Week 3

AIM:

In order to perform a Structural Analysis with the given CAD Geometry (HOOD reinforcement) by using ANSA. The process involved as follows

• Importing CAD Geometry into ANSA
• Topology Operation
• Performing Geometry Cleanup
• Mid-surface Extraction
• Applying given Quality Criteria - Presentation Parameters and Meshing Parameters
• Mesh Generation
• Checking the model for Quality Criteria

PROCEDURE:

• Import the CAD Geometry into ANSA

• TOPOLOGY OPERATION

  The Topology is used to recover the results of (Hot Points – Release) and (CONS – Release) functions. It is also used to recover the Topological conditions of a Face that was undeleted by the (Faces – Undelete) function.

  Since the Topology is done already, we start with the Geometry cleanup.

• GEOMETRY CLEANUP

  Geometry cleanup is done in order to get a better Mesh flow.

  Before that, Go to MESH - Modules > Perimeters > Length. Now Length perimeter pop-up appears. Window select the whole Geometry and middle mouse click to set perimeters length of 5mm. Do the same for the Macros. 

  In the given Geometry (Hood) we have a total of five parts. 

  • Outer extract of the hood
  • Inner extract of the hood
  • Two Inner Hinges L & R
  • Hood Latch F
  Geometry checks is done in order to look whether we have any errors on the CAD Geometry.

• Now we can see on the Geometry check pop-up that ANSA is showing some errors on the CAD Geometry. The errors are unchecked faces, and Needle Faces

• In order to solve the error we have to select all by (Ctrl + A) and right mouse click then hit on FIX. Now ANSA has fixed all the errors.

• MID-SURFACE EXTRACTION

  Now the CAD Geometry is ready to take Mid-surface. We have a total of five parts of the Hood. So for each part we have to take Mid-surface. First we'll start with the Inner extract of the Hood.

  Before taking Mid-surface we have to measure the thickness on the edge perimeters. 

• The measured value is 0.75mm. To get the offset value we have to divide 0.75/2, we get 0.375.

  To take Mid-surface Go to Modules - and Faces > OFFSET then FEATURE AREA SELECTION. Also TURN ON Cross Hatches. Now select the middle surface of the Geometry and middle mouse click to take an offset. An Offset value pop-up appears. Set the Offset value of 0.375. Since the Offset direction is on Z Axis we give the value as -0.375 to get the offset exactly to the middle of the Geometry. And hit ok.

  Now the Mid-surface has been created. In order to separate the Mid-surface from the Geometry use (!NOT) option. (!NOT) option keeps only the selected entities. Select on the Mid-surface and do a middle mouse click. Now only the selected entity is visible. Use (+AND) then window select on the visible entity to bring all the neighbouring entities exist. Do it until you see No neighbouring areas found on the INFO tab. Here we have the Mid-surface extracted.

• Similarly we have to take Mid-surface for the other parts too. 

• After Mid-surface extraction set separate PID (Property ID) for each Mid-surface extracted. To do Modules - Faces > Set PID. A selection window pop-up appears. Faces/Shells checked. Window select the whole surface and do a middle mouse click. A Property Help pop-up appears. Go to New > PSHELL > Set a Name then click OK. New Property ID is created. In order to apply double click on the created PID. PID is successfully applied. Similarly create PID for each Mid-surface extracted. Totally we have 5 PIDs for the extracted Mid-surface.

• After Setting the PID. We have to do some surface cleanup. We might have some unwanted construction lines throughout the Surface to be eliminated. By eliminating unwanted construction lines and capturing the fillet areas in a proper way will lead us to Good MESH flow. It was very interesting to find which of the construction lines not necessary and creating construction lines wherever required. Most challenging part was capturing the Fillet region. To overcome the challenge of capturing the Fillet I used a set of commands. In order to remove the unwanted construction lines Go to TOPO - Modules > Faces > Cut. Right mouse click on the construction lines to remove it. If we unknowingly removed a construction line which is required, to bring it back TOPO - Modules > CONS > Release. Even if we remove the lines from the surface there will be a reference line of the lost line. Now select the line (CONS) middle mouse click. The CONS will be released and forms a SINGLE CONS. Then we have to do a Topology to connect the CONS. TOPO - Modules > Faces > Topo. Box select and do a Topo on the CONS which forms Double CONS. Now we regained the lost line. While removing and creating construction lines we might get some unwanted hot points. And there will be some unwanted hot points in the edges too. To remove those hot points. Go to TOPO - Modules > Hot points > Delete. To delete do a box selection with left mouse click on the hot point. On Narrow fillet areas the middle construction lines were captured by TOPO - Modules > Dach > Divide Face. This command was used to create a middle construction line. The curved area of the fillet are captured in 90 degree angle. Which will result in best MESH flow. After completing the surface cleanup the Surface is now ready for Meshing.

