Monitor digits = 16

Gert-Jan · January 5, 2020, 11:57

Hi All,

I performed a run in double precision with the expert parameter "monitor digits" set to 16. This should give more numbers on axes in the solver manager. But I don't see any effect. Any idea? Anyone over used this option?

Regards, Gert-Jan

ghorrocks · January 5, 2020, 16:23

I have never used that option but if you view it through solver manager it might be solver manager truncating it. I would use the command line option to extract the data directly (the command is cfx5mondata I think) or look at the file directly (it is a text file in the solver directory when the run is progressing).

Gert-Jan · January 6, 2020, 08:20

Following your suggestion, I extracted the data from the res file, but it did not make any difference. I asked ANSYS and will update here when possible.

Opaque · January 6, 2020, 11:08

Did you compare the monitor files (named mon in the running directory) with the default setting, and your setting (=16)?

Are they any different?

Gert-Jan · January 6, 2020, 14:09

If I am informed correctly, it has to do with the Enthalpy being a large number.
In my case I am studying very small temperature differences, and consequently even smaller differences in Enthalpy. When subtracting these large enthalpies, CFX looses relevant digits which is reflected in the temperature that is derived from the enthalpy.

Opaque · January 6, 2020, 15:22

as far as I know, the monitor digits is just a formatting parameter. That is, how many digits are printed out to the monitor file (mon) .

It has nothing to do with precision of the calculations.

Gert-Jan · January 6, 2020, 15:32

This is what I heard through the grapevine. I'm investigating this as we speak.

January 5, 2020, 16:23		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,719 Rep Power: 143	I have never used that option but if you view it through solver manager it might be solver manager truncating it. I would use the command line option to extract the data directly (the command is cfx5mondata I think) or look at the file directly (it is a text file in the solver directory when the run is progressing). __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

January 6, 2020, 08:20		#3
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,835 Rep Power: 27	Following your suggestion, I extracted the data from the res file, but it did not make any difference. I asked ANSYS and will update here when possible.

January 6, 2020, 11:08		#4
Opaque Senior Member Join Date: Jun 2009 Posts: 1,815 Rep Power: 32	Did you compare the monitor files (named mon in the running directory) with the default setting, and your setting (=16)? Are they any different?

January 6, 2020, 14:09		#5
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,835 Rep Power: 27	If I am informed correctly, it has to do with the Enthalpy being a large number. In my case I am studying very small temperature differences, and consequently even smaller differences in Enthalpy. When subtracting these large enthalpies, CFX looses relevant digits which is reflected in the temperature that is derived from the enthalpy.

January 6, 2020, 15:22		#6
Opaque Senior Member Join Date: Jun 2009 Posts: 1,815 Rep Power: 32	as far as I know, the monitor digits is just a formatting parameter. That is, how many digits are printed out to the monitor file (mon) . It has nothing to do with precision of the calculations.

January 6, 2020, 15:32		#7
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,835 Rep Power: 27	This is what I heard through the grapevine. I'm investigating this as we speak.