# problem in using of additional variable in wall velocity

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 July 13, 2012, 10:09 problem in using of additional variable in wall velocity #1 New Member   adsl Join Date: Jun 2012 Posts: 4 Rep Power: 5 Hi,everyone！ I try to use of additional variable (velo_x) in wall velocity, but i meet this solving error message: Error processing expression 'global frame vector associated with Wall U'. The expression is invalid because: velo is not available for use in this term Error processing expression(s): Wall U = velo_x Wall V = 0 [m s^-1] Wall W = 0 [m s^-1] +--------------------------------------------------------------------+ | An error has occurred in cfx5solve: | | | | C:\Program Files\ANSYS Inc\v140\CFX\bin\winnt-amd64\ccl2flow.exe | | was interrupted by signal QUIT (3) | +--------------------------------------------------------------------+ This run of the ANSYS CFX Solver has finished. How can i solve this error?

 July 13, 2012, 10:12 #2 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,098 Rep Power: 19 what is the expression for "velo_x"? or is it just a constant value?

 July 13, 2012, 10:17 #3 New Member   adsl Join Date: Jun 2012 Posts: 4 Rep Power: 5 hi, velo_x = ctstep [m s^-1]

 July 13, 2012, 10:24 #4 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,098 Rep Power: 19 ctstep is the current time step, am I right? So you want to ramp the wall velocity. Not all variables can be used for solver input in cfx. Try the same referencing to the flow-time.

 July 13, 2012, 10:48 #5 New Member   adsl Join Date: Jun 2012 Posts: 4 Rep Power: 5 thanks, when i use expression in the wall velocity, not exist this error. i want to define wall velocity with additional variable, how solve this problem? how can i convert the value in additional variable to expression or constant value for use the wall velocity?

 July 13, 2012, 10:56 #6 Senior Member     Alex Join Date: Jun 2012 Location: Germany Posts: 1,098 Rep Power: 19 I don't know. But if the wall velocity works when you apply an expression to it, why don't you do it this way?

 July 13, 2012, 11:24 #7 New Member   adsl Join Date: Jun 2012 Posts: 4 Rep Power: 5 I use of additional variable for save value in last iteration with “Update Loop = TRANS_LOOP”, and then i use this value in new iteration. So i am forced using of additional variable.

 May 30, 2015, 11:59 #8 New Member   Diego Jaimes Join Date: Feb 2015 Posts: 6 Rep Power: 2 Hi, I just have the same problem that you had it years ago. Did you solve it?. Please if you could help me, let me know. I really will appreciate. jaimesdiegop@hotmail.com. Thanks for your time.

 May 30, 2015, 21:24 #9 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,823 Rep Power: 85 Please describe what you are trying to do Diego and we will try to help.

 May 31, 2015, 12:41 #10 New Member   Diego Jaimes Join Date: Feb 2015 Posts: 6 Rep Power: 2 Hi ghorrocks, I'm working with a tool wich is immerse in a fluid, and I want to set my wall velocity in function of the Drag Force of the tool. So I need to set my wall velocity in function of my last time step solution. I know how to do it in two ways: one is trying to set in my Wall Velocity an Additional Variable (but CFX does not let me do it), and the other one is if I can catch in a Expression the "hybrid" values of a location (but if I set for examples "areaAve(variable)@location", I only got the conservative values). Please if you know how to set an Additional variable in the wall velocity, or if you know how to get the "hybrid" values in some expression, please let me know. PS: When I'm trying to get the "hybrid" values, Im trying to set it up on my PRE, not in my POST with the "hybrid" buttom. Thank you very much for your help.

 May 31, 2015, 19:29 #11 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 10,823 Rep Power: 85 Before we think about how to implement it, can you explain why you want to do this? Why is the wall velocity a function of the drag force? Can you show an image of what you are doing.

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