# Boundary Conditions¶

Boundary conditions define how a system (e.g. a structure or a fluid) interacts with its environment. Fixations, loads, known pressures, known flow velocities etc. are all examples of boundary conditions. A boundary condition basically consists of three pieces of information:

1. Boundary condition type

SimScale offers a large set of boundary condition types for simulations. This section links to descriptions of the available boundary condition types.

2. Boundary condition value

Depending on its type, a boundary condition may need zero, one or multiple values.

3. A list of assigned entities of the domain

A boundary condition is usually valid on a part of the domain’s boundary. That means, each boundary condition must have at least one topological entity (i.e. nodes, edges or faces) assigned.

## Boundary condition types¶

SimScale offers many boundary condition types for different types of applications. Some boundary conditions are available almost everywhere while others are very specific. The following list shows the available boundary condition types and provides links where you can find more information such as what the boundary condition type means and where they can be used. For advanced users the pages also show how the boundary condition types translate to the solver input files.