ENH: implement power series nose cones (#475)

CHANGELOG.md

@@ -55,6 +55,7 @@ You can install this version by running `pip install rocketpy==1.3.0`
 
 - ENH: CP and Thrust Eccentricity Effects Generate Roll Moment [#617](https://github.com/RocketPy-Team/RocketPy/pull/617)
 - ENH: Add Prandtl-Gauss transformation to NoseCone and Tail [#609](https://github.com/RocketPy-Team/RocketPy/pull/609)
+- ENH: Implement power series nose cones[#603](https://github.com/RocketPy-Team/RocketPy/pull/603)
 - DOC: Adds prometheus data, Spaceport America 2022 [#601](https://github.com/RocketPy-Team/RocketPy/pull/601)
 - ENH: Pre-calculate attributes in Rocket class [#595](https://github.com/RocketPy-Team/RocketPy/pull/595)
 - ENH: Complex step differentiation [#594](https://github.com/RocketPy-Team/RocketPy/pull/594)

rocketpy/rocket/aero_surface.py

@@ -132,14 +132,15 @@ class NoseCone(AeroSurface):
         Nose cone length. Has units of length and must be given in meters.
     NoseCone.kind : string
         Nose cone kind. Can be "conical", "ogive", "elliptical", "tangent",
-        "von karman", "parabolic" or "lvhaack".
+        "von karman", "parabolic", "powerseries" or "lvhaack".
     NoseCone.bluffness : float
         Ratio between the radius of the circle on the tip of the ogive and the
         radius of the base of the ogive. Currently only used for the nose cone's
         drawing. Must be between 0 and 1. Default is None, which means that the
         nose cone will not have a sphere on the tip. If a value is given, the
         nose cone's length will be slightly reduced because of the addition of
-        the sphere.
+        the sphere. Must be None or 0 if a "powerseries" nose cone kind is
+        specified.
     NoseCone.rocket_radius : float
         The reference rocket radius used for lift coefficient normalization,
         in meters.
@@ -151,6 +152,10 @@ class NoseCone(AeroSurface):
         rocket radius is assumed as 1, meaning that the nose cone has the same
         radius as the rocket. If base radius is given, the ratio between base
         radius and rocket radius is calculated and used for lift calculation.
+    NoseCone.power : float
+        Factor that controls the bluntness of the shape for a power series
+        nose cone. Must be between 0 and 1. It is ignored when other nose
+        cone types are used.
     NoseCone.name : string
         Nose cone name. Has no impact in simulation, as it is only used to
         display data in a more organized matter.
@@ -187,6 +192,7 @@ def __init__(
         base_radius=None,
         bluffness=None,
         rocket_radius=None,
+        power=None,
         name="Nose Cone",
     ):
         """Initializes the nose cone. It is used to define the nose cone
@@ -198,7 +204,9 @@ def __init__(
             Nose cone length. Has units of length and must be given in meters.
         kind : string
             Nose cone kind. Can be "conical", "ogive", "elliptical", "tangent",
-            "von karman", "parabolic" or "lvhaack".
+            "von karman", "parabolic", "powerseries" or "lvhaack". If
+            "powerseries" is used, the "power" argument must be assigned to a
+            value between 0 and 1.
         base_radius : float, optional
             Nose cone base radius. Has units of length and must be given in
             meters. If not given, the ratio between ``base_radius`` and
@@ -209,11 +217,16 @@ def __init__(
             nose cone's drawing. Must be between 0 and 1. Default is None, which
             means that the nose cone will not have a sphere on the tip. If a
             value is given, the nose cone's length will be reduced to account
-            for the addition of the sphere at the tip.
+            for the addition of the sphere at the tip. Must be None or 0 if a
+            "powerseries" nose cone kind is specified.
         rocket_radius : int, float, optional
             The reference rocket radius used for lift coefficient normalization.
             If not given, the ratio between ``base_radius`` and
             ``rocket_radius`` will be assumed as 1.
+        power : float, optional
+            Factor that controls the bluntness of the shape for a power series
+            nose cone. Must be between 0 and 1. It is ignored when other nose
+            cone types are used.
         name : str, optional
             Nose cone name. Has no impact in simulation, as it is only used to
             display data in a more organized matter.
@@ -233,6 +246,23 @@ def __init__(
                     f"Bluffness ratio of {bluffness} is out of range. It must be between 0 and 1."
                 )
         self._bluffness = bluffness
+        if kind == "powerseries":
+            # Checks if bluffness is not being used
+            if (self.bluffness is not None) and (self.bluffness != 0):
+                raise ValueError(
+                    "Parameter 'bluffness' must be None or 0 when using a nose cone kind 'powerseries'."
+                )
+
+            if power is None:
+                raise ValueError(
+                    "Parameter 'power' cannot be None when using a nose cone kind 'powerseries'."
+                )
+
+            if power > 1 or power <= 0:
+                raise ValueError(
+                    f"Power value of {power} is out of range. It must be between 0 and 1."
+                )
+        self._power = power
         self.kind = kind
 
