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Articoli di riviste sul tema "Hybrid Cartesian/unstructured meshes"

Autore: Grafiati

Pubblicato: 25 gennaio 2025

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1

Gansen, A., M. El Hachemi, S. Belouettar, O. Hassan e K. Morgan. "A 3D Unstructured Mesh FDTD Scheme for EM Modelling". Archives of Computational Methods in Engineering 28, n. 1 (17 gennaio 2020): 181–213. http://dx.doi.org/10.1007/s11831-019-09395-z.

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AbstractThe Yee finite difference time domain (FDTD) algorithm is widely used in computational electromagnetics because of its simplicity, low computational costs and divergence free nature. The standard method uses a pair of staggered orthogonal cartesian meshes. However, accuracy losses result when it is used for modelling electromagnetic interactions with objects of arbitrary shape, because of the staircased representation of curved interfaces. For the solution of such problems, we generalise the approach and adopt an unstructured mesh FDTD method. This co-volume method is based upon the use of a Delaunay primal mesh and its high quality Voronoi dual. Computational efficiency is improved by employing a hybrid primal mesh, consisting of tetrahedral elements in the vicinity of curved interfaces and hexahedral elements elsewhere. Difficulties associated with ensuring the necessary quality of the generated meshes will be discussed. The power of the proposed solution approach is demonstrated by considering a range of scattering and/or transmission problems involving perfect electric conductors and isotropic lossy, anisotropic lossy and isotropic frequency dependent chiral materials.

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2

Busto, Saray, Michael Dumbser e Laura Río-Martín. "Staggered Semi-Implicit Hybrid Finite Volume/Finite Element Schemes for Turbulent and Non-Newtonian Flows". Mathematics 9, n. 22 (21 novembre 2021): 2972. http://dx.doi.org/10.3390/math9222972.

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This paper presents a new family of semi-implicit hybrid finite volume/finite element schemes on edge-based staggered meshes for the numerical solution of the incompressible Reynolds-Averaged Navier–Stokes (RANS) equations in combination with the k−ε turbulence model. The rheology for calculating the laminar viscosity coefficient under consideration in this work is the one of a non-Newtonian Herschel–Bulkley (power-law) fluid with yield stress, which includes the Bingham fluid and classical Newtonian fluids as special cases. For the spatial discretization, we use edge-based staggered unstructured simplex meshes, as well as staggered non-uniform Cartesian grids. In order to get a simple and computationally efficient algorithm, we apply an operator splitting technique, where the hyperbolic convective terms of the RANS equations are discretized explicitly at the aid of a Godunov-type finite volume scheme, while the viscous parabolic terms, the elliptic pressure terms and the stiff algebraic source terms of the k−ε model are discretized implicitly. For the discretization of the elliptic pressure Poisson equation, we use classical conforming P1 and Q1 finite elements on triangles and rectangles, respectively. The implicit discretization of the viscous terms is mandatory for non-Newtonian fluids, since the apparent viscosity can tend to infinity for fluids with yield stress and certain power-law fluids. It is carried out with P1 finite elements on triangular simplex meshes and with finite volumes on rectangles. For Cartesian grids and more general orthogonal unstructured meshes, we can prove that our new scheme can preserve the positivity of k and ε. This is achieved via a special implicit discretization of the stiff algebraic relaxation source terms, using a suitable combination of the discrete evolution equations for the logarithms of k and ε. The method is applied to some classical academic benchmark problems for non-Newtonian and turbulent flows in two space dimensions, comparing the obtained numerical results with available exact or numerical reference solutions. In all cases, an excellent agreement is observed.

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3

Hoagland, Dylan S., e Yousry Y. Azmy. "PARAMETRIC STUDY OF PARALLEL BLOCK JACOBI / SOURCE ITERATION HYBRID METHODS IN 2-D CARTESIAN GEOMETRY AND CONSTRUCTION OF THE INTEGRAL TRANSPORT MATRIX METHOD MATRICES VIA GREEN’S FUNCTIONS". EPJ Web of Conferences 247 (2021): 03017. http://dx.doi.org/10.1051/epjconf/202124703017.

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Parallel Block Jacobi (PBJ) [1] is an asynchronous spatial domain decomposition with application in solving the neutron transport equation due to its extendibility to massively parallel solution in unstructured spatial meshes (grids) without the use of the computationally complex and expensive sweeps required by the Source Iteration (SI) method in these applications. [2] However, PBJ iterative methods suffer a lack of iterative robustness in problems with optically thin cells, [1] which we have previously demonstrated to be a consequence of PBJ’s asynchronicity. To mitigate this effect, we have developed multiple PBJ / SI hybrid methods which employ a PBJ method (Parallel Block Jacobi - Integral Transport Matrix Method (PBJ-ITMM) or Inexact Parallel Block Jacobi (IPBJ)) along with SI. [3,4] In this work, we perform a parametric study to determine performance of numerous PBJ / SI hybrid methods as a function of multiple problem parameters. This parametric study reached 5 main conclusions: 1) our hybrid approach is more effective with PBJ-ITMM than with IPBJ, 2) for PBJ-ITMM, there is a hybrid method that mitigates the aforementioned iterative slowdown in optically thin cells without diminishing the method’s potential parallelism in unstructured grids, 3) this hybrid method is most effective in problems with large, continuous regions of very thin cells, 4) the best performing hybrid method consistently executes within a factor of ten slower than current state-of-the-art acceleration methods that are not efficiently extendable to the massively parallel regime, and 5) both PBJ-ITMM and IPBJ are observed to be viable approaches for our desired applications. In the pursuit of implementing PBJ-ITMM in unstructured grids, we conclude with a description of the Green’s Function ITMM Construction (GFIC) algorithm, which allows for the ITMM matrices to be constructed using the pre-existing SI sweep algorithm already present in unstructured grid SN transport codes.

