Get position of minval/maxval of a simulated field

vjewtou · September 8, 2017, 20:31

Hi all,

I would like to calculate the transient (x0, y0) position of the minimum of a field (pressure for example) projected on a horizontal section.

I have looked online how to do this but couldn't find anything that does what I need. Does anyone please know how to do this?

I need this to track the center of a simulated vortex and calculate angular momentum about its axis, using a user field function defined by: (x-x0)*v-(y-y0)*u,
where (x, y) are horizontal coordinates, and (u, v) are the horizontal components of velocity.

Thanks in advance!

ping · September 11, 2017, 08:16

a series of reports and thresholds should be able to do this.
you could start with a min report to get the value of the require field.
then create a user field function that is a very small fraction larger than that field report.
then create a threshold of using the new user field as the input scalar in below mode and it will create a subset of cells hopefully just one that is the one required.
then do an average report of this threshold part to report on cell centroid x.
likewise for y and you have the require coordinates at each timestep.
i am pretty sure if you search a bit wider on the steve support portal you will find related articles.

vjewtou · September 11, 2017, 21:18

Thank you!

Your message helped me a lot. What I did was first to make a pressure isosurface (with a value close to the minimum), and then making a vertical threshold of that isosurface between 0 and 10 m above the surface. Finally, I make a report to calculate the surface average and get X and Y positions.

September 8, 2017, 20:31	Get position of minval/maxval of a simulated field	#1
vjewtou New Member Val Jewtoukoff Join Date: May 2017 Posts: 4 Rep Power: 9	Hi all, I would like to calculate the transient (x0, y0) position of the minimum of a field (pressure for example) projected on a horizontal section. I have looked online how to do this but couldn't find anything that does what I need. Does anyone please know how to do this? I need this to track the center of a simulated vortex and calculate angular momentum about its axis, using a user field function defined by: (x-x0)v-(y-y0)u, where (x, y) are horizontal coordinates, and (u, v) are the horizontal components of velocity. Thanks in advance!

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September 11, 2017, 08:16		#2
ping Senior Member Ping Join Date: Mar 2009 Posts: 556 Rep Power: 20	a series of reports and thresholds should be able to do this. you could start with a min report to get the value of the require field. then create a user field function that is a very small fraction larger than that field report. then create a threshold of using the new user field as the input scalar in below mode and it will create a subset of cells hopefully just one that is the one required. then do an average report of this threshold part to report on cell centroid x. likewise for y and you have the require coordinates at each timestep. i am pretty sure if you search a bit wider on the steve support portal you will find related articles.

September 11, 2017, 21:18		#3
vjewtou New Member Val Jewtoukoff Join Date: May 2017 Posts: 4 Rep Power: 9	Thank you! Your message helped me a lot. What I did was first to make a pressure isosurface (with a value close to the minimum), and then making a vertical threshold of that isosurface between 0 and 10 m above the surface. Finally, I make a report to calculate the surface average and get X and Y positions.