Acoustic analysis uses various unit systems (/UNITS), but uses the SI system as the default.
For more information about available units systems, see System of Units in the Coupled-Field Analysis Guide.
The following table lists the physical quantities used for an acoustic analysis in the SI units system:
Table 4.4: SI Units
| Unit Name | Unit Symbol | Quantity | Expressed in terms of other SI units |
| meter | m | length | |
| kilogram | kg | mass | |
| second | s | time | |
| kelvin | K | thermodynamic temperature | |
| hertz | Hz | frequency | |
| newton | N | force, weight | kg⋅m/s2 |
| pascal | Pa | pressure | N/m2 |
| joule | J | energy, heat | N⋅m |
| watt | W | power | J/s |
| ρ | mass density | kg/m3 | |
| c | sound speed | m/s | |
| η | dynamic viscosity | Pa⋅s | |
| κ | thermal conductivity | W/m⋅K | |
| cp | heat coefficient at a constant pressure per mass | J/K | |
| cv | heat coefficient at a constant volume per mass | J/K | |
| Z | impedance | N⋅s/m3 |
Support for defining a custom system of units is available via the /UNITS command. Typically, the length and mass conversion factor, as well as the offset of the temperature, are defined. The program converts the remaining quantities, including the static pressure, reference pressure, and reference power. The matrices may have better matrix conditions with other systems of units than either the SI or MKS system for acoustic fluid-structure interaction (FSI) models.