Week 2 Challenge : Surface meshing on a Pressure valve

                                                                                                                 SURFACE MESHING ON A PRESSURE VALVE USING ANSA

                                                                                                                                               (WEEK-2 CHALLENGE)

1. AIM

Our aim is to mesh the surface of a pressure valve in ANSA v22.1.0 using tria element type and target mesh length of 1mm, 3mm, 5mm.  

2. THEORY/EQUATIONS/FORMULAE USED

ANSA is a computer-aided engineering tool for Finite Element Analysis and CFD Analysis widely used in the automotive industry. It is developed by BETA CAE Systems. The software is distributed worldwide by a number of BETA CAE Systems subsidiaries and business agents. In the United States, it is distributed by Beta CAE Systems, USA, based in Farmington Hills, Michigan.

ANSA maintains the association between CAD geometry and the FE mesh. This means that the FE meshes are better representations of their geometric parents. Also it is easy to maintain and update any changes in the geometry by simply reworking the updated area instead of recreating the FE from scratch. It carries several proprietary algorithms for meshing suitable for both CFD and structural models. ANSA was initially standing for 'Automatic net generation for structural analysis', but the software has gone beyond that very quickly.

3. GENERAL PROCEDURE

• Firstly the softwares are downloaded and installed in the system.
• Geometry is imported in ANSA, firstly the diagnosis is carried out to check for any errors, then the errors are rectified, Property ID’s are defined and necessary surfaces, coons and hot points are created in topology deck.
• Mesh Parameters such as target length, Perimeters and macros length, Quality parameters such as Min and max mesh length are defined before surface mesh is created using various algorithms available such as free mesh, Spot mesh etc as required in Mesh deck. Check the quality and refine the mesh as required.

4. DISCRETIZATION
   • Geometric Model

The 3D geometry file of a pressure valve is imported in ANSA as per the figure given below.   

                                                                                                                         Fig: Wireframe – Pressure Valve

                                                                                                                     Fig: 3D Geometry – Pressure Valve

• Meshing Process
  • After the model is imported, the draw mode is changed to PID and the available perimeter points, cons are checked. 
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  • As it can be observed that there are lot openings in the model, diagnosis is carried out using checks manager for any errors such as unchecked faces, collapsed cons, triple cons, single cons, needle faces, cracks, overlap faces, etc. [Check > Geometry>Execute]
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  • As expected there is lot of errors that needs to be rectified before heading for meshing and most of it is single cons.
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  • The openings/ errors are rectified by creating new faces in order to convert the single cons into double cons and filled up the cracks as well by various surface type options such as existing surface, planar, fitted, coons and fill hole. [TOPO > faces > new], [TOPO > cons > fill hole].

• The properties ID (PID) are created in order to identify each surface and named as inlet, outlet, body, spring, base surface, valve head, and column accordingly as shown in the figure below. [Properties > New > PSHELL > PSHELL]

• More importantly the parent PID is deleted by checking the surfaces in order to avoid duplicates.                                                                                    
• Once all the errors are rectified and PID is created, now move onto Mesh deck. 

• Specify the mesh length in both perimeter and macros as per the case. [MESH > Perimeters > Length]
• Define the target mesh length and element type such as quad, tria, mixed etc as per the case. [MESH Perimeters]

• Set the min and max mesh length in quality parameters as per the case. [Quality Perimeters]

• Once everything is set, create the surface mesh by using spot mesh algorithm by selecting individual PID surfaces. [MESH > Mesh Generations > Spot Mesh]
• Finally, disable the perim and double cons option to see the surface mesh clearly for all cases.

 Case 1 - Mesh Length = 5mm

 Case 2 - Mesh Length = 3mm

 Case 3 - Mesh Length = 1mm

5. CONCLUSION

• The surface mesh on a pressure valve is created in ANSA v22.1.0 using the Graphical User Interface (GUI) commands for three cases by varying mesh lengths.
• Surface topology is cleaned by rectifying various geometrical errors such as cracks, single cons, etc by closing the holes, creating new surfaces to convert the single cons to double cons and also by deleting certain cons which are very closer to each other in order to avoid any error while meshing.  
• Surface meshing is carried out into three different cases using tria element type and target mesh length of 5mm, 3mm and 1mm. In each of the cases the mesh length is maintained same for all the PID surfaces.
• Case 1 with a mesh length of 5 mm has a total of 8824 elements, Case 2 with a mesh length of 3 mm has a total of 23874 elements, and Case 3 with a mesh length of 1 mm has a total of 210162 elements respectively.
• It can be seen that there is an increase in number of element with decrease in target mesh length.
• It can be observed that same target mesh length for the entire PID surface does not suit for case 1 and 2 as the mesh length is large for the spring and valve head PID surface curvatures. But for Case 3 with mesh length 1mm is suitable for the entire PID.
• It is very important to set the target mesh length by checking the sizes of all the PID surfaces of the complete model before meshing in order to capture the surface curvature especially with better accuracy. The accuracy can be increased even further by reducing the target length of the element.
• It can be concluded by saying that the target mesh length should be varied as per the PID surface accordingly in order to capture the surface curvature accurately.