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Ali Kashefi - One of the best experts on this subject based on the ideXlab platform.
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a Coarse Grid projection method for accelerating free and forced convection heat transfer computations
Results in Mathematics, 2020Co-Authors: Ali KashefiAbstract:Coarse Grid projection (CGP) methodology is used to accelerate the computations of sets of decoupled nonlinear evolutionary and linear static equations. In CGP, the linear equations are solved on a Coarsened mesh compared to the nonlinear equations, leading to a reduction in central processing unit time. The accuracy of CGP has been assessed for the advection–diffusion equation along with the pressure Poisson equation. Here we add another decoupled equation to this set: the energy equation. In this article, we examine the influence of CGP methodology for the first time on thermal fields. CGP is validated with two different test cases: first, natural convection induced by a hot circular cylinder located in the center of a cold square cylinder, and second, the flow over a circular cylinder with the condition of constant cylinder temperature. For the first test case, the velocity and temperature fields as well as the local Nusselt number on the surface of the inner hot cylinder calculated by CGP reveal good agreement with the non-CGP data. For the second test case, the Nusselt number and the spatial structure of the temperature field obtained by CGP are in a good agreement with the non-CGP data for different Prandtl numbers. In general, CGP is able to maintain excellent to reasonable accuracy of the temperature filed, while achieves speedup factors ranged approximately from 1.7 to 3.7.
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A Coarse-Grid incremental pressure projection method for accelerating low Reynolds number incompressible flow simulations
Iran Journal of Computer Science, 2020Co-Authors: Ali KashefiAbstract:Coarse-Grid projection (CGP) multiGrid techniques are applicable to sets of equations that include at least one decoupled linear elliptic equation. In CGP, the linear elliptic equation is solved on a Coarsened Grid compared to the other equations, leading to savings in computation time and complexity. One of the most important applications of CGP is when a pressure correction scheme is used to obtain a numerical solution to the Navier–Stokes equations. In that case, there is an elliptic pressure Poisson equation. Depending on the pressure correction scheme used, the CGP method and its performance in terms of acceleration rate and accuracy level vary. The CGP framework has been established for non-incremental pressure projection techniques. In this article, we apply CGP methodology for the first time to incremental pressure correction schemes. Both standard and rotational forms of the incremental algorithms are considered. The influence of velocity Dirichlet and natural homogenous boundary conditions in regular and irregular domains with structured and unstructured triangular finite element meshes is investigated. $$L^2$$ L 2 norms demonstrate that the level of accuracy of the velocity and the pressure fields is preserved for up to three levels of Coarsening. For the test cases investigated, the speedup factors range approximately from 1.2 to 102.7.
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a Coarse Grid projection method for accelerating incompressible mhd flow simulations
arXiv: Computational Physics, 2020Co-Authors: Ali KashefiAbstract:Coarse Grid projection (CGP) is a multiresolution technique for accelerating numerical calculations associated with a set of nonlinear evolutionary equations along with the stiff Poisson equations. In this article we use CGP for the first time to speed up incompressible magnetohydrodynamics (MHD) flow simulations. Accordingly, we solve the nonlinear advection-diffusion equation on a fine mesh, while we execute the electric potential Poisson equation on the corresponding Coarsened mesh. Mapping operators connect two Grids together. A pressure correction scheme is used to enforce the incompressibility constrain. The study of incompressible flow past a circular cylinder in the presence of Lorentz force is selected as a benchmark problem with a fixed Reynolds number but various Stuart numbers. We consider two different situations. First, we only apply CGP to the electric potential Poisson equation. Second, we apply CGP to the pressure Poisson equation as well. The maximum speedup factors achieved here are approximately 3 and 23 respectively for the first and second situations. For the both situations we examine the accuracy of velocity and vorticity fields as well as the lift and drag coefficients. In general, the results obtained by CGP are in an excellent to reasonable range of accuracy and are significantly consistently more accurate than when we use Coarse Grids for the discretization of both the advection-diffusion and electric potential Poisson equations.
