MESHING WITH THE MAPPING METHOD	Chapter 20
Creating the Remaining Edges and Splines

Figure 20-36 Geometry window: Ten circular splines generated for both valve seat regions

Creating the Remaining Edges and Splines

Next, we need to add more edges and splines to control the surfaces of the intake port and cylinder head. We will first work with the template, where features that are good candidates for control purposes are more obvious.

Starting with Valve 2, the step-like stub can be seen to have several automatically-generated edges. Upon inspection, they are on mesh lines that divide horizontal and vertical template faces. There are also large angles between the cell faces on either side of the vertices belonging to those edges, making the latter an important feature. The edges belonging to the stub region of Valve 2 seem to be complete.

The intake port region of the template contains a few automatically-generated edges, around the port face and around the symmetry area across the siamese portion of the port. These edges represent features surrounding special boundary regions so they should be kept. We would like, however, to add a circular edge that wraps around the top of the valve chamber. This edge will eventually be used to separate the horizontal surface on the top of the valve chamber from the vertical surface on the side of the chamber.

•Click Create in the Edge section of the Edge or Spline Tool panel to create this extra edge, shown in Figure 20-38

Unlike splines, edges are defined strictly in terms of vertices that belong to existing

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cells. Therefore, the variety of pick modes available for splines does not exist for them. However, edges are created in chain mode by default, meaning that when two non-neighbouring vertices are selected, any intervening vertices will be automatically included in the edge. As a result, every vertex along an arc does not need to be picked to define the edge.

Because edges will be mapped to their corresponding splines starting from their first to their last points, the arrows which indicate the end of the spline or edge must be kept consistent in terms of their locations and directions, as shown in Figure 20-37.

Spline Edge

Cross-hair

Figure 20-37 Location and direction of arrows in the Geometry and Template windows

Figure 20-38 Template window: Arc-like edge on top corner of intake valve chamber

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Creating the Remaining Edges and Splines

Several edges need to be created to border the region where we have removed cells for the spark plug cut-out (see Figure 20-26). Zoom in on this region and observe that there is an edge that conforms to the shape of the template before cell removal. This edge can be easily fixed by using the “Split” function:

•Click Split in the Edge or Spline Tool panel

•Left-click the two edge knots at the ends of the spark plug cut-outs to split the edge into three edges. The middle one does not follow a mesh line and so it should be cleared with the Clear edge button.

Several other edges need to be defined along mesh lines that represent sharp features and large angles between adjacent template cell faces, as shown in Figure 20-39. While creating these edges, recall that edges cannot cross themselves or each other and that they must be joined end-to-end. It is usually helpful to keep similarly aligned edges along a consistent direction.

Figure 20-39 Template window: Edges at the spark plug cut-out

On both ends of the cylinder head, there are flat triangular regions. In “Creating the 2D Base Template”, we captured the intersection between the flat surface and the angled region of the cylinder dome with a mesh line in the template through the use of “Left/Right Triangles”. That mesh line is a feature that should have an edge on it, as shown in Figure 20-40. Remember again that edges can not intersect themselves or cross each other and that they must be joined end-to-end. Where those edges meet the automatically-generated edges at the cylinder wall and symmetry plane perimeters of the cylinder head, the “Split” function should be used so that edges are joined end-to-end. Conversely, a few of the automatically-generated edges at the cylinder radius can be joined with the “Join” function into one edge. By

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	default, es-ice splits edges at the cylinder radius at points where they are closest to
	each valve. These automatically-generated control points are normally useful, but
	the geometry of the tutorial example is simple enough to make them unnecessary.

Figure 20-40 Template window: Edges on cylinder head at the intake side

After all edges have been created, you can proceed to create the additional splines needed. The location, starting/ending knots, ID numbers and direction of the splines should be consistent with that of their corresponding edges. To aid with the ID numbering, you can manually renumber edges and splines using

1.the edge/spline,#,renumber,# command, or

2.the “Associate” button in the Edge or Spline Tool panel, or

3.the “Pick ID” function located on the left-side of the Edge or Spline Tool.

Activating the “Pick ID” button and clicking the “Create” button to create splines allows you to pick an existing edge and then create a spline with the same ID number as the edge. Note that the reverse is also true if the “Create” button for creating edges is clicked.

Figure 20-41 shows all the edges needed for this tutorial example.

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