Tetra Meshing of given component according to quality criteria

Tetra Meshing of given component according to quality criteria

Rear View Mirro

Objective

• Follow the geometrical cleanup.
• Defeaturing geometry according to given quality criteria.
• Setting up properties i.e PID setup, material ID and the meshing parameters
• 2D meshing component with the tria elements
• Defining the volume for generating unstructured mesh.

Procedure

• Click on ANSA icon. It will ask you to choose the working directory and layout to work.
• You can use the performance mode for graphical issue.
• Type (-performance_mode3) to get good results in below window.

• Select ANSA and hit OK.
• Click on Import geometry. It might be .step, igs, or in another format.

• It will appears as a shaded view in Entity mode. On left side it will shows the database.
• Database include some important tabs like properties and material.
• You have to make the component fine to get actual view of cad geometry, and follow the topology.

• When you fine all the areas you will get the exact idea about how the surface looks. As shown below.

• Now we have to clear the geometry issues spotted in the check geometry.
• Here if needed we have to set the PID according to the section.

• Now we are remaining with only surfaces which we are going to use for meshing.
• All analysis depends on a good meshing so we are going to mesh individual components.

1. Geomertry Cleanup

• Here we have separated the different surfaces according to the thickness of the component with different PID as shown in the picture below.
• Now click on the inner extract component. We have to check the component for the proper surface, which is free from any errors. Such as middle face, cracks, single, double, triple cons before taking mid surface.
• For checking the geometry, we have to go to the geometry checks manager to get error free surface.

• Removal of this errors in geometry lead to get the good and clear middle surface.
• We can remove errors individually or all together, it depends on the complexity of error.
• Errors can be removed manually or automatically. But manually fixing will give the better results.
• After removal of all the errors we will get a clear surface. Now we can go for the middle surface.

1. Defeature the Surfaces according to quality criteria

• Now defeature the lines which will affect the elements failure. According quality criteria ie min- max length defeature the lines of components.

• Now we have fully equivalence mid surface. We have to clean the surface to get clean and clear meshing. It will avoid the pinholes, very small edge and surface fillets automatically. We have to set the parameters according to requirement.
• Topo mode joins the surfaces together to get continue surface.

• Removing the unwanted lines we get the surface which is required for meshing.
• Set the property id for extracted mid surface. Property may define the thickness of the shell elements.

1. Setting up parameters and quality criteria

• Set the required mesh size, type of mesh and order of meshing required, according to customer requirements and accuracy required.
• Here it is ortho tria and tria as we are going to produce unstructured tetra mesh.

Eg. Target Element Size= 1mm as shown in picture.

• Now click on edit criteria. This is where we have to specify the criteria for the Quality index of meshing.
• Set all the quality criteria and save the details as a file.

• These are the criteria on which our meshing gets checked on quality of meshing.

E.g. Min/ Max Size of element, Aspect ratio, Warpage, Min/Max Quad angle, Skewness etc.

1. Meshing

• After geometric cleanup and setting the conditions now we are going for meshing.
• We have to finalize the target mesh size and set the perimeter length. Setting of the perimeter length for meshing divides the surfaces into the imaginarily small parts for required meshing.
• Select the surface as displayed surface. Choose element size as per requirement. Here it is
• Use mesh type as Mixed. And hit the mesh button on screen.
• Adjust the nodes according to requirements. Make sure the mesh flow is good. Adjust each area of meshing with care to get a quality mesh. Hit middle mouse button to exit the mesh.

• Mesh flow near cutouts and at edge will specify mesh quality. Now meshing is done. It’s time to check the quality of the mesh.

1. Quality Check

• Click on quality index. It will show the no. of elements failing in quality criteria which we have specified previously. The quality of elements are only seen in the hidden mode. Change the mode to hidden and check the quality of elements.
• The tria failing over quality may leads to the failure of upcoming tetra mesh.

• So the quality index will show the failing elements or worst elements in the meshing. We have to avoid these elements during meshing. We can overcome these elements by remeshing certain areas again which is a good way to do it.
• Click on F11 and select the elements. Select the element from the outer edge to reconstruct the surface.

• Make a square to remeshing. It will easy to reconstruct targeted area. This is way to get remesh all the surface again and again. Repeating this procedure, you will refine mesh.
• Now again we can check for the quality criteria. In quality index we can use the tools like place node, node optimize, element optimize, split option, paste, split quad, combine tria etc
• These tools also help to get rid off from bad mesh.
• Place Node use to place a node at a required position. We can use element optimize to adjust the element as per meshing thresholds specified earlier. These options will adjust the element at minor level..
• Apart from these entire tools smooth tool is used for very minor adjustments in the elements to complete quality criteria.
• After doing all this you will get a quality mesh which will pass all the quality criteria. In industry point of view the tolerance is given for quality criteria’s it may be in 5% to 10%.

1. Creating Volume

• Now we are going to define the volume as we converting 2D mesh to 3D.
• Click on upper right corner to change to volume mesh.
• Go to list in volume tab, where you get list of volume. Right now no volume is defined here.

• First you have to define the volume manually.
• Before that we have to check the geometry and pre volume meshing checks in checks manger. This check ensure there is no any problem like leak in model or any penetration.

• Now define the volume by any method i.e Manual or Auto
• If you click on auto then it will automatically creates the volume.
• Now the status of volume is also shown in the list as given below

• Now we have to click each volume and we have to remesh the volume according to the required algorithm in the ANSA.
• As we are doing this meshing using Tetra FEM.

• The list is now showing the volume is meshed. The list shows the type and status of meshing as shown below.
• Now follow the same procedure for each volume and mesh the all volumes to get a tetra mesh.
• Check the meshing is done click on the bounds tab near hidden mode tab. If color is red then the meshing is done i.e. tetra meshing.
• Check the quality of meshing in the hidden mode for quality evolution of the mesh.

• Turn off the CAD, FE so that all volume can be seen.

• All volumes together after switching off CAD, FE, Bounds.

Conclusion:

1. Topology is very important in solid component meshing. We require to defeature the component very carefully according to quality criteria set.
2. We have to use ortho tria for curved surfaces as the surface we require should be smooth. The ortho tria have the better convergence than regular tria The regular tria can be used for plane surfaces.
3. During definition of volume the geometry should be free from leaks. Any error in geometry will not form the closed volume.
4. Elements violating threshold are zero. So the quality of mesh is good. And we can decide good mesh quality based on the mesh flow as well. So below figure shows the good mesh flow. So we can conclude the meshing is of good quality.