Past conent: Palabos Summer School 2021
The Palabos library: overview and model development
Presenters: Jonas Latt and Christophe Coreixas
Video recording: overview and model development (Jonas Latt)
Slides: overview and model development (Jonas Latt)
Slides: LB collision models and their implementation in Palabos (Christophe Coreixas)
We introduce the scope and the history of the Palabos library and present it in the light of ongoing research and open challenges. Topics which are touched upon are the utilization of modern collision models, (adaptive and non-adaptive) mesh refinement, and GPGPU programming. The presentation then provides an overview on how to implement new models and new physics in Palabos. In contrast with past year (Summer School 2020) which had a strong focus on the development of data processors, this year's talk addresses the full development package: collision models for everything fully local, data processors for non-local ingredients, lattice descriptors to manage the data layout in memory. We will also have a look at various collision models implemented in Palabos and investigate criteria to help select the appropriate model for given circumstances.
Partially Saturated Bounce-Back boundaries in Palabos and application to porous media
We will discuss during this session which Partially Saturated Method (PSM) is implemented in Palabos, and how to use it. The PSM can be used to "smoothen" curved boundaries, or to represent porous media at a corse-scale, when pore-scale resolution is too expensive. The latter will be illustrated by the simulation of flow in a thrombus. In particular, we will see how to compute the macroscopic velocity, how to impose a specific permeability to the medium, and how to modify the permeability over time.
Link-wise boundary conditions
Presenter: Francesco Marson
During this session, you will learn how to interpret the link-wise boundary conditions in a unified manner and use some of them in Palabos. Link-wise boundary conditions represent a major family of boundary conditions for LBM. Their main characteristic is the computation of unknown boundary populations through independent actions along each lattice direction. This fact provides them with easy implementation procedures and kinetic insights. For this reason, they are one of the most widespread techniques in the Lattice Boltzmann community, and their application extends from porous media to turbulent particulate flows. We will supply a unified description of these techniques, offering an overview of their operational mechanism. Then we will dive into some details of the most used schemes and their implementation in Palabos. At the end of this session, you will be able to discriminate link-wise methods among other boundary conditions and to use and interpret them with a general mindset.
Advection-diffusion with sharp interfaces, coupled with a fluid
Numerous transport problems involve couplings between advection-diffusion and fluid equations. Numerical solutions of advection-dominated problems, especially with sharp interfaces are challenging when using Eulerian (i.e. mesh-based) approaches. The Lattice Boltzmann Method (LBM) can solve the advection-diffusion equation using for instance the BGK model. However, we will explore some limits of the LBM for advection-diffusion and how we can get around the problem using alternative techniques which are implemented in Palabos.
Hybrid CPU-GPU simulations for fully resolved blood flow with Red Blood Cells
The main focus of this course will be cellular blood flow simulations, i.e., explicit modeling of the trajectories and deformations of blood cells (red blood cells, platelets) inside the blood plasma. More in detail, Palabos will be used for the simulation of the fluid phase (blood plasma) and the immersed boundary method, while an in-house finite element solver will be used for the resolution of deformable bodies physics. Furthermore, a hands-on section will be conducted in order to present how to run the project taking the advantage of the HPC systems and GPU as well. By the end of the session, the users should be able to run and get more information to customize and evolve this project.
Mesh refinement is of crucial importance for many engineering applications especially for high Reynolds number flows. In the frame of the lattice Boltzmann method, the transitions are particularly sharp because of the cartesian nature of the mesh and must be handled with great care. In this session, we will discuss the theoretical aspects of mesh refinement in the lattice Boltzmann method and its implementation in Palabos. Finally, we will see how to set up the mesh to perform the simulation of a high Reynolds number flow and then perform an actual simulation.
Preparation: Hands-on sessions are carried out on the participants’ own laptops, which should be prepared in advance to be equipped with a C++ compiler, MPI, and Paraview. Typical configurations could be (1) a Linux Laptop, (2) a Windows Laptop with a properly configured Linux sub-system, (3) a Mac with a development environment (e.g. through Homebrew). Before attending the class, try to download and compile Palabos.