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Coarse Grid projection methodology a partial mesh refinement tool for incompressible flow simulations
Bulletin of The Iranian Mathematical Society, 2020Co-Authors: Ali KashefiAbstract:We discuss Coarse Grid projection (CGP) methodology as a guide for partial mesh refinement of incompressible flow computations for the first time. Based on it, if for a given spatial resolution the numerical simulation diverges or the velocity outputs are not accurate enough, instead of refining both the advection–diffusion and the Poisson Grids, the CGP mesh refinement suggests to only refine the advection–diffusion Grid and keep the Poisson Grid resolution unchanged. The application of the novel mesh refinement tool is shown in the cases of flow over a backward-facing step and flow past a cylinder. For the backward-facing step flow, a three-level partial mesh refinement makes a previously diverging computation numerically stable. For the flow past a cylinder, the error of the viscous lift force is reduced from 31.501 to 7.191% (with reference to the standard mesh refinement results) by the one-level partial mesh refinement technique.
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a Coarse Grid incremental pressure projection method for accelerating low reynolds number incompressible flow simulations
arXiv: Computational Physics, 2018Co-Authors: Ali KashefiAbstract:Coarse Grid projection (CGP) multiGrid techniques are applicable to sets of equations that include at least one decoupled linear elliptic equation. In CGP, the linear elliptic equation is solved on a Coarsened Grid compared to the other equations, leading to savings in computations time and complexity. One of the most important applications of CGP is when a pressure correction scheme is used to obtain a numerical solution to the Navier-Stokes equations. In that case there is an elliptic pressure Poisson equation. Depending on the pressure correction scheme used, the CGP method and its performance in terms of acceleration rate and accuracy level vary. The CGP framework has been established for non-incremental pressure projection techniques. In this article, we apply CGP methodology for the first time to incremental pressure correction schemes. Both standard and rotational forms of the incremental algorithms are considered. The influence of velocity Dirichlet and natural homogenous boundary conditions in regular and irregular domains with structured and unstructured triangular finite element meshes is investigated. $L^2$ norms demonstrate that the level of accuracy of the velocity and the pressure fields is preserved for up to three levels of Coarsening. For the test cases investigated, the speedup factors range from 1.248 to 102.715.
Dragan Savic - One of the best experts on this subject based on the ideXlab platform.
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multi layered Coarse Grid modelling in 2d urban flood simulations
Journal of Hydrology, 2012Co-Authors: Albert S Chen, Barry Evans, Slobodan Djordjevic, Dragan SavicAbstract:Summary Regular Grids are commonly used in 2D flood modelling due to wide availability of terrain models and low pre-processing required for input preparation. Despite advances in both computing software and hardware, high resolution flood modelling remains computationally demanding when applied to a large study area when the available time and resources are limited. Traditional Grid Coarsening approach may reduce not only the computing demands, but also the accuracy of results due to the loss of detailed information. To keep key features that affect flow propagation within Coarse Grid, the approach proposed and tested in this paper adopts multiple layers in flood modelling to reflect individual flow paths separated by buildings within a Coarse Grid cell. The cell in each layer has its own parameters (elevation, roughness, building coverage ratio, and conveyance reduction factors) to describe itself and the conditions at boundaries with neighbourhood cells. Results of tests on the synthetic case study and the real world urban area show that the proposed multi-layered approach greatly improves the accuracy of Coarse Grid modelling with an insignificant additional computing cost. The proposed approach has been tested in conjunction with the UIM model by taking the high resolution results as the benchmark. The implementation of the proposed multi-layered methodology to any regular Grid based 2D model would be straightforward.
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a Coarse Grid approach to representing building blockage effects in 2d urban flood modelling
Journal of Hydrology, 2012Co-Authors: Albert S Chen, Barry Evans, Slobodan Djordjevic, Dragan SavicAbstract:Summary The latest information and communications technology has enabled flood modelling in urban areas using high quality terrain data to simulate the detailed flow dynamics in local areas. However, the computational cost rises exponentially as the resolution goes finer. The advance of computing hardware is still a limiting factor for large-scale area or risk/uncertainty analysis modelling with fine resolution that describes the details of building features. Grid Coarsening is the straightforward way to reduce the computing efforts for 2D flood modelling. The traditional approach to Grid Coarsening usually takes the average elevation of a fine Grid as the new terrain model for the Coarse Grid. This approach often results in loss of information that introduces errors to modelling. In this study, the building features in Coarse Grids were abstracted using the building coverage ratio (BCR) and the conveyance reduction factor (CRF) parameters in a 2D model to simulate flooding in urban areas. The outcome of 2D case studies showed the proposed model can minimise the errors due to terrain averaging and provide a much better accuracy of modelling results at a marginally increased computing cost.