         self.evaluate_lift_coefficient()
@@ -275,6 +305,22 @@ def length(self, value):
         self.evaluate_center_of_pressure()
         self.evaluate_nose_shape()
 
+    @property
+    def power(self):
+        return self._power
+
+    @power.setter
+    def power(self, value):
+        if value is not None:
+            if value > 1 or value <= 0:
+                raise ValueError(
+                    f"Power value of {value} is out of range. It must be between 0 and 1."
+                )
+        self._power = value
+        self.evaluate_k()
+        self.evaluate_center_of_pressure()
+        self.evaluate_nose_shape()
+
     @property
     def kind(self):
         return self._kind
@@ -336,7 +382,11 @@ def kind(self, value):
                 lambda x: self.base_radius
                 * ((2 * x / self.length - (x / self.length) ** 2) / (2 - 1))
             )
-
+        elif value == "powerseries":
+            self.k = (2 * self.power) / ((2 * self.power) + 1)
+            self.y_nosecone = Function(
+                lambda x: self.base_radius * np.power(x / self.length, self.power)
+            )
         else:
             raise ValueError(
                 f"Nose Cone kind '{self.kind}' not found, "
@@ -347,6 +397,7 @@ def kind(self, value):
                 + '\n\t"tangent"'
                 + '\n\t"vonkarman"'
                 + '\n\t"elliptical"'
+                + '\n\t"powerseries"'
                 + '\n\t"parabolic"\n'
             )
 
@@ -360,6 +411,13 @@ def bluffness(self):
 
     @bluffness.setter
     def bluffness(self, value):
+        # prevents from setting bluffness on "powerseries" nose cones
+        if self.kind == "powerseries":
+            # Checks if bluffness is not being used
+            if (value is not None) and (value != 0):
+                raise ValueError(
+                    "Parameter 'bluffness' must be None or 0 when using a nose cone kind 'powerseries'."
+                )
         if value is not None:
             if value > 1 or value < 0:
                 raise ValueError(
@@ -507,6 +565,18 @@ def evaluate_lift_coefficient(self):
         )
         return None
 
+    def evaluate_k(self):
+        """Updates the self.k attribute used to compute the center of
+        pressure when using "powerseries" nose cones.
+
+        Returns
+        -------
+        None
+        """
+        if self.kind == "powerseries":
+            self.k = (2 * self.power) / ((2 * self.power) + 1)
+        return None
+
     def evaluate_center_of_pressure(self):
         """Calculates and returns the center of pressure of the nose cone in
         local coordinates. The center of pressure position is saved and stored

