Coupled reservoir geomechanics and multiphase flow in fractured porous media.

As a result of a rapid pressure reduction and lack of understanding of hydromechanical behaviour at the fracture matrix interface, a considerable amount of hydrocarbon reserves will remain in place in fractured reservoirs. Therefore, rigid numerical modelling of multiphase flow in geologically complex reservoirs is an essential issue for petroleum reservoir engineers

Multiphase flow modelling in fractured reservoirs using a novel computational fluid dynamics approach.

Numerical modelling of multiphase flow in naturally fractured reservoirs is a challenging issue for petroleum reservoir engineers. As a result of high degree heterogeneity in flow characteristics in fractured reservoirs, several mathematical, discretization, and numerical methods are introduced to forecast the hydrodynamic behaviour of naturally fractured reservoirs. This paper demonstrates two different numerical modelling approaches that have been developed using the discrete- fracture matrix model (DFM) for studying the behavior of multiphase flow in fractured porous media. The first model utilizes the viscous loss term as a source term in the momentum equation to capture the value of permeability in both free channel (fracture) and porous matrix. On the other hand, the second model is based on the coupled Navier-Stokes equation in the free channel of fracture and viscous loss term as a mass source term to measure the permeability in the porous matrix. Later, the Corey method is employed to observe saturation, relative permeability, and capillary pressure at the fracture matrix interface. Both models are validated against a Berea Sandstone imbibition core flooding experimental data. Furthermore, the first and second model numerical simulation results match with the Berea Sandstone experimental core flooding data within a 4.2% and 29% error margin, respectively. The simulation results prove that the first model which uses viscous loss term to capture permeability in the fracture and porous matrix is more accurate in comparison to the implementation of the Navier-Stokes equation in the fracture channel in the second model

Development of plasma-sprayed molybdenum carbide-based anode layers with various metal oxides for SOFC.

Air plasma-sprayed (APS) coatings provide an ability to deposit a range of novel fuel cell materials at competitive costs. This work develops three separate types of composite anodes (Mo-Mo2C/Al2O3, Mo-Mo2C/ZrO2, Mo-Mo2C/TiO2) using a combination of APS process parameters on Hastelloy®X for application in intermediate temperature proton-conducting solid oxide fuel cells. Commercially available carbide of molybdenum powder catalyst (Mo-Mo2C) and three metal oxides (Al2O3, ZrO2, TiO2) was used to prepare three separate composite feedstock powders to fabricate three different anodes. Each of the modified composition anode feedstock powders included a stoichiometric weight ratio of 0.8:0.2. The coatings were characterized by scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction, nanoindentation, and conductivity. We report herein that three optimized anode layers of thicknesses between 200 and 300µm and porosity as high as 20% for Mo-Mo2C/Al2O3 (250-µm thick) and Mo-Mo2C/TiO2 (300µm thick) and 17% for Mo-Mo2C/ZrO2 (220-µm thick), controllable by a selection of the APS process parameters with no addition of sacrificial pore-forming material. The nanohardness results indicate the upper layers of the coatings have higher values than the subsurface layers in coatings with some effect of the deposition on the substrate. Mo-Mo2C/ZrO2 shows high electrical conductivity

Indentation based strength analysis of adhesively bonded leading-edge composite joints in wind turbine blades.

Wind turbine is a source of non-polluting renewable energy. Whether a wind turbine is viable depends entirely on the structural integrity of turbine blade. To assess the structural integrity of wind turbine blades it is necessary to investigate the loading behaviour of adhesively bonded composite joints. Finite Element (FE) along with Cohesive Zone Modelling (CZM) methods were implemented to investigate the elastic indentation contact of adhesively bonded leading-edge composite joints in wind turbine blades. The CZM was validated by replicating existing experimental and numerical work on composite-to-adhesive bonds applied to wind turbine structures. This validated model was then used to investigate the structural integrity of a variety of leading-edge joint configurations, adhesive thicknesses and bond finishes under indentation. Numerical results showed that an off-centre adhesive joint configuration was desirable and capable of withstanding between 39-96% more load than centred joints. Direct indenter to adhesive contact was shown to reduce fracture resistance by up to 4.7%. An adhesive joint based on a lap joint configuration was proposed as an alternative to current designs

Cyclic nanoindentation and nano-impact fatigue mechanisms of functionally graded TiN/TiNi film.

The mechanisms of nanoscale fatigue of functionally graded TiN/TiNi films have been studied using multiple-loading cycle nanoindentation and nano-impact tests. The functionally graded films were sputter-deposited onto silicon substrates, in which the TiNi film provides pseudo-elasticity and shape memory behavior, while a top TiN surface layer provides tribological and anti-corrosion properties. Nanomechanical tests were performed to investigate the localised film performance and failure modes of the functionally graded film using both Berkovich and conical indenters with loads between 100 uN and 500 mN. The loading history was critical to define film failure modes (i.e. backward depth deviation) and the pseudo-elastic/shape memory effect of the functionally graded layer. The results were sensitive to the applied load, loading mode (e.g. semi-static, dynamic) and probe geometry. Based on indentation force-depth profiles, depth-time data and post-test surface observations of films, it was concluded that the shape of the indenter is critical to induce localised indentation stress and film failure, and generation of pseudo-elasticity at a lower load range. Finite element simulation of the elastic loading process indicated that the location of subsurface maximum stress near the interface influences the backward depth deviation type of film failure

Zinc oxide nanoparticles modified-carbon paste electrode used for the electrochemical determination of Gallic acid.

