Local model of a scientific collaboration in physics network compared with the global model

2010 ◽  
Vol 389 (23) ◽  
pp. 5530-5537 ◽  
Author(s):  
A.A. Roohi ◽  
A.H. Shirazi ◽  
A. Kargaran ◽  
G.R. Jafari
Keyword(s):  
Scientific Collaboration ◽  
Global Model ◽  
Local Model

scholarly journals Modeling of the buckstay system of membrane-walls in watertube boiler construction

2014 ◽  
Vol 18 (suppl.1) ◽  
pp. 59-72 ◽  
Author(s):  
Hasan Nagiar ◽  
Tasko Maneski ◽  
Vesna Milosevic-Mitic ◽  
Branka Gacesa ◽  
Nina Andjelic
Keyword(s):  
Finite Element ◽  
Orthotropic Plate ◽  
Global Model ◽  
Local Model ◽  
Thermal Loads ◽  
Water Tube ◽  
Bending Load ◽  
Specific Geometry ◽  
Structural Parts ◽  
Help Model

Membrane walls are very important structural parts of water-tube boiler construction. Based on their specific geometry, one special type of finite element was defined to help model the global boiler construction. That is the element of reduced orthotropic plate with two thicknesses and two elasticity matrixes, for membrane and bending load separately. A global model of the boiler construction showed that the high value of stress is concentrated in plates of the buckstay system in boiler corners. Validation of the new finite element was done on the local model of the part of membrane wall and buckstay. A very precise model of tubes and flanges was compared to the model formed on the element of a reduced orthotropic plate. Pressure and thermal loads were discussed. Obtained results indicated that the defined finite element was quite favorable in the design and reconstruction of the boiler substructures such as a buckstay system.

Fuel-Sensitive Ignition Delay Models for a Local and Global Description of Direct Injection Internal Combustion Engines

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Kyoung Hyun Kwak ◽  
Claus Borgnakke ◽  
Dohoy Jung
Keyword(s):  
Ignition Delay ◽  
Alternative Fuels ◽  
Internal Combustion Engines ◽  
Cetane Number ◽  
Global Model ◽  
Local Model ◽  
Delay Model ◽  
Lower Accuracy ◽  
Delay Models ◽  
Single Calibration

Models for ignition delay are investigated and fuel-specific properties are included to predict the effects of different fuels on the ignition delay. These models follow the Arrhenius type expression for the ignition delay modified with the oxygen concentration and Cetane number to extend the range of validity. In this investigation, two fuel-sensitive spray ignition delay models are developed: a global model and a local model. The global model is based on the global combustion chamber charge properties including temperature, pressure, and oxygen/fuel content. The local model is developed to account for temporal and spatial variations in properties of separated spray zones such as local temperature, oxidizer, and fuel concentrations obtained by a quasi-dimensional multizone fuel spray model. These variations are integrated in time to predict the ignition delay. Often ignition delay models are recalibrated for a specific fuel but in this study, the global ignition delay model includes the Cetane number to capture ignition delay of various fuels. The local model uses Cetane number and local stoichiometric oxygen to fuel molar ratio. The model is therefore capable of predicting spray ignition delays for a set of fuels with a single calibration. Experimental dataset of spray ignition delay in a constant volume chamber is used for model development and calibration. The models show a good accuracy for the predicted ignition delay of four different fuels: JP8, DF2, n-heptane, and n-dodecane. The investigation revealed that the most accurate form of the models is from a calibration done for each individual fuel with only a slight decrease in accuracy when a single calibration is done for all fuels. The single calibration case is the more desirable outcome as it leads to general models that cover all the fuels. Of the two proposed models, the local model has a slightly better accuracy compared to the global model. Results for both models demonstrate the improvements that can be obtained for the ignition delay model when additional fuel-specific properties are included in the spray ignition model. Other alternative fuels like synthetic oxygenated fuels were included in the investigation. These fuels behave differently such that the Cetane number does not provide the same explanation for the trend in ignition delay. Though of lower accuracy, the new models do improve the predictive capability when compared with existing types of ignition delay models applied to this kind of fuels.

scholarly journals Study of the combined effects of data assimilation and grid nesting in ocean models – application to the Gulf of Lions

