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wing_skin.py
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wing_skin.py
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" wing skin "
from gpkit import Model, Variable, parse_variables
from gpkitmodels.GP.materials.cfrp import CFRP
class WingSkin(Model):
""" Wing Skin model
Variables
---------
W [lbf] wing skin weight
g 9.81 [m/s^2] gravitational acceleration
t [in] wing skin thickness
Jtbar 0.01114 [1/mm] torsional moment of inertia
Cmw 0.121 [-] negative wing moment coeff
rhosl 1.225 [kg/m^3] sea level air density
Vne 45 [m/s] never exceed vehicle speed
Upper Unbounded
---------------
W, croot
Lower Unbounded
---------------
S
LaTex Strings
-------------
W W_{\\mathrm{skin}}
t t_{\\mathrm{skin}}
Jtbar \\bar{J/t}
Cmw C_{m_w}
rhosl \\rho_{\\mathrm{SL}}
Vne V_{\\mathrm{NE}}
"""
material = CFRP()
def setup(self, surface):
exec parse_variables(WingSkin.__doc__)
croot = self.croot = surface.croot
S = self.S = surface.S
self.loading = WingSkinL
rho = self.material.rho
tau = self.material.tau
tmin = self.material.tmin
return [W >= rho*surface.S*2*t*g,
t >= tmin,
tau >= 1/Jtbar/croot**2/t*Cmw*S*rhosl*Vne**2
]
class WingSkinL(Model):
"wing skin loading model for torsional loads in skin"
def setup(self, static):
taucfrp = Variable("\\tau_{CFRP}", 570, "MPa", "torsional stress limit")
Cmw = Variable("C_{m_w}", 0.121, "-", "negative wing moment coefficent")
rhosl = Variable("\\rho_{sl}", 1.225, "kg/m^3",
"air density at sea level")
Vne = Variable("V_{NE}", 45, "m/s", "never exceed vehicle speed")
return []