MIDSURFACING AND MESHING(2D) ON CAR HOOD USING HYPERMESH
AIM :
- To extract midsurface for car hood component.
- To perform topology cleanup on extracted midsurfaces.
- To deploy meshing on midsurfaces according to given qualitycriteria.
OVERVIEW :
- The hood
The hood or bonnet is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment, or trunk for maintenance and repair.
fig:hood opening of the car
- Midsurface & Meshing
Midsurface meshing is opted for components where the geometry thickness is small when compared with the span length of the components, so if you see most of the automotive structures are of sheet metal and plastics, where the length of the component is large when compared to the thickness, hence for this reason we opt for mid surface extraction.
since the car hood which have small geometrical thickness we extract midsurface first and then we deploy meshing according to the given quality criteria.
PROCEDURE :
first step to do after importing the model is to delete the solids from given model since mesh can only be done on geometric surfaces.we can delete it directly by clicking 
delete icon which appears on tool bar itself under the hypermesh workspace or by pressing f2 and selectimg all the displayed solid components.the image below shows the difference between surface and solid component after deleting the solids.
after deleting the solids we are going to extract midsurface from all the components like hinge,latch,inner and outer panel.
- EXTRACTION OF MIDSURFACE
This car hood model is having seperate components like hinges,latch,inner and outer body for which we extract midsurface for them individually by hiding the other components.
before extraction of midsurface delete the solid components of the model and delete unnecessary points that present on the model since they create isuues while cleaning topology.
after deleting the solids all we have is surfaces which have to be selected for taking midsurface in between them.it can be done by choosing automidsurface option under GEOMETRY-MIDSURFACE tab.we can choose advance techniques for creating midsurface in proper way without any errors or distortion by selecting "extraction options", here we choose SKIN OFFSET as an extraction option to capture midsurface
- There are smooth transitions along the faces. Sometimes, certain non-smooth transitions may be handled by increasing the default geometry feature angle.
- There are no smooth transitions at edges/holes from one face to another one, the transitions should be sharp enough.
- No ribs are present. There should only be one face(plate) in the input.
- No variations in thickness are taken into account.
after extracting the midsurface we crosscheck whether the midsurface is aligned exactly in the middle of the thickness or not by measuring The thickness of the components .here from the below image we can see that the thickness is 0.75 and the extracted midsurface also aligned properly in the middle with the distance of 0.375.
below images shows the extracted midsurface from the parent geometries of all the components of hood.
fig:extracted midsurface of innerpanel of hood
fig:extracted midsurface of outer panel of hood
fig:extracted midsurface of hinges
fig:extracted midsurface of latch
After extracting the midsurface we are going to inspect the midsurface to check for geometric errors and clean them up.
the whole point of Geometry cleanup is correcting the connectivity errors between adjacent surfaces which possibly include free edges or unconnected adjacent surfaces,duplicate surfaces,missing surfaces etc and for having good meshflow and minimum quality errors in the mesh it is better to toggle some lines and make some new cuts on the surface geometry keeping in mind about the minimum and maximum size of the element we are going to mesh.in the below images we can see at some feature areas we toggled and made some new cuts without affecting the geometry.the tools we use here are mostly in quickedit panel.go to geometry-quickedit-toggle edge to remove the lines which we need most probably we will be removing the lines which are at a distance lower than minimum element length later that we use quickedit-splitsurfnode or splitsurf/line tool to make some new cuts.
fig:geometry cleanup on inner panel of hood
here we removed so many lines which might give so many low element length quality errors in mesh and if we observe the corners make so much issues like having trias which cant be resolved manually, so we make a cut in such a way so that the tria will not be formed in that region,even if it formed we can drag and manage it with mesh edit tools.
fig:geometry cleanup on outer panel of hood
Now we move on to the important step which is meshing.to mesh a surface we have to specify element size, element type and some quality criteria values which is already given to us in the challenge.to enter the criteria values we will select preferences-criteria file settings and enter all the values.
we first mesh the feature areas which are little complex and then proceed with flat areas since we can manage the trias and mesh flow easily on flat surfaces and free edges.there are some of thumb rules which we must follow while meshing to get good result,they are
- features should be captured
- no back to back trias
- there should be connectivity between elements
- no opposite trias
- no trias in fillets or hemmings (can be compromised a little bit at some converging fillet corners)
- no rotational quads
- no trias in corners or edges
there are few components in this model which are having symmetric geometry.we can take advantage of those with help of reflect option in tools which helps us in saving lot more time.
while meshing we turn on align and size in mesh options to get proper mesh according to the size and shape of the surface with low quality errors.
these are some of the images of the model where we meshed with zero quality errors.
fig:latch component after meshing
fig:hinge component after meshing
fig:inner panel of hood after meshing
fig:outer panel of hood after meshing
fig:complete meshing of all the components of hood with zero quality errors.
After meshing we need to check the connectivity between elements which might form free edges.to find those free edges we select tools-edges-elements and by selecting the displayed elements we select all the elements appear don screen which we continue to check for connectivity by giving suitable tolerance value and by clicking on preview equivalence we can see where the elements do not have connectivity or alignments.then later by clicking on equivalence they will be resolved, and then we select "find edges" and select all the elements to check the free edges. later we can delete the free edges which are saved in separate component.the below image shows the free boundary edges other than that there are no free edges anywhere on the component.
Checking whether if there is any duplicate elements are present.to check we go to tools-check elemets-2d-duplicates and found that there are no duplicates.if found we can delete them easily by clicking on "save failed" and then we select retrieve option from elements in delete subpanel.the below image shows that we have found zero duplicate elements which is a good sign.
RESULT:
- Extracted midsurface for car hood component.
- Performed topology cleanup on extracted midsurfaces.
- Deployed meshing on midsurfaces according to given qualitycriteria.