"""
Computation of load cases
"""
# This file is part of FAST-OAD : A framework for rapid Overall Aircraft Design
# Copyright (C) 2021 ONERA & ISAE-SUPAERO
# FAST is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
import numpy as np
from openmdao.core.explicitcomponent import ExplicitComponent
from fastoad.model_base import Atmosphere
[docs]class Loads(ExplicitComponent):
"""
Computes gust load cases
Load case 1: with wings with almost no fuel
Load case 2: at maximum take-off weight
Based on formulas in :cite:`supaero:2014`, ยง6.3
"""
[docs] def setup(self):
self.add_input("data:geometry:wing:area", val=np.nan, units="m**2")
self.add_input("data:geometry:wing:span", val=np.nan, units="m")
self.add_input("data:weight:aircraft:MZFW", val=np.nan, units="kg")
self.add_input("data:weight:aircraft:MFW", val=np.nan, units="kg")
self.add_input("data:weight:aircraft:MTOW", val=np.nan, units="kg")
self.add_input("data:aerodynamics:aircraft:cruise:CL_alpha", val=np.nan)
self.add_input("data:load_case:lc1:U_gust", val=np.nan, units="m/s")
self.add_input("data:load_case:lc1:altitude", val=np.nan, units="ft")
self.add_input("data:load_case:lc1:Vc_EAS", val=np.nan, units="m/s")
self.add_input("data:load_case:lc2:U_gust", val=np.nan, units="m/s")
self.add_input("data:load_case:lc2:altitude", val=np.nan, units="ft")
self.add_input("data:load_case:lc2:Vc_EAS", val=np.nan, units="kn")
self.add_output("data:mission:sizing:cs25:sizing_load_1", units="kg")
self.add_output("data:mission:sizing:cs25:sizing_load_2", units="kg")
[docs] def setup_partials(self):
self.declare_partials("*", "*", method="fd")
# pylint: disable=too-many-locals
# pylint: disable=invalid-name
[docs] def compute(self, inputs, outputs, discrete_inputs=None, discrete_outputs=None):
sea_level_density = Atmosphere(0).density
wing_area = inputs["data:geometry:wing:area"]
span = inputs["data:geometry:wing:span"]
mzfw = inputs["data:weight:aircraft:MZFW"]
mfw = inputs["data:weight:aircraft:MFW"]
mtow = inputs["data:weight:aircraft:MTOW"]
cl_alpha = inputs["data:aerodynamics:aircraft:cruise:CL_alpha"]
u_gust1 = inputs["data:load_case:lc1:U_gust"]
alt_1 = inputs["data:load_case:lc1:altitude"]
vc_eas1 = inputs["data:load_case:lc1:Vc_EAS"]
u_gust2 = inputs["data:load_case:lc2:U_gust"]
alt_2 = inputs["data:load_case:lc2:altitude"]
vc_eas2 = inputs["data:load_case:lc2:Vc_EAS"]
# calculation of mean geometric chord
chord_geom = wing_area / span
# load case #1
m1 = 1.05 * mzfw
n_gust_1 = self.__n_gust(
m1,
wing_area,
Atmosphere(alt_1).density,
sea_level_density,
chord_geom,
vc_eas1,
cl_alpha,
u_gust1,
)
n1 = 1.5 * max(2.5, n_gust_1)
n1m1 = n1 * m1
# load case #2
n_gust_2 = self.__n_gust(
mtow,
wing_area,
Atmosphere(alt_2).density,
sea_level_density,
chord_geom,
vc_eas2,
cl_alpha,
u_gust2,
)
n2 = 1.5 * max(2.5, n_gust_2)
mcv = min(0.8 * mfw, mtow - mzfw)
n2m2 = n2 * (mtow - 0.55 * mcv)
outputs["data:mission:sizing:cs25:sizing_load_1"] = n1m1
outputs["data:mission:sizing:cs25:sizing_load_2"] = n2m2
@staticmethod
def __n_gust(mass, wing_area, rho, sea_level_density, chord_geom, vc_eas, cl_alpha, u_gust):
"""
Computes a reference gust load.
:param mass:
:param wing_area:
:param rho:
:param sea_level_density:
:param chord_geom:
:param vc_eas: Vc (Equivalent AirSpeed)
:param cl_alpha:
:param u_gust:
:return:
"""
mu_g = 2 * mass / rho / wing_area / chord_geom / cl_alpha
k_g = 0.88 * mu_g / (5.3 + mu_g) # attenuation factor
n_gust = 1 + (sea_level_density / 2 / 9.81) * k_g * u_gust * (
vc_eas * cl_alpha / mass / wing_area
)
return n_gust