Journal articles on the topic 'Grid'
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Higashi, Tatsuichiro, Yuko Iwasaki, Yasuo Ohnishi, and Sueharu Horinouchi. "A-Factor and Phosphate Depletion Signals Are Transmitted to the Grixazone Biosynthesis Genes via the Pathway-Specific Transcriptional Activator GriR." Journal of Bacteriology 189, no. 9 (March 2, 2007): 3515–24. http://dx.doi.org/10.1128/jb.00055-07.
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ABSTRACT Grixazone (GX), which is a diffusible yellow pigment containing a phenoxazinone chromophore, is one of the secondary metabolites under the control of A-factor (2-isocapryloyl-3R-hydroxymethyl-γ-butyrolactone) in Streptomyces griseus. GX production is also induced by phosphate starvation. The whole biosynthesis gene cluster for GX was cloned and characterized. The gene cluster consisting of 13 genes contained six transcriptional units, griT, griSR, griR, griAB, griCDEFG, and griJIH. During cultivation in a phosphate-depleted medium, the six promoters were activated in the order (i) griR, (ii) griC and griJ, and (iii) griT, griS, and griA. Disruption of griR, which encodes a SARP family transcriptional regulator, abolished the transcriptional activation of all other genes in the cluster. In addition, ectopic expression of griR from a constitutively active promoter resulted in GX overproduction even in the absence of AdpA, a key transcriptional activator in the A-factor regulatory cascade, and in the presence of phosphate at a high concentration. GriR monomers bound direct repeat sequences in the griC and griJ promoters in a cooperative manner. Therefore, the early active genes (griCDEFG and griJIH), all of which, except for griG (which encodes a transporter-like protein), encode the GX biosynthesis enzymes, were directly activated by GriR. The transcription of griR was greatly reduced in the presence of phosphate at a high concentration and was hardly detected in the absence of AdpA. These findings showed that both A-factor and phosphate depletion signals were required for griR transcription and both signals were transmitted to the GX biosynthesis genes solely via the griR promoter.
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Evazi, M., and H. Mahani. "Unstructured-Coarse-Grid Generation Using Background-Grid Approach." SPE Journal 15, no. 02 (March 3, 2010): 326–40. http://dx.doi.org/10.2118/120170-pa.
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Summary Reservoir flow simulation involves subdivision of the physical domain into a number of gridblocks. This is best accomplished with optimized gridpoint density and a minimized number of gridblocks, especially for coarse-grid generation from a fine-grid geological model. In any coarse-grid generation, proper distribution of gridpoints, which form the basis of numerical gridblocks, is a challenging task. We show that this can be achieved effectively by a novel grid-generation approach based on a background grid that stores gridpoint spacing parameters. Spacing parameter (L) can be described by Poisson's equation (∇2L = G), where the local density of gridpoints is controlled by a variable source term (G); see Eq. 1. This source term can be based on different gridpoint density indicators, such as permeability variations, fluid velocity, or their combination (e.g., vorticity) where they can be extracted from the reference fine grid. Once a background grid is generated, advancing-front triangulation (AFT) and then Delaunay tessellation are invoked to form the final (coarse) gridblocks. The algorithm produces grids varying smoothly from high- to low-density gridpoints, thus minimizing use of grid-smoothing and -optimization techniques. This algorithm is quite flexible, allowing choice of the gridding indicator, hence providing the possibility of comparing the grids generated with different indicators and selecting the best. In this paper, the capabilities of approach in generation of unstructured coarse grids from fine geological models are illustrated using 2D highly heterogeneous test cases. Flexibility of algorithm to gridding indicator is demonstrated using vorticity, permeability variation, and velocity. Quality of the coarse grids is evaluated by comparing their two-phase-flow simulation results to those of fine grid and uniform coarse grid. Results demonstrate the robustness and attractiveness of the approach, as well as relative quality/performance of grids generated by using different indicators.
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Thormann, Bernd, and Thomas Kienberger. "Estimation of Grid Reinforcement Costs Triggered by Future Grid Customers: Influence of the Quantification Method (Scaling vs. Large-Scale Simulation) and Coincidence Factors (Single vs. Multiple Application)." Energies 15, no. 4 (February 14, 2022): 1383. http://dx.doi.org/10.3390/en15041383.
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The integration of future grid customers, e.g., electric vehicles, heat pumps, or photovoltaic modules, will challenge existing low-voltage power grids in the upcoming years. Hence, distribution system operators must quantify future grid reinforcement measures and resulting costs early. On this account, this work initially evaluates different methods to quantify future grid reinforcement needs, applied by the current state of research. Thereby, it indicates the significance of large-scale grid simulations, i.e., simulating several thousand low-voltage grids, to quantify grid reinforcements accurately. Otherwise, a selected area’s total grid reinforcement costs might be misjudged significantly. Due to its fast application, deterministic grid simulations based on coincidence factors are most commonly used in the current state of research to simulate several thousand grids. Hence, in the second step, recent studies’ approaches to applying grid customers’ coincidence factors are evaluated: While simplified approaches allow fast simulation of numerous grids, they underestimate potential grid congestion and grid reinforcement costs. Therefore, a fully automated large-scale grid simulation tool is developed in this work to allow the simulation of multiple grids applying grid customers’ coincidence factors appropriately. As a drawback, the applied deterministic framework only allows an estimation of future grid reinforcement costs. Detailed determination of each grid’s grid reinforcement costs requires time-resolved grid simulations.
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Bhandari, Khem Raj, and Narayan Prasad Adhikari. "Grid Integration of Solar and Solar/Wind Hybrid Mini-Grid Projects: A Case of Solar/Wind Hybrid Mini-Grid Project Implemented by AEPC." Journal of the Institute of Engineering 15, no. 3 (October 13, 2020): 42–48. http://dx.doi.org/10.3126/jie.v15i3.32004.
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Alternative Energy Promotion Center (AEPC) has been scaling up renewable energy technologies through Mini-grid power supply in Nepal’s off-grid areas in order to fulfill community electricity demands for both households and electricity-based enterprises. It is likely that, in some of the off-grid renewable energy (RE) mini-grid service areas, Nepal Electricity Authority (NEA) grid line might reach in near future. The objective of this study is to highlight success stories of solar and solar/wind mini-grids implemented by AEPC and for their longer-term sustainable operation grid integration policy of isolated mini-grid systems will require. Till the date AEPC has successfully electrified more than 20 rural communities through solar and solar/wind hybrid mini-grid systems. Some of these isolated mini-grid projects will seek grid interconnections in near future due to NEA distribution system expansion trend. When the isolated mini-grids will be connected to the national grid power network in future, the mini-grid can feed surplus electricity to the local utility grid line and will receive deficit electricity from the local utility grid system to serve the consumers connected to the local grid network. The methodology applied to this study is assessment of existing solar and solar/wind mini-grid projects, technological intervention required for grid integration, reviewing grid-connection policy of distributed renewable generations in the country and recommendation of relevant policy option for grid connection of rural mini-grids. Grid integration of isolated solar and solar/wind mini-grids will have positive impacts to the sustainability of the present isolated mini-grids, will help in retaining existing mini-grids end users, energy produced by mini-grid systems will be optimally utilized, the existing mini-grid power will contribute to stabilize weak national grid electrical parameters. The outcome of the study will recommend need of policy options as well as technological interventions in order to do grid integration of solar and solar/wind hybrid mini-grid systems in Nepal.
