Automotive Hood Part Meshing Using ANSA

Mid Surfacing and Meshing an Automotive Hood with Quality Criteria and Thickness

Aim:

To create a mesh with the given quality Criteria and to make sure the element given is free from geometrical errors.

Methodology:

The methodology for the given element is as follows:

1. Perform a Geometrical Check ( if Errors present fix them)
2. Extraction of Mid surface
3. Giving the Quality Criteria.
4. Creating a mesh
5. Adding thickness to the meshed element.

Given Model:

The Model given is the Hood or bonnet of the car. The quality Criteria is as below

S. No.	Quality Criteria	Value
1	Target/ Average Length	5
2	Minimum Length	2
3	Maximum Length	8
4	Aspect Ratio	3
5	Warping	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

Theory:

ANSA (Automatic Net generation for Structural Analysis):

ANSA is a computer-aided engineering tool for Finite Element Analysis and CFD Analysis widely used in the automotive industry. It is developed by BETA CAE Systems.

ANSA maintains the association between CAD geometry and the Finite Element (FE) mesh. This means that the FE meshes are better representations of their geometric parents. Also, it is easy to maintain and update any changes in the geometry by simply reworking the updated area instead of recreating the FE from scratch. It carries several proprietary algorithms for meshing suitable for both CFD and structural models.

The software takes a shell material to the solid geometry and converts it into the finite elements so that the model can get accurate simulation results in a shorter time.

Hood:

The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment, or trunk for maintenance and repair. It generally covers the engine and other essential accessories like battery, Radiator, electrical components, etc. of the car which are exposed outside. The hood release system is common on most vehicles and usually consists of an interior hood latch handle, hood release cable, and hood latch assembly. The hood latch handle is usually located below the steering wheel, beside the driver's seat or set into the door frame.

Working:

The given frame is a bonnet of a car and the design can be made into 2 parts, outer hood, and the Inner hood. The later contains intricate structures in it so that it can provide the structural strength while the former contains a uniform structure and is created to resist the airflow and provide an aerodynamic flow. The Outer hood has a hem to it and the Inner hood is placed in it.

Procedure:

Opening the File:
The file is downloaded initially. To open the file, follow the steps.
Open ANSA >> Give Command Arguments >> OK >> Click Ctrl +O (for opening the file) >> Select the File>> Click Ok.
On the Whole to describe the Opening of the file, click on the ANSA app, and wait for the launcher dialog box to appear. Once it appears, the dialog box contains the information called Additional ANSA command arguments are seen there will be an input box just below it. The argument has to be changed to “-performance_mode 3” (This means the performance of the app and it has Slower drawing and yet better quality.) then click ok to continue. The ANSA is now opened and then you can either open the file by using file option and open or Ctrl + O option.

Click on the above icon to proceed with the opening of the application.

The command arguments are given once the application opens the above dialog box.

Checking for any errors:

This process is just used to check the topology of the model. In order to check the Topology follow the process as Tools>> Checks >> Geometry>> Execute. Once executed, it might show a green bar stating there are no errors in the geometry or it may show the dialog box showing the errors present in it. These errors can be fixed either by going on with them individually or once Right-clicked on the mouse an additional list pops- up. Fix option will be present in that pop-up when it is clicked the errors which can be fixed are executed and it might contain only a few errors which should be fixed manually and if no errors are present then it will show the green bar stating executed.

The process is called geometric clean- up. It can be done either completely or part-wise of the parent geometry.

The Geometry clean up is successful for the initial Design.

Checking the PID:
The PID is used to create a property of the particular model parts or the total model. To create a new PID or to check the existing PID’s. Click Lists >> Properties.
You can see the Properties which are created before. To create a new PID, right-click on the dialog box, the drop-down appears. Click New >> PSHELL>> PSHELL.
Then a New PID is created. To assign a part to the PID. Select the element needed to be assigned and do the middle click on the mouse to confirm.

The images show the step by step procedure to check and create a new PID.

The above image shows that after clicking the new PID shell, a new name can be created. This process can be done multiple times so that each part can be assigned to each new PID created.

Creating a New PID is not enough. Assigning the part/ model to the PID is necessary. The above images show the steps to apply the Part to the PID so that the part can be retrieved easily.

Creating the Midpoint:

To give the mid surface location the thickness of the element/ model should be known. And to know the model thickness that measure tool is used. Click Utilities >> Measure >> Select the Nodes >> Click Ok. Check the thickness at different locations.

The measure tool dialog box shows the Selection option and nodes are chosen to find the length between two hot points. the images show the procedure in an order.

The length or thickness (in this case) are checked at different locations for both outer and inner hood. The images show that the model consists of the same thickness at different locations around the model.

Mid-surface is created to use it to do the meshing as it does not affect the parent geometry but carry out the preprocessing simulation. The mid surface is created by using the module buttons in Topo Mode. In Module Buttons, Click Offset>> Faces in Faces Module then click on the face for which the mid surface is to be created. Click middle- click on the mouse to confirm and a dialog box appears in which the mid surface location is to be given.

The images show the stepwise guidance to carry- on with the mid surface extraction.

Mid surface generation is seen as the described in the image. The images are seen in both normal and wire-frame mode.

Create a PID for Mid Surface:

PID for mid surfaces is created so that the element can be retrieved easily. To create the PID for mid surface, the above method (Checking the PID) can be used to create a new PID.

The images show how to assign the property to both Outer and Inner Hood respectively.

Creating a proper topology for the outer hood:

To check if the Outer Hood Mid surface is free from errors, Geometric clean- up should be done. Once the Clean-up is completed with the execution without errors, the topology is to be checked to get the proper mesh flow.

The image shows us the Outer Hood Mid Surface doesn't have any topological errors.

