Documents published in Scipedia

• Algorithmic Differentiation for an effcient CFD solver

  B. Maugars, S. Bourasseau, C. Content, B. Michel, B. Berthoul, J. Nunez Ramirez, I. Salah el Din, P. Raud, L. Hascoët

  eccomas2022.

  
  

  Abstract

  We illustrate the benefits of Algorithmic Differentiation (AD) for the development of aerodynamic flow simulation software. In refining the architecture of the elsA CFD solver, developed jointly by ONERA and Safran, we consider AD as a key technology to cut development costs of some derivatives of interest, namely the tangent, adjoint, and Jacobian. We first recall the mathematical background of CFD applications which involve these derivatives. Then, we briefly present the software architecture of elsA (Cambier et al. [12]) and the design choices which give it its HPC capability while highlighting how these choices strongly constrain the applicability of AD. To meet our efficiency requirements, we select the Source-Transformation approach to AD through the Tapenade tool which is justified by a series of experiments and benchmarks. Finally, we present results on large scale configurations.

  Abstract
  We illustrate the benefits of Algorithmic Differentiation (AD) for the development of aerodynamic flow simulation software. In refining the architecture of the elsA CFD solver, [...]

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• A runtime-based dynamic mesh partitioning approach

  G. Baldan, R. Borrell, J. Jägersküpper

  eccomas2022.

  
  

  Abstract

  Large-scale parallel numerical simulations are fundamental for the understanding of a wide variety of aeronautical problems. Mesh decomposition is applied to make use of parallel hardware. In particular, when using a massively parallel architecture, not only the final quality of the mesh subdivision is relevant. Also the partitioning algorithm itself needs to be robust as well as efficient. A strategy for dynamic mesh partitioning based on runtime measurements is presented. We integrate the 'Geometric Mesh Partitioner' (GeMPa), which is a partitioning library based on Hilbert Space-Filling Curve (HSFC), in the FlowSimulator (FS) software. FS is a platform designed to run multi-disciplinary simulations on massively parallel cluster architectures. The algorithm performance is evaluated on an unstructured mesh representing the ONERA M6 wing. In particular, the load imbalance among processes is evaluated and compared with a well-known graph-based partitioning approach. Finally, we analyze how the number of processes influences the load imbalance.

  Abstract
  Large-scale parallel numerical simulations are fundamental for the understanding of a wide variety of aeronautical problems. Mesh decomposition is applied to make use of parallel [...]

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• Numerical simulation of multiphase flows with incompressible viscoelastic flows and elastic solids

  A. Caboussat

  eccomas2022.

  
  

  Abstract

  A numerical model for the simulation of multiphase flows with free surfaces is presented. The model allows to incorporate in a unified manner several phases ranging from incompressible Newtonian flows, Oldroyd-B viscoelastic flows and neo-Hookean elastic solids deformations. We advocate a Eulerian modeling of the multiphase flows, relying on the volume fraction of liquid, describing multiple phases with those different rheologies.One advantage of the Eulerian approach is to allow for large deformations of elastic solids, and changes of topologies. The numerical framework relies on an operator splitting strategy and a two-grid method. The numerical model is validated with a numerical experiment based on the collision between two elastic bodies with free surfaces.

  Abstract
  A numerical model for the simulation of multiphase flows with free surfaces is presented. The model allows to incorporate in a unified manner several phases ranging from incompressible [...]

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• D2Q9 model of upwind lattice Boltzmann scheme for hyperbolic scalar conservation laws

  M. Anandan, R. Suswaram

  eccomas2022.

  
  

  Abstract
  D2Q9 model of upwind lattice Boltzmann scheme for hyperbolic scalar conservation laws.

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• A practical algorithm to build geometric models of cardiac muscle tissue

  M. Potse, L. Cirrottola, A. Froehly

  eccomas2022.

  
  

  Abstract

  Cardiac muscle tissue has a unique, network-like structure. Three-dimensional models of this structure are needed for simulations of cardiac electrophysiology and mechanics. We developed an algorithm to produce such models artificially, using an implicit surface expressed on a tailored unstructured multi-domain mesh to define the cell membranes. The algorithm first creates a random network of cell centers, observing angle and distance criteria inferred from real tissue. The space around the network edges is assigned to the cellular domains based on the nearest half-edge. The network is then immersed in a regular tetrahedral mesh which is refined to fit the domain boundaries and to offer sufficient density around the cell membrane. The refinements are alternated with mesh improvement operations to maintain an acceptable mesh quality. On the refined mesh a level-set function is expressed that defines the cell membrane. The remeshing code Mmg3d is then used to discretize the level set while retaining the domains, and to improve the quality of the final mesh. A serial implementation of the algorithm was able to produce meshes of a few hundreds of cardiac cells in 15 minutes, but we are still facing difficulties in the remesher, likely resulting from the unusual complexity of these meshes. It was still possible, however, to correctly mesh a small network of cells that was designed to be replicated by successive mirroring. This allowed us to build models of upto 1 cm3of tissue (10 million cells and 370 billion tetrahedra) that now serve in performance tests of a large-scale simulation code.