Albert S Chen - One of the best experts on this subject based on the ideXlab platform.
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Multi-layered Coarse Grid modelling in 2D urban flood simulations
Journal of Hydrology, 2020Co-Authors: Albert S Chen, Barry Evans, Slobodan Djordjević, Dragan A. SavićAbstract:Copyright © 2012 Elsevier. NOTICE: This is the author’s version of a work accepted for publication by Elsevier. Changes resulting from the publishing process, including peer review, editing, corrections, structural formatting and other quality control mechanisms, may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Hydrology Vol. 470-471, DOI: 10.1016/j.jhydrol.2012.06.022Regular Grids are commonly used in 2D flood modelling due to wide availability of terrain models and low pre-processing required for input preparation. Despite advances in both computing software and hardware, high resolution flood modelling remains computationally demanding when applied to a large study area when the available time and resources are limited. Traditional Grid Coarsening approach may reduce not only the computing demands, but also the accuracy of results due to the loss of detailed information. To keep key features that affect flow propagation within Coarse Grid, the approach proposed and tested in this paper adopts multiple layers in flood modelling to reflect individual flow paths separated by buildings within a Coarse Grid cell. The cell in each layer has its own parameters (elevation, roughness, building coverage ratio, and conveyance reduction factors) to describe itself and the conditions at boundaries with neighbourhood cells. Results of tests on the synthetic case study and the real world urban area show that the proposed multi-layered approach greatly improves the accuracy of Coarse Grid modelling with an insignificant additional computing cost. The proposed approach has been tested in conjunction with the UIM model by taking the high resolution results as the benchmark. The implementation of the proposed multi-layered methodology to any regular Grid based 2D model would be straightforward
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multi layered Coarse Grid modelling in 2d urban flood simulations
Journal of Hydrology, 2012Co-Authors: Albert S Chen, Barry Evans, Slobodan Djordjevic, Dragan SavicAbstract:Summary Regular Grids are commonly used in 2D flood modelling due to wide availability of terrain models and low pre-processing required for input preparation. Despite advances in both computing software and hardware, high resolution flood modelling remains computationally demanding when applied to a large study area when the available time and resources are limited. Traditional Grid Coarsening approach may reduce not only the computing demands, but also the accuracy of results due to the loss of detailed information. To keep key features that affect flow propagation within Coarse Grid, the approach proposed and tested in this paper adopts multiple layers in flood modelling to reflect individual flow paths separated by buildings within a Coarse Grid cell. The cell in each layer has its own parameters (elevation, roughness, building coverage ratio, and conveyance reduction factors) to describe itself and the conditions at boundaries with neighbourhood cells. Results of tests on the synthetic case study and the real world urban area show that the proposed multi-layered approach greatly improves the accuracy of Coarse Grid modelling with an insignificant additional computing cost. The proposed approach has been tested in conjunction with the UIM model by taking the high resolution results as the benchmark. The implementation of the proposed multi-layered methodology to any regular Grid based 2D model would be straightforward.
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a Coarse Grid approach to representing building blockage effects in 2d urban flood modelling
Journal of Hydrology, 2012Co-Authors: Albert S Chen, Barry Evans, Slobodan Djordjevic, Dragan SavicAbstract:Summary The latest information and communications technology has enabled flood modelling in urban areas using high quality terrain data to simulate the detailed flow dynamics in local areas. However, the computational cost rises exponentially as the resolution goes finer. The advance of computing hardware is still a limiting factor for large-scale area or risk/uncertainty analysis modelling with fine resolution that describes the details of building features. Grid Coarsening is the straightforward way to reduce the computing efforts for 2D flood modelling. The traditional approach to Grid Coarsening usually takes the average elevation of a fine Grid as the new terrain model for the Coarse Grid. This approach often results in loss of information that introduces errors to modelling. In this study, the building features in Coarse Grids were abstracted using the building coverage ratio (BCR) and the conveyance reduction factor (CRF) parameters in a 2D model to simulate flooding in urban areas. The outcome of 2D case studies showed the proposed model can minimise the errors due to terrain averaging and provide a much better accuracy of modelling results at a marginally increased computing cost.
