Boundary Conditions

Boundary conditions define how a system (for example, a structure or a fluid) interacts with the environment. Fixations, loads, pressures, flow rates, or velocities are all examples of boundary conditions.

A boundary condition consists of three pieces of information:

1. Boundary condition types: 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 assignments: A boundary condition is usually only assigned to the domain’s boundary. Each boundary condition must be linked to at least one surface or where something enters or exits the domain.
3. Boundary condition values: This is where we define the value of the condition (speed, temperature, force, etc.);

Boundary Condition Types

SimScale offers many boundary condition types for different types of applications. Boundary conditions are only displayed when they can be applied to the type of analysis being worked on. The following list shows the available boundary condition types, what each type means, and where they can be used. For advanced users, the page also shows how the boundary condition types translate to the solver input files.

Fluid Dynamics

• Velocity inlet and Velocity outlet
• Pressure inlet and Pressure outlet
• Natural convection inlet-outlet
• Wall
• Periodic
• Symmetry
• Wedge
• Custom
• Empty 2D

Solid Mechanics

• Pressure
• Follower pressure
• Force
• Nodal load
• Fixed value
• Surface load
• Volume load
• Centrifugal force
• Remote force
• Symmetry plane
• Remote displacement
• Fixed support
• Rotating motion
• Elastic support
• Bolt preload
• Point mass

Thermodynamics

• Fixed value temperature
• Convective heat flux
• Surface heat flux
• Volume heat flux

Creating and Assigning a Boundary Condition

To create a new boundary condition, click on the ‘+ button‘ next to Boundary conditions. Pick the desired one from the list:

After creating a boundary condition, assign the desired entities by clicking on them.

All of the fluid dynamics boundary conditions are assigned to faces exclusively. For solid mechanics and thermodynamics, some boundary conditions only be assigned to volumes, such as Volume heat flux.

Lastly, some of the solid mechanics boundary conditions accept assignments of both faces and volumes, such as the Rotating motion boundary condition.

Boundary Condition Values

For simple cases, boundary conditions are defined by a single value of a given variable (velocity, temperature, pressure…). For advanced cases where a fixed value is not enough, alternative techniques are available:

• Tables
• Formulas

Last updated: December 1st, 2021