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Old   February 18, 2009, 09:24
Default Time derivative
  #1
Dmitry
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Hi. I want to calculate dp/dt (static pressure time-derivative) in my transient calculation and store it. Is it possible to access to pressure value at previous time step in UDF?
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Old   February 18, 2009, 10:27
Default Re: Time derivative
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Grzegorz
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Yes, it is possible. You can use C_P_M1(c,t) or C_P_M2(c,t) for previous and second previous time step, respectively (see User's Guide - 3.2.3 Cell Macros). You can also use memory storage C_UDMI to save current pressure field and in next time step acces to it and refill it with new values. Hope this help.
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Old   February 19, 2009, 14:48
Default Re: Time derivative
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Dmitry
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Thank you. But the problem stil remains. I use C_UDMI to save previous time step pressure: C_UDMI(c,t,0)=C_P_M1(c,t) in my UDF in DEFINE_ADJUST macros. I get error message: FLUENT received fatal signal (ACCESS_VIOLATION) after first iteration.
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Old   February 19, 2009, 14:50
Default Re: Time derivative
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Grzegorz
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Did your solution is calculated or did you start it from very begining?
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Old   February 19, 2009, 15:09
Default Re: Time derivative
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Dmitry
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Yes, my solution calculated some time steps. Firstly I did 5 time steps without using of C_P_M1, then I put it in my UDF, reinterpreted it and tried to run calculation. But I have error.
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Old   February 19, 2009, 15:17
Default Re: Time derivative
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Grzegorz
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Send me your udf - kondora@imc.pcz.czest.pl
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Old   February 20, 2009, 08:54
Default Re: Time derivative
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mange
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did you remember to allow memory access for your C_UDMI ?

/m
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Old   February 20, 2009, 10:27
Default Re: Time derivative
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Dmitry
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What does it mean /m? I use other C_UDMI(c,t,1), C_UDMI(c,t,2) and so on to store my variables and I have no problems to access them.
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Old   February 20, 2009, 10:33
Default Re: Time derivative
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mange
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I mean in the panel of user memory you have to specify how many fields you want to allocate memory for. by default it is 0.
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