ENH: added parachute radius

Author: ArthurJWH

rocketpy/rocket/parachute.py

@@ -103,6 +103,7 @@ def __init__(
         lag=0,
         noise=(0, 0, 0),
         parachute_radius=1.5,
+        parachute_height=None,
         porosity=0.0432,
     ):
         """Initializes Parachute class.
@@ -156,6 +157,15 @@ def __init__(
             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 Pa.
+        parachute_radius : float, optional
+            Radius of the inflated parachute in meters. Default value is 1.5.
+            Units are in meters.
+        parachute_height : float, optional
+            Height of the inflated parachute in meters.
+            Default value is the radius parachute. Units are in meters.
+        porosity : float, optional
+            Porosity of the parachute material, which is a measure of how much air can
+            pass through the parachute material. Default value is 0.0432.
         """
         self.name = name
         self.cd_s = cd_s
@@ -164,6 +174,9 @@ def __init__(
         self.lag = lag
         self.noise = noise
         self.parachute_radius = parachute_radius
+        if parachute_height is None:
+            parachute_height = parachute_radius
+        self.parachute_height = parachute_height
         self.porosity = porosity
         self.noise_signal = [[-1e-6, np.random.normal(noise[0], noise[1])]]
         self.noisy_pressure_signal = []
@@ -269,6 +282,7 @@ def to_dict(self, include_outputs=False):
             "lag": self.lag,
             "noise": self.noise,
             "parachute_radius": self.parachute_radius,
+            "parachute_height": self.parachute_height,
             "porosity": self.porosity,
         }
 
@@ -296,8 +310,9 @@ def from_dict(cls, data):
             sampling_rate=data["sampling_rate"],
             lag=data["lag"],
             noise=data["noise"],
-            parachute_radius=data["parachute_radius"],
-            porosity=data["porosity"],
+            parachute_radius=data.get("parachute_radius", 1.5),
+            parachute_height=data.get("parachute_height", None),
+            porosity=data.get("porosity", 0.0432),
         )
 
         return parachute

rocketpy/simulation/flight.py

@@ -771,6 +771,9 @@ def __simulate(self, verbose):
                             lambda self, parachute_radius=parachute.radius: setattr(
                                 self, "parachute_radius", parachute_radius
                             ),
+                            lambda self, parachute_height=parachute.height: setattr(
+                                self, "parachute_height", parachute_height
+                            ),
                             lambda self, parachute_porosity=parachute.porosity: setattr(
                                 self, "parachute_porosity", parachute_porosity
                             ),
@@ -1023,6 +1026,9 @@ def __simulate(self, verbose):
                                             lambda self, parachute_radius=parachute.radius: setattr(
                                                 self, "parachute_radius", parachute_radius
                                             ),
+                                            lambda self, parachute_height=parachute.height: setattr(
+                                                self, "parachute_height", parachute_height
+                                            ),
                                             lambda self, parachute_porosity=parachute.porosity: setattr(
                                                 self, "parachute_porosity", parachute_porosity
                                             ),
@@ -1973,7 +1979,8 @@ def u_dot_parachute(self, t, u, post_processing=False):
 
         # Get Parachute data
         cd_s = self.parachute_cd_s
-        R = self.parachute_radius
+        parachute_radius = self.parachute_radius
+        parachute_height = self.parachute_height
         porosity = self.parachute_porosity
 
 
@@ -1992,7 +1999,7 @@ def u_dot_parachute(self, t, u, post_processing=False):
         # tf = 8 * nominal diameter / velocity at line stretch
 
         # Calculate added mass
-        ma = ka * rho * (4 / 3) * np.pi * R**3 # ma = ka * rho * (4 / 3) * np.pi * R**2 * height
+        ma = ka * rho * (4 / 3) * np.pi * parachute_radius**2 * parachute_height
 
         # Calculate freestream speed
         freestream_x = vx - wind_velocity_x
@@ -2001,14 +2008,14 @@ def u_dot_parachute(self, t, u, post_processing=False):
         free_stream_speed = (freestream_x**2 + freestream_y**2 + freestream_z**2) ** 0.5
 
         # Determine drag force
-        pseudo_drag = -0.5 * rho * cd_s * free_stream_speed # * Area
+        pseudo_drag = -0.5 * rho * cd_s * free_stream_speed
         # pseudo_drag = pseudo_drag - ka * rho * 4 * np.pi * (R**2) * Rdot
         Dx = pseudo_drag * freestream_x # add eta efficiency for wake
         Dy = pseudo_drag * freestream_y
         Dz = pseudo_drag * freestream_z
         ax = Dx / (mp + ma)
         ay = Dy / (mp + ma)
-        az = (Dz - 9.8 * mp) / (mp + ma)
+        az = (Dz - mp * self.env.gravity.get_value_opt(z)) / (mp + ma)
 
         if post_processing:
             self.__post_processed_variables.append(