Project 1 Challenge: Shell (2D) Meshing of Ip substrate Model using ANSA Preprocessor tool

Course: Preprocessor for Structural Analysis using ANSA

Submitted by: Amanpreet Singh Whan

Supervisor: David Nirmal Paul

January 30, 2021

Abstract

A vehicle instrument panel assembly typically comprises a variety of components mounted on an instrument panel carrier structure that extends transversely across the vehicle between the vehicle's A-pillars. The report presents a strategy that was adopted to mesh the given IP substrate CAD model using the ANSA Pre-Processor tool for the fulfillment of the Project 1 Challenge Task. The shell meshing is a three-step process that includes geometry clean-up, mid surface extraction and finally performing meshing using setting quality and mesh parameters. The max quads percentage and max trais percentage were found to be 95.28% and 4.72 % respectively. Lastly, a total of 502(1.09%) Off elements were also found in the regions where triple cons either intersect each other or are present very close to geometry construction lines.

List of Figures

Figure 1-Workflow overview of ANSA Pre Processor.

Figure 2-- Imported given Instrument Panel Substrate CAD Model.

Figure 3-Topo performed and oriented Model.

Figure 4- IP Substrate Model presentation before Length parameters command activated.

Figure 5- IP Substrate Model presentation resolution after Length parameters command activated.

Figure 6-Geometry clean-up executed and its resulted errors.

Figure 7-Error free given Instrument Panel Substrate CAD Model.

Figure 8- Extracted Mid surface of given Instrument Panel Substrate CAD Model.

Figure 9- List of the Assigned PIDs to different features of the IP Substrate extracted Mid Surface.

Figure 10- Mesh Parameters and Quality set as per challenge requirements.

Figure 11-Fully Meshed IP substrate extracted Mid Surface.

Figure 12- Meshed regions of the extracted mid surface that has quality failing elements.

Figure 13-Meshed scene of IP substrate mid surface in shadow mode.

Figure 14-Meshed model scene after selecting the "Draw as Solid" command.

Table of Contents

Abstract.

List of Figures.

1 Introduction.

2 Aims.

3 Methodology and Results.

3.1 Import CAD Model and do Geometry Clean-Up.

3.2 Mid Surface Extraction.

3.3 Meshing.

4 Discussion.

5 Conclusion.

6 Learning Outcomes.

Appendix.

1 Introduction

A vehicle instrument panel assembly typically comprises a variety of components mounted on an instrument panel carrier structure that extends transversely across the vehicle between the vehicle's A-pillars. The instrument panel carrier structure may be made from several separate sections, such as a structural base section and an airbag module receiving section that is joined together.

The typical vehicle instrument panel assembly further includes a number of trim pieces, such as a deployment door for an airbag module, that are secured to the instrument panel carrier structure and that cover the various components mounted on the instrument panel carrier structure. Components that are typically mounted on the instrument panel carrier structure include a passenger-side airbag module, an inflatable/deployable knee bolster or an energy-absorbing knee bolster, and a glove box. Each of these components is usually fastened to the instrument panel carrier structure by some form of metal bracketing.

2 Aims

1. Check and fix all the geometry errors of the given Model for Geometry Clean-up purposes.
2. Extract/ Generate Middle Surface for the component of the given CAD model.
3. Perform 2D or Shell Meshing of the model as per given Mesh Quality Criterion to generate an overall good mesh flow for the entire model.
4. Investigate and Improve the mesh quality wherever required.

3 Methodology and Results

The section describes the different stages that were performed using an engineering tool, ANSA Pre-Processor for the successful generation of an overall good mesh for the completion of the Project 1 IP substrate challenge. These stages can be further broadly sub-categorized into three key steps, starting from importing of cad model to geometry clean-up for mid surface generation and finally carry out meshing of the extracted mid surface as per quality requirements.

ANSA Pre Processor is an advanced computer-aided engineering tool extensively used for FEA (Finite Element Analysis) and CFD (Computational Fluid Dynamics) analysis in the automotive and aerospace industry. ANSA pre-processor is a CAE software developed by BETA CAE Systems and follows a strict workflow when numerically solving a given problem. Figure 1 represents the workflow overview implemented in the software.

3.1 Import CAD Model and do Geometry Clean-Up

After opening the ANSA Pre-processor software, the first and the foremost step is to import the CAD geometry and perform topology using the topo command in the faces section of Topo Module Buttons for the entire model.

Since the given model is a plastic component and does not have a uniform thickness, so, its refinement was necessary for presentation resolution before proceeding with the extraction of the middle surface. The model can be refined either using Auxiliaries-> fine in Topo Module Buttons or by simply setting a value of length for the entire model in the Perimeters section of Mesh Module Buttons. Considering the complexity of the fine operation, Mesh perimeters-> Length was chosen to be the easiest and preferable choice.

