the meaning of "mag"?

Yanci · November 17, 2014, 20:16

Hello there,

I met some problems about unit. What is the result of the following formula?

(2.0)*mag(symm(fvc::grad(U)))

Is it the square of strain rate (unit:s^-2) ?

What is the meaning of "mag"?

hjasak · November 18, 2014, 03:20

mag = magnitude

Yanci · November 18, 2014, 06:46

Thank you for your reply.
Dose this means "mag(symm(fvc::grad(U)))" has no unit?
But the error information shows the unit of "(2.0)*mag(symm(fvc::grad(U)))*nu()" is "[0 2 -2 0 0 0 0]". Why is it the unit of nu [0 2 -1 0 0 0 0]?

RodriguezFatz · November 18, 2014, 08:13

nu is the kinematic viscosity with unit m^2/s.
U is velocity with unit m/s
grad is derivative with unit 1/m
Multiply all of them and you get m^2/s * m/s * 1/m = m^2/s^2
Everything is fine.

November 17, 2014, 20:16	the meaning of "mag"?	#1
Yanci New Member Yongxiao Wang Join Date: Nov 2014 Posts: 16 Rep Power: 13	Hello there, I met some problems about unit. What is the result of the following formula? (2.0)*mag(symm(fvc::grad(U))) Is it the square of strain rate (unit:s^-2) ? What is the meaning of "mag"? nepomnyi likes this.

November 18, 2014, 03:20		#2
hjasak Senior Member Hrvoje Jasak Join Date: Mar 2009 Location: London, England Posts: 1,908 Rep Power: 34	mag = magnitude __________________ Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk

November 18, 2014, 08:13		#4
RodriguezFatz Senior Member Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 28	nu is the kinematic viscosity with unit m^2/s. U is velocity with unit m/s grad is derivative with unit 1/m Multiply all of them and you get m^2/s * m/s * 1/m = m^2/s^2 Everything is fine. __________________ The skeleton ran out of shampoo in the shower.

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November 18, 2014, 06:46		#3
Yanci New Member Yongxiao Wang Join Date: Nov 2014 Posts: 16 Rep Power: 13	Thank you for your reply. Dose this means "*mag(symm(fvc::grad(U)))" has no unit? But the error information shows the unit of "*(2.0)mag(symm(fvc::grad(U)))nu()" is "[0 2 -2 0 0 0 0]**". Why is it the unit of nu [0 2 -1 0 0 0 0]?