The Experts below are selected from a list of 72996 Experts worldwide ranked by ideXlab platform
Peter Camps - One of the best experts on this subject based on the ideXlab platform.
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hierarchical octree and k d tree Grids for 3d radiative transfer simulations
Astronomy and Astrophysics, 2014Co-Authors: Waad Saftly, M Baes, Peter CampsAbstract:Context. A crucial ingredient for numerically solving the three-dimensional radiative transfer problem is the choice of the Grid that discretizes the transfer medium. Many modern radiative transfer codes, whether using Monte Carlo or ray tracing techniques, are equipped with hierarchical octree-based Grids to accommodate a wide dynamic range in densities. Aims. We critically investigate two different aspects of octree Grids in the framework of Monte Carlo dust radiative transfer. Inspired by their common use in computer graphics applications, we test hierarchical k-d tree Grids as an alternative for octree Grids. On the other hand, we investigate which node subdivision-stopping criteria are optimal for constructing of hierarchical Grids. Methods. We implemented a k-d tree Grid in the 3D radiative transfer code SKIRT and compared it with the previously implemented octree Grid. We also considered three different node subdivision-stopping criteria (based on mass, optical depth, and density gradient thresholds). Based on a small suite of test models, we compared the efficiency and accuracy of the different Grids, according to various Quality metrics. Results. For a given set of requirements, the k-d tree Grids only require half the number of cells of the corresponding octree. Moreover, for the same number of Grid cells, the k-d tree is characterized by higher discretization accuracy. Concerning the subdivision stopping criteria, we find that an optical depth criterion is not a useful alternative to the more standard mass threshold, since the resulting Grids show a poor accuracy. Both criteria can be combined; however, in the optimal combination, for which we provide a simple approximate recipe, this can lead to a 20% reduction in the number of cells needed to reach a certain Grid Quality. An additional density gradient threshold criterion can be added that solves the problem of poorly resolving sharp edges and strong density gradients. Conclusions. We advocate the use of k-d trees and the proposed combination of criteria to set up hierarchical Grids for 3D radiative transfer. These recipes are straightforward for implementing and should help to develop faster and more accurate 3D radiative transfer codes.
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hierarchical octree and k d tree Grids for 3d radiative transfer simulations
arXiv: Instrumentation and Methods for Astrophysics, 2013Co-Authors: Waad Saftly, M Baes, Peter CampsAbstract:A crucial ingredient for numerically solving the 3D radiative transfer problem is the choice of the Grid that discretizes the transfer medium. Many modern radiative transfer codes, whether using Monte Carlo or ray tracing techniques, are equipped with hierarchical octree-based Grids to accommodate a wide dynamic range in densities. We critically investigate two different aspects of octree Grids in the framework of Monte Carlo dust radiative transfer. Inspired by their common use in computer graphics applications, we test hierarchical k-d tree Grids as an alternative for octree Grids. On the other hand, we investigate which node subdivision-stopping criteria are optimal for constructing of hierarchical Grids. We implemented a k-d tree Grid in the 3D radiative transfer code SKIRT and compared it with the previously implemented octree Grid. We also considered three different node subdivision-stopping criteria (based on mass, optical depth, and density gradient thresholds). Based on a small suite of test models, we compared the efficiency and accuracy of the different Grids, according to various Quality metrics. For a given set of requirements, the k-d tree Grids only require half the number of cells of the corresponding octree. Moreover, for the same number of Grid cells, the k-d tree is characterized by higher discretization accuracy. Concerning the subdivision stopping criteria, we find that an optical depth criterion is not a useful alternative to the more standard mass threshold, since the resulting Grids show a poor accuracy. Both criteria can be combined; however, in the optimal combination, for which we provide a simple approximate recipe, this can lead to a 20% reduction in the number of cells needed to reach a certain Grid Quality. An additional density gradient threshold criterion can be added that solves the problem of poorly resolving sharp edges and... (abridged).
Lutz Lampe - One of the best experts on this subject based on the ideXlab platform.