2006 ◽  
Vol 3 (3) ◽  
pp. 291-318
Author(s):  
L. Vandenbulcke ◽  
A. Barth ◽  
M. Rixen ◽  
A. Alvera-Azcárate ◽  
Z. Ben Bouallegue ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Boundary Conditions ◽  
Global Model ◽  
Local Model ◽  
Local Models ◽  
Coastal Zones ◽  
Efficient System ◽  
Nested Models ◽  
Ocean Forecasting ◽  
Grid Nesting

Abstract. Modern operational ocean forecasting systems routinely use data assimilation techniques in order to take observations into account in the hydrodynamic model. Moreover, as end users require higher and higher resolution predictions, especially in coastal zones, it is now common to run nested models, where the coastal model gets its open-sea boundary conditions from a low-resolution global model. This configuration is used in the ''Mediterranean Forecasting System: Towards environmental predictions'' (MFSTEP) project. A global model covering the whole Mediterranean Sea is run weekly, performing 1 week of hindcast and a 10-day forecast. Regional models, using different codes and covering different areas, then use this forecast to implement boundary conditions. Local models in turn use the regional model forecasts for their own boundary conditions. This nested system has proven to be a viable and efficient system to achieve high-resolution weekly forecasts. However, when observations are available in some coastal zone, it remains unclear whether it is better to assimilate them in the global or local model. We perform twin experiments and assimilate observations in the global or in the local model, or in both of them together. We show that, when interested in the local models forecast and provided the global model fields are approximately correct, the best results are obtained when assimilating observations in the local model.

Global-Local Analysis of a Composite Riser

2014 ◽  
Author(s):  
Venkata M. K. Akula
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Coefficient Of Thermal Expansion ◽  
Structural Response ◽  
Global Model ◽  
Local Model ◽  
Cross Sectional ◽  
Beam Elements ◽  
Aspect Ratios ◽  
Hexahedral Elements

Composite materials are often utilized in weight-critical applications, owing to their higher specific strength\stiffness characteristics. In addition, composite materials also possess qualities such as better corrosion resistance, lower coefficient of thermal expansion, etc., which makes them a potential material choice for riser systems in high pressure and high temperature environments. However, design certification of risers using the finite element method requires modeling and analysis techniques, centric to the multi-layered nature of composite structures. Riser systems, owing to their high aspect ratios, have traditionally been modeled with beam elements. The methodology for extracting the stress results and certifying a metallic riser is well established in the Oil and Gas industry. However, for analyzing a composite riser, three-dimensional shell or hexahedral elements are generally required to capture the through-the-thickness (or pipe cross-sectional) variation of structural response, especially in critical regions such as touchdown point, pipe-intersection zones, etc. In this paper, a method for analyzing a detailed local model (discretized with shell\hexahedral elements) driven by results from a global model (meshed with beam elements) is presented. The global model captures the structural response whereas the local model provides cross-sectional stress\strain information for individual layers. Although the method is illustrated for a composite riser, it is also applicable to metallic structures.

Finite element modeling of underground water flow with Ranney wells

2007 ◽  
Vol 7 (3) ◽  
pp. 41-50 ◽  
Author(s):  
M. Kojić ◽  
N. Filipović ◽  
B. Stojanović ◽  
V. Ranković ◽  
M. Krstić ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Boundary Conditions ◽  
Water Flow ◽  
Groundwater Resources ◽  
Underground Water ◽  
Global Model ◽  
Local Model ◽  
Fe Model ◽  
Surface Boundary

The objectives of this study were to define the regional and local groundwater flow, and to give quantitative estimates of the groundwater dynamic parameters and of the available groundwater resources. To achieve these objectives, numerical tools are required to quantitatively model flow through porous saturated and unsaturated media. We have developed a general finite element (FE) model for underground water flow and specific algorithms for Ranney wells. Solutions for steady and unsteady conditions are obtained by using two basic models: global and local. The global model consists of 3D finite elements and 1D finite elements with the equivalent well permeability representing Ranney wells. The local models are generated around wells, using solutions for all quantities from 3D global model at a cylindrical surface which bounds the local model. The local model consists of a fine 3D FE mesh and 1D elements used to model each of the well screens. We developed a software for pre- and post-processing, Lizza, which can be used for easy modeling of complex engineering underground water flow problems with Ranney wells. The FE package PAK-P is used as the solver. This software can handle flow regions with general irregular boundaries. The flow region itself may be composed of layers of nonuniform soils having an arbitrary degree of local anisotropy. Flow can occur in the vertical plane, the horizontal plane, or in a three dimensional region exhibiting radial symmetry about the vertical axis. The water flow model includes constant or time-varying prescribed head and flux boundaries, as well as boundaries controlled by atmospheric conditions. At a soil surface, boundary conditions may change during the time evolution from prescribed flux to prescribed head type conditions (and vice versa). The model also include a seepage face boundary through which water leaves the saturated part of the flow domain, and free drainage boundary conditions. The results of modeling several real engineering projects (Belgrade Water Supply Center) are presented.