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4

Zhang, Yang, e Chunhua Zhou. "Reduction of Numerical Oscillations in Simulating Moving-Boundary Problems by the Local DFD Method". Advances in Applied Mathematics and Mechanics 8, n. 1 (21 dicembre 2015): 145–65. http://dx.doi.org/10.4208/aamm.2014.m590.

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AbstractIn this work, the hybrid solution reconstruction formulation proposed by Luo et al. [H. Luo, H. Dai, P. F. de Sousa and B. Yin, On the numerical oscillation of the direct-forcing immersed-boundary method for moving boundaries, Computers & Fluids, 56 (2012), pp. 61–76] for the finite-difference discretization on Cartesian meshes is implemented in the finite-element framework of the local domain-free discretization (DFD) method to reduce the numerical oscillations in the simulation of moving-boundary flows. The reconstruction formulation is applied at fluid nodes in the immediate vicinity of the immersed boundary, which combines weightly the local DFD solution with the specific values obtained via an approximation of quadratic polynomial in the normal direction to the wall. The quadratic approximation is associated with the no-slip boundary condition and the local simplified momentum equation. The weighted factor suitable for unstructured triangular and tetrahedral meshes is constructed, which is related to the local mesh intervals near the immersed boundary and the distances from exterior dependent nodes to the boundary. Therefore, the reconstructed solution can account for the smooth movement of the immersed boundary. Several numerical experiments have been conducted for two- and three-dimensional moving-boundary flows. It is shown that the hybrid reconstruction approach can work well in the finite-element context and effectively reduce the numerical oscillations with little additional computational cost, and the spatial accuracy of the original local DFD method can also be preserved.

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5

Rüger, Andreas, e Dave Hale. "Meshing for velocity modeling and ray tracing in complex velocity fields". GEOPHYSICS 71, n. 1 (gennaio 2006): U1—U11. http://dx.doi.org/10.1190/1.2159061.

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In seismic processing, velocity fields are commonly represented on finely sampled Cartesian grids. Attractive alternatives are unstructured grids such as meshes composed of triangles or tetrahedra. Meshes provide a space-filling framework that enables editing of velocity models while facilitating numerical tasks such as seismic modeling and inversion. In this paper, we introduce an automated process to generate meshes of subsurface velocity structures for highly resolved velocity fields without providing additional external constraints such as horizons and faults. Our analysis shows that these new meshes can represent both smooth and discontinuous velocity profiles accurately and with less computer memory than grids.

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6

Wei, Ran, Futing Bao, Yang Liu e Weihua Hui. "Robust Three-Dimensional Level-Set Method for Evolving Fronts on Complex Unstructured Meshes". Mathematical Problems in Engineering 2018 (25 settembre 2018): 1–15. http://dx.doi.org/10.1155/2018/2730829.

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With a purpose to evolve the surfaces of complex geometries in their normal direction at arbitrarily defined velocities, we have developed a robust level-set approach which runs on three-dimensional unstructured meshes. The approach is built on the basis of an innovative spatial discretization and corresponding gradient-estimating approach. The numerical consistency of the estimating method is mathematically proven. A correction technology is utilized to improve accuracy near sharp geometric features. Validation tests show that the proposed approach is able to accurately handle geometries containing sharp features, computation regions having irregular shapes, discontinuous speed fields, and topological changes. Results of the test problems fit well with the reference results produced by analytical or other numerical methods and converge to reference results as the meshes refine. Compared to level-set method implementations on Cartesian meshes, the proposed approach makes it easier to describe jump boundary conditions and to perform coupling simulations.

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7

Fridrich, David, Richard Liska, Ivan Tarant, Pavel Váchal e Burton Wendroff. "CELL-CENTERED LAGRANGIAN LAX-WENDROFF HLL HYBRID SCHEME ON UNSTRUCTURED MESHES". Acta Polytechnica 61, SI (10 febbraio 2021): 68–76. http://dx.doi.org/10.14311/ap.2021.61.0068.

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We have recently introduced a new cell-centered Lax-Wendroff HLL hybrid scheme for Lagrangian hydrodynamics [Fridrich et al. J. Comp. Phys. 326 (2016) 878-892] with results presented only on logical rectangular quadrilateral meshes. In this study we present an improved version on unstructured meshes, including uniform triangular and hexagonal meshes and non-uniform triangular and polygonal meshes. The performance of the scheme is verified on Noh and Sedov problems and its second-order convergence is verified on a smooth expansion test.Finally the choice of the scalar parameter controlling the amount of added artificial dissipation is studied.

