Week 6-Meshing of Hood Challenge

#5 // Week 6- Meshing of Hood Challenge.

AIM: To mesh the given hood model with target element length as 5. also clear all the quality criteria’s given and mesh hood model by using mixed [not quad] option.

OBJECTIVE:

1. To generating Mid-surface and geometry clean up on the given hood model.
2. Mesh the component given and assign thickness.

Element Target Length = 5 Units.

3. Clear the given quality criteria.

THEORY:

Hood-

A Car hood, also referred to as a bonnet in some other countries is the hinged cover that rests over the engine of a front-engine vehicle. Its purpose is to provide access to the engine for repair and maintenance.

PROCEDURE:

1. Import CAD file to hyperwork environment.
2. Delete solid surfaces.
3. Geometry clean-up.
4. Thickness measurement.
5. Mid-surface extraction.
6. Property and thickness assigning.
7. Mask/Unmask symmetry surfaces.
8. Defeaturing.
9. Assign quality criteria.
10. Meshing.
11. Quality errors clean-up (Eliminate off eliments).
12. Check for free edges.
13. Check for normals.
14. Check for dependency.

1) Import CAD file to hyperwork environment: -

Import the “.step” model file using File > Import > Geometry > Select file type as STEP > Locate the file > Open > Click on the file > Import command.

2) Delete solid surfaces: -

Now change the geometry colour mode from Auto to By Topo and delete all solid faces for the given component. For deleting the faces, go to Tool > delete > solids > displayed > delete entities.

>>solid (in topo mode view)....

>>Surfaces (After delete the solids)....

3) Geometry Clean-up: -

Once the model is imported, move to geometry clean-up just to check if there's any duplicate surface or free edges or missing surfaces are present or not. For this enable wireframe geometry mode and then try to observe and find irregularities and discontinuities in the model. If found then fix it manually.

4) Thickness measurement: -

Measure thickness of all the components using Geom > distance > two points.

> Inner_extract measurement.. > Outer_extract measurement..

>Hinge_reinforcement_extract measurement.. > Latch_reinforcement_extract measurement..

5) Midsurface Extraction: -

Midsurface extraction is the next step after geometry clean-up and for that, go to Geom > midsurface > extraction options (offset+planes+sweeps) > auto extraction > surfs > displayed > extract.

> Inner_extract Midsurface.. > Outer_extract Midsurface..

>Hinge_reinforcement_extract Midsurface.. > Latch_reinforcement_extract Midsurface..

6) Property and thickness assigning: -

Rename all the midsurface components for convenience and create separate property cards for all the midsurface components and give thickness to them. Create material card and assign material to all the property cards and then assign property cards to their respective midsurface components.

7) Mask symmetry surfaces: -

If there's symmetry present in the components, then one half of the component can be mask to save defeaturing and meshing time because otherwise we have to defeature and mesh the same half of the component twice which is not a good decision to take so that's why it is wise to delete symmetrical half of the component and work on the other half which can be reflected on the other side later once work is done. Go to Tool > Mask > surfs > Select the surfaces > mask.

8) Defeaturing: -

Defeaturing is nothing but to remove the unnecessary surface radius, holes, edges. Often, the CAD model does contain many detailed features because of manufacturing constraints but very small entities can be a problem. If we have very small faces with sharp angles then failing probabilities of the surface meshing arise. Therefore, we should check the CAD model for very small entities and remove them before trying to create a mesh for it. For this go to Geom > defeature. We can also toggle unnecessary construction lines using Geom > quick edit > toggle // add/remove points // split surf to node // split surf to line command.

The fillet region in outer panel has been failed for quality. So, the fillet region has been defeatured for meeting the quality criteria values in this case as shown below and mainly outer and inner panel contain many of the defeatured regions.

9) Assign quality criteria: -

Every mesh produced has to go through the set of quality check. If quality check fails other steps like boundary conditions and applying loads will not be feasible, so element quality check is performed and no element is allowed to fail under this quality criteria. If the elements fail then these failed elements should be corrected and the elements should match the quality criteria. To assign quality criteria to the model, go to Preferences > Criteria File Settings / Parameters file settings.

10) Meshing:-

Before meshing, we have to make sure that quality criteria values are properly entered and quality criteria is applied. Now go to 2D > automesh > surfs > element size - 5 > element type - mixed > mesh. This will mesh the selected target surface with average element length of 5mm. Adjust the number of nodes on the either of sides, to get a good mesh flow and to make sure that rotational quads are not formed on the surface.

11) Quality errors clean-up (Eliminate off eliments): -

It is not possible to get perfect mesh flow with no failing elements in the first attempt itself so quality error clean-up is very crucial and essentials step. We have to try for getting as less numbers of trias as it can get and also there should not be any failing element present in the mesh if it is there, then it needs to get resolved. Some clean-up tools like split, swap, combine, replace, drag tria can be used to perform quality error clean-up and for this, go to 2D > qualityindex > cleanup tools.

> Or we can observed off elements by element color mode.

[Note:

• After mesh all the component and clear all the quality errors. Rebuild the mesh for getting better mesh flow and clear quality. For that go to, 2D > rebuild mesh > select elements/surfs > edit parameters > rebuild.
• By going through quality index > clean up tools > smooth/place node/swap edge/node optimize/element optimize. Etc clear all the quality criteria’s and improve the mesh.

• For symmetrical components, meshed the half of the symmetry by unmask another half and reflect it in to other half. (always select mid-point as base and analysis the direction of reflation.)
• For reflecting the mesh and surfs go to, tools > reflect > select N1 N2 N3 B > elements > duplicate > reflect.
• Do same process for others symmetrical components.
• 
• Go to Tool > edges > elements (displayed) > put min tolerance > preview equivalence > equivalence.
• 
• After that go for elements(displayed) > find edges & check their if any free elements edges left inside, if have go to delete(f2) & delete few adjacent elements then by 2D ruled option back those elements in place. (Those process performed accordingly for clear the inside elements gaps.)
• Also use replace node, combine, align options to improve the quality of the mesh.
• For eliminate off elements use translate option (shift+F4) & translate the node and element a bit for clear off elements.
• Also, some elements are distorted from surfaces/ feature lines, to make it align bake use node edit (F7) & project (shift+F7) options.
• Atlast check for duplicate elements by shrink element option or Tool > check elems > duplicates.

………]

>> /After Eliminate off elements & check with given Quality criteria..

12) Check for free edges: -

There should not be any free edge remaining through mesh after meshing because having free edges means there is no proper connection between meshing nodes/elements which is not at all acceptable so go to Tool > edges > elements > find edges. Free edges can be recognized by red con, if there is any red con found in between mesh through the meshing other than the areas having only single surface and no sharing surface then it is a free edge.

13) Check for normals: -

After completing all operations check for all components elements are align in same normals direction in each faces.

Go to Tool > normals > elements > display.

14) Check for dependency: -

To check dependency elements with surfaces, go to Tool > dependency > elements (displayed) > check.

Its shown us '0' node are found with multiple dependency.

Final view of models:-

> FE along with surfaces..

> FE for all components..

> all component view together..

CONCLUSIONs / RESULT:

Successfully perform geometry clean-up, generated mid surface and meshed with 2D (mixed) shell elements as per given hood model with best mesh flow possible also identified and resolved element failures as per given quality criteria and learned to assign thickness and property to respective components.