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Arad, Nur. "Grid-distortion on nonrectangular grids." Computer Aided Geometric Design 15, no. 5 (May 1998): 475–93. http://dx.doi.org/10.1016/s0167-8396(98)00003-x.
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Bernth, Henrik, and Chris Chapman. "A comparison of the dispersion relations for anisotropic elastodynamic finite-difference grids." GEOPHYSICS 76, no. 3 (May 2011): WA43—WA50. http://dx.doi.org/10.1190/1.3555530.
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Several staggered grid schemes have been suggested for performing finite-difference calculations for the elastic wave equations. In this paper, the dispersion relationships and related computational requirements for the Lebedev and rotated staggered grids for anisotropic, elastic, finite-difference calculations in smooth models are analyzed and compared. These grids are related to a popular staggered grid for the isotropic problem, the Virieux grid. The Lebedev grid decomposes into Virieux grids, two in two dimensions and four in three dimensions, which decouple in isotropic media. Therefore the Lebedev scheme will have twice or four times the computational requirements, memory, and CPU as the Virieux grid but can be used with general anisotropy. In two dimensions, the rotated staggered grid is exactly equivalent to the Lebedev grid, but in three dimensions it is fundamentally different. The numerical dispersion in finite-difference grids depends on the direction of propagation and the grid type and parameters. A joint numerical dispersion relation for the two grids types in the isotropic case is derived. In order to compare the computational requirements for the two grid types, the dispersion, averaged over propagation direction and medium velocity are calculated. Setting the parameters so the average dispersion is equal for the two grids, the computational requirements of the two grid types are compared. In three dimensions, the rotated staggered grid requires at least 20% more memory for the field data and at least twice as many number of floating point operations and memory accesses, so the Lebedev grid is more efficient and is to be preferred.
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M, Ponrekha, and Sujatha Balaraman. "A detailed study on Transient Stability Enhancement of Grid-Forming Inverters." Journal of Electrical Engineering and Automation 5, no. 2 (June 2023): 151–65. http://dx.doi.org/10.36548/jeea.2023.2.001.
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The integration of the weak grids along with the clean energy that comes from the natural resources requires stable interconnection of Voltage-Source Inverters (VSIs) with weak grids. During severe voltage sags, weak grid integrated VSIs may fail synchronization with the grid.These inverters' transient stability under severe grid disruptions is weak and significantly different from that of synchronous machines. To prevent the side band oscillations in the weak grids, the emerging inverters based on grid-forming are preferred over the grid following inverters in the weak grids. These inverters synchronise with the grid using a power-based synchronisation technique in order to prevent the instability brought on by a typical Phase Locked Loop in weak AC grids. This study presents a comprehensive review of the transient stability improvement of Grid-Forming VSIs.
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Coveney, Peter V. "Scientific Grid computing." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, no. 1833 (July 18, 2005): 1707–13. http://dx.doi.org/10.1098/rsta.2005.1632.
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We introduce a definition of Grid computing which is adhered to throughout this Theme Issue. We compare the evolution of the World Wide Web with current aspirations for Grid computing and indicate areas that need further research and development before a generally usable Grid infrastructure becomes available. We discuss work that has been done in order to make scientific Grid computing a viable proposition, including the building of Grids, middleware developments, computational steering and visualization. We review science that has been enabled by contemporary computational Grids, and associated progress made through the widening availability of high performance computing.
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Yan, Huang, Li Shanshan, Zhou Chuyuan, Li Xinxing, Lv Minghao, Fan Diao, Tan Xuli, and Wang Aoming. "Research and Construction of a Global Hexagonal Marine Gravity Gradient Reference Map for Navigation." Geofluids 2023 (March 23, 2023): 1–22. http://dx.doi.org/10.1155/2023/4141572.
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A high-precision marine gravity gradient reference map is key to enabling underwater gravity gradient matching navigation. At present, the construction of the reference maps is based on quadrilateral geographic grids. However, quadrilateral grids lead to detriangulation at high latitudes, which limits the global applicability of such maps to underwater gravity navigation. To circumvent the limitations of quadrilateral grids, a hexagonal grid is introduced for constructing the reference map. This paper analyzes the characteristics of the icosahedral Snyder equal area aperture 4 hexagon (ISEA4H) and H3 grid systems and selects an appropriate grid system. In addition, we calculate and analyze the grid model errors and matching positioning errors of hexagonal and quadrilateral grids at the same resolution. The experimental results show that the grid model and matching positioning errors of a hexagonal grid system are more than 14% and 15% less than those of a quadrilateral grid system, respectively, indicating the feasibility and effectiveness of applying hexagonal grids to gravity gradient matching navigation. Given the low construction efficiency of a marine hexagonal grid gravity gradient reference map, we propose an efficient CPU+GPU hybrid parallel scheme. A global total tensor marine hexagonal grid gravity gradient reference map model is then constructed.
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Tristan, A., A. Emde, M. Reisinger, M. Stauch, and A. Sauer. "Energieflexibilität im Industrial Smart Grid*/Energy Flexibility in Industrial Smart Grids – Methodical approach for incorporating energy flexibility measures in an Industrial Smart Grid." wt Werkstattstechnik online 109, no. 05 (2019): 301–6. http://dx.doi.org/10.37544/1436-4980-2019-05-3.
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Durch den Übergang in Smart Grids erhalten Stromnetze die notwendige Flexibilität, um auf die steigende Volatilität der Stromversorgung zu reagieren. Das standardisierte Smart-Grid-Architecture-Modell und die Use-Case-Methodik dienen dabei als Rahmen, um Smart Grids zu entwickeln. Ein methodischer Rahmen für den Aufbau von Industrial Smart Grids fehlt derzeit noch, ist aber besonders notwendig, um Energieflexibilitätsmaßnahmen für Industrieanlagen umzusetzen. Der hier vorgestellte methodische Ansatz liefert eine Blaupause für den Aufbau eines Industrial Smart Grid für Energieflexibilität. Mithilfe der Anpassung des Smart-Grid-Architecture-Modells und der Use-Case-Methodik wird ein Industrial-Smart-Grid-Architecture-Modell umgesetzt. Through their transition into Smart Grids, electrical power grids gain the neccesary flexibiltiy to respond to increasing electrical supply volatility. The standardized Smart Grid Architecture Model and Use Case Methodology serve as framework to develop Smart Grids. Currently, there is still a lack of such a methodical framework for setting up Industrial Smart Energy Grids and it is particularly necessary to implement energy flexibility measures in industrial plants. The methodical approach presented here provides a blueprint for building an Industrial Smart Grid for energy flexibility by adapting the Smart Grid Architecture Model and the use case methodology .
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Xu, S., B. Wang, and J. Liu. "On the use of Schwarz–Christoffel conformal mappings to the grid generation for global ocean models." Geoscientific Model Development 8, no. 10 (October 29, 2015): 3471–85. http://dx.doi.org/10.5194/gmd-8-3471-2015.
