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Old   September 3, 2009, 08:51
Default CFX cel problem
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rahmi
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Hi everybody,
Im working on transient heat transfer model and i need write an expression which calculates temperatures as a function of time, like an array data
T(1)+T(2) + ....
T(1) =temperature value at a time =1.
Any help very appreciated .
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Old   September 3, 2009, 18:19
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CEL cannot access historical data. This is the main failing of CEL expressions and I hope ANSYS puts something in someday to fix it.

Some options, none of which are very good:
1) Write the CEL variable into an additional variable which can then be read back in at the next timestep. This is VERY inefficient if you only want to pass a single number as this variable exists at all nodes so takes up lots of memory.
2) Use a fortran routine
3) If it is post-processing you can export the data as the simulation runs and do the processing in another package (matlab, excel, whatever)
4) for some functions (eg mesh motion) you can get the last timestep value by CEL expressions on the current timestep - for instance the value of the expression which positioned the mesh last timestep can be evaluated by working out the position of the mesh in the current timestep.
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Old   September 4, 2009, 02:16
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Thank you for your interest and reply. I have no idea and any docüments about writing a fortran subroutine for cfx. So do you have any advise for starting point.
Thanks in advance.
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Old   September 4, 2009, 02:20
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Arda Ersan
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Hello Mr. Uyar

You can use R12 version of CFX for transient graphs. This is a new feature. In CFD-Post R12 you can plot transient graphs.

In R11 most reliable situation is adding monitor point so you can see monitor graph in solver manager then export monitor data to excell etc.

Regards
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Old   September 4, 2009, 06:15
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Thank you for your reply cfdman. I want to write a function, the variables are Temperature and time. Like that f(T,t)=10^((T(t)-121.1)/10)
and i want to calculate f(T,1)+f(T,2)+f(T,3) .... I dont want to transfer the datas to excel. I just want to see the functions datas on the 3d view. So the best solution seems to me writing a fortran subroutine but i dont have clue for that.
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Old   September 4, 2009, 06:35
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Rahmi Bey,

İsminizden Türk olduğunuza kanaat getirdiğim için Türkçe cevap veriyorum.

12 versiyonu kullanıyorsanız zaman-sıcaklık grafiğini post-processing de çizdirebilirsiniz. Çizdirdiğiniz bu grafiğin noktalarının (f(1),f(2) gibi) koordinatlarını export edersiniz ve daha sonra bu verileri işleyerek (eğri uydurma vs gibi) istediğiniz fonsiyonları elde edebilirsiniz.

Eğer daha düşük versiyon kullanıyorsanız monitör point eklerseniz çözüm esnasında her timestep te o değerin değişikliği grafik üzerinde görebilirsiniz. Ayrıca .out file dan her timestep teki değerini okuyabilirsiniz. Daha sonra bunları gene aynı şekilde eğri uydurma ile denkleme dönüştürebilirsiniz.

Bence FORTRAN kullanmaya ihtiyaç yok. Yukarıdaki yöntemlerle de bu iş yapılabilir. Daha önce kullanmadıysanız tevsiye etmem meşakkatli bir opsiyon.

Umarım yardımcı olabilmişimdir.
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Old   September 4, 2009, 08:09
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Arda Bey ilginiz için çok teşekkür ederim .
Benim yapmak isteğimi bir de türkçe anlatayım pek iyi ifade edemedim ingilizce. Normalde ben siziin söyledikleriniz yapabiliyorum. Fakat benim yapmak istediğim tam olarak 3B olarak nasıl sıcaklık dağılımını görüyorsam, sıcaklık ve zamana bağlı olan bir fonskiyonun outputunu aynı şekilde görmek istiyorum. Bu fonksiyonda önceki timestepler için sıcaklık değerlerini toplamam gerekiyor. Diyelim ki 300 saniyedeyiz F(300)=T(1)+T(2)+.....T(300) gibi bir hesaplama yapmam gerekiyor. her bir timestep de daha önceki timesteplerin sıcaklık değerlerinin toplamı olan bir fonksiyon.
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Old   September 5, 2009, 16:42
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Hi Mr. Rahmi Uyar,

u will able to do this extracting (creating) the temperature [K] versus time [s] using a monitor point at ANSYS CFX Pre. Use a software as ORIGIN PRO 7.5, Microsoft Office Excel, SigmaPlot 9.0, to build this expression. If you use a constant timestep, (makes timestep [s] times step [-] to find the time [s] for each timestep[-] of your transient simulation) with the temperature, it´s just working on Excel after. In this site, u will find an example of point of monitoring and how to impose a heat flux experimental data: http://rapidshare.de/files/48289359/...oring.rar.html or http://rapidshare.com/files/27638726...oring.rar.html . It´s cool ! I´ve already did it!

we hold him in high regard,
Rogerio.


Quote:
Originally Posted by Rahmi Uyar View Post
Hi everybody,
Im working on transient heat transfer model and i need write an expression which calculates temperatures as a function of time, like an array data
T(1)+T(2) + ....
T(1) =temperature value at a time =1.
Any help very appreciated .

Last edited by rogbrito; September 6, 2009 at 09:13.
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Old   September 5, 2009, 16:45
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Rogerio Jack
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I beg your pardon?

Quote:
Originally Posted by Rahmi Uyar View Post
Arda Bey ilginiz için çok teşekkür ederim .
Benim yapmak isteğimi bir de türkçe anlatayım pek iyi ifade edemedim ingilizce. Normalde ben siziin söyledikleriniz yapabiliyorum. Fakat benim yapmak istediğim tam olarak 3B olarak nasıl sıcaklık dağılımını görüyorsam, sıcaklık ve zamana bağlı olan bir fonskiyonun outputunu aynı şekilde görmek istiyorum. Bu fonksiyonda önceki timestepler için sıcaklık değerlerini toplamam gerekiyor. Diyelim ki 300 saniyedeyiz F(300)=T(1)+T(2)+.....T(300) gibi bir hesaplama yapmam gerekiyor. her bir timestep de daha önceki timesteplerin sıcaklık değerlerinin toplamı olan bir fonksiyon.
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Old   September 5, 2009, 18:02
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Quote:
u will able to do this extracting (creating) the temperature [K] versus time [s] using a monitor point at ANSYS CFX Pre (10 up to 12 versions).
This has been supported in all versions of CFX from version 5.

Quote:
U must to use a constant timestep, (making timestep [s] times step [-] to find the time [s] for each timestep[-] of your transient simulation) with your temperature
All you have to do is include the current simulation time in the exported data and you can handle variable time steps as well. There is no limitation requiring constant time step.
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Old   September 7, 2009, 06:16
Default cfx subroutine
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Thank you all your interest and help again. I think i could not explain what i wanted to do exactly.
I have a function F(x)=INTEGRAL[10^(T(t)-121.1)/10)]dt and i want to integrate this function for all points in the 3d sample automatically through time.
I can monitor one point in post-processing and export the data to Excel and than i can calculate the integral using numerical methods, but I want the CFD to do this automatically for me. Because i need all the points data so that i can see the profile of the given function in the 3d shape like the temperature distribution.

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Old   September 7, 2009, 07:33
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OK, I see now. Firstly, you have not defined what your integral is over. Is it over the entire time history? You can program access to the entire time history in fortran but this is not a very good approach as storing the entire temperature field every time step will quickly fill your memory up.

Is the function such that for a given timestep, you can just increment a new amount on top of the value of the last timestep? If this approach is valid then you don't need a time history, you just need the last timestep. I think this can be done using an additional variable where the additional variable is a function of itself (this should return the value from the last timestep, but check this before using it) and add the additional components from the integral.
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