scholarly journals Study of the combined effects of data assimilation and grid nesting in ocean models – application to the Gulf of Lions

Ocean Science ◽  
2006 ◽  
Vol 2 (2) ◽  
pp. 213-222 ◽  
Author(s):  
L. Vandenbulcke ◽  
A. Barth ◽  
M. Rixen ◽  
A. Alvera-Azcarate ◽  
Z. Ben Bouallegue ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Boundary Conditions ◽  
Global Model ◽  
Local Model ◽  
Local Models ◽  
Coastal Zones ◽  
Efficient System ◽  
Nested Models ◽  
Ocean Forecasting ◽  
Grid Nesting

Abstract. Modern operational ocean forecasting systems routinely use data assimilation techniques in order to take observations into account in the hydrodynamic model. Moreover, as end users require higher and higher resolution predictions, especially in coastal zones, it is now common to run nested models, where the coastal model gets its open-sea boundary conditions from a low-resolution global model. This configuration is used in the "Mediterranean Forecasting System: Towards environmental predictions" (MFSTEP) project. A global model covering the whole Mediterranean Sea is run weekly, performing 1 week of hindcast and a 10-day forecast. Regional models, using different codes and covering different areas, then use this forecast to implement boundary conditions. Local models in turn use the regional model forecasts for their own boundary conditions. This nested system has proven to be a viable and efficient system to achieve high-resolution weekly forecasts. However, when observations are available in some coastal zone, it remains unclear whether it is better to assimilate them in the global or local model. We perform twin experiments and assimilate observations in the global or in the local model, or in both of them together. We show that, when interested in the local models forecast and provided the global model fields are approximately correct, the best results are obtained when assimilating observations in the local model.

Thermomechanical Modeling of Direct Chip Interconnection Assembly

1993 ◽  
Vol 115 (4) ◽  
pp. 382-391 ◽  
Author(s):  
E. K. Buratynski
Keyword(s):  
Global Analysis ◽  
Numerical Procedure ◽  
Calibration Procedure ◽  
Global Model ◽  
Conductive Adhesive ◽  
Local Model ◽  
Assembly Process ◽  
Anisotropic Properties ◽  
Anisotropic Conductive Adhesive ◽  
Thermomechanical Modeling

Efforts to model thermomechanical aspects of the Direct Chip Interconnection (DCI) assembly process are described. DCI is a method to simultaneously attach and electrically interconnect bare chips to a substrate using Anisotropic Conductive Adhesive Films (ACAF). Emphasis has been placed on describing the numerical procedure used in the analysis. The major components of the analysis include a calibration procedure to “numerically measure” anisotropic properties of the film, a curing model to capture “frozen-in” stresses, a global analysis that considers the overall assembly station but does not resolve details of the interconnection, and a local model, coupled to the global model, that resolves details about the interconnection. Typical results are shown to demonstrate the capabilities of the model.

Separation efficiency of a hydrodynamic separator using a 3D computational fluid dynamics multiscale approach

2014 ◽  
Vol 69 (5) ◽  
pp. 1067-1073 ◽  
Author(s):  
Vivien Schmitt ◽  
Matthieu Dufresne ◽  
Jose Vazquez ◽  
Martin Fischer ◽  
Antoine Morin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Separation Efficiency ◽  
Perforated Plate ◽  
Global Model ◽  
Trapping Efficiency ◽  
Local Model ◽  
Multiscale Approach ◽  
Hydrodynamic Behavior ◽  
Particle Trajectories

