Week 2 Challenge : Surface meshing on a Pressure valve
AIM :
To generate surface meshing for the pressure valve geometry for 3 different target mesh lengths.
OBJECTIVES :
1. To check for geometrical errors and perform Topology clean-up for the given model.
2. 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.
3. Write a detailed report on the meshing process and explain which case is giving good results and why.
INTRODUCTION :
A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system. Pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is relieved by allowing the pressurized fluid to flow from an auxiliary passage out of the system.
When the set pressure is exceeded, the relief valve becomes the "path of least resistance," as it is forced open and a portion of the fluid is diverted through the auxiliary route. As the fluid is diverted, the pressure inside the vessel stops rising. Once it reaches the valve's reseating pressure, the valve closes.
Procedure:-
The first and foremost step to be carried out is importing the given geometry model into the ANSA software. The imported geometry of the pressure valve is as shown.
As we can observe, the imported geometry contains various missing surfaces, single CONS and various other such errors. We first need to resolve all these errors before meshing the geometry. We do this in various steps, namely.
1. TOPO CLEAN-UP
In this step, we first run a geometry check by using the check manager, so as to figure out all the errors and warnings in the geometry. We can see that it displays various errors such as geometry and intersection errors, which we need to resolve one by one.
We now resolve these errors one by one. The first step is resolving the surface errors such as missing faces, small holes, and so on. We do this by creating a new COONS face enclosed by the single CONS, as well as by using the “fill hole” function, to cover up all the open surfaces and thereby get rid of all the single CONS in the process. We create new surfaces as shown.
Finally, we orient the geometry to display grey surfaces on the outside and yellow surfaces on the inside. Thereby, we solve all the surface errors of the geometry by creating new faces. We can observe that there are no more double CONS left and hence, the geometry errors have been resolved.
2. PID CREATION
After the topo clean-up of the geometry, the next step is assigning the property ID's (PID’s) to the various components of the pressure valve. Each component is visualized by a different color, representing its particular PID as shown below.
CASE – 1 : TARGET LENGTH = 5 mm
In this case study, we are going to generate meshing of a target length of 5 mm for the pressure valve geometry. To do this, we first assign the perimeter length and macros length as 5 mm for the geometry. This creates equally distributed points or nodes which are 5 mm apart, along the boundaries and faces of the geometry. The next step is defining the quality criteria for the same. As we require a target length of 5 mm, we define the minimum length of the mesh parameter as 4 mm and the maximum length as 6 mm. This makes sure that the meshing is generated within this range. After defining the parameters and quality criteria, we finally generate Tria CFD Meshing for the entire visible geometry. We obtain a coarse mesh as shown.
From the images shown, we can observe that the components of the pressure valve (especially the spring) have not been clearly captured, due to the high target length value. To capture the details more precisely, we are going to refine the meshing, in further cases.
CASE – 2 : TARGET LENGTH = 3 mm
In this case study, we are going to generate a medium refined mesh of target length 3 mm and observe the differences. We first set the perimeter length and macros length of the geometry to 3 mm. Next, we define the quality parameters of the minimum length as 2 mm and the maximum length to be 4 mm such that the generated mesh is within that range. After setting the quality parameters and target lengths as shown, we finally generate the Tria CFD Meshing for the geometry as follows.
From the images, we can observe that the meshing is a bit more refined but the details of some of the components are still not perfectly captured, though it is a bit better as compared to the first case. Hence, we need to refine it more.
CASE – 3 : TARGET LENGTH = 1 mm
In this final case study, we refine the mesh to a target length of 1 mm. To do so, we first set the perimeter length and macros length to a value of 1 mm. We then set the quality parameters to a minimum length of 0.5 mm and a maximum length of 1.5 mm so as to make sure the mesh length stays within that range. Finally, we generate the Tria CFD Meshing for the geometry as shown.
From the images, we can observe that all the details of the components such as curvatures and also the spring have been clearly captured due to the fine meshing.
CONCLUSIONS :
From the case studies conducted above, we can infer that as the mesh size or target length of the meshing reduces, the details of the components, such as their curvatures and spirals are captured more precisely. As we can see, when compared to target length of 5 mm, the spring component is captured more in detail by the 1 mm mesh length. Therefore, a smaller mesh length captures finer details of the geometry. Also, as the mesh becomes more refined, the number of elements also gradually increases, which leads to an increase in computational time. Hence, finer the mesh, larger the element count.