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Configuration file

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Christoph Fröhlich edited this page Jan 7, 2022 · 7 revisions

General section

  • SimulationIndex: Index of simulation defined in the ork file, start counting from 0
  • NumberOfSimulations: Number of simulations, which will be performed by diana
  • OrkFile: the name of your ork file

Parameter deviations

Configure the deviations for every supported parameter in the ini-file. If not specified otherwise, normal distribution is used with mean value from the original ork file and the standard deviation set in your ini file. Currently supported are:

  • Section Aerodynamics
    • FinCant (degree): Cant angle of the fins, calculated for every fincan in the design
    • ParachuteCd (unitless): Drag coefficient, calculated for every parachute in the design, factor 1+f on original value
    • Roughness (m): Surface roughness used for drag calculation. Only discrete roughness-categories are used by OpenRocket, see its Source Code
  • Section LaunchRail
    • TiltMean (degree, optional): consider that for the first simulation the values set in OR will be used
    • Tilt (degree)
    • AzimuthMean (degree, 0 is north): consider that for the first simulation the values set in OR will be used
    • Azimuth (degree)
    • Guidance (degree): Clearance of rocket within launch rail
  • Section Staging (optional): Useful for rockets with more than one stage. Define the staging event (burnout, launch, etc) and the nominal delay in the ork file. A uniform distribution with the interval (NominalDelay + StageSeparationDelayDeltaNeg, NominalDelay + StageSeparationDelayDeltaPos) is then applied without changing the staging event.
    • StageSeparationDelayDeltaNeg (in s, optional)
    • StageSeparationDelayDeltaPos (in s, optional)
  • Section Aerodynamics
    • CaxialFactor (unitless): factor 1+f on original Caxial
    • CsideFactor (unitless): factor 1+f on original Cside
    • CNFactor (unitless): factor 1+f on original CN
  • Section Propulsion
    • ThrustFactor (unitless): Factor applied to thrust curve, factor 1+f on original value
    • ThrustFactorMax (unitless): Upper limit of factor
    • ThrustFactorMin (unitless): Lower limit of factor
    • NozzleCrossSection (mm^2): Used within the thrust model. Thrust increase is parameterized via the nozzle diameter, which is applied for all stages. (set 0 to deactivate this feature).
  • Section Ignition (optional): Useful for rockets with more than one stage. Define the ignition event of the motors and the nominal delay in the ork file. A uniform distribution with the interval (NominalDelay + IgnitionDelayDeltaNeg, NominalDelay + IgnitionDelayDeltaPos) is then applied without changing the ignition event.
    • IgnitionDelayDeltaNeg (in s, optional)
    • IgnitionDelayDeltaPos (in s, optional)
  • Section WindModel (optional)
    • DataFile (optional): see Wind Data. If no wind data is provided, the standard settings in the ork file are used.

Notes on thrust model

Assuming that the nozzle of the rocket motor is optimized for low altitudes, the motor exhaust will be under-expanded at higher altitudes. Considering the ideal thrust equation F=mdot*ve + (p_e-p_inf)*Ae, the latter pressure differential component will increase the thrust in this condition. The thrust model used in ortools does not account for any efficiency losses due to the under-expansion and has to be considered by the user, e.g., by setting a lower nozzle exit area. More details can be found in this report

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