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Abstract. In this article we propose two grid generation methods for global ocean general circulation models. Contrary to conventional dipolar or tripolar grids, the proposed methods are based on Schwarz–Christoffel conformal mappings that map areas with user-prescribed, irregular boundaries to those with regular boundaries (i.e., disks, slits, etc.). The first method aims at improving existing dipolar grids. Compared with existing grids, the sample grid achieves a better trade-off between the enlargement of the latitudinal–longitudinal portion and the overall smooth grid cell size transition. The second method addresses more modern and advanced grid design requirements arising from high-resolution and multi-scale ocean modeling. The generated grids could potentially achieve the alignment of grid lines to the large-scale coastlines, enhanced spatial resolution in coastal regions, and easier computational load balance. Since the grids are orthogonal curvilinear, they can be easily utilized by the majority of ocean general circulation models that are based on finite difference and require grid orthogonality. The proposed grid generation algorithms can also be applied to the grid generation for regional ocean modeling where complex land–sea distribution is present.
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Miura, Hiroaki, and Masahide Kimoto. "A Comparison of Grid Quality of Optimized Spherical Hexagonal–Pentagonal Geodesic Grids." Monthly Weather Review 133, no. 10 (October 1, 2005): 2817–33. http://dx.doi.org/10.1175/mwr2991.1.
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Abstract Construction and optimization methods of spherical hexagonal–pentagonal geodesic grids are investigated. The objective is to compare grid structures on common ground. The distinction between two types of hexagonal–pentagonal grids is made. Three conventional grid optimization methods are summarized. In addition, three new optimization methods are proposed. Six desirable conditions for an ideal grid are described, and the grid optimization methods are organized in view of such conditions. Interval uniformity, area uniformity, isotropy, and bisection of cell faces are systematically investigated for optimized grids. There are compensations of preferable grid features in each optimization method, and an optimal method cannot be decided based only on the research of grid features. It is suggested that grid optimization methods should be selected based on research of numerical schemes.
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Wei, Rui, Yuxin Li, Jun Yin, and Xieyao Ma. "Comparison of Weighted/Unweighted and Interpolated Grid Data at Regional and Global Scales." Atmosphere 13, no. 12 (December 9, 2022): 2071. http://dx.doi.org/10.3390/atmos13122071.
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Uniform grid data are widely used in climate science and related interdisciplinary fields. Such data usually describe the hydrometeorological states averaged over uniform latitude–longitude grids. While these data have larger grid areas in the tropics than other high-latitude regions, less attention has been paid to the areal weights of these grid data. Here, we revisited two methods available for processing these uniform grid data, including weighted sample statistics and grid interpolation. The former directly considers the grid area differences using geodetic weights; the latter converts the uniform grids to equal-area grids for conventional data analysis. When applied to global temperature and precipitation data, we found larger differences between weighted and unweighted samples and smaller differences between weighted and interpolated samples, highlighting the importance of areal weights in grid data analysis. Given the different results from various methods, we call for explicit clarification of the grid data processing methods to improve reproducibility in climate research.
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Lauritzen, P. H., J. T. Bacmeister, P. F. Callaghan, and M. A. Taylor. "NCAR_Topo (v1.0): NCAR global model topography generation software for unstructured grids." Geoscientific Model Development 8, no. 12 (December 14, 2015): 3975–86. http://dx.doi.org/10.5194/gmd-8-3975-2015.
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Abstract. It is the purpose of this paper to document the NCAR global model topography generation software for unstructured grids (NCAR_Topo (v1.0)). Given a model grid, the software computes the fraction of the grid box covered by land, the grid-box mean elevation (deviation from a geoid that defines nominal sea level surface), and associated sub-grid-scale variances commonly used for gravity wave and turbulent mountain stress parameterizations. The software supports regular latitude–longitude grids as well as unstructured grids, e.g., icosahedral, Voronoi, cubed-sphere and variable-resolution grids.
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Holloway, Mary V., Heather L. McClusky, Donald E. Beasley, and Michael E. Conner. "The Effect of Support Grid Features on Local, Single-Phase Heat Transfer Measurements in Rod Bundles." Journal of Heat Transfer 126, no. 1 (February 1, 2004): 43–53. http://dx.doi.org/10.1115/1.1643091.
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Locally averaged heat transfer measurements in a rod bundle downstream of support grids with and without flow-enhancing features are investigated for Reynolds numbers of 28,000 and 42,000. Support grids with disk blockage flow-enhancing features and support grids with split-vane pair flow enhancing features are examined. Grid pressure loss coefficients and feature loss coefficients are determined based on pressure drop measurements for each support grid design. Results indicate the greatest heat transfer enhancement downstream of the support grid designs with disk blockages. In addition, the local heat transfer measurements downstream of the split-vane pair grid designs indicate a region of decreased heat transfer below that of the hydrodynamically fully developed value. This decreased region of heat transfer is more pronounced for the lower Reynolds number case. A correlation for the local Nusselt numbers downstream of the standard support grid designs is developed based on the blockage of the support grid. In addition, a correlation for the local Nusselt numbers downstream of support grids with flow-enhancing features is developed based on the blockage ratio of the grid straps and the normalized feature loss coefficients of the support grid designs. The correlations demonstrate the tradeoff between initial heat transfer enhancement downstream of the support grid and the pressure drop created by the support grid.
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Henshaw, William D. "Automatic grid generation." Acta Numerica 5 (January 1996): 121–48. http://dx.doi.org/10.1017/s0962492900002634.
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Current methods for the automatic generation of grids are reviewed. The approaches to grid generation that are discussed include Cartesian, multi-block-structured, overlapping and unstructured. Emphasis is placed on those methods that can create high-quality grids appropriate for the solution of equations of a hyperbolic nature, such as those that arise in fluid dynamics. Numerous figures illustrate the different grid generation techniques.
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Muntean, Ioan Lucian, and Alexandra Ioana Badiu. "Application Plugins for Distributed Simulations on the Grid." International Journal of Computers Communications & Control 6, no. 4 (December 1, 2011): 701. http://dx.doi.org/10.15837/ijccc.2011.4.2096.
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Computing grids are today still underexploited by scientific computing communities. The main reasons for this are, on the one hand, the complexity and variety of tools and services existent in the grid middleware ecosystem, and, on the other hand, the complexity of the development of applications capable to exploit the grids. We address in this work the challenge of developing grid applications that keep pace with the rapid evolution of grid middleware. For that, we propose an approach based on plugins for grid applications that encapsulate a set of commonly used type of grid operations. We further propose more complex high-level functionalities, such as the plugins for remote exploration of simulation scenarios and for monitoring of the behavior of end-user applications in grids. We provide an example of a grid application constructed with these software components and evaluate based on it the performance of our approach in the context of the simulation of biological neurons. The results obtained on test and production grids demonstrate the usefulness of the proposed plugins, with a small performance overhead compared to traditional grid tools.
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Madani, V., and D. Novosel. "Getting a grip on the grid." IEEE Spectrum 42, no. 12 (December 2005): 42–47. http://dx.doi.org/10.1109/mspec.2005.1549781.
