid Earth***122**(2017).**Thermodynamic Modeling with Equations of State: Present Challenges with Established Methods**

Ø. Wilhelmsen, A. Aasen, G. Skaugen, P. Aursand, A. Austegard, E. Aursand, M. Aa. Gjennestad, H. Lund, GL, and M. Hammer,*Ind. Eng. Chem. Res.***56**(2017).**Electrohydrodynamic channeling effects in narrow fractures and pores**

A. Bolet, GL, J. Mathiesen,*Physical Review E***97**, 043114 (2018) [arXiv].**Controlling wetting with electrolytic solutions: phase-field simulations of a droplet-conductor system**

GL, A. Bolet, J. Mathiesen,*Physical Review E***98**, 013101 (2018) [arXiv].**A hierarchy of non-equilibrium two-phase flow models**

GL, Tore Flåtten,*ESAIM: Proceedings and Surveys*, accepted (2019) [arXiv].**Bernaise: A flexible framework for simulating two-phase electrohydrodynamic flows in complex domains**

GL, A. Bolet, J. Mathiesen,*Frontiers in Physics***7**, 21 (2019) [arXiv].

### Theses

**Fluid Flows with Complex Interfaces: Modelling and Simulation from Pore to Pipe**

Advisor: Joachim Mathiesen (PhD thesis, NBI, University of Copenhagen, 2018).**The Breaking Process of an Idealized Polymeric Bundle under Applied Tensile Stress**

Advisors: Alex Hansen, Pietro Ballone (MSc thesis, NTNU, 2014).**A Mathematical Study of Non-Equilibrium Two-Phase Flow**(Project thesis, NTNU, 2013).