# Trelis Boundary Conditions

In Trelis, boundary conditions are applied to sidesets or nodesets.  Sidesets and nodesets can contain geometry or mesh.  This means that models can be remeshed without worrying about losing boundary condition data if the boundary condition is applied to a geometry-based sideset/nodeset.

The sideset/nodeset used by a boundary condition will be visible to the user, and the user can modify the sideset/nodeset separately from the boundary condition.  Sidesets/nodesets can be assigned to (or removed from) a boundary condition at any time.

Boundary conditions are broken into four groups: Restraints, loads, contact, and cfd. Each restraint that is created will belong to a restraint set, each load will belong to a load set, and each contact definition will belong to a contact set. A boundary condition set consists of any number of restraints, contact pairs, and loads. CFD boundary conditions do not belong to boundary condition sets.

Table 1: Overview of boundary condition entities available in Trelis

 Entity Description and scope FEA Boundary Conditions Acceleration Creates an acceleration boundary condition (acts on a body, volume, surface, curve, or vertex) Velocity Creates a velocity boundary condition (acts on a body, volume, surface, curve, or vertex) Boundary Condition Set Creates a BC set (contains restraint, load and contact sets) Contact Region Creates a contact region between two surfaces or two curves Contact Pair Creates a contact pair between two previously defined contact regions Convection Creates a convection boundary condition (acts on 2d elements) Displacement Creates a displacement boundary condition (acts on a body, volume, surface, curve or vertex) Temperature Create a temperature boundary condition (acts on a surface, curve or vertex) Force Creates a force boundary condition (acts on a surface, curve or vertex) Pressure Creates a pressure boundary condition (acts on a surface or curve) Heat flux Creates a heat flux boundary condition (acts on a surface or curve) CFD Boundary Conditions Inlet Velocity Creates an inlet velocity boundary condition Inlet Pressure Creates an inlet pressure boundary condition Inlet Massflow Creates an inlet massflow boundary condition Outlet Pressure Creates an outlet pressure boundary condition Farfield Pressure Creates a farfield pressure boundary condition Axis Creates an axis boundary condition Exhaust Fan Creates an exhaust fan boundary condition Fan Creates an fan boundary condition Inlet Vent Creates an inlet vent boundary condition Intake Fan Creates an intake fan boundary condition Interface Creates an interface boundary condition Interior Creates an interior boundary condition Mass Flow Inlet Creates an mass flow inlet boundary condition Outflow Creates an outflow boundary condition Outlet Vent Creates an outlet vent boundary condition Periodic Creates an periodic boundary condition Periodic Shadow Creates an periodic shadow boundary condition Porous Jump Creates an porous jump boundary condition Radiator Creates an radiator boundary condition Symmetry Creates a symmetry boundary condition (acts on a surface) Wall Creates an wall boundary condition