Week 3

Aim- To pre-process (mesh) a given hood model with given quality criteria and to provide thickness afterwards.

Procedure-

Step 1-

First of all the model was downloaded and opened in ANSA’19 and we performed a geometry check to look for TOPO errors in the CAD model provided.

And as expected it had some minor TOPO errors like unchecked faces ,needle faces etc which was automatically fixed by using the fix option of ANSA and afterwards for quality purpose we also applied TOPO to let ANSA automatically rectify the topo errors.

Fig 1 TOPO errors (before)

Fig 2 TOPO errors(after)

Step 2-

After that a close inspection was made to understand the cad for better capturing of mid surface (manually).

Step 3-

After that we started capturing the mid surface manually using the offset operator. While using the offset operator one thing we had to make sure was of the side where the mid surface was going to be appear and if required we also had to use the – sign to reverse the direction of the mid surface.

Fig 3 Using offset operator

Step 4 –

The procedure was applied for both the panels of the hood i.e inner as well outer panel.

The inner panel was a bit complex and required more precision while mid surface extraction because of the complex geometrical surfaces such as fillets and curves than the outer panel because outer panel was less complex than the inner one.

This was all about the mid surface extraction and once we were done with it we were good to go with the mesh module to mesh the mid surface we had extracted.

Meanwhile extracting mid surface we used some common operators frequently.

They are-

• Not operator- to control what we want in the working space
• Inot operator - to control what we want in the working space
• Delete operator – to delete unnecessary features
• Store lock- to lock our view

Mesh module-

Step 5-

We switched to mesh module from the topo module and under mesh generating segment there were variety of mesh algorithms like FREE mesh ,spot mesh ,best mesh, batch mesh etc.

Now as per the geometric location, use, results we had to choose among these algorithms and find out the best mesh which also fulfils our quality criterion requirements.

Quality criteria was as following-

Minimum Length	3
Maximum Length	7
Aspect	3
Warpage	15
Skewness	45
Jacobian	0.7
Minimum Quad Angle	45
Maximum Quad Angle	135
Minimum Tria Angle	30
Maximum Tria Angle	120
Tria Percentage	15
These criterias were to be fed in the quality criterion module of ansa.

Step 6-

After that we had now to rearrange the construction lines so that the mesh should fit better and should look uniform. For that we had to toggle unnecessary construction lines and at some places where required create lines using the cut operator.

Now we started with the inner panel and meshed the inner panel.we first meshed the complex areas like fillets curves etc and then normal areas.

Basically the concept was to mesh in a manner where complex areas to be given priority in meshing sequence.

Step 7 –

Once we were done meshing the inner panel we then switched to hidden mode from the right bottom part which enables us to visualise the elements which are failing the quality criteria by coloring them with respective colors.

Fig 4 Hidden Mode

Step 8 –

Now after switching to hidden we could easily see the elements which were failing the quality criteria and now we had to fix them.

For fixing them we used a couple of operators like-

• Split- to spilt element into 2 using nodes or edge
• Swap- swap to consecutive elements with each other
• Join- join to consecutive elements
• Paste – to paste 2 nodes
• Move grid – to move element edge using node
• Edge2perimeter – to change the edge of elements into a cone
• Smooth – to smoothen the elements
• Reconstruct – to reconstruct the mesh in a particular area

So these were the operators we used frequently with one after another as per requirement and were able to get rid of elements which were failing quality criteria i.e off elements.

There was no sequence of using them , we just had to use them one after another after looking for off elements we were dealing with

Step 9 –

The same procedure was applied for outer hood panel mid surface too.

Then we set PID as inner and outer panel mid surface and we provided the thickness to mid surface generated same as of the parent body.

Fig 5 Mesh check

Outcomes-

1. We got to learn about how to fix TOPO errors.
2. We got to know how to manually extract mid surface.
3. There shouldn’t be enough tri elements(although the quality was allowed to 15% but in industry usually we want it to be less than 5%)
4. There shouldn’t be tri elements scattered everywhere, they should be placed in a uniform manner.
5. Two tri elements shouldn’t share same edge or node.
6. The mesh should be uniform.
7. we learnt how to work on off elements.

Google drive link - https://drive.google.com/file/d/1PIGb7nWF9X6XUYLmivtZ6y9gdZQUemaD/view?usp=sharing