Week 3

WEEK 3

Challenge Name: 2D Meshing of a Car Hood.

Aim:

To fix the Geometric Errors of the given model and to create the 2D meshing with proper mesh flow taking into account all the quality criteria provided.

Steps:

• Import the Model into ANSA software.
• Geometrical Clean up and Topology.
• Extraction of Mid Surface.
• Assigning New Property ID(PID) to the Mid Surface.
• De featuring as per requirement.
• Meshing

Given Quality Criteria:

Sl No.	Quality Criteria	Values
1	Target Length	5
2	Minimum Length	2
3	Maximum Length	7
4	Aspect Ratio	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
12	Tria Percentage	15

PROCEDURE:

Step 1:

• Import Hood.STP File into the ANSA.
• The above Input Model has a thickness of 0.75mm and 1.2mm.

• Model has 4 different components names as below:
• Upper Hood

• Lower Hood

• Side Latches

• Center Latch

Step 2:

Geometry Cleanup And Topology :

• The given model undergoes geometric checks and all the errors has to be reviewed and corrected until there is zero error and then the model ready for mid surfacing.
• Go to “Checks” command and select “Geometry” command.
• The geometrical errors will be represented in the pop up menu.
• Fix each errors automatically or manually by taking necessary command actions.

• Now the Geometry is Cleaned up and ready for Mid surface creation.

Step 3:

Extraction of Mid Surface:

In this process, the mid surfaces of all the 4 components are taken and is separated from the parent element. Steps for mid surfacing are as follows:

• Select “Offset’’ command under the Faces.
• Select the faces for which the mid surface has to be extracted by using the “Feature’’ option.

• Give the Offset value in the window popup.
• The mid surface created will be indicated by the red line in the geometry.
• This can be extracted from the geometry by using INot and PID Region command.
• The mid surface of the model is shown below.

• Similarly the mid surface has to be created for all the components

Step 4:

Assigning New Property ID(PID) to the Mid Surface:

Once the mid surfaceis crested, each component should be given a new property ID and renamed.

• After creating the mid surface ,Click on "Set PID" Command under Faces and Select "Faces/Shells" Command as shown in the picture below.
• To assign a new property, right click on the property tab, Go to "NEW" command and click on "PSHELL". New Property Card will be popup on the screen as shown below.

• Similarly, the Property ID hs to be assigned separately and indicated by using different color codes.

• Hence, new Property ID has been assigned to the Mid surface.

Step 5:

Defeaturing as per requirement:

De featuring is a technique of removing unnecessary cons, surfaces and radius which the CAD model contains which may result in non-uniform mesh flow, if not removed.

In this model the minimum element length is 3mm.So all the surfaces beyond the minimum length should be removed for better quality of mesh flow.

Step 6:

Meshing:

• Go to "Mesh" mode from "Topo" mode and assign the mesh parameters.
• Go to "Mesh Parameters" command and enter the values which are necessary.

• Enter the Quality Criteria given.
• Go to "Quality Criteria" Command(F11) select the required quality criterias.

• Mesh the Component.
• Go to "Best" command in the mesh generation option.
• Avoid Rotating quads and trias for good mesh flow.

• Thus the mesh is completed for the component.
• The different meshed components are shown below.

• Meshing of Top Hood (T=0.75mm)

• Meshing of Lower Hood (T=0.75mm)

• Meshing of Latches (T=1.2mm)

Steps Followed to remove Trias Using "Paste” Command.

• Find the opposite faced trias in the meshed component.
• Use "Paste" command under grids and select the nodes to be pasted as shown in the fig below.
• Press the middle mouse click button for confirmation.
• Two opposites faced trias are eliminated.

Steps followed to remove Trias Using "Split " Command

• Identify the trias facing to the free edges or two trias facing in same direction in the meshed component.
• Use "Split" command under Elements and select the path on which direction of the tria should move as shown in the fig below.
• Press middle mouse click button for confirmation.

• Trias near the free edges can be removed using the “Split” command as shown below.

• Similarly the rotating quad can be removed by converting the quad into two trais and it can further be removed using "Paste" and "Split" command.

Result:

The given car hood was meshed as per requirements considering all the quality criteria given and the desired thickness was assigned.

Learning Outcomes:

• Geometrical Cleanup and checking for error and fixing it.
• Releasing the triple cons.
• Creating mid surface and assigning New PID.
• Meshing of component according to the Quality criteria.
• Removing trias using Split/Swap and Paste command.
• Removing the rotating quads by Split/Swap command.

Conclusion:

Thus 2D mesh was created for the given hood component of a car according to the desired element quality criteria using ANSA workbench.