scalar field only on one part of a surface

Edward1 · June 8, 2016, 07:05

Good morning/evening everyone,

I'm using a file created by someone else with several channels linked together (that is more or less a "double-T" entrance with a main channel after). The whole model consists in 2 surfaces : "top and bottom" and "sides".
I would like to compute wall shear stress (or any other values) only on one piece of these geometries. It means that I'm trying to split/cut "top and bottom" in 2 parts (or two derived parts, I don't care) that will have to be "stick" to the real walls "top and bottom". (I don't want the entrance, just the wall shear stress in the main channel).
I've already been able to split in into "top" and "bottom" but not more.

Have you any idea to solve this issue?

I hope that it is clear enough,
many thanks in advance

Edward

PS : please apologize my bad English.

kirrer · June 8, 2016, 08:37

You can use derived parts as you indicate to do this. Note that you can also use a derived part as the input to another derived part. For instance, if you use thresholds to split "channel" into "top" and "bottom" based on Position in z axis, then you can split "top" into "top front" and "top back" based on Position in x axis. Each subsequent derived part will still refer to the cells or faces of the original mesh, regardless of whether it's based on the original mesh or a derived part thereof.

I hope I understood your question - but, I could also be missing it. If this is not clear, or the answer you are looking for, can you provide more information - such as a screenshot of the geometry and how you want to further divide it?

Edward1 · June 8, 2016, 09:03

thanks for that answer. Actually you've perfectly understood my question. I didn’t know that we can specify a position along x-axis to split a surface. Could you tell me more precisely how to do it, using constrained plane?
It is probably easy, but so far I've just got a line instead of a plane when I tried to define my sub-surface.

kirrer · June 8, 2016, 11:37

My advice is first to create a scalar scene, and on that scene plot the scalar you want to use to split (for example, position in x axis). Find the value where you want to make your division - you can get this from the color of the scalar, or press the period key (.) when your mouse cursor hovers over the location - this will report the scalar value in the output window. Then, create a threshold part (derived part). You can see full directions in the manual, but essentially select the part which is the base of the derived part (like your "top" mentioned above), then select the field function used to create a threshold (like Position in x axis), then select the condition used for the threshold (position in x below 0.05 m, above 0.1m, between 0.05 and 0.1m, etc). Click create, add a geometry displayer to visualize it if you like, and then you can use that new derived part the same way you would have used a boundary in the past (for example, make a Surface Average report of Wall Shear Stress).

Note that you do not use a constrained plane with this method - much easier to use thresholds. I'm not even sure if you could do it with constrained planes, except for splitting the original geometry and recreating the mesh (using the surface repair tool).

Hope that helps!

Edward1 · June 10, 2016, 06:39

Hi kirrer,

Thanks for your help. That exactly what I was looking for. I took me a couple of hours to get results different to 0 but now it seems to be ok

munibadshah · January 18, 2019, 15:25

How to divide a plane (Scene I have generated in Star_CCM+) into multiple equal halves as shown in the picture. I want to get the weighted area average of field function in each area separately. Thank you

bluebase · January 28, 2019, 08:46

Hi Moon,

i don't know if there is an elegant way.
The following method is somewhat laborous.

Create a new threshold in derived parts. Select your domain of interest as parts input (this would likely be a plane section). Use one axis of the Field Function "Position" as scalar field input. Set the range of the respective column/row.
Then, create another new threshold. Select the previous threshold as parts input. Use another axis of "Position" as scalar field input. Select a suitable range again.

Repeat these steps until you end up with a thresholds which filtered out everything but the respective cell in the desired grid.

These derived parts could then be taken as input for reports.

Please Check continuity over those 16 threshold cells. The above method does not guarantee that all cells are included.