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Ramakrishnan, L. "Grid computing - Securing next-generation grids." IT Professional 6, no. 2 (March 2004): 34–39. http://dx.doi.org/10.1109/mitp.2004.1278860.
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HEINZLREITER, PAUL, and DIETER KRANZLMÜLLER. "VISUALIZATION SERVICES ON THE GRID: THE GRID VISUALIZATION KERNEL." Parallel Processing Letters 13, no. 02 (June 2003): 135–48. http://dx.doi.org/10.1142/s0129626403001203.
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Two important tools of today's science and engineering are computational grids and visualization. While grid infrastructures offer a means to process large amounts of data across different, possibly distant resources, visualization aids in understanding the meaning of data. The Grid Visualization Kernel (GVK) addresses the connection of grid applications and visualization clients on the grid. The visualization capabilities of GVK are provided as flexible grid services via dedicated interfaces and protocols, while GVK itself relies on Globus services to implement the functionality of the visualization pipeline. This paper describes the concept of GVK and its core functionality for grid visualization services, and discusses how to use visualization in the grid environment.
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Unruh, Peter, Maria Nuschke, Philipp Strauß, and Friedrich Welck. "Overview on Grid-Forming Inverter Control Methods." Energies 13, no. 10 (May 20, 2020): 2589. http://dx.doi.org/10.3390/en13102589.
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In this paper, different control approaches for grid-forming inverters are discussed and compared with the grid-forming properties of synchronous machines. Grid-forming inverters are able to operate AC grids with or without rotating machines. In the past, they have been successfully deployed in inverter dominated island grids or in uninterruptable power supply (UPS) systems. It is expected that with increasing shares of inverter-based electrical power generation, grid-forming inverters will also become relevant for interconnected power systems. In contrast to conventional current-controlled inverters, grid-forming inverters do not immediately follow the grid voltage. They form voltage phasors that have an inertial behavior. In consequence, they can inherently deliver momentary reserve and increase power grid resilience.
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Liang, Xin, and Guan-Nan Liu. "Application of a new single staggered grid method to the heat transfer problems." Thermal Science 23, Suppl. 3 (2019): 631–37. http://dx.doi.org/10.2298/tsci180612075l.
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In this paper, a new single staggered grid method is proposed to solve the fluid dynamic problems numerically. The advantages of the new grid method are analyzed in comparison with the classical grid algorithms such as the staggered grids, collocated grids and semi-staggered grids. The discretization of the basic equations for the fluid dynamics on the new single staggered grids is derived and the corresponding SIMPLE algorithm is introduced. As an example, the heat transfer problem of fluid-flow at a right angle is solved to prove the validity of the new single staggered grid method.
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Luo, Fuli, Xuesheng Zhao, Wenbin Sun, Yalu Li, and Yuanzheng Duan. "An Overall Uniformity Optimization Method of the Spherical Icosahedral Grid Based on the Optimal Transformation Theory." Atmosphere 12, no. 11 (November 17, 2021): 1516. http://dx.doi.org/10.3390/atmos12111516.
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The improvement of overall uniformity and smoothness of spherical icosahedral grids, the basic framework of atmospheric models, is a key to reducing simulation errors. However, most of the existing grid optimization methods have optimized grid from different aspects and not improved overall uniformity and smoothness of grid at the same time, directly affecting the accuracy and stability of numerical simulation. Although a well-defined grid with more than 12 points cannot be constructed on a sphere, the area uniformity and the interval uniformity of the spherical grid can be traded off to enhance extremely the overall grid uniformity and smoothness. To solve this problem, an overall uniformity and smoothness optimization method of the spherical icosahedral grid is proposed based on the optimal transformation theory. The spherical cell decomposition method has been introduced to iteratively update the grid to minimize the spherical transportation cost, achieving an overall optimization of the spherical icosahedral grid. Experiments on the four optimized grids (the spring dynamics optimized grid, the Heikes and Randall optimized grid, the spherical centroidal Voronoi tessellations optimized grid and XU optimized grid) demonstrate that the grid area uniformity of our method has been raised by 22.60% of SPRG grid, −1.30% of HR grid, 38.30% of SCVT grid and 38.20% of XU grid, and the grid interval uniformity has been improved by 2.50% of SPRG grid, 2.80% of HR grid, 11.10% of SCVT grid and 11.00% of XU grid. Although the grid uniformity of the proposed method is similar with the HR grid, the smoothness of grid deformation has been enhanced by 79.32% of grid area and 24.07% of grid length. To some extent, the proposed method may be viewed as a novel optimization approach of the spherical icosahedral grid which can improve grid overall uniformity and smoothness of grid deformation.
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Holloway, Mary V., Timothy A. Conover, Heather L. McClusky, Donald E. Beasley, and Michael E. Conner. "The Effect of Support Grid Design on Azimuthal Variation in Heat Transfer Coefficient for Rod Bundles." Journal of Heat Transfer 127, no. 6 (June 1, 2005): 598–605. http://dx.doi.org/10.1115/1.1863274.
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Support grids are an integral part of nuclear reactor fuel bundle design. Features, such as split-vane pairs, are located on the downstream edge of support grids to enhance heat transfer and delay departure from nucleate boiling in the fuel bundle. The complex flow fields created by these features cause spatially varying heat transfer conditions on the surfaces of the rods. Azimuthal variations in heat transfer for three specific support grid designs, a standard grid, split-vane pair grid, and disc grid, are measured in the present study using a heated, thin film sensor. Normalized values of the azimuthal variations in Nusselt number are presented for the support grid designs at axial locations ranging from 2.2 to 36.7 Dh. Two Reynolds numbers, Re=28,000 and Re=42,000 are tested. The peak-to-peak azimuthal variation in normalized Nusselt number is largest just downstream of the support grids and decreases to a minimum value by the end of the grid span. A comparison of the azimuthal heat transfer characteristics between the support grids indicates distinctive results for each type of support grid design tested. The split-vane pair grid exhibits the largest peak-to-peak variation in azimuthal heat transfer of +30% to −15% just downstream of the grid at 2.2 Dh. The disc grid has the most uniform azimuthal heat transfer distribution with a peak-to-peak value of ±4% for all axial locations tested.
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Boone, John M., Olga V. Makarova, Vladislav N. Zyryanov, Cha-Mei Tang, Derrick C. Mancini, Nikolaie Moldovan, and Ralu Divan. "Development and Monte Carlo Analysis of Antiscatter Grids for Mammography." Technology in Cancer Research & Treatment 1, no. 6 (December 2002): 441–47. http://dx.doi.org/10.1177/153303460200100604.
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Mammography arguably demands the highest fidelity of all x-ray imaging applications, with simultaneous requirements of exceedingly high spatial and contrast resolution. Continuing technical improvements of screen-film and digital mammography systems have led to substantial improvements in image quality, and therefore improvements in the performance of anti-scatter grids are required to keep pace with the improvements in other components of the imaging chain. The development of an air-core honeycomb (cellular) grid using x-ray lithography and electroforming techniques is described, and the production of a 60 mm × 60 mm section of grid is reported. A crossed grid was constructed with 25 μm copper septa, and a period of 550 μm. Monte Carlo and numerical simulation methods were used to analyze the theoretical performance of the fabricated grid, and comparisons with other grid systems (Lorad HTC and carbon fiber interspaced grids) were made over a range of grid ratios. The results demonstrate essentially equivalent performance in terms of contrast improvement factor (CIF) and Bucky factor (BF) between Cu and Au honeycomb grids and the Lorad HTC (itself a copper honeycomb grid). Gold septa improved both CIF and BF performance in higher kVp, higher scatter geometries. The selectivity of honeycomb grids was far better than for linear grids, with a factor of ∼3.9 improvement at a grid ratio of 5.0. It is concluded that using the fabrication methods described, that practical honeycomb grid structures could be produced for use in mammographic imaging, and that a substantial improvement in scatter rejection would be achieved using these devices.
