Order of elements

Definition

Flux provides for the user two types of finite elements: first order elements or second order elements.

Type of element	Location of nodes	Interpolation function
	Automatic mesh generator	Mapped mesh generator
First order			Linear (1st order polynomial)
Second order			Quadratic (2nd order polynomial)

Type of element

Location of nodes

Interpolation function

Automatic mesh generator

Mapped mesh generator

First order

Linear

(1st order polynomial)

Second order

Quadratic

(2nd order polynomial)

With second order elements, the number of nodes is far larger than with first order ones but accuracy is largely increased.

For a 2D application, the mesh generation is completed with meshing the faces, and second order face elements are directly generated.

In 3D, meshing the volumes leads to first order volume elements.

In several physical configurations, it is possible to solve with first order elements.

Generally, it is better to generate the second order elements.

To generate second order volume elements:

Step	Action
1	Activate the command: in the Mesh menu, click on Mesh > Generate second order elements or in the Mesh toolbar, click on the icon
→	Elements of second order are generated. The number of mesh elements is increased.

Step

Action

1

Activate the command:

in the Mesh menu, click on Mesh > Generate second order elements

or in the Mesh toolbar, click on the icon

→

Elements of second order are generated.

The number of mesh elements is increased.

To come back to first order volume elements:

Step	Action
1	Activate the command: in the Mesh menu, click on Mesh > Generate first order elements
→	Mesh elements are the first order elements.

Step

Action

1

Activate the command:

→

Mesh elements are the first order elements.