Pressure valve Cleaning topology and mesh generation

Objectives:

• To clean up the given topology of pressure valve model using ANSA
• To mesh the given model using proper meshing tools.
• Three different mesh sizes of 17 mm, 7 mm, 2mm were compared with each other.

Procedure:

Generating mesh for any geometry is a two step proccess

• Cleaning of the given topology
• Mesh generation for different types of application.

In this assignment, a general purpose mesh is generated for different elements sizes.

Topological corrections:

The different tools that were used and there functions are given below:

(1) Cut: This function cuts (splits) an existing Face or joins if inverse operation is applied (right mouse button). In order to achieve this, two Hot Points must exist on the boundary at the positions where the Face has to be split. A Face may also be cut by selecting Welding Spots instead of Hot Points.

• Heal Cut: it is an option that allows the user to close openings along the perimeter of a face.

(2) Delete: This function deletes selected Faces. As the Face is deleted the neighboring topological conditions change. If the picked Face to be deleted serves as a parent Face to other linked Faces, then extra confirmation is required for the deletion, and an option to convert all linked Faces to geometry is given.

(3) Intersect: This function defines the intersection between two groups of Faces and/or FE elements that penetrate each other. Topology can be applied automatically if required. In case that the two groups can define a closed volume between them, Boolean operations can be applied.

(4) Topo> Faces> New: This function defines a new surface by selecting its boundary curves and creates a corresponding face that covers the new surface. The calculated surface appears as a net. The majorily used options under these settings are:

• COONS: This function defines a new multi-patch Face and Surface, using the COONS interpolation principal. This is an easy way to define a new surface by its boundary curves. After the mathematical definition is finished, the calculated surface appears as a net. A relative window gives the ability to accept or to reject the calculated surface. When only three boundary sides are selected, there is the ability to choose between two alternative definitions for the fourth generated side, one is to be straight and the other is to have a shape similar to its opposite side.

• FITTED: The FITTED option is used for the definition of a non-planar Face. The created Face fits to the selected boundaries.

Mesh setup:

Different tools that were used to setup mesh were given below:

(1) MESH>Perimeters>Length: This function defines the element length on selected perimeter segments. The element length may be explicitly declared or may be declared as a factor to be multiplied by the existing element length.

(2) MESH>Mesh Generation>Free: This function automatically meshes Macro Areas and FE shell areas using the Free meshing method, taking into account the element type already selected and the defined meshing parameters. The meshing algorithm may be applied to selected unmeshed Macros, or to all visible Macros according to the chosen option (Selected or Visible respectively). The Re-Generate option applied to selected Macro Areas where, firstly, erases existing mesh, if any, and secondly meshes them using the Free meshing algorithm. The Free meshing method creates the least possible number of shell elements, taking into account the shell element distortion, minimum and maximum length. The resulting shell elements are of first or second order shell elements according to the status of the 2nd Ord flag.

The procedure for topological corrections with figures are given below:

Initial geometry:

Corrected geometry:

Outer casing:

From the above figure we can see that various operations have been performed in the outer walls of the pressure walls. Various functions like COONS, fitted surface generation, Heal cut and several other operations are performed to rectify the corrections in the topology.

Inner spring mechanism:

To attach the spring from the surface of the valve intersect opertion is conducted by using the following procedure:

• The intersect command is activated by left clicking the intersect button under faces section.
• For the intersect to take place we must make 2 selection to merge two or more surface.
• For the first surface spring is selected using left mouse button and then middle mouse button is used to confirm the selection.
• Then pressure valve surface selected for the second surface and middle mouse button is used to confirm selection and an intersection is formed between the spring and the pressure valve.
• Then excess parts of the spring which is present inside the pressure valve were deleted using delete option in the faces section.

Then PIDs were assigned to different parts of the valve.

Generated Mesh:

17mm Mesh:

7mm Mesh:

2mm Mesh:

Results:

• It can be seen from the generated figures that 17mm lenght is worst generared mesh as it does not retain the shape of the pressure valve also the element size so big that the smaller elements in some places are left unmeshed.
• For the 7mm mesh it can be seen that the mesh generated is better than 17 mm mesh as it represent the shape of pressure valve and also element size is small enough to generate complete mesh.
• For the 2mm mesh it can be that the mesh retains the shape of pressure valve more perfectly and also element size is so perfect that all the elements are meshed. Therefore, 2mm element lenght is the best for meshing