# Export Data Access Macross. Plot Second-Order Pressure.

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 May 11, 2017, 15:46 Export Data Access Macross. Plot Second-Order Pressure. #1 New Member   Brian Join Date: May 2017 Posts: 2 Rep Power: 0 Hello community! I'm new in Fluent and I want to know if what I'm trying to do is possible and if it is, how can I do it. I need to plot the Interstitial Fluid Pressure for a solid tumor surrounded by interstitial fluid being subjected to focused ultrasound waves (both high intensity and low intensity). I have an UDF for first-order parameters defined like this: DEFINE_SOURCE(msource,c,t,dS,eqn) { real source; source = (CSV * (VFP - C_P(c, t) - SIG * (PIV-PIF))) - (CSL * (C_P(c, t) - ILP)); dSn[eqn] = 0.0; return source; } (One for tumor tissue and another for normal tissue). C_P(c, t) stands for the data access macros that accesses the pressure in a cell designated by the pointer c contained in the cell thread designated by the pointer t. The variables CSV, CSL, VFP, SIG, PIV, PIF, ILP are all constant-valued parameters that may take on different values over different cell-threads. I need to calculate the second-order pressure for this problem, which is a function of C_P(c, t) and the fluid velocity as follows <> = a *<> + b *<> Being a and b constants, the first-order fluid velocity and the second-order pressure. My attempt to solve this, due to my lack of experience with Fluent is import the calculated values of C_P(c, t) and then write another UDF for the second-order pressure as above and finally import that UDF to solve for . Also I want the instantaneous values of over stationary surfaces, not just the mean-valued terms. Is this possible? Is there another way to do something like this? I'm looking forward to your answers! Thank you very much for your time. My best regards! Brian.

May 13, 2017, 12:35
#2
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Lucky
Join Date: Apr 2011
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This could even be done with a custom-field-function instead of a UDF route, but custom-field-functions can't be run in parallel unless you have the latest v18.

Quote:
 Originally Posted by BrianGrass My attempt to solve this, due to my lack of experience with Fluent is import the calculated values of C_P(c, t) and then write another UDF for the second-order pressure as above and finally import that UDF to solve for .
This is basic programming / computer science here. Either you have a separate routine to calculate C_P(c,t) or you duplicate that routine into the P_2. The choice is your's and either can work. But if you calculate them separately you need to have UDM assigned for both, which isn't a big deal anyway.

When you are in a steady solver x-velocity is the mean velocity. When you are in a transient solver x-velocity is the instantaneous velocity and the mean variables have a new name.

 May 13, 2017, 15:15 #3 New Member   Brian Join Date: May 2017 Posts: 2 Rep Power: 0 Thank you very much! Do you know of any tutorial that explain how to do that?

 Tags data access macross, fluent, second-order pressure