Shell Meshing of an Automotive Hood in ANSA

AIM:

To check for geometrical errors in the given component and mesh the component using the given Quality Criteria.

OBJECTIVE:

The main objective of the project is to learn and improvise the methods of mid-surface extraction, namely manual and automatic mid-surface generation, and meshing the component.

PROCESS:

1. Perform geometry checks (and resolve errors if any).
2. Extract the mid-surface of the component.
3. Assign thickness for the mid-surface and assign the quality criteria for meshing.
4. Mesh the component and resolve any element issues/errors.

SOFTWARE USED:

ANSA (Automatic Net generation for Structural Analysis) v19.0.1 64-bit

MODEL:

The given model is an automotive bonnet or hood. A bonnet or hood is a sheet-metal component that is used to cover the engine compartment in passenger cars. Bonnets / hoods are generally made from the same material as the other body components. They may include steel, aluminium, carbon fibre, etc.

Hoods mainly contain 2 parts, inner part and outer part. The inner part is the one which contains complex geometries and curves and the outer part is a plain sheet-metal which is used for aerodynamic purposes. Other than the inner and outer part, a hood also contains the latch reinforcement and hinge reinforcement. A latch reinforcement is a mechanically operated latch used to open and close the hood.

Outer hood:

Inner hood:

Latch reinforcement:

PERFORMING GEOMETRY CHECK:

The Geometry check can be seen under the Tools tab on the left top toolbar under CHECKS > GEOMETRY.

Now, the CHECKS MANAGER dialog box appears. On clicking the Execute button, the Geometry check is performed by ANSA on the CAD model and the Geometry discrepancies present in the CAD model are shown.

The errors can be fixed manually or can be fixed by ANSA. To fix the errors automatically by ANSA, right click on the error and click “FIX” to fix the errors. The errors can be fixed one by one or altogether at once as desired.

After the Geometry checks are done, re-checking can be done to ensure that there are no more errors left unsolved. When the errors are resolved, we can proceed to the next step.

MID-SURFACE EXTRACTION:

Before exacting the mid-surface, the thickness of the surface needs to be known. The thickness of a surface can be measured using the MEASURE command. It can be found under the UTILITIES tab in the left top.

In the MEASURE command dialog box, the measurement can be done between 2 nodes or 2 CONS, as required. Upon selecting the 2 nodes / CONS, the distance between them can be known.

According to the thickness of the surface, the mid-surface is generated. There are 2 methods of mid-surface generation / extraction. One is manual mid-surface generation and the other is Automatic mid-surface generation. Here, we will use the Manual method of mid-surface generation. The mid-surface is generated using the Faces > Offset command. Under Offset, the Face option is selected. Then the surface whose mid-surface is to be extracted is selected and the offset value is given.

Here, a negative value is used since the direction is towards the outer side and the mid-surface needs to be generated between the upper and lower surface. Upon accepting, it can be seen that the face is offset and a mid-surface is generated accordingly.

Similarly, the mid-surface is generated for all the surfaces. Then the mid-surface is separated from the parent surface as shown below.

Now, the generated mid-surface needs to be given a thickness. For this we need to assign a Property ID or PID. A Property ID or PID is normally assigning a particular component or part a distinctive feature so that it can be identified easily or can be retrieved easily.

The PID is set in the PROPERTIES command. It can be found in the LISTS tab in the top left . In the PROPERTIES command, a new PID needs to be created.

Here, in the setting, the PSHELL option is used when the component is a sheet-metal type. In case of a non-sheet-metal type component such as a casting is used, the PCOMP option should be used.

The name of the PID is given and the thickness & colour is also given. The setting of PID should be done separately for each of the components as they need to be meshed separately and then be combined together. After the PIDs are set, the components can also be viewed separately along with their respective colour in the PID visualisation mode as shown.

Now we have to assign the Quality Criteria for meshing the model. After assigning the Quality Criteria, we need to assign the mesh parameters. Quality Criteria defines the limit for the failure of the mesh elements. These are the Quality Criteria values for each parameter.

Average length                   5

Min. length                         3

Max. length                        7

Aspect                               3

Warpage                            15

Skewness                          45

Jacobian                            0.7

Min. Quad angle                  45

Max. Quad angle                135

Min. Tria angle                    30

Max. Tria angle                  120

Tria percentage                  15

The QUALITY CRITERIA command can be seen under the UTILITIES tab. The above values need to be entered into the respective fields.

These value need to be entered under the SHELLS tab since the given component is a sheet-metal type. In case of a plastic or casting component, we need to enter them in the SOLIDS tab. After assigning the Quality parameters, in the PRESENTATION PARAMETERS tab, tick  the “ ELEMENTS% “ check box and slide the slider in the bottom towards “ALL DETAILS”. This would show the % of the Quad and Tria elements out of the total no. of elements in the mesh.

Then click on APPLY and on OK. Next, we need to assign the MESH PARAMETERS. Similarly, this can be seen under the UTILITIES tab. It defines the type of mesh we are going to use to mesh the component.

In the MESH PARAMETERS dialog box, under the BASIC tab, the type of Meshing is selected.

Then the type of elements required in the mesh is selected. Since we will be using both Quad & Tria elements, MIXED option is selected.

Then the order of meshing is selected as required. Then, the Target element length and the Min. & Max. element lengths are given and accepted.

MESHING:

Meshing is done in the MESH module. There are many methods of meshing. In this case, BEST meshing is used. First, the command is selected. Then the area to be meshed is selected and when accepted, the meshing is done on the model.

Now, to identify if all the elements are passing for quality, switch to HIDDEN visualisation mode from the SHADOW mode. It can be seen that some of the elements are failing. This can be seen with the Quality Criteria colour code present in the right side bottom. The parameter which is failing can be matched with the element’s colour.

Some of the elements are failing for Skewness and some for Min. Length. This can be identified with the green and red colour elements. Some of the elements are failing for Min. Length and Angle. This can be seen with the red colour. These quality issues need to be solved so that all the elements pass for quality.

With the help of RECONSTRUCT command, the mesh elements can be reconstructed over the selected areas. Similarly, the meshing is done for all the other components.

LEARNING OUTCOME:

From this project, the 1^st order meshing of a component with Tria and Quad elements in 2D is learnt using ANSA v19.0.1 .

CONCLUSION:

Thus the given Automotive hood model is meshed with the given Quality Criteria using 1^st order elements in 2D meshing with Tria and Quad elements.

To view the model in Google drive click here.