Taha Abbas Bin Rashid - One of the best experts on this subject based on the ideXlab platform.
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effect of granular properties on hydrodynamics in Coarse Grid riser flow simulation of geldart a and b particles
Powder Technology, 2020Co-Authors: Taha Abbas Bin RashidAbstract:Abstract In this work, a three-dimensional Coarse-Grid two-fluid model (TFM) simulation by varying granular properties like granular viscosity, frictional viscosity, and solids pressure has been performed. Simulated predictions were subsequently compared with experimental results in the case of Geldart A or B particles. Laminar flow behavior is also studied and Coarse-Grid simulation predictions were less realistic for laminar flow. This flow regime which although consumes less computational resources falls short for large-scale riser scale up. Flow regime in our simulation was fast fluidization and simulation predicts with minimum error near riser inlet. More specifically, granular viscosity, frictional viscosity and solids pressure for Type A particles predict with minimum error especially near riser inlet at a lower height. For Type B particles, these three solid properties correspond closely with experimental results near inlet at a lower height whereas, at a higher height, turbulence increases and simulation results deviate from experimental studies.
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comprehensive validation analysis of sub Grid drag and wall corrections for Coarse Grid two fluid modeling
Chemical Engineering Science, 2019Co-Authors: Taha Abbas Bin RashidAbstract:Abstract Development and validation of sub-Grid models are of pivotal importance for Coarse-Grid two-fluid modeling of gas-particle fluidization. In prior study (Zhu et al., 2018, Chem. Eng. Sci. 192, 759–773), we developed an effective three-marker sub-Grid drag model to consider the local heterogeneity in gas-particle flows. In this study, we perform a comprehensive 3D hydrodynamic validation analysis of the developed model to its predictability. Specifically, the validation covers more flow situations with respect to rapid, turbulent and bubbling fluidization. Besides, we introduce a simplified wall correction factor for assessing how the bounding walls impact on flow hydrodynamics. Computational results accord well with the experimental data over various flow regimes. The developed model can adequately capture the macroscopic flow properties without an additional wall modification. Compared with the fine-Grid two-fluid modeling using the uniform drag model for a lab-scale riser, approximately 44 times speedup in computational time is achieved via the developed model. A much more significant reduction in computational time can be consequently expected for industrial-scale reactors.
Anne Staples - One of the best experts on this subject based on the ideXlab platform.
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a Coarse Grid projection method for accelerating incompressible flow computations
Journal of Computational Physics, 2013Co-Authors: Anne StaplesAbstract:We present a Coarse-Grid projection (CGP) method for accelerating incompressible flow computations, which is applicable to methods involving Poisson equations as incompressibility constraints. The CGP methodology is a modular approach that facilitates data transfer with simple interpolations and uses black-box solvers for the Poisson and advection-diffusion equations in the flow solver. After solving the Poisson equation on a Coarsened Grid, an interpolation scheme is used to obtain the fine data for subsequent time stepping on the full Grid. A particular version of the method is applied here to the vorticity-stream function, primitive variable, and vorticity-velocity formulations of incompressible Navier-Stokes equations. We compute several benchmark flow problems on two-dimensional Cartesian and non-Cartesian Grids, as well as a three-dimensional flow problem. The method is found to accelerate these computations while retaining a level of accuracy close to that of the fine resolution field, which is significantly better than the accuracy obtained for a similar computation performed solely using a Coarse Grid. A linear acceleration rate is obtained for all the cases we consider due to the linear-cost elliptic Poisson solver used, with reduction factors in computational time between 2 and 42. The computational savings are larger when a suboptimal Poisson solver is used. We also find that the computational savings increase with increasing distortion ratio on non-Cartesian Grids, making the CGP method a useful tool for accelerating generalized curvilinear incompressible flow solvers.