> For the complete documentation index, see [llms.txt](https://docs.aviumtechnologies.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aviumtechnologies.com/user-guide/solver.md).

# Solver

The APM Solver solves for the potential flow around arbitrary bodies. The bodies are represented by structured or unstructured mesh in **.stl** format. The APM Preprocessor is first used to preprocess the mesh. During this step, the APM Preprocessor creates a **.mdl** file. The APM Solver uses the **.mdl** file to solve for the potential flow around the body. Please refer to the following sections for more information about the APM Solver:

## Steady simulations

For steady simulations the wake is assumed to be a flat surface extending to "infinity". Visit the [steady simulations section](/user-guide/solver/steady-simulations.md) for more information.

## Unsteady simulations

For unsteady simulations the wake is assumed "free", i.e. it is allowed to deform and interact with itself and the body. Visit the [unsteady simulations section](/user-guide/solver/unsteady-simulations.md) for more information.

## Wake

The wake can be aligned with the average trailing edge bisector, the freestream velocity vector, or with a specific vector (predefined). Visit the [wake section](/user-guide/solver/wake.md) for more information.

### Interactions with the body

The wake can interact with downstream body parts (e.g. horizontal and/or vertical tails) without causing numerical instabilities. Visit the [interaction with the body section](/user-guide/solver/wake/interaction-with-the-body.md) for more information.

### Viscous vortex particle wake

The wake can be represented by viscous vortex particles. Visit the [viscous vortex particle wake section](/user-guide/solver/wake/viscous-vortex-particle-wake.md) for more information.