Shell (2-D) Meshing Of A Car Hood

Shell (2-D) Meshing Of A Car Hood

Aim: To create the shell (2-D) meshing for a car hood model by eliminating geometrical errors and considering the given element quality criteria using ANSA.

Element Quality Criteria:

S.No	Quality Criteria	Value
1	Target/Average length	5
2	Minimum Length	3
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
12	Tria Percentage	15

Procedure:

The meshing is done by following steps

1. Import Hood.stp in to the ANSA

2. CAD Geometry clean up and topology

3. Mid-surface extraction

4. Setting the PID

5. Defeaturing

6. Shell meshing

1. Import Hood.stp in to the ANSA: Import the given Hood model_1.stp in to the ANSA Shown in the fig.1.1 and make orientation of all visual faces show in fig.1.2a, fig.1.2b and 1.2c for outer panel, inner panel and latches respectively.

Fig.1.1: Imported File

Fig.1.2a: Outer Panel

Fig.1.2a: Inner Panel

Fig.1.2c: Latches

2. CAD Geometry clean up and topology: In this step the given model undergo geometry check (Tools>Checks>Geometry) where ANSA check for any geometrical errors such as collapsed faces, cracks, single con, triple con etc. those errors are shown in fig. 2.1.

Fig.2.1: Geometry Errors

Geometrical errors are cleared by using release triple cons and topo, deleting the overlapped faces and creating new faces. fig.2.2 shows the fixed all Geometrical errors.

Fig.2.2: Geometry Clean Up

Before going to the Mid-surface check geometrical errors for all individual.

3. Mid-surface extraction: the given model has all sheet metal parts and Before going to the Mid surface extraction make a note for thickness of all parts (Utilities>Measure).

S.No	Name	Thickness (mm)
1	Outer Panel	0.75
2	Inner Panel	0.75
3	Latches	1.2

Mid-surface extraction done by manually because it is easy to extract. We can retain all CAD surfaces. Due to CAD surfaces we can easily conclude mid-surface position By comparing with it. Where as in auto mid-surface it is difficult to retain CAD surfaces.

Here mid-Surface extracted by Offset method (Topo>Faces>Offset>Faces) shown in the fig.3.1.

Fig.3.1: Mid-Surface Extraction by Offset

While extracting the mid-surface by Offset method it will ask for the offset distance along with direction. With respect to direction input the value. The value may be +ve or -ve depending on direction shown in the fig.3.2.

Fig.3.2: Offset Method

Mid-surface extracted for all parts shown in the fig.3.3a, 3.3b and 3.3c.

Fig.3.3a: Outer panel Mid-Surface

Fig.3.3b: Inner panel Mid-Surface

Fig.3.3c: Latches Mid-Surface

4. Setting the PID: setting PID (Property ID) for each mid surface done by using Set PID (Topo>Faces>Set PID). ANSA asked to select faces after conforming the faces Property Help window will pop up, in that window create new PID by right clicking mouse button and select New>PSHELL. Another PSHELL window will popup there we can assign the Name, MID (material ID) and thickness shown in the fig.4.1. We can modify the colors of each PID.

Fig.3.3c: Setting The PID

5) Defeaturing: Update the element length as per given element Quality criteria (Mesh>Perimeters>Length) which is Target/Average length 5. Removing all unnecessary edges, fillet radiuses etc. also maintain distance between two cons or nodes not less than Minimum Length of 3. Before and after defeaturing for outer panel, inner panel and latches shown in the fig.5.1, 5.2 and 5.3 respectively.

Fig.5.1: Outer Panel

Fig.5.2: Inner Panel

Fig.5.2: Latches

6. Shell Meshing: Assign given element Quality criteria in to the ANSA (Utilities>Quality criteria) and Mesh Parameters (Utilities>Mesh Parameters) shown in Fig.6.1. Here we are going to Generate Shell Mesh which is preferred for 2D mesh.

Fig.6.1: Quality Criteria & Mesh Parameters

Start meshing Process by Best Mesh (MESH>Mesh Generation>Best).

Modify mesh flow using Reconstruct (MESH>Shell Mesh>Reconstruct), Smooth (MESH>Shell Mesh>Smooth) and Split (MESH>Elements>Split). Make sure that while doing mesh all the element Quality criteria mush satisfied. Avid maxium opposite trais and quad elements.

In fig.6.2, 6.3 and 6.4 show the mesh flow.

Fig.6.2: Outer Panel Mesh Flow

Fig.6.3: Inner Panel Mesh Flow

Fig.6.4: latches Mesh Flow

Thickness assigned to the all parts by selecting Draw Shell As Solid (Utilities>Quality criteria>Presentation Parameters) and shown on the fig.6.5, fig.6.6, Ans fig.6.7.

Fig.6.5: Outer Panel Thickness

Fig.6.6: Inner Panel Thickness

Learning Outcome:

1. Learnt user inter face of ANSA.
2. Learnt CAD geometry clean up, topology, Mid-surface extraction And Defeaturing.
3. Learnt shell meshing and making good mesh flow with considering the Quality criteria

Conclusion

Shell (2-D) mesh is done Successfully for a car hood model by eliminating geometrical errors and considering the given element quality criteria using ANSA.

(Find the attached file of Hood model_Complete_mesh.stp)