MESHING OF A CAR HOOD USING ANSA PREPROCCESOR

AIM : Succesfully mesh the provided hood of a car using Ansa

Components

• Outer panel
• Inner panel
• Left & Right Hinge
• Latch

PROCEDURE

1. Geometry cleanup
2. Extracton of midsurface
3. Meshing of all components
4. Checking quality
5. Assigning thickness
6. Conclusion

GEOMETRY CLEANUP

• When the geometry is first opened in Ansa, it can be seen as a single entity from the image below
• 
• In order to make the operation easy, lock positions are created for all the separate parts in order to operate on these parts separately. This is done by using the inot function to separate all parts and save a lock for each of them. Below are the list of parts.

Inner Hood

Outer_Hood

Latch

Left Hinge & Right Hinge

• An automatic geometry check is made on all of these lock screens to check for errors in geometry surfaces by specifying, ( single,triple and double cons , cracks, collapse cons etc). It can be seen below the results.
• 

The errors are fixed automaticallly and manually to prepare the components for meshing. The final results is seen below where the checks was successfull.

EXTRACTION OF MIDSURFACE

• Midsurface of the components are created in order to make a shell mesh on the components.This is because it is more efficient and time saving than using 3D meshing.
• The midsurface can be generated automatically and manually.This task, i chose to use the manual option. The "offset" function is used to offset the surfaces of all the components by a distance which is equall to half the thickness of the components. After offsetting, the surfaces are all joined together using "topo".
• The midsurface of all components are generated separately and saved in lock screens.
• The final geometry check is done to make sure there are no errors in the midsurface generated.
• Symmetry is recognized here when extracting the middle surfaces in order to speed up the process. The better half can always be mirrored when the operation is completed.
• Some problems which i faced during midsurfacing was the occurence of blue cons which appeared at certain places . I later realized i was creating duplicated of some surfaces and deleted them

Midsurface_Inner_Hood

Midsurface_Outer_Hood

Midsurface_Latch

Midsurface_Left & Right_Hinge

MESHING OF COMPONENTS

• Before meshing is done, all geometries must be cleaned up in order to control the rquired mesh sizes.
• For a mesh of target element size of 5, all cons and lines which form spaces with length below 2mm must be controlled. In a sense that, we must re-edit these cons to increase their sizes to 2mm and above.
• This can be done by using the perimeter length of 5mm across all components and carefuly checking for cons and edges lesser than 2mm to be editted.
• Editting is done by using the "cut" function to create cons and remove cons.
• All circles should be captured with even number of elements and they should be rotated and maked to position them parallel.
• After clean up, meshing can be started
• The element mesh size is set to 5mm and mixed element type is chosen
• All components are meshed using this mesh type and considering the following criterias for optimum mesh flow

1. All rotating quads should be eliminated from the mesh
2. Minimum tria elements should be present
3. All opposite tria elements should be combined to form quads
4. No tria elements should be in contact with any feature lines
5. Tria elements should be well spaced from each other and should not be in contact with each other.
6. No tria elements should be present at the edges of the components

These criterias where used to provide optimum mesh flow for the meshing of components.

Meshing of components was done by utilizing symmetric components and was later mirrored to optain full part mesh

Meshed_Outer_Hood

Meshed_Inner_Hood

Meshed_Latch

Meshed_Hinges

Checking Quality

Quality parameters for this mesh can be seen below.

S.No	Quality Criteria	Value
1	Target/Average length	5
2	Minimum Length	2
3	Maximum Length	7
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Tria Angle	30
11	Maximum Tria Angle	120
10	Tria Percentage	15

According to these , the mesh is checked and corrected at all areas that are failing. Below are some images of failed meshes

Components passing quality

MESHING PROBLEMS

Another problem i faced was the meshing of the corners of the outer component.It can be seen the lenght of the parts is very lesser than 2mm from the image below.Therefore any time i mesh element fail to pass minimum lenght criteria.

Solution

This was solved by deleting the hot points and changing the number of point to give the geometry below.The elements passed lenght quality criteria after this.

CONCLUSION

The components were all meshed successfully and mirrored using the trandform>copy>Symmetry comands. All elements passed the quality test and can be seen below that there are no off elements and trias % was less than 2%

Thickness

Thickness was assigned to all components by creating PID's for each of them and also Draw shell as solids was activated to show the shell thicknes

FINAL IMAGE

NB : THIS CHALLENGE HELP ME GAIN KNOWLEDGE IN USING ANSA TO GENERATE MIDSURFACE AND MESH SUCCESSFULLY WITH PASSING ELEMENT QUALITY.