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8

Skamarock, William C., Joseph B. Klemp, Michael G. Duda, Laura D. Fowler, Sang-Hun Park e Todd D. Ringler. "A Multiscale Nonhydrostatic Atmospheric Model Using Centroidal Voronoi Tesselations and C-Grid Staggering". Monthly Weather Review 140, n. 9 (1 settembre 2012): 3090–105. http://dx.doi.org/10.1175/mwr-d-11-00215.1.

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Abstract The formulation of a fully compressible nonhydrostatic atmospheric model called the Model for Prediction Across Scales–Atmosphere (MPAS-A) is described. The solver is discretized using centroidal Voronoi meshes and a C-grid staggering of the prognostic variables, and it incorporates a split-explicit time-integration technique used in many existing nonhydrostatic meso- and cloud-scale models. MPAS can be applied to the globe, over limited areas of the globe, and on Cartesian planes. The Voronoi meshes are unstructured grids that permit variable horizontal resolution. These meshes allow for applications beyond uniform-resolution NWP and climate prediction, in particular allowing embedded high-resolution regions to be used for regional NWP and regional climate applications. The rationales for aspects of this formulation are discussed, and results from tests for nonhydrostatic flows on Cartesian planes and for large-scale flow on the sphere are presented. The results indicate that the solver is as accurate as existing nonhydrostatic solvers for nonhydrostatic-scale flows, and has accuracy comparable to existing global models using icosahedral (hexagonal) meshes for large-scale flows in idealized tests. Preliminary full-physics forecast results indicate that the solver formulation is robust and that the variable-resolution-mesh solutions are well resolved and exhibit no obvious problems in the mesh-transition zones.

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9

Ahuja, Vineet, Ashvin Hosangadi e Srinivasan Arunajatesan. "Simulations of Cavitating Flows Using Hybrid Unstructured Meshes". Journal of Fluids Engineering 123, n. 2 (29 gennaio 2001): 331–40. http://dx.doi.org/10.1115/1.1362671.

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A new multi-phase model for low speed gas/liquid mixtures is presented; it does not require ad-hoc closure models for the variation of mixture density with pressure and yields thermodynamically correct acoustic propagation for multi-phase mixtures. The solution procedure has an interface-capturing scheme that incorporates an additional scalar transport equation for the gas void fraction. Cavitation is modeled via a finite rate source term that initiates phase change when liquid pressure drops below its saturation value. The numerical procedure has been implemented within a multi-element unstructured framework CRUNCH that permits the grid to be locally refined in the interface region. The solution technique incorporates a parallel, domain decomposition strategy for efficient 3D computations. Detailed results are presented for sheet cavitation over a cylindrical head form and a NACA 66 hydrofoil.

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10

Mut, Fernando, Gustavo C. Buscaglia e Enzo A. Dari. "New Mass-Conserving Algorithm for Level Set Redistancing on Unstructured Meshes". Journal of Applied Mechanics 73, n. 6 (1 febbraio 2006): 1011–16. http://dx.doi.org/10.1115/1.2198244.

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The level set method is becoming increasingly popular for the simulation of several problems that involve interfaces. The level set function is advected by some velocity field, with the zero-level set of the function defining the position of the interface. The advection distorts the initial shape of the level set function, which needs to be re-initialized to a smooth function preserving the position of the zero-level set. Many algorithms re-initialize the level set function to (some approximation of) the signed distance from the interface. Efficient algorithms for level set redistancing on Cartesian meshes have become available over the last years, but unstructured meshes have received little attention. This presentation concerns algorithms for construction of a distance function from the zero-level set, in such a way that mass is conserved on arbitrary unstructured meshes. The algorithm is consistent with the hyperbolic character of the distance equation (‖∇d‖=1) and can be localized on a narrow band close to the interface, saving computing effort. The mass-correction step is weighted according to local mass differences, an improvement over usual global rebalancing techniques.

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11

Jung, Min Kyu, e Oh Joon Kwon. "Development of a 2-D flow solver on unstructured and adaptive Cartesian meshes". Journal of Mechanical Science and Technology 26, n. 12 (dicembre 2012): 3989–97. http://dx.doi.org/10.1007/s12206-012-0893-6.

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12

Sørensen, K. A., O. Hassan, K. Morgan e N. P. Weatherill. "Agglomerated multigrid on hybrid unstructured meshes for compressible flow". International Journal for Numerical Methods in Fluids 40, n. 3-4 (20 settembre 2002): 593–603. http://dx.doi.org/10.1002/fld.316.

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13

Pan, Dartzi. "An Immersed Boundary Method on Unstructured Cartesian Meshes for Incompressible Flows with Heat Transfer". Numerical Heat Transfer, Part B: Fundamentals 49, n. 3 (settembre 2006): 277–97. http://dx.doi.org/10.1080/10407790500290709.

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14

Nakahashi, Kazuhiro. "Aeronautical CFD in the age of Petaflops-scale computing: From unstructured to Cartesian meshes". European Journal of Mechanics - B/Fluids 40 (luglio 2013): 75–86. http://dx.doi.org/10.1016/j.euromechflu.2013.02.005.

