Week 5 Challenge Task: Solid (3D) MESHING OF REAR-VIEW Mirror cad MODEL USING ANSA PREPROCESSOR TOOL

Course: Preprocessor for Structural Analysis using ANSA

NOVEMBER 18,2020

Submitted by: Amanpreet Singh Whan

Supervisor: David Nirmal Paul

Abstract

The report presents a strategy that was adopted to mesh the interior Rear-View Mirror CAD design using the ANSA Pre-Processor tool for the fulfilment of the Week 5 Challenge task. Solid meshing is a four-step process that includes importing a given CAD model, geometry clean-up, Tria meshing, and finally performing tetra meshing of generated volumes using setting quality and mesh parameters. The max quads elements are found to be 0 while 123720 tria elements (100%) and 581425 tetra elements (100%) are present in the meshed model.

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.

3.3 Meshing.

4 Discussion.

5 Conclusion.

6 Learning Outcomes.

Appendix.

List of Figures

Figure 1-Workflow overview of ANSA Pre Processor.

Figure 2- Imported given Rear-View Mirror CAD Model.

Figure 3- Topo performed and oriented Rear-View CAD Model.

Figure 4-Geometry Check-Up command executed and its resulted error.

Figure 5-Eliminating errors using Auto Fix command.

Figure 6- Error free given Rear-View Cad Model.

Figure 7—Rear view Mirror presentation before Length parameters command activated.

Figure 8-Rearview mirror Model presentation resolution after Length parameters command activated.

Figure 9- Mesh Parameters and Quality set as per challenge requirements.

Figure 10- Rear end mirror housing meshed scene.

Figure 11-Rear end mirror housing meshed scene in PID mode.

Figure 12-Front end mirror housing meshed scene.

Figure 13-Front end mirror housing meshed zoomed scene in PID mode.

Figure 14- Spherical head Meshed scene.

Figure 15- Spherical head Meshed scene in PID mode.

Figure 16- Mounting Arm meshed scene.

Figure 17- Mounting Arm meshed scene in PID mode.

Figure 18-Complete Rear View Mirror meshed scene in PID mode.

Figure 19- Rear end Mirror housing Tetra Rapid Volume meshed scene.

Figure 20- Front end Mirror housing Tetra Rapid Volume meshed scene.

Figure 21- Spherical head volume mesh scene.

Figure 22-Mounting arm volume meshed scene.

Figure 23-Tetra or Unstructured Mesh scene for Rear View Mirror CAD Model.

Figure 24- List of volumes created for Tetra Rapid Mesh for the given Model.

Figure 25-An example representing deploying of tria and ortho tria mesh on planar and curved surfaces respectively.

Figure 26- Manipulated construction lines for given rearview mirror CAD design.

Figure 27- Tetra Mesh cut scenes of different regions.

1 Introduction

The interior rear-view mirror of an automotive vehicle having a front and a back end comprises a mounting base adapted to be secured to the vehicle; a mounting arm extending rearwardly from the mounting base and terminating in a spherical head; a mirror housing having a backing plate with right hand side region extending forwardly towards mounting base at a predetermined angle relative to left hand side region to increase the rear view of the vehicle for the driver; a socket fixed to the mirror housing within the first recess to receive spherical head for unitary movement with mirror housing; a secondary mounting arm attached to the backing plate within second recess with secondary spherical head extending rearwardly from the back end of the backing plate; a convex mirror having a socket to receive the spherical head of the secondary mounting arm and adjustably mount the convex mirror within the second recess for independent movement of the convex mirror relative to the mirror housing.

2 Aims

• Check and fix all the geometry errors of the given Model for Geometry Clean-up purposes.
• Set the length perimeters and the type of mesh required.
• Perform 3D or Solid Meshing of the components of the model as per the given Mesh Quality Criterion to generate an overall good mesh flow for the entire model.
• 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 of the rear-view mirror CAD model for the completion of the Week 5 Challenge Task. These stages can be further broadly sub-categorised into four key steps, starting from importing of cad model to geometry clean-up, carrying out of meshing as per asked quality requirements, nd finally generating a volume mesh using tetra rapid mesh algorithm for the given CAD model.

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 motive 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.

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.

The model can be refined either using the 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 operation, Mesh perimeters-> Length was chosen to be easiest and preferable choice.

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

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:

• The Perimeters length was set to 1 mm 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
Min length	0.5
Max length	2

Table 2- Mesh Parameters and its assigned values

Mesh Parameters
Parameters	Value
Target length	1
Minimum target length	0.5
Maximum target length	2
Distortion distance	20%
Distortion angle	0

• ‘Spot Mesh’ Mesh Generation algorithm was used to produce mesh for the model.

• Next, a volume was generated for the meshed rear-view mirror CAD model and then the generated volume was meshed using Tetra Rapid Mesh algorithm.

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

The results of the meshed interior rear-view mirror are presented in the following pictures.

4 Discussion

ANSA Pre-Processor was used to mesh the Rear-View Mirror CAD model as per asked Quality Criteria and Mesh Parameters to generate a good overall mesh flow for the successful completion of the Tool Week 5 Challenge task. To fulfill the requirements of the challenge, geometry clean-up, initial tria/ortho tria meshing, and finally 3D meshing using tetra rapid mesh algorithm for generated volumes were performed and the obtained results are presented in the figures shown above.

In figures 4 and 5, it can be seen that the provided CAD model had multiple errors such as needle faces, cracks, unchecked faces,and triple cons which were fixed using the automated fix option.

The solid or 3D meshing is a two-step process. In the initial step, the given model has to be meshed using either a tria or ortho tria mesh algorithm and later after generating volume for the model it has to be meshed using tetra rapid mesh algorithm. Tria mesh algorithm cannot be applied on curved and circular surfaces as it leads to distortion of the surface by generating kinks and dips on it. Therefore, ortho tria mesh algorithm was used for the curved surfaces and tria mesh algorithm was used for planar surfaces while generating mesh for the given Rear-View CAD model. The following figure represents an example showing surfaces where ortho tria and tria mesh algorithm was implemented.

The construction lines were 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. Following are the figures that represent the areas of the given model where manipulation of the construction lines has been completed to generate a good mesh flow.

Figures 18 and 23 instruct that there are not any off and collapsed elements existing within the meshed rear-view mirror CAD model. Moreover, a total of 123720 tria elements and 581425 tetra elements are present in the meshed model.

5 Conclusion

In conclusion, the main aim of the challenge was to do a geometry clean-up of the interior Rear-View Mirror of an automobile and generate tetra or unstructured mesh using tetra rapid mesh algorithm. The max quads elements were found to be 0 whereas 123720 tria elements and 581425 tetra elements are present in the meshed model.

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 learned about different commands that are required to generate Solid meshing. 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

The Link to access the tetra meshed file:

https://drive.google.com/file/d/1baLQqcNWm9xi6OtEAt985B5ieIn2I-Fa/view?usp=sharing