Zinc oxide nanoparticles (nano-ZnO) was used to modify carbon paste electrode (CPE) for a fast and sensitive electrochemical determination of gallic acid (GA). The study was carried out using cyclic voltammetry (CV) and differential voltammetry (DPV) techniques, where the nano-ZnO-modified electrode exhibited an efficient and sensitive oxidation of GA. The cyclic voltammetric result showed a significant enhancement of the peak current from 250μA to about 410μA. The electrochemical behaviour of GA on the nano-ZnO modified carbon paste electrode was studied using DPV, showing a sensitivity of the electrode in a concentration range of 1 x 10−6 to 5.0 x 10−5 mol L−1, with a correlation coefficient R2 of 0.9968 and a limit of detection of 1.86 x 10−7 mol L−1 (S/N =3). The proposed electrode was used successfully for the determination of GA in red wine with recoveries of 103%

Influence of test methodology and probe geometry on nanoscale fatigue mechanisms of diamond-like carbon thin film

The aim of this paper is to investigate the mechanism of nanoscale fatigue using nano-impact and multiple-loading cycle nanoindentation tests, and compare it to previously reported findings of nanoscale fatigue using integrated stiffness and depth sensing approach. Two different film loading mechanisms, loading history and indenter shapes are compared to comprehend the influence of test methodology on the nanoscale fatigue failure mechanisms of a DLC film. An amorphous 100 nm thick DLC film was deposited on a 500 μm silicon substrate using sputtering of graphite target in pure argon atmosphere. Nano-impact and multiple-load cycle indentations were performed in the load range of 100 μN to 1000 μN and 0.1 mN to 100 mN, respectively. Both test types were conducted using conical and Berkovich indenters. Results indicate that for the case of a conical indenter, the combination of nano-impact and multiple-loading cycle nanoindentation tests provides information on the life and failure mechanism of the DLC film, which is comparable to the previously reported findings using the integrated stiffness and depth sensing approach. However, the comparison of results is sensitive to the applied load, loading mechanism, test-type and probe geometry. The loading mechanism and load history are therefore critical which also lead to two different definitions of film failure. The choice of exact test methodology, load and probe geometry should therefore be dictated by the in-service tribological conditions, and where necessary both test methodologies can be used to provide better insights of failure mechanism. Molecular dynamics (MD) simulations of the elastic response of nanoindentation are reported, which indicate that the elastic modulus of the film measured using MD simulation was higher than that experimentally measured. This difference is attributed to the factors related to the presence of material defects, crystal structure, residual stress, indenter geometry and loading/unloading rate differences between the MD and experimental results

Microstructural evaluation of suspension thermally sprayed WC-Co nanocomposite coatings.

Microstructural and sliding wear evaluations of nanostructured coatings deposited by Suspension High Velocity Oxy-Fuel (S-HVOF) spraying were conducted in as-sprayed and HIPed (Hot Isostatically Pressed) conditions. S-HVOF coatings were nanostructured via ball milling of the WC-12Co start powder, and deposited via an aqueous based suspension using modified HVOF (TopGun) spraying. Microstructural evaluations of these hardmetal coatings included TEM (Transmission Electron Microscopy), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that nanostructured features inherited from the start powder in S-HVOF spraying were retained in the resulting coatings. The decarburisation of WC due to a higher surface area to volume ratio was also observed in the S-HVOF coatings. Nanostructured and amorphous phases caused by the high cooling rates during thermal spraying crystallized into complex eta-phases after the HIPing treatment. Sliding wear performance indicated that the coating wear was lower for the HIPed coatings

Influence of post-treatment on the microstructural and tribomechanical properties of suspension thermally sprayed WC-12 wt%Co nanocomposite coatings.

The potential to improve the tribomechanical performance of HVOF-sprayed WC-12Co coatings was studied by using aqueous WC-12Co suspensions as feed-stock. Both as-sprayed and hot-isostatic-pressed (HIPed) coatings were studied. Mathematical models of wear rate based on the structure property relationships, even for the conventionally sprayed WC-Co hardmetal coatings, are at best based on the semiempirical approach. This paper aims to develop these semiempirical mathematical models for suspension sprayed nanocomposite coatings in as-sprayed and heat-treated (HIPed) conditions. Microstructural evaluations included transmission electron microscopy, X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that the HIPing post-treatment resulted in crystallization of amorphous coating phases and increase in elastic modulus and hardness. Influence of these changes in the wear mechanisms and wear rate is discussed. Results are also compared with conventionally sprayed high-velocity oxy-fuel hardmetal WC-Co coatings