  Abstract
  Cardiac muscle tissue has a unique, network-like structure. Three-dimensional models of this structure are needed for simulations of cardiac electrophysiology and mechanics. [...]

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• Efficient implementation of a high-order compressible Navier-Stokes equations solver running on Graphics Processing Units

  F. Gisbert, A. Sotillo, J. Pueblas

  eccomas2022.

  
  

  Abstract
  This paper presents the implementation of a compressible Navier-Stokes equations solver that runs on multiple GPUs.

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• FEATURE DETECTION ALGORITHMS AND MODAL DECOMPOSITION METHODS

  B. Begiashvili, J. Garicano Mena, S. Le Clainche, E. Valero Sánchez

  eccomas2022.

  
  

  Abstract

  Various modal decomposition techniques have been developed in the last decade [1­11]. We focus on data-driven approches, and since data flow volume is increasing day by day, it is important to study the performance of order reduction and feature detection algorithms. In this work we compare the performance and feature detection behaviour of energy and frequency based algorithms (Proper Orthogonal Decomposition [1­3] and Dynamic Mode Decomposition [4­6, 8­11]) on two data set testcases taken from fluid dynamics.

  Abstract
  Various modal decomposition techniques have been developed in the last decade [1­11]. We focus on data-driven approches, and since data flow volume is increasing day by [...]

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• Lattice-Boltzmann simulations of traffic-related atmospheric pollutant dispersion in urban areas

  M. Pasquier, S. Jay, P. Sagaut

  eccomas2022.

  
  

  Abstract

  The developing field of urban physics includes computational fluid dynamics (CFD) as a tool to model wind comfort, heat management and pollutant dispersion in cities. In particular, road traffic emissions significantly contribute to air pollution and should be considered in atmospheric dispersion simulations. To this end, the lattice-Boltzmann method (LBM) offers a promising alternative to traditional finite-volume CFD solvers in terms of computational cost and accuracy. At IFP Energies Nouvelles (IFPEN), a recent emission model relying on real-life driving data recorded with a mobile application was used to construct urban emission maps. However, it has not been coupled yet with a precise unsteady CFD solver, which could provide local unsteady and accurate information about local concentration fields. We propose to combine the LBM open-source code OpenLB with the emission model designed at IFPEN to simulate traffic-induced pollutant dispersion in an urban-like environment. The LBM code is used to solve the Navier-Stokes equations as well as the passive scalar transport with a double distribution function (DDF) approach. The solver is successfully validated on the well-known CODASC test case and a first evaluation of the impact of a representative urban setting on pollutant dispersion with non-uniform sources is proposed.

  Abstract
  The developing field of urban physics includes computational fluid dynamics (CFD) as a tool to model wind comfort, heat management and pollutant dispersion in cities. In particular, [...]

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• An Immersed Boundary Method for the CFD Solver Airbus-CODA

  V. Llorente, D. Lodares, E. Ferrer, E. Valero

  eccomas2022.

  
  

  Abstract

  This work implements and analyses an Immersed Boundary Method based on Volume Pezalization for the flow simulator Airbus-CODA (CFD for ONERA, DLR, and AIRBUS). The Immersed Boundary Volume Penalization has unique advantages, e.g. easy to implement, straightforward formulation for moving geometries, and numerical errors can be controlled apriori [1, 2], showing the potential for aeronautical applications. Numerical experiments will assess the accuracy of the Immersed Boundary Volume Penalization in CODA.

  Abstract
  This work implements and analyses an Immersed Boundary Method based on Volume Pezalization for the flow simulator Airbus-CODA (CFD for ONERA, DLR, and AIRBUS). The Immersed [...]

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• Momentum-conserving ROMs for the incompressible Navier-Stokes equations

  H. Rosenberger, B. Sanderse

  eccomas2022.

  
  

  Abstract

  Projection-based model order reduction of an ordinary differential equation (ODE) results in a projected ODE. Based on this ODE, an existing reduced-order model (ROM) for finite volume discretizations satisfies the underlying conservation law over arbitrarily chosen subdomains. However, this ROM does not satisfy the projected ODE exactly but introduces an additional perturbation term. In this work, we propose a novel ROM with the same subdomain conservation properties which also satisfies the perturbed ODE exactly. We apply this ROM to the incompressible Navier-Stokes equations and show with regard to the mass equation how the novel ROM can be constructed to satisfy algebraic constraints. Furthermore, we show that the resulting mass-conserving ROM allows us to derive kinetic energy conservation and consequently nonlinear stability, which was not possible for the existing ROM due to the presence of the perturbation term.

  Abstract
  Projection-based model order reduction of an ordinary differential equation (ODE) results in a projected ODE. Based on this ODE, an existing reduced-order model (ROM) for [...]

  • 10
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