Week 4

Aim

• To check the given model for geometrical errors and mesh with given quality criteria.
• To assign thickness to the mesh model.

PROCEDURE

The model assigned was that of a bottle cap.

Step-1: To study the areas of the model.

1. Outer shell
2. Large thread
3. Small thread
4. Outer ribs
5. Inner ribs

Step-2: To do the standard geometry cleans-up.

• Ran pre-surface meshing geometry check and it had numerous amount of errors.
• It was fixed by auto-fix to save time.
• Measurements at various points were taken and the thickness varied with feature.
• All the exterior surfaces were oriented properly.

Step-3: To create and prepare the mid-surface.

• The mid-surface created by offsetting the skin to middle of the surface.
• Middle surface was then joined together by topo.
• The mid-surface was then de-featured by joining the cons on the surface.
• The perimeter length was set to 1mm as required.
• Again measurements were taken around feature to make sure that the elements stick to required quality criteria.
• The threads were captured by creating a curve on the thread. The curve was projected onto the mid-surface and new vertical surface was created using ‘new’ in faces tab.
• To capture the steps on inner top edge of the bottle cap a curve was created using ‘Middle’ in curve tab in middle of thickness of the step. The attached portion was projected onto the middle surface and then new surface was made between the two cons. As the features were in a circular pattern the generated middle surface was copied onto every feature.
• In order to do the ‘Rotation’ in Transform tab a centroid was created using ‘COG’ in points tab.
• Then needed extensions on the outer ribs were performed in order to attach them to main middle surface. They resulted in triple cons. The extension was performed using ‘Extensions’ in faces tab.
• The mid-surface once finished was checked and properly trimmed for creating the best mesh possible mesh. Some areas had to trimmed away and some cuts had to be joined using Cut in faces tab.

Step-4: To type in the quality criteria and establish the mesh parameters.

• The quality criteria were keyed in.
• The mesh parameters was established, the average length was 5 mm, min-length-3mm, max-length-7 mm.
• The mesh chosen was a mix of trias and quads, because it yields better results.

Step-5: Meshing and checking.

• To mesh the component mid-surface "best mesh" was used, as it yielded the better result.
• Large areas were topologically cut into smaller ones and individually meshed to get a better mesh flow. These cuts had to be Introduced at many place which were then removed without changing the established mesh flow.
• Mesh flow was checked to avoid elements failing the quality criteria many times. Troublesome mesh areas were reconstructed until a satisfactory result was produced.Hhowever the model due to its feature created some off elements.
• Opposite trias were eliminated using "Split" and "Swap" after which the area was made proper again using "Smooth".
• The areas were symmetrical and hence could have copied the mesh. But since the associativty of the mesh with surface was not mentioned i went with manually meshing both the areas individually.

Step-6: Giving thickness to the mid-surface.

• Each of mid-surfaces was individually selected and new shell property identity was created.
• Thickness correspondingly was given as their parent geometry.
• Each mid-surface was then given a new material.
• The the shell elements were made to solid elements and checked its characterstics with the parent geometry.

RESULT

The model was preprocessed as needed. Its topology was corrected and FE model was created.

LEARNING OUTCOMES

As for this model midsurfacing was a real challenge. Becuase it had so many different elements with different thickness and hence differebt PID's. In the area of meshing certain outcome were inevitable due to the features of the model. Altogether the model provided good oppurtunity for learning.

The pictures give brief idea of the process of preprocessing.