Mid surfacing and Meshing an Automotive Hood along with Quality Criteria and Thickness using ANSA

ABSTRACT:

• By using CAE Pre-Processing Tool ANSA & to develop 2D meshing for an Automobile Hood or Bonnet, it usually protects and covers the components mainly Engine, Battery, Radiator and AC parts which include compressor condenser etc.
• The Hood or Bonnet these days come with different types of materials and shapes according to the usage the cost constraints. Here we use a sedan Hood to demonstrate and material mainly used is Steel.

METHODOLOGY:

1. Importing the CAD geometry and Assigning Property ID (PID) for each part
2. Checking out the errors.
3. Extracting Mid-Surface (3D to 2D interpretation)
4. Assigning Quality Criteria
5. Meshing and Improving Mesh Quality.

INTRODUCTION:

Keeping safety, strength and many design aspects, Hood or Bonnet has to undergo many conditions and final CAD outcome is considered for pre-processing in ANSA.

The main parts include in this geometry:

• Outer Panel
• Inner Panel
• Both supporting Hinges (Left and Right)
• Latch

Excluded parts:

• Hood Shock Absorbers
• Other supporting parts including Heat Shield

PROCEDURE:

1. Importing CAD Geometry of HOOD or Bonnet in ANSA and Assigning Property ID (PID) for each part:

• For any component, we need to assign Property ID(PID) for each and every part so as to differentiate individual checks in our process in later stages.
• This helps in switching to different parts specified upon user requirement.

Note: Image demonstrating the colour in order to specify the parts, colours may vary in the next steps.

2. Checking Out for Errors:

• After successfully importing the Hood CAD geometry we need to perform the geometry check under CHECKS Manager in order to see any geometrical problems of the model such as Unmeshed Macros, Unchecked Faces, Needle Faces, Collapsed Cons, Triple Cons, Overlaps and Cracks.
• ANSA detects some errors and we need to ensure that these needs to fixed manually or by just running the automatic fix command and confirm that there are no geometry errors there in the model.

• Make sure that the Hood is always Gray which indicates Positive in ANSA where yellow stands as Negative.
• Use the Orient option under Faces in Topo Mode to change the colour of the model to Gray if it’s so. (Orient<Visible)

3. Extracting Mid-Surface:

• In order to Mesh the component, it needs to undergo mid-surfacing for all the components/parts as the component becomes a 2D object after extracting Mid-Surface and it will be ideally good for Meshing.
• There are different methods a CAE engineer can use for Mid-Surfacing the component and the best would be Mid-SurfaceModules Buttons in Topo Mode.
• Here I used Offset Mid-surfacing as its easy and much efficient.
• Always enable Cross Hatch while extracting Mid-surface as it helps to select a particular region and space so as to avoid unnecessary errors.
• Create separate PID for all the Mid-Surfaces Extracted in the Property ID Manager in order to obtain the results at the end.
• Make sure that all the PID’s are created and remove any Hot Points if any.
• Bulb indicates the part selected in the PID Manager.

4. Assigning Quality Criteria:

• Give Average/Target length to all the individual Mid-Surfaces using the Perimeters<Length.
• Average length alters the shell elements length of the component.
• Remaining values are assigned in the Quality Manager or just tapping F11 key.
• Each element in the Mesh should qualify the Quality Criteria given.
• After assigning the values given for the quality check, we need to perform the topological clean up before meshing.

Topological Clean-Up:

• So as to acquire the smooth flow of mesh a CAE engineer should do topological clean up for each and every corner of the model and examine, remove unwanted CONS by using different options available under Module Buttons, mostly used keys are cut, release, insert & delete.

5. Meshing and Improving Mesh Quality.

Meshing:

• After Topological Clean up, consider meshing each and every part separately
• One can use different methods in order the Mesh the surfaces, I used the Best Meshing option under Mesh Generation in Mesh Modules Buttons.
• Best Mesh ensure the user a good Mesh flow across the part and ANSA provides a decent outcome.
• Once the Meshing is done, try to reconstruct the Mesh generated and Smooth it for enhancing the Mesh.

Improving Mesh Quality:

• Once the Meshing is done with the desired quality criteria, we need to ensure there should be no unnecessary rotating Trias or Quad elements in the model.
• In 2D objects, the allowed elements are Triangle (Tria) with 3 Nodes & Quadrilateral (Quad) elements with 4 Nodes.
• Nonlinear Tria & Quads are avoided.

• Trias and Quad elements can be adjusted using the Split & Swap options under Element Option, smooth the elements again and again till the flow is fine and accurate, avoid OFF elements whenever possible.

• And OFF elements should be zero in order to achieve quality.
• Try to reconstruct the OFF elements until it becomes Zero in order to gain the quality
• In some cases, use the Paste option under the Grids bar to clean the Tria and Quad elements from the Edges.

• No Tria elements on the edges

RESULT:

• A 3D Automobile Hood is Meshed successfully converting it into 2D surface thereby extracting its Mid-Surface giving the quality criteria and performed the Meshing, Improving Mesh Quality using different tools with the help of ANSA.
• As ANSA is a trial and error tool user should follow the steps again and again in order to get the desired output.

Learning Outcome:

• Able to analyse the model, extracting the property ID for different parts involved.
• Checking the Geometry and creating Mid-Surface for each part (3D to 2D extraction).
• To assign Quality criteria.
• Generating Mesh & checking the quality of Mesh.

Google Drive Link: https://drive.google.com/file/d/1nOZT5D8-Cn5DCcMAWgMtiwzwbWoRc-E0/view?usp=sharing