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Weller, Hilary, John Thuburn, and Colin J. Cotter. "Computational Modes and Grid Imprinting on Five Quasi-Uniform Spherical C Grids." Monthly Weather Review 140, no. 8 (August 1, 2012): 2734–55. http://dx.doi.org/10.1175/mwr-d-11-00193.1.
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Abstract Currently, most operational forecasting models use latitude–longitude grids, whose convergence of meridians toward the poles limits parallel scaling. Quasi-uniform grids might avoid this limitation. Thuburn et al. and Ringler et al. have developed a method for arbitrarily structured, orthogonal C grids called TRiSK, which has many of the desirable properties of the C grid on latitude–longitude grids but which works on a variety of quasi-uniform grids. Here, five quasi-uniform, orthogonal grids of the sphere are investigated using TRiSK to solve the shallow-water equations. Some of the advantages and disadvantages of the hexagonal and triangular icosahedra, a “Voronoi-ized” cubed sphere, a Voronoi-ized skipped latitude–longitude grid, and a grid of kites in comparison to a full latitude–longitude grid are demonstrated. It is shown that the hexagonal icosahedron gives the most accurate results (for least computational cost). All of the grids suffer from spurious computational modes; this is especially true of the kite grid, despite it having exactly twice as many velocity degrees of freedom as height degrees of freedom. However, the computational modes are easiest to control on the hexagonal icosahedron since they consist of vorticity oscillations on the dual grid that can be controlled using a diffusive advection scheme for potential vorticity.
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Yang, Chao-Tung, Wen-Jen Hu, and Kuan-Chou Lai. "On Construction of a Multi-Grid Resource Selection Strategy on Grids." International Journal of Grid and High Performance Computing 6, no. 1 (January 2014): 38–62. http://dx.doi.org/10.4018/ijghpc.2014010103.
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Grid computing is now in widespread use, integrating geographical computing resources across multiple virtual organizations to achieve high performance computing. A single grid does not often provide a vast resource because virtual organizations have inadequate computing resource restrictions for management on an organizational scale. This paper presents a new grid architecture named Multi-Grid, which integrates multiple computational grids from different virtual organizations. This study builds a resource broker on multiple grid environments, integrating a number of single grids from different virtual organizations without the limit of organizations. The purpose of the multiple-grid resource is to avoid wasting resources. In addition, this study proposes a Multi-Grid Resource Selection Strategy (MRGSS) for the resource broker to better allocate resources before submitting jobs, to avoid network congestion that consequently causes a decrease in performance.
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Wang, Qing Hua, Shi En Ri, Hiroshi Tsuda, Satoshi Kishimoto, Yoshihisa Tanaka, and Yutaka Kagawa. "Fabrication of Multi-Scale Grid Patterns as Deformation Carriers in Optical Methods." Applied Mechanics and Materials 782 (August 2015): 271–77. http://dx.doi.org/10.4028/www.scientific.net/amm.782.271.
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Multi-scale grid is an essential deformation carrier in optical methods for multi-scale deformation measurement. In this study, several new-type multi-scale grids were designed and fabricated by electron beam lithography. Each pattern includes several periodically distributed dots with the same spacing but different sizes. As a consequence, the grayscale of the whole grid pattern periodically changes. The peak parts of the grayscale generate a secondary grid, i.e., the large-scale grid. The ratio of the large-scale grid pitch to the small-scale grid pitch can be easily adjusted according to the requirement. The natural integration between the small-scale grid and the large-scale grid works well in eliminating the mutual disturbance between the different-scale grids. Besides, this type of grid has a very high success rate in fabrication owing to the small differences in size between the big dots and the small dots. The proposed multi-scale grid pattern is expected to serve as the deformation carrier in moiré methods and geometric phase analysis for multi-scale deformation measurement.
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Li, Meng, Zhoubo He, Chaoyuan Xiao, Tianli Qiu, Yuansheng Yang, Peng Ma, Chengui Lu, et al. "Grid ionization chamber based on stainless steel woven wire mesh." Journal of Instrumentation 17, no. 08 (August 1, 2022): P08038. http://dx.doi.org/10.1088/1748-0221/17/08/p08038.
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Abstract The grid electrode of the grid ionization chamber (GIC) is devoted to eliminating the dependence of the anode pulse amplitude on the initial position and orientation of the ionization. The traditional methods of grid production require cumbersome processes and advanced instruments. In this paper, a bonded stainless steel woven wire mesh (SSWWM) grid electrode manufacturing method is proposed. Compared with the traditional grid electrode, the SSWWM grid features the advantages of simple fabrication, low cost, and high mechanical strength. The energy resolutions of the 40-mesh, 60-mesh and 80-mesh SSWWM grids and orthogonal mesh grid realized by the traditional wire winding method were tested using an 241Am source (around 5.486 MeV). The results show that the optimum energy resolution of the SSWWM and orthogonal mesh grids is approximately 47 keV full width at half-maximum (FWHM). The optimal energy resolutions of the 40-mesh and 60-mesh SSWWM grids are comparable, but the initial operating voltages corresponding to the energy resolution plateau are different, mainly because of the effect of the different geometric parameters of the SSWWM grid on the electron transmittance. A simulation program was used to study the electron transmittance of the SSWWM grid. The simulation results are in agreement with the experimental results, indicating that the simulation program can be used as a reference for the selection of the geometric parameters of the SSWWM grid.
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Zerroukat, M., and T. Allen. "On the Solution of Elliptic Problems on Overset/Yin–Yang Grids." Monthly Weather Review 140, no. 8 (August 1, 2012): 2756–67. http://dx.doi.org/10.1175/mwr-d-11-00272.1.
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Abstract The heterogeneity and the singularity of the grid are major factors in the weak scalability of longitude–latitude grid–based atmospheric models on massively parallel machines. Overset grids and, in particular, the Yin–Yang grid, are potential solutions to this problem. Using semi-implicit time marching schemes requires the solution of an elliptic problem on the particular grid. For overset/composite grids to be a viable approach, the solution of the elliptic problem has to be at least as accurate and efficient as using a single grid. This paper proposes combining the overset/Yin–Yang composite elliptic problems in one system using Krylov-type solvers and shows that the solution on overset grids is highly efficient because of the improved grid’s homogeneity.
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An, Lei, Xinyi Lan, Mianbin Wang, and Jinchao Li. "Research on power grid effective assets input-output evaluation based on super-efficient DEA model." E3S Web of Conferences 118 (2019): 01054. http://dx.doi.org/10.1051/e3sconf/201911801054.
