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Creating Patches

Figure 20-41 Template window: Edge display

One important edge/spline pair that should be explained in more detail is the pair that extends for most of the cylinder radius. In the template, this edge helps to divide the horizontal cell faces of the top of the cylinder head from the vertical cell faces of the cylinder wall. With this in mind, the corresponding spline needs to be created in the geometry.

The strategy here is to create a spline that will approximately divide the geometry’s horizontal surfaces from the vertical surfaces. Across a filleted curve, an appropriate transition line should be used such that a balance is maintained between horizontal and vertical template faces that will eventually map to various sections of the curved surface.

Creating Patches

We have not yet performed any mapping, but we have laid the groundwork for mapping all vertices contained in the edges we have defined. The latter bound surfaces in the template that should be mapped to corresponding shell surfaces. Just as we assigned vertices along feature lines to edges (so that they could be mapped to splines), we must also assign vertices on the surfaces of the template between the edges to patches so that they can be mapped to the surface shells of the geometry.

Patches are only created for the port, stub and cylinder dome surfaces. This is done almost with one mouse click, using the edges already created. The first step is to gather only the two edges located at the top of the valve stems being modelled in the template, as shown in Figure 20-42. As will be seen later, having these two edges in the currently active edge set will prevent the automatic patch generation process from creating unwanted patches along the valve.

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Collect these edges

in the Eset, and create patches

using the Patch Tool

Figure 20-42 Template window: Two essential edges and final patches

•Click Patch in the Select panel to open the Patch or Vshell Tool panel

•Set the patch Type option to Shell since we intend to have all our patches projected to geometry shells

•Click Auto Bound

•Click on any cell face except those that represent the valve stem

The picked cell face acts as a seed face and patches are created by growing the patched area outwards until it hits an edge in the currently active edge set. Thus, the entire region is patched. The ID number and size of the patches that are formed depend on the space between the created edges, not just those in the currently active edge set. All patches created are automatically put into the currently active patch set.

•Click Patch in the Plot Tool to replot and display patches in the currently active patch set and produce a legend for them

Notice that there is one patch on the symmetry plane and cylinder wall. This should be cleared since the symmetry plane and cylinder wall are special regions that are recognised by es-ice and dealt with automatically.

•Click Clear in the Patch or Vshell Tool

•Left-click any face in the template representing the symmetry plane or cylinder wall

•Type q or click on a blank part of the Template window to quit

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The Mapping Process

The Mapping Process

The mapping process involves vertices that are included in the edges and patches. These vertices are also surface vertices of the template. Other surface vertices on the symmetry plane and cylinder wall, as well as most interior vertices of the template, will be moved at a later stage. It is therefore possible that some of the mapped vertices will push into those that are not mapped and result in confusing plots in which the mapped surfaces can not be clearly seen. es-ice has a facility for isolating cell faces associated with surface mapping so that this confusion is eliminated. To invoke it, type the following command:

cmark

You will be reminded that your currently active cell set will be changed, so answer yes. This will invoke a series of commands that will build a new, currently active cell set and plot only the faces of cells belonging to patches in the currently active patch set. To improve visualization, the Edge and Patch buttons should be turned off in the Plot Tool panel. The resulting plot in Figure 20-43 shows only those faces of the template that are to be mapped.

Figure 20-43 Template window: Result of the cmark command

The currently active cell set of the geometry should also be modified to have only shells associated with the cmark result on the template, so as to serve as a target for the mapping process. This will be the geometry shells for the cylinder head, intake port and exhaust stub only, as shown in Figure 20-44.

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Figure 20-44 Geometry window: Target geometry shells for mapping

•Click Mapping in the Select panel to open

the Map Tool panel

This panel is divided into three sections. We will proceed through the buttons and steps of each section from top to bottom, starting with the edges:

•In the Edge section at the top of the panel, set the pull-down menu option to All

•Click Map edges

This will map all edges previously created to their appropriate splines. Replot the window, as shown in Figure 20-45, to see the effect of this stage of mapping.

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Figure 20-45 Template window: Result of mapping all edges

You will next work with the surface:

•In the Surface section, set the pull-down menu option to All and keep the default settings of the next two pull-down menus (Map and Full elliptic)

•Change the last pull-down menu option to Target Cset

•Click Map patches to map all the patches, as shown in Figure 20-46

Figure 20-46 Template window: Result of mapping all patches

•Click Project patches to project the patches to the shells in the current geometry cell set and perform surface smoothing on the vertices of the patches using the Full elliptic smoothing method, as shown in Figure 20-47.

By isolating the geometry shells that are the target of the mapping and projection operations, es-ice will not be confused by extraneous geometry surfaces and tolerance issues. The window will automatically be re-plotted after each patch is projected and smoothed. Note that some patches were neither mapped nor projected as indicated in the es-ice output window. This is because those patches are small and do not contain vertices that are not already defined through edges. In other words,

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	all vertices in those patches that did not get mapped nor projected are already
	included in edges that were already mapped.

Figure 20-47 Template window: Final mapped and projected result

At this point, the mapped template should be visually checked. You should zoom in to several areas from a variety of perspectives to ensure that no faces are badly distorted or skewed. Areas of particular concern are the regions of closest approach between the valve seat and the cylinder circumference. Also, any corners that might exist on the valve chambers and arms should be carefully inspected.