• We can see the captured fillet areas and removal of unwanted construction lines in these Figs. The highlighted lines in yellow are the captured and necessary construction lines. Light colored lines are the unwanted removed construction lines.

• MESH GENERATION AND QUALITY

  To start with the MESHING process we have to set the given Quality Criteria and Mesh Parameters

  S.No	Quality Criteria	Value
  1	Target/Average length	5
  2	Minimum Length	3
  3	Maximum Length	7
  4	Aspect	3
  5	Warpage	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
  10	Tria Percentage	15

  12      Tria Per node                    2

  To do so, Press F11 in the Keyboard. A Quality Criteria - Presentation Parameter Pop-up appears. Set the above given values.

• In the Presentation Parameters - Enable Elements % and and slide the Detail on demand effect slider to the (all details). Then hit APPLY then OK.

  Next Open the MESH PARAMETERS in Utilities TAB. Then feed in the (Basic)  

  Mesh - GENERAL

  Mixed Type – MIXED (Consist of Quad and Tria elements)

  Order of Mesh – 1^ST ORDER

  Then we have to add our Target length of the mesh flow as 5mm. And set the Min. Length as 3mm and Max Length as 7mm. Then hit ok.

• In meshing we’ll be using three main Modules. Which are,

  • MESH GENERATION
  • SHELL MESH AND
  • ELEMENTS

  To start Meshing. Go to MESH - Mesh Generation > Best Mesh. Best Mesh automatically generates mesh on the selected Macro area by using Algorithms based on the given Quality Criteria. Some areas may fail during Mesh flow. To solve the Quality issues we have to use RECONSTRUCTION command from SHELL MESH module. RECONSTRUCTION creates high quality surface MESH and solves the quality failed areas with high quality mesh flow according to the Values set in Quality Criteria and Mesh Parameters. After a reconstruction SMOOTH command is used to refine the mesh construction. SMOOTH command uniforms the mesh generation without changing the mesh orientation. Some areas we have to use SPLIT and SWAP command from Elements module in order to eliminate, split/swap or move the Tria element. With SPLIT command The Tria elements can be eliminated and arranged with directional flow of the neighboring Tria elements. With SWAP command such as Opposite Trias, Back to back Trias are separated. The Trias can be either swapped to left or right direction of the Mesh flow. Even the SPLIT command help in solving Opposite Trias, Back to back Trias in some areas. I also eliminated most of the possible Trias from the Meshed surface. A rearranged the Trias falling on the Fillet area. I used PASTE command from Grids Module to rearrange/move a step back the falling Trias from the fillet region.

• Challenges faced

• Here I had the mesh flow went away from the Construction lines due to bad Capturing of the Fillet region. First I erased the MESH flow on the particular fillet with Erase mesh on Mesh generation. Then I captured again by removing the ununiformed construction lines with Faces > CUT (right mouse click) from TOPO Module and created a uniform construction line with CUT command (left mouse click) in TOPO Module. Also deleted some unnecessary hot points from the lines. Captured a middle construction line using Dach > Divide Face in TOPO Module. The Datch Divide Face splits the selected area into two half to create a middle construction line (by selecting the Fillet area where the center line is required and middle mouse click can be achieved). Then Remeshed on the Area again with Best Mesh command in Mesh Generation. The result shown below.

• Now I achieved a better mesh flow and the Mesh is oriented with the construction lines. Similarly reworked on the fillet areas wherever I faced this kind of issue.

  Completed Mesh in all parts shown below.

• Quality Criteria - Minimum length failed. OFF element areas are shown below.

• Here the hemming region is where the reinforced inner extract component will attach. Hence the thickness is less it failed for the minimum length Quality criteria.

  The other minimum length failed area is on the Narrow fillet region. Hence we have a narrow fillet here it failed for the minimum length Quality criteria. It is shown below.

• Now MESH Generation is completed. And the MESH is ready for FEA.

• CONCLUSION

  • Geometry Cleanup is done by fixture Unchecked faces and Needle faces Errors.
  • PERIMETERS and MACROS are set to 5mm for refined edges.
  • Mid-surface Extraction is done.
  • Surface cleanup done for better MESH flow.
  • Given Quality Criteria - Presentation Parameters and Meshing Parameters are applied.
  • MESH generated.
  • Checked the model for Quality Criteria and Quality issues were solved.

  Meshed product is ready for FEA.