Time Averaged Shear Stress

wanna88 · May 17, 2012, 03:56

Hi Lance,

"Say that you have calculated TAWSS in excel/matlab and know the value at each coordinate. Then, in CFD-post goto file/export and export any variable (say e.g. velocity) at the wall of interest. Check "line and face connectivity" and you'll get a file with coordinates and the variable + face connectivity.
Now, simply replace the variable you exported with your calculated values of TAWSS, and then import the file as a user surface.
Nope, whatever you name your variable to in the .csv-file will show up in the variables list in post.
No need for CFX-pre at all. "

Based on the above, I have calculated the TAWSS in excel. Then, in the CFD post, I load results of my fluent at 1 time point. Then, in the CFD post, I go to the file/export and export wall shear at the wall part. I also check line and face connectivity.
Then, I replaced the value of wall shear stress into TAWSS and then import back the file as a user surface.
then the variable in the csv file show up in the variable list in post. When I checked the imported file, seems nothing happen.

Is there any mistake in my steps?

Thank you.

Regards,
Naimah

Lance · May 21, 2012, 03:45

If the variable shows up in the list it should work. Could you give an example on the data you import to post?

wanna88 · May 21, 2012, 04:40

Hi Lance,

I have imported the data in .csv file. there is X, Y, Z and wall shear stress value. There are 2 cases in .csv file. I changed the values of WSS to the TAWSS.
Actually in my CFD post there are 2 cases in which is cases 4.20 at 5 s and cases 4.20 at 4.20 s.
I only want to look at case 4.20 at 4.20 s.
However in the excel, this two cases are together.

When I imported into CFD post, the 2 cases separated.

Is there anything wrong?

Thank you.

Regards,
Naimah

Lance · May 21, 2012, 05:08

I havent tried two cases at the same time, so I dont know if that works. Try to remove the case you dont need.
Also, I wouldnt use spaces in the variable names.

wanna88 · May 21, 2012, 05:29

"Also, I wouldnt use spaces in the variable names"

Sorry, which spaces did you refered?
I don get it.

Lance · May 21, 2012, 05:32

The variable name seems to be "wall part_1 in Case FFF 1 00420"

wanna88 · June 11, 2012, 02:19

Hi Lance,

I m not successful plotting time average wall shear stress in the CFD post.
Herewith I attached the steps taken.
Can you help me to look into it?

Thank you.

Regards,
Naimah

Rupali · March 31, 2020, 04:26

I am simulating an unsteady blood flow and I need to plot contour of Time Averaged Wall Shear Stress (TAWSS) and Oscillatory Shear Index (OSI) at different time steps of the cardiac cycle. Is there any procedure to do that CFD-post. Please suggest me an apt solution for the same.

ghorrocks · March 31, 2020, 06:42

Have a look at the capabilities of CFD-Post, it can do quite powerful post processing.

If you define exactly what you want to see then we might help you. (Wall shear stress of what? A point on a wall? Averaged over a wall surface? And define Oscillatory Shear Index)

Rupali · March 31, 2020, 07:39

I want to calculate the values and plot the contours of TAWSS, OSI and RRT at different time steps of the entire transient cycle on the three-dimensional arterial wall. Suggest some way to plot these variables in either CFD post or in tecplot.

ghorrocks · March 31, 2020, 08:02

Please don't use jargon - you will need to define what Time Averaged Wall Shear Stress, Oscillatory Shear Index and RRT are. These terms are not general CFD terms so I don't know what their definitions are.

If you want to post an image here is the FAQ on it: https://www.cfd-online.com/Wiki/Ansy...n_the_forum.3F

But don't forget the basics. Have you done the CFD-Post tutorials? They are available on the ANSYS Customer website and ANSYS Academic sites. These tutorials teach you the basics.

Rupali · April 6, 2020, 07:21

How to define the new time-varying functions and further plot their contours in CFD post. Please suggest a suitable way.

ghorrocks · April 6, 2020, 07:28

Thanks.

TAWSS needs to be calculated as a transient statistic as the simulation runs. It cannot be done post-processing. So have a look at transient statistics in the output tab in CFX-Pre.

OSI is a similar equation to TAWSS and will require a transient statistic.

RRT is a simple function of TAWSS and OSI and can be done either as the simulation runs or in post-processing. This would be just a simple CEL expression - have a look in the CFX tutorials for examples of CEL expressions.

Rupali · April 6, 2020, 07:37

I am Fluent solver. Also, defining an expression for TAWSS and OSI in fluent after the simulation for post processing will be a correct method?

ghorrocks · April 6, 2020, 08:28

I cannot help you with calculating these equations in the Solver for Fluent. Try the Fluent forum for that.