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15

Androsov, Alexey, Vera Fofonova, Ivan Kuznetsov, Sergey Danilov, Natalja Rakowsky, Sven Harig, Holger Brix e Karen Helen Wiltshire. "FESOM-C v.2: coastal dynamics on hybrid unstructured meshes". Geoscientific Model Development 12, n. 3 (21 marzo 2019): 1009–28. http://dx.doi.org/10.5194/gmd-12-1009-2019.

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Abstract. We describe FESOM-C, the coastal branch of the Finite-volumE Sea ice – Ocean Model (FESOM2), which shares with FESOM2 many numerical aspects, in particular its finite-volume cell-vertex discretization. Its dynamical core differs in the implementation of time stepping, the use of a terrain-following vertical coordinate, and the formulation for hybrid meshes composed of triangles and quads. The first two distinctions were critical for coding FESOM-C as an independent branch. The hybrid mesh capability improves numerical efficiency, since quadrilateral cells have fewer edges than triangular cells. They do not suffer from spurious inertial modes of the triangular cell-vertex discretization and need less dissipation. The hybrid mesh capability allows one to use quasi-quadrilateral unstructured meshes, with triangular cells included only to join quadrilateral patches of different resolution or instead of strongly deformed quadrilateral cells. The description of the model numerical part is complemented by test cases illustrating the model performance.

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Bakhvalov, Pavel Alexeevisch. "Implementation of the Flux Correction method on hybrid unstructured meshes". Keldysh Institute Preprints, n. 38 (2017): 1–28. http://dx.doi.org/10.20948/prepr-2017-38.

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Ahn, Hyung Taek, e Graham F. Carey. "An enhanced polygonal finite-volume method for unstructured hybrid meshes". International Journal for Numerical Methods in Fluids 54, n. 1 (2007): 29–46. http://dx.doi.org/10.1002/fld.1390.

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18

Yang, S. Y., e K. H. Chen. "Numerical Study of Turbulent Flows Over Vibrating Blades with Positive Interblade Phase Angle". Journal of Mechanics 23, n. 2 (giugno 2007): 149–58. http://dx.doi.org/10.1017/s1727719100001179.

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AbstractIn this paper, a locally implicit scheme on unstructured dynamic meshes is presented to study transonic turbulent flows over vibrating blades with positive interblade phase angle. The unsteady Favre-averaged Navier-Stokes equations with moving domain effects and a low- Reynolds-number k-ε turbulence model are solved in the Cartesian coordinate system. To treat the viscous flux on quadrilateral-triangular meshes, the first-order derivatives of velocity components and temperature are calculated by constructing auxiliary cells and Green's theorem for surface integration is applied. The assessment of accuracy of the present scheme on quadrilateral-triangular meshes is conducted through the calculation of the turbulent flow around an NACA 0012 airfoil. Based on the comparison with the experimental data, the accuracy of the present approach is confirmed. From the distributions of magnitude of the first harmonic dynamic pressure difference coefficient which include the present solution and the related experimental and numerical results, it is found that the present solution approach is reliable and acceptable. The unsteady pressure wave, shock wave and vortex-shedding phenomena are demonstrated and discussed.

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Schlottke-Lakemper, Michael, Hans Yu, Sven Berger, Matthias Meinke e Wolfgang Schröder. "A fully coupled hybrid computational aeroacoustics method on hierarchical Cartesian meshes". Computers & Fluids 144 (febbraio 2017): 137–53. http://dx.doi.org/10.1016/j.compfluid.2016.12.001.

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20

Li, Jinxi, Jie Zheng, Jiang Zhu, Fangxin Fang, Christopher Pain, Jürgen Steppeler, Michael Navon e Hang Xiao. "Performance of Adaptive Unstructured Mesh Modelling in Idealized Advection Cases over Steep Terrains". Atmosphere 9, n. 11 (13 novembre 2018): 444. http://dx.doi.org/10.3390/atmos9110444.

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Advection errors are common in basic terrain-following (TF) coordinates. Numerous methods, including the hybrid TF coordinate and smoothing vertical layers, have been proposed to reduce the advection errors. Advection errors are affected by the directions of velocity fields and the complexity of the terrain. In this study, an unstructured adaptive mesh together with the discontinuous Galerkin finite element method is employed to reduce advection errors over steep terrains. To test the capability of adaptive meshes, five two-dimensional (2D) idealized tests are conducted. Then, the results of adaptive meshes are compared with those of cut-cell and TF meshes. The results show that using adaptive meshes reduces the advection errors by one to two orders of magnitude compared to the cut-cell and TF meshes regardless of variations in velocity directions or terrain complexity. Furthermore, adaptive meshes can reduce the advection errors when the tracer moves tangentially along the terrain surface and allows the terrain to be represented without incurring in severe dispersion. Finally, the computational cost is analyzed. To achieve a given tagging criterion level, the adaptive mesh requires fewer nodes, smaller minimum mesh sizes, less runtime and lower proportion between the node numbers used for resolving the tracer and each wavelength than cut-cell and TF meshes, thus reducing the computational costs.

