Documents published in Scipedia

• 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 [...]

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• Numerical simulation of the micro-extrusion process of printable biomaterials

  A. Amani, D. Kizildag, J. Castro, L. del Mazo, M. Pegueroles, M. Ginebra

  eccomas2022.

  
  

  Abstract

  This work aims to gain a better understanding of how the rheological properties of printable materials affect their processability, as well as the quality of the final product, which at the end can lead to reducing time and costs of the process and increase product development. As the first step, the proper rheological non-Newtonian models are extracted from experimental studies. Later, three-dimensional numerical simulation of extrusion process is performed in the context of Direct Numerical Simulation (DNS) of governing equations, where the whole physics of fluid motion is taken into account. A finite-volume fractional step approach is used to solve the Navier-Stocks equations on collocated arbitrary meshes. Geometrical volume-of-fluid (GVOF) interface capturing approach is used to resolve the topological changes of the moving interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. Besides the contribution of this work to the advancement of numerical techniques applied to multiphase complex flows, obtained results will shed light on the nature of non-Newtonian extrusion process with vast applications in the 3D printer industrial sectors.

  Abstract
  This work aims to gain a better understanding of how the rheological properties of printable materials affect their processability, as well as the quality of the final product, [...]

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• The X-Mesh method applied to Multiphase Flows

  Q. Antoine, J. Remacle, J. Lambrechts, N. Moes

  eccomas2022.

  
  

  Abstract

  The accurate modeling of moving boundaries and interfaces is a difficulty present in many situations in computational mechanics. In this paper we use a new approach, X-Mesh, to simulate with the finite element method the interaction between two immiscible fluids while keeping an accurate description of the interface without mesh regeneration. The method is validated with complex problems such as Rayleigh-Taylor instabilities, sloshing and dambreak. The quality of the results and the efficiency of the method show the potential of this approach to simulate such physical phenomena.

  Abstract
  The accurate modeling of moving boundaries and interfaces is a difficulty present in many situations in computational mechanics. In this paper we use a new approach, X-Mesh, [...]

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• DNS and LES on unstructured grids: playing with matrices to preserve symmetries using a minimal set of algebraic kernels

  F. Trias, X. Álvarez-Farré, À. Alsalti-Baldellou, A. Gorobets, A. Oliva

  eccomas2022.

  
  

  Abstract

  The essence of turbulence are the smallest scales of motion. They result from a subtle balance between two differential operators differing in symmetry: the convective operator is skew-symmetric, whereas the diffusive is symmetric and negative-definite. On the other hand, accuracy and stability need to be reconciled for numerical simulations of turbulent flows in complex configurations. With this in mind, a fully-conservative discretization method for collocated unstructured grids was proposed [Trias et al., J.Comp.Phys. 258, 246-267, 2014]: it preserves the symmetries of the differential operators and it has shown to be a very suitable approach for DNS and LES. On the other hand, an efficient cross-platform portability is nowadays one of the greatest challenges for CFD codes. In this regard, our leitmotiv reads: relying on a minimal set of (algebraic) kernels is crucial for code portability and maintenance! In this context, this work focuses on the computation of eigenbounds for the above-mentioned convection and diffusion matrices which are needed to determine the time-step `a la CFL. A new inexpensive method that allows this, without explicitly constructing these time-dependent matrices is proposed and tested. It only requires a sparse-matrix vector product where only the vector changes on time. Hence, apart from being significantly more efficient than the standard CFL condition, cross-platform portability is straightforward.

  Abstract
  The essence of turbulence are the smallest scales of motion. They result from a subtle balance between two differential operators differing in symmetry: the convective operator [...]

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• The interaction between an isolated roughness element and free-stream turbulence

  M. Gholamisheeri, K. Durovic, S. Mamidala, J. Fransson, A. Hanifi, D. Henningson

  eccomas2022.

  
  

  Abstract

  Control and delay of the laminar-turbulent transition is a key parameter in reducing skin friction and drag. The flow characteristics, surface roughness, and environmental noise can affect the onset of transition. The present work investigates, numerically and experimentally, the interaction of the free-stream turbulence (FST) and an isolated cylindrical roughness element, and the resulting impact on the transition onset in a flat-plate boundary layer. High-fidelity direct numerical simulations (DNS) are performed for a roughness element immersed in the boundary layer over a flat plate with an asymmetrical leading edge, with and without FST. The numerical results are compared to hot-wire anemometry measurements performed in the Minimum Turbulence Level wind tunnel at KTH. The initial numerical and experimental results show that in the absence of FST, for the chosen flow parameters, highand low-speed streaks are generated downstream of the roughness element while the flow remains laminar and globally stable. When FST is added, the spanwise spacing of the streaky structures changes and the transition location of the boundary layer moves upstream. It was found that the aspect ratio of the streaky structures does not vary significantly.

  Abstract
  Control and delay of the laminar-turbulent transition is a key parameter in reducing skin friction and drag. The flow characteristics, surface roughness, and environmental [...]

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