Preprocessing - IP substrate - Midsurface Extraction using ANSA for Structural Analysis

Objective:

• Clean geometry check
• Extract the midsurface for the given models
• Checking the mesh quality and eliminating the mesh errors.

Procedure:

• Geometry cleanup:

The imported model is checked for the geometry errors using the checks

manager. If there is any problem, it should be corrected and the geometry is made clean.

• Extracting the mid-surface:

Then the mid-surface should be extracted. It can be extracted either manually or automatically using appropriate methods or a combination of both can be explained. It is based on the thickness variation and time constraints. In manual method, the faces are selected, and the offset value is given. In automatic method, the mid-surface is extracted in a form FE model straight. For this, the whole part is selected, maximum thickness value, target element size are given in prior.

• Assigning PID and thickness:

Now, the regions with different thickness are assigned with different Pl D's and the thickness values are assigned accordingly.

• Mesh generation:

Then,if the mid surface is a CAD geometry, then the model is meshed with the target element size defined.

• Meeting the quality criteria:

Now, the mesh elements are corrected to meet the quality criteria specified below.

Mesh criteria:

S. No.	Quality Criteria	Value
1.	Aspect Ratio	3
2.	Skewness	45
3.	Warping	30
4.	Taper	0.5
5.	Min. Length	3mm
6.	Max. Length	7mm
7.	Min. angle Quad	45
8.	Max. angle Quad	135
9.	Min. angle Tria	30
10.	Max. angle Tria	110
11.	Tria %	15

Target Element size : 5mm

Element Type : Mixed

Model 1 :

The following model is cleaned up and are free of geometrical errors

Fig1 : Clean of Topo Errors

For the flat faces with less complex geometry,

TOPO > FACES > OFFSET

For complex geometry,

TOPO >FACES > MIDDLE > MULTI

Then the ribs are mid extracted, and they are extended to meet the original mid surface. Then they are assigned with different PID's and according thickness

Fig 2 : After Midsurface Extraction

After assigning thickness, the model is meshed using the following option.

MESH ----> MESH GENERATION ---> MIXED

And the mesh elements are now corrected to meetup the mentioned quality criteria

Fig 3 : Fixed Quality according to the given criteria

Model 2 :

Fig 4 : After geometry clean-up

The following model is cleaned up and the middle surface is extracted using the following options.

TOPO > FACES > MID- SURFACE > CASTING

There the target element size is given as 5 mm. So the middle surface is extracted automatically in the form of FE model as shown below.

Fig 5 : After Midsuface Extraction

Now, the middle surface can be checked using the following algorithm,

TOPO > FACES > MID-SURFACE > CHECK MIDDLE SURFACE

To automatically assign PID and appropriate thickness,

TOPO > FACES > MID-SURFACE > CALCULATE THICKNESS

Now the FE middle surface is assigned with the PID's and the thickness values. But it should be cross-checked by the user and should be refined for better results.

As the surface is already in the form of FE model, now it should be corrected to meet the quality criteria mentioned. After correction,

Fig 6 : After Meeting Quality Criteria

Model 3:

Fig 7 : Model is free from Topological Errors

On the above model, Midsurface Extraction is done using the same procedure as described in the model before.

FigFig 8 : After Midsurface Extraction

Surface Mesh checks & quality errors are eliminated.

Fig 9 : After Meeting Quality Criteria

Model 4:

Fig 10 : Model is free from Topological Errors

On the above model, Midsurface Extraction is done using the same procedure as described in the model before.

Fig 11 : After Midsurface Extraction

Surface Mesh checks & quality errors are eliminated.

Fig 12 : After Meeting Quality Criteria

Model 5 :

Similar procedure as the first model was followed to extract the mesh with assigned thickness.

Some of the surfaces were missing in the mesh which was fixed by creating new surfaces. The alignment for the ribs was fixed

All surface mesh errors were successfully resolved.

Fig 13 : All clean checks on this model

Conclusion :

• For models that have thickness value less than the target element size, midplanes must be extracted and meshed in order to mesh the entire model including the thickness area.
• "Casting: Mid surface" and "Calculate Thickness: Mid surface" commands can be used to automatically extract a meshed midplane and assign thickness to it. The mesh generated by the algorithm may not be accurate and must be manually compared with the original model to check for any errors.
• All IP substrate models ware meshed and all surface mesh errors were resolved.

Link : https://drive.google.com/open?id=1Wu9Y08VmrKwtMEgw-7q7Q4JepSpYG_IE