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Haugesund, Norway

Vevatne J.N.,Norwegian University of Science and Technology | Rimstad E.,Norwegian University of Science and Technology | Hope S.M.,Norwegian University of Science and Technology | Hope S.M.,Polytec Research Institute | And 2 more authors.
Frontiers of Physics | Year: 2014

Fracturing and refreezing of sea ice in the Kara sea are investigated using complex network analysis. By going to the dual network, where the fractures are nodes and their intersections links, we gain access to topological features which are easy to measure and hence compare with modeled networks. Resulting network reveal statistical properties of the fracturing process. The dual networks have a broad degree distribution, with a scale-free tail, high clustering and efficiency. The degree–degree correlation profile shows disassortative behavior, indicating preferential growth. This implies that long, dominating fractures appear earlier than shorter fractures, and that the short fractures which are created later tend to connect to the long fractures. The knowledge of the fracturing process is used to construct growing fracture network (GFN) model which provides insight into the generation of fracture networks. The GFN model is primarily based on the observation that fractures in sea ice are likely to end when hitting existing fractures. Based on an investigation of which fractures survive over time, a simple model for refreezing is also added to the GFN model, and the model is analyzed and compared to the real networks. © 2014 Vevatne, Rimstad, Hope, Korsnes and Hansen.

Ytrehus T.,Norwegian University of Science and Technology | Helgaker J.F.,Norwegian University of Science and Technology | Helgaker J.F.,Polytec Research Institute
Journal of Fluids Engineering, Transactions of the ASME | Year: 2013

The transportation of natural gas through high pressure transmission pipelines has been modeled by numerically solving the conservation equations for mass, momentum, and energy for one-dimensional compressible viscous heat conducting flow. Since the one-dimensional version is a result of averages over the pipe cross-section and the flow is normally turbulent, the order of averaging in space and time is an issue; in particular, for the dissipation term. The Reynolds decomposition and time averaging should be performed first, followed by the contraction to the one-dimensional version by the cross-sectional averaging. The result is a correction factor, which is close to unity, on the usual expression of the dissipation term in the energy equation. This factor will, to some extent, affect the temperature distribution along the pipeline. For low Reynolds numbers (Reâ‰104) it reduces the dissipation by as much as 7%, irrespective of roughness. For high Reynolds numbers (Re ≥ 107) and roughness in the high range of the micron decade, the dissipation is increased by 10%. If the pipeline is also thermally isolated such that the flow can be considered adiabatic, the effect of turbulent dissipation gains further importance. Copyright © 2013 by ASME.

Stensholt S.,Polytec Research Institute
Computers and Mathematics with Applications | Year: 2015

We evaluate the Lattice-Boltzmann model that combines the free energy approach for multiphase flow with the bounce-back boundary condition. This method requires a virtual ordering parameter to be assigned to the wall nodes. Existing literature has assigned a single ordering parameter for the entire wall node, but this is too coarse to give accurate simulations since it allows for a spurious interaction of different phases through the wall nodes. The consequences are illustrated by examining rough and hydrophobic surfaces where contact angles can be predicted using the Cassie-Baxter equation. It is found that the single value approach gives a large systemic error in the measured contact angles. Considerable improvement can be obtained by assigning different values of the ordering parameter to each side of the wall node. © 2015 Elsevier Ltd.

Soldal M.,NGI Inc | Park J.,NGI Inc | Lamech L.O.,University of Oslo | Tran T.,University of Oslo | And 3 more authors.
3rd EAGE Workshop on Rock Physics: From Rocks to Basin - Applying Rock Physics in Prospect Evaluation and Reservoir Characterization | Year: 2015

In this study, liquid CO2 is injected into fully brine saturated reservoir core samples in the laboratory, and consequently changes in electrical resistivity, acoustic velocities (ultrasonic frequency) and their anisotropy are measured. To enhance the spatial resolution, a system enabling velocity and resistivity measurements at different points and in different directions along the specimen's axial direction has been developed. Electrical resistivity and acoustic velocity and amplitude are all clearly influenced by porescale heterogeneity and fluid flow pattern and it is important to study this interaction. So far, focus has been related to CO2 geological storage, but the outline of the study is believed to also be applicable for CO2 injection for enhanced oil recovery (EOR). The study is still ongoing and some preliminary results are presented here and discussed.

Helgaker J.F.,Polytec Research Institute | Helgaker J.F.,Norwegian University of Science and Technology | Muller B.,Polytec Research Institute | Ytrehus T.,Polytec Research Institute
Journal of Offshore Mechanics and Arctic Engineering | Year: 2014

Transmission of natural gas through high pressure pipelines has been modeled by numerically solving the governing equations for one-dimensional compressible flow using implicit finite difference methods. In the first case the backward Euler method is considered using both standard first-order upwind and second-order centered differences for the spatial derivatives. The first-order upwind approximation, which is a one-sided approximation, is found to be unstable for CFL numbers less than 1, while the centered difference approximation is stable for any CFL number. In the second case a cell centered method is considered where flow values are calculated at the midpoint between grid points. This method is also stable for any CFL number. However, for a discontinuous change in inlet temperature, the method is observed to introduce unphysical oscillations in the temperature profile along the pipeline. A solution strategy where the hydraulic and thermal models are solved separately using different discretization techniques is suggested. Such a solution strategy does not introduce unphysical oscillations for discontinuous changes in inlet boundary conditions and is found to be stable for any CFL number. The one-dimensional flow model is validated using operational data from a high pressure natural gas pipeline. © 2014 by ASME.

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