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# Moving Clip Planes

Creating Clip Planes that Moving relative to the Geometry.

In the context of an InCylinder model, it is often useful to have a clip through the cylinder which moves with the piston motion. In the simplest form, you want a clip which is half way between the top of the combustion dome and the piston surface. You can then maintain at a position relative to the top and bottom (eg 25%, or 50% of cylinder height). A similar operation can be done to maintain a fixed distance from some moving reference geometry. (eg 5 mm above piston at all times).

An example below illustrates a clip which maintains itself at 1/2 cylinder height throughout the cycle. It is in essence at a location half way between the piston and combustion dome.

Single Moving Clip Relative to Cylinder Height

You can easily create additional clips at different locations (instead of 50%, create multiple clips at 20%, 40%, 60%, 80% of cylinder height using the same method):

Multiple Moving Clip Planes Relative to Cylinder Height

Using a very similar approach, you can maintain a fixed distance (instead of relative to cylinder height as shown above). In this method, you use a single reference geometry, and specify that the clip is at some fixed distance relative to the reference moving geometry:

Clip Planes offset at fixed distance from moving object

So, how would you go about creating such clip planes in EnSight? The method below is applicable for any flavor of EnSight (FREE, EDC, Desktop, Standard, etc). The method actually uses the fact that a clip plane can be considered an IsoSurface of a Coordinate location.

For the creation of Clips relative to Cylinder Height (as a % of Cylinder Height):

• Step 1: Select the Fluid parent corresponding to the cylinder
• Step 2: Calculate the component in the cylinder movement direction (this case Z):

CoordZ = Coordinates[Z]

• Step 3: Calculate a Min and Max value of CoordZ:

MinZ = Min(plist,CoordZ)
MaxZ = Max(plist,CoordZ)

• Step 4: Calculate a new Normalized Z coordinate :

Normalized_Z = (CoordZ – MinZ)/(MaxZ-MinZ)

• Step 5: Create an isosurface of Normalized_Z. A value of 0.5 will always remain ½ way between top and bottom of fluid domain. Multiple isosurfaces with initial value of 0.2, 4 values, with offset = 0.2 will yield 4 surfaces at 20%, 40%, 60%, 80% of cylinder volume height.

For the creation of Clips Offset from the Piston (fixed location relative to reference):

• Step 1: Select the Fluid parent corresponding to the cylinder
• Step 2: Calculate the component in the cylinder movement direction (this case Z):

CoordZ = Coordinates[Z]

• Step 3: Selecting just the Piston, calculate a Max value of CoordZ:

MaxZ_cylinder = Max(plist,CoordZ)

• Step 4: Calculate a new Relative Z coordinate :

Relative_Z = (CoordZ – MaxZ)

• Step 5: Create an isosurface of Relative_Z. This can be specified in model units (for example in this model, a value of 5e-3 will be 5 mm above piston