rocketpy/rocket/rocket.py

@@ -1024,7 +1024,14 @@ def add_tail(
         return tail
 
     def add_nose(
-        self, length, kind, position, bluffness=0, name="Nose Cone", base_radius=None
+        self,
+        length,
+        kind,
+        position,
+        bluffness=0,
+        power=None,
+        name="Nose Cone",
+        base_radius=None,
     ):
         """Creates a nose cone, storing its parameters as part of the
         aerodynamic_surfaces list. Its parameters are the axial position
@@ -1038,14 +1045,17 @@ def add_nose(
             Nose cone length or height in meters. Must be a positive
             value.
         kind : string
-            Nose cone type. Von Karman, conical, ogive, and lvhaack are
-            supported.
+            Nose cone type. Von Karman, conical, ogive, lvhaack and
+            powerseries are supported.
         position : int, float
             Nose cone tip coordinate relative to the rocket's coordinate system.
             See `Rocket.coordinate_system_orientation` for more information.
         bluffness : float, optional
             Ratio between the radius of the circle on the tip of the ogive and
             the radius of the base of the ogive.
+        power : float, optional
+            Factor that controls the bluntness of the nose cone shape when
+            using a 'powerseries' nose cone kind.
         name : string
             Nose cone name. Default is "Nose Cone".
         base_radius : int, float, optional
@@ -1067,6 +1077,7 @@ def add_nose(
             base_radius=base_radius or self.radius,
             rocket_radius=base_radius or self.radius,
             bluffness=bluffness,
+            power=power,
             name=name,
         )
         self.add_surfaces(nose, position)

tests/unit/test_aero_surfaces.py

@@ -0,0 +1,72 @@
+import pytest
+from rocketpy import NoseCone
+
+NOSECONE_LENGTH = 1
+NOSECONE_BASE_RADIUS = 1
+NOSECONE_ROCKET_RADIUS = 1
+NOSECONE_KIND = "powerseries"
+
+
+@pytest.mark.parametrize(
+    "power, bluffness",
+    [
+        (0, None),
+        (None, None),
+        (0, 0.5),
+        (None, 0.5),
+        (0.5, 0.1),
+        (-1, None),
+        (10, None),
+    ],
+)
+def test_powerseries_nosecones_invalid_inputs(power, bluffness):
+    """Checks if Exceptions are raised correctly when invalid inputs
+    are passed for the creation of power series nose cones
+    """
+
+    # Tests for invalid power parameter
+    with pytest.raises(ValueError):
+        NoseCone(
+            length=NOSECONE_LENGTH,
+            base_radius=NOSECONE_BASE_RADIUS,
+            rocket_radius=NOSECONE_ROCKET_RADIUS,
+            kind=NOSECONE_KIND,
+            power=power,
+            bluffness=bluffness,
+        )
+
+
+@pytest.mark.parametrize(
+    "power, invalid_power, new_power",
+    [
+        (0.1, -1, 0.05),
+        (0.5, 0, 0.7),
+        (0.9, 10, 1),
+    ],
+)
+def test_powerseries_nosecones_setters(power, invalid_power, new_power):
+    """Checks if Exceptions are raised correctly when the 'power' or
+    'bluffness' attributes are changed to invalid values. Also checks
+    that modifying the 'power' attribute also modifies the 'k' attribute.
+    """
+    test_nosecone = NoseCone(
+        length=NOSECONE_LENGTH,
+        base_radius=NOSECONE_BASE_RADIUS,
+        rocket_radius=NOSECONE_ROCKET_RADIUS,
+        kind=NOSECONE_KIND,
+        power=power,
+        bluffness=None,
+    )
+    # Test invalid power value modification
+    with pytest.raises(ValueError):
+        test_nosecone.power = invalid_power
+
+    # Test invalid bluffness value modification
+    with pytest.raises(ValueError):
+        test_nosecone.bluffness = 0.5
+
+    # Checks if self.k was updated correctly
+    test_nosecone.power = new_power
+    expected_k = (2 * new_power) / ((2 * new_power) + 1)
+
+    assert pytest.approx(test_nosecone.k) == expected_k