Do I need to change mechnical properties after using transformpoint scale utility?

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 November 1, 2012, 23:31 Do I need to change mechnical properties after using transformpoint scale utility? #1 Member   Sangeeta Join Date: Jul 2012 Location: Kingston, Canada Posts: 70 Rep Power: 7 Hello everyone, I am solving a case for 3D cube geometry. First, I have created cube mesh for 1mX1mX1m dimension then transferred the geometry to smaller scale (0.00005, 0.00005, 0.00005) by using transformPoint scale utility. I am using mechanical and thermal properties (e.g. Youngs modulus, conductivity, specific heat etc.) for the case. Do I need to change the dimensions of mechanical and thermal properties after reducing mesh size. For example: E = 210 X 10^9 N/m^2 Since this value is in "m", if I change cube dimensions in "mm" should it be E = 210 X 10^3 N/mm^2 ? Does anyone have any idea about it? Best regards, Sangeeta

 November 2, 2012, 03:47 #2 Senior Member   Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 383 Rep Power: 14 Hello Sangeeta, OpenFOAM will use meters for all it's computations (if SI units are specified in \$HOME/OpenFOAM/OpenFOAM-2.1.x/etc/controlDict), so all your material properties have to be specified in the usual SI unit. So I would expect you just keep E = 210 X 10^9 N/m^2, regardless of the size of your problem. Regards, Tom

November 2, 2012, 12:41
#3
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Sangeeta
Join Date: Jul 2012
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Quote:
 Originally Posted by tomf Hello Sangeeta, OpenFOAM will use meters for all it's computations (if SI units are specified in \$HOME/OpenFOAM/OpenFOAM-2.1.x/etc/controlDict), so all your material properties have to be specified in the usual SI unit. So I would expect you just keep E = 210 X 10^9 N/m^2, regardless of the size of your problem. Regards, Tom

Hi Tom,

Thank you for the reply. Do you think that it will not going to affect final results if I do not change mechanical and thermal properties in mm?

Best regards,
Sangeeta

November 3, 2012, 07:19
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Tom Fahner
Join Date: Mar 2009
Location: Breda, Netherlands
Posts: 383
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Quote:
 Originally Posted by Sargam05 Hi Tom, Thank you for the reply. Do you think that it will not going to affect final results if I do not change mechanical and thermal properties in mm? Best regards, Sangeeta
Hi Sangeeta,

This section in the userguide basically explains the role of dimensions:

http://www.openfoam.org/docs/user/ba...hp#dx18-100002

So if you plan to use SI units, use default SI units for properties i.e. kg, m, s, K, kgmol, A, cd or combinations thereof. For your problem make sure that the dimensions are specified in meters as well (0.005 for 5 mm). OpenFOAM will not know about millimeters, it only knows meters.

Regards,
Tom

 November 8, 2012, 12:35 #5 Member   Sangeeta Join Date: Jul 2012 Location: Kingston, Canada Posts: 70 Rep Power: 7 Hi Tom, Thank you for the reply. I appreciate it! Sangeeta

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