Meshing the CAD model of the hood of a car for structural analysis using ANSA.

Objective:

Perform CAD model check and implement meshing according to the required quality criteria.

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

Procedure:

1. Import the CAD model of the hood of the car into ANSA interface.

2. Perform an intial geometry check and fix the errors if any.

Intial check:

Final check:

3. Visually check the orientation and rectify if any descrepancies arise.

4. There are four components in the assembly of the hood model. Inner hood has the maximum number of features. Hence, for inner hood and outer hood automatic midsurfacing is used (Midsurface command) where as for the latch and the two hinges manual midsurfacing is used (Offset command).

Each component is meshed separately. Therefore, inner hood is isolated first. Using the measure command, thickness of the inner hood is known and the offset value for the mid surface is evaluated.

The thickness for the inner hood and outer hood is the same, 0.75mm. Thickness for the laych and the hinges were 1.2mm.

Using mid surface command, mid surface is generated for the inner hood and outer hood at an offset of 0.375mm. By using the mid surface command, original inner hood and outer hood is deleted and a new PID is generated as a skin.

Using offset command, mid surface is generated for the latch and hinges at 0.6mm. The mid surface generated is isolated and saved as a new PID.

Topology is performed on each component individually.

After generating mid surface for each component, another geometry check is conducted.

5. In the mesh interface, quality criteria and mesh attributes are assigned as required. Geometry changes as required are performed on the features of the hood. Best command is used to generate mesh. Quality check is performed on the generated mesh. Mesh is adjusted accordingly such that it obeys the required quality criteria.

Inner hood:

Nodes in red colour in the above picture show the marking of nodes after editing the geometry.

Outer hood:

To capture the geometry of the hem at the border of the hood correctly, the peak of the hem were connected to the end of the hem and to the other node on the hood.

Latch:

Hinges:

Mesh clean up is done using the combination of following commands as and when required:

1. Reconstruct

2. Delete nodes

3. Cut

4. Smooth

5. Split

Meshed hood model:

6. After successful meshing, thickness is assigned to each component.

Inner hood - 0.75mm

Outer hood - 0.75mm

Latch - 1.2mm

Hinges - 1.2mm

In the presentation parameters, "draw shell as a solid" feature is switched on.

Conclusion:

Since, the inner hood contained most of the features, maximum time was consumed to rectify all the errors to acheive an error-free mesh. The hem on the outer hood was captured successfully and hence, uniform mesh was obtained all along the hem.

Hot points were added, removed and moved as required to obtain uniform mesh as much as possible. Final mesh obtained was error free and satisfies all the required quality criterias.

Therefore, the model of the hood is ready for further structural analysis.