Pre-processing for Structural Analysis on Hood using ANSA

Objective:

• For the Automobile's Hood component, geometrical cleanup to be done & rectify the issues faced during meshing. Mesh will be done under given element Quality criteria. After meshing the component its thickness will be assigned to sub-parts such as Inner hood, Outer hood & Latches.

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	Warping	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum Triangle Angle	30
11	Maximum Triangle Angle	120
10	Triangle Percentage	15

CAD Model-Processing:

The Automobiles component is a Hood model in sheet metal form. This hood model comprises of three subparts. They are

• Outer Hood Model
• Inner Hood Model
• Latches Model

Outer Hood Model:

The thickness of this Outer Hood Sheet metal is 0.75mm

Inner Hood Model:

The thickness of this Outer Hood Sheet metal is 0.75mm

Latches Model:

The thickness of this Outer Hood Sheet metal is 1.25mm

These CAD sub part's views were stored as shown above. This makes the further process more simple & systematic.

Geometry clean up Processing:

These CAD models were now to be checked against any geometrical errors such us normal orientation, Needle faces, etc. This can be done with the ANSA's checks manager which helps us to find the surface errors on the CAD geometry. In the checks manager, some options can be checked ON / OFF depending on the parameters required to be checked.

In the checks manager by clicking the Execute button ANSA will check for the surface errors on the visible geometry.

The above image shows us the surface errors found on the geometry. There were 44 surface errors found by the checks manager.

Using several surface repairing tools provided by the ANSA these errors should be rectified. some errors can be automatically rectified using the AutoFix option in the checks manager.

After fixing the surface geometry the status icon on the checks managers shows a Green Trick Marks which resembles that the Geometry is error-free. The above three images show that the Outer Hood, Inner Hood & the Latches geometry passed according to the checks manager criteria.

Mid-Surface Extraction:

After clearing all the geometry errors we can generate the mid surface for the geometry. This is to be done using the Mid Surface option which creates a new surface between the upper & lower sheet surface. This is to be done to make the meshing process easier. Here the CAD geometry is a sheet metal that has uniform thickness all over the cross-section. So Mid Surface Extract tool can be used instead of Offsetting individual faces that help to consume less time.

The skin offset value for the latches parts is 0.6mm since the sheet metal thickness for latches parts are 1.2mm (Refer above Image). But for Outer hood & Inner Hood geometry, the skin offset value is 0.375mm as they both use the sheet metal with the same thickness of 0.75mm (Refer Below Image).

After extracting the mid surfaces for each part, those view states were stored as shown above which makes the further process easier.

Setting up Quality Criteria:

In quality, criteria wizard the given parameters are entered so that the ANSA could check the mesh generated is under these criteria.

Mesh Preparation:

Before the meshing process some of the features to be checked manually in order to generate mesh under defined quality criteria.

Check for the number of edges found at the circle region and make sure it's in even number, not an odd number.

Making the edge of the circle parallel to the near edge of the geometry could reduce the mesh errors. This can be done using meshing tools available in ANSA.

Removal of Unnecessary perimeters:

Some of the unnecessary perimeter lines & hot points can be removed which makes the meshing to be done under defined quality criteria. Here in this model, the average length of an element is set to 5mm with tolerance the range can be within 3-7mm. So the parametric lines lesser or greater than the provided tolerance then those lines must be removed or altered without defeaturing the geometry.

Before Removing (Latch Model):

After Removing (Latch Model):

Before Removing (Outer Hood Model):

After Removing (Outer Hood Model):

Before Removing (Inner Hood Model):

After Removing (Inner Hood Model):

Meshing Process:

Before meshing the length of a single element is provided as 5mm so that all the nodes are rearranged with a distance of 5mm.

After meshing some elements in this component fails upon the defined quality criteria. This can be solved with the Mesh Repair Tools available in ANSA to eliminate all the errors. Make sure that the triangle element is not present at the border perimeter in order to get accurate FEA calculation. There are a total of 5267 numbers of elements that had failed under this quality criterion.

The above picture the inner hood model with zero errors thus passing the quality criteria. The element parameters for all other parts can be found from the below After Mesh Elements table.

These values are measured only in the Mid Surface Region not considering the thickness.

Mid-Surface to Solid Conversion:

The model is not ready yet for FEA calculations since the meshing is done only over the surfaces, not on solid geometry. These surfaces along with the mesh elements can be converted into solids by assigning the thickness of the generated mid surfaces.

From the property dialog box the thickness to be assigned for the mid surfaces as shown in the above picture.

After assigning the thickness for the respective surfaces the solid sheet has not appeared on the graphical window. In order to view the Solid Mesh of the parts Check the Draw Shell as solid option in quality criteria under the presentation parameters tab as shown above.

The above image represents the pre-processed Hood with the solid meshing. The Total elements found in the solid mesh is 90756 Nos. In which 90343 Nos are Quad elements contributing 99.54% & 413 Nos of Triangle elements contributing 0.46% of the entire Hood component.