The Join option disables the Con but does not eliminate the Con. The Cons can be retrieved again by using other buttons.

Creating a proper topology for the inner hood:

Similar to Outer Hood Mid Surface topology, Inner hood Topology clean-up is to be done. Inner Hood has complicated structures which are needed to be fixed to get a proper mesh.

The image shows that there are no errors in the Inner Hood Mid Surface and also it shows the joined elements to make the mesh flow proper.

Setting the Quality Criteria and Meshing Parameters:

Before proceeding with the mesh, the quality criteria and meshing parameters are to be given to meet the requirement. The quality criteria are opened by either clicking F11 on the keyboard or by clicking Utilities >> Quality Criteria.

The Quality Criteria which are given are stated below should be entered in the shell icon.

S. No.	Quality Criteria	Value
1	Target/ Average Length	5
2	Minimum Length	2
3	Maximum Length	8
4	Aspect Ratio	3
5	Warping	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

Quality Criteria can be explained in detail by using images.

After Giving Quality Parameters in the Shell icon, click on apply and then click Presentation Parameters and select element percentage and Detail on Demand effect to all details.

Image shown above states that in the Graphics Tab Elements % is selected and In Detail on Demand Effect Tab, All Details are selected

The Meshing parameters are also added from Utilities >> Meshing Parameters.

The Mesh parameters are given based on the Quality Criteria given above.

Creating the mesh for outer and Inner Hood:

To create a mesh for any model, in modules select mesh. Click Modules >> Mesh. Once the mesh module buttons are opened and seen. Initially for outer hood mesh can be created by using tools like Hot Points, Perimeters, Mesh Generation, Shell Mesh, Elements. Firstly when the mid surface is opened in mesh mode, click Length in Perimeters. The procedure is as follows Length >> Perimeters, Macros. Select the entire mesh and confirm it, once it is done a dialog box appears stating the length as 5 in both perimeters and macros simultaneously.

In mesh generation, Select Best and select the element to mesh and confirm it.

The Images shows a selection of tools and the element are shown. The mesh pattern is formed.

Image shows that there are some mesh element have some Off Elements.

The Mesh might not be as perfect as it should be and contains many Off elements (Which doesn’t meet the Quality Criteria) to remove the off elements or to reduce them Reconstruct option is used. It can be seen in Shell Mesh >> Reconstruct.

Once the Off elements are fixed or reduced the mesh should be made softer. To make the mesh softer Smooth option is used. It can be seen in Shell Mesh >> Smooth.

If the Off elements are still present then it should be eliminated by using manual methods. Such as by using Split to reduce and remove the tria’s which can be eliminated.

The Split Option is used to remove the tria elements. Once removed the image shows that there are some Off elements at that Split area.

To Remove the Off elements Smooth Option is used again.

The Paste option is used to make the opposite tria’s into a single line.

Make sure that there are opposite tria’s and also rotating quads should be eliminated.

Adding Thickness to the mesh:

The thickness of the mesh can be added in the Property icon and by selecting the part to which the thickness needs to be given.

To check if the Model shows the given thickness, Go to Quality Criteria >> Presentation Parameters >> Draw Shell as Solid>> OK.

The images below show that the thickness has been added to both the Inner and Outer Hood Mid Surface.

TERMS USED:

Hemming:

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part to achieve a tight fit. Normally hemming operations are used to connect parts, to improve the appearance of a part, and to reinforce part edges.

Topology:

Topology gives the Shape and structure of the model. It describes how the elements are bounded and connected.

PID:

PID means Property ID. It generally gives a definition or class to a particular part.

Mid Surface:

Mid surface creates a surface on the mid-plane which can be used to mesh.

Aspect Ratio:

Aspect Ratio is the ratio of the width to the height of the FE part.

The aspect ratio should be the maximum of the ratio between them i.e `max (a/b)`

Warping:

• Ideally, all the nodes of the quadrilateral element should lie on the same plane but at curvatures and complicated geometry profiles, it is not possible. Generally, a measure of planeness of a Quadrilateral is called Warping Factor or Warping Angle.
• It is defined as the angle between normal of two (triangular) planes formed by splitting the quad element along diagonals.
• Maximum Angle out of the two possibilities is reported as "Warp Angle".
• In the case of solid elements, an element's face deviates from being planar. The quad is divided into two trias along its diagonal, and the angle between the trias normals is measured.

Skewness:

Skewness refers to distortion or asymmetry in a symmetrical bell curve, or normal distribution, in a set of data. If the curve is shifted to the left or the right, it is said to be skewed. Skewness can be quantified as a representation of the extent to which a given distribution varies from a normal distribution.

Jacobian:

The Jacobian is a measure of the normals of the element faces relative to each other.

The value of the Determinant of the jacobian matrix is calculated for each integration point of the element.

The reported deviation is calculated as the ratio of the smallest value over the largest.

Result:

The proper mesh is created with no errors and mid surfacing of an Automotive Hood along with quality criteria and thickness.

The image shows the outer Hood Meshed model

The image shows the Inner hood meshed model

The image shows the Total Model with the thickness given as 0.75 for both Inner and Outer model.

Learning Outcomes:

The Basics of ANSA can be learned by practicing in this model. The following outcomes are learned

• Geometric Clean-up.
• Topological Correcting.
• Creating of Mid Surface.
• Creating the Mesh.
• Correction of mesh errors.
• Adding the Thickness.

Tools Used:

The tools used are shown in the image format

The above Image are the tools used for giving the model a proper direction.

The above image shows the module buttons of Topo and mesh mode respectively

The above images show the tools required to view edit the model.

Google Drive Link: https://drive.google.com/drive/folders/1p0eGWxbz2_PexhssEgujRKxoC0PF1Ibv?usp=sharing