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Pei, Weicheng, Yuyan Jiang e Shu Li. "High-Order CFD Solvers on Three-Dimensional Unstructured Meshes: Parallel Implementation of RKDG Method with WENO Limiter and Momentum Sources". Aerospace 9, n. 7 (11 luglio 2022): 372. http://dx.doi.org/10.3390/aerospace9070372.

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In aerospace engineering, high-order computational fluid dynamics (CFD) solvers suitable for three-dimensional unstructured meshes are less developed than expected. The Runge–Kutta discontinuous Galerkin (RKDG) finite element method with compact weighted essentially non-oscillatory (WENO) limiters is one of the candidates, which might give high-order solutions on unstructured meshes. In this article, we provide an efficient parallel implementation of this method for simulating inviscid compressible flows. The implemented solvers are tested on lower-dimensional model problems and real three-dimensional engineering problems. Results of lower-dimensional problems validate the correctness and accuracy of these solvers. The capability of capturing complex flow structures even on coarse meshes is shown in the results of three-dimensional applications. For solving problems containing rotary wings, an unsteady momentum source model is incorporated into the solvers. Such a finite element/momentum source hybrid method eliminates the reliance on advanced mesh techniques, which might provide an efficient tool for studying rotorcraft aerodynamics.

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Marić, Tomislav, Holger Marschall e Dieter Bothe. "lentFoam – A hybrid Level Set/Front Tracking method on unstructured meshes". Computers & Fluids 113 (maggio 2015): 20–31. http://dx.doi.org/10.1016/j.compfluid.2014.12.019.

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Peters, Sergio, e Clovis R. Maliska. "A staggered grid arrangement for solving incompressible flows with hybrid unstructured meshes". Numerical Heat Transfer, Part B: Fundamentals 71, n. 1 (2 gennaio 2017): 50–65. http://dx.doi.org/10.1080/10407790.2016.1257221.

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Lin, T. J., Z. Q. Guan, J. H. Chang e S. H. Lo. "Vertex-Ball Spring Smoothing: An efficient method for unstructured dynamic hybrid meshes". Computers & Structures 136 (maggio 2014): 24–33. http://dx.doi.org/10.1016/j.compstruc.2014.01.028.

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Maltsev, Vadim, Dean Yuan, Karl W. Jenkins, Martin Skote e Panagiotis Tsoutsanis. "Hybrid discontinuous Galerkin-finite volume techniques for compressible flows on unstructured meshes". Journal of Computational Physics 473 (gennaio 2023): 111755. http://dx.doi.org/10.1016/j.jcp.2022.111755.

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Zeng, Yao Yuan, Wen Tao Zhao e Zheng Hua Wang. "A Hybrid Hypergraph Partitioning Algorithm for Scientific Computing". Advanced Materials Research 753-755 (agosto 2013): 2900–2903. http://dx.doi.org/10.4028/www.scientific.net/amr.753-755.2900.

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Hypergraph partitioning is an increasingly important and widely studied research topic in parallel scientific computing. In this paper, we present a multiway hypergraph partitioning algorithm, mixed simulated annealing algorithm for global optimization and tabu search algorithm for local optimization. Experiments on the benchmark suite of several unstructured meshes show that, for 2-, 4-, 8-, 16-and 32-way partitioning, the quality of partition produced by our algorithm are on the average 6% and the maximum 17% better than those produced by partitioning software hMETIS in term of the cutsize metric.

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Degond, Pierre, Alexei Lozinski, Bagus Putra Muljadi e Jacek Narski. "Crouzeix-Raviart MsFEM with Bubble Functions for Diffusion and Advection-Diffusion in Perforated Media". Communications in Computational Physics 17, n. 4 (aprile 2015): 887–907. http://dx.doi.org/10.4208/cicp.2014.m299.

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AbstractThe adaptation of Crouzeix-Raviart finite element in the context of multi-scale finite element method (MsFEM) is studied and implemented on diffusion and advection-diffusion problems in perforated media. It is known that the approximation of boundary condition on coarse element edges when computing the multiscale basis functions critically influences the eventual accuracy of any MsFEM approaches. The weakly enforced continuity of Crouzeix-Raviart function space across element edges leads to a natural boundary condition for the multiscale basis functions which relaxes the sensitivity of our method to complex patterns of perforations. Another ingredient to our method is the application of bubble functions which is shown to be instrumental in maintaining high accuracy amid dense perforations. Additionally, the application of penalization method makes it possible to avoid complex unstructured domain and allows extensive use of simpler Cartesian meshes.

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Płażek, Joanna, Krzysztof Banaś e Jacek Kitowski. "Comparison of Message-Passing and Shared Memory Implementations of the GMRES Method on MIMD Computers". Scientific Programming 9, n. 4 (2001): 195–209. http://dx.doi.org/10.1155/2001/681621.

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In this paper we compare different parallel implementations of the same algorithm for solving nonlinear simulation problems on unstructured meshes. In the first implementation, making use of the message-passing programming model and the PVM system, the domain decomposition of unstructured mesh is implemented, while the second implementation takes advantage of the inherent parallelism of the algorithm by adopting the shared-memory programming model. Both implementations are applied to the preconditioned GMRES method that solves iteratively the system of linear equations. A combined approach, the hybrid programming model suitable for multicomputers with SMP nodes, is introduced. For performance measurements we use compressible fluid flow simulation in which sequences of finite element solutions form time approximations to the Euler equations. The tests are performed on HP SPP1600, HP S2000 and SGI Origin2000 multiprocessors and report wall-clock execution time and speedup for different number of processing nodes and for different meshes. Experimentally, the explicit programming model proves to be more efficient than the implicit model by 20—70%, depends on the mesh and the machine.

