# Regions: generalities

## Problems

A real device is composed of a certain number of components (magnets, magnetic poles, magnetic cores, coils, …) that have particular physical characteristics (hard magnetic material, soft magnetic material, current, …).

Any component of a device with more complex geometry can be described by several volumes. In this case, it is necessary to group the different volumes in the same region in order to associate the physical properties to this region.

## Region: definition

A region is a group of geometric elements of the same type (point, line, face and volume region), having the same physical properties.

This definition includes:

• the concept of regrouping the geometric entities
• the concept of defining the physical properties

These two concepts are presented in the following sections.

## Geometrical approach

From a geometric approach, we distinguish four types of regions, corresponding to the four types of geometric entities: points, lines, faces, volumes.

These four types of regions are listed in the table below.

A region … gathers a group of …
volume volumes
face faces
line lines
point points
having the same physical properties

## Physical approach

From a physical approach, we can distinguish two types of regions: material regions and regions known as non-material regions.

These two types of regions are listed in the table below.

A region … is used to … Example

material

( with material )

model a material region magnetic part, conducting part, air-gap, …

non-material

( without material )

impose boundary conditions normal field crossing a face, imposed potential on a line, …

## Defining in regions: some advice

A region has to be created for each component of the studied device if:

• its physical properties are different from those of the other components (turn-return sides of a coil in 2D, magnet oriented at 45° and magnet oriented at 60°, …)
• we wish to compute a specific quantity postprocessing (inductance of a coil, force on a blade, …)