integral over time

joseduartedasilva · April 1, 2011, 12:51

I wish to calculate a quantity which is the result of the value obtained by a expression, at the present time with the value of that expression in time earlier. How can I do this in CFX?

stumpy · April 1, 2011, 13:56

In general you need User Fortran to do that. There is a trick using Additional Variables that can make that work, but it's a hidden feature and won't work in all cases. Search this forum for "Update Loop = TRANS_LOOP" to find that info.

ghorrocks · April 3, 2011, 06:54

If it is a post-processing parameter you can write the input of the function as a monitor point, export the data and do the time integral somewhere else (excel, matlab etc).

joseduartedasilva · June 14, 2011, 13:13

stumpy,Thanks for your tip!

Using your suggestion I was able to calculate the integral over time for an expression that is a function of time. This integral represents the thermal damage caused to the biological tissue.

Now, I need to change the values of density, thermal conductivity and specific heat of cells whose thermal damage (integral over time) reached a certain value. Can I do this in function of thermal damage in ANSYS CFX-? How can I do this?
.

Thanks.
J.Duarte

stumpy · June 14, 2011, 14:07

You can make Thermal Conductivity and Cp a function of your Additional Variable - just enter expressions for them in your material properties. I assume this is a solid domain? If so, I don't think you can make Density variable (well, perhaps you can make it variable, but I'm not sure it will give the correct result). Perhaps you can change Cp instead of Density - if you only care about the thermal capacitance in the end, then adjust Cp to produce the same change in thermal capacitance as the change in density would have produced.

April 1, 2011, 12:51	integral over time	#1
joseduartedasilva New Member Duarte Join Date: Aug 2010 Location: Recife - Brasil Posts: 3 Rep Power: 15	I wish to calculate a quantity which is the result of the value obtained by a expression, at the present time with the value of that expression in time earlier. How can I do this in CFX?

June 14, 2011, 13:13	Integral over time	#4
joseduartedasilva New Member Duarte Join Date: Aug 2010 Location: Recife - Brasil Posts: 3 Rep Power: 15	stumpy,Thanks for your tip! Using your suggestion I was able to calculate the integral over time for an expression that is a function of time. This integral represents the thermal damage caused to the biological tissue. Now, I need to change the values of density, thermal conductivity and specific heat of cells whose thermal damage (integral over time) reached a certain value. Can I do this in function of thermal damage in ANSYS CFX-? How can I do this? . Thanks. J.Duarte Last edited by joseduartedasilva; June 14, 2011 at 13:29.

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April 1, 2011, 13:56		#2
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	In general you need User Fortran to do that. There is a trick using Additional Variables that can make that work, but it's a hidden feature and won't work in all cases. Search this forum for "Update Loop = TRANS_LOOP" to find that info.

April 3, 2011, 06:54		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,692 Rep Power: 143	If it is a post-processing parameter you can write the input of the function as a monitor point, export the data and do the time integral somewhere else (excel, matlab etc).

June 14, 2011, 14:07		#5
stumpy Senior Member Join Date: Apr 2009 Posts: 531 Rep Power: 21	You can make Thermal Conductivity and Cp a function of your Additional Variable - just enter expressions for them in your material properties. I assume this is a solid domain? If so, I don't think you can make Density variable (well, perhaps you can make it variable, but I'm not sure it will give the correct result). Perhaps you can change Cp instead of Density - if you only care about the thermal capacitance in the end, then adjust Cp to produce the same change in thermal capacitance as the change in density would have produced.