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With the deepening of power system reform, the precise investment and lean development of power grids have become the focus of power grid enterprises. It is of great significance to carry out evaluation research on the efficiency of input and output of effective assets of power grids. Based on the analysis of the status quo of effective asset evaluation in China’s power grid, this paper combines the model of super-efficient DEA with the analysis of effective asset output efficiency of power grid to construct an evaluation system of effective asset input and output efficiency of power grids, and takes the national power grid as an example for calculation and analysis. This paper objectively evaluates the internal and external factors affecting the efficiency of the effective assets of the grid, and provides quantitative analysis support for the effective asset investment decision of the grid.
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Dang, Hui Xue, Feng Li Yang, and Jing Bo Yang. "Grid Validations for Downburst Simulations." Applied Mechanics and Materials 249-250 (December 2012): 159–63. http://dx.doi.org/10.4028/www.scientific.net/amm.249-250.159.
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Downbursts, which resulted from the flow downdraft in thunderstorms, have become one of the most destructive disasters to buildings including transmission towers, etc. This disaster has drawn researchers’ interests and progresses have been continuously made by employing test and numerical tools. Accounting for the grid validations in the numerical simulation of downbursts, eight grids with different grid point distributions are generated, and then their corresponding flow fields are calculated by solving Navier-Stokes equations. The numerical results are compared with test results to investigate the influence of grid distributions onto numerical results. The results indicate that, numerical fidelity could be improved by refining grids in the zone with strong horizontal wind; while local grid refinement at inlet boundary could deteriorate numerical accuracy when the grid point number is kept constant, hence uniform grid distribution is recommended at inlet boundary without any grid refinement.
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Thilmany, Jean. "Getting on the Grid." Mechanical Engineering 125, no. 03 (March 1, 2003): 46–48. http://dx.doi.org/10.1115/1.2003-mar-1.
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This review discusses grid computing that is a low-cost way to harness the central processing units of a group of workstations. The grid can be made up of any number of central processing units (CPU), and they may be far-flung or within the same company, or even in the same department. Grid computing puts to work on the grid all available CPUs at idle workstations and thus does away with the need for powerful servers or supercomputers. Sun Microsystems Inc., Santa Clara, CA, and IBM of Armonk, New York, have both released software within the past three years that can divide and farm out pieces of an application to several thousand linked computers. Microsoft is developing grid-computing software for use with its products, as are Hewlett-Packard, Palo Alto, CA, and others. Grid software is written in Linux, the open-standards operating system. However, because no gatekeeping technology is currently in place for grids, the hard work of IT managers seeking to implement grid technology comes when negotiating policies among departments and setting up grids accordingly.
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Rizvi, Syed, and Ahmed Abu-Siada. "Active Power Sharing in a Micro-Grid with Multiple Grid Connections." Designs 6, no. 2 (March 1, 2022): 24. http://dx.doi.org/10.3390/designs6020024.
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This paper presents a mechanism for active power sharing among multiple dispatchable and distributed generation units within a micro grid comprising one or multiple interconnections with the main grid. Ideally, a micro grid should act as a constant load or a constant voltage source when connected to the main grid. However, to achieve ideal operation, natural load variations and the intermittency of renewable energy sources within the microgrid need to be adequately and timely compensated for by dispatchable power sources. While several control algorithms have been reported in the literature to achieve ideal microgrid operation, the majority of the proposed methods assumed a micro grid with a single interconnection to the main grid. In the real world, micro grids may have to maintain multiple live links with the main grid for several technical and operational reasons such as reliability, power-dispatch restriction, and operational limitations requirements. Therefore, a new method of active power sharing is proposed in this paper, which is equally effective for micro grids with one or multiple grid connections. The robustness of the proposed method is examined under different microgrid operating conditions. The results reveal the flexibility of the proposed method to adapt under various real-world operating conditions.
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Ding, Jianguo, Attia Qammar, Zhimin Zhang, Ahmad Karim, and Huansheng Ning. "Cyber Threats to Smart Grids: Review, Taxonomy, Potential Solutions, and Future Directions." Energies 15, no. 18 (September 17, 2022): 6799. http://dx.doi.org/10.3390/en15186799.
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Smart Grids (SGs) are governed by advanced computing, control technologies, and networking infrastructure. However, compromised cybersecurity of the smart grid not only affects the security of existing energy systems but also directly impacts national security. The increasing number of cyberattacks against the smart grid urgently necessitates more robust security protection technologies to maintain the security of the grid system and its operations. The purpose of this review paper is to provide a thorough understanding of the incumbent cyberattacks’ influence on the entire smart grid ecosystem. In this paper, we review the various threats in the smart grid, which have two core domains: the intrinsic vulnerability of the system and the external cyberattacks. Similarly, we analyze the vulnerabilities of all components of the smart grid (hardware, software, and data communication), data management, services and applications, running environment, and evolving and complex smart grids. A structured smart grid architecture and global smart grid cyberattacks with their impact from 2010 to July 2022 are presented. Then, we investigated the the thematic taxonomy of cyberattacks on smart grids to highlight the attack strategies, consequences, and related studies analyzed. In addition, potential cybersecurity solutions to smart grids are explained in the context of the implementation of blockchain and Artificial Intelligence (AI) techniques. Finally, technical future directions based on the analysis are provided against cyberattacks on SGs.
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Amin, S. M., and A. M. Giacomoni. "Smart Grid, Safe Grid." IEEE Power and Energy Magazine 10, no. 1 (January 2012): 33–40. http://dx.doi.org/10.1109/mpe.2011.943112.
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Meinecke, Steffen, Leon Thurner, and Martin Braun. "Review of Steady-State Electric Power Distribution System Datasets." Energies 13, no. 18 (September 15, 2020): 4826. http://dx.doi.org/10.3390/en13184826.
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Publicly available grid datasets with electric steady-state equivalent circuit models are crucial for the development and comparison of a variety of power system simulation tools and algorithms. Such algorithms are essential to analyze and improve the integration of distributed energy resources (DERs) in electrical power systems. Increased penetration of DERs, new technologies, and changing regulatory frameworks require the continuous development of the grid infrastructure. As a result, the number and versatility of grid datasets, which are required in power system research, increases. Furthermore, the used grids are created by different methods and intentions. This paper gives orientation within these developments: First, a concise overview of well-known, publicly available grid datasets is provided. Second, background information on the compilation of the grid datasets, including different methods, intentions and data origins, is reviewed and characterized. Third, common terms to describe electric steady-state distribution grids, such as representative grid or benchmark grid, are assembled and reviewed. Recommendations for the use of these grid terms are made.
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Weller, H. "Non-orthogonal version of the arbitrary polygonal C-grid and a new diamond grid." Geoscientific Model Development 7, no. 3 (May 9, 2014): 779–97. http://dx.doi.org/10.5194/gmd-7-779-2014.
