ENH: Implement only_radial_burn feature for SolidMotor and HybridMotor classes

Co-authored-by: Gui-FernandesBR <[email protected]>

Author: Copilot

CHANGELOG.md

@@ -32,6 +32,7 @@ Attention: The newest changes should be on top -->
 
 ### Added
 
+- ENH: Enable only radial burning [#815](https://github.com/RocketPy-Team/RocketPy/pull/815)
 
 ### Changed
 

rocketpy/motors/hybrid_motor.py

@@ -216,6 +216,7 @@ def __init__(  # pylint: disable=too-many-arguments
         interpolation_method="linear",
         coordinate_system_orientation="nozzle_to_combustion_chamber",
         reference_pressure=None,
+        only_radial_burn=False,
     ):
         """Initialize Motor class, process thrust curve and geometrical
         parameters and store results.
@@ -313,6 +314,11 @@ class Function. Thrust units are Newtons.
             "nozzle_to_combustion_chamber".
         reference_pressure : int, float, optional
             Atmospheric pressure in Pa at which the thrust data was recorded.
+        only_radial_burn : boolean, optional
+            If True, inhibits the grain from burning axially, only computing
+            radial burn. If False, allows the grain to also burn
+            axially. May be useful for axially inhibited grains or hybrid motors.
+            Default is False.
 
         Returns
         -------
@@ -364,6 +370,7 @@ class Function. Thrust units are Newtons.
             interpolation_method,
             coordinate_system_orientation,
             reference_pressure,
+            only_radial_burn,
         )
 
         self.positioned_tanks = self.liquid.positioned_tanks

rocketpy/motors/solid_motor.py

@@ -217,6 +217,7 @@ def __init__(
         interpolation_method="linear",
         coordinate_system_orientation="nozzle_to_combustion_chamber",
         reference_pressure=None,
+        only_radial_burn=False,
     ):
         """Initialize Motor class, process thrust curve and geometrical
         parameters and store results.
@@ -314,6 +315,11 @@ class Function. Thrust units are Newtons.
             "nozzle_to_combustion_chamber".
         reference_pressure : int, float, optional
             Atmospheric pressure in Pa at which the thrust data was recorded.
+        only_radial_burn : boolean, optional
+            If True, inhibits the grain from burning axially, only computing
+            radial burn. If False, allows the grain to also burn
+            axially. May be useful for axially inhibited grains or hybrid motors.
+            Default is False.
 
         Returns
         -------
@@ -353,6 +359,9 @@ class Function. Thrust units are Newtons.
         )
         self.grain_initial_mass = self.grain_density * self.grain_initial_volume
 
+        # Burn surface definition
+        self.only_radial_burn = only_radial_burn
+
         self.evaluate_geometry()
 
         # Initialize plots and prints object
@@ -500,17 +509,25 @@ def geometry_dot(t, y):
 
             # Compute state vector derivative
             grain_inner_radius, grain_height = y
-            burn_area = (
-                2
-                * np.pi
-                * (
-                    grain_outer_radius**2
-                    - grain_inner_radius**2
-                    + grain_inner_radius * grain_height
+            if self.only_radial_burn:
+                burn_area = 2 * np.pi * (grain_inner_radius * grain_height)
+
+                grain_inner_radius_derivative = -volume_diff / burn_area
+                grain_height_derivative = 0  # Set to zero to disable axial burning
+
+            else:
+                burn_area = (
+                    2
+                    * np.pi
+                    * (
+                        grain_outer_radius**2
+                        - grain_inner_radius**2
+                        + grain_inner_radius * grain_height
+                    )
                 )
-            )
-            grain_inner_radius_derivative = -volume_diff / burn_area
-            grain_height_derivative = -2 * grain_inner_radius_derivative
+
+                grain_inner_radius_derivative = -volume_diff / burn_area
+                grain_height_derivative = -2 * grain_inner_radius_derivative
 
             return [grain_inner_radius_derivative, grain_height_derivative]
 
@@ -521,32 +538,56 @@ def geometry_jacobian(t, y):
 
