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BUG: Zero Mass Flow Tank causing Empty Velocity Data #677

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Merged
merged 1 commit into from
Sep 8, 2024
Merged

BUG: Zero Mass Flow Tank causing Empty Velocity Data #677

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@ Attention: The newest changes should be on top -->

### Fixed

- BUG: Zero Mass Flow Rate in Liquid Motors breaks Exhaust Velocity [#677](https://github.com/RocketPy-Team/RocketPy/pull/677)
- DOC: Fix documentation dependencies [#651](https://github.com/RocketPy-Team/RocketPy/pull/651)
- DOC: Fix documentation warnings [#645](https://github.com/RocketPy-Team/RocketPy/pull/645)
- BUG: Rotational EOMs Not Relative To CDM [#674](https://github.com/RocketPy-Team/RocketPy/pull/674)
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10 changes: 5 additions & 5 deletions rocketpy/motors/liquid_motor.py
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Expand Up @@ -266,16 +266,16 @@ def exhaust_velocity(self):
"""
times, thrusts = self.thrust.source[:, 0], self.thrust.source[:, 1]
mass_flow_rates = self.mass_flow_rate(times)
exhaust_velocity = np.zeros_like(mass_flow_rates)

# Compute exhaust velocity only for non-zero mass flow rates
valid_indices = mass_flow_rates != 0
valid_times = times[valid_indices]
valid_thrusts = thrusts[valid_indices]
valid_mass_flow_rates = mass_flow_rates[valid_indices]

ext_vel = -valid_thrusts / valid_mass_flow_rates
exhaust_velocity[valid_indices] = (
-thrusts[valid_indices] / mass_flow_rates[valid_indices]
)

return np.column_stack([valid_times, ext_vel])
return np.column_stack([times, exhaust_velocity])

@funcify_method("Time (s)", "Propellant Mass (kg)")
def propellant_mass(self):
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3 changes: 2 additions & 1 deletion rocketpy/motors/motor.py
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Expand Up @@ -483,7 +483,8 @@ def total_mass_flow_rate(self):
rate should not be greater than `total_mass_flow_rate`, otherwise the
grains mass flow rate will be negative, losing physical meaning.
"""
return -1 * self.thrust / self.exhaust_velocity
average_exhaust_velocity = self.total_impulse / self.propellant_initial_mass
return self.thrust / -average_exhaust_velocity

@property
@abstractmethod
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