Week 3

MID-SURFACING AND MESHING OF HOOD COMPONENT

Hood is an essential part of the vehicle. It protects the engine and avoid any kind of impacts. In order to meet these requirements, analysis of hood rises as a compulsory step. So the quality of meshing needs to be good and meet the given criteria for an accurate analysis.

AIM: -

1. Check for geometrical errors and fix them to extract a proper mid-surface.
2. Perform geometry cleanup, close gaps, modify or create new faces etc.
3. Mesh the part with a uniform mesh and an average element length of 5 mm.
4. Improve the mesh by manually optimizing the shape and type of the elements.

PROCEDURE: -

• Open the hood model.stp file. Go to File>Open.
• We can now view the faces in gray and yellow. Gray color represents the positive side of the faces while Yellow the negative one. The orientation is currently random. Activate the Faces>Orient>Visible function.

fig: INNER EXTRACT COMPONENT BEFORE AND AFTER THE GEOMETRY CLEANUP

• Check the geometry to identify the problematic areas. Click on the “Checks” button, located in the “Tools” toolbar on the top of the screen and select “Geometry”. Keep the default options and click Execute.
• We will get different type of errors such as needle face, crack between cons, tripple cons and missing surface. In order to solve the tripple con release the triple con using the "Release" tool in cons. Then select the tripple con and do middle click. Use the Faces>Topo tool to combine the surfaces.
• Depending on the type of the problem ansa also offers the option to automatically fix it. Select the problems from the check manager window and click right mouse button and choose fix from the list.

fig: TOPOLOGY REFINEMENT OF THE OUTER EXTRACT

fig: LATCH REINFORCEMENT BEFORE AND AFTER THE GEOMETRY CLEANUP

• Now midsurface is extracted using the Skin option under Topo>Faces>Midsurface tool. As the thickness of the sheet metal component is constant throughout, Skin option will save us a lot of time.
• The Macros>SET PID function can be used to assign multiple different PIDs to selected macro areas. Assign thickness of 0.75 to the INNER and OUTER Extract. Also, the thickness for latch reinforcement and hinge reinforcement is 1.2.
• Activate the Auxiliaries>Fine function found in the TOPO Menu. Left click a couple of times on the crosshatches of the faces in order to reduce the resolution length.
• To eliminate the red cons between surfaces the Faces>Topo function can be used, select with a box selection the area and confirm with the middle mouse button.

fig: HINGE REINFORCEMENT AFTER GEOMETRY CLEANUP

• Delete the hot points by Hot Points>Delete function and select with the left mouse button.
• Activating the “Slide” flag allows us to select nodes of a perimeter and slide them along it. This is useful in order to change the orientation of a hole.
• We will assign a uniform distance between perimeter Nodes or element length. Click the Perimeters>Length function. Select all the Macro Areas with the left mouse button making a box selection. Confirm with the middle mouse button. Type in a value of "5" in the length field and press Enter.
• Perimeter segment that is too short to have even one perimeter node. Activate the Mesh>Perimeters>Num+/- function. Use the left mouse button to increase the number of nodes and right mouse button to decrease the number.
• ANSA provides shell mesh quality check of the generated Geometry Mesh elements. Select the threshold value of each quality criterion and the criteria has to be active for each quality check. Similarly we have to set the meshing parameters. Set the target length as 5mm, minimum element length as 2mm and maximum element length as 7mm.

S.No	Quality Criteria	Value
1	Target/Average length	5
2	Minimum Length	2
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

• Click the Mesh>Mesh Generation>Best function. Select with the left mouse button the macros of the component and confirm with the middle mouse button.The Reconstruct option means erase and mesh from new with the current algorithm and settings.

fig: MESHING OF THE INNER EXTRACT

fig: MESHING OF OUTER EXTRACT

• Mesh improvement can be carried out using various tools. Split option can be found in Elements in Mesh deck. It can be used to eliminate the rotating quads and trias elements. Also, join option can be used to remove the edge and convert two side by side tria into quad element.
• The function Elements>Swap can be used in order to swap a common edge of two elements. After that apply Mesh>Shell mesh>Smooth command to make the small adjustment needed to get the curvature for the entire mesh.
• Also paste tool can be used to eliminate two opposite trias and coarser the mesh pattern. PASTE option can be found in GRIDS in the MESH deck.

fig: ELMINATING THE FAILED ELEMENTS IN LATCH REINFORCEMENT

fig: ELEMENT QUALITY CHECK FOR THE HINGE REINFORCEMENT

CONCLUSION: -

1. Performed the manual topology cleanup, midsurface extraction and 2-D meshing for all the components of the hood.
2. Achieved the mentioned quality criteria for all the components of the hood.

LEARNING OUTCOME: -

1. Understanding about Geometric Tools, Topology cleanup and different Tools used in TOPO deck.
2. Learnt about mid surface extraction & thickness assignment for sheet metal components, 2D meshing, Quality checkup and different tools used in Mesh deck.

GOOGLE DRIVE LINK TO VIEW THE MODEL: -

https://drive.google.com/file/d/1FoR9ds6Vbv2zJyeyn8kSYlQbliJL66Zt/view?usp=sharing