Old time step value to set boundary condition

- July 15, 2019 at 6:11 pm
  
  BiomedModeller
  Subscriber
  
  Dear all,
  I am trying to assign Windkessel model (RCR) to an outlet of an artery. To do this without Fortran routines, I require to access to the value of pressure in last time step. There is a workaround using "Probe" function and monitor points. However, it cannot be used to define an expression to set the boundary condition. Any hint how to solve this issue?
  Thanks
- July 16, 2019 at 5:04 am
  
  DrAmine
  Ansys Employee
  
  You can use workaround using arithmetic average over last two time steps with the probe expression. As ASC you can check that on the portal.
- July 16, 2019 at 1:56 pm
  
  BiomedModeller
  Subscriber
  
  Dear Amine,
  Thanks for the reply.
  I did do that and it worked well. The problem is CFX does not allow me to use it as an expression to define boundary condition. I want to use the value of old pressure in outlet BC definition and CFX says you cannot use probe in BC definition. What do you suggest?
- July 16, 2019 at 3:28 pm
  
  DrAmine
  Ansys Employee
  
  Try assigning that To algebraic variable. If it does not work let us know.
- July 16, 2019 at 5:55 pm
  
  BiomedModeller
  Subscriber
  
  We have done that as well. Gives the return code 1 error bellow:
  
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  |                  User Defined Monitor Information                  |
  
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  Monitor Point: MP current Q
  
                          Arithmetic Sum
  
  Monitor Point: MP current P
  
                          Arithmetic Sum
  
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  |                    Writing crash recovery file                     |
  
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     Details of error:-
  
  Error detected by routine MAKDAT
  
  CDANAM = LVAR CDTYPE = INTR ISIZE = 123
  
  CRESLT = OLD
  
  
  
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  |                An error has occurred in cfx5solve:                 |
  
  |                                                                    |
  
  | The ANSYS CFX solver exited with return code 1.   No results file |
  
  | has been created.                                                  |
  
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- July 16, 2019 at 5:56 pm
  BiomedModeller
  Subscriber
  The Ansys manual emphasizes for the probe that:
  
  Note: The probe function does not calculate a value for a statistic until the defined interval is complete. As a result, a “probe” function that retrieves a statistic from an expression-based monitor:
  - Should not be used in a CEL expression for a quantity that is required at all times, for example, a boundary condition.
- July 22, 2019 at 2:37 pm
  
  BiomedModeller
  Subscriber
  
  Any update please?
- July 23, 2019 at 10:51 am
  
  DrAmine
  Ansys Employee
  
  You can provide a good starting value for that variable if used all time.
  
  If still not helping you will need to use User Fortran.