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 were input and output use consistent units and the user can specify any metric system of units.

= Commands

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

The (units) settings determine metric units for length (which can be km, m, dm cm, mm um (or microns), or nm), mass (which can be kg, g, mg, ug), and time (which can be s (or sec), ms (or msec), or us). Alternatively, if none of the length, mass, and time attributes are provided, the code will run with generic units for length (L), mass (M), and time (T). The default (if this command is not used) is to use "Legacy Units." If this command is used, you must specify all three attrobites or specify none (to use generic units). More details on unit specificatiions are provided <a href="units.html">here</a>.

Table

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 in the main header. The units required when using "Legacy Units" and in and some common "Consistent Units" systems are in the following table (note that you can use an metric consistent units are are not limited to those listed in the table):

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
Alt Strain	%	none	none	none	none
Energy	J	E = F-L	J	nJ	erg
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/(mm-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