ENH: Spherical Caps Included in Total Length

rocketpy/motors/tank_geometry.py

@@ -369,28 +369,47 @@ def __init__(self, radius, height, spherical_caps=False, geometry_dict=dict()):
         height : float
             Height of the cylindrical tank, in meters.
         spherical_caps : bool, optional
-            If True, the tank will have spherical caps. The default is False.
+            If True, the tank will have spherical caps at the top and bottom
+            with the same radius as the cylindrical part. If False, the tank
+            will have flat caps at the top and bottom. Defaults to False.
         geometry_dict : dict, optional
             Dictionary containing the geometry of the tank. See TankGeometry.
         """
         super().__init__(geometry_dict)
+        self.height = height
         self.has_caps = False
-        self.add_geometry((-height / 2, height / 2), radius)
-        self.add_spherical_caps() if spherical_caps else None
+        if spherical_caps:
+            self.add_geometry((-height / 2 + radius, height / 2 - radius), radius)
+            self.add_spherical_caps()
+        else:
+            self.add_geometry((-height / 2, height / 2), radius)
 
     def add_spherical_caps(self):
         """
         Adds spherical caps to the tank. The caps are added at the bottom
-        and at the top of the tank. If the tank already has caps, it raises a
-        ValueError.
-        """
+        and at the top of the tank with the same radius as the cylindrical
+        part. The height is not modified, meaning that the total volume of
+        the tank will decrease.
+        """
+        print(
+            "Warning: Adding spherical caps to the tank will not modify the "
+            + f"total height of the tank {self.height} m. "
+            + "Its cylindrical portion height will be reduced to "
+            + f"{self.height - 2*self.radius(0)} m."
+        )
+
         if not self.has_caps:
             radius = self.radius(0)
-            height = self.total_height
-            bottom_cap_range = (-height / 2 - radius, -height / 2)
-            upper_cap_range = (height / 2, height / 2 + radius)
-            bottom_cap_radius = lambda h: (radius**2 - (h + height / 2) ** 2) ** 0.5
-            upper_cap_radius = lambda h: (radius**2 - (h - height / 2) ** 2) ** 0.5
+            height = self.height
+            bottom_cap_range = (-height / 2, -height / 2 + radius)
+            upper_cap_range = (height / 2 - radius, height / 2)
+
+            def bottom_cap_radius(h):
+                return abs(radius**2 - (h + (height / 2 - radius)) ** 2) ** 0.5
+
+            def upper_cap_radius(h):
+                return abs(radius**2 - (h - (height / 2 - radius)) ** 2) ** 0.5
+
             self.add_geometry(bottom_cap_range, bottom_cap_radius)
             self.add_geometry(upper_cap_range, upper_cap_radius)
             self.has_caps = True

tests/conftest.py

@@ -370,7 +370,7 @@ def pressurant_tank(pressurant_fluid):
     rocketpy.MassBasedTank
         An object of the CylindricalTank class.
     """
-    geometry = CylindricalTank(0.135 / 2, 0.846, spherical_caps=True)
+    geometry = CylindricalTank(0.135 / 2, 0.981, spherical_caps=True)
     pressurant_tank = MassBasedTank(
         name="Pressure Tank",
         geometry=geometry,
@@ -401,7 +401,7 @@ def fuel_tank(fuel_fluid, fuel_pressurant):
     -------
     rocketpy.UllageBasedTank
     """
-    geometry = CylindricalTank(0.0744, 0.658, spherical_caps=True)
+    geometry = CylindricalTank(0.0744, 0.8068, spherical_caps=True)
     ullage = (
         -Function("data/SEBLM/test124_Propane_Volume.csv") * 1e-3
         + geometry.total_volume
@@ -435,7 +435,7 @@ def oxidizer_tank(oxidizer_fluid, oxidizer_pressurant):
     -------
     rocketpy.UllageBasedTank
     """
-    geometry = CylindricalTank(0.0744, 0.658, spherical_caps=True)
+    geometry = CylindricalTank(0.0744, 0.8068, spherical_caps=True)
     ullage = (
         -Function("data/SEBLM/test124_Lox_Volume.csv") * 1e-3 + geometry.total_volume
     )

tests/test_tank.py

@@ -13,9 +13,9 @@
     TankGeometry,
 )
 
-pressurant_params = (0.135 / 2, 0.846)
-fuel_params = (0.0744, 0.658)
-oxidizer_params = (0.0744, 0.658)
+pressurant_params = (0.135 / 2, 0.981)
+fuel_params = (0.0744, 0.8068)
+oxidizer_params = (0.0744, 0.8068)
 
 parametrize_fixtures = pytest.mark.parametrize(
     "params",
@@ -33,7 +33,7 @@ def test_tank_bounds(params, request):
     tank, (expected_radius, expected_height) = params
     tank = request.getfixturevalue(tank)
 
-    expected_total_height = expected_height + 2 * expected_radius
+    expected_total_height = expected_height
 
     assert tank.geometry.radius(0) == pytest.approx(expected_radius, abs=1e-6)
     assert tank.geometry.total_height == pytest.approx(expected_total_height, abs=1e-6)
@@ -45,8 +45,8 @@ def test_tank_coordinates(params, request):
     tank, (radius, height) = params
     tank = request.getfixturevalue(tank)
 
-    expected_bottom = -(height / 2 + radius)
-    expected_top = height / 2 + radius
+    expected_bottom = -height / 2
+    expected_top = height / 2
 
     assert tank.geometry.bottom == pytest.approx(expected_bottom, abs=1e-6)
     assert tank.geometry.top == pytest.approx(expected_top, abs=1e-6)
@@ -60,7 +60,9 @@ def test_tank_total_volume(params, request):
     tank, (radius, height) = params
     tank = request.getfixturevalue(tank)
 
-    expected_total_volume = np.pi * radius**2 * height + 4 / 3 * np.pi * radius**3
+    expected_total_volume = (
+        np.pi * radius**2 * (height - 2 * radius) + 4 / 3 * np.pi * radius**3
+    )
 
     assert tank.geometry.total_volume == pytest.approx(expected_total_volume, abs=1e-6)
 
@@ -73,9 +75,9 @@ def test_tank_volume(params, request):
     tank, (radius, height) = params
     tank = request.getfixturevalue(tank)
 
-    total_height = height + 2 * radius
-    bottom = -(height / 2 + radius)
-    top = height / 2 + radius
+    total_height = height
+    bottom = -height / 2
+    top = height / 2
 
     expected_volume = tank_volume_function(radius, total_height, bottom)
 
@@ -91,8 +93,8 @@ def test_tank_centroid(params, request):
     tank, (radius, height) = params
     tank = request.getfixturevalue(tank)
 
-    total_height = height + 2 * radius
-    bottom = -(height / 2 + radius)
+    total_height = height
+    bottom = -height / 2
 
     expected_centroid = tank_centroid_function(radius, total_height, bottom)
 
@@ -111,8 +113,8 @@ def test_tank_inertia(params, request):
     tank, (radius, height) = params
     tank = request.getfixturevalue(tank)
 
-    total_height = height + 2 * radius
-    bottom = -(height / 2 + radius)
+    total_height = height
+    bottom = -height / 2
 
     expected_inertia = tank_inertia_function(radius, total_height, bottom)