Week 2 Challenge : Surface meshing on a Pressure valve

Aim: To mesh a pressure valve using three different mesh sizes and find out the optimal mesh size.

Objectives:

• Check for the geometrical errors and perform topology cleanup.
• Set three different target lengths as three different cases and mesh the model. Target length = 1mm, 3mm and 5mm (3 cases)
• Element type to be used is Tria
• Apply any one target length from above at a time for the entire model as one case thereby create 3 different models for 3 cases.

Procedure:

The geometry of the pressure valve given is as shown below. It is a simple valve which consist of an inlet, outlet, valve head and spring that controls the flow.

As we can see from the above pictures, the geometry has a lot of openings and holes. These features are not supposed to be in the geometry.

We also performed a topology check that shows as follows. For the topology check we enabled the single cons option, which identifies entities such as lines that are shared only by one surface meaning openings.

We solve these errors by filling all the openings on the geometry. For a CFD volumetric mesh these openings are not desirable hence we use the new option in the Faces tab. this will pop up a new menu as shown.

Existing surface option fills an opening on an existing surface. Coons option lets us select coons one by one and fills the opening. Fitted option does the same and also provides alternatives on the how the surface will be filled.

There is also another option called Fill-Hole in the Cons tab which as the name suggests fills the holes on surfaces. Using these option we fill all the openings and the resultant geometry is as shown.

Once all the holes are filled we delete the lines that are on the same plane & too close to each other or has the smallest distance between them. Most of these lines are unnecessary. If these lines are present in the geometry, it will be problem when the target length is greater than the distance between these lines. This error results in the deformation of the geometry.

Once all these lines in the exterior are deleted we run the toology check and it gives a green status as shown in the fig below.

Notice that we have disabled triple cons option. If we had the triple cons option activated the following error would show up.

The 4 errors that are being shown there are the triple cons that we created when we sealed the valve head. This triple con is required as the geometry need to be air tight. Hence we disable to look for triple cons in the check and proceed with the next part which is to assign PID to the components.

Using the help of the property manager present in the top toolbar and the tools provided in the bottom toolbar we name the components as follows.

Now we can move to meshing.

Case 1: Target length = 5mm

• To mesh select the meshing module, select length then select Perimeters, select the model and input length as 5mm.
• 
• Repeat the above step but now select Macros.
• In the meshing parameter give maximum target length as 7mm and minimum target length as 3mm. Select tria for mesh type.

• In the quality criteria give maximum target length as 7mm and minimum target length as 3mm

We can use the PID region option and select the components one by one to mesh the geometry. The internal components can be selected hiding the exterior components either by suing the not command or by using the property manager tool.

Mesh Results:

External surface.

Valve Head.

Column

Spring

The total number of elements generated are 9134 and zero quad cells. The external surface of the pressure valve is captured well with minor defeaturing at some curves but the internal components such as spring and the valve head are defeatured because the minimum target length is larger than that of the coil diameter of the spring and the fillet radius of the valve head. The column is also defeatured because of the target length.

Case 2 Target length = 3mm

• To mesh select the meshing module, select the length under Perimeteres and give 3mm. Do this for Macros also.
• In the meshing parameter give maximum target length as 5mm and minimum target length as 1mm. For mesh type select tria.
• In the quality criteria give maximum target length as 5mm and minimum target length as 1mm

Upon meshing we get the following results.

External surface

Valve head

Column

Spring

The total number of elements generated are 24722 and zero quad cells. The external surface of the pressure valve is well captured but the internal components such as spring and the valve head are defeatured. The column is captured correctly with less defeaturing.

Case 3 Target length = 1 mm

• To mesh select the meshing module, select the length under Perimeteres and give 1mm. Do this for Macros also.
• In the meshing parameter give maximum target length as 2mm and minimum target length as 0.5mm. For mesh type select tria.
• In the quality criteria give maximum target length as 2mm and minimum target length as 0.5mm

Upon meshing we get the following results.

Results

External surface

Valve head

Column

Spring

The total number of elements genertaed are 211482 and zero quad cells. the external surface and the internal components of the pressure valve are meshed well when compared to the other two cases.

Conclusion

• From the above 3 cases it is concluded that the case 3 with 1mm target length has little to no defeaturing and has retained the geometry of all components.
• Hence case 3 is giving the best results, but it increased the computational time.
• To decrease the computational time the number of elements need to be decreased without having defeaturing. To achieve this the components need to be meshed individually with different target lengths.
• From the above 3 cases for the inlet, outlet and base a taget length of 5mm gives good result. While the body and the column a target length if 3mm gives good result. For the valve head and the spring a target length of 1mm gives good results.