Prop model #63
Prop model #63
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… termination of firing after pressure limit exceeded
…ation of firing after pressure limit exceeded. Also commented out unused variables and updated calculations
om-deshmukh-dev
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Maryy1235,
adamrnasir,
cameron-goddard and
tmf97
tmf97
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tmf97
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This is looking pretty dang good! Didn't have the chance to dive into the "meat" of the evaluate step yet - will try to get to that tonight.
Please fix the failing unit test.
| d = 3 * 0.0254 # (m) | ||
| h = (3.968 + 1.618) * 0.0254 # (m) | ||
| d2 = 0.05 * 0.0254 # (m) | ||
| #d2mm = d2 * 1000 | ||
| d3 = 0.305 * 0.0254 # (m) | ||
| #A1 = np.pi * d ** 2 / 4 #Cross-sectional area of the nozzle throat (m^2) | ||
| A2 = np.pi * d2 ** 2 / 4 #Cross-sectional area of the nozzle exit (m^2) | ||
| A3 = np.pi * d3 ** 2 / 4 # Cross-sectional area of the combustion chamber (m^2) | ||
| vc = h * np.pi * d ** 2 / 4 | ||
| plim1 = 45 * 6894.76 # Pascals | ||
| plim2 = 100 * 6894.76 # Pascals | ||
| #RH2 = 4.124e3 # J/kg*K | ||
| #RO2 = 0.2598e3 # J/kg*K | ||
| RH2O = 0.4615e3 # J/kg*K |
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Are any of these values look like system parameters rather than a state the needs to be propagated as part of the sim. Please put all numerical parameters into parameters.py, update the parameters in the config JSONs, and get the values here with self.parameters...
For fundamental physical/chemical constants, we might want to make a constants.py file or something and import it here.
src/core/models/propulsion_model.py
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| gamma = CpH2O / CvH2O # Ratio of specific heats for water vapor | ||
| calc = (gamma + 1) / (2 * (gamma - 1)) | ||
| arearatio = A2 / A3 | ||
| int = arearatio * 1 / ((1 + (gamma - 1) / 2) ** calc) |
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Please don't overwrite the standard python int
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Haha my bad I was trying to write a shorthand for intermediate and choose int. I'll fix that
src/core/models/propulsion_model.py
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| a = np.sqrt(gamma * RH2O * T3) #Local speed of sound | ||
| v_eq = M3*a*np.sqrt(gamma*RH2O*T3) #Equivalent velocity | ||
| F = mdot * v_eq #Array storing force at each dt time interval | ||
| Pc = P[-1] |
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nit: Please use more descriptive variable names. chamber_pressure_in_pascals or chamber_pressure is clunkier but more understandable that Pc
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Will update, thanks
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| force_propulsion_thrusters: float = 0.0 | ||
| fuel_mass: float = 0.0 | ||
| dry_mass: float = 0.0 |
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Do we/are there plans to do anything with the dry_mass state?
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I thought it would be useful for the integrator when updating the position, velocity, and angular velocity to know the current mass of the cubesat (dry mass + fuel mass)
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Ah I see. The reason I asked is because the dry mass of the spacecraft really should not change throughout the mission (unless you're simulating some truly bizarre mission cases, like having a micrometeoroid cleave off some of the spacecraft's brackets) so having it in state.py seemed a bit strange to me at first since every variable in there is constantly changing. However, even if it's not changing, the dry mass is still a fundamental state of the system so I think it should stay here.
Summary
This is the first implementation of the propulsion model. Given the current state, the propulsion model outputs an average force outputted by the cubesat since the last prop model call.
This PR addresses Jira ticket CISLUNAR-445
Testing
Testing of the calculations & formulas was done by hand and in matlab, however actual test cases have yet to be implemented as we don't have propulsion data to compare against. In a future pull request, I will include test cases to ensure values are within reasonable ranges.
Notes
State variables in this iteration are updated by the integrator.
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