Week 12:Project-1-Meshing of Door Inner Panel Challenge

                                                         PROJECT 1

                               PREPROCESSING DOOR PANEL OF CAR USING HYPERMESH

OBJECTIVE:

• Import the CAD geometry of door inner panel
• Clean up the geometry until no topological error is found
• Extract Mid-Surface for the geometry
• Meshing according to given quality criteria
• Improving mesh flow without any quality issues
• Assign thickness for mid surface

Quality Criteria Used:

                                         

PROCEDURE:

1. Import Geometry: Go to File >> Import >> Model/Geometry

       

                                                                                            Imported CAD geometry

2. Checking parent geometry:

• Scan the entire geometry
• Under visualization options we can see there are four types of edges which are 1) Red colour for free edge 2) Green for shared edge 3) Blue for supressed edge 4) Yellow for non-manifold(t-joints).
• We can also adjust the level of solid transparency in the visualization options.
• Topology repair consists of correcting connectivity error between adjacent surfaces. The errors include unconnected adjacent surfaces, duplicate surfaces, missing surfaces.

                                              

                                                                                                              Visualization in wireframe mode

 

                                              

                                                                                                    Successfully removed all the free edges

 

• The goal of topology clean-up is to restore the surface data to a perfectly clean representation of the part.
• Sometimes we can visually detect duplicates, there will be a glitch on the surface indicating that it is a duplicate surface.
• We can also check for duplicate from the defeature panel.
• Go to geometry >> defeature >> Duplicates >> Surfaces (Displayed) >> Clean-up Tol = 0.01 (Default) > Find > Delete

 

 

 

3. Geometry clean-up and defeaturing

• First, we should defeature small fillets which will cause minimum size errors
• We can do this by using Geometry >> defeature >> surface fillets
• Select the required surfaces with fillets
• Select the minimum and maximum radius and hypermesh will automatically detect all the fillets

                                             

                                                                                                       Selecting all the ribs with fillets

 

                                             

                                                                                                           Fillets detected

 

• Once check whether all the right fillets are selected or you can also manually select them and click on remove
• Sometimes they might not attach properly. Use Geometry >> quick edit >> replace point option
• We can also use this option to paste nearby nodes while doing geometry clean-up.

 

             

                                                                                              Joining points using replace option

 

                                                                        

                                                                                                             Fillets defeatured successfully

 

4. Mid-Surface Generation

• As this is a plastic component, I would not recommend auto-mid generation option
• If you observe the geometry, there are lots of features with varying thicknesses
• So, I will manually find the thickness of each surface and offset them individually
• After offsetting we can join them easily
• First offset the biggest surface so that small features can be attached to that easily
• You can see in the picture below that I have selected all the bigger surfaces (back side of panel) and did offset. Make sure you duplicate all the selected surfaces before doing offset.

                                                          

                                                                                                                       Offset of big surfaces

• Once all the bigger surfaces mid is done. We can create mid surfaces for small features and attach them on to the bigger mid surface

                                                  

                                                                                                                     Offset operation for u-shaped feature

 

                                                    

 

• Now create lines around this feature using geometry >> lines >> extra edge option

                                                    

                                                                                                         Creating lines around U-shaped feature

• Project these lines on to the bigger surface and join both surfaces

                                                    

                                                                                                       U-shaped feature successfully joined to mid surface

5. Mid-Surface generation for Ribs

• There are two ways to create a mid-surface for ribs. One is using the middle line option and the other is using the final edit tools option
• Middle line option can be used for ribs that have the same thickness throughout
• Follow these pictures below. Go to geometry >> lines, create a middle line, and project that on to the mid surface and then we can create a new surface between those 2 lines.

                                                  

                                                                                                              Creating middle line for ribs

 

                                                  

                                                                                                                     Middle line created successfully

 

                                                     

                                                                                                                               Selecting lines for trimming on to surface

 

                                                      

                                                                                                                         Lines are projected successfully on to surface

 

                                                     

                                                                                                                     Creating new surface between 2 lines

• Now extend these new surfaces on to the mid surface. Use geometry >> surface edit >> extend >> select surfaces to extend and surfaces to target
• Triple con or non-manifold (yellow lines) will form as it is a t joint

                                                   

                                                                                                    Mid surface of ribs

 

• Similarly, follow the above procedure to create the mid surface of ribs for the entire geometry.

