ENH: Introduce Net Thrust with pressure corrections (#789)

* wind factor bug corrected

the wind factor wasn't applied to the env.wind_velocity properties

* BUG: StochasticModel visualize attributes of a uniform distribution

It showed the nominal and the standard deviation values and it doesn't make sense in a uniform distribution. In a np.random.uniform the 'nominal value' is the lower bound of the distribution, and the 'standard deviation' value is the upper bound. Now, a new condition has been added for the uniform distributions where the mean and semi range are calculated and showed. This way the visualize_attribute function will show the whole range where the random values are uniformly taken in

* variable names corrections

* Corrections requested by the pylint test

* ENH: Add pressure corrections for thrust in SolidMotor

The thrust generated by a SolidMotor is now adjusted for the atmospheric pressure. To achieve that, a new attribute, 'vacuum_thrust', has been created. The 'net_thrust' is the result of 'vacuum_thrust' minus the atmospheric pressure multiplied by the nozzle area.

* ENH: pylint recommendations done

* ENH: net thrust method extended to the rest of the motor classes

* BUG: __post_processed_variables inconsistent array

* ENH: ruff reformatting

* Update rocketpy/motors/motor.py

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

* ENH: Avoid breaking change

* ENH: Pressure Thrust method added

* BUG: call to the thrust function wrong

* BUG: pressure thrust evaluated when motor is turned off

* ENH: CHANGELOG updated

* DOC: definition of exhaust velocity improved

---------

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

Author: kevin-alcaniz

CHANGELOG.md

@@ -35,6 +35,7 @@ Attention: The newest changes should be on top -->
 - ENH: Implement Multivariate Rejection Sampling (MRS) [#738] (https://github.com/RocketPy-Team/RocketPy/pull/738) 
 - ENH: Create a rocketpy file to store flight simulations [#800](https://github.com/RocketPy-Team/RocketPy/pull/800)
 - ENH: Support for the RSE file format has been added to the library [#798](https://github.com/RocketPy-Team/RocketPy/pull/798)
+- ENH: Introduce Net Thrust with pressure corrections [#789](https://github.com/RocketPy-Team/RocketPy/pull/789)
 
 ### Changed
 

rocketpy/motors/empty_motor.py

@@ -19,6 +19,7 @@ def __init__(self):
             reshape_thrust_curve=False,
             interpolation_method="linear",
             coordinate_system_orientation="nozzle_to_combustion_chamber",
+            reference_pressure=0,
         )
 
         # Mass properties

rocketpy/motors/hybrid_motor.py

@@ -29,6 +29,8 @@ class HybridMotor(Motor):
         "combustion_chamber_to_nozzle".
     HybridMotor.nozzle_radius : float
         Radius of motor nozzle outlet in meters.
+    HybridMotor.nozzle_area : float
+        Area of motor nozzle outlet in square meters.
     HybridMotor.nozzle_position : float
         Motor's nozzle outlet position in meters, specified in the motor's
         coordinate system. See
@@ -147,7 +149,11 @@ class HybridMotor(Motor):
         HybridMotor.propellant_I_22 and HybridMotor.propellant_I_33 for
         more information.
     HybridMotor.thrust : Function
-        Motor thrust force, in Newtons, as a function of time.
+        Motor thrust force obtained from thrust source, in Newtons, as a
+        function of time.
+    HybridMotor.vacuum_thrust : Function
+        Motor thrust force when the rocket is in a vacuum. In Newtons, as a
+        function of time.
     HybridMotor.total_impulse : float
         Total impulse of the thrust curve in N*s.
     HybridMotor.max_thrust : float
@@ -167,7 +173,10 @@ class HybridMotor(Motor):
         Total motor burn duration, in seconds. It is the difference between the
         ``burn_out_time`` and the ``burn_start_time``.
     HybridMotor.exhaust_velocity : Function
-        Propulsion gases exhaust velocity, assumed constant, in m/s.
+        Effective exhaust velocity of the propulsion gases in m/s. Computed
+        as the thrust divided by the mass flow rate. This corresponds to the
+        actual exhaust velocity only when the nozzle exit pressure equals the
+        atmospheric pressure.
     HybridMotor.burn_area : Function
         Total burn area considering all grains, made out of inner
         cylindrical burn area and grain top and bottom faces. Expressed
@@ -181,6 +190,9 @@ class HybridMotor(Motor):
         Method of interpolation used in case thrust curve is given
         by data set in .csv or .eng, or as an array. Options are 'spline'
         'akima' and 'linear'. Default is "linear".
+    HybridMotor.reference_pressure : int, float
+        Atmospheric pressure in Pa at which the thrust data was recorded.
+        It will allow to obtain the net thrust in the Flight class.
     """
 
     def __init__(  # pylint: disable=too-many-arguments
@@ -203,6 +215,7 @@ def __init__(  # pylint: disable=too-many-arguments
         reshape_thrust_curve=False,
         interpolation_method="linear",
         coordinate_system_orientation="nozzle_to_combustion_chamber",
+        reference_pressure=None,
     ):
         """Initialize Motor class, process thrust curve and geometrical
         parameters and store results.
@@ -298,6 +311,8 @@ class Function. Thrust units are Newtons.
             positions specified. Options are "nozzle_to_combustion_chamber" and
             "combustion_chamber_to_nozzle". Default is
             "nozzle_to_combustion_chamber".
+        reference_pressure : int, float, optional
+            Atmospheric pressure in Pa at which the thrust data was recorded.
 