Best regards,
Sebastian

munibadshah · February 12, 2019, 23:25

Thank you Sebastian. Actually I did in the same way But now I want to create surface average of a circular area at the center of each square section as we calculate properties by using probe. I want to have the same size surface area say 30 gage wire (0.01in). Do you have any idea to do it quickly. Thank you

June 8, 2016, 07:05	scalar field only on one part of a surface	#1
Edward1 New Member Join Date: Jun 2016 Posts: 11 Rep Power: 9	Good morning/evening everyone, I'm using a file created by someone else with several channels linked together (that is more or less a "double-T" entrance with a main channel after). The whole model consists in 2 surfaces : "top and bottom" and "sides". I would like to compute wall shear stress (or any other values) only on one piece of these geometries. It means that I'm trying to split/cut "top and bottom" in 2 parts (or two derived parts, I don't care) that will have to be "stick" to the real walls "top and bottom". (I don't want the entrance, just the wall shear stress in the main channel). I've already been able to split in into "top" and "bottom" but not more. Have you any idea to solve this issue? I hope that it is clear enough, many thanks in advance Edward PS : please apologize my bad English.

June 8, 2016, 11:37		#4
kirrer New Member Kevin Join Date: Oct 2012 Posts: 29 Rep Power: 13	My advice is first to create a scalar scene, and on that scene plot the scalar you want to use to split (for example, position in x axis). Find the value where you want to make your division - you can get this from the color of the scalar, or press the period key (.) when your mouse cursor hovers over the location - this will report the scalar value in the output window. Then, create a threshold part (derived part). You can see full directions in the manual, but essentially select the part which is the base of the derived part (like your "top" mentioned above), then select the field function used to create a threshold (like Position in x axis), then select the condition used for the threshold (position in x below 0.05 m, above 0.1m, between 0.05 and 0.1m, etc). Click create, add a geometry displayer to visualize it if you like, and then you can use that new derived part the same way you would have used a boundary in the past (for example, make a Surface Average report of Wall Shear Stress). Note that you do not use a constrained plane with this method - much easier to use thresholds. I'm not even sure if you could do it with constrained planes, except for splitting the original geometry and recreating the mesh (using the surface repair tool). Hope that helps! Edward1 and clement1564 like this.

June 10, 2016, 06:39		#5
Edward1 New Member Join Date: Jun 2016 Posts: 11 Rep Power: 9	Hi kirrer, Thanks for your help. That exactly what I was looking for. I took me a couple of hours to get results different to 0 but now it seems to be ok kirrer likes this.

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June 8, 2016, 08:37		#2
kirrer New Member Kevin Join Date: Oct 2012 Posts: 29 Rep Power: 13	You can use derived parts as you indicate to do this. Note that you can also use a derived part as the input to another derived part. For instance, if you use thresholds to split "channel" into "top" and "bottom" based on Position in z axis, then you can split "top" into "top front" and "top back" based on Position in x axis. Each subsequent derived part will still refer to the cells or faces of the original mesh, regardless of whether it's based on the original mesh or a derived part thereof. I hope I understood your question - but, I could also be missing it. If this is not clear, or the answer you are looking for, can you provide more information - such as a screenshot of the geometry and how you want to further divide it?

January 28, 2019, 08:46		#7
bluebase Senior Member Sebastian Engel Join Date: Jun 2011 Location: Germany Posts: 566 Rep Power: 20	Hi Moon, i don't know if there is an elegant way. The following method is somewhat laborous. Create a new threshold in derived parts. Select your domain of interest as parts input (this would likely be a plane section). Use one axis of the Field Function "Position" as scalar field input. Set the range of the respective column/row. Then, create another new threshold. Select the previous threshold as parts input. Use another axis of "Position" as scalar field input. Select a suitable range again. Repeat these steps until you end up with a thresholds which filtered out everything but the respective cell in the desired grid. These derived parts could then be taken as input for reports. Please Check continuity over those 16 threshold cells. The above method does not guarantee that all cells are included. Best regards, Sebastian

February 12, 2019, 23:25		#8
munibadshah New Member Moon Join Date: Jan 2019 Posts: 3 Rep Power: 7	Thank you Sebastian. Actually I did in the same way But now I want to create surface average of a circular area at the center of each square section as we calculate properties by using probe. I want to have the same size surface area say 30 gage wire (0.01in). Do you have any idea to do it quickly. Thank you