Week 2 Challenge : Surface meshing on a Pressure valve

AIM:

This project aims to mesh a pressure valve using three different mesh sizes and find out the optimal mesh size.

OBJECTIVES:

• Check for geometrical errors and perform Topology cleanup.
• 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).
• The element type to be used is triangular.
• Apply any one target length from the above at a time for the entire model as One case thereby creating 3 different models for 3 cases.

PROCEDURE:

The geometry of the pressure valve can be found here. It is a simple valve that consists of an inlet, an outlet, and a spring that controls the outflow.

It is as shown in fig.

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 in 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.

The existing surface option fills an opening on an existing surface. Coons options let us select coons one by one and fill the opening. The fitted option does the same and also provides alternatives on 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 options 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 have the smallest distance between them. Most of these lines are unnecessary. If these lines are present in the geometry, it will be a problem when the target length is greater than the distance between these lines. This error results in deformation of the geometry.

Once all these lines in the exterior are deleted we run a topology check and it will give a green signal as shown in the fig below.

Notice that we have disabled the triple cons option. If we had the triple cons option 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 needs to be watertight. Hence we disable looking for triple cons in the check and proceed with the next part which is PID in 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 that everything is sorted we move on to meshing

Case 1 Target length = 5mm

1. To mesh select the meshing module, select the Length under Perimeters, and give 5 mm as the Perimeter and in Macros.
2. In the meshing, the parameter gives a Maximum target length of 7 mm and a Minimum target length of 3 mm, for mesh type select Tria.
3. In the quality, criteria give a Maximum target length of 7 mm and a Minimum target length of 3 mm.

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

The total number of elements generated is 8168 and no unmeshed or quad cells. The external surface of the pressure valve is captured well with minor defeaturing at some curves but the internal components such as the spring and the base head were defeatured because the minimum target length was larger than that of the coil diameter and the fillet radius of the valve head. The column is also defeatured because of the target length.

Case 2 Target length = 3 mm

1. To mesh select the meshing module, select the Length under Perimeters, and give 3 mm as the Perimeter and in Macros.
2. In the meshing, the parameter gives the Maximum target length as 5 mm and a Minimum target length as 1 mm, for mesh type select Tria.
3. In the quality, criteria give the Maximum target length as 5 mm and the Minimum target length as 1 mm.

The total number of elements generated is 23936 and no unmeshed or quad cells. The external surface of the pressure valve is well captured but the internal components such as the spring and the base head were defeatured because the minimum target length was larger than that of the coil diameter and the fillet radius of the valve head. The column is captured correctly with less defeaturing.

Case 3 Target length = 1 mm

1. To mesh select the meshing module, select the Length under Perimeters, and give 1 mm as the Perimeter and in Macros.
2. In the meshing, the parameter gives the Maximum target length as 2 mm and Minimum target length as 0.5 mm, for mesh type select Tria.
3. In the quality, criteria give the Maximum target length as 2 mm and Minimum target length as 0.5 mm.

The total number of elements generated is 210184 and no unmeshed or quad cells. The external surface and the internal components of the pressure valve are captured well when compared to the other two cases.

CONCLUSION:

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