Theoretically you can evaluate those equations in post processing providing you have saved transient results files at high enough time resolution. I am assuming you have not saved these files, which means you will need to do it in the solver.

March 31, 2020, 04:26	Plot contours of Time Average Wall Shear Stress and Oscillatory Shear Index	#28
Rupali New Member Rupali Join Date: Oct 2019 Posts: 14 Rep Power: 7	I am simulating an unsteady blood flow and I need to plot contour of Time Averaged Wall Shear Stress (TAWSS) and Oscillatory Shear Index (OSI) at different time steps of the cardiac cycle. Is there any procedure to do that CFD-post. Please suggest me an apt solution for the same.

March 31, 2020, 06:42		#29
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Have a look at the capabilities of CFD-Post, it can do quite powerful post processing. If you define exactly what you want to see then we might help you. (Wall shear stress of what? A point on a wall? Averaged over a wall surface? And define Oscillatory Shear Index) __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 31, 2020, 07:39		#30
Rupali New Member Rupali Join Date: Oct 2019 Posts: 14 Rep Power: 7	I want to calculate the values and plot the contours of TAWSS, OSI and RRT at different time steps of the entire transient cycle on the three-dimensional arterial wall. Suggest some way to plot these variables in either CFD post or in tecplot. Last edited by Rupali; March 31, 2020 at 07:41. Reason: Images are not displayed

March 31, 2020, 08:02		#31
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Please don't use jargon - you will need to define what Time Averaged Wall Shear Stress, Oscillatory Shear Index and RRT are. These terms are not general CFD terms so I don't know what their definitions are. If you want to post an image here is the FAQ on it: https://www.cfd-online.com/Wiki/Ansy...n_the_forum.3F But don't forget the basics. Have you done the CFD-Post tutorials? They are available on the ANSYS Customer website and ANSYS Academic sites. These tutorials teach you the basics. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

April 6, 2020, 07:28		#33
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Thanks. TAWSS needs to be calculated as a transient statistic as the simulation runs. It cannot be done post-processing. So have a look at transient statistics in the output tab in CFX-Pre. OSI is a similar equation to TAWSS and will require a transient statistic. RRT is a simple function of TAWSS and OSI and can be done either as the simulation runs or in post-processing. This would be just a simple CEL expression - have a look in the CFX tutorials for examples of CEL expressions. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

May 17, 2012, 03:56		#21
wanna88 Member Naimah Join Date: Nov 2011 Posts: 58 Rep Power: 15	Hi Lance, "Say that you have calculated TAWSS in excel/matlab and know the value at each coordinate. Then, in CFD-post goto file/export and export any variable (say e.g. velocity) at the wall of interest. Check "line and face connectivity" and you'll get a file with coordinates and the variable + face connectivity. Now, simply replace the variable you exported with your calculated values of TAWSS, and then import the file as a user surface. Nope, whatever you name your variable to in the .csv-file will show up in the variables list in post. No need for CFX-pre at all. " Based on the above, I have calculated the TAWSS in excel. Then, in the CFD post, I load results of my fluent at 1 time point. Then, in the CFD post, I go to the file/export and export wall shear at the wall part. I also check line and face connectivity. Then, I replaced the value of wall shear stress into TAWSS and then import back the file as a user surface. then the variable in the csv file show up in the variable list in post. When I checked the imported file, seems nothing happen. Is there any mistake in my steps? Thank you. Regards, Naimah

May 21, 2012, 03:45		#22
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	If the variable shows up in the list it should work. Could you give an example on the data you import to post?

May 21, 2012, 05:08		#24
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	I havent tried two cases at the same time, so I dont know if that works. Try to remove the case you dont need. Also, I wouldnt use spaces in the variable names.

May 21, 2012, 05:29		#25
wanna88 Member Naimah Join Date: Nov 2011 Posts: 58 Rep Power: 15	"Also, I wouldnt use spaces in the variable names" Sorry, which spaces did you refered? I don get it.

May 21, 2012, 05:32		#26
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	The variable name seems to be "wall part_1 in Case FFF 1 00420"

April 6, 2020, 07:37		#34
Rupali New Member Rupali Join Date: Oct 2019 Posts: 14 Rep Power: 7	I am Fluent solver. Also, defining an expression for TAWSS and OSI in fluent after the simulation for post processing will be a correct method?

April 6, 2020, 08:28		#35
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	I cannot help you with calculating these equations in the Solver for Fluent. Try the Fluent forum for that. Theoretically you can evaluate those equations in post processing providing you have saved transient results files at high enough time resolution. I am assuming you have not saved these files, which means you will need to do it in the solver. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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