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cost efficient qos aware data acquisition point placement for advanced metering infrastructure
IEEE Transactions on Communications, 2018Co-Authors: Fariba Aalamifar, Lutz LampeAbstract:In an advanced metering infrastructure (AMI), data acquisition points (DAPs) are responsible for collecting traffic from several smart meters and automated devices and transmitting them to the utility control center. Although the problem of optimized data collector placement has already been addressed for wireless broadband and sensor networks, the DAP placement is quite a new research area for AMIs. In this paper, we investigate the minimum required number of DAPs and their optimized locations on top of the existing utility poles in a distribution Grid, such that the smart Grid Quality of service requirements can best be provided. In order to solve the problem for large-scale AMIs, we devise a novel heuristic algorithm using a greedy approach for identifying potential pole locations for the DAP placement and the Dijkstra’s shortest path algorithm for constructing reliable routes. We employ the characteristics of medium access schemes from the IEEE 802.15.4g smart utility network (SUN) standard and consider mission-critical and non-critical smart Grid traffic. The performance and the time complexity of our algorithm are compared with those obtained by the IBM CPLEX software for small scenarios. Finally, we apply our devised DAP placement algorithm to examples of realistic smart Grid AMI topologies.
A Guardone - One of the best experts on this subject based on the ideXlab platform.
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An interpolation-free ALE scheme for unsteady inviscid flows computations with large boundary displacements over three-dimensional adaptive Grids
Journal of Computational Physics, 2017Co-Authors: Cecile Dobrzynski, A GuardoneAbstract:A novel strategy to solve the finite volume discretization of the unsteady Euler equations within the Arbitrary Lagrangian–Eulerian framework over tetrahedral adaptive Grids is proposed. The volume changes due to local mesh adaptation are treated as continuous deformations of the finite volumes and they are taken into account by adding fictitious numerical fluxes to the governing equation. This peculiar interpretation enables to avoid any explicit interpolation of the solution between different Grids and to compute Grid velocities so that the Geometric Conservation Law is automatically fulfilled also for connectivity changes. The solution on the new Grid is obtained through standard ALE techniques, thus preserving the underlying scheme properties, such as conservativeness, stability and monotonicity. The adaptation procedure includes node insertion, node deletion, edge swapping and points relocation and it is exploited both to enhance Grid Quality after the boundary movement and to modify the Grid spacing to increase solution accuracy. The presented approach is assessed by three-dimensional simulations of steady and unsteady flow fields. The capability of dealing with large boundary displacements is demonstrated by computing the flow around the translating infinite- and finite-span NACA 0012 wing moving through the domain at the flight speed. The proposed adaptive scheme is applied also to the simulation of a pitching infinite-span wing, where the bi-dimensional character of the flow is well reproduced despite the three-dimensional unstructured Grid. Finally, the scheme is exploited in a piston-induced shock-tube problem to take into account simultaneously the large deformation of the domain and the shock wave. In all tests, mesh adaptation plays a crucial role.
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finite volume solution of two dimensional compressible flows over dynamic adaptive Grids
Journal of Computational Physics, 2015Co-Authors: D Isola, A Guardone, Giuseppe QuarantaAbstract:A novel Finite Volume (FV) technique for solving the compressible unsteady Euler equations is presented for two-dimensional adaptive Grids over time dependent geometries. The interpretation of the Grid modifications as continuous deformations of the underlying discrete finite volumes allows to determine the solution over the new Grid by direct integration of the governing equations within the Arbitrary Lagrangian-Eulerian (ALE) framework, without any explicit interpolation step. The Grid adaptation is performed using a suitable mix of Grid deformation, edge-swapping, node insertion and node removal techniques in order to comply with the displacement of the boundaries of the computational domain and to preserve the Quality of the Grid elements. Both steady and unsteady simulations over adaptive Grids are presented that demonstrate the validity of the proposed approach. The adaptive ALE scheme is used to perform high-resolution computations of the steady flow past a translating airfoil and of the unsteady flow of a pitching airfoil in both the airfoil and the laboratory reference, with airfoil displacement as large as 200 airfoil chords. Grid adaptation is found to be of paramount importance to preserve the Grid Quality in the considered problems.
