using dimensional variables as dimentionless

h.mortezaee · July 11, 2015, 12:02

hi everyone , im trying to define an expression for my subdomain energy source that is function of coordinates but i cant because coordinates like x,y or xGlobal,yGlobal have [m] dimension , How can i fix this problem , i tried to do this ( x/1[m] ) but it didnt work ,
please help me

h.mortezaee · July 11, 2015, 12:08

for information , im modeling the energy deposition of proton beam from cyclotron in the compressed N2 gas ,

ghorrocks · July 12, 2015, 06:02

Why is having the x,y,z variables in metres a problem? You can change to other units systems if you like.

The expression x/1[m] will return a unitless value - so what did not work about it?

h.mortezaee · July 12, 2015, 07:22

no it didnt return unitless value , for example if this is my expression " (x/1[m])^2 [kg m^2 s^-3] "
the error given is " Bad expression value 'energy' detected in parameter 'Total Source' in object '/FLOW:Flow Analysis 1/DOMAIN

efault Domain/SUBDOMAIN:Subdomain 1/SOURCES/EQUATION SOURCE:energy'.
CEL error:
Exponent must be dimensionless to right of '^' operator at position 9.
Actual dimensions: 'kg m^2 s^-3'."

h.mortezaee · July 12, 2015, 07:27

my bad , it just needed parenthesis ,

, so stupid ,
thankyou Glenn

July 11, 2015, 12:02	using dimensional variables as dimentionless	#1
h.mortezaee Member hani mortezaee Join Date: Sep 2014 Posts: 30 Rep Power: 11	hi everyone , im trying to define an expression for my subdomain energy source that is function of coordinates but i cant because coordinates like x,y or xGlobal,yGlobal have [m] dimension , How can i fix this problem , i tried to do this ( x/1[m] ) but it didnt work , please help me

July 12, 2015, 07:22		#4
h.mortezaee Member hani mortezaee Join Date: Sep 2014 Posts: 30 Rep Power: 11	no it didnt return unitless value , for example if this is my expression " (x/1[m])^2 [kg m^2 s^-3] " the error given is " Bad expression value 'energy' detected in parameter 'Total Source' in object '/FLOW:Flow Analysis 1/DOMAINefault Domain/SUBDOMAIN:Subdomain 1/SOURCES/EQUATION SOURCE:energy'. CEL error: Exponent must be dimensionless to right of '^' operator at position 9. Actual dimensions: 'kg m^2 s^-3'."

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July 11, 2015, 12:08		#2
h.mortezaee Member hani mortezaee Join Date: Sep 2014 Posts: 30 Rep Power: 11	for information , im modeling the energy deposition of proton beam from cyclotron in the compressed N2 gas ,

July 12, 2015, 06:02		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Why is having the x,y,z variables in metres a problem? You can change to other units systems if you like. The expression x/1[m] will return a unitless value - so what did not work about it?

July 12, 2015, 07:27		#5
h.mortezaee Member hani mortezaee Join Date: Sep 2014 Posts: 30 Rep Power: 11	my bad , it just needed parenthesis , , so stupid , thankyou Glenn