Week 8-3D Tetra Meshing Challenge

TO CREATE TETRAHEDRAL MESHING ON GIVEN MODELS BY USING HYPERMESH

Aim: To create tetrahedral meshing on given models by using hypermesh.

OBJECTIVE:

1. To perform geometry cleanup on the surface using hypermesh.
2. To create 3D Tetramesh from 2D shell elements and then check the tet collapse parameter.
3. To generate 3D Tetramesh by using Quick tetra meshing and then check for tet collapse.
4. To generate 3D Tetramesh by using volume tetra meshing and then check for tet collapse.

1. CAD MODEL 1

PROCEDURE:

1.1 CAD MODEL:

Open the hyperwork software, and then we have to set user profile interface i.e. Optistruct or RADIOSS. Optistruct is implicit solver which handles small deformations. And RADIOSS is explicit solver which handles large deformation. So we will use RADIOSS as user interface.

First we have to import the required file i.e. Housing model, which is in. stp format. So to import the. stp file format model in hyperworks, we have to follow: File--->Import---->Geometry---->STEP---->select file--->Import. Once model is opened, then we will switch the geometry color mode from “auto mode” to “By Topo”. Once mode is changed model will look like as shown in picture below.

Figure 1: CAD model of Housing model

Housing model consist of following components i.e.

1.1.1 Outer component

1.1.2 Inner component

1.1.1 Outer component

Once outer is selected to make it visible in hyperworks window. It will show the solid component. And we have need for surface only. So, we have to delete the solid by using delete option. In order to use delete option. Under collectors select delete then select solid as displayed and then have to select delete entity. Once solid is deleted, we will only have surface. And the model will look like as shown in picture below.

By default, “auto mode” is selected in “geometry color mode”. If auto mode is on we cannot check the free edges, CONS, suppressed edges and sharp edges etc. which are the main criteria for geometry check.

Now we will switch the geometry color mode from “auto mode” to “By Topo”. Once mode is changed model will look like as shown in picture below.

Figure 2: CAD model of Outer component

Free edges are shown in red color. In this surface edge is not connected to any other surface edge.

Shared edges are shown in green color. This is the boundary between two connected surfaces.

Suppressed edges are shown in blue color.

1.1.2 Inner component

We have to follow similar process for as discussed earlier.

Figure 3: CAD model of Inner component

1.2 Geometry cleanup:

To perform geometry cleanup operation, we will use autocleanup panel. Cleanup operations include the equivalencing of "red" free edges, fixing of small surfaces (relative to the element size), and detection of features such as beads. It also performs specified surface editing/defeaturing operations like the removal of pinholes (less than specified size), removal of edge fillets, and the addition of a layer of washer elements around holes.

To perform this operation, we have to follow:

Geometry---->autocleanup---->select surface: all---->autocleanup

In order to resolve those errors which are not auto detected, we have to manually perform spline / filler, ruled options to repair geometrical errors by following Geom---->Surfaces---->select spline/filler or ruled.

Spline/filler subpanel option helps to create surfaces by filling in gaps, such as a hole in existing surface. And ruled subpanel option helps to create surfaces by interpolating linearly between lines or nodes.

Once geometrical errors are resolved model will look like as shown in picture below.

As we will perform defeaturing, which will help us to provide good meshing flow by eliminating unnecessary CONS on flat surfaces. To suppress these unnecessary CONS we have to perform toggle function by following

Geom---->edge edit---->toggle.

Once toggle operation is done model will look like as shown in picture below.

Figure 4: Geometry cleanup of Outer component

1.3 Quality criteria parameters

Figure 5: Quality criteria parameters for CAD model 1

1.4 Discretization of component:

1.4.1 2D Shell elements:

A mesh is a network that is formed of cells and points. A meshing is the process of subdividing the structure from infinite number of points to the finite number of node and elements. This process is also known as discretization.

And we have to maintain the distance between two nodes equal to the average target length i.e. 5mm. This can be done by following certain steps i.e.
2D---->automesh---->select surface---->element size---->mesh type: Trias---->mesh.

In order to fix quality meshing we will use some of useful function such as remesh, rebuild mesh, smooth, split elements, align nodes, replace nodes etc.

We will also use normal panel which is under tool. Normal panels help to display and reverse the normal of elements or surfaces.

Once discretization is done, we need to verify the connectivity between the nodes throughout. To verify and correct connectivity we will use equivalence by following certain steps.

Tool---->edges---->select element---->preview equivalence---->equivalence

we can also increase the tolerance value if the nodes are not getting highlighted.

1.4.2 Element quality checking

During meshing we have to take care of element quality. Element quality help us to understand how much the element has deviated from the ideal element. Because during meshing poor elements will misrepresent the geometry and will lead to inappropriate results. To perform quality check operation, we have to follow certain steps i.e.

2D---->quality index

In quality index we have cleanup tools which helps us to fix element quality such as drag tria elements, element optimize, split quad element and combine tria element etc.

Figure 6: Discretization of Outer component	Figure 7: Discretization of Inner component

1.4.3 2D to 3D conversion:

To perform tetramesh on outer & inner component, we will use algorithm type is Tetra mesh to generate meshing in interior of volume by following:

3D---->tetramesh---->Tetra mesh.

Figure 8: Discretization process of CAD model 1

Also, for better mesh quality, we should have to fill Tetramesh parameters such as Max-Min tetra size, Tet collapse, smoothing etc. Once Tetra mesh is generated, model will look like as shown in picture below.

Figure 9: Discretization of Outer component	Figure 10: Discretization of Inner component

Also we have to make sure, there should be no kinks and dips on the surface of components. If we get any collapse, we have to rectify those elements by moving nodes manually. Some of the methods that can helps use for improving the quality of elements are as follow:

• Manual adjustment
• Tetra remesh

So, we have no TET collapse issues in both outer and inner components as shown in picture below.

Figure 11: quality checking of Outer component	Figure 12: quality checking of Inner component

2. CAD MODEL 2:

PROCEDURE:

2.1 CAD MODEL:

To open CAD model 2, we have to follow same procedure as explained earlier for CAD model 1. In this file format for CAD model 2 is .iges. So to open this file format, we have to follow: File--->Import---->Geometry---->IGES---->select file--->Import. Once model is opened, then we will switch the geometry color mode from “auto mode” to “By Topo”. Once mode is changed model will look like as shown in picture below. And we have only need for surface. So, we have to delete the solid by using delete option.

Figure 13: CAD model 2

2.2 Geometry cleanup:

To perform geometry cleanup operation, we will use autocleanup panel. And operations that we have to perform for CAD model 2 are same as explained earlier for CAD model 1. Once geometry cleanup is done model will look like as shown in picture below.

Figure 14: Geometry cleanup of CAD model 2

2.3 Quality criteria parameters

Figure 15: Quality criteria parameters of CAD model 2

2.4 Discretization of component:

2.4.1 Quick TetraMesh:

To mesh this component, we will use quickmesh. This operation generates 2D mesh automatically and converts into 3D mesh. In order to perform this operation, we have to follow:

Step: 1---->	step: 2---->	Step: 3

Once Quick TetraMesh is done, model will look like as shown in picture below.

Figure 16: Discretization of CAD model 2

When we will check this model for Tet collapse issue. Then following elements are found fail as shown in picture below.

Figure 17: Discretization of CAD model 2

So to resolve this Tet collapse issue, we have to follow same procedure as explained earlier for CAD model 1. Once tet collapse issues are resolved model will look like as shown in picture below.