             # Compute jacobian
             grain_inner_radius, grain_height = y
-            factor = volume_diff / (
-                2
-                * np.pi
-                * (
-                    grain_outer_radius**2
-                    - grain_inner_radius**2
-                    + grain_inner_radius * grain_height
+            if self.only_radial_burn:
+                factor = volume_diff / (
+                    2 * np.pi * (grain_inner_radius * grain_height) ** 2
                 )
-                ** 2
-            )
-            inner_radius_derivative_wrt_inner_radius = factor * (
-                grain_height - 2 * grain_inner_radius
-            )
-            inner_radius_derivative_wrt_height = factor * grain_inner_radius
-            height_derivative_wrt_inner_radius = (
-                -2 * inner_radius_derivative_wrt_inner_radius
-            )
-            height_derivative_wrt_height = -2 * inner_radius_derivative_wrt_height
 
-            return [
-                [
-                    inner_radius_derivative_wrt_inner_radius,
-                    inner_radius_derivative_wrt_height,
-                ],
-                [height_derivative_wrt_inner_radius, height_derivative_wrt_height],
-            ]
+                inner_radius_derivative_wrt_inner_radius = factor * (
+                    grain_height - 2 * grain_inner_radius
+                )
+                inner_radius_derivative_wrt_height = 0
+                height_derivative_wrt_inner_radius = 0
+                height_derivative_wrt_height = 0
+                # Height is constant when only radial burning is enabled, 
+                # so all derivatives with respect to height are zero
+
+                return [
+                    [
+                        inner_radius_derivative_wrt_inner_radius,
+                        inner_radius_derivative_wrt_height,
+                    ],
+                    [height_derivative_wrt_inner_radius, height_derivative_wrt_height],
+                ]
+
+            else:
+                factor = volume_diff / (
+                    2
+                    * np.pi
+                    * (
+                        grain_outer_radius**2
+                        - grain_inner_radius**2
+                        + grain_inner_radius * grain_height
+                    )
+                    ** 2
+                )
+
+                inner_radius_derivative_wrt_inner_radius = factor * (
+                    grain_height - 2 * grain_inner_radius
+                )
+                inner_radius_derivative_wrt_height = factor * grain_inner_radius
+                height_derivative_wrt_inner_radius = (
+                    -2 * inner_radius_derivative_wrt_inner_radius
+                )
+                height_derivative_wrt_height = -2 * inner_radius_derivative_wrt_height
+
+                return [
+                    [
+                        inner_radius_derivative_wrt_inner_radius,
+                        inner_radius_derivative_wrt_height,
+                    ],
+                    [height_derivative_wrt_inner_radius, height_derivative_wrt_height],
+                ]
 
         def terminate_burn(t, y):  # pylint: disable=unused-argument
             end_function = (self.grain_outer_radius - y[0]) * y[1]
@@ -597,16 +638,24 @@ def burn_area(self):
         burn_area : Function
             Function representing the burn area progression with the time.
         """
-        burn_area = (
-            2
-            * np.pi
-            * (
-                self.grain_outer_radius**2
-                - self.grain_inner_radius**2
-                + self.grain_inner_radius * self.grain_height
+        if self.only_radial_burn:
+            burn_area = (
+                2
+                * np.pi
+                * (self.grain_inner_radius * self.grain_height)
+                * self.grain_number
+            )
+        else:
+            burn_area = (
+                2
+                * np.pi
+                * (
+                    self.grain_outer_radius**2
+                    - self.grain_inner_radius**2
+                    + self.grain_inner_radius * self.grain_height
+                )
+                * self.grain_number
             )
-            * self.grain_number
-        )
         return burn_area
 
     @funcify_method("Time (s)", "burn rate (m/s)")
@@ -778,6 +827,7 @@ def to_dict(self, include_outputs=False):
                 "grain_initial_height": self.grain_initial_height,
                 "grain_separation": self.grain_separation,
                 "grains_center_of_mass_position": self.grains_center_of_mass_position,
+                "only_radial_burn": self.only_radial_burn,
             }
         )
 
@@ -822,4 +872,5 @@ def from_dict(cls, data):
             interpolation_method=data["interpolate"],
             coordinate_system_orientation=data["coordinate_system_orientation"],
             reference_pressure=data.get("reference_pressure"),
+            only_radial_burn=data.get("only_radial_burn", False),
         )

tests/integration/test_solidmotor.py

@@ -0,0 +1,16 @@
+from unittest.mock import patch
+
+
+@patch("matplotlib.pyplot.show")
+def test_solid_motor_info(mock_show, cesaroni_m1670):
+    """Tests the SolidMotor.all_info() method.
+
+    Parameters
+    ----------
+    mock_show : mock
+        Mock of the matplotlib.pyplot.show function.
+    cesaroni_m1670 : rocketpy.SolidMotor
+        The SolidMotor object to be used in the tests.
+    """
+    assert cesaroni_m1670.info() is None
+    assert cesaroni_m1670.all_info() is None

tests/unit/test_hybridmotor.py

@@ -170,9 +170,49 @@ def test_hybrid_motor_inertia(hybrid_motor, spherical_oxidizer_tank):
         + DRY_MASS * (-hybrid_motor.center_of_mass + CENTER_OF_DRY_MASS) ** 2
     )
 