The Project patches process is an iterative process, so repeated projections can result in successive improvements of the surface mesh. Also, a different surface smoothing method could be used with this process. The most common alternative to the default Full elliptic method is the Elliptic method. For more complex modifications, splines can be redefined, edges re-mapped and patches redefined and re-projected on an individual basis. The spacing of edges and patches can also be changed individually. The default spacing for both edges and patches is Original, but sometimes the Linear option can be used to improve the surface mapping result.

The valve surface is next and to see the effect of this mapping, look at a section plot through the valves:

•Turn off the effects of the cmark operation by deselecting the Marked option in the Plot Tool panel

•To inspect the cell set to be used for the CFD calculation, select Sets > Cset > Recall > 1 Active cells from the pull-down menus (equivalent to command cset,recall,1)

•Turn off the Fill option in the Plot Tool panel to improve visualization

•Click Map valves to map the top of the valve surface

•Replot the window and zoom in to see the effect of this mapping, shown in Figure 20-49

Note that if the Map corners button is toggled On, it will ensure that the corner vertices of the rectangular grid (edge nos. 1 and 2 in Figure 20-48) are mapped to point ‘p10’ (which was used to create the valve image, see Figure 5-13 on page 5-11 of the User Guide). If this toggle is not turned on, edge nos. 1 and 2 are mapped to spline nos. 1 and 2, which are created automatically at point ‘p10’. So, if you are not

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satisfied with the placement of point ‘p10’, you may move the spline (up or down) and re-map edge nos. 1 and 2.

Figure 20-48 Automatically generated spline nos. 1 and 2 and edge nos. 1 and 2

Figure 20-49 Template window: Result after “Map Valves”

We will finally work on the mesh interior. We only wish to map the interior vertices of the static part of the mesh since the moving vertices will be handled during the CFD analysis run. The template’s current cell set needs to be changed so that it covers only the non-moving section, composed of cells located above the valves.

•Click Gather cells to perform this operation automatically

•Plot the result, shown in Figure 20-50. Notice that only the intake port and exhaust stub are in the template’s currently active cell set.

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Figure 20-50 Template window: Result after “Gather Cells”

•Keep the defaults of all pop-up menus in this section as Elliptic, Original spacing and Negative volume

•Click Map interior to map the interior vertices of the currently active cell set on the screen

•Click Smooth interior to perform volume smoothing on those vertices using the elliptic method and trying to maintain the original vertex spacing

As with the Project patches process, the Smooth interior process is an iterative process so repeated smoothings can result in successive improvements:

•Click Smooth interior again to perform another iteration of the volume smoothing

•Replot the window to see the effect of this mapping, shown in Figure 20-51

Figure 20-51 Template window: Result after “Map Interior” and “Smooth Interior”

•Finally, click Check cells to check the currently active cell set for negative volumes

Since the currently active cell set contains cells that are static and will not move, if no negative volumes are currently present among these cells, we can be confident that none will be present in this region during the CFD analysis.

•You can now recall the active cells using command cset,recall,1

to display the template shown in Figure 20-52.

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Recall that only surface vertices contained in patches and internal vertices of the mesh’s static region have been moved. Since there are vertices that have not been moved yet, the mesh may look distorted in some places but this can be ignored at this stage.

Figure 20-52 Template window: 3D template after mapping

es-ice assumes that template surface vertices of the cylinder wall will be located at the cylinder radius. With the spline that was previously created, it is necessary for some template vertices on this wall to be projected to geometry shells that have a smaller radius than the cylinder. Geometry Cset 1 is labelled Cylinder shells and is reserved for shells that are not at the cylinder radius and to which template vertices of the cylinder wall will be mapped. These shells provide a surface to which the corresponding template surface of the cylinder wall, composed of vertical faces, can be projected.

•Isolate the geometry shells for the cylinder dome and notice that the lower boundary has vertices on the cylinder radius and at the z = 0 location.

•Using a combination of zone (cset,dele,zone) and cursor delete (cset,delete,cursor) operations, remove cells above the previously created spline. This operation can be performed in a somewhat approximate fashion since we need to include all necessary shells below the spline but can tolerate some extra shells above it, as shown in Figure 20-53.

•Once this is done, the currently active cell set needs to be saved in Geometry Cset 1 by clicking update cset 1 in the training panel.

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Figure 20-53 Geometry window: Shells placed into Geometry Cset 1

The user is recommended to save the work up to this point by saving the current working session into a new save_es-ice file. The work up to this point is also saved in file save_es-ice.3-flat of the tutorial example files.

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To generate files required by pro-STAR and STAR:

•Click Star Setup in the Select panel to open the Star Setup panel

•Make sure that the Reset smoothers, Use unwarper and Use Star controls toggle buttons are selected.

•Select Prostar 4.16 from the Prostar pull-down menu

•Click Star setup to save the geometry changes and create the files needed to set up the model for STAR-CD.

One can also enter es-ice command line options in the Extra Parameters box. To search for command line options, click on the List button above the box. In the new window that opens, type the text to search for in the Search box and then click Enter. The options must be separated by a space, or can be on a new line.

The work up to this point is saved in file save_es-ice.4-starsetup of the tutorial example files.

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