# Boundary conditions

Boundary conditions (BC) are physical definitions on domain boundary surfaces for thermal conditions and electromagnetism. Here are listed **all boundary conditions used in CENOS**, as well as the **most common usage for each BC**.

## Thermal BC

Thermal BC's are boundary conditions through which the heat exchange between domains is defined.

### Fixed temperature

*Fixed temperature* boundary condition defines a fixed temperature on the boundary surface.

When *Motion* is used on infinite billet, the surface through which the billet enters the computational domain can be defined with *Fixed Temperature*.

### Heat flux

*Heat flux* boundary condition defines a constant heat flux density on the boundary surface.

Can be used if the heat flux going through a specific area is known

### Heat flow

*Heat flow* boundary condition defines a constant heat flow (in watts) on the boundary surface.

Can be used if the heat flow going through a specific area is known

### Convection

*Convection* boundary condition defines the heat flux as dependent from the ambient temperature and heat transfer coefficient. *Convection* is defined as:

*Convection* is used on the workpiece-air interface to define heat exchange when temperature is low. Usually used together with *Radiation*.

To **learn more** about *Convection* definition, **click here**.

### Radiation

*Radiation* boundary condition defines the thermal radiation to infinity on the boundary surface, where the heat flux is defined as:

*Radiation* is used on the workpiece-air interface to define heat exchange when temperature is high. Usually used together with *Convection*.

To **learn more** about *Radiation* definition, **click here**.

### Combined

*Combined* boundary condition allows you to combine multiple BC such as *Convection*, *Radiation*, *Heat Flux* and *Heat Flow* on a single domain surface.

*Combined* is used on workpiece-air interface to define both *Convection* and *Radiation* for a complete heat trasfer definition over wide temperature range.

### Adiabatic

*Adiabatic* boundary condition defines 0 heat flux on the surface.

*Adiabatic* is used on symmetry surfaces for domains with thermal analysis.

### Interface

*Interface* boundary condition defines boundary surface as the internal surface between two domains.

Used to define interface between two domains which both have thermal analysis definition.

### Thermal Contact Resistance

*Thermal Contact Resistance* boundary condition defines thermal resistance between two domains.

Used to define interface between two domains who both have thermal analysis definition.

## Electromagnetics

Electromagnetic BC's are boundary conditions through which the magnetic flux is defined.

### Infinity

*Infinity* boundary condition defines a zero vector potential on the boundary surface.

*Infinity* is used to define the outer surface of the air box.

### Flux parallel

*Flux parallel* boundary condition defines the magnetic field lines as parallel to the boundary surface.

*Flux parallel* is used to define symmetry boundary conditions on the sides of slices and sectors.

To **learn more** about *Flux parallel* definition, **click here**.

### Flux normal

*Flux normal* boundary condition defines the magnetic field lines as normal to the boundary surface.

*Flux normal* is used to define symmetry boundary conditions on top and bottom of slices and sectors.

To **learn more** about *Flux normal* definition, **click here**.

### Interface

*Interface* boundary condition defines boundary surface as the internal surface between two domains.

Used to define interface between two domains from which only one has thermal analysis definition.

### Surface Impedance

*Surface Impedance* boundary condition can be accessed only through the *Surface Impedance* domain. It defines the boundary surface as an infinitely thin layer for VH frequency skin layer resolution.

*Surface Impedance* is used to replace manual skin layer resolution through mesh at very high frequency setup.

### Symmetry axis

*Symmetry axis* is a 2D-axial-symmetric specific boundary condition which defines 0 vector potential on the symmetry axis.

*Symmetry axis* is used in every 2D axial-symmetric case to define rotational axis.

## Current source

Current BC's are accessed only under the *Current source* domain and through which the current or voltage flowing through the conductor are defined.

### Voltage

*Voltage* boundary condition defines the voltage on the boundary surface.

*Voltage* is used to define the voltage on one of inductor terminals. For the other terminal use *Ground*.

### Current

*Current* boundary condition defines a positive current supply to the boundary surface and the value of current.

*Current* is used to define current on one of the inductor terminals. For the other terminal use *Ground*.

### Ground

*Ground* boundary condition defines a negative current supply to the boundary surface.

*Ground* is used to define one of the inductor terminals. For the other terminal use *Voltage* or *Current*.