ANSA- Pressure Valve Model Cleanup and Meshing

PRESSURE VALVE MESHING

Objective:

To clean the given pressure valve model, assign Property ID's (PID's).The model is then meshed to check for the best element size.

Methodology:

The geometry is to checked for any defects. The tools required to fix geometry defects are in the Topo module.

STAGE:1 (Geometry Cleanup) in Topo Module

1. There are many holes in the input model. (Wireframe Mode)
   
   
   These can be fixed by using:
   Cons>Fill Hole, an edge on the hole surface is selected to fill the entire hole with a surface.
   Holes are solved for automatically based on their location with respect to other adjacent surfaces.
   A hole completely inside a surface is made one surface with the surface in which the hole is present.eg: "hole 1" .
   A hole bordering different surfaces is made into a different surface and assigned its own cross hatch.eg: "hole 3,4"
   
   
2. The fill hole option creates a surface without considering the shape of the hole. The "hole 2" cannot be filled as such, but requires the rectangular portion to form one surface and the triangular spike to form a another surface shared with the adjacent surface.
   Faces>Cut, choose the two hot points in the spike that has to be healed.
   
   This option creates an additional surface for the triangular spike. This face is deleted and the two hot points that remain are deleted. The hole is then filled.
   
   
3. The next portion to look for defects is the valve head with spring. Using PID region the wall is selected and the "-" NOT option is applied. This hides the wall, showing the valve head and spring. In the wireframe mode(Ctrl+Shift) it can be observed that the spring intersects the valve head, and thus requires to be cleaned.
   
   To remove the unnecessary portion of the spring that is inside the valve head, Use Faces>Intersect- Choose the two sets of faces which are to be intersected. This involves one surface splitting the other into two separate surfaces by inserting CONS at the intersection. The inserted CON is a triple CON- shown in blue.
   
   Now, because the spring not only intersects the valve head at the face shown above it becomes necessary to choose all the faces with which the spring intersects, to completely split the split the spring into two portions. Then it becomes possible to delete the unnecessary portion inside the spring.
   The spring is carefully intersected with valve head, so that the triple CON forms a closed loop. This intern is indicative that the spring has been completely divided into two portions.
   
   The Screenshot shows only the triple cons in a closed loop. The inner portion of the spring which is now separate from the outer portion, can be selected using PID region and deleted.
   
   This is repeated for the lower portion the spring also.

Results:

Finally the Checks Manager>Geometry is run to check the geometry for defects. The collapsed cons can be auto-fixed in the Checks manager. The final cleaned up model is ready to be meshed

STAGE:2 (Assign PID's) in Topo Module

Each surface in the model is allotted an appropriate Property ID (PID) based on their functions. Using various selection tools, it is possible to choose necceasary faces and group them into a property ID.

1. Faces>Set PID- Choose the necessary faces, >New- Choose properties >Enter. This creates the desired property for the selected faces.
2. This step is repeated for the entire model. Different colours are assigned for each property.
3. The properties can then be viewed using "Properties" in Lists or Ctrl+P;
   

Results:

Here each property can be viewed by clicking on the Property and the corresponding property highlights in the model. When Inlet is clicked on in the Property Window, the face CONs are highlighted as shown below.

STAGE:3 (Meshing) in Mesh Module

For the model to be meshed, CONs are first divided along their length using:
Perimeters>Length- the CONs to be divided are selected.

Then to mesh the model:
Mesh Generation> Spot Mesh(Select Element type, order etc.)- Choose faces to be meshed.

1. Element Size: 15mm
   Due to very large element size in comparison to model faces, some of the faces are removed as sown below:
   
   Two faces failed to mesh in this model. The mesh can be seen to be very coarse for this model, and hence cannot be used.
   
   
2. Element Size: 7mm
   Most of the faces look good, and all the faces have been meshed for this element length. But some portions (valve head and spring) shows high amounts of distortion in geometry.
   
   Here, the decision of choosing this element size depends on application. If the affected geometry does not affect the process, then they can be neglected, otherwise the mesh can be made finer in those regions.
   
   
3. Element Size: 2mm
   All of the geometry features are seen to have been captured with approximate accuracy. This element size seems to be good enough for this model length. The distortions present in the previous cases are absent altogether in this model.
   
   
   

Conclusion:

From among the three element sizes, it is necessary to use element size 2mm, as it captures the necessary geometry details.
It should be noted that this alone is not enough to choose element length, as other factors like mesh convergence have to be taken into consideration.