Comparison of Manual Mesh, Batch Mesh, Casting (Mid Mesh).  

Comparison of Manual Mesh,Batch Mesh,Casting (Mid Mesh).

 

Aim -

• To Mesh the given component by manual mesh,by batch mesh method and by casting (Mid Mesh method) and to compare three of them.

Objective -

• To do geometric clean up on the component.
• To extract midsurface by manually using offset tool,by using skin tool.
• To do manual mesh,batch mesh and casting (mid mesh) on the given component.
• To do discretization and mesh the component.
• To do comparison of all the three methods.

Procedure -

Phase 1-Importing

• Hence we are importing a given CAD geometry into the ANSA.
• There are file formates like IGES,STEP,Parasolid where we can import these file formats into any CAD,CAE Softwares.
• In ANSA we can import all the CAD Software file formates like 
  

 

Figure 1-Supported File Formats.

• IGES [Initial Graphics Exchange Specification].
• STEP [Standard for the Exchange of Product Model Data].
• Solidworks.
• Catia V5,V6
• Simens NX CAD
• Inventor
• Creo
• Solid Edge
• Rhinoceros 3D
• IGES,STEP,These two are standard file formats which are mostly used in industries.But now a days in industries,they are aslo using parasolid file format.
• Now import the model into ANSA GUI.The Model given to us is in STEP File Format.
• Go to Main Pull Down Menus >> File >> Open.

 

Figure 2-Importing/Opening the Model.

 

Figure 3-Model Imported into GUI.

 

Phase 2-Topo and Geometric Clean Up

• Here,after importing the model into GUI.
• We can see the macros are not connected and there are free edges present in the model.
• To get rid off this or to get equivalence,Do topo on the model by window selection.
• To do Topo,Go to Topo Module >> Faces >> Topo >> Window Selection.

 

Figure 4-Topo Module.

 

• After doing topological clean up,you can see the model without free edges shown in figure 5 .

 

Figure 5-After Doing Topo.

 

• Now after doing topo,do a geometric clean up on the component.

• Here we will be doing some geometry checks on the parent component.
• We have to fix the geometrical errors in the parent component,Then only we will be able to extract auto midsurface using skinoffset or manual offset from faces.
• To fix the geometry checks go to Tool Bar >> Checks >> Geometry.

Step-1

Figure 6-Checks Manager.

 

• After clicking on the check geometry,The geometric errors will be displayed.
• We can fix that geometric errors by manually or automatically.
• For this hood model,We can fix that errors automatically by auto fix.
• While checking for errors in the geometry make sure to check this options in the checks manager.

Step-2

Figure 7-Check Geometry Options.

 

Terminologies for Geomerty Options -

• Unchecked faces - Faces that failed for the shadow operation. 
• Needle Faces - Degenerated faces are faces that have their opposite CONS coincident. 
• Collapsed Cons - A CONS where it's starting and ending position coincide.
• Triple Cons - Areas where three or more faces have a common boundary.
• Cracks - Red CONS at inner areas.[Holes are excluded].
• Single Bounds - Red CONs at outer areas.[Holes included].

Step-3

Figure 8-ANSA Check Manager.

Step-4

Figure 9-Geometric Errors.

 

• Here in the Checks window all problems are reported with red color.
• Under Description column the kind of problem is explained.
• Focus functions are available in order to isolate geometrical problems and handle them easier.Select to fix all or specific reported problems by pressing right mouse button on the header of the list or one or more highlighted problems.

 Step-5

Figure 10-Fixing Errors.

Figure 11-Errors Fixed.

• [Note: All problems except triple CONS can be fixed by the automatic fixing.]
• [Note: Right mouse clicking on Check Geometry line, performs an action to all listed problems.In case where not all problems are fixed automatically, retry or proceed to fix them manually.For this component no need to fix manually because all the errors have been fixed with auto fix.]

 

• Similarly do the same process for the Outer Extract,Hinge Reinforcement Extract and Latch Reinforcement Extract.
• Here for the Outer Extract we have toggle the lines in the hemming regions because that hemming lines will be failing for minimum length,So we have to toggle that lines while meshing on it.

