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• Zhang, Dawang; Campbell, James; Eriksen, Jon Alm; Flekkøy, Eirik Grude; Måløy, Knut Jørgen & MacMinn, Christopher W. [Vis alle 7 forfattere av denne artikkelen] (2023). Frictional fluid instabilities shaped by viscous forces. Nature Communications. 14(1). doi: 10.1038/s41467-023-38648-6. Fulltekst i vitenarkiv Vis sammendrag

  Multiphase flows involving granular materials are complex and prone to pattern formation caused by competing mechanical and hydrodynamic interactions. Here we study the interplay between granular bulldozing and the stabilising effect of viscous pressure gradients in the invading fluid. Injection of aqueous solutions into layers of dry, hydrophobic grains represent a viscously stable scenario where we observe a transition from growth of a single frictional finger to simultaneous growth of multiple fingers as viscous forces are increased. The pattern is made more compact by the internal viscous pressure gradient, ultimately resulting in a fully stabilised front of frictional fingers advancing as a radial spoke pattern.

• Campbell, James; Sandnes, Bjørnar; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2022). Dynamics of Dendritic Ice Freezing in Confinement. Crystal Growth & Design. ISSN 1528-7483. 22(4), s. 2433–2440. doi: 10.1021/acs.cgd.1c01488. Fulltekst i vitenarkiv Vis sammendrag

  We use high-speed photography to observe the dendritic freezing of ice between two closely spaced parallel plates. Measuring the propagation speeds of dendrites, we investigate whether there is a confinement-induced thermal influence upon the speed beyond that provided by a single surface. Plates of thermally insulating plastic and moderately thermally conductive glass are used alone and in combination, at temperatures between −10.6 and −4.8 °C, with separations between 17 and 135 μm wide. No effect of confinement was detected for propagation on glass surfaces, but a possible slowing of propagation speed was seen between insulating plates. The pattern of dendritic growth was also studied, with a change from curving to straight dendrites being strongly associated with a switch from a glass to a plastic substrate.

• Olsen, Kristian Stølevik & Campbell, James (2020). Diffusion entropy and the path dimension of frictional finger patterns. Frontiers in Physics. 8:83, s. 1–5. doi: 10.3389/fphy.2020.00083. Fulltekst i vitenarkiv Vis sammendrag

  The authors investigate, using both analytical and numerical methods, the entropy associated with a diffusion process inside frictional finger patterns. The entropy obtained from simulations of diffusion inside the pattern is compared to analytical predictions based on an effective continuum description. The analytical result predicts that the entropy depends in a particular way on the path dimension of the system, which governs the scaling of simple paths in the system. The findings indicates that there is a close analogy between the frictional fingers in the continuum and minimum spaning trees on the lattice, as the path dimension is found, through studies of the entropy, to be close to the defining value for the minimum spanning tree universality class.

• Olsen, Kristian Stølevik; Flekkøy, Eirik Grude; Angheluta, Luiza; Campbell, James; Måløy, Knut Jørgen & Sandnes, Bjørnar (2019). Geometric universality and anomalous diffusion in frictional fingers. New Journal of Physics. 21(6). doi: 10.1088/1367-2630/ab25bf. Fulltekst i vitenarkiv Vis sammendrag

  Frictional finger trees are patterns emerging from non-equilibrium processes in particle-fluid systems. Their formation share several properties with growth algorithms for minimum spanning trees(MSTs) in random energy landscapes. We propose that the frictional finger trees are indeed in the same geometric universality class as the MSTs, which is checked using updated numerical simulation algorithms for frictional fingers. We also propose a theoretical model for anomalous diffusion in these patterns, and discuss the role of diffusion as a tool to classify geometry.

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