Challenge

Tetra Meshing

AAshwin K10 Dec 2020

OBJECTIVE:

To provide a tetra mesh to the given component and clear all the elements for tet collapse

PRE-REQUISITES:

A 3-D mesh is the structural build of a 3-D model consisting of polygons. 3D meshes use reference points in X, Y and Z axes to define shapes with height, width and depth.
There are two types of 3-D meshing:

i) Tetra Meshing (with 3-D Tria Elements)

ii) Hexa Meshing (with 3-D Quad Elements)

Tetra elements are preferred in the industry as it is easy to mesh a complex geometry.
Tet collapse is one of the quality parameters, which will be checked while generating Tetrahedral elements.

Tet collapse=Min of (h/√A) ÷ 1.24

where, “h” represents the Height, between the Node (N1) and the opposite face of the Triangle, “A” represents the Area of Opposite Face (area of the Triangle).

PROCEDURE:

I) Initial Setup:

Select Radioss from the user interface menu.

Click on Import -> Import geometry -> Select the Required file.

Delete the solids from the model by clicking on Delete -> Solids -> All -> Delete Entities.

The following models are obtained:

SL NO.	Name	Model
1	Chassis
2	Crank Housing
3	Housing

II) Meshing:

There are three methods to generate Tetra Meshing:

a) Conversion of 2D tria to Tetrahedral Elements:

i) This is one of the best methods to get a tetra mesh.

ii) First, we need to provide a 2-D mesh by clicking on 2-D -> Automesh -> Surface -> Select Surface -> Element size= 5 -> Mesh type= Trias -> Check Align and Size box under Flow -> Mesh.

[Note: Shortcut for Mesh tool is F12]

iii) After obtaining a 2-D mesh make sure all the elements are passing the quality criteria.

iv) Once the quality criterias are met click on 3-D -> Tetra mesh -> Elements -> Mesh.

v) Below image shows the tetra mesh:

b) Quick Tetra Mesh:

i) This is one of the easiest methods to generate a tetra mesh.

ii) First, we need to click on View -> Utility -> Geom/Mesh -> Quick TetraMesh -> Select component -> Mesh size=6 -> Mesh type -> Trias -> Mesh.

iii)The following image shows the tetra mesh:

c) Using the Volume Tetra Mesh:

i) Click on 3-D -> Tetra mesh -> Volume Tetra -> Surface -> Check the 'Use Curvature' and 'Use Proximity ' boxes -> Mesh.

[Note: By Checking the 'Use Curvature' box we can get a good mesh around curved surfaces]

[Note: By Checking the 'Use Proximity' box we can get the same minimum element size around curved surfaces ]

ii) The following image shows the tetra mesh:

iii) To be sure about getting a tetra mesh, we can mask a few elements and check.

iv) To do so, click on Tool -> Mask -> Elements -> Select a few elements -> Mask.

[Note: Shortcut for Mask tool is F5]

v) The below image shows a successful tetra mesh:

III) Clearing Tet Collapse:

There are three methods we can use to clear Tet Collapse:

a) Translate tool:

i) Find out all the elements that are failing for tet collapse.

ii) To do so, click on Tool -> Check elements -> 3-D -> Tet Collapse= 0.15 -> Save failed.

iii) To display only the failing elements click on Tool -> Mask -> Retrieve -> Mask -> Reverse All.

iv) Click on Tool -> Translate -> Select Node -> Select N1, N2 and N3 (based on direction the selected node needs to move) -> Magnitude=0.1 -> Translate +/ Translate-.

b) Distance tool:

i) Find out all the elements that are failing for tet collapse.

ii) To do so, click on Tool -> Check elements -> 3-D -> Tet Collapse= 0.15 -> Save failed.

iii) To display only the failing elements click on Tool -> Mask -> Retrieve -> Mask -> Reverse All.

iv) Click on Geom -> Distance -> Two Nodes -> Increase or Decrease distance by entering a value in the box.

[Note: Shortcut for Distance tool is F4]

c) Tetra Remesh:

i) We have to first enter tet collapse value by clicking on 3-D -> Tetra mesh -> Tetra mesh Parameters -> Tet Collapse= 0.15 -> Min Tetra size = 2.