import numpy as np
from ..mathutils.function import Function
from ..prints.parachute_prints import _ParachutePrints
[docs]
class Parachute:
"""Keeps parachute information.
Attributes
----------
Parachute.name : string
Parachute name, such as drogue and main. Has no impact in
simulation, as it is only used to display data in a more
organized matter.
Parachute.cd_s : float
Drag coefficient times reference area for parachute. It is
used to compute the drag force exerted on the parachute by
the equation F = ((1/2)*rho*V^2)*cd_s, that is, the drag
force is the dynamic pressure computed on the parachute
times its cd_s coefficient. Has units of area and must be
given in squared meters.
Parachute.trigger : callable, float, str
This parameter defines the trigger condition for the parachute ejection
system. It can be one of the following:
- A callable function that takes three arguments:
1. Freestream pressure in pascals.
2. Height in meters above ground level.
3. The state vector of the simulation, which is defined as:
`[x, y, z, vx, vy, vz, e0, e1, e2, e3, wx, wy, wz]`.
The function should return True if the parachute ejection system should
be triggered and False otherwise.
- A float value, representing an absolute height in meters. In this
case, the parachute will be ejected when the rocket reaches this height
above ground level.
- The string "apogee" which triggers the parachute at apogee, i.e.,
when the rocket reaches its highest point and starts descending.
Note: The function will be called according to the sampling rate
specified.
Parachute.triggerfunc : function
This parameter defines the trigger function created from the trigger
parameter. It is used to evaluate the trigger condition for the
parachute ejection system. It is a callable function that takes three
arguments:
1. Freestream pressure in pascals.
2. Height in meters above ground level.
3. The state vector of the simulation, which is defined as:
`[x, y, z, vx, vy, vz, e0, e1, e2, e3, wx, wy, wz]`.
The function should return True if the parachute ejection system should
be triggered and False otherwise.
Note: The function will be called according to the sampling rate
specified.
Parachute.sampling_rate : float
Sampling rate, in hertz, for the trigger function.
Parachute.lag : float
Time, in seconds, between the parachute ejection system is triggered
and the parachute is fully opened.
Parachute.noise_bias : float
Mean value of the noise added to the pressure signal, which is
passed to the trigger function. Unit is in pascal.
Parachute.noise_deviation : float
Standard deviation of the noise added to the pressure signal,
which is passed to the trigger function. Unit is in pascal.
Parachute.noise_corr : tuple, list
Tuple with the correlation between noise and time.
Parachute.noise_signal : list of tuple
List of (t, noise signal) corresponding to signal passed to
trigger function. Completed after running a simulation.
Parachute.noisy_pressure_signal : list of tuple
List of (t, noisy pressure signal) that is passed to the
trigger function. Completed after running a simulation.
Parachute.clean_pressure_signal : list of tuple
List of (t, clean pressure signal) corresponding to signal passed to
trigger function. Completed after running a simulation.
Parachute.noise_signal_function : Function
Function of noiseSignal.
Parachute.noisy_pressure_signal_function : Function
Function of noisy_pressure_signal.
Parachute.clean_pressure_signal_function : Function
Function of clean_pressure_signal.
"""
[docs]
def __init__(
self,
name,
cd_s,
trigger,
sampling_rate,
lag=0,
noise=(0, 0, 0),
):
"""Initializes Parachute class.
Parameters
----------
name : string
Parachute name, such as drogue and main. Has no impact in
simulation, as it is only used to display data in a more
organized matter.
cd_s : float
Drag coefficient times reference area of the parachute.
trigger : callable, float, str
This parameter defines the trigger condition for the parachute
ejection system. It can be one of the following:
- A callable function that takes three arguments:
1. Freestream pressure in pascals.
2. Height in meters above ground level.
3. The state vector of the simulation, which is defined as:
[x, y, z, vx, vy, vz, e0, e1, e2, e3, wx, wy, wz].
The function should return True if the parachute ejection system
should be triggered and False otherwise.
- A float value, representing an absolute height in meters. In this
case, the parachute will be ejected when the rocket reaches this
height above ground level.
- The string "apogee" which triggers the parachute at apogee, i.e.,
when the rocket reaches its highest point and starts descending.
Note: The function will be called according to the sampling rate
specified next.
sampling_rate : float
Sampling rate in which the parachute trigger will be checked at.
It is used to simulate the refresh rate of onboard sensors such
as barometers. Default value is 100. Value must be given in hertz.
lag : float, optional
Time between the parachute ejection system is triggered and the
parachute is fully opened. During this time, the simulation will
consider the rocket as flying without a parachute. Default value
is 0. Must be given in seconds.
noise : tuple, list, optional
List in the format (mean, standard deviation, time-correlation).
The values are used to add noise to the pressure signal which is
passed to the trigger function. Default value is (0, 0, 0). Units
are in pascal.
Returns
-------
None
"""
self.name = name
self.cd_s = cd_s
self.trigger = trigger
self.sampling_rate = sampling_rate
self.lag = lag
self.noise_signal = [[-1e-6, np.random.normal(noise[0], noise[1])]]
self.noisy_pressure_signal = []
self.clean_pressure_signal = []
self.noise_bias = noise[0]
self.noise_deviation = noise[1]
self.noise_corr = (noise[2], (1 - noise[2] ** 2) ** 0.5)
self.clean_pressure_signal_function = Function(0)
self.noisy_pressure_signal_function = Function(0)
self.noise_signal_function = Function(0)
alpha, beta = self.noise_corr
self.noise_function = lambda: alpha * self.noise_signal[-1][
1
] + beta * np.random.normal(noise[0], noise[1])
self.prints = _ParachutePrints(self)
self.__evaluate_trigger_function(trigger)
def __evaluate_trigger_function(self, trigger):
"""This is used to set the triggerfunc attribute that will be used to
interact with the Flight class.
"""
if callable(trigger):
self.triggerfunc = trigger
elif isinstance(trigger, (int, float)):
# The parachute is deployed at a given height
def triggerfunc(p, h, y):
# p = pressure considering parachute noise signal
# h = height above ground level considering parachute noise signal
# y = [x, y, z, vx, vy, vz, e0, e1, e2, e3, w1, w2, w3]
return True if y[5] < 0 and h < trigger else False
self.triggerfunc = triggerfunc
elif trigger.lower() == "apogee":
# The parachute is deployed at apogee
def triggerfunc(p, h, y):
# p = pressure considering parachute noise signal
# h = height above ground level considering parachute noise signal
# y = [x, y, z, vx, vy, vz, e0, e1, e2, e3, w1, w2, w3]
return True if y[5] < 0 else False
self.triggerfunc = triggerfunc
else:
raise ValueError(
f"Unable to set the trigger function for parachute '{self.name}'. "
+ "Trigger must be a callable, a float value or the string 'apogee'. "
+ "See the Parachute class documentation for more information."
)
[docs]
def __str__(self):
"""Returns a string representation of the Parachute class.
Returns
-------
string
String representation of Parachute class. It is human readable.
"""
return "Parachute {} with a cd_s of {:.4f} m2".format(
self.name.title(),
self.cd_s,
)
[docs]
def __repr__(self):
"""Representation method for the class, useful when debugging."""
return (
f"<Parachute {self.name} "
+ f"(cd_s = {self.cd_s:.4f} m2, trigger = {self.trigger})>"
)
[docs]
def info(self):
"""Prints information about the Parachute class."""
self.prints.all()
return None
[docs]
def all_info(self):
"""Prints all information about the Parachute class."""
self.info()
# self.plots.all() # Parachutes still doesn't have plots
return None