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Rick Fenrich edited this page Aug 14, 2017 · 2 revisions

The units of the input variables and output quantities of interest are very important. MULTI-F assumes SI units for both. There are several ways to check that your units are correct:

  1. Ensure the units of values in the input file and config file are the same as those listed here.
  2. When an analysis is run with the verbose option a table is printed to the screen comparing old design variable values and new design variable values (as updated from the input file). Scan this table briefly to see whether the design variable values have changed by a large amount (i.e. orders of magnitude) which may suggest a units problem.
  3. Send your config and input file to a MULTI-F developer.

Input Variable Units

WALL: m
XXX_THICKNESS_LOCATIONS: none (dimensionless scaled by nozzle length)
XXX_THICKNESS_VALUES: m
XXX_THICKNESS: m
BAFFLES_LOCATION: none (dimensionless scaled by nozzle length)
XXX_HEIGHT: m
XXX_LOCATIONS: m or degrees (for pointwise output location specification only)
XXX_DENSITY: kg/m^3
XXX_ELASTIC_MODULUS: Pa
XXX_SHEAR_MODULUS: Pa
XXX_POISSON_RATIO: none
XXX_MUTUAL_INFLUENCE_COEFS: none
XXX_THERMAL_CONDUCTIVITY: W/m-K
XXX_THERMAL_EXPANSION_COEF: 1/K
XXX_FAILURE_STRAIN: none
XXX_YIELD_STRESS: Pa
XXX_MAX_SERVICE_TEMPERATURE: K
HEAT_XFER_COEF_TO_ENV: W/m^2-K

NOTE: In the documentation the units for elastic modulus and shear modulus are given in GPa not Pa, thermal expansion coefficient is given in 10^-6*1/K not 1/K, yield stress is given in MPa not Pa, and failure strains are given in percentages not dimensionless. This is standard in engineering applications. Be sure to provide basic SI units in the config and input files; do not use GPa, MPa, 10^-6, or %.

Output Units

MASS: kg
VOLUME: m^3
THRUST: N (values ~30,000 expected)
XXX_TEMPERATURE: K (values ~400 to 1000 expected)
XXX_STRESS: Pa (values ~1e5 to 1e8 expected)
XXX_TEMP_RATIO: none (values ~1e-3 to 2 expected)
XXX_FAILURE_CRITERIA: none (values ~1e-3 to 2 expected)
WALL_PRESSURE: Pa (values ~1e5 expected)
PRESSURE: Pa (values ~1e5 expected)
VELOCITY: m/s (values ~0.1 to 500 expected)

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