Tool Test-2

AIM:

1. To eliminate geometrical and topological errors in the given model(intake manifold).

2. To create both surface and solid mesh on the given model and arrive at a conclusion.

PROCEDURE:

PERFORMING THE GEOMETRY CLEAN-UP:

1. The given model is an intake manifold of a car engine that supplies fuel/air mixture to all the cylinder heads present within the engine. When we import the model to the ANSA software the model will look like this.

There will be unchecked faces,unnecessary single cons and triple cons and also some unoriented faces. They must be fixed in order to proceed with the 2-D mesh.

2. Perform a complete topology on the model to convert single cons into double cons. This can be done with the help of TOPO option from the FACES menu.

3. Run the CHECKS manager for the geometry of the model. The CHECKS manager will show some unchecked faces and some needle face errors. Use the AUTOFIX option by right clicking on the error displayed to remove that particular error. To remove all errors select all the warnings displayed by the CHECKS manager and do an AUTOFIX as a whole. This will remove all the errors and ANSA will show a green status tick to ensure that there are no existing errors. 

4. Perform a complete orientation on the model by using the ORIENT option from the FACES menu. This will convert the model into a grey feature indicating the outer surfaces and converts faces that were yellow in colour.

5. After doing the geometry checks, topology and orientation the intake manifold model should look like this.

6. Now the model is perfect and we can proceed with the 2-D meshing(surface meshing).

PERFORMING THE SURFACE MESHING:

1. Since this model's thickness is undetermined,we need not have to extract the mid-surface. We can perform the meshing on the parent body itself. But before meshing,we must set the target element length and remove some construction lines on the model that may be a threat to quality.

2. Go to the MESH module and click on LENGTH option from the PERIMETERS menu. Select the entire model and in the length box specify the value as 3mm (Since our given target element length is 3mm). The entire model will be refined to a value of 3mm.

The above picture shows that the target element length has been set as 3mm.

3. Define the quality parameters required. Since the min and max.length are the only criteria required for this model, go to the QUALITY CRITERIA tab and click on SHELLS menu. This will display the quality parameters for the 2-D mesh only. Select the min and max.length and enter the values as 1mm and 5mm. A screenshot of the quality criteria is attached below.

4. Now the mesh parameters are to be specified. Click on the MESH PARAMETERS menu and enter the values of target element length, min and max.length. Then select the type of element as tria and ortho tria(As we are following the tetra mesh approach ie.unstructured mesh). 

5. Eliminate macros in the model which may be less than 1mm so as to capture the mesh without failing for quality. Use CUT option from FACES menu or MACROS-CUT in the MESH MODULE to remove construction lines.

6. Now we can proceed with the surface mesh. Mesh the model area by area using the SPOT MESH option from the MESH GENERATION menu(SPOT MESH gives the most optimum mesh result). Use the RECONSTRUCT option in the SHELL MESH menu to clear off elements and to also obtain a better mesh flow.

7. After completing the surface mesh our model will look like this.  

Note that there should not be any elements failing for min and max.length in the 2-D mesh. Also check if there are zero quad elements. Now we can proceed with the volume mesh or 3-D mesh.

GENERATING THE VOLUME MESH:

1. After completing the surface mesh go to the VOLUME MESH module. We have to generate a volume before applying the tetra mesh to the model. Go to DEFINE option in the VOLUMES menu. Use the MANUAL method to define the model. Select the entire model using box selection and click on OK. ANSA will display a volumes list. Right click on the list menu to define a new volumetric property and click OK. 

We can create any name for the volumetric property. In addition to that,the list will display the type of volume mesh and the status of mesh on the volume.

3. Again we have to specify the quality parameters for the volume mesh. Include the min.length,max.length and the collapse parameters in the QUALITY CRITERIA tab. Enter the collapse value as 0.2,min and max.length values as 1 and 5mm in the SOLIDS menu.

4. We can apply the tetra mesh on the generated volume in a single shot. There are two methods used:

a). We can either use the UNSTRUCTURED MESH option from the VOLUME MESH module. Generally there are only two types of mesh used in tetra meshing. One is the TETRA RAPID and the other is the TETRA FEM. Choose any one of the unstructured mesh to apply it on the volume by clicking on the options displayed in the VOLUME MESH module.

b). Go to the LIST option in the VOLUMES menu. There will be our defined volume appearing at the top of the list as a PSOLID ID. Right click on the ID and a drop down menu appears. Click on the REMESH option in the dropdown menu and ANSA will ask the type of unstructured mesh to apply. Select on any one of the displayed methods and the mesh will be applied instantly.

5. Now the 3-D mesh is applied. But we cannot clear all elements for quality in a volume mesh. The important criteria in the 3-D mesh is the collapse parameter which we can fix. Switch off the min and max.length criteria to view only the lements failing for collapse. Use the FIX QUALITY in the IMPROVE menu or go to MESH module and click on MV FREE option in the GRIDS menu. Allow the elements to fail for the max.length. 

6. There will be raised edges and dips on the surface of the model when we try to fix the quality for the volume mesh. They should be cleared. Use the ORIGIN option in the GRIDS menu to clear the dips in the surface. Use the MV FREE option in the GRIDS menu for raised edges.

7. Now the volume generated will look like this.

Switch off the GEOMETRY in the view menu to look at the volume generated. Keep the visiblity in the SHADOW mode to identify the raised edges and dips on the surface.

LEARNING OUTCOMES AND CONCLUSION:

1. We learnt on how to create a finite element model without extracting the mid-surface.

2. We learnt on the basic concepts of unstructured mesh and its applications. We also got to know about the COLLAPSE qualilty criteria and also the various types of unstructured mesh.

3. We also learnt that in a solid mesh or 3-D mesh we cannot fully clear all elements that are failing for quality.