Structural Analysis and Design of Foundations: A Comprehensive Handbook for S...
UnderstandingElmerFEM.pptx
1.
2. The Elmer Grid Code that generates the
geometry
Coordinate System = Cartesian 2D
Subcell Divisions in 2D = 1 1
Subcell Limits 1 = 0 1
Subcell Limits 2 = 0 1
Material Structure in 2D
1
End
Materials Interval = 1 1
Boundary Definitions
! type out int double of the boundaries
1 0 1 1
End
Element Degree = 1
Surface Elements = 100
3. Coordinate System
The choices are Cartesian 1D, Cartesian 2D, Cartesian 3D, Polar and
Axisymmetric.
Axisymmetric and Cartesian 2D have currently no difference.
A Cartesian 3D grid is the default.
5. Subcell Divisions in 2D
The FEM mesh is composed of subcells that are topologically squares.
This keywords should be followed by the number of subcells in the main
directions, n1, n2 and n3.
Thus the number of arguments may be 1, 2 or 3 depending on the dimension of
the geometry definition.
Any change in this field should be correspondingly updated in the subcell limits
field
6. Subcell Limits
The size of the subcells are defined by ni + 1 boundaries in each coordinate
direction.
These values define the physical dimensions of the mesh before possible
manipulation.
This keyword exists for all active coordinate directions.
This means that we have to specify subcell limits for each coordinate direction
separately
Subcell limits are the no of boundaries of each subcell
7. Material Structure in 2D
The subcells form a n1 × n2 matrix in 2D.
The material structure of this plane may therefore be given by a matrix consisting
of integers relating to different materials.
These numbers may then later be referred when creating the mesh and boundary
conditions.
In 1D the structure is simply a vector.
In 3D the material structure refers to the structure of the xy-plane before extrusion
or rotation takes place.
8. Materials Interval
Elements are created only for those materials that lie in the interval defined by the
two integers.
This is on easy way to define different meshes for different physical phenomena.
In 3D the interval refers to the materials that should be present in the extrusion.
9. Boundary Definitions
There may be several boundaries. Each is defined by a line of four parameters.
For example,
type out int double
Note that this field should be finished by End.
Each boundary requires a typethat refers to the number of the boundary condition.
It may then later be referred to when setting up the boundary conditions.
The boundaries are created in such a way that the material intshould have
elements created. The outmay be an empty subcell.
If the value of the flag double is 2 or more secondary nodes on the boundary will
be created. This enables the use of discontinuous boundary conditions.
10. Element Degree
The mesh generator may produce linear, quadratic and cubic elements. The
elements are initially always topologically rectangles and may have 4, 5, 8, 9, 12 or
16 nodes.
11. Surface elements
The mesh generator may produce linear, quadratic and cubic elements.
The elements are initially always topologically rectangles and may have 4, 5, 8, 9,
12 or 16 nodes.
12. Modification 1 : Increase number of
Subcells
Change the line
Subcell Divisions in 2D = 1 1 (This is 1 x 1 square grid )
To
Subcell Divisions in 2D = 2 3 (this is 2 x 3 rect grid )
We have to make two corresponding modifications to see this change happen:
Modification 1 :Subcell limits will change. Change them to
Subcell Limits 1 = 0 1 to Subcell Limits 1 = 0 1 2 (along x dir)
Subcell Limits 2 = 0 1 to Subcell Limits 2 = 0 1 2 3 (along y dir)
Modification 1 : Material structure will change Change it to specify material for each subcell
Material Structure in 2D
1 1
1 1
1 1
End
13. Modification 2 : Remove material to
change shape
The above modification gives us freedom to change the material structure
We can give a material structure to the subcells . Let it be
1 1
1 1
1 1
If we change it to
1 1
1 0
1 1
It will look like a C
And If we change it to
1 0
1 0
1 1
It will look like L
Material 0 means no material
14. Modification 3 : Introduce a new
material(step 1)
The above modification gives us freedom to change the material structure . Let us now introduce a couple of new materials (Material 2 and material 3 )
We can give a material structure to the subcells . Let it be
1 1
1 1
1 1
If we change it to
1 1
1 2
1 1
It will look like a rectangle with a cell reserved for incorporating new material in middle right cell
And If we change it to
1 2
1 3
1 1
It will look like rectangle with a the top right cell reserved for material 2 and middle right cell for material 3
However, the material interval field must be updated
15. Modification 3 : Introduce a new
material(step 2)
To incorporate new materials 2 and 3, change the material interval field to
Materials Interval = 1 1 to Materials Interval = 1 3
16. Modification 4 : Define boundary for new
materials
Change the boundary Boundary Definitions to create new boundaries
Change Boundary Definitions from
! type out int double of the boundaries
1 0 1 1
To
! type out int double of the boundaries
1 0 1 1
2 0 2 1
3 0 3 1
End
You can see that new boundaries are being created at the boundaries of material 2 and
3
17. Modification 5 : Create intermediate
boundaries
In order to create boundary name boundary 3, between material 2 and material 1 , and another boundary named
boundary 4 between material 3 and material 2, we change the boundary definitions from
! type out int double of the boundaries
1 0 1 1
2 0 2 1
3 0 3 1
End
To
! type out int double of the boundaries
1 0 1 1
2 0 2 1
3 0 3 1
End