         Returns
         -------
@@ -314,6 +329,7 @@ class Function. Thrust units are Newtons.
             reshape_thrust_curve=reshape_thrust_curve,
             interpolation_method=interpolation_method,
             coordinate_system_orientation=coordinate_system_orientation,
+            reference_pressure=reference_pressure,
         )
         self.liquid = LiquidMotor(
             thrust_source,
@@ -326,6 +342,7 @@ class Function. Thrust units are Newtons.
             reshape_thrust_curve,
             interpolation_method,
             coordinate_system_orientation,
+            reference_pressure,
         )
         self.solid = SolidMotor(
             thrust_source,
@@ -346,6 +363,7 @@ class Function. Thrust units are Newtons.
             reshape_thrust_curve,
             interpolation_method,
             coordinate_system_orientation,
+            reference_pressure,
         )
 
         self.positioned_tanks = self.liquid.positioned_tanks
@@ -371,6 +389,11 @@ def exhaust_velocity(self):
         -------
         self.exhaust_velocity : Function
             Gas exhaust velocity of the motor.
+
+        Notes
+        -----
+        This corresponds to the actual exhaust velocity only when the nozzle
+        exit pressure equals the atmospheric pressure.
         """
         return Function(
             self.total_impulse / self.propellant_initial_mass
@@ -676,6 +699,7 @@ def from_dict(cls, data):
             grains_center_of_mass_position=data["grains_center_of_mass_position"],
             nozzle_position=data["nozzle_position"],
             throat_radius=data["throat_radius"],
+            reference_pressure=data["reference_pressure"],
         )
 
         for tank in data["positioned_tanks"]:

rocketpy/motors/liquid_motor.py

@@ -29,6 +29,8 @@ class LiquidMotor(Motor):
         "combustion_chamber_to_nozzle".
     LiquidMotor.nozzle_radius : float
         Radius of motor nozzle outlet in meters.
+    LiquidMotor.nozzle_area : float
+        Area of motor nozzle outlet in square meters.
     LiquidMotor.nozzle_position : float
         Motor's nozzle outlet position in meters, specified in the motor's
         coordinate system. See
@@ -122,7 +124,11 @@ class LiquidMotor(Motor):
         LiquidMotor.propellant_I_22 and LiquidMotor.propellant_I_33 for
         more information.
     LiquidMotor.thrust : Function
-        Motor thrust force, in Newtons, as a function of time.
+        Motor thrust force obtained from thrust source, in Newtons, as a
+        function of time.
+    LiquidMotor.vacuum_thrust : Function
+        Motor thrust force when the rocket is in a vacuum. In Newtons, as a
+        function of time.
     LiquidMotor.total_impulse : float
         Total impulse of the thrust curve in N*s.
     LiquidMotor.max_thrust : float
@@ -142,7 +148,13 @@ class LiquidMotor(Motor):
         Total motor burn duration, in seconds. It is the difference between the
         burn_out_time and the burn_start_time.
     LiquidMotor.exhaust_velocity : Function
-        Propulsion gases exhaust velocity in m/s.
+        Effective exhaust velocity of the propulsion gases in m/s. Computed
+        as the thrust divided by the mass flow rate. This corresponds to the
+        actual exhaust velocity only when the nozzle exit pressure equals the
+        atmospheric pressure.
+    LiquidMotor.reference_pressure : int, float
+        Atmospheric pressure in Pa at which the thrust data was recorded.
+        It will allow to obtain the net thrust in the Flight class.
     """
 
     def __init__(
@@ -157,6 +169,7 @@ def __init__(
         reshape_thrust_curve=False,
         interpolation_method="linear",
         coordinate_system_orientation="nozzle_to_combustion_chamber",
+        reference_pressure=None,
     ):
         """Initialize LiquidMotor class, process thrust curve and geometrical
         parameters and store results.
@@ -230,6 +243,8 @@ class Function. Thrust units are Newtons.
             positions specified. Options are "nozzle_to_combustion_chamber"
             and "combustion_chamber_to_nozzle". Default is
             "nozzle_to_combustion_chamber".
+        reference_pressure : int, float, optional
+            Atmospheric pressure in Pa at which the thrust data was recorded.
         """
         super().__init__(
             thrust_source=thrust_source,
@@ -242,6 +257,7 @@ class Function. Thrust units are Newtons.
             reshape_thrust_curve=reshape_thrust_curve,
             interpolation_method=interpolation_method,
             coordinate_system_orientation=coordinate_system_orientation,
+            reference_pressure=reference_pressure,
         )
 
         self.positioned_tanks = []
@@ -264,7 +280,8 @@ def exhaust_velocity(self):
         -----
         The exhaust velocity is computed as the ratio of the thrust and the
         mass flow rate. Therefore, this will vary with time if the mass flow
-        rate varies with time.
+        rate varies with time. This corresponds to the actual exhaust velocity
+        only when the nozzle exit pressure equals the atmospheric pressure.
         """
         times, thrusts = self.thrust.source[:, 0], self.thrust.source[:, 1]
         mass_flow_rates = self.mass_flow_rate(times)
@@ -511,6 +528,7 @@ def from_dict(cls, data):
             nozzle_position=data["nozzle_position"],
             interpolation_method=data["interpolate"],
             coordinate_system_orientation=data["coordinate_system_orientation"],
+            reference_pressure=data["reference_pressure"],
         )
 
         for tank in data["positioned_tanks"]: