Assignment 1-2D Meshing Challenge

Aim: Extracting mid surface, geometry cleanup, meshing and quality check on three different geometries by using hypermesh.

OBJECTIVE:

1. To extracting mid surface on three different geometries i.e. Practice, Clip Repair and Mounting Bracket.
2. To perform geometry cleanup on the extracted mid surface using hypermesh.
3. Discretization of extracted midsurface.
4. To check the mesh quality as per quality criteria.
5. To assign proper thickness for each geometries.

PROCEDURE:

A. CAD MODEL 1-Practice:

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, which is in .hm format. So to import the .hm file format model in hyperworks, we have to follow:

File--->Import---->Model---->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.

Once Practice model is selected to make it visible in hyperworks window. It will show the solid component. And we have need for surface only. From which we will extract mid surface. 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 1: CAD model of Practice model.

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. Geometry cleanup:

In Practice model we have edges dis-connectivity. Which means these edges have no shared edges and are acting like a free edge as shown in picture above.

In order to resolve these issues, we can perform toggle function under edge edit in geometry module by increasing the tolerance value. If this operation will not work, then we can perform either autocleanup and manually 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.

BEFORE	AFTER

Figure 2: Geometry cleanup of Practice model.

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

Figure 3: Geometry cleanup of Practice model.

2. Quality criteria parameters

Figure 4: Quality criteria parameters.

3. Mid Surface Extraction:

Mid surface is the surface between two surfaces. If thickness of component is uniform throughout then mid surface generates proper. Mid surface helps to reduce number of nodes and elements created on the surface. Which in turns helps to reduce storage space required to store entire component as well as also reduce the processing time required to analyze the entire component. In this case component is having thickness 0.91mm and is same throughout.

To extract the mid surface, we have to follow: Geometry---->midsurface---->automidsurface----> Select surface i.e. displayed---->closed solid---->extract.

Once mid surface is extracted, model will look like as shown in picture below.

Figure 5: Mid Surface Extraction of Practice model.

Once mid surface is extracted, then we have to follow geometry cleanup on extracted mid surface. We also have to ignore holes less than dia 5mm for better feature capturing. We have to follow above mentioned steps in order to perform geometry cleanup.

BEFORE	AFTER

Figure 6: Mid Surface Extraction of Practice model.

Once geometry cleanup is done for extracted midsurface, finally midsurface is ready for meshing as shown in picture below.

Figure 7: Mid Surface Extraction of Practice model.

4. Discretization of component:

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: mixed---->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 model will look like as shown in picture below:

Figure 8: Discretization of Practice model.

Now 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.

5. Result and Conclusion

5.1 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 9: Element quality checking of Practice model.

So from above mentioned picture, we can analyze practice model is passing quality criteria.

To create shell as solid, we have to create property for each component of inner door model. And then we have assign thickness to each property. And finally we have to assign created properties to their respective components. Once thickness is assigned model will look like as shown in picture below.

Figure 10: Shell as solid of Practice model.

B. CAD MODEL 2-Clip Repair:

Procedure to open CAD model 2 is same as explained above for Practice model. Once model is opened, it will look like as shown in picture below.

Figure 11: CAD model of Clip Repair model.

1. Mid Surface Extraction:

To extract the mid surface, we have to follow same steps as explained earlier for CAD model 1. Once mid surface is extracted model will look like as shown in picture below.

Figure 12: Mid Surface Extraction of Clip Repair model.

From above picture we can see by using auto midsurface option, some of the fillet surfaces are missed. In order to rectify these fillet surface, we will use offset surface option, and then will use trim with surface to surface option. Once these operations are done, model will look like as shown in picture below.

Figure 13: Mid Surface Extraction of Clip Repair model.

2. Geometry cleanup:

To perform geometry cleanup operation, steps are same as explained in above case. As we can see from above picture, clip repair model is symmetric about centre. So we will delete other half of the model by following:

Geom---->Surface edit---->trim with planes---->select surface(displayed)---->Select N1,N2,N3 and B---->Trim

Once this operation is finished model will look like as shown in picture below.

Figure 14: Geometry cleanup of Clip Repair model.

3. Quality criteria parameters

Figure 15: Quality criteria parameters.

4. Discretization of component:

Steps to perform meshing is same as explained earlier for CAD model 1. Once meshing is done on half of the clip repair model, model will look like as shown in picture below.

Figure 16: Discretization of Clip Repair model.

Now we have to reflect the half of the clip repair model to the other half by following steps as explained below.

Tool---->reflect---->select surface: Displayed---->select nodes----->reflect.

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

Figure 17: Discretization of Clip Repair model.

Now we need to verify the connectivity between the nodes throughout. To verify and correct connectivity we will use equivalence by following certain steps as shown below.

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

Figure 18: Discretization of Clip Repair model.

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

5. Result and Conclusion

5.1 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 19: Element quality checking of Clip Repair model.

So from above mentioned picture, we can analyze practice model is passing quality criteria expect few elements. These failing elements cannot be changed for better feature capturing.

To create shell as solid, we have to create property for each component of inner door model. And then we have to assign thickness to concern property. And finally we have to assign created properties to their respective components. Once thickness is assigned model will look like as shown in picture below.

Figure 20: Shell as solid of Clip Repair model.

C. CAD MODEL 3-Mounting Bracket:

Procedure to open CAD model 3 is same as explained above for Practice model. Once model is opened, it will look like as shown in picture below.

Figure 21: CAD model of Mounting Bracket model.

1. Mid Surface Extraction:

To extract the mid surface, we have to follow same steps as explained earlier for CAD model 1. Once mid surface is extracted model will look like as shown in picture below.

Figure 22: Mid Surface Extraction of Mounting Bracket model.

From above picture we can see by using auto midsurface option, some of the fillet surfaces are missed. In order to rectify these fillet surface, we will use offset surface option, and then will use trim with surface to surface option. Once these operations are done, model will look like as shown in picture below.

Figure 23: Mid Surface Extraction of Mounting Bracket model.

2. Geometry cleanup:

To perform geometry cleanup operation, steps are same as explained in above case. As we can see from above picture, clip repair model is symmetric about centre. So we will delete other three parts of the model as shown in picture below.

Figure 24: Geometry cleanup of Mounting Bracket model.

3. Quality criteria parameters

Figure 25: Quality criteria parameters.

4. Discretization of component:

Steps to perform meshing is same as explained earlier for CAD model 1. Once meshing is done on one part of the mounting bracket model, model will look like as shown in picture below.

Figure 26: Discretization of Mounting Bracket model.

Now we have to rotate the one part of the mounting bracket model about center z-axis to 90degree by following steps as explained below.

Tool---->rotate---->select elements: Displayed---->select Z-axis; B----> specify angle----->rotate.

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

Figure 27: Discretization of Mounting Bracket model.

Now we need to verify the connectivity between the nodes throughout. To verify and correct connectivity we will use equivalence by following certain steps as shown below.

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

Figure 28: Discretization of Mounting Bracket model.

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

5. Result and Conclusion

5.1 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 29: Element quality checking of Mounting Bracket model.

So from above mentioned picture, we can analyze mounting bracket model is passing quality criteria.

To create shell as solid, we have to create property for each component of inner door model. And then we have to assign thickness to concern property. And finally we have to assign created properties to their respective components. Once thickness is assigned model will look like as shown in picture below.

Figure 30: Shell as solid of Mounting Bracket model.

CONCLUSIONS

1. Mid surface for three different geometries are extracted successfully.
2. Geometry cleanup on all extracted mid surfaces are done successfully.
3. Discretization and quality check is carried out successfully on extracted midsurface.
4. Proper thickness is assigned successfully for each geometries.