Phase 3-Creating new PIDS and Assigning Entities

• Here we have to do 3 methods of mesh like

1) Manual Mesh

2) Batch Mesh

3) Casting (Mid Mesh)

• For this I'm creating new three PIDS and copying the parent component and assigning the parent component to that PIDS.
• I'm renaming these PIDS as Parent as shown in figure 12.

Step-1

Figure 12-Renamed the PIDS.

• Now transform the surfaces and copy the surfaces to the PIDS.

Step-2

Figure 13-Utilities Panel.

Step-3

 

Figure 14-Copying the Entities.

Step-4

Figure 15-Make the Property as Current and Proceed to Translate.

[Note : Right Click on the PID and make it us Current,Then only we will be able to translate the surface to that PID.]

Step-5

Figure 16-Transformation Options.

 

• Here in the transformation options,In PID sub panel and in ID offset sub panel,change it to current property and in id offset panel change it copy and then proceed to translate the entities.

Step-6

Figure 17-Transformation Options.

Step-7

Figure 18-Entities have been Copied.

 

Phase 4-2D Meshing 

1) Manual Mesh

4:1 MidSurface Generation-

• Before extracting the mid surface for the components we need to give perimeter and macros length on the components while extracting mid surface.
• This makes the component to get a desired shape,So it will be easy to extarct a midsurface without any errors.The possiblities of errors will be less.
• To give perimieters and macros length on the componets,
• Go to Mesh Module >> Perimeters >> Length.

 

Figure 19-Permieter Length Tool.

 

Figure 20-Enter the Value as 1 according to the component size.

 

• Simillarly do the same thing for the macros also.
• Mesh Module >> Perimeters >> Length.
• This tool defines the element length on selected perimeter segments or macro areas.
• The element length may be explicitly declared or may be declared as a factor to be multiplied by the existing element length.
• To generate midsurface 
• Go to Topo Module >> Faces >> Offset >> Faces >> Select the Face >> Give Offset Value and Direction.
• This tool turns the solid description of a thin part into thin shell description by isolating the outer or inner skin of the solid description. 
• Here we are extracting midsurface instead of skin.Cozz we are doing everything manually in this method,so proceed with manual extract.
• Before extracting the midsurface,Orient the faces to oneside and then extract midsurface.

 

Figure 21-Oriented to One Side.

 

• After orienting,extract the midsurface using feature option to select the faces to extract mid surface.

 

Figure 22-Extracting MidSurface.

 

Figure 23-MidSurface Extracted.

 

• Once geometry cleanup is completed (e.g. surfaces are stitched together — no unwanted free surface edges inside the geometry), meshing is next.

Some rules of thumb when meshing:

• The mesh should look rather smooth and regular (keep in mind that the analysis is based on your mesh and the mesh quality is key.
• Use the simplest element type suited for the problem.
• Start with a coarse mesh and understand the modeling results; then use a finer mesh if needed.
• Try to keep mesh related uncertainties to a minimum if possible. Keep it simple as it can get more complicated on its own.

 

Figure 24-2D Element Shapes.

 

• Different Element Type Options for Shell Meshing:

Figure 38-Element Types.

 

4:2 Enter the Mesh Parameters and Quality Criteria what they given for the Hood Model

• Select and set the respective quality criteria for the corresponding elements to perform the Quality Checks (Hidden Mode). Also set the general presentation settings concerning the ANSA workspace
• Use the F11 key to open the Quality Criteria and Presentation Parameters management window (F11 Menu).
• Tool Bar >> Quality Criteria (F11) >> Enter the Values.
• Tool Bar >> Parameter >> Enter the Values.