                                                     

                                                                                                             Mid lines projected on to mid surface

 

• Go to 2D>> auto-mid >> Final edit tools option for auto mod generation. This option is usually used for ribs that contain varying thicknesses. 
• select the opposite surfaces as shown below and make sure you tick those extraction options as these will connect generated surface to the main mid surface automatically 

       

                                                                                                         Final edit tools for auto mid generation

 

                                                               

                                                                                                        Auto-mid formed using final edit tools

 

•      I have created a mid-line at the top of the cylinder as shown below and offset its walls to generate mid surface
•      Now create a surface between mid-line and mid surface of cylinder. This helps us to achieve the height of mid surface same as parent geometry                                                                                            

      

               Mid-line created on top of Cylinder                                                           Off-setting walls of the cylinder           

 

               

                                Feature1                                                                                               Feature2     

• These features are captured as cross-shaped surfaces shown below 

      

                                     Intersecting mid-surface of features                                Yellow lines formed as a result of intersection     

 

                                 

                                                                Mid surface generated for the entire geometry 

 

6. MESHING AND IMPROVEMENT OF THE MESH

• Now mesh each surface separately to achieve better mesh.
• 1^st we need to input quality parameters. Go to >> Preferences >> Criteria file settings and enter the values or import criteria file.
• I have used the 'Mixed’ option to generate the mesh for this challenge because we are preparing the model for crash & safety simulations. The quad-only mesh is preferred for durability and structural simulations.
• We can also divide the regions manually to achieve better mesh flow. Trias will be there in some areas, but they should be in the direction of mesh flow.

                                       

                                                                                            Meshing without dividing regions will lead to bad mesh flow

 

 

• Therefore, I have divided the regions in way that the mesh flow will be good. Usually this is done while doing geometry clean up on mid surface
• You can see in the picture below that we got better mesh after splitting the surfaces. Follow this strategy for the entire geometry while meshing

                  

                                                                                             Dividing into regions for better mesh flow   

• Mesh flow at some regions are shown below

 

                                                                        Better mesh flow achieved as a result good geometry clean-up

• Opposite trias and rotating quads can be easily eliminated by remeshing the elements in that area.

                                      

                                                    Opposite trias                                                                      Opposite trias removed after remeshing

7. Connecting Mesh:

 

• After generating mesh on each surface individually, we need to connect the mesh.
• Connecting mesh will give us better load transformation while simulation
• There will be no use of the mesh if you do not connect them properly
• Use 2D >> replace option to connect nearby nodes

    

           Un-connected mesh                                                                                       Connected mesh

 

• Connecting mesh is nothing but stitching 2 meshes. This will affect mesh flow
• We need to either smooth the mesh or align the nodes after connecting
• I have used align option. Go to geometry >> node edit >> align.

    

                                                         Aligning mesh                                                                    Mesh connected and aligned successfully

 

8. Clean Up tools for clearing off elements and to achieve better mesh flow

• Use 2D >> Quality index tool >> Clean up tools (Smooth, drag tria elements, Element optimize, combine tria element, Split quad element, Place node) to eliminate all off elements.
• Smooth: This option helps us to achieve better mesh flow. After clearing off elements, we usually use smooth in that area.
• Drag Tria Element: we can drag any tria element out of the geometry easily. This option helps us to remove trias easily
• Split Quad Element: Splits one quad into two trias. We use this to reduce rotating quads
• Combine Tria Elements: Combines two tria elements into one Quad element. Helps in Reducing tria percentage
• Element Optimize: Smooths the quality by adjusting the neighbouring elements. Helps in Clearing elements for quality
• Place Node: This option allows us to manually change the position of a single node. Helps us to clear off elements

 

9. Rotating holes:

• Holes should be moved parallel to the edges
• Holes should always contain even number of nodes. This helps us to achieve better mesh.
• First create temp nodes around the holes and one exactly in the middle (this acts as base node while rotating).
• Now, use tools >> rotate >> nodes option to moves the entire nodes parallel to surface

  

                  Before rotating                                                                                                       Nodes after rotating

 

                                                   

                                                                                          Holes captured with better mesh flow

 

10. Equivalence:

• After meshing the whole geometry. Use tools >> edges option to check whether there are any free edges in-between the elements
• clear all the free edges using equivalence. 

                                     

                                                                                      

•  Since there are no unnecessary free edges. we can proceed forward. 

11. Assigning thickness:

• Create different properties for different surfaces. Measure the thickness of each surfaces or features and assign property to each of them.
• All the features and ribs are captured perfectly 
• After assigning thickness check the mid-surface using transparency mode while enabling parent geometry. Then you can easily understand whether the surface has gained thickness or not. 

   

                                                                     Features are captured perfectly

• You can see in the picture below that all the surfaces are matched according to parent geometry  

 

                                

                                                                        Checking thickness using transparency mode

 

 

 

Learning Outcomes:

• Able to do geometry clean-up with no errors.
• Able to generate mid surface for complex geometry.
• Aware of all the quality criterias and quality parameters during mesh generation.
• Understood mesh generation and implemented mesh generation for complex geometry.
• Learned how to improve mesh flow, remove off elements and remove trias to achieve better mesh flow.
• Assigned thickness for all the features

 

Conclusion:     

After completion, there are no quality issues found in the door panel model. Mesh flow is good. Trias percentage is 1.3%. Therefore, pre-processing of the Door Panel is successfully done using HYPERMESH.