The aim of this study is to investigate the use of computational fluid dynamics (CFD) to predict the solid separation efficiency of a hydrodynamic separator. The numerical difficulty concerns the discretization of the geometry to simulate both the global behavior and the local phenomena that occur near the screen. In this context, a CFD multiscale approach was used: a global model (at the scale of the device) is used to observe the hydrodynamic behavior within the device; a local model (portion of the screen) is used to determine the local phenomena that occur near the screen. The Eulerian–Lagrangian approach was used to model the particle trajectories in both models. The global model shows the influence of the particles' characteristics on the trapping efficiency. A high density favors the sedimentation. In contrast, particles with small densities (1,040 kg/m3) are steered by the hydrodynamic behavior and can potentially be trapped by the separator. The use of the local model allows us to observe the particle trajectories near the screen. A comparison between two types of screens (perforated plate vs expanded metal) highlights the turbulent effects created by the shape of the screen.

Virtual mitochondrion: towards an integrated model of oxidative phosphorylation complexes and beyond

2010 ◽  
Vol 38 (5) ◽  
pp. 1215-1219 ◽  
Author(s):  
Jean-Pierre Mazat ◽  
Jonathan Fromentin ◽  
Margit Heiske ◽  
Christine Nazaret ◽  
Stéphane Ransac
Keyword(s):  
Oxidative Phosphorylation ◽  
Integrated Model ◽  
Global Model ◽  
Local Model ◽  
Central Metabolism ◽  
Chemiosmotic Theory ◽  
Respiratory Complexes ◽  
The Individual

The modelling of OXPHOS (oxidative phosphorylation) in order to integrate all kinetic and thermodynamic aspects of chemiosmotic theory has a long history. We briefly review this history and show how new ways of modelling are required to integrate a local model of the individual respiratory complexes into a global model of OXPHOS and, beyond that, into a reliable overall model of central metabolism.

Fuel Sensitive Ignition Delay Models for a Local and Global Description of Direct Injection Internal Combustion Engines

2014 ◽  
Author(s):  
Kyoung Hyun Kwak ◽  
Claus Borgnakke ◽  
Dohoy Jung
Keyword(s):  
Ignition Delay ◽  
Alternative Fuels ◽  
Internal Combustion Engines ◽  
Direct Injection ◽  
Cetane Number ◽  
Global Model ◽  
Local Model ◽  
Delay Model ◽  
Delay Models ◽  
Single Calibration

Models for ignition delay in a direct injection compression ignition engine are investigated and fuel specific properties are included to predict the effects of different fuels on the ignition delay. These models follow the Arrhenius type expression for the ignition delay modified with the oxygen concentration and Cetane number to extend the range of validity. In this investigation two fuel-sensitive spray ignition delay models are developed: a global model and a local model. The global model is based on the global combustion chamber charge properties including temperature, pressure and oxygen/fuel content. The local model is developed to account for temporal and spatial variations in properties of separated spray zones such as local temperature, oxidizer and fuel concentrations obtained by a quasi-dimensional multi-zone fuel spray model. These variations are integrated in time to predict the ignition delay. An ignition delay model is typically re-calibrated for a specific fuel being used. In this study, the global ignition delay model includes the Cetane number to capture ignition delay of various fuels. The local model uses Cetane number and local stoichiometric oxygen to fuel molar ratio. Due to those variables, the model is capable of predicting spray ignition delays for a set of fuels with a single calibration step. Experimental dataset of spray ignition delay in a constant volume chamber is used for model development and calibration. The models show a good accuracy for the predicted ignition delay of four different fuels: JP8, DF2, n-heptane and n-dodecane. The investigation revealed that the most accurate form of the models is from a calibration done for each individual fuel with only a slight decrease in accuracy when a single calibration is done for all fuels. The single calibration case is the more desirable outcome as it leads to general models that cover all the fuels. Of the two proposed models the local model has a slightly better accuracy compared to the global model. Results for both models demonstrate the improvements that can be obtained for the ignition delay model when additional fuel specific properties are included in the spray ignition model. Other alternative fuels like synthetic oxygenated fuels were included in the investigation. These fuels behave differently such that the Cetane number does not provide the same explanation for the trend in ignition delay. Though of lower accuracy, the new models do improve the predictive capability when compared with existing types of ignition delay models applied to this kind of fuels.

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