Week 2 Challenge : Surface meshing on a Pressure valve

Aim:  Surface meshing on a Pressure valve

Objective:

• check for the geometrical errors and perform Topology clean up accordingly.
• Set three different target lengths as three different cases and mesh the model. 
• Target length = 1mm, 3 mm and 5 mm (i.e. 3 cases)
• Element type = Tria

Procedure:

Importing:

• Import the geometry into ANSA by selecting File > Open > .ansa file which we need for meshing

Topological clean up:

• Perform geometry checks to see the errors present in our geometry
• Geometry check can be done by selecting checks and inside it select geometry checks.

 

• Inside geometry checks, select the checks we want to perform, and then click on execute.
• 
• After we execute, we can see all the errors present in our geometry.
• 
• We can also see the errors highlighted on geometry.

 

Errors present in our geometry:

1.Single Cons :

• These are present where there are open surfaces.
• We can click on the Error and it will highlight the error in the geometry.
• We can hide the double and triple Cons to see the single cons alone,
• Also we can press ctrl + shift to enter into wire frame mode and see the errors clearly, Single coons are highlighted in red colour.

 

2. Cracks between cons:

• This error occurs when there are tiny gaps and holes between two cons

 

Methods to fix the errors:

1.Creating new surfaces:

• We can create a new surface where there are gaps and open surfaces present in our geometry
• This is done by selecting TOPO > Surfaces > New

• There are four options under new surfaces. These are the different types of algorithms present inside ANSA to create a new surface.

Let us go through each options and fix errors in our geometry:

1. EXISTING SURF :

• This option used to create surface by selecting the Cons.

• We can individually select cons, or we can use loop option to select the entire loop of cons.

• After selecting cons click middle mouse button, and we need to select the face. New surface is created where there was gap present before

 

2.PLANAR:

• Planar is used to create flat surfaces, this cannot be used on curved surfaces.

3.FITTED:

• It is used to created surface which fits to the surrounding geometry and shape.

 

4.COONS:

• Surface is created by selecting the coons.

Fil Hole option:

• It is present under cons
• 
• This can be used to fill large and small holes which are present in the geometry.
• Select the cons and the hole is closed with the new surface.
• 
• 
• We use all the options we discussed above and fix the geometry and check for errors again.

• Even though there are no errors, check the geometry if there are open surfaces present, since we need closed geometry to create a mesh.
• We have a open surface at the bottom surface.
• 
• Create new surface by COONS
• 
• 
• Perform geometry check, we can see there are three Cons error present
• This is present where we created a new surface to fill the hole in bottom surface.
• This is not actually an error, as we have deliberately created a surface where there was gap to close the geometry
• 
• It indicates there are three surfaces are connected, we can ignore this error.

Creating PIDs:

• After topological clean up next step is to create PIDs.
• Enter into PID mode by selecting PID option
• 
• 
• Click on the properties options to see the PIDs present, since we haven’t created any PIDs the only PID present is the default PID which includes whole geometry.
• 

Create individual PIDs for:

• Inlet
• Outlet
• Body
• Bottom surface
• Spring
• Valve head
• Column

 

• To create PIDs right click, select new , PSHELL , PSHELL
• 
• Create a name for PID
• 
• After right click on the created PID and select apply. Select the surface on which this PID needs to be created and apply

 

• We can even change the colour of the PID by double clicking on the colour of the PID and select the colour which we want to apply to our PID.

 

• Similarly create PID for inlet.

Creating PID for the body:

• Hide the inlet and outlet by turning off light bulb in the PID properties.
• We can now only see the body, but we also have some components inside.
• 
• If we select the body and apply, even the inside objects are selected as body.
• To Select only surface, select PID region option and this will select only the surface.

 

 

 

• Hide the inlet, outlet and Body PIDs to see the inside components.
• 
• We have 4 components inside: (1) valve head (2) Column (3) Spring (4) Bottom surface
• First create bottom surface PID.
• 
• Create Spring PID by using PID region option.
• 

Valve head PID:

• To create valve head PID, first disconnect the attachment between head and column, else the entire object is selected for PID
• 
• To fix this hide the attachment by using NOT option which is connecting head and column
• 
• Now apply the PID for head and column.
• 
• Now add the connection which we hid to column PID.
• This is done by selecting apply option in column PID and selecting the connection between the column and head.
• 
• Now delete the empty PID which was present by default
• When we hit delete, there will be error.
• To fix this first select Undelete option and then delete the PID.
• 
• When we use undelete option there will be glitched surfaces present.
• 
• These indicates there are more then one surface that is overlapping
• Now we can delete the default PID.

MESHING:

• Individually mesh each PIDs by hiding the PIDs from the properties

Inlet meshing:

• Under meshing select length and give values for Perimeters and Macros

 

• Under mesh parameters give target length as 5mm and element type as Tria and minimum length as 3mm
• 
• Under quality critaria give max length as 7mm and min length as 3mm
• 
• Now under mesh select spotmesh generate the mesh.
• 
• Similarly mesh for each individual PIDs with target length as 5mm.

Outlet:

Body:

Valve head:

Column:

Spring:

Base surface:

Final whole body mesh:

 

Case 2 :

Target length : 3mm

minimum target length = 1mm

Maximum target length = 5mm

Inlet:

Outlet:

Body:

Valve head:

Column:

Spring:

Bottom surface:

Whole body mesh:

Case 3 :

Target length : 1mm

minimum target length = 0.5mm

Maximum target length = 3mm

Inlet:

 

Outlet:

 

Body:

 

Valve head:

 

Column:

 

Spring:

 

Bottom surface:

 

Whole body mesh:

Learning outcome:

Topological correction:

• how to check topological errors and fix them
• Fixing geometric errors
• Different types of surface creations
• Filling holes and closing the open geometry for meshing.

PID creation:

• Creating new PIDs 
• Colouring the PIDs
• Deleting the existig PIDs
• Selecting PIDs by PID region and PID option

Meshing:

• Giving values to perimeters and macros
• Setting up mesh paramters
• Setting up minimum length and maximum length
• Setting quality criteria
• Generating mesh

Results:

Individual ANSA files for each target length:

5mm target length

3mm target length

1mm target length

inference:

• Comparing mesh of spring for each case:

             5mm                                            3mm                                               1mm

• The Spring mesh in 5mm looks like a flat surface because the element size is larger than the smallest distance between two nodes in the Spring

Effect of target element size on the increase in number of elements:

• As we can see from the results, the number of elements increrases exponentially for decrease in element size by 2mm

Effect of element size on mesh and mehs time:

• Decrease in element size, captures the curvatures very well
• As we can see from comparing the valve head for different cases 1mm target length captures the surface more accurately\

• But the time to mesh increases

Conclusion:

• 1mm target length captures the curvatures and surfaces very accurately comapred to 3mm and 5mm
• Order in which the target element size is better: 1mm > 3mm > 5mm