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
The ConsistentUnits command is currently not supported for scripted input files. The problem is that the tools that create such files (NairnFEAMPM and NairnFEAMPMViz) enforce their own units that are currently incompatible with consistent units settings. This situation will change in the fuiture.
Altthough visualization tools cannot create input files using consistent units, they can read (and correctly interpret) output from simulations generated from raw XML files that use consistent. The units are selected in the Header element of XML files using:
<ConsistentUnits length='(units)' mass='(units)' time='(units)/>
where the (units) settings determine metric units as follows:
- 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
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 attributes or specify none (to use generic units).
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 |
| 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 |