Mesh Cleanup on 2D SHELL Elements | HYPERMESH

OBJECTIVE:

• To carry out geometry cleanup on the given 3 models.
• Extract the midsurface.
• Clean midsurface geometry.
• Fill holes of dia less than 5mm.
• Create 2D mesh with target length 5mm, min 3.5mm max 7mm.
• Assign proper thickness.

GEOMETRY CLEANUP:

The models for which the geometry cleanup is to be done has been shown below:

Fig 1 - Model 1

Fig 2- Model 2

Fig 3- Model 3

To cleanup the geometry following operations were done:

Filler surf: To fill the surface.

Trim with surface / plane: To trim the extended surface, selecting the extended surface & then selecting the perpendicular surface.

Toggle edge: To stitch the broken edge, stitch the broken edge and convert it to broken edge.
This can also be used to supress the unwanted lines (green lines turn to blue) & un-supress the lines which is needed (blue lines turns to green).

Delete: This option can be used to delete any unwanted lines or entities which is not required.

Edge edit: The edges which lie close to each other is merged otherwise the elements in the mesh would have some defects.

Add/remove points: To get rid of the unnecessary point which is present in the geometry.

2D MESHING:

The models which are shown above are less than 6 mm thickness. Shell element is preferred as using shell elements the number of nodes generated would be less which will reduce the simulation time.
In automotive industry all the exterior components which are having uniform thickness are meshed using shell elements.

For 2D meshing we extract the midsurface. To extract the mid surface the geometry should be closed there should not be any red edges.

The midsurfaces are shown below for the above three models:

Fig 4 - Model 1 (midsurface)

Fig 5 - Model 2 (midsurface)

Fig 6 - Model 3 (midsurface)

The midsurfaces shown above have been cleanedup using the operatons which has been discussed.
Meshing the above midsurfaces using 2D automesh option.

MESH CLEANUP:

Equivalance: The nodes might not be connected so for connectivity we use this option to connect the nodes.

Delete edges: After the equivalance has been done it is necessary to check whether there are no edges in between the edges, if there is any edges then it should be deleted.

Project: If there is any discrepency in the geometry this option is useful, the things which are going out of geometry control needs to be brought back to the geometry.

Delete: The temporary nodes can be deleted.

Smooth: To smooth the mesh elements this option is used, if the target element size is 6mm some of the mesh gets bigger while some smaller.

QUALITY CRITERIA:

Minimum & maximum length: The minimum length of the element has been set to 3.5 mm while the maximum length has been set to 7 mm. The element size is very critical in many analysis as the time step depends on the element size. Time step is the time required for the shock wave to propagate along the smallest distance of the element.

Aspect ratio: It is the ratio of the longest edge of an element to its shortest edge. It tells us that the element is not distorted.

Warping: If one particular node is out of range with it's other three node. It is the criteria related to quad elements only, as quads elements can be splitted. It is the factor related to the bending of the quad elements.

Jacobian: It measures the distortion of the element shape w.r.t an ideal shape defined for that particular element type.

Fig 7 - Dialogue box quality criteria

After Taking care of the quality criteria and assigning thickness:

Fig 8 - Model 1

Fig 9 - Model 2

Fig 10 - Model 3

CONCLUSION:

• Cleaned the original geometry.
• Extracted the midsurfaces for the given three models.
• Meshed the model using 2D elements maintaining the quality criteria.
• Assigned proper thickness to the mesh generated.