Piecewise linear transformation in diffusive flux discretization

To ensure the discrete maximum principle or solution positivity in finite volume schemes, diffusive flux is sometimes discretized as a conical combination of finite differences. Such a combination may be impossible to construct along material discontinuities using only cell concentration values. This is often resolved by introducing auxiliary node, edge, or face concentration values that are explicitly interpolated from the surrounding cell concentrations. We propose to discretize the diffusive flux after applying a local piecewise linear coordinate transformation that effectively removes the discontinuities. The resulting scheme does not need any auxiliary concentrations and is therefore remarkably simpler, while being second-order accurate under the assumption that the structure of the domain is locally layered.Comment: 11 pages, 1 figures, preprint submitted to Journal of Computational Physic

Co-refinement of fault surfaces : convexification process

The aim of this work is to develop an algorithm that allows the common refinement of non-coincident meshes composed of arbitrary 3D surfaces elements (triangles, quad elements). This study is motivated by computations in geologic applications which involve complex geometries with heterogeneous components and geologic faults. The resulting meshes are linked through a continuous bijection in order to ensure the accuracy and the conservativity of the data transferring through the surfaces. The strategy adopted consists, first, of the simultaneous convexification of the two surfaces by the mean of points connections. A projection according to given normals is then achieved. The mesh quality improved by applying a surface smoothing should accelerate the procedure convergence

Modeling Fluid Flow in Faulted Basins

This paper presents a basin simulator designed to better take faults into account, either as conduits or as barriers to fluid flow. It computes hydrocarbon generation, fluid flow and heat transfer on the 4D (space and time) geometry obtained by 3D volume restoration. Contrary to classical basin simulators, this calculator does not require a structured mesh based on vertical pillars nor a multi-block structure associated to the fault network. The mesh follows the sediments during the evolution of the basin. It deforms continuously with respect to time to account for sedimentation, erosion, compaction and kinematic displacements. The simulation domain is structured in layers, in order to handle properly the corresponding heterogeneities and to follow the sedimentation processes (thickening of the layers). In each layer, the mesh is unstructured: it may include several types of cells such as tetrahedra, hexahedra, pyramid, prism, etc. However, a mesh composed mainly of hexahedra is preferred as they are well suited to the layered structure of the basin. Faults are handled as internal boundaries across which the mesh is non-matching. Different models are proposed for fault behavior such as impervious fault, flow across fault or conductive fault. The calculator is based on a cell centered Finite Volume discretisation, which ensures conservation of physical quantities (mass of fluid, heat) at a discrete level and which accounts properly for heterogeneities. The numerical scheme handles the non matching meshes and guaranties appropriate connection of cells across faults. Results on a synthetic basin demonstrate the capabilities of this new simulator

Health outcomes of older patients colonized by multi-drug resistant bacteria (MDRB): a one-year follow-up study.

The objective of this study was to examine whether asymptomatic colonization with MDRB would affect outcomes in older patients one year after hospitalization in a geriatric ward. Patient samples were analyzed to identify specific MDRBs, including methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase-producing Enterobaceriaceae (ESBLE), and vancomycin-resistant enterococci (VRE). Among 337 patients screened at hospital admission, 62 (18%) carried one or more MDRB isolates (MRSA: n=23; ESBLE: n=39; VRE: n=2). At 12 months after admission, 320 patients were interviewed by telephone (17 patients lost to follow up) to assess all-cause mortality, nursing home admissions, functional decline, and hospital readmissions. All-cause mortality rates were similar in MDRB carriers (34%; n=61) and non-carriers (30%; n=259) (P=0.512). Nursing home admission, functional decline, and hospital readmission did not differ between the two groups. In this population, predictors of mortality were: male gender (P=0.002), cognitive disorders at admission (P=0.028), low pre-albumin level at admission (P=0.048), a high level of co-morbidities (P=0.002), and a history of an acute condition in the three months prior to initial hospital admission (P=0.024). In conclusion, in this cohort of older patients, asymptomatic MDRB colonization was not significantly associated with adverse health outcomes at a one-year follow-up after hospitalization. The potential limitations of the study were the small sample size, relatively high mortality rate, and lack of MDRB reassessment during the follow-up