from abc import ABC, abstractmethod
import numpy as np
[docs]
class AeroSurface(ABC):
"""Abstract class used to define aerodynamic surfaces."""
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def __init__(self, name, reference_area, reference_length):
self.reference_area = reference_area
self.reference_length = reference_length
self.name = name
self.cpx = 0
self.cpy = 0
self.cpz = 0
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@staticmethod
def _beta(mach):
"""Defines a parameter that is often used in aerodynamic
equations. It is commonly used in the Prandtl factor which
corrects subsonic force coefficients for compressible flow.
This is applied to the lift coefficient of the nose cone,
fins and tails/transitions as in [1].
Parameters
----------
mach : int, float
Number of mach.
Returns
-------
beta : int, float
Value that characterizes flow speed based on the mach number.
References
----------
[1] Barrowman, James S. https://arc.aiaa.org/doi/10.2514/6.1979-504
"""
if mach < 0.8:
return np.sqrt(1 - mach**2)
elif mach < 1.1:
return np.sqrt(1 - 0.8**2)
else:
return np.sqrt(mach**2 - 1)
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@abstractmethod
def evaluate_center_of_pressure(self):
"""Evaluates the center of pressure of the aerodynamic surface in local
coordinates.
Returns
-------
None
"""
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@abstractmethod
def evaluate_lift_coefficient(self):
"""Evaluates the lift coefficient curve of the aerodynamic surface.
Returns
-------
None
"""
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@abstractmethod
def evaluate_geometrical_parameters(self):
"""Evaluates the geometrical parameters of the aerodynamic surface.
Returns
-------
None
"""
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@abstractmethod
def info(self):
"""Prints and plots summarized information of the aerodynamic surface.
Returns
-------
None
"""
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@abstractmethod
def all_info(self):
"""Prints and plots all the available information of the aero surface.
Returns
-------
None
"""
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def compute_forces_and_moments(
self,
stream_velocity,
stream_speed,
stream_mach,
rho,
cp,
*args,
): # pylint: disable=unused-argument
"""Computes the forces and moments acting on the aerodynamic surface.
Used in each time step of the simulation. This method is valid for
the barrowman aerodynamic models.
Parameters
----------
stream_velocity : tuple
Tuple containing the stream velocity components in the body frame.
stream_speed : int, float
Speed of the stream in m/s.
stream_mach : int, float
Mach number of the stream.
rho : int, float
Density of the stream in kg/m^3.
cp : Vector
Center of pressure coordinates in the body frame.
args : tuple
Additional arguments.
kwargs : dict
Additional keyword arguments.
Returns
-------
tuple of float
The aerodynamic forces (lift, side_force, drag) and moments
(pitch, yaw, roll) in the body frame.
"""
R1, R2, R3, M1, M2, M3 = 0, 0, 0, 0, 0, 0
cpz = cp[2]
stream_vx, stream_vy, stream_vz = stream_velocity
if stream_vx**2 + stream_vy**2 != 0: # TODO: maybe try/except
# Normalize component stream velocity in body frame
stream_vzn = stream_vz / stream_speed
if -1 * stream_vzn < 1:
attack_angle = np.arccos(-stream_vzn)
c_lift = self.cl.get_value_opt(attack_angle, stream_mach)
# Component lift force magnitude
lift = 0.5 * rho * (stream_speed**2) * self.reference_area * c_lift
# Component lift force components
lift_dir_norm = (stream_vx**2 + stream_vy**2) ** 0.5
lift_xb = lift * (stream_vx / lift_dir_norm)
lift_yb = lift * (stream_vy / lift_dir_norm)
# Total lift force
R1, R2, R3 = lift_xb, lift_yb, 0
# Total moment
M1, M2, M3 = -cpz * lift_yb, cpz * lift_xb, 0
return R1, R2, R3, M1, M2, M3