In the next step, go to the Checks Manager and select geometry from the options list. The main function of the Checks geometry is to locate geometrical issues such as unmeshed macros, unchecked faces, needle faces, collapsed cons, triple cons, and cracks. Even though most of these errors can be easily eliminated using the Auto-Fix command but issues concerning triple cons must be fixed manually by releasing Cons or Hot-points (nodes) and joining cons/ nodes back again using the topo command. Before executing the Checks geometry operation, make sure to turn on the most essential above stated geometry issues.

What follows hereafter is the set of images showing different results obtained before and after the completion of geometry clean-up using ANSA Pre-Processor software.

3.2 Mid Surface Extraction

The mid surface can be generated both manually and automatically. A manual mid surface can be obtained using the Faces->Offset command in the Faces section of Topo module buttons. Moreover, the mid-surface generated using manual operation must be assigned a new PID which can be easily done using the Set PID command in the faces section. However, ANSA directly assigns a new PID to a Mid Surface that is extracted automatically, and it is usually accomplished using the Mid Surface->Skin command in the faces section.

The results of the mid surfaces obtained manually (using the commands, Faces->offset and Curves-> Middle) for the different regions of the given CAD model are presented in the following pictures.

3.3 Meshing

Meshing is a phase where the CAD geometry is discretized to represent the computational domain in which the solver will discover a solution. A refined mesh helps to achieve better results.

The meshing conducted for the given model is explained in the following steps:

• After the extraction of mid surface, the Perimeters length was set to 4mm in the perimeters section of the Mesh module buttons. This will help to generate a mesh of constant element size.

• In the next step, the values of Quality Criteria and Mesh Parameters were entered as per challenge requirements to get a good flow of the mesh over the model. The values used for the quality criteria and mesh parameters are presented in the following tables.

Table 1-Quality criteria and its respective assigned values.

Quality Criteria
Criteria	Value
Aspect Ratio	3
Skewness	45
Warping	15
Jacobian	0.7
Min length	2
Max length	6
Min angle quads	45
Max angle quads	135
Min angle trias	30
Max angle trias	120
Tria Percentage	15

Table 2- Mesh Parameters and its assigned values.

Mesh Parameters
Parameters	Value
Target length	4
Minimum target length	1
Maximum target length	6
Distortion distance	20%
Distortion angle	0

• A combination of the ‘Best’ and ‘Spot Mesh’ Mesh Generation algorithms was used to produce mesh for the model.

• Quality failing elements were eliminated using multiple approaches which include Reconstruction of mesh, smoothing of mesh, Moving & Pasting Grids and Splitting, Swapping & Joining of elements.

The results of the meshed model are presented in the following pictures.

4 Discussion

ANSA Pre-Processor was used to mesh the Instrument Panel Substrate CAD model as per asked Quality Criteria and Mesh Parameters to generate a good overall mesh flow for the successful completion of the Project 1 Challenge. To fulfill the requirements of the challenge, Geometry clean-up along with Mid Surface extraction and Meshing was performed and the obtained results are presented in the figures shown above.

In figure 6, it can be clearly seen that the provided CAD model had multiple errors such as needle faces, cracks, unchecked faces, and triple cons which were fixed using both manual and automated approaches.

Since the given CAD model has non-uniform thickness throughout, the mid extraction was not possible by simply using the Offset-> Faces command. Therefore, Curves-> Middle command was also used to extract mid surfaces in the regions of varied thicknesses.

In PID mode, by selecting the extracted mid surface and the parent component while keeping the parent component in transparency mode and it was found that the mid extracted falls exactly in the middle of the parent component of geometry, concluding mid extraction performed was accurate and precise.

The construction lines were suppressed or manipulated by a certain amount in some critical areas of the geometry where quality could possibly fall to generate an overall good flow of the mesh for the entire model.

Figure 11 instructs a total of 502 (1.09%) off or quality failed elements are present in the meshed model. The quality has failed in the locations where triple cons intersect each other or are present very close to the construction lines. However, these errors cannot be eliminated and can be neglected.

5 Conclusion

In conclusion, the main aim of the challenge was to do a geometry clean-up of the IP Substrate CAD model, generate its mid surface and perform 2D meshing. The max quads percentage was found to be 95.28% while the max trias percentage was found to be 4.72%. Moreover, 502 or 1.09% quality failed elements were found in the areas either where triple cons are very close to construction lines or in the areas where triple cons intersect each other. Lastly, the meshed model was assigned a thickness by enabling the ‘Draw shell as solid’ command in the Quality Criteria- Presentation Parameters tab.

6 Learning Outcomes

Throughout this challenge, I have gained knowledge about different commands that are used to fix geometry errors and are used to generate the mid surface of any CAD Model with both auto and manual options. I have also learned that the Mesh Quality can be fixed using several operations like ‘mesh reconstruction’, ‘mesh smoothing,’ ‘grids move or paste’, and ‘elements split and join’.

Appendix

Link to access the completed challenge:

https://drive.google.com/file/d/1JCagU3-tXBk2OSz6ue72oJWTf0O7FNxC/view?usp=sharing