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Abstract. Quasi-uniform grids of the sphere have become popular recently since they avoid parallel scaling bottlenecks associated with the poles of latitude–longitude grids. However quasi-uniform grids of the sphere are often non-orthogonal. A version of the C-grid for arbitrary non-orthogonal grids is presented which gives some of the mimetic properties of the orthogonal C-grid. Exact energy conservation is sacrificed for improved accuracy and the resulting scheme numerically conserves energy and potential enstrophy well. The non-orthogonal nature means that the scheme can be used on a cubed sphere. The advantage of the cubed sphere is that it does not admit the computational modes of the hexagonal or triangular C-grids. On various shallow-water test cases, the non-orthogonal scheme on a cubed sphere has accuracy less than or equal to the orthogonal scheme on an orthogonal hexagonal icosahedron. A new diamond grid is presented consisting of quasi-uniform quadrilaterals which is more nearly orthogonal than the equal-angle cubed sphere but with otherwise similar properties. It performs better than the cubed sphere in every way and should be used instead in codes which allow a flexible grid structure.
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Weller, H. "Non-orthogonal version of the arbitrary polygonal C-grid and a new diamond grid." Geoscientific Model Development Discussions 6, no. 4 (November 29, 2013): 6035–74. http://dx.doi.org/10.5194/gmdd-6-6035-2013.
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Abstract. Quasi-uniform grids of the sphere have become popular recently since they avoid parallel scaling bottlenecks associated with the poles of latitude-longitude grids. However quasi-uniform grids of the sphere are often non-orthogonal. A version of the C-grid for arbitrary non-orthogonal grids is presented which gives some of the mimetic properties of the orthogonal C-grid. Exact energy conservation is sacrificed for improved accuracy and the resulting scheme numerically conserves energy and potential enstrophy well. The non-orthogonal nature means that the scheme can be used on a cubed sphere. The advantage of the cubed sphere is that it does not admit the computational modes of the hexagonal or triangular C-grids. On various shallow-water test cases the non-orthogonal scheme on a cubed sphere has accuracy less than or equal to the orthogonal scheme on an orthogonal hexagonal icosahedron. A new diamond grid is presented consisting of quasi-uniform quadrilaterals which is more orthogonal than the equal-angle cubed sphere but with otherwise similar properties. It performs better than the cubed sphere in every way and should be used instead in codes which allow a flexible grid structure.
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Patino, Diego Alejandro, and Andres Eduardo Nieto Vallejo. "Scale Prototype Ring Main Unit for the Measurement and Control of Nodes in a Smart Grid." Revista Politécnica 14, no. 26 (June 2018): 113–24. http://dx.doi.org/10.33571/rpolitec.v14n26a10.
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Smart grids are playing a key role in modern electric power grids, improving load control, assuring safer operations and collecting valuable information of the electrical conditions of the grid. In a smart grid, a RTU (Remote Terminal Unit) is a device that is able to measure the electric variables of the grid and sends all the information to a MTU (Master Terminal Unit), which is responsible of controlling the operations of the grid. RMU (Ring Main Unit) devices are used in electric power grids to protect loads and to disconnect them in case of failure to prevent damage. This article presents the design of a special RMU capable of measuring voltage, current and frequency, detecting electric faults, and making automatic self-healing in order to manage the flow of energy in the smart grid to guarantee energy supply to the critical loads (hospitals). The RMU devices were installed on a scaled smart grid in order to show its operation capabilities.
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Li, Jun, and Donald Brown. "Upscaled Lattice Boltzmann Method for Simulations of Flows in Heterogeneous Porous Media." Geofluids 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/1740693.
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An upscaled Lattice Boltzmann Method (LBM) for flow simulations in heterogeneous porous media at the Darcy scale is proposed in this paper. In the Darcy-scale simulations, the Shan-Chen force model is used to simplify the algorithm. The proposed upscaled LBM uses coarser grids to represent the average effects of the fine-grid simulations. In the upscaled LBM, each coarse grid represents a subdomain of the fine-grid discretization and the effective permeability with the reduced-order models is proposed as we coarsen the grid. The effective permeability is computed using solutions of local problems (e.g., by performing local LBM simulations on the fine grids using the original permeability distribution) and used on the coarse grids in the upscaled simulations. The upscaled LBM that can reduce the computational cost of existing LBM and transfer the information between different scales is implemented. The results of coarse-grid, reduced-order, simulations agree very well with averaged results obtained using a fine grid.
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Li, Qingmei, Xin Chen, Xiaochong Tong, Xuantong Zhang, and Chengqi Cheng. "An Information Fusion Model between GeoSOT Grid and Global Hexagonal Equal Area Grid." ISPRS International Journal of Geo-Information 11, no. 4 (April 17, 2022): 265. http://dx.doi.org/10.3390/ijgi11040265.
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In order to cope with the rapid growth of spatiotemporal big data, data organization models based on discrete global grid systems have developed rapidly in recent years. Due to the differences in model construction methods, grid level subdivision and coding rules, it is difficult for discrete global grid systems to integrate, share and exchange data between different models. Aiming at the problem of information fusion between a GeoSOT grid and global hexagonal equal area grid system, this paper proposes the GeoSOT equivalent aggregation model (the GEA model). We establish a spatial correlation index method between GeoSOT grids and global hexagonal equal area grids, and based on the spatial correlation index, we propose an interoperable transformation method for grid attributes information. We select the POI (points of interest) data of Beijing bus and subway stations and carry out the transformation experiment of hexagonal grid to GeoSOT grid information so as to verify the effectiveness of the GEA model. The experimental results show that when the 17th-level GeoSOT grid is selected as the particle grid to fit the hexagonal grid, the accuracy and efficiency can be well balanced. The fitting accuracy is 95.51%, and the time consumption is 30.9 ms. We establish the associated index of the GeoSOT grid and the hexagonal grid and finally realized the exchange of information.
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Hesselmann, Andreas, Hans-Joachim Werner, and Peter J. Knowles. "Thermochemical evaluation of adaptive and fixed density functional theory quadrature schemes." Journal of Chemical Physics 157, no. 23 (December 21, 2022): 234106. http://dx.doi.org/10.1063/5.0119622.
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A systematic study is made of the accuracy and efficiency of a number of existing quadrature schemes for molecular Kohn–Sham Density-Functional Theory (DFT) using 408 molecules and 254 chemical reactions. Included are the fixed SG-x (x = 0–3) grids of Gill et al., Dasgupta, and Herbert, the 3-zone grids of Treutler and Ahlrichs, a fixed five-zone grid implemented in Molpro, and a new adaptive grid scheme. While all methods provide a systematic reduction of errors upon extension of the grid sizes, significant differences are observed in the accuracies for similar grid sizes with various approaches. For the tests in this work, the SG-x fixed grids are less suitable to achieve high accuracies in the DFT integration, while our new adaptive grid performed best among the schemes studied in this work. The extra computational time to generate the adaptive grid scales linearly with molecular size and is negligible compared with the time needed for the self-consistent field iterations for large molecules. A comparison of the grid accuracies using various density functionals shows that meta-GGA functionals need larger integration grids than GGA functionals to reach the same degree of accuracy, confirming previous investigations of the numerical stability of meta-GGA functionals. On the other hand, the grid integration errors are almost independent of the basis set, and the basis set errors are mostly much larger than the errors caused by the numerical integrations, even when using the smallest grids tested in this work.