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Bergot, Morgane, e Marc Duruflé. "Approximation of H(div) with High-Order Optimal Finite Elements for Pyramids, Prisms and Hexahedra". Communications in Computational Physics 14, n. 5 (novembre 2013): 1372–414. http://dx.doi.org/10.4208/cicp.120712.080313a.

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AbstractClassical facet elements do not provide an optimal rate of convergence of the numerical solution toward the solution of the exact problem in H(div-norm for general unstructured meshes containing hexahedra and prisms. We propose two new families of high-order elements for hexahedra, triangular prisms and pyramids that recover the optimal convergence. These elements have compatible restrictions with each other, such that they can be used directly on general hybrid meshes. Moreover the H(div) proposed spaces are completing the De Rham diagram with optimal elements previously constructed for H1 and H(curl) approximation. The obtained pyramidal elements are compared theoretically and numerically with other elements of the literature. Eventually, numerical results demonstrate the efficiency of the finite elements constructed.

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Hwang, C. J., e J. L. Liu. "Inviscid and Viscous Solutions for Airfoil/Cascade Flows Using a Locally Implicit Algorithm on Adaptive Meshes". Journal of Turbomachinery 113, n. 4 (1 ottobre 1991): 553–60. http://dx.doi.org/10.1115/1.2929114.

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A numerical solution procedure, which includes a locally implicit finite volume scheme and an adaptive mesh generation technique, has been developed to study airfoil and cascade flows. The Euler/Navier–Stokes, continuity, and energy equations, in conjunction with Baldwin-Lomax model for turbulent flow, are solved in the Cartesian coordinate system. To simulate physical phenomena efficiently and correctly, a mixed type of mesh, with unstructured triangular cells for the inviscid region and structured quadrilateral cells for the viscous, boundary layer, and wake regions, is introduced in this work. The inviscid flow passing through a channel with circular arc bump and the laminar flows over a flat plate with/without shock interaction are investigated to confirm the accuracy, convergence, and solution-adaptibility of the numerical approach. To prove the reliability and capability of the present solution procedure further, the inviscid/viscous results for flows over the NACA 0012 airfoil, NACA 65-(12)10 compressor, and one advanced transonic turbine cascade are compared to the numerical and experimental data given in related papers and reports.

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31

HITOMI, Daisuke, Takashi NAKAMURA, Yasutaka SEINO, Shiro IKUTA e Hitoshi SUGIYAMA. "10308 Numerical Analysis of Flows in the Multi-branch Ducts Using Hybrid Unstructured Meshes". Proceedings of Conference of Kanto Branch 2006.12 (2006): 347–48. http://dx.doi.org/10.1299/jsmekanto.2006.12.347.

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32

Oyarzun, G., R. Borrell, A. Gorobets, O. Lehmkuhl e A. Oliva. "Direct Numerical Simulation of Incompressible Flows on Unstructured Meshes Using Hybrid CPU/GPU Supercomputers". Procedia Engineering 61 (2013): 87–93. http://dx.doi.org/10.1016/j.proeng.2013.07.098.

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33

Asada, Hiroyuki, Yousuke Ogino, Kanako Yasue e Keisuke Sawada. "A Third Order Accurate Cellwise Relaxation Implicit Discontinuous Galerkin Scheme for Unstructured Hybrid Meshes". Mathematical Problems in Engineering 2014 (2014): 1–20. http://dx.doi.org/10.1155/2014/176752.

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A third order accurate cellwise relaxation implicit Discontinuous Galerkin (DG) scheme for RANS simulations using unstructured hybrid meshes is presented. A scalar parabolic equation is first examined to clarify what is really important in construction of implicit matrix to keep its diagonal dominance for the third and fourth order cellwise relaxation implicit DG schemes. In addition, discussions are given to approximated construction of implicit matrix for reducing computational cost. Then, the third order accurate cellwise relaxation implicit DG scheme for RANS simulations is successfully developed utilizing the expertise learned in the study of solving the parabolic equation. Superior spatial accuracy of the third order accurate cellwise relaxation implicit DG scheme for RANS simulations, while retaining reasonable convergence properties, is demonstrated for typical aerospace applications.

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34

Friess, Marie Billaud, Jérôme Breil, Pierre-Henri Maire e Mikhail Shashkov. "A Multi-Material CCALE-MOF Approach in Cylindrical Geometry". Communications in Computational Physics 15, n. 2 (febbraio 2014): 330–64. http://dx.doi.org/10.4208/cicp.190912.080513a.

