ENH: Moving initial volume calculation to Parachute class

Added a new parameter to parachute class

Author: ArthurJWH

rocketpy/rocket/parachute.py

@@ -1,5 +1,6 @@
 from inspect import signature
 
+import math
 import numpy as np
 
 from rocketpy.tools import from_hex_decode, to_hex_encode
@@ -98,6 +99,9 @@ class Parachute:
     Parachute.height : float, None
         Length of the unique semi-axis (height) of the inflated hemispheroid
         parachute in meters.
+    Parachute.initial_radius : float, None
+        Initial radius of the parachute on deployment in meters. Used to model the
+        parachute inflation.
     Parachute.porosity : float
         Geometric porosity of the canopy (ratio of open area to total canopy area),
         in [0, 1]. Affects only the added-mass scaling during descent; it does
@@ -118,6 +122,7 @@ def __init__(
         noise=(0, 0, 0),
         radius=1.5,
         height=None,
+        initial_radius=None,
         porosity=0.0432,
     ):
         """Initializes Parachute class.
@@ -179,6 +184,9 @@ def __init__(
             Length of the unique semi-axis (height) of the inflated hemispheroid
             parachute. Default value is the radius of the parachute.
             Units are in meters.
+        initial_radius : float, optional
+            Initial radius of the parachute on deployment in meters. Used to model the
+            parachute inflation. Default value is the parachute radius (no inflation).
         porosity : float, optional
             Geometric porosity of the canopy (ratio of open area to total canopy area),
             in [0, 1]. Affects only the added-mass scaling during descent; it does
@@ -202,6 +210,13 @@ def __init__(
         self.noise_signal_function = Function(0)
         self.radius = radius
         self.height = height or radius
+        self.initial_radius = initial_radius or radius
+        self.initial_volume = (
+            (4 / 3)
+            * math.pi
+            * (self.parachute_height / self.parachute_radius)
+            * (min(self.parachute_radius, self.rocket.radius)) ** 3
+        )
         self.porosity = porosity
         self.added_mass_coefficient = 1.068 * (
             1
@@ -308,6 +323,7 @@ def to_dict(self, **kwargs):
             "noise": self.noise,
             "radius": self.radius,
             "height": self.height,
+            "initial_radius": self.initial_radius,
             "porosity": self.porosity,
         }
 
@@ -341,6 +357,7 @@ def from_dict(cls, data):
             noise=data["noise"],
             radius=data.get("radius", 1.5),
             height=data.get("height", None),
+            initial_radius=data.get("initial_radius", None),
             porosity=data.get("porosity", 0.0432),
         )
 

rocketpy/rocket/rocket.py

@@ -1485,6 +1485,7 @@ def add_parachute(
         noise=(0, 0, 0),
         radius=1.5,
         height=None,
+        initial_radius=None,
         porosity=0.0432,
     ):
         """Creates a new parachute, storing its parameters such as
@@ -1552,6 +1553,9 @@ def add_parachute(
             Length of the unique semi-axis (height) of the inflated hemispheroid
             parachute. Default value is the radius of the parachute.
             Units are in meters.
+        initial_radius : float, optional
+            Initial radius of the parachute on deployment in meters. Used to model the
+            parachute inflation. Default value is the parachute radius (no inflation).
         porosity : float, optional
             Geometric porosity of the canopy (ratio of open area to total canopy area),
             in [0, 1]. Affects only the added-mass scaling during descent; it does
@@ -1567,15 +1571,16 @@ def add_parachute(
             Flight simulation.
         """
         parachute = Parachute(
-            name,
-            cd_s,
-            trigger,
-            sampling_rate,
-            lag,
-            noise,
-            radius,
-            height,
-            porosity,
+            name=name,
+            cd_s=cd_s,
+            trigger=trigger,
+            sampling_rate=sampling_rate,
+            lag=lag,
+            noise=noise,
+            radius=radius,
+            height=height,
+            initial_radius=initial_radius,
+            porosity=porosity,
         )
         self.parachutes.append(parachute)
         return self.parachutes[-1]

rocketpy/simulation/flight.py

@@ -765,19 +765,11 @@ def __simulate(self, verbose):
                                 "parachute_added_mass_coefficient",
                                 added_mass_coefficient,
                             ),
-                            lambda self: setattr(
+                            lambda self,
+                            initial_volume=parachute.initial_volume: setattr(
                                 self,
                                 "parachute_volume",
-                                (4 / 3)
-                                * math.pi
-                                * (self.parachute_height / self.parachute_radius)
-                                * (
-                                    min(
-                                        self.parachute_radius,
-                                        self.rocket.radius,
-                                    )
-                                )
-                                ** 3,
+                                initial_volume,
                             ),
                             lambda self: delattr(self, "__t0")
                             if hasattr(self, "__t0")
@@ -1004,19 +996,10 @@ def __check_and_handle_parachute_triggers(
                     "parachute_added_mass_coefficient",
                     added_mass_coefficient,
                 ),
-                lambda self: setattr(
+                lambda self, initial_volume=parachute.initial_volume: setattr(
                     self,
                     "parachute_volume",
-                    (4 / 3)
-                    * math.pi
-                    * (self.parachute_height / self.parachute_radius)
-                    * (
-                        min(
-                            self.parachute_radius,
-                            self.rocket.radius,
-                        )
-                    )
-                    ** 3,
+                    initial_volume,
                 ),
                 lambda self: delattr(self, "__t0") if hasattr(self, "__t0") else None,
             ]
@@ -2742,9 +2725,12 @@ def u_dot_parachute(self, t, u, post_processing=False):
 
         # Initialize parachute geometrical parameters
         inflated_radius = (
-            (3 * self.parachute_volume * self.parachute_radius) / (4 * math.pi * self.parachute_height)
+            (3 * self.parachute_volume * self.parachute_radius)
+            / (4 * math.pi * self.parachute_height)
         ) ** (1 / 3)
-        inflated_height = inflated_radius * self.parachute_height / self.parachute_radius
+        inflated_height = (
+            inflated_radius * self.parachute_height / self.parachute_radius
+        )
 
         # Calculate the surface area of the parachute
         if self.parachute_radius > self.parachute_height: