Week 12:Project 2-Meshing of Rear Wheel Holder challenge

Aim: Extracting mid surface, geometry cleanup, meshing and quality check on Rear Wheel Holder model by using hypermesh.

OBJECTIVE:

1. To extracting mid surface on Rear Wheel Holder model.
2. To perform geometry cleanup on the extracted mid surface using hypermesh.
3. Discretization on extracted midsurface.
4. To check the mesh quality as per quality criteria.

PROCEDURE:

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. Project_2, which is in .iges format. So to import the .iges file format model in hyperworks, 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.

Once Rear Wheel Holder 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 Rear Wheel Holder 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.

2. Geometry cleanup:

In order to perform geometry cleanup, first we will observe that we have 14 different component assemblies as shown in picture below.

Figure 2: Geometry cleanup of Rear Wheel Holder model.

So, now we will organize all 14 components in to single component by following steps mentioned below.

Tool---->Organize---->Collectors---->Select surface: Displayed---->Select: Destination component---->Move

Figure 3: Geometry cleanup of Rear Wheel Holder model.

In Rear Wheel Holder 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. Also, we have to remove the buttons size feature because it will be difficult to capture these areas as well mesh flow will not be proper. Except this feature, all the other features have captured with proper element quality.

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.

Figure 4: Before Geometry cleanup.	Figure 5: After Geometry cleanup.
Figure 6: Before Geometry cleanup.	Figure 7: After Geometry cleanup.

3. Quality criteria parameters

Figure 8: Quality criteria parameters.

4. 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 0.75mm and is same throughout.

To extract the mid surface, we have to follow: Geometry---->surface edit---->offset----> Select surface i.e. duplicate ---->offset value i.e. thickness----> vector direction ---->offset.

Once mid surface is extracted and geometry cleanup on extracted mid surface is done, model will look like as shown in picture below.

Figure 9: Mid Surface Extraction of Rear Wheel Holder model.

5. 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 10: Discretization of Rear Wheel Holder model.

After reflecting the elements in the model 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.

6. Result and Conclusion

6.1 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 11: Element quality checking of Rear Wheel Holder model.

So from above mentioned picture, we can analyze from inner side door 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.

All the components are successfully done for mid surface extraction, geometry cleanup, meshing and quality checking.

Figure 12: Shell as Solid.	Figure 13: CAD model of Rear Wheel Holder model.