Week 4

AIM:

In order to perform a Structural Analysis with the given CAD Geometry (BOTTLE CAP) by using ANSA. The process involved as follows

• Importing CAD Geometry into ANSA
• Topology Operation
• Performing Geometry Cleanup
• Mid-surface Extraction (Manually)
• Applying given Quality Criteria - Presentation Parameters and Meshing Parameters
• Mesh Generation
• Checking the model for Quality Criteria

PROCEDURE:

Import the CAD Geometry into ANSA

TOPOLOGY OPERATION

The Topology is used to recover the results of (Hot Points – Release) and (CONS – Release) functions. It is also used to recover the Topological conditions of a Face that was undeleted by the (Faces – Undelete) function.

Before doing Topo, Let us refine the Geometry with perimeters length. To do so, Go to MESH - Modules > Perimeters > Length. Now Length perimeter pop-up appears. Window select the whole Geometry and middle mouse click to set perimeters length of 1mm. Do the same for the Macros. Now we can see that the model is refined.

Do a Topo for the Geometry by Modules > Faces > Topo. Window select the whole model and Middle mouse click will do the operation.

GEOMETRY CLEANUP

Geometry cleanup is done in order to get a better Mesh flow. To do so, Go to Checks Manager > Geometry.

Now we can see on the Geometry check pop-up that ANSA is showing some errors on the CAD Geometry. The errors are Triple CONS, Needle Faces, unchecked faces and Cracks between CONS. In order to solve the error we have to select all by (Ctrl + A) and right mouse click then hit on FIX. Now ANSA has fixed all the errors. In some parts ANSA can’t solve the error. In Those areas we have to fix it manually. To do so select a set type of same errors and right mouse click > show only. ANSA would show only the error areas. To find where exactly you have the error, Go to Neighbor > 1^st level will bring the area visible. Then we can fix it manually.

MID-SURFACE EXTRACTION

Now the Geometry is ready for Mid-Surface extraction. The CAD Geometry is a Casted part (Plastic component). Here we will do a manual Mid-Surface. Before that, I’ve created some construction lines using Faces > Cut to separate the large curved macros in the geometry and on Threads too. Which makes easier to extract the Mid-Surface from the CAD Geometry.

The tool which I used for Mid-Surface extraction is Curves Middle in Module > Curves and Modules > Faces > Offset / Middle. Curves middle is a great command for manual Mid-Surface extraction in complicated areas. A new command which I learnt in this challenge and it’s cool to work with. Some part where the geometry will have two or more construction lines forming separate curves and bend where we would find it difficult to take Mid-Surface which won’t result in achieving a complete MID i.e by using Faces > Middle or Offset. That is when the Curves middle command comes into picture like a rockstar. Let us say we have a curved Rib. At the edge of the Rib, Select the first CON then do a middle mouse click and then second CON middle mouse click. That will create a curve in the exact center of the Rib. Do this action both the sides on exact facing of the MID should be. So now we have two middle curves of the Rib. Either you can create one and Project the curve on the other side by CONS Project in Modules. That Depends on the part we work on. Then we have to create a New surface out of the Curves. To do so, Modules > Faces > New (FITTED or COONS) will do the work. Mid created. On flat surfaces Modules > Faces > Offset / Middle can be used. Faces Offset we will be familiar with. Faces Middle - This function creates a middle Face between two selected Faces. We don’t have to feed in offset values. ANSA itself programs the offset value between two faces and creates the Mid-Surface. Similarly do the same on other parts. The below Fig shows the Mid Curves generated and the new surface creation out of it.

Since we have symmetrical Teeth. After taking a Mid-Surface we have to create two COG points in order to Transform and Copy the MID to form the rest. To do so Go to Modules > Points > on COG select the circular CON and click middle mouse click to create the first COG point. Then a second circular CON which is a little higher than the first one. Then middle mouse click to create second COG points. COG points are the reference point where ANSA uses it to define the direction of circular Transformation (copy). Now go to Utilities > Transform > Copy a Selection window appears. Select the Entities to Transform and middle mouse click. Copy Entities pop-up appears. Click on Rotate command > Feed in the number of steps 36, Click on ‘x’ and select the 1^st COG point and click on ‘dx’ then select the 2^nd COG point ANSA will detect the direction of plane, Then the Angle value i.e Total Angle divided by Number of Steps (360/36). So the Angle value is 10 degree. Now middle mouse click. A Transformation pop-up appears. Click on OK and select Finish.

So we have the MID transformed to the similar parts. This action can be followed to Transform (copy) similar Entities.

Mid-Surface extraction is completed. Now we have to extend the faces to connect them to the surface. To do so Modules > Faces > Extend. This function extends Faces (source), according to a specified distance or until they reach a target Face or target group of Faces, by adding new Faces as extensions to the source ones. During this command Topology is done automatically and it form Triple CONS. As we can see in the below Fig. that the faces are extended.