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AbstractIn this paper we present recent developments concerning a Cell-Centered Arbitrary Lagrangian Eulerian (CCALE) strategy using the Moment Of Fluid (MOF) interface reconstruction for the numerical simulation of multi-material compressible fluid flows on unstructured grids in cylindrical geometries. Especially, our attention is focused here on the following points. First, we propose a new formulation of the scheme used during the Lagrangian phase in the particular case of axisymmetric geometries. Then, the MOF method is considered for multi-interface reconstruction in cylindrical geometry. Subsequently, a method devoted to the rezoning of polar meshes is detailed. Finally, a generalization of the hybrid remapping to cylindrical geometries is presented. These explorations are validated by mean of several test cases using unstructured grid that clearly illustrate the robustness and accuracy of the new method.

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35

Ji, Xing, Wei Shyy e Kun Xu. "A Gradient Compression-Based Compact High-Order Gas-Kinetic Scheme on 3D Hybrid Unstructured Meshes". International Journal of Computational Fluid Dynamics 35, n. 7 (9 agosto 2021): 485–509. http://dx.doi.org/10.1080/10618562.2021.1991329.

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36

Parmananda, Mukul, Amaresh Dalal e Ganesh Natarajan. "Unified framework for buoyancy induced radiative-convective flow and heat transfer on hybrid unstructured meshes". International Journal of Heat and Mass Transfer 126 (novembre 2018): 908–25. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2018.05.092.

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37

May, Georg, Francesca Iacono e Antony Jameson. "A hybrid multilevel method for high-order discretization of the Euler equations on unstructured meshes". Journal of Computational Physics 229, n. 10 (maggio 2010): 3938–56. http://dx.doi.org/10.1016/j.jcp.2010.01.036.

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38

Qi, Yanfu, Xiu Li, Changchun Yin, Zhipeng Qi, Jianmei Zhou, Yunhe Liu e Bo Zhang. "Weighted Goal-oriented Adaptive Finite-element for 3D Transient EM Modeling". Journal of Environmental and Engineering Geophysics 24, n. 2 (giugno 2019): 249–64. http://dx.doi.org/10.2113/jeeg24.2.249.

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The unstructured finite-element method has been widely used in 3D time-domain electromagnetic (EM) modeling due to its flexibility for modeling rugged topography and complex underground structures. However, how to generate high-quality grids becomes the key to high-accuracy EM responses. We have developed a weighted goal-oriented adaptive finite-element method based on hybrid posterior error estimation in combination with unstructured vector finite-element method and Backward Euler scheme to create an effective mesh. By introducing a weighting factor and adjusting the relative weights of the hybrid posterior errors, the numerical accuracy and convergence rate are greatly improved. To handle the huge difference of EM responses at different time channels, we introduce another weighting factor defined by the exponential power of time to achieve a synchronous refinement of shallow and deep meshes. The numerical experiments on a homogenous half-space model show that our algorithm performs better than the traditional adaptive method both from the accuracy and convergence. Further, we also test the effectiveness of our algorithm for modeling different abnormal bodies under a topographic earth.

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39

Subramaniam, S., e D. C. Haworth. "A probability density function method for turbulent mixing and combustion on three-dimensional unstructured deforming meshes". International Journal of Engine Research 1, n. 2 (1 aprile 2000): 171–90. http://dx.doi.org/10.1243/1468087001545128.

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A hybrid Lagrangian-Eulerian methodology is developed for numerical simulation of turbulent mixing and combustion in arbitrary three-dimensional time-dependent geometric configurations. The context is a probability density function (PDF) based approach intended for modelling in cylinder processes in reciprocating piston internal combustion (IC) engines. Issues addressed include mean estimation, particle tracking and particle number-density control on three-dimensional unstructured deforming meshes. The suitability of the methodology for statistically time-dependent three-dimensional turbulent flow with large density variations is demonstrated via simulations of turbulent freon vapour/air mixing on an unstructured deforming mesh representing an idealized IC engine [13]. Computed profiles of mean and r.m.s. freon mole fractions show good quantitative agreement with measurements. Moreover, inherent advantages of the Lagrangian-Eulerian PDF approach are demonstrated, compared to Eulerian finite volume solutions of an (approximately) equivalent set of moment equations. The new approach is, by design, compatible with existing computational fluid dynamics codes that are used for multidimensional modelling of in-cylinder thermal fluids processes. This work broadens the accessibility of PDF methods for practical turbulent combustion systems.

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40

Kim, J. W., e O. J. Kwon. "NUMERICAL STUDY OF VARIABLE GEOMETRY NOZZLE FLOW USING A MESH DEFORMATION TECHNIQUE ON HYBRID UNSTRUCTURED MESHES". Journal of computational fluids engineering 18, n. 3 (30 settembre 2013): 26–33. http://dx.doi.org/10.6112/kscfe.2013.18.3.026.

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41

Bakhvalov, P. A., e T. K. Kozubskaya. "Construction of edge-based 1-exact schemes for solving the Euler equations on hybrid unstructured meshes". Computational Mathematics and Mathematical Physics 57, n. 4 (aprile 2017): 680–97. http://dx.doi.org/10.1134/s0965542517040030.

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42

Amann, Finn, Ilhan Özgen, Morgan Abily, Jiaheng Zhao, Dongfang Liang, Kenichiro Kobayashi, Satoru Oishi, Philippe Gourbesville e Reinhard Hinkelmann. "Integral porosity shallow water model at district scale - Case study in Nice". E3S Web of Conferences 40 (2018): 06018. http://dx.doi.org/10.1051/e3sconf/20184006018.