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El-Sherbiny, Aisha, and Raymond A. Poirier. "Comprehensive study of some well-known molecular numerical integration methods." Canadian Journal of Chemistry 87, no. 10 (October 2009): 1313–21. http://dx.doi.org/10.1139/v09-090.
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In a previous study, we compared, both in terms of accuracy and efficiency, the performance of some of the well-known grids, which use the Becke partitioning scheme for molecular numerical integration. We concluded, based on the number of electrons only, that the MultiExp grid performed well compared with the grids proposed by Becke, Gill et al., and Treutler and Ahlrichs. In this work, we re-examine the performance of the same set of grids in addition to the SG-0 grid and a benchmark grid. These grids are evaluated by integrating the Hartree–Fock electron density to calculate the number of electrons, dipole moment, potential energy, and Coulomb repulsion energy. Our results show that, except for the large benchmark grid, none of these grids were completely satisfactory.
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Tuncer, I. H., S. Weber, and W. Sanz. "Investigation of Periodic Boundary Conditions in Multipassage Cascade Flows Using Overset Grids." Journal of Turbomachinery 121, no. 2 (April 1, 1999): 341–47. http://dx.doi.org/10.1115/1.2841320.
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A Navier–Stokes solution method with overset grids is applied to unsteady multipassage cascade flows, and the unsteady blade loadings are compared against the single-passage solutions with the direct store interblade boundary condition. In the overset grid solutions, the multipassage domain is discretized with O-type grids around each blade and a rectangular background grid. Blade grids are allowed to move in time relative to the background grid, as prescribed by the oscillatory plunging motion. The overset grid method uses a simple, robust numerical algorithm to localize moving intergrid boundary points and to interpolate solution variables across grids. Computational results are presented for two and four-passage, subsonic and transonic flows through a turbine and a compressor cascade. The overset grid solutions over the multipassage periodic domains agree well with the single-passage solutions and the experimental data. It is concluded that the time linearization error introduced by the direct store approach is negligible in the range of flow conditions studied.
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Kong, Bojun, Jian Zhu, Shengbo Wang, Xingmin Xu, Xiaokuan Jin, Junjie Yin, and Jianhua Wang. "Comparative Study of the Transmission Capacity of Grid-Forming Converters and Grid-Following Converters." Energies 16, no. 6 (March 9, 2023): 2594. http://dx.doi.org/10.3390/en16062594.
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The development trend of high shares of renewables and power electronics has increased the demand for new energy converters in the power system, but there is a lack of systematic research on the stability of different types of converters when transmitting power, which is worth exploring in depth. In this study, the power transfer capabilities of grid-forming and grid-following converters are investigated separately through an equivalent circuit diagram and phasor diagram when connected to the grid, and a quantitative relationship between converters’ power transmission limit and short circuit ratio under static stability conditions is obtained, leading to the conclusion that, in terms of power transmission, grid-forming converters are more suitable for weak grids with high damping and low inertia, whereas grid-following converters are more suitable for strong grids with high inertia. The conclusions are further verified by constructing the converter grid-connected models for different grid strengths through the PLECS simulation platform and the real-time simulation RTBOX1 and F28379D launchpad platform.
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Cui, Pengcheng, Bin Li, Jing Tang, Jiangtao Chen, and Youqi Deng. "A modified adjoint-based grid adaptation and error correction method for unstructured grid." Modern Physics Letters B 32, no. 12n13 (May 10, 2018): 1840020. http://dx.doi.org/10.1142/s0217984918400201.
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Grid adaptation is an important strategy to improve the accuracy of output functions (e.g. drag, lift, etc.) in computational fluid dynamics (CFD) analysis and design applications. This paper presents a modified robust grid adaptation and error correction method for reducing simulation errors in integral outputs. The procedure is based on discrete adjoint optimization theory in which the estimated global error of output functions can be directly related to the local residual error. According to this relationship, local residual error contribution can be used as an indicator in a grid adaptation strategy designed to generate refined grids for accurately estimating the output functions. This grid adaptation and error correction method is applied to subsonic and supersonic simulations around three-dimensional configurations. Numerical results demonstrate that the sensitive grids to output functions are detected and refined after grid adaptation, and the accuracy of output functions is obviously improved after error correction. The proposed grid adaptation and error correction method is shown to compare very favorably in terms of output accuracy and computational efficiency relative to the traditional featured-based grid adaptation.
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Salkuti, Surender Reddy. "Challenges, issues and opportunities for the development of smart grid." International Journal of Electrical and Computer Engineering (IJECE) 10, no. 2 (April 1, 2020): 1179. http://dx.doi.org/10.11591/ijece.v10i2.pp1179-1186.
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The development smart grids have made the power systems planning and operation more efficient by the application of renewable energy resources, electric vehicles, two-way communication, self-healing, consumer engagement, distribution intelligence, etc. The objective of this paper is to present a detailed comprehensive review of challenges, issues and opportunities for the development of smart grid. Smart grids are transforming the traditional way of meeting the electricity demand and providing the way towards an environmentally friendly, reliable and resilient power grid. This paper presents various challenges of smart grid development including interoperability, network communications, demand response, energy storage and distribution grid management. This paper also reviews various issues associated with the development of smart grid. Local, regional, national and global opportunities for the development of smart grid are also reported in this paper.
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Boyle, R. J., and A. A. Ameri. "Grid Orthogonality Effects on Predicted Turbine Midspan Heat Transfer and Performance." Journal of Turbomachinery 119, no. 1 (January 1, 1997): 31–38. http://dx.doi.org/10.1115/1.2841008.
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The effect of five different C-type grid geometries on the predicted heat transfer and aerodynamic performance of a turbine stator is examined. Predictions were obtained using two flow analysis codes. One was a finite difference analysis, and the other was a finite volume analysis. Differences among the grids in terms of heat transfer and overall performance were small. The most significant difference among the five grids occurred in the prediction of pitchwise variation in total pressure. There was consistency between results obtained with each of the flow analysis codes when the same grid was used. A grid-generating procedure in which the viscous grid is embedded within an inviscid type grid resulted in the best overall performance.
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Xu, Yifei, Priyesh Srivastava, Xiao Ma, Karan Kaul, and Hao Huang. "A Fast Gridding Method for Capturing Geological Complexity and Uncertainty." SPE Journal 27, no. 01 (November 16, 2021): 632–42. http://dx.doi.org/10.2118/203902-pa.
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Summary In this paper, we introduce an efficient method to generate reservoir simulation grids and modify the fault juxtaposition on the generated grids. Both processes are based on a mapping method to displace vertices of a grid to desired locations without changing the grid topology. In the gridding process, a grid that can capture stratigraphical complexity is first generated in an unfaulted space. The vertices of the grid are then displaced back to the original faulted space to become a reservoir simulation grid. The resulting inversely mapped grid has a mapping structure that allows fast and easy fault juxtaposition modification. This feature avoids the process of updating the structural framework, which may be time-consuming. There is also no need to regenerate most of the reservoir properties in the new grid. To facilitate juxtaposition updates within an assisted history matching workflow, several parameterized fault throw adjustment methods are introduced. Grid examples are given for reservoirs with Y-faults, overturned beds, and complex channel-lobe systems. NOTE: This paper is also published as part of the 2021 SPE Reservoir Simulation Conference Special Issue.