Fuel Variables and Subsystems Revamp

[cmbenne3]

Summary

This PR fixes 2 connected issues with the fuel subsystems.

Removes 2 variables, and updates fortran_to_aviary to correctly handle the new assignments:

1. Aircraft.Fuel.DENSITY_RATIO (instead user should just specify the absolute FUEL_DENSITY)
2. Aircraft.Fuel.CAPACITY_FACTOR (This variable is from legacy FLOPS and has no physical meaning. Switch to using Aircraft.Fuel.WING_FUEL_FRACTION)

Adds a new post-mission exec comp subsystem to calculate the excess fuel for the mission. (Excess_fuel = TOTAL_FUEL_CAPACITY - UNUSABLE_FUEL_MASS - TOTAL_FUEL_MASS), where total_fuel_mass includes fuel burned in the mission, reserve fuel, and fuel margin).

Adds a new constraint for the optimization to force that excess fuel must be greater than zero.

Adds a new control variable Aircraft.Fuel.IGNORE_EXCESS_FUEL_CONSTRAINT to control the addition of the constraint, which adds functionality similar to the FLOPS WTIN.IFUFU parameter. If set=True then the constraint will not be added and Aviary will converge even if there is not enough capacity for the required mission fuel (this is the current behaviour). The default has been set = False (which makes more sense for most users).

flops_defaults updated to correctly interpret IFUFU and set Aircraft.Fuel.IGNORE_EXCESS_FUEL_CONSTRAINT as boolean.

Excess fuel output added to dashboard under mission summary.

A new preprocessors function has been added to check the fuel capacity variables are consistent with each other, and to add an assumption that they're zero if they are missing. This fixes a bug where it was possible to setup a circular calculation reference that prevented aviary from converging if those variables were missing (and it was difficult for the user to debug).

The units of the fuel density input for FLOPS and GASP fuel calculations have been made consistent throught aviary and set to lbm/galUS.

Related Issues

• Resolves Improve Fuel Capacity/Volume/Density/Ratio variables #470 Add an Excess Fuel Output to Dashboard for FLOPS Missions #828

Backwards incompatibilities

If existing aircraft models fail with the addition of the excess fuel constraint then that indicates that those models were invalid in the first place.
Existing aircraft models with density_ratio and capacity_factor variables may not give identical answers if values were changed from defaults

New Dependencies

None