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Importing and Scaling the Geometry |
Chapter 2 SURFACE PREPARATION IN STAR-CCM+
The following tutorial data file is used in this chapter:
TRIMMING_TUTORIALS/Geometry.dbs
CAD geometry normally consists of many separate surfaces. Depending on the surface discretisation tool, vertex mismatches can occur between the various surfaces that prevent the discretised geometry surface from being closed. While an open geometry is acceptable for use with the es-ice Mapping method, the Trimming method requires a closed surface. When the engine volume is converted to a solid body within the CAD program, the separate surfaces making up the surface discretisation are closed and connected.
The following section provides a step-by-step guide for preparing a surface discretisation using STAR-CCM+ v8.02. Note that using earlier or later versions of STAR-CCM+ may require a different procedure.
Importing and Scaling the Geometry
Begin by importing and scaling the geometry in STAR-CCM+. In that environment, the default length unit is metres so the dimensions of the imported geometry are assumed to be in metres. In es-ice, there are no defined units so a dimension could be in metres, millimetres, etc. depending on the units you are working with. As the es-ice trimming tutorial assumes that dimensions are in millimetres, you need to scale the mesh by a factor of 1000.
•Launch STAR-CCM+ and start a new simulation
•From the menu bar, select File > Import > Import Surface Mesh...
•In the file browser, select Geometry.dbs
•In the Import Surface Options panel, accept the default options, as shown in Figure 2-1, and click OK to begin importing the geometry
Figure 2-1 Importing the CAD geometry
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•Right-click the Geometry > Parts > Geometry node and select Transform >
Scale
•In the Scale Parts panel, set Scale Factor to 1000
•Click Apply followed by Close
Creating Features
The next step is to define the geometry Features. These features are converted into line cells in es-ice, thus maintaining sharp edges and other points of interest when generating a volume mesh (similar to splines in previous versions of es-ice).
First, you use the Repair Features tools to define Features automatically based on a supplied Sharp edge angle criterion. Next, you manually add and remove selected Features. Generally, Features are required for the valve seats and liner top and bottom (if the Mark sharp edges operation did not capture them). It is also necessary to remove Features that were captured due to faceting but do not represent the real geometry.
To launch the Surface Repair tools and generate features at an angle of 20 degrees:
•Right-click the Geometry > Parts > Geometry node and select Repair
Surface...
•In the Surface Preparation Options panel, accept the default settings shown in Figure 2-2 and click OK to activate the Surface Repair tool
Figure 2-2 Surface Preparation options
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In the top left pull-down menu, change the Mode |
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to Repair Features |
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Click Mark Features by Angle (or press G on |
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the keyboard) |
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In the Mark Feature Edges Options dialog, set |
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Sharp edge angle to 20 |
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Clear the Mark boundary perimeters |
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checkbox and click OK |
In the following steps, you add extra Features to the surface geometry. Surface mesh edges are highlighted in pink when selected in the display. Double-clicking selects the edge and any other edge with similar face-normal angles. You can also use the <Ctrl> button to select multiple edges.
To add Features:
•In the Graphics window, existing Features are marked with thick black lines and the surface mesh is represented with thin lines
•The mesh display can be turned on or off depending on user preference. Click Mesh Toggle in the Vis toolbar and select Mesh Off
•Tick the checkbox next to Edges to select edges with the cursor (as opposed to Faces or
Vertices)
•Double-click one of the edges that is a Feature. For example, Figure 2-3 shows a close-up of the intake port meeting the cylinder head in which Feature 3 is selected. Further examples are shown on the next page
•Click Flag edges as feature (or press F on the keyboard) to mark the edges as
Features
•Repeat the previous steps to continue adding Features, as shown in Figures 2-3 to 2-7.
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Figure 2-3 Example of missing Features on the intake port
Figure 2-4 Example of Features on the rear side of the intake port
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Figure 2-5 Example of missing Features on the exhaust port
Figure 2-6 Example of missing Features on the spark plug
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