ConsistentUnits Command

Introduction

NairnFEA and NairnMPM were initially developed using a specific set of units. The internal calculations were (for the most part) based on mm-g-seconds units (although there were some exceptions). The units for input of properties and output of results also usually followed this system, but not always. With the addition of the ConsistentUnits command (available since NairnFEA version 5, NairnMPM version 11, and OSParticulas version 2) all code can now be run in a new mode where input and output use consistent units and the user can specify any metric system of units. The old mode (which is still available) is called "Legacy Units" while the new mode is called "Consistent Units."

ConsistentUnits Command

If an input file has no ConsistentUnits command, the input file is assumed be using "Legacy" units. To convert to using any set of consistent, metric units, the file should add one ConsistentUnits command. In scripted files, the command is:

ConsistentUnits <(length),(mass),(time)>

and this command must be used before the Analysis Command. In XML files, the units are selected in the Header element using:

<ConsistentUnits length='(length)' mass='(mass)' time='(time)/>

where the the parameters in scripted command (and attributes in XML command) are:

• (length) can be km, m, dm cm, mm um (or microns), or nm
• (mass) can be kg, g, mg, or ug
• (time) can be s (or sec), ms (or msec), or us

In scripted files, you must provide all three parameters or none, where providing none will assume SI units of "m", "kg", and "s". If attributes are missing in XML files, they will be labeled as generic units of "L" for length, "M" for mass, and "T" for time.

When running with consistent units, you must make sure all other input commands and material properties are entered using the chosen units. When visualizing results in this system (i.e., using NairnFEAMPM and NairnFEAMPMViz), the visualization tools will read the units mode and display results in valid units (some options in those tools let you change the units used to display results). If you are visualizing results with third-party tools, the output results will be in the same consistent units used for input commands. A problems with using generic units (L, M, and T) is the output files have no documentation of units assumed for the calculations.

Legacy and Consistent Units

The original system of units is called "Legacy Units" while the new method is called "Consistent Units." The Legacy units can still be used (to allow backward compatibility of old input files) and it corresponds to any input file that omits the ConsistentUnits command. The units required when using "Legacy Units" and in the second column. The units required for "Generic" units and for some common "Consistent Units" systems are in the remaining columns (note that you can use any metric consistent units are are not limited to those listed in the table). When this documentation refers to units, it will refer to units class by name in the first column. You can refer to this table to see the units needed for "Legacy" units or for various sets of consistent units.

Unit	Legacy	Consistent	SI	mmgs	cgs
Length	mm	L	m	mm	cm
Mass	g	M	kg	g	g
Density	g/cm3	M/L3	kg/m3	g/mm3	g/cm3
Time	s	T	s	s	s
Alt Time	ms	T	s	s	s
Velocity	mm/s	L/T	m/s	mm/s	cm/s
Alt Velocity	m/s	L/T	m/s	mm/s	cm/s
Acceleration	mm/s2	L/T2	m/s2	mm/s2	cm/s2
Force	N	F = M-L/T2	N	μN	dyne
Pressure	MPa	P = F/L2	Pa	Pa	Ba
Linear Momentum	N-s	p = M-L/T	N-s	μN-s	dyne-s
Alt Strain	%	none	none	none	none
Energy	J	E = F-L	J	nJ	erg
Alt Energy	μJ	E = F-L	J	nJ	erg
Torque	J	t = F-L	J	nJ	erg
Angular Momentum	J-s	t = F-L-T	J-s	nJ-s	erg-s
Energy Release	J/m2	E/L2	J/m2	nJ/mm2	erg/cm2
Stress Intensity	MPa-m0.5	P-L0.5	Pa-m0.5	Pa-mm0.5	Ba-cm0.5
Viscosity	cPoise	P-T	Pa-s	Pa-s	Poise
Diffusion	mm2/s	L2/T	m2/s	mm2/s	cm2/s
Solvent Flux	kg/(m2-s)	M/(L2-T)	kg/(m2-s)	g/(mm2s)	g/(cm2-s)
Conductivity	W/(m-K)	E/(L-K-s)	W/(m-K)	nW/(mm-K)	erg/(cm-K-s)
Heat Capacity	J/(kg-K)	E/(M-K)	J/(kg-K)	nJ/(g-K)	erg/(g-K)
Heat Flux	W/m2	E/L2	W/m2	nW/mm2	erg/cm2
Heat of Fusion	J/kg	E/M	J/kg	nJ/g	erg/g