 

Target/Average Length- 3 Units

Sl. No.	Quality Criteria	Function / Definition	Value
1	Aspect Ratio Ratio	Ratio of Max. Length by Min. Length	3
2	Skewness	Deviation from the ideal shape	45
3	Warping	Angle between the 2 planes of the same element(Quad)	15
4	Jacobian	Transformation of Coordinate System.	0.7
5	Min. Length	Shortest length of any given element	1
6	Max. Length	Longest length of any given element	5
7	Min angle Quad	Minimum angle in any given Quad element	45
8	Max angle Quad	Maximum angle in any given Quad element	135
9	Min angle Tria	Minimum angle in any given Tria element	30
10	Max angle Tria	Maximum angle in any given Tria element	120
11	Tria %	Percentage of Tria on any meshed surface	15

 

 

Figure 25-Quality Criteria Panel.

 

• Now enter the Mesh Parameters
• Go to Tool Bar >> Mesh Parameters >> Enter the Values.

Figure 26-Mesh Parameters.

 

[Note : Save the Mesh Parameter and Criteria file for that component and save it in any other drives,Cause whenever we open that component,we can open the Element Criteria file and Parameter file,So criteria and mesh paremeters will be applied habitually instead of entering again.]

 

1) Aspect Ratio

• This is the ratio of the longest edge of an element to either its shortest edge or the shortest distance from a corner node to the
  opposing edge ("height to closest node").

 

Figure 27-Aspect Ratio Calculation.

 

2) Skewness

• Skew of triangular elements is calculated by finding the minimum angle between the vector from each node to the opposing
  mid-side, and the vector between the two adjacent mid-sides at each node of the element. 
• For Skewness: Ideal=0,But < 45 is acceptable.

 

 

Figure 28-Skew Angle.

 

3) Warping

• This is the amount by which an element (or in the case of solid elements, an element face) deviates from being planar. Since
  three points define a plane, this check only applies to quads. The quad is divided into two trias along its diagonal, and the angle
  between the trias’ normals is measured.

Figure 29-Warp Angle.

 

4) Taper

• Taper ratio for the quadrilateral element is defined by first finding the area of the triangle formed at each corner grid point.These
  areas are then compared to one half of the area of the quadrilateral.                                          

 

 

Figure 30-Taper Angle.

 

5) Minimum and Maximum Length

• The shortest distance from a corner node to its opposing edge (or face, in the case of tetra elements) referred to as height to
  closest node. 

 

4:3 Conditions to be followed while meshing

• Feature Capturing
  

• Feature capturing is must while meshing.All the nodes must be connected to the shared edges.

• Tria Management
  

• Avoig higher number of trias.
  
  

• Important Parameter's in tria management
  

1. No trias in corner's or edge's.
2. No opposite trias.
3. No back to back trias.
4. No trias in fillets or hemmings(We can have minimum but anyhow try to avoid).
5. No rotational quads.
6. No trias should share a boundary with feature line.
7. Connectivity between elements.
8. Split and perform the mesh.
9. Use mixed type mesh for irregular shaped surfaces and quads only for rectangular/square surfaces(Opposite sides should be parallel and equal).

4:4 Begin meshing the surfaces

• Start meshing from the centre regions or from least free edges.You will get proper mesh density and proper mesh flow.

Why Meshing is Needed ?

• Finite Element Method reduces the degrees of freedom from infinite to finite with the help of discretization or meshing (nodes and elements). One of the purposes of meshing is to actually make the problem solvable using Finite Element. By meshing, you break up the domain into pieces, each piece representing an element.

How to Begin Mesh ?

• Start meshing form the least free edges,Like start meshing from the center.
• It will be easy to get proper mesh flow and we will get uniform mesh density.
• Don't mesh form the edges,It will be difficult and you will get many error,So start meshing from the center.
• Choose the element type while meshing.
• For this component we will be using mixed element type and working on it.
• We can also quads element type.This type can be used when we have rectangular surface.
• We can use Tria Element type.This type can be used for 3d tetra meshing.

Start Meshing

• To begin mesh,Switch form topo module to the mesh module.
• Before Meshing set the perimeter and macro length to the component.
• Here set the perimeter and macro length as target element size.
• It will split according to the target element size,So it will be easy for us to mesh.
• To Mesh >> Go to Mesh Module >> Mesh Generation >> Best Mesh >> Select the area.
• While Meshing Switch from shaded mode to the hidden mode,Then only we will be able to see the visibility  element quality.

