PRE-PROCESSING OF HOOD ASSEMBLY FOR STRUCTURAL ANALYSIS USING ANSA

OBJECTIVE :

In this challenge, a structural mesh is performed (mid surface mesh), by cleaning up an
auto motive’s hood assembly, consequently meshing the complete geometry with the
target size (5mm) and quality criteria respectively.

METHODOLOGY :

1. Importing the CAD geometry which is a .stp file and is transferred to ANSA readable file.ansa.
2. Performing Geometry checks and cleaning up all the topological errors those encountered when transforming from one extension to another ( ANSA readable). Topological errors are needle faces, single cons, triple cons, cracks, overlapping faces, collapsed cons, and unchecked faces.
3. Setting-up PID\'s ( Property identities) and MIDs (Material Identities) and thickness for each individual component by using any of the three different features available in the ANSA tool i.e Offset middle and MID surface.
4. 2D meshing with mixed elements (Triangular & quadrilateral).
5. Checking mesh quality with specified aspect ratio, skewness, warping, minimum and maximum element length, etc

QUALITY CRITERIA TO BE FOLLOWED :

PROCEDURE:-

1. Geometry Clean-up of the Inner Hood panel.
2. Extracting the middle surface from Inner & Outer Panels.
3. Meshing the Inner Panel & Releasing the FE mode.
4. Creating the Area for HEMMING.
5. Assigning the Thickness and PID\'s.
6. Meshing the model with given parameters.

GEOMETRY CLEANUP :

Universal delete: To delete any type of entity by selecting them.
New faces (COONS & FITTED) : To create new faces.
Topo: It projects the nodes to the cons and aligns it to the surface.
Insert (Hot point): It inserts a hot point over a con.
Project (Hot point): To project a hot point on a con which is in the neighboring cons
Delete (Hot point): To delete the unwanted hot points.
Paste (Cons): To paste two or more Cons together

INNER HOOD :

OUTER HOOD :

LATCH AND HINGE REINFORCEMENT :

SYMMETRY CHECKS :

Use rm dbl to check whether the geometry is symmetry or not

MID SURFACE EXTRACTION :

Mid surface extraction is the art of creating a middle surface from the existing outer and inner surfaces or skins of a solid geometry.

By using the offset tool and by selecting only one of the parts a surface will be created
with the same dimensions in between the thickness of it, .0375 from the selected surface.
The same will be done for the other part, with the same distance due to having the same
thickness material.

Before Extraction :

After Extraction :

And similarly, the mid surface of the outer hood can also be extracted from the above same steps.

HEMMING:-

Hemming means it\'s a type of connection where inner and outer closure panels are joined together. It is done by folding the flange of the outer panel over the inner one. These are used at doors, tailgates, and hood, etc.

Inner and outer hood hemmed connection

Hemmed region of hood

ASSIGNING PIDs AND THICKNESS :

1. The property ID for the mid surface hood panel and assigning thickness to it.
2. A mathematical value for the thickness of the mid-surfaces extracted is assigned.
3. The thickness of the shell element is the same as the assigned thickness.
4. This thickness is not used for meshing.
5. The Thickness for the Hemming Region is 2.25mm, it is calculated by using the formula [2*(Outer panel thickness) + inner panel Thickness).
6. The thickness of the inner panel = 0.75mm
7. The thickness of the outer panel = 0.75mm

MESH AND QUALITY CRITERIA PARAMETERS :

1. Since it is BIW component, It is better to Extract the mid surface before meshing
2. The hood is a thin component comparative to its other dimensions, so instead of 3D meshing we mesh using 2D element.
3. This will save our meshing time as well as computation time for analysis.
4. Meshing the hood using a 2D element without the mid surface is not good as it will show improper thickness behavior.
5. We take the mid surface for the hood and after meshing we apply thickness which is equal to original sheet thickness.

Completed surface mesh and PID ready for FEA analysis,

DRIVE LINK :

https://drive.google.com/open?id=1hNOwi1LbfL45dGurtMBnqJSoIkJRImSq