Waad Saftly - One of the best experts on this subject based on the ideXlab platform.
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hierarchical octree and k d tree Grids for 3d radiative transfer simulations
Astronomy and Astrophysics, 2014Co-Authors: Waad Saftly, M Baes, Peter CampsAbstract:Context. A crucial ingredient for numerically solving the three-dimensional radiative transfer problem is the choice of the Grid that discretizes the transfer medium. Many modern radiative transfer codes, whether using Monte Carlo or ray tracing techniques, are equipped with hierarchical octree-based Grids to accommodate a wide dynamic range in densities. Aims. We critically investigate two different aspects of octree Grids in the framework of Monte Carlo dust radiative transfer. Inspired by their common use in computer graphics applications, we test hierarchical k-d tree Grids as an alternative for octree Grids. On the other hand, we investigate which node subdivision-stopping criteria are optimal for constructing of hierarchical Grids. Methods. We implemented a k-d tree Grid in the 3D radiative transfer code SKIRT and compared it with the previously implemented octree Grid. We also considered three different node subdivision-stopping criteria (based on mass, optical depth, and density gradient thresholds). Based on a small suite of test models, we compared the efficiency and accuracy of the different Grids, according to various Quality metrics. Results. For a given set of requirements, the k-d tree Grids only require half the number of cells of the corresponding octree. Moreover, for the same number of Grid cells, the k-d tree is characterized by higher discretization accuracy. Concerning the subdivision stopping criteria, we find that an optical depth criterion is not a useful alternative to the more standard mass threshold, since the resulting Grids show a poor accuracy. Both criteria can be combined; however, in the optimal combination, for which we provide a simple approximate recipe, this can lead to a 20% reduction in the number of cells needed to reach a certain Grid Quality. An additional density gradient threshold criterion can be added that solves the problem of poorly resolving sharp edges and strong density gradients. Conclusions. We advocate the use of k-d trees and the proposed combination of criteria to set up hierarchical Grids for 3D radiative transfer. These recipes are straightforward for implementing and should help to develop faster and more accurate 3D radiative transfer codes.
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hierarchical octree and k d tree Grids for 3d radiative transfer simulations
arXiv: Instrumentation and Methods for Astrophysics, 2013Co-Authors: Waad Saftly, M Baes, Peter CampsAbstract:A crucial ingredient for numerically solving the 3D radiative transfer problem is the choice of the Grid that discretizes the transfer medium. Many modern radiative transfer codes, whether using Monte Carlo or ray tracing techniques, are equipped with hierarchical octree-based Grids to accommodate a wide dynamic range in densities. We critically investigate two different aspects of octree Grids in the framework of Monte Carlo dust radiative transfer. Inspired by their common use in computer graphics applications, we test hierarchical k-d tree Grids as an alternative for octree Grids. On the other hand, we investigate which node subdivision-stopping criteria are optimal for constructing of hierarchical Grids. We implemented a k-d tree Grid in the 3D radiative transfer code SKIRT and compared it with the previously implemented octree Grid. We also considered three different node subdivision-stopping criteria (based on mass, optical depth, and density gradient thresholds). Based on a small suite of test models, we compared the efficiency and accuracy of the different Grids, according to various Quality metrics. For a given set of requirements, the k-d tree Grids only require half the number of cells of the corresponding octree. Moreover, for the same number of Grid cells, the k-d tree is characterized by higher discretization accuracy. Concerning the subdivision stopping criteria, we find that an optical depth criterion is not a useful alternative to the more standard mass threshold, since the resulting Grids show a poor accuracy. Both criteria can be combined; however, in the optimal combination, for which we provide a simple approximate recipe, this can lead to a 20% reduction in the number of cells needed to reach a certain Grid Quality. An additional density gradient threshold criterion can be added that solves the problem of poorly resolving sharp edges and... (abridged).
