Overset meshes are one of several approaches to representing complex geometry in CFD and other types of physical simulations. An overset mesh consists of a set of overlapping component meshes (often structured grids) that each represent a portion of the simulation domain. The component meshes communicate with other parts of the domain by interpolating from neighboring grids at their outer edges. This is often simpler than trying to create a single unstructured mesh to represent the entire domain, and when used with structured grids also enables the use of efficient and accurate numerical methods.

Overkit automates tasks commonly required for setting up overset meshes, such as:

1. Hole cutting of boundary geometry and overlapped coarse grids
2. Determination of donors and receivers for inter-grid communication
3. Generation of interpolation weights

Disclaimer: Overkit is still in experimental stages of development, so it's likely that some things won't work as well as they could. It's also likely that the API will change from version to version. You have been warned. :)

Overkit requires working Fortran and C compilers (tested on GNU >= 4.4, Intel >= 12) and CMake. It currently has no other third-party library/tool dependencies.

Overkit uses CMake, so the build process is similar to that of other CMake-based build systems. Here's an example build procedure:

  cd ~/overkit-src
  mkdir build && cd build
  cmake .. -DCMAKE_INSTALL_PREFIX=/usr/local/overkit
  make
  make install

See CMake's documentation for more details.

Use the flag -DEXAMPLES=On when configuring to build some example programs that use Overkit to generate overset grids.

Documentation will remain somewhat sparse for the time being as I'm planning to do some restructuring of the API. In the meantime, the best way to learn how it works is to look at the code in the examples directory and browse the source code corresponding to the routines that are used.

There are currently several known issues:

• The disjoint fringes option isn't fully implemented for cubic interpolation. Use fringe padding to compensate -- a value of 2 or 3 should be enough.
• Boundary hole cutting functionality is rather fragile at the moment. If it fails, try turning it off and roughly pre-blanking out the points that overlap with the boundary region (blanking a square region enclosing the boundary is often enough).
• Donor selection needs to be improved; it occasionally gives unexpected results near junctions of three or more grids.

Overkit is one of several software projects produced by the University of Illinois Center for Exascale Simulation of Plasma-Coupled Combustion (XPACC): http://xpacc.illinois.edu.

This material is based in part upon work supported by the Department of Energy, National Nuclear Security Administration, under Award Number DE-NA0002374.