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AIM: Pre-processing of the car instrument panel using ANSA KEYWORDS: Mid-surface Extraction, Shell Meshing. OBJECTIVE: Introduction to shell meshing i.e. 2D meshing Geometry check & Topological error clean up Mid surface generation Meshing the geometry The quality criteria to be…
Akash M
updated on 30 Oct 2021
AIM: Pre-processing of the car instrument panel using ANSA
KEYWORDS: Mid-surface Extraction, Shell Meshing.
OBJECTIVE:
The quality criteria to be followed:
S No. |
Quality criteria |
Value |
1 |
Target/Average length |
4 |
2 |
Minimum length |
2 |
3 |
Maximum length |
6 |
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 |
12 |
Tria Percentage |
15 |
ABSTRACT: In this project, the instrument panel of the car dashboard is taken for the pre-processing stage of CAE. The pre-processing of this model is done using BETA-CAE-ANSA software. The mid surface extraction and shell meshing are mainly demonstrated here in this project. Also, the good practices to be followed during shell meshing are discussed here.
METHODOLOGY:
Introduction:
The instrument panel, as the largest inner trim part which is directly shown to the passenger, have not only beauty and function requires but also NVH and safety request. The vibration and the noise on the dashboard can be directly felt by the passenger. Thus FEA analysis of the instrument panel plays a very important role in the NVH character of the whole vehicle.
Dashboard can be made from medal as simplest and cheapest way. This could be the same base metal as the car, which is stell or aluminium. The more expensive luxury cars are made of exotic wood with a highly polished finish. Usually, top layer on old car is PVC. More recently, dashboard coverings have been made of PVC blended with something called ABS. ABS is an acronym for a block copolymer made of acrylonitrile, butadience and styrene.
PROCEDURE:
Import model
Firstly, we need to import the model and study geometry.
Geometry cleanup
After importing geometry into the ANSA environment we observe many topological errors while doing the geometry checkup as shown below.
keeping the feature as a single con, triple con, crack, needle face checked, etc. click the execute button, you will see many errors. For proceeding further we need to get rid of these errors. There two options you can follow i.e. 1) manual fixing of these errors one by one or by just telling ANSA to fix by itself. If you want to fix the errors by the manual method you need one by one approach the error area and fix it by either deleting the small redundant surface, releasing the triple cons, deleting hot points, repairing surfaces, etc.
otherwise, you can use the hybrid option to minimize your time consumption by auto fixing most of the areas and rest manual fixing. The reason since mesh needs to be generated it not enough that CAD model just looks correct but instead involves cleanup aspects as well as topological aspects.
Next, we have to measure the thickness throughout the part & assure uniform thickness across the entire part. If thickness changes are observed then all alike thickness has to be kept under a separated property ID.
So by measuring and storing data for thickness for sub-parts such as main panel substrate, ribs, pillars, etc.can be done so that we can extract the mid surface.
Orientation
Orientation must be checked thoroughly by the user every time working on a model. All models should have the correct orientation because the orientation issue will cause the final time issue when you merge the model with a complete vehicle. It is always preferred to maintain the continuity over the surface either grey or yellow throughout the face.
There are two way to extract mid surface
1) The manual mid surface method
2) The Auto mid surface method
Manual mid surface generation
This can be done by manually selecting the surface and giving an offset option in the direction opposite to the grey surface
Note:
1) While giving the offset make sure you do not press YES or else you can delete the parent geometry
2) use Fine option under the auxiliary section in TOPO mode to get a better resolution. (select fine and click on the curved and circular areas)
Auto mid surface generation
If the geometry is closed then we can go for auto mid surface generation option but it will auto-delete the parent geometry.
steps 1) press the mid surface tab under face 2) select the full geometry 3) confirm the mid location
Here I have used the manual offset method extract mid surface as the surface thickness varies and ANSA is unable to segregate separated surfaces for auto mid surface generation.
Note:
Mid surface Generation for small ribs:
Use middle option and select both sides of the rib. Then a mid surface will be formed. The other method to generate mid for the ribs is to create curves on the middle of the ribs and create new face by selecting those curves and extend the mid of the ribs to the base mid.
The dog house in this model should be captured as cross pattern in mid surfaces since the dog houses are solid (Hallow from inside ) and is not having any thickness
Quality Criterion Setup
We can say that result quality is directly proportional to the element quality. The parameters like skew, included angle, Jacobian, warpage, etc. are the measure of how far a given element deviates from the ideal shape. If we talk about a square which means 90 degrees and equal side similarly equilateral triangle 60 degrees and each side equal.
To set up the quality criteria press the F11 key and check the boxes of the parameters of the required quality with required values and apply
Meshing and Mesh improvement
Change the mode from 'Topo' to 'Mesh' mode
Before starting the mesh we need to set the element length. To do so we have to click the 'length' button under the 'parameters section'. After clicking the select in the pop-up window parameter and select the whole geometry and confirm enter the value 5 and confirm do the same for macros option. This alters the element length in the geometry by altering the no of hot points at the periphery as well as at your macro areas.
Also, set the meshing parameters before proceeding to mesh
2D Meshing/shell meshing
As we know that the quads elements are better than triangular elements and parabolic elements are better than linear elements
But if the quads are better than tria then what is the need for using tria elements?
Best practices to follow to get better mesh flow.
1) Back to back tria element are avoided
2) on a planer surface tria should be avoided by merging them using split
3) no mesh transition on radius fillets/Curvatures (carried to planer surface )
4) Hole feature should be even-numbered equally spaced
5) Avoid Trias at edges and on the features and construction lines
6) Avoid zig -zag distribution preferred smooth mesh(straight aligned nodes)
7) Rotating Quads are not preferred
8)constant mesh size (by using tries) Is preferred due to min. element length and time step criteria
9) Remove the redundant and excess construction line to get uniform mesh flow.
10) Divide the surface near the feature into to get better mesh flow pattern
11) Defeature the areas which are going to fail the quality criteria.
12) Mesh density near the critical areas ( features) is preferred.
so as we are now aware of what are the good practices for getting a better mesh flow. Now we can start our meshing process on ANSA
We should remove all redundant and unnecessary construction lines in order to get better mesh flow.
Now we can finally start meshing the component and can get the better mesh flow by keeping in mind the best practices followed in meshing
We have multiple options to mesh (shell mesh)
All three works on the different algorithms but here in this model, we will use the best mesh algorithm. Also after creating the best mesh we can reconstruct and smooth the mesh to get better mesh flow. ( shown below)
Note:
Meshed Parts Results
All the parts have meshed as per quality requirement and had good mesh flow (Smooth)
Property ID:
Property ID for different thicknesses of the Mid surface should be assigned.
Difficult to capture feature and failing elements
1)
2)
CONCLUSION:
The panel had been captured quite a well-using shell mesh. The total element 42716 out of which 1750 are Tria element and 40966 are Quads which makes 4.10% which is a decent percentage of Tria element(as shown in figure.17). Also, the 86 no. of elements are failing as shown above report. Most of the areas of fillets are captured using dach options and defeaturing is done in areas where construction lines are too close. The mesh flow is smooth nearer to target length as 4 mm and within the quality parameter.
LEARNING OUTCOME
Drive Link: https://drive.google.com/file/d/1O_y7rsSgH9vPDqN0NmYqFea8_vWazEcT/view?usp=sharing
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