Figure 18: Qualirty check of CAD model 2

3. CAD MODEL 3:

PROCEDURE:

CAD MODEL:

To open CAD model 3, we have to follow same procedure as explained earlier for CAD model 1. File format for CAD model 3 is .iges. So to open this file format, we have to follow: File--->Import---->Geometry---->IGES---->select file--->Import. Once model is opened, then we will switch the geometry color mode from “auto mode” to “By Topo”. Once mode is changed model will look like as shown in picture below. And we have only need for surface. So, we have to delete the solid by using delete option.

Figure 19: CAD model 3

CAD model 3 consists of following components i.e.

3.1 Casing

3.2 Central hub

3.3 Hub

3.1 Casing:

Once casing is selected, to make it visible in hyperworks window. It will show the solid component. And we have need for surface only. So, we have to delete the solid by using delete option. In order to use delete option. Under collectors select delete then select solid as displayed and then have to select delete entity. Once solid is deleted, we will only have surface. Procedure will be same for both the casings. And the model will look like as shown in picture below.

To perform geometry cleanup operation, we will use autocleanup panel. And operations that we have to perform for CAD model 3 are same as explained earlier for CAD model 1. Once geometry cleanup is done model will look like as shown in picture below.

Figure 20: CAD model of casing

3.1.1 Quality criteria parameters

Figure 21: Quality criteria parameters of CAD model 3

3.1.2 Discretization of component:

Volume tetra Mesh:

To mesh this component, we will use volume tetra mesh. This operation generates 2D mesh automatically and converts into 3D mesh. In order to perform this operation, we have to follow:

Figure 22: Discretization process of CAD model 3

Once meshing is done model will look like as shown in picture below.

Figure 23: Discretization of Casing model

Now we have to check our model for tet collapse issues. Once model is checked for tet collapse quality parameter, model will look like as shown in picture below.

Figure 24: Quality check of Casing model

3.2 Central hub

Once central hub is selected, to make it visible in hyperworks window. It will show the solid component. And we have need for surface only. So, we have to delete the solid by using delete option. In order to use delete option. Under collectors select delete then select solid as displayed and then have to select delete entity. Once solid is deleted, we will only have surface. And the model will look like as shown in picture below.

To perform geometry cleanup operation, we will use autocleanup panel. And operations that we have to perform for CAD model 3 are same as explained earlier for CAD model 1. Once geometry cleanup is done model will look like as shown in picture below.

Figure 25: CAD model of central hub

3.2.1 Discretization of component:

Volume tetra Mesh:

To mesh this component, we will use volume tetra mesh. Procedure to perform this operation is same as explained earlier for casing. Once meshing is done model will look like as shown in picture below.

Figure 26: Discretization of central hub model

Now we have to check our model for tet collapse issues. Once model is checked for tet collapse quality parameter, model will look like as shown in picture below.

Figure 27: Quality check of central hub model

3.3 Hub

Once hub is selected, to make it visible in hyperworks window. It will show the solid component. And we have need for surface only. So, we have to delete the solid by using delete option. In order to use delete option. Under collectors select delete then select solid as displayed and then have to select delete entity. Once solid is deleted, we will only have surface. Procedure will be same for both the hubs. And the model will look like as shown in picture below.

To perform geometry cleanup operation, we will use autocleanup panel. And operations that we have to perform for CAD model 3 are same as explained earlier for CAD model 1. Once geometry cleanup is done model will look like as shown in picture below.

Figure 28: CAD model of hub

3.3.1 Discretization of component:

Volume tetra Mesh:

To mesh this component, we will use volume tetra mesh. Procedure to perform this operation is same as explained earlier for casing. Once meshing is done model will look like as shown in picture below.

Figure 29: Discretization of hub model

Now we have to check our model for tet collapse issues. Once model is checked for tet collapse quality parameter, model will look like as shown in picture below.

Figure 30: Quality check of hub model

Result and Conclusion

1. Successfully created the 3D Tetramesh from 2D shell elements with quality check parameters.
2. Successfully generated the 3D Tetramesh by using Quick tetra meshing with quality check parameters.
3. Successfully generated the 3D Tetramesh by using volume tetra meshing with quality check parameters.