Figure 31-Drawing Styles Panel.

 

• Before meshing,Do some geometric clean ups and then proceed to mesh.

Figure 32-Making a cut and toggling the edges to avoid the elements failing for minimum quality.

 

Figure 33-Proper Representation.

 

• Now slide the holes which are not parallel to the free edges to get a proper and good mesh flow.
• To slide the holes,Go to Mesh Module >> Perimeters >> Slide >> Select Hot Point or Node.

Figure 34-Slided the Holes Parallel to Free Edges.

 

Figure 35-Discretization.

 

• Discretization in the sense,the process of dividing a geometry into finite elements to prepare for analysis.
• After splitting the surfaces,Now start to mesh the surfaces.
• We are splitting and making the cuts to the surfaces to get the proper mesh flow on the component.

 

Figure 36-Manual Mesh.

 

2) Batch Mesh- 

• Batch Mesh is a fully GUI driven tool available within ANSA, which performs automatic mesh generation on Geometry or FE through customizable meshing sessions. In addition, Batch Mesh can be fully controlled and executed through scripts, as an integral part of the Pre-Processing process.
• It is often required to mesh specific areas of a Model with different meshing parameters and exactly this is the principal concept of the tool.
• The user creates them using the ANSA Batch Mesh Manager and assigns the respective parts,sub-assemblies or properties automatically to be meshed. For each separate Batch Meshing Session the user has only to define (input/read) the following parameters.
• Mesh Parameters contain all parameters needed for the mesh generation, requirements for the numerous features treatment tools as well as quality improvement settings.
• Quality Criteria contain all the quality requirements that the created mesh has to respect. It also provides the capability to define threshold ranges.
• The Meshing Scenario as well as the parameter files (mesh parameters and quality criteria) are created once within ANSA and can be saved to be re-used for similar analysis.

4:5 MidSurface Generation for Batch Mesh-

• To do batch mesh,Extract a midsurface using skin for the component and assign that midsurface to the different property and rename that property as Batch_Mesh_MidSurface.
• To extract midsurface,Go to Topo >> Faces >> MidSurface >> Skin.

Figure 37-MidSurface Extraction.

• To run any Batch Meshing procedure the following steps are needed:
  1) Open Batch Mesh Manager and create a New meshing scenario
  2) Assign entities to be meshed
  3) Input/Load the Mesh Parameters
  4) Input/Load the Quality Criteria
  5) Run Batch Mesh.
  6) View Statistics.

Figure 38-Tool Bar.

• Open the Batch Mesh Manager. Use the New >> Meshing Scenario. A Batch Meshing Scenario containing a Default Batch Mesh Session is created.

Figure 39-Batch Mesh Manager.

 

 

Figure 40-Adding Content to Meshing Scenario.

Input the Mesh Parameters-

• Open the Mesh Parameters Window of the Default_Session and specify the desired Mesh type,Order and Target Length in the Mesh tab. When finished press ok to exit the window.

Input Quality Criteria-

• Open the Quality Criteria Window and specify the desired thresholds, for instance the aspect ratio, skewness, warping, internal angle, element length criteria, etc.When finished press ok to exit the window.

Figure 41-Batch Mesh Manager.

 

Figure 41-Batch Mesh Done Within 1 Min.

 

Figure 42-Before Reconstructing and Smoothening.

 

Figure 43-After Reconstructing and Smoothening.

 

3) Casting (Mid Mesh)-

• For all models, even for the most complicated with a lot of ribs and thickness variation, there is the capability to move a step forward and generate FE surface mesh in the middle position of the model. 

Advantages of Casting -

1. Fully automated process.
2. Function can be applied by specifying only a minimum thickness value.
3. Although it is recommended to use the function on clean geometry, it can be used in geometry with problems as well.
4. Generated surface mesh id of a very good quality with user specified target element length and type.
5. Thickness value is automatically applied on each element.
6. Time needed to improve areas is much less than to extract the middle surface and fix it manually.

