Rotational Valve Mesher

6.10.2 Rotational Valve Mesher

This provides access to the meshing algorithms and meshing parameters for the various valve types. The Valve Template Mesher advantage is, that optimizes the mesh in the region of valve closure, based on the unique valve template parameters. This enables the creation of mesh with appropriate quality and minimal user effort.

The mesh related settings can be accessed as follows:

Mesh Panel > Valve Template Mesher

The following mesh related settings are available in the Geometry Tab of the Properties Panel as shown in Figure 6.562 and Figure 6.563

Create/Replace Mesh: Allows to select the parameters from the Create/Replace Mesh drop-down list as follows:

New Mesh: To create a new mesh.
Store Build Mesh: To store the mesh settings without generating any mesh.
Replace: circumferential valve: To replace the existing mesh with new mesh settings.

Mesh Name: Allows user to name the mesh prior to mesh creation. The option is available when New Mesh or Store Build Mesh is selected under Create/Replace Mesh.

Setup Options: The options Template Mode or Extended Mode does not alter the valve mesh related parameters. They change the accessibility of other advanced settings during the model setup as explained in Model section. As such, the user is free to select any of these options during meshing.

Valve Type: Circumferential Valve is selected under the drop-down menu of Valve Type.

Figure 6.562 - Valve Type

Figure 6.563 - Build Mesh

On defining the above settings, further meshing parameters are specified for:

Valve Surfaces: The Valve Surfaces corresponds to the moving boundaries of a valve chamber. They are assigned as follows:

Select the valve surfaces under CAD Surfaces in Geometric Entities Panel.
Click Add Surfaces icon to the right of Valve Surfaces or click Select Valve Surfaces tab in the Properties Panel.

Cylinder Surfaces:The Cylinder Surfaces of a valve chamber corresponds to the boundaries along which the mesh will slide and compress as the valve opens and closes.

Select cylinder surfaces under CAD Surfacesin Geometric Entities Panel.
Click Add Surfaces icon to the right of Cylinder Surfaces or click Select Cylinder Surfaces tab in the Properties Panel. The Select Cylinder Surfaces operation automatically follows the Select Valve Surfaces operation.

Valve End Surfaces: The valve ends corresponds to the stationary boundaries of a valve chamber (not included in the cylinder surfaces). They are assigned as follows:

Select valve end surfaces under CAD Surfaces in Geometric Entities Panel.
Click the Add Surfaces icon to the right of Valve End Surfaces or click Select Valve End Surfaces tab in the Properties Panel. The Select Valve End Surfaces operation automatically follows the Select Cylinder Surfaces operation.

Center of Rotation: The point about which the valve rotates. Specify this parameter in co-ordinates. Basically, it is pin center (Cam ring pivot point)

Rotational Axis Vector: This is axis of rotation about which the valve rotates. Specify the unit vector in terms of co-ordinates.

Reference Point: This is the origin of the conformaly mapped space used in the meshing operation. It is generally taken to lie near the centroid of the volume being meshed. Specify this parameter in co-ordinates.

Minimum Gap Size: This is a numerical limit to avoid physical contact between valve and vale end surfaces when the valve is in closed position physically. At the same time, it also limits the over-compressing of mesh between valve and valve end surfaces while closing the valve. In other words, it is the minimum distance from the valve end at which the valve stops moving and limits the compression of mesh numerically.

This is used by the valve mesher to optimize the mesh between the valve and valve end surfaces.
During valve motion, for any angle displacement value in the Dynamics module between zero and minimum gap size, the valve always stays at the minimum gap position. The valve end surface is considered as the reference for valve displacement value. The zero displacement value in the Dynamics module corresponds to the valve touching the valve end physically.

There is no default for Minimum Gap Size. It requires a user input value (greater than zero). To the extent that it does not create an excessive number of mesh cells, a small (micron scale) Minimum Gap Size is recommended. A possible disadvantage of using a small (micron scale) Minimum Gap Size during meshing is that it can create a mesh with an excessive number of grid cells if the contact area for the valve face is large relative to the Minimum Gap Size. This disadvantage can be avoided by meshing using a Minimum Gap Size larger than the actual minimum gap, and then subsequently reducing Minimum Gap Size to the desired value for the simulation in the dynamic module.

Maximum Displacement: This is related to the amount of mesh displacement which can occur as the valve moves in the Opening Direction. During Meshing, it is used by the valve template mesher to optimize the mesh. Specify the value for the maximum value of displacement.

It is recommended to set this Displacement to the approximate maximum distance the valve is expected to rotate from pin center or if that is not known, to a value slightly less or more than the maximum distance the valve could possibly open.

The parameters Critical Edge Angle, Curvature Resolution, Maximum Cell Size, Minimum Cell Size and Cell Size on Surfaces are described in the General Mesher.

Deform Zone Layers: This specifies the number of mesh layers between the valve and the valve end surfaces. It is the number of grid lines/cells ‘N’ between the valve and valve end surfaces. The number of grid lines/cells generated between the valve and valve end surfaces is usually (N-1), but may not be exact due to the complexity of spool valve mesh itself. Specify the value in terms of positive integer.

Deform Zone Coarsening Level: This is an integer value used to determine the level of mesh coarsening outside the "deforming zone", where the vale and the valve end surfaces will be in physical contact. This value can usually be kept as the default value 1 in the mesh generation process. With a value of N (N greater than 1), the mesh outside the deforming zone is usually coarsened for (N-1) levels following the binary tree mesh structure. The actual mesh coarsening may not be as exact as (N-1), due to the complexity of the valve mesh itself. Specify the value in terms of positive integer.

Once, the parameters of circumferential valve meshing are defined, click Build Circumferential Valve Mesh in the Geometry Tab of the Properties Panel. The mesh is created and added under the Built Meshes (circumferential valve) and Volumes (circumferential valve) in the Geometric Entities Panel. Also, Circumferential Valve module is added to the Model Panel. Creating mesh with template mesher automatically assigns the proper boundary conditions (Cylinder surfaces, Valve end, and Valve) in the process.