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A novel cell-centred control-volume distributed multi-point flux approximation (CVD-MPFA) finite-volume formulation is presented for discrete fracture–matrix simulations on unstructured grids in three-dimensions (3D). The grid is aligned with fractures and barriers which are then modelled as lower-dimensional surface interfaces located between the matrix cells in the physical domain. The three-dimensional pressure equation is solved in the matrix domain coupled with a two-dimensional (2D) surface pressure equation solved over fracture networks via a novel surface CVD-MPFA formulation. The CVD-MPFA formulation naturally handles fractures with anisotropic permeabilities on unstructured grids. Matrix–fracture fluxes are expressed in terms of matrix and fracture pressures and define the transfer function, which is added to the lower-dimensional flow equation and couples the three-dimensional and surface systems. An additional transmission condition is used between matrix cells adjacent to low permeable fractures to couple the velocity and pressure jump across the fractures. Convergence and accuracy of the lower-dimensional fracture model is assessed for highly anisotropic fractures having a range of apertures and permeability tensors. A transport equation for tracer flow is coupled via the Darcy flux for single and intersecting fractures. The lower-dimensional approximation for intersecting fractures avoids the more restrictive CFL condition corresponding to the equi-dimensional approximation with explicit time discretisation. Lower-dimensional fracture model results are compared with equi-dimensional model results. Fractures and barriers are efficiently modelled by lower-dimensional interfaces which yield comparable results to those of the equi-dimensional model. Pressure continuity is built into the model across highly conductive fractures, leading to reduced local degrees of freedom in the CVD-MPFA approximation. The formulation is applied to geologically complex fracture networks in three-dimensions. The effects of the fracture permeability, aperture and grid resolution are also assessed with respect to convergence and computational cost. [ABSTRACT FROM AUTHOR]

Our ability to process information about an object’s location in depth varies along the horizontal and vertical axes. These variations reflect functional specialisation of the cerebral hemispheres as well as the ventral/dorsal visual streams for processing stimuli located in near and far space. Prior research has demonstrated visual field superiorities for processing near space in the lower and right hemispaces and for far space in the upper and left hemispaces. No research, however, has directly tested whether the functional specialisation of the visual fields actually makes objects look closer when presented in the lower or right visual fields. To measure biases in the perception of depth, we employed anaglyph stimuli where participants made closer/further judgments about the relative location of two spheres in a three-dimensional virtual space. We observed clear processing differences in this task where participants perceived the right and lower spheres to be closer and the left and upper spheres to be further away. Furthermore, no relationship between the horizontal and vertical dimensions was observed suggesting separate cognitive/neural mechanisms. Not only does this methodology clearly demonstrate differences in perceived depth across the visual field, it also opens up many possibilities for studying functional asymmetries in three-dimensional space. [ABSTRACT FROM AUTHOR]

In this paper, the Cauchy problem for the three-dimensional (3-D) isentropic compressible Navier-Stokes equations with degenerate viscosities is considered. By introducing some new variables and making use of the "quasi-symmetric hyperbolic"–"degenerate elliptic" coupled structure to control the behavior of the fluid velocity, we prove the global-in-time well-posedness of regular solutions with vacuum for a class of smooth initial data that are of small density but possibly large velocities. Here the initial mass density is required to decay to zero in the far field, and the spectrum of the Jacobi matrix of the initial velocity are all positive. The result here applies to a class of degenerate density-dependent viscosity coefficients, is independent of the BD-entropy, and seems to be the first on the global existence of smooth solutions which have large velocities and contain vacuum state for such degenerate system in three space dimensions. [ABSTRACT FROM AUTHOR]