[Note: tool tips are available on all options. They become visible by hovering the cursor on the field description area.]

 

Figure 44-Automatic MidSurface Mesh generator(Casting).

 

• Minimum thickness:Minimum thickness value that appears on the model.
• Element type: Controls the type of the elements to be generated.
• Target element length:Target element length value. It cannot be lower than minimum thickness.
• In case the model consists of long beams, a Sharpen fillets with radius < option is given.Input the desired value and all fillets with a radius less than the specified one will be sharpened.

Figure 45-Sharpen Fillets.

• In case the model consists of long beams,Connect weldings with thickness ratio can automatically extend/paste the created FEelements. The search distance is specified as a ratio of local thickness.

Figure 46-Connect Weldings.

 

[Note : Sharpen fillets with radius < is recommended to be used together with Connect weldings with thickness ratio for a better result.]

 

Figure 47-Mid Casting Done Within 1 min 55 sec.

 

Figure 48-Before Splitting,Reconstructing and Smoothening.

 

Figure 49-Splitting/Discretizing the Surfaces.

 

Figure 50-After Reconstructing,Smoothening,Joining the Splitted the Lines.

 

Phase 5-Comparison of Manual Mesh,Batch Mesh,Casting(Mid Mesh)

• Now here,We are comparing all the three methods results

1) Manual Mesh

• MidSurface is generated by offset from faces panel in topo module.
• Here meshing is done by best,spot algorithms etc.,
• Here the parent component will be deleted,If we won't click No when the software states delete original faces.

Advantages-

• The mesh flow will be good and proper as we will be doing everything manually,So mesh flow will be good.

Disadvantages-

• More Preliminary Work will be done here like splitting the surfaces,reconstructing,smoothening,splitting the elements to get good mesh flow.
• Time consumption will be high here when compared to other 2 methods.

2) Batch Mesh

• The MidSurface is generated by skin offset from the faces panel in topo module.
• Here the mesh is done automatically.
• It can perform geometry cleanup and automeshing (in batch mode) for given CAD files.
• It performs a variety of geometry cleanup operations to improve the quality of the mesh created for the selected element size and type. 

Advantages -

• The time consumption is very low.It meshed the entire component less than 1 minute.

Figure 51-Time Taken to mesh the component by batch mesh method.

• It will also gives the better mesh flow.

Disadvantages-

• It Won't capture the feature lines properly.
• It will toggle the feature lines and mesh the component.
• It won't slide the holes and make them parallel to the free edges.

3) Casting(Mid Mesh)

This Casting is mostly used for the plastic components.

Advantages-

• Here it will extract the midsurface automatically.
• It will mesh the on the midsurface automatically according to the required target element length.
• It is also applicable for both plastic and sheetmetal components.
• The time consumption is also very less.It meshed the component within 2 minutes.

Figure 52-Time taken to mesh the component by casting method.

Disadvantages-

• Here after mesh,it will delete the midsurface.
• Here the mesh flow will not be good,So we have rework it on again to get a proper mesh flow.
• Holes will not be parallel to the free edges.
• We can't modify or rearrange the feature lines.

Final CAD Model Image-

 

Figure 53-Manual Mesh.

 

Figure 54-Batch Mesh.

 

Figure 55-Casting [Mid Mesh].

Result-

• Hence all the three methods Manual Mesh,Batch Mesh,Casting [Mid Mesh] has been done.
• Hence while comparing all the three methods,Manual mesh is giving the better results.
• Rest of them are not giving proper results when compared to manual mesh.
• Batch Mesh is also fine but in batch mesh the feature lines are toggled and the holes are not slided parallel to the free edges.
• Casting is not giving proper mesh flow,we have to rework it on again to get proper mesh flow,So manual mesh is fine and it is giving better results.

Learning Outcomes-

• In this Week 7 Challenge,I came to know
• How to perform a Batch mesh,Casting [Mid Mesh] to the components.
• Identify the suitable method according to the timeline given to us.