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After three hours of intense rainfall, the city of Nice was flash flooded on October 3, 2015, resulting in casualties and severe damages in property. This study presents a porous shallow water-model based numerical simulation of the flash flood event in a district of Nice, and compares the results with a high-resolution conventional shallow water model. This contribution aims to discuss practical aspects of applying a porous shallow water model to a real world case. The porous shallow water model is an integral porosity-type shallow water model. It uses unstructured triangular meshes. The conventional shallow water model is a distributed memory parallelized high-performance computing code, that uses a uniform Cartesian grid. The study site is an approximately 5 km2 spanning district of the city of Nice, France. Topography information is available in a 1m resolution and in addition, the available digital elevation model includes inframetric structures such as walls and small bridges. In the presentation of the case study, challenges of the pre-processing step of the integral porosity shallow water model are addressed. Notably, a method to semi-automatically generate “good” triangular meshes using the open-source geoinformation system QGIS and the mesh generator Gmsh is presented. During the post-processing step, the results of the porous model are mapped back onto the high-resolution topography to make the results more meaningful. The agreement between the high-resolution reference solution and the porous model results are poor. A speed up of about 10 to 15 was observed for the present case.

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43

Adami, P., e F. Martelli. "Three-dimensional unsteady investigation of HP turbine stages". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 220, n. 2 (1 marzo 2006): 155–67. http://dx.doi.org/10.1243/095765005x69189.

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Abstract (sommario):

This article deals with a three-dimensional unsteady numerical simulation of the unsteady rotor—stator interaction in a HP turbine stage. The numerical approach consists of a computational fluid dynamics (CFD) parallel code, based on an upwind total variation diminishing finite volume approach. The computation has been carried out using a sliding plane approach with hybrid unstructured meshes and a two-equation turbulent closure. The turbine rig under investigation is representative of the first stage of aeronautic gas turbine engines. A brief description of the cascade, the experimental setup, and the measuring technique is provided. Time accurate CFD computations of pressure fluctuations and Nusselt number are discussed against the experimental data.

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44

Woodgate, M. A., e G. N. Barakos. "An implicit hybrid method for the computation of rotorcraft flows". Aeronautical Journal 122, n. 1256 (ottobre 2018): 1522–56. http://dx.doi.org/10.1017/aer.2018.108.

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Abstract (sommario):

ABSTRACTThere is a wide variety of CFD grid types including Cartesian, structured, unstructured and hybrids, as well as, numerous methodologies of combining these to reduce the time required to generate high-quality grids around complex configurations. If the grid methodologies were implemented in different codes, they should be written in such a way as to obtain the maximum performance from the available computer resources. A common interface should also be required to allow for ease of use. However, it is very time consuming to develop, maintain and add extra functionally to different codes. This paper examines the possibility of taking an existing CFD solver, the Helicopter Multi-Block (HMB) CFD method, and implementing a new grid type while reusing as much as possible the original code base. The paper presents some of the challenges encountered in extending the code which was written for a single mesh type, to a more flexible solver that is still computationally efficient but can cope with a variety of grid types.

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45

You, Ju-Yeol, e Oh-Joon Kwon. "Numerical Comparisons Between URANS and Hybrid RANS/LES at a High Reynolds Number Flow Using Unstructured Meshes". International Journal of Aeronautical and Space Sciences 11, n. 1 (1 marzo 2010): 41–48. http://dx.doi.org/10.5139/ijass.2010.11.1.041.

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46

Soukov, S. A., A. V. Gorobets e P. B. Bogdanov. "OpenCL Implementation of Basic Operations for a High-order Finite-volume Polynomial Scheme on Unstructured Hybrid Meshes". Procedia Engineering 61 (2013): 76–80. http://dx.doi.org/10.1016/j.proeng.2013.07.096.

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47

Gao, Wei, e Ruxun Liu. "A hybrid finite volume/finite element method for incompressible generalized Newtonian fluid flows on unstructured triangular meshes". Acta Mechanica Sinica 25, n. 6 (18 luglio 2009): 747–60. http://dx.doi.org/10.1007/s10409-009-0281-3.

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48

Gao, Wei, Ru-Xun Liu e Hong Li. "A hybrid vertex-centered finite volume/element method for viscous incompressible flows on non-staggered unstructured meshes". Acta Mechanica Sinica 28, n. 2 (aprile 2012): 324–34. http://dx.doi.org/10.1007/s10409-012-0038-2.

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49

Abgrall, R., A. Larat e M. Ricchiuto. "Construction of very high order residual distribution schemes for steady inviscid flow problems on hybrid unstructured meshes". Journal of Computational Physics 230, n. 11 (maggio 2011): 4103–36. http://dx.doi.org/10.1016/j.jcp.2010.07.035.

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50

Yang, Yaqing, Liang Pan e Kun Xu. "Three-dimensional third-order gas-kinetic scheme on hybrid unstructured meshes for Euler and Navier–Stokes equations". Computers & Fluids 255 (aprile 2023): 105834. http://dx.doi.org/10.1016/j.compfluid.2023.105834.

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