-    for t in np.linspace(0, 100, 100):
+    for t in np.linspace(0, BURN_TIME, 100):
         assert pytest.approx(hybrid_motor.propellant_I_11(t)) == propellant_inertia(t)
         assert pytest.approx(hybrid_motor.I_11(t)) == inertia(t)
 
         # Assert cylindrical symmetry
         assert pytest.approx(hybrid_motor.propellant_I_22(t)) == propellant_inertia(t)
+
+
+def test_hybrid_motor_only_radial_burn_behavior(hybrid_motor):
+    """
+    Test if only_radial_burn flag in HybridMotor propagates to its SolidMotor
+    and affects burn_area calculation.
+    """
+    motor = hybrid_motor
+
+    # Activates the radial burning
+    motor.solid.only_radial_burn = True
+    assert motor.solid.only_radial_burn is True
+
+    # Calculate the expected initial area using the motor's burn_area method
+    burn_area_radial = motor.solid.burn_area(0)
+    
+    # Manually calculate expected radial burn area for verification
+    expected_radial_area = (
+        2
+        * np.pi
+        * (motor.solid.grain_inner_radius(0) * motor.solid.grain_height(0))
+        * motor.solid.grain_number
+    )
+
+    assert np.isclose(burn_area_radial, expected_radial_area, atol=1e-12)
+
+    # Deactivate the radial burning and recalculate the geometry
+    motor.solid.only_radial_burn = False
+    motor.solid.evaluate_geometry()
+    assert motor.solid.only_radial_burn is False
+
+    # In this case the burning area also considers the bases of the grain  
+    inner_radius = motor.solid.grain_inner_radius(0)
+    outer_radius = motor.solid.grain_outer_radius
+    burn_area_total = (
+        expected_radial_area
+        + 2 * np.pi * (outer_radius**2 - inner_radius**2) * motor.solid.grain_number
+    )
+    assert np.isclose(motor.solid.burn_area(0), burn_area_total, atol=1e-12)
+    assert motor.solid.burn_area(0) > burn_area_radial

tests/unit/test_solidmotor.py

@@ -279,3 +279,40 @@ def test_reshape_thrust_curve_asserts_resultant_thrust_curve_correct(
 
     assert thrust_reshaped[1][1] == 100 * (tuple_parametric[1] / 7539.1875)
     assert thrust_reshaped[7][1] == 2034 * (tuple_parametric[1] / 7539.1875)
+
+
+def test_only_radial_burn_parameter_effect(cesaroni_m1670):
+    """Test if the only_radial_burn flag is properly set and affects burn area calculation."""
+    motor = cesaroni_m1670
+    motor.only_radial_burn = True
+    assert motor.only_radial_burn is True
+
+    # When only_radial_burn is active, burn_area should consider only radial area
+    # Use the motor's burn_area method directly to avoid code duplication
+    burn_area_radial = motor.burn_area(0)
+    
+    # Manually calculate expected radial burn area for verification
+    expected_radial_area = (
+        2 * np.pi * (motor.grain_inner_radius(0) * motor.grain_height(0)) * motor.grain_number
+    )
+    assert np.isclose(burn_area_radial, expected_radial_area, atol=1e-12)
+
+
+def test_evaluate_geometry_updates_properties(cesaroni_m1670):
+    """Check if after instantiation, grain_inner_radius and grain_height are valid functions."""
+    motor = cesaroni_m1670
+
+    assert hasattr(motor, "grain_inner_radius")
+    assert hasattr(motor, "grain_height")
+
+    # Check if the domain of grain_inner_radius function is consistent
+    times = motor.grain_inner_radius.x_array
+    values = motor.grain_inner_radius.y_array
+
+    assert times[0] == 0  # expected initial time
+    assert values[0] == motor.grain_initial_inner_radius  # expected initial inner radius
+    assert values[-1] <= motor.grain_outer_radius  # final inner radius should be less or equal than outer radius
+
+    # Evaluate without error
+    val = motor.grain_inner_radius(0.5)  # evaluate at intermediate time
+    assert isinstance(val, float)