Bottle Cap Mesh Using ANSA

Generation of Mid Surface, Mesh of the Bottle Cap

Aim:

To create a Mid-Surface and 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. Assigning Thickness to Mid surface.
4. Giving the Quality Criteria.
5. Creating a mesh
6. Adding thickness to the meshed element.

Given Model:

The Model given is the Bottle Cap. The quality Criteria is as below

S. No.	Quality Criteria	Value
1	Target/ Average Length	1
2	Minimum Length	0.5
3	Maximum Length	3
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:

1. 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.

2. Bottle Cap:

• A bottle cap or bottle top seals the top opening of a bottle.
• A cap is typically colorfully decorated with the logo of the brand of beverage.
• Plastic caps are used for plastic bottles, while metal with plastic backing is used for glass; the metal is usually steel.
• Plastic caps may have a pour spout. Flip-Top caps like Flapper closures provide controlled dispensing of dry products.
• Caps for plastic bottles are often made of a different type of plastic from the bottle.

Working:

• The easiest and most common method to produce the Bottle cap is Injection Moulding.
• Injection Moulding is the process for producing parts by injecting molten material into a mold, or mold. Injection moulding can be performed with a host of materials mainly including metals (known as die-casting), glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers.
• Material for the part is fed into a heated barrel, mixed, and injected into a mold cavity, where it cools and hardens to the configuration of the cavity.
• Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars.
• Advances in 3D printing technology, using photopolymers that do not melt during the injection moulding of some lower temperature thermoplastics, can be used for some simple injection molds.

Procedure:

1. 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.

• The above image shows the initial design when the file is opened.

2. Checking for any errors:

• This process is used to check the topology of the model.
• For Topology, Click Topo>> Select Model >> Middle-Click on Mouse.

• 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.

3. 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.

4. 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 Check the thickness at different locations.

• 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>> Skin in Faces 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 offset value is given as the thickness of the selected surface divided by 2 and the direction in which the offset is going to be done is shown with an arrow symbol.

• For the Selection of Multiple Areas for the same feature, the Middle Multi option is used.

• Click Middle ( in Faces Button)>> Multi >> Select the Entities in the Red, Green, and Blue (RGB) (Where Red, Green are the either sides of the features and Blue is the Thickness of the Feature.

5. Creating the Rotating Element Mid-Surfacing:

• There are many Teeth Elements in the given model. It is very time taking process to take the mid surfacing for each element.
• To reduce the time and to perform a better flow of midpoints, Transform (Rotate) is used.
• There are few pre-requisites needed to make the mid surface of the feature to rotate.
• Initially Click on the On COG in Point Button Tab.

• Select any two Circles which are at different heights.

• Click on the Transform Option in the Utilities, Select the Entities, and then Select Rotate option.

• Give the Number of Steps i.e. (the Number of Duplications to be done -1)[Why ‘-1’ is used because there will be an existing feature which is used as the default entity to duplicate so the total number of duplications -1 is used]
• Here, The angle option is used to the angle between each duplication. It is calculated by the total angle of the circle (which is generally 360) by the number of the entities wanted for duplication.

• In X tab Select lowest Circle COG, and dX tab, Select the other circle COG.
• Click OK and the Duplication is successfully done.

6. Creating an Angular corners for a curved fillets:

• The curved fillets mid-surface height is difficult to determine. We can change the curved fillets to and angular corners without changing the model.
• Dach option is used to change the fillet.
• Click Dach( in Faces Buttons) >> Dach.

• Initially, after clicking the Dach option, select an entity, and click ok.

• The entity is changed into a corner from a fillet element.

6. 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 Mid surface part is selected as each part has its thickness and to differentiate each of those parts different PIDs are taken.

7. Adding Thickness to the Mid-Surfaces:

• The Thickness of the given model varies from feature to feature. To create a proper mesh flow, Thickness is added to individual features.

• The different thickness is assigned to different mid-surface parts as the new PID. These are assigned as below.
• The below PID names have T2B and B2T. They simply mean as Top to Bottom and Bottom to Top respectively.

Fig. 1 and 2 Shows the Teeth and Outer circular

8. 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	1
2	Minimum Length	0.5
3	Maximum Length	3
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

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

9. Creating the Mesh Flow:

• 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 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 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 1 in both perimeters and macros simultaneously.
• In mesh generation, Select Best and select the element to mesh and confirm it.

• 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 Paste option is used to make the opposite tria’s into a single line.
• Make sure that there are no opposite tria’s and also rotating quads should be eliminated.

10. 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.

TERMS USED:

1. Topology:

• Topology gives the Shape and structure of the model.

2. PID:

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

3. Mid Surface:

• Mid surface creates a surface on the mid-plane which can be used to mesh. The Mid Surface is a projection of the main surface which is projected at the center of it.

Quality Criteria Understanding:

Quality Criteria are given to check the product is meeting the requirement.

1. Aspect Ratio:

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

2. 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.
• Ideal Value = 0° ( Acceptable < 5° to 10°)

3. 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.

4. Jacobian:

• The Jacobian is a measure of the normal 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.

5. Minimum Length:

• The Minimum Length is required to create a proper mesh. The Minimum length is generally the least number which is an acceptable length for the mesh to create.

6. Maximum Length:

• The Maximum Length which is required to create a proper mesh. The Maximum length is generally the largest number which is an acceptable length for the mesh to generate to create a proper mesh without any errors.

7. Minimum and Maximum Angle Of Quads:

• The Smallest and Largest quad angle which is acceptable. The Acceptable range for minimum Angle of quads is 45-90 and the Maximum angle of quad is 90-135.

8. Minimum and maximum Angle of Trias:

• The Smallest and Largest tria angle which is acceptable. The Acceptable range for minimum Angle of tria is 30-60 and the Maximum angle of Tria is 60-90.

9. Tria percentage:

• Tria percentage is the percentage of the Tria elements which are acceptable in the mesh flow.
• Ex: If the Tria percentage is given as 2. If the Percentage is more than 2 then the following mesh isn’t considered proper.
• Therefore, Tria percentage should be less than the given criteria. It doesn’t affect the mesh but it might create some bending problems as they have constant strain across the element. It makes the job tough for the FE solver to calculate the bending response.

Errors Faced:

• There are many errors faced but they were just simple topological errors and are solved with ease.
• The main errors are faced while meshing some components.
• The errors are basically between triple cons of one feature to another feature.

• Since the feature are connected those elements can’t be removed are changed and therefore there will be Off elements present in the model.

• DE featuring can’t be done since and change in the feature deals with an error with model and which further leads to deformation of the model.

Result:

The proper mesh is created with no errors and mid surfacing of a Bottle Cap along with quality criteria and thickness.

• With Thickness Given to the meshed surface, the images are shown below.

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 using Offset, Middle, Middle (Multi), and Middle( Curves).
• Creating the Mesh.
• Correction of mesh errors.
• Adding the Thickness.

Google Drive Link: https://drive.google.com/file/d/1h0ECJJ6l3G_ADFvHWMHvwvFat32Kx-H7/view?usp=sharing