# Writing a CEL expression for y position at a specific timestep

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 March 27, 2019, 17:40 Writing a CEL expression for y position at a specific timestep #1 New Member   Nick Thomas Join Date: Sep 2018 Posts: 27 Rep Power: 5 I am creating a deforming mesh and my equation for the motion is dependent of the starting position of a surface. Is there a way in CEL that I can use this value (the y position of every point on a cylinder at t=0) in a transient simulation? In other words, the y position of the cylinder will be changing but I only want to use its original position as a constant in my expression.

 March 28, 2019, 03:57 #2 Senior Member   M Join Date: Dec 2017 Posts: 455 Rep Power: 9 It should be possible but I still got some understanding problems. Is this a rigid body motion or do you actually deform the cylinder? CFX gives you several options to perform mesh deformation. Lets say you want to displace the cylinder points by 1mm per timestep, you can use relative mesh displacement, which applies the deformation relative to the last timestep.

 March 28, 2019, 07:38 #3 Senior Member   Join Date: Jun 2009 Posts: 1,560 Rep Power: 28 The initial coordinates (Initial X, Initial Y, Initial Z) are available via CEL, say MyDispX= Initial X + ....

March 28, 2019, 13:48
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Nick Thomas
Join Date: Sep 2018
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Quote:
 Originally Posted by Opaque The initial coordinates (Initial X, Initial Y, Initial Z) are available via CEL, say MyDispX= Initial X + ....
Thanks, that does the trick!

However, I am trying to use the Y coordinates at every node on a surface so that displacement is unique to each node on the wall. The cylinder moves at a constant velocity and then is displaced back to the start, but I am hoping each bit of the wall will relocate once it reaches a certain point. In other words the cylinder wall will be split during the displacement process. Is this possible? Trying "Initial Y@Cylinder Walls" does not work.

 March 28, 2019, 14:08 #5 Senior Member   Join Date: Jun 2009 Posts: 1,560 Rep Power: 28 Not sure what you are trying to do. Recall expressions have local context, i.e. if you are evaluating MyDisp = Initial Y + 2 [cm] on the Cylinder Walls, I assume the expression is also used under Cylinder Walls where BOUNDARY: Cylinder Walls BOUNDARY CONDITIONS: MESH MOTION: Option = ... Displacement = MyDisp END END END There is no need to refer to the location, it is IMPLIED. Perhaps I need better context of what your goal is

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