65 research outputs found

    Viscous fingering in fractured porous media

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    The effect of heterogeneities induced by highly permeable fracture networks on viscous miscible fingering in porous media is examined using high-resolution numerical simulations. We consider the planar injection of a less viscous fluid into a two-dimensional fractured porous medium which is saturated with a more viscous fluid. This problem contains two sets of fundamentally different preferential flow regimes; the first is caused by the viscous fingering and the second is due to the permeability contrasts between the fractures and rock matrix. We study the transition from a regime where the flow is dominated by the viscous instabilities, to a regime where the heterogeneities induced by the fractures define the flow paths. We find that fractures greatly affect the viscous fingering, even for small permeability differences between the rock matrix and the fractures. The interaction between the viscosity contrast and permeability contrast causes channeling of the less viscous fluid through the fractures and back to the rock. This channeling stabilizes the displacement front in the rock matrix, and the viscous fingering ceases for the higher permeability contrast. Several different fracture geometries are considered, and we observe a complex interplay between the geometries and unstable flow. While we find that the most important dimensionless number determining the effect of the fracture network is a weighted ratio of the permeability of the fractures and the permeability of the rock matrix, the exact point for the cross-over regime is highly dependent on the geometry of the fracture network.Comment: To reproduce simulations, see "R. L. Berge, I. Berre, E. Keilegavlen, and J. M. Nordbotten. Viscous fingering in fractured porous media. Zenodo. doi: 10.5281/zenodo.3249931, June 2019

    Finite volume discretization for poroelastic media with fractures modeled by contact mechanics

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    A fractured poroelastic body is considered where the opening of the fractures is governed by a nonpenetration law, whereas slip is described by a Coulomb‐type friction law. This physical model results in a nonlinear variational inequality problem. The variational inequality is rewritten as a complementary function, and a semismooth Newton method is used to solve the system of equations. For the discretization, we use a hybrid scheme where the displacements are given in terms of degrees of freedom per element, and an additional Lagrange multiplier representing the traction is added on the fracture faces. The novelty of our method comes from combining the Lagrange multiplier from the hybrid scheme with a finite volume discretization of the poroelastic Biot equation, which allows us to directly impose the inequality constraints on each subface. The convergence of the method is studied for several challenging geometries in 2D and 3D, showing that the convergence rates of the finite volume scheme do not deteriorate when it is coupled to the Lagrange multipliers. Our method is especially attractive for the poroelastic problem because it allows for a straightforward coupling between the matrix deformation, contact conditions, and fluid pressure.publishedVersio

    Acoustic pharyngometry - A new method to facilitate oral appliance therapy

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    Background There is lack of reliable and accurate methods to predict treatment outcomes of oral appliance (OA) treatment. Acoustic pharyngometry (AP) is a non-invasive technique to evaluate the volume and minimal cross-sectional area of the upper airway, which may prove useful to locate the optimal position of OAs. Objective This retrospective study aimed to evaluate the effect of applying AP to OA treatment of patients with obstructive sleep apnoea (OSA). Methods All patients (n = 244) treated with OAs following an AP protocol at two dental clinics between 2013 and 2018 were invited to participate. A total of 129 patients accepted the invitation, and 120 patients (75 men, 45 women) were included in the analyses. Mean baseline age, BMI and apnoea hypopnea index (AHI) were 59.1 ± 0.9 years, 27.8 ± 0.4 and 21.9 ± 1.1, respectively. Mean follow-up time was 318 ± 24 days. Results AHI at follow-up was 6.4 ± 0.7, resulting in a treatment success rate of 86.7% (≥50% reduction of baseline AHI). The number of failures ( 5 hours usage per night, when worn. Conclusion The AP protocol applied seems to contribute to the excellent effect of OA treatment in this study. Further research on the application of AP in OA treatment is necessary in order to clarify its possible beneficial contribution to improving OA therapy.publishedVersio