# Material regions in 2D applications

## Introduction

A region is always defined:

• in a geometric approach, (regrouping of geometric entities)
• in a physical approach, (definition of physical properties)

## Geometric approach

From the geometric appraoch we can distinguish, with 2D problems, three types of regions, corresponding to three types of geometric entities: face, line, and points.

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

A region … is used to describe … Example
face a volume part of random shape main elements
line

a thin part

(of small thickness)

contact air-gaps, thin sheets, current sheets, …
point

a filiform part

(of small cross-section)

bus-bars, …

In a 2D study:

• all the faces (except in specific cases) belong to face regions
• only few lines (and/or points) belong to line regions (and/or point regions)

## Physical approach

A material region is used to model a material medium. A material region must be comprised of a material. The physical properties of the material medium are those of the material of the region.

A region is defined…
geometrically by … physically by…
face a group of faces a type, a material
line a group of lines

a type, a material

and a thickness

point a group of points

a type, a material

and a cross-section

## Use of the line regions

It is recommended to use the line regions when the shape of the faces (in the 2D domain) is such that the mesh quality is poor. It is the case of faces with one the dimensions that is small in relation to the others, or to the surrounding faces.

The process is then the following:

• replacement of that face by a line (or a point)
• use of a line region (or point region)