Units of measure?

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dcasteel
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Joined: 22 Mar 2011, 16:45
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Units of measure?

Post by dcasteel »

Is there a simple reference sheet defining what the units of measure are for all of the variables?

I'm hoping someone has made up a "cheat sheet" since there are no lables or tool tips in ElmerGUI.

Timestep I'm assuming is seconds not milliseconds?
Temperatures are in kelvin?
Would velocity be meters/sec?
Pressure in bar or atmospheres? 1 atm (atmosphere) = 1.01325 bar

Thanks
Don
Captain Slow
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Joined: 10 Nov 2009, 19:17

Re: Units of measure?

Post by Captain Slow »

This has been answered many times before. Elmer assumes you use a consistent set of units-IE if you input everything in SI units, your output will be in SI units.
dcasteel
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Re: Units of measure?

Post by dcasteel »

Thanks, that helps a lot
hazelsct
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Re: Units of measure?

Post by hazelsct »

Default constants (Model -> Setup; top of the .sif file) are in SI units.
petroo
Posts: 148
Joined: 13 Jan 2010, 19:07
Location: Aachen, Germany

Re: Units of measure?

Post by petroo »

Captain Slow wrote:This has been answered many times before. Elmer assumes you use a consistent set of units-IE if you input everything in SI units, your output will be in SI units.
Yes, but what about the "almost SI units"? (See also my comment on the neighboring thread on the "material library extension" discussion.) We had some nasty problems in the past when entering new material data and combining them with existing ones. Even if you drop those old awkward units like calories, yard, deg Fahrenheit and such, there is plenty of room for errors with the SI-resembling units. Do you take "kg" or "g" for the weight? Is it "kJ/kg", or "J/kg"? Is it "W/cm·K" or "kW/m·K", and so on.

My suggestion: Mandatory unit entry for every physical value, with a simple check in Elmer, whether units match. Warn, if they don't. No automatic recalculation of numerical values based on given units, but expression of warnings if unsuitable units are intermingled.

The required consistency is not always easy to check if data are taken from different sources, especially so, if data are taken from Elmer material libraries where the units are not documented.

Regards,

Peter
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