P G Tucker - One of the best experts on this subject based on the ideXlab platform.
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A semi-implicit immersed boundary method for simulating viscous flow-induced sound with moving boundaries
2021Co-Authors: Cheng L, Du L, Wang X, Sun X, P G TuckerAbstract:© 2020 Elsevier B.V. In this paper, a semi-implicit immersed boundary body force model is derived from the compressible Navier–Stokes equations, to directly predict the viscous flow-induced sound from moving objects on a fixed Cartesian Grid. To overcome the conflict of Grid Quality with efficiency in simulating moving-boundary problems with high-order computational aeroacoustics methods, a prediction–correction technique is utilized. This accurately satisfies no-slip wall boundary conditions at every time step without any feedback treatment. A particular contribution of the work is the introduction of a numerical model equation to analyze the body force convergence. This is useful to pre-evaluate the generated Cartesian and body-surface Grids. Several benchmark aeroacoustic problems are simulated to validate the present model. Results show that the unsteady force and far-field sound directivity agree well with the previous direct numerical simulation results. The work further suggests that the developed body force model/CAA methods are capable of predicting interaction noise, especially those associated with oscillating multiple objects
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A semi-implicit immersed boundary method for simulating viscous flow-induced sound with moving boundaries
2021Co-Authors: Cheng L, Du L, Wang X, Sun X, P G TuckerAbstract:In this paper, a semi-implicit immersed boundary body force model is derived from the compressible Navier–Stokes equations, to directly predict the viscous flow-induced sound from moving objects on a fixed Cartesian Grid. To overcome the conflict of Grid Quality with efficiency in simulating moving-boundary problems with high-order computational aeroacoustics methods, a prediction–correction technique is utilized. This accurately satisfies no-slip wall boundary conditions at every time step without any feedback treatment. A particular contribution of the work is the introduction of a numerical model equation to analyze the body force convergence. This is useful to pre-evaluate the generated Cartesian and body-surface Grids. Several benchmark aeroacoustic problems are simulated to validate the present model. Results show that the unsteady force and far-field sound directivity agree well with the previous direct numerical simulation results. The work further suggests that the developed body force model/CAA methods are capable of predicting interaction noise, especially those associated with oscillating multiple objects
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hybrid hamilton jacobi poisson wall distance function model
Computers & Fluids, 2011Co-Authors: P G TuckerAbstract:Abstract Expensive to compute wall distances are used in key turbulence models and also for the modeling of peripheral physics. A potentially economical, robust, readily parallel processed, accuracy improving, differential equation based distance algorithm is described. It is hybrid, partly utilising an approximate Poisson equation. This also allows auxiliary front propagation direction/velocity information to be estimated, effectively giving wall normals. The Poisson normal can be used fully, in an approximate solution of the eikonal equation (the exact differential equation for wall distance). Alternatively, a weighted fraction of this Poisson front direction (effectively, front velocity, in terms of the eikonal equation input) information and that implied by the eikonal equation can be used. Either results in a hybrid Poisson–eikonal wall distance algorithm. To improve compatibility of wall distance functions with turbulence physics a Laplacian is added to the eikonal equation. This gives what is termed a Hamilton–Jacobi equation. This hybrid Poisson–Hamilton–Jacobi approach is found to be robust on poor Quality Grids. The robustness largely results from the elliptic background presence of the Poisson equation. This elliptic component prevents fronts propagated from solid surfaces, by the hyperbolic eikonal equation element, reflecting off zones of rapidly changing Grid density. Where this reflection (due to poor Grid Quality) is extreme, the transition of front velocity information from the Poisson to Hamilton–Jacobi equation can be done more gradually. Consistent with turbulence modeling physics, under user control, the hybrid equation can overestimate the distance function strongly around convex surfaces and underestimate it around concave. If the former trait is not desired the current approach is amenable to zonalisation. With this, the Poisson element is automatically removed around convex geometry zones.