After Mid-surface extraction set separate PID (Property ID) for each Mid-surface extracted. To do Modules - Faces > Set PID. A selection window pop-up appears. Faces/Shells checked. Window select the whole surface and do a middle mouse click. A Property Help pop-up appears. Go to New > PSHELL > Set a Name then click OK. New Property ID is created. In order to apply double click on the created PID. PID is successfully applied. Similarly create PID for each Mid-surface extracted. Also assign the thickness of each Mid-Surface. As shown in the below Fig.

After Mid-surface extraction, we have to do some surface cleanup. Remove unwanted hot points and Construction lines throughout the Surface. And Divide the surface by creating construction lines. To do so Go to Modules > Cut which will lead us to a Good MESH flow.

Do an Orient Visible under Faces after Geometry Cleanup. This function sets a uniform orientation direction to all visible Faces. This results in a good mesh flow.

Now the Mid-Surface is ready to MESH.

For casted parts, Mid-Surface can also be taken using Faces > Mid Surface > Casting and an Automatic Mid-Surface Mesh generator pop-up appears. There we can feed in the given values. ANSA would generate a Meshed MID surface. Which is a time saver. Mostly used in Industries.

MESH GENERATION AND QUALITY

To start with the MESHING process we have to set the given Quality Criteria

S.No	Quality Criteria	Value
1	Target/Average length	1
2	Minimum Length	.5
3	Maximum Length	3
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Tria Angle	30
11	Maximum Tria Angle	120
12	Tria Percentage	15

13 Tria Per node 2

To do so, Press F11 in the Keyboard. A Quality Criteria - Presentation Parameter Pop-up appears. Set the above given values.

In the Presentation Parameters - Enable Elements % and and slide the Detail on demand effect slider to the (all details). Then hit APPLY then OK.

Next Open the MESH PARAMETERS in Utilities TAB. Then feed in the (Basic)

Mesh - GENERAL

Mixed Type – MIXED (Consist of Quad and Tria elements)

Order of Mesh – 1^ST ORDER

Then we have to add our Target length of the mesh flow as 1mm. And set the Min. Target Length as 0.5mm and Max Target Length as 3mm. Then hit ok.

To start Meshing. Go to MESH - Mesh Generation > Best Mesh. Best Mesh automatically generates mesh on the selected Macro area by using Algorithms based on the given Quality Criteria. Some areas may fail during Mesh flow.

Challenges faced

BEFORE

Here I had a quality failure for Skewness, Angle, Min length & Trias per node. This is caused when I extended the Rib with an unwanted hot point to the cylindrical surface. Due to which the mesh got constrained and results in Quality failure. It also had a Single CONS which is not intersected with the surface during extension. Then I erased the mesh using Erase in Mesh generation Module and released the CON with Release in CONS Module. Now the Hot point is removed using Delete in Hot points Module. And Topo is done to paste the Single CONS back to the surface forms a Triple CONS. The same operation is followed on the other Ribs. After when i Remeshed on the Area again with Best Mesh command in Mesh Generation. The end result is shown in the below Fig.

AFTER

Next most of the OFF elements (Quality failed elements) were resolved on the possible areas by using RECONSTRUCT, IMPROVE and SMOOTH (in Shell Mesh under Mesh module) is done simultaneously. RECONSTRUCTION creates high quality surface MESH and solves the quality failed areas with high quality mesh flow according to the Values set in Quality Criteria and Mesh Parameters. After a reconstruction SMOOTH command is used to refine the mesh construction. SMOOTH command uniforms the mesh generation without changing the mesh orientation. I also reduced the number of Trias by eliminating them using SPLIT and SWAP commands. The SPLIT and SWAP command from Elements module used in order to eliminate, split/swap or move the Tria element. With SPLIT command The Tria elements can be eliminated and arranged with directional flow of the neighboring Tria elements. With SWAP command such as Opposite Trias, Back to back Trias are separated. The Trias can be either swapped to left or right direction of the Mesh flow. Even the SPLIT command help in solving Opposite Trias, Back to back Trias in some areas. I also used PASTE command from Grids Module to rearrange/move a step back to eliminate the Opposite Trias in some areas.

BEFORE

AFTER

Quality Criteria – Aspect Ratio, Skewness, Warping, Angle, Minimum length, Jacobian and Trias per node failed. Here the areas were constrained, hence the elements failed for Quality. OFF element areas are shown below.

Now MESH Generation is completed. And the MESH is ready for FEA.

CONCLUSION

• Geometry Cleanup is done by fixture of Triple CONS, Needle Faces, unchecked faces and Cracks between CONS.
• PERIMETERS and MACROS are set to 1mm for refined edges.
• Mid-surface Extraction of Casted Bottle Cap is done Manually.
• Surface cleanup done for better MESH flow.
• Given Quality Criteria - Presentation Parameters and Meshing Parameters applied
• Mesh generated.
• Checked the model for Quality Criteria and Quality issues were solved.