Pre-Processing the hood of a car

PRE-PROCESSING THE HOOD OF A CAR

AIM:

The aim of this project is to do a geometry cleanup and generate a 2-D mesh on a hood component of a car. In order to achieve a clean mesh-flow, the mesh is refined after successful mesh generation on the component while satisfying certain mesh quality criteria.

INTRODUCTION:

The pre-processing stage of CAE in product design and the testing environment involves checking the geometry designed by a CAD engineer for errors like missing/additional surfaces, orientation, etc. and then successfully meshing the product which then can be successfully exported to the solver for analysis.

A car hood is a crucial component in an automobile system as it provides protection and user access to the main components (engine, battery, etc) that are essential to run the car.

The hood component used for this project consists of four main parts,

1. Outer hood surface - Acts as a cover for the inside components

2. Inner hood surface - Provides stiffness for the outer cover and hosts components to lock the hood

3. Latch - Used to lock the bonnet to the bumper of the car.

4. Hinge - adjoined at both ends providing a locking feature when the hood is in open

SETUP:

1. Importing CAD:

The CAD geometry designed by a CAD/Design engineer can be imported into the ANSA software either as a .step or as a .iges format. These are the most popular formats and ANSA would fail to recognize any other format (.prt, .x_t, etc.)

It is recommended to set a specific limit on tolerance and resolution prior to importing the CAD.

2. Geometry cleanup:

There is a high chance that the imported CAD may face having some errors. These errors may include orientation issues, duplicate or missing surface, sharp edges (which could cause errors while meshing), etc.

-The orientation of the CAD is aligned entirely using Faces-> Orient-> Visible.

Then the file is checked for geometry errors where many needle faces are visualized.

- These needle faces can be eliminated using the Autofix command which eliminates these errors.

3. Midsurface extraction

Midsurface is extracted for every 4 components individually using the following feature:

Faces-> Mid-surfacing-> Skin

Since each of the components constitutes different thicknesses, midsurfacing each individually is advisable. The original thickness and the offset distance for every component are,

Outer - t=0.75; o=0.375

Inner - t=0.75; o=0.375

Latch - t=1.2; o=0.6

Hinge (2) - t=1.2; o=0.6

-After the extraction, a topology clear based on the given tolerance is performed on the entire part.

-Each of the midsurfaced components is then saved onto different lock views hence each component can be accessed individually for meshing.

-Check for geometry errors to verify that the mid surface operation had been successful.

-A property id is created for each individual component representing the thickness of that component. This can be done by,

Faces-> Set PID-> t

4. Mesh quality criteria

The following quality criteria are set in the MESH tab

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

After meshing the errors for the quality criteria can be visualized using the "Hidden" option.

5. Meshing

1. Outer hood surface

-Before performing the mesh operation, the components must be divided into sub components using cons adjoining hotpoints. This helps us generate a smooth mesh flow with more quads and less (<15%) trias.

The following operation have been carried out in the outer hood surface:

-Two peak lines at fillet surrounding the outer hood was deleted and only a single con is used to represent the peaks.

- Original cons which could cause improper mesh flow in the geometry were eliminated and cons of a consistent patter were saved.

2. Inner hood surface

The following operations were carried out to generate a smooth mes-flow:

- Small holes were renumbered to have even number of holes

- Small holes whose perimeter looks like polygon were slid such that all four sides are parallel to the edges of the hood.

- Beads were made to have single cons at their peaks

- Irregular pattern shaped cons on the hood surface were eliminated and each holes and beads were contained within cons to generate smooth pattern and more quads.

- Hotpoints causing under/over valued perimeter length were eliminated.

3. Reinforcements

The following operations were carried out in the latch and hinges to generate a smooth mesh-flow:

- The opening of the latch is split into sections thereby mixed elements are generated at critical intricate areas and smooth quads at the plain surfaces.

- Small holes were renumbered to have even number of holes

- Small holes whose perimeter looks like polygon were slid such that all four sides are parallel to the edges of the hood.

Finally, the thickness of the midsurface of the shell components are measured and visualized in the Quality parameter-> Presentation parameter-> Draw shell as solid.

CONCLUSION

Hence the entire geometry was checked for errors and the mid-surface was successfully extracted prior to mesh generation. Similarly to generate smooth mesh-flow the mesh was refined using certain features in the mesh module.

Finally, a percentage of just 2.1% of tria elements were achieved and other quality criteria were met for the entire system.

Learning Outcomes:

This project gave me an insight and understanding of,

1. How geometrical errors can be eliminated

2. Mid-surfacing using both automatic and manual methods.

3. The different type of mesh quality parameters and how they can be computed in ANSA

4. Mesh generation using the hybrid best method and mesh refinement.

Model file

https://drive.google.com/file/d/1SorWMn-Dg0tMHYiXpOF6noiUTnVCVE1r/view?usp=sharing