VEMPIC

A reference implementation for VEMPIC, a fluid simulator that combines cut-cell meshes, the Virtual Element Method, and the PIC framework. This library uses Mandoline to construct its cut-cell meshes, so please make sure you can build Mandoline's dependencies as well.

Organization

There is a core set of tools in the root ./include and ./src directories for VEM. If you're interested in conformal VEM look at the Point* code, if you're interested in non-Conformal VEM look at the Flux* code. In the ./applications diretory there are a number of examples applications of VEM.

In Two dimensions:

poisson - a poisson equation solver, GUI includes some fun advection tools IIRC
wavesim - a semi-implicit wave simulator
fluidsim - the two dimensional implementation of VEMPIC

In Three dimensions:

fluidsim - the full three dimensional VEMPIC

Status

The code, as it is, buildable, but requires some extra work to run the examples because I need to document the input format and change some hardcoded output directories. I'll also be switching to meson instead of cmake, which will result in substantial changes on the dependencies held in Mandoline. For now please treat this codebase as a reference rather than as an implementation to build upon. As I plan on using this codebase for future projects it should naturally be cleaned up over time, just as Mandoline underwent some feature development and cleanup to make this project work.

Compilation

VEMPIC depends on a C++20 enabled compiler. Recently I have only tried compiling with the following:

gcc with version = 11.3.0
cmake with version = 3.19.7 . On Ubuntu the following should build

apt install git cmake build-essential gcc

I prefer using Ninja build system over make, so the following will use the ninja command instead of make.

mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=Release -GNinja
ninja

Build Issues

As it is, this code has a number of dependencies that are somewhat fickle to build. Here's a few tips.

cutmesh.pb.h not found

Sometimes CMake fails to build the protobuf header cutmesh.pb.h before building Mandoline sources, which depend on it. This can be explicitly built with

ninja cutmesh_proto

in the build directory.

Embree undefined references

On my AMD Zen3 Linux machine I had difficulty building Embree without disabling some ISA. My solution was to disable some ISA:

${CMAKE_CMDS} -DEMBREE_MAX_ISA=NONE -DEMBREE_ISA_SSE2=OFF -DEMBREE_ISA_SSE42=OFF -DEMBREE_ISA_AVX=ON -DEMBREE_ISA_AVX2=ON -DEMBREE_ISA_AVX412=OFF

If you're using AMD and are using Excavator or any of hte Zen series processors the above should work. If you are using intel you're on a relatively recent Intel processor (Skylake or later) but not too new (Alder Lake with new microcode) then this step can probably be ignored...