Week 2 Challenge : Surface meshing on a Pressure valve

                                            SURFACE MESHING ON A PRESSURE VALVE

l. AIM:

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

ll. OBJECTIVE

1. Check for geometrical errors and perform Topology cleanup.

2. Set three different target lengths as three different cases and mesh the model. Target lengths= 1,3,5 mm respectively.

3. Element Type to be used as Triangular.

4. Apply any one target length from the above at a time for the entire model as One case. Submit 3 different models for 3 cases.

lll. METHODOLOGY

A.  Cleaning all the topology Errors and assigning the parts and PID'S

1. Initial Geometry.

The initial geometry is as shown in the figure. We need to clean the geometry and generate the surface mesh. 

Initial Geometry

2. Checking the Errors in the geometry.

Errors in geometry

We can see from the above picture, the geometry has a lot of openings and holes.

These features are not supposed to be in the geometry.

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

3. Topology Cleanup

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

• The existing surface option fills an opening on an existing surface. 
• Coons option lets us select coons one by one and fills the openings.
• The fitted option does the same also provides an alternative 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 the surfaces. Using these options we fill all the openings and the resultant geometry is shown as follow

Cleaned Geometry

Once all the holes are filled we delete the lines that are in the same plane which are 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 the 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 base. This triple con is required as the geometry need to be water-tight. Hence we disable to look triple cons in the check.

4. Assigning the PIDS

 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:

List of PIDS                                                                                   Column

Inlet, Outlet, Botton surface and Body

Valve Head                                                                                                        Spring

B. Meshing

Case 1: Target length = 5mm

1) To mesh select the meshing module, select the Length under Perimeters and give 5 mm as Perimeter and in Macros.

2) in the meshing parameter give Maximum target length as 7 mm and Minimum target length as 3 mm, for mesh-type select Tria.

3) In the quality criteria give Maximum target length as 7 mm and Minimum target length as 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 manager tool.

 The total number of elements generated is 8832 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 spring and the basehead 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 Perimeter and in Macros.

2) in the meshing parameter give Maximum target length as 5 mm and Minimum target length as 1 mm, for mesh-type select Tria.

3) In the quality criteria give Maximum target length as 5 mm and Minimum target length as 1 mm.

The total number of elements generated is 23914 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 defactures 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 = 1mm

1) To mesh select the meshing module, select the Length under Perimeters and give 1 mm as Perimeter and in Macros.

2) in the meshing parameter give 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 Maximum target length as 2 mm and Minimum target length as 0.5 mm.

The total number of elements is 210040 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.

lV. CONCLUSION

• From the above 3 cases, it is concluded that the case 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 base surface a target length of 5 mm gives good results. While for the body and the column a target length of 3 mm gives good results. For the Valve head and spring, a target length of 1 mm gives the best results.