Problem variables

FAST-OAD process relies on OpenMDAO, and process variables are OpenMDAO variables.

For any component, variables are declared as inputs or outputs as described here.

FAST-OAD uses the promotion system of OpenMDAO, which means that all variables that are exchanged between FAST-OAD registered systems 1 have a unique name and are available for the whole process.

The list of variable names and descriptions for a given problem can be obtained from command line (see How to get list of variables).

Variable naming

Variables are named with a path-like pattern where path separator is :, e.g.:

  • data:geometry:wing:area

  • data:weight:airframe:fuselage:mass

  • data:weight:airframe:fuselage:CG:x

The first path element distributes variables among three categories:

  • data: variables that define the aircraft and its behaviour. This is the main category

  • settings: model settings. Generally coefficients for advanced users

  • tuning: coefficients that allow to do some assumptions (e.g.: “what if wing mass could be reduced of 20%?”)

The second path element tells about the nature of the variable (geometry, aerodynamics, weight, …).

The other path elements depend of the variable. The number of path elements is not fixed.

Serialization

For writing input and output files, FAST-OAD relies on the path in the variable names.

For example, for the three variables above, the matching part in XML file will be:

<data>
    <geometry>
        <wing>
            <area units="m**2">150.0</area>
        </wing>
    </geometry>
    <weight>
        <fuselage>
            <mass units="kg">10000.0</mass>
            <CG>
                <x units="m">20.0</x>
            </CG>
        </fuselage>
    </weight>
</data>

Note: Units are given as a string according to OpenMDAO units definitions

1

see Register your system(s)