A new upscaling method for flow simulation of fractured systems

Fractured reservoirs have gained continuous attention in oil and gas industry since a huge amount of reserves are stored in such reservoirs. Fractures add complexity in reservoir models and thus have potentially large effects on the reservoir simulation results. Though a lot of fine scale fracture models for reservoir simulation have been developed to capture the fracture effects, they are generally complicated and time consuming for the cases with large number of fractures and problems (for example, some inverse problems and optimization problems) where lots of forward simulations are required. Upscaling is a method to fasten the flow simulations by constructing reduced models in coarse scale to approximate the original fine scale models. It is important to construct coarse models in a proper way since the approximated models will generate errors as opposed to the fine scale models. Therefore, a new upscaling method is proposed in this work to capture the effects of fractures in fractured reservoir. First, two hypothetical flow problems are presented to provide pressure solutions for calculation of parameters in coarse models. Unsteady state method, one of these two flow problems, is firstly introduced in this work to obtain reasonable pressure solutions for reservoirs without source term. Second, we developed two partitioning methods to associate coarse grids with fine grids. Since these two partitioning approaches are suitable for different types of fracture networks, we proposed a multi-level partitioning method that is a general approach and could capture fracture effects of different fracture patterns. Third, we developed an efficient time-stepping algorithm for the unsteady state problem to reduce the computational efforts of upscaling process. The applicability of the new upsclaing methodology is verified from numerical tests of different types of reservoirs with different fracture patterns and well configurations. Errors of pressure solution, oil saturation, and production solutions are generally limited below 5% in coarse scale. Furthermore, speedup of simulation is significant in all of the presented numerical testsPetroleum and Geosystems Engineerin

Influence of inductance variation on performance of a permanent magnet claw pole soft magnetic composite motor

Winding inductance is an important parameter in determining the performance of electrical machines, particularly those with large inductance variation. This paper investigates the influence of winding inductance variation on the performance of a three-phase three-stack claw pole permanent magnet motor with soft magnetic composite (SMC) stator by using an improved phase variable model. The winding inductances of the machine are computed by using a modified incremental energy method, based on three-dimensional nonlinear time-stepping magnetic field finite element analyses. The inductance computation and performance simulation are verified by the experimental results of an SMC claw pole motor prototype

SIRT1/3 Activation by Resveratrol Attenuates Acute Kidney Injury in a Septic Rat Model

Sepsis often results in damage to multiple organ systems, possibly due to severe mitochondrial dysfunction. Two members of the sirtuin family, SIRT1 and SIRT3, have been implicated in the reversal of mitochondrial damage. The aim of this study was to determine the role of SIRT1/3 in acute kidney injury (AKI) following sepsis in a septic rat model. After drug pretreatment and cecal ligation and puncture (CLP) model reproduction in the rats, we performed survival time evaluation and kidney tissue extraction and renal tubular epithelial cell (RTEC) isolation. We observed reduced SIRT1/3 activity, elevated acetylated SOD2 (ac-SOD2) levels and oxidative stress, and damaged mitochondria in RTECs following sepsis. Treatment with resveratrol (RSV), a chemical SIRT1 activator, effectively restored SIRT1/3 activity, reduced acetylated SOD2 levels, ameliorated oxidative stress and mitochondrial function of RTECs, and prolonged survival time. However, the beneficial effects of RSV were greatly abrogated by Ex527, a selective inhibitor of SIRT1. These results suggest a therapeutic role for SIRT1 in the reversal of AKI in septic rat, which may rely on SIRT3-mediated deacetylation of SOD2. SIRT1/3 activation could therefore be a promising therapeutic strategy to treat sepsis-associated AKI

Field-free spin-orbit torque-induced switching of perpendicular magnetization in a ferrimagnetic layer with vertical composition gradient

Current-induced spin-orbit torques (SOTs) are of interest for fast and energy-efficient manipulation of magnetic order in spintronic devices. To be deterministic, however, switching of perpendicularly magnetized materials by SOT requires a mechanism for in-plane symmetry breaking. Existing methods to do so involve the application of an in-plane bias magnetic field, or incorporation of in-plane structural asymmetry in the device, both of which can be difficult to implement in practical applications. Here, we reported bias-field-free SOT switching in a single perpendicular CoTb layer with an engineered vertical composition gradient. The vertical structural inversion asymmetry induces strong intrinsic SOTs and a gradient-driven Dzyaloshinskii-Moriya interaction (g-DMI), which breaks the in-plane symmetry during the switching process. Micromagnetic simulations are in agreement with experimental results, and elucidate the role of g-DMI in the deterministic switching. This bias-field-free switching scheme for perpendicular ferrimagnets with g-DMI provides a strategy for efficient and compact SOT device design.Comment: 27 pages, 5 figure