101 lines
3.0 KiB
C++
101 lines
3.0 KiB
C++
#include "model/MotorModel.h"
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#include "utils/math/Constants.h"
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namespace model
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{
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MotorModel::MotorModel()
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{
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}
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MotorModel::~MotorModel()
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{
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}
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double MotorModel::getMass(double simTime) const
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{
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// the current mass is the emptyMass + the current prop mass
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// If ignition hasn't occurred, return the totalMass
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if(!ignitionOccurred)
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{
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return data.totalWeight;
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}
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else if(simTime - ignitionTime <= data.burnTime)
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{
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double thrustTime = simTime - ignitionTime;
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// Find the right interval in the massCurve
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auto i = massCurve.cbegin();
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while(i->first <= thrustTime)
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{
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// If thrustTime is equal to a data point that we have, then just return
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// the mass at that time. Otherwise it fell between two points and we
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// will interpolate
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if(i->first == thrustTime)
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{
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// return empty mass + remaining propellant mass
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return emptyMass + i->second;
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}
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else
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{
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i++;
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}
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}
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// linearly interpolate the propellant mass. Then return the empty mass + remaining prop mass
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double tStart = std::prev(i)->first;
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double tEnd = i->first;
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double propMassStart = std::prev(i)->second;
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double propMassEnd = i->second;
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double slope = (propMassEnd - propMassStart) / (tEnd - tStart);
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double currentMass = emptyMass + propMassStart + (thrustTime - tStart) * slope;
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return currentMass;
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}
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else
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{
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return emptyMass;
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}
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}
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void MotorModel::setMetaData(const MetaData& md)
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{
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data = md;
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emptyMass = data.totalWeight - data.propWeight;
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// Calculate the Isp for the motor, as we'll need this for the computing the mass flow rate.
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// This will be the total impulse in Newton-seconds over
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// the propellant weight. The prop mass is in grams, hence the division by 1000.0 to get kg
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isp = data.totalImpulse / (utils::math::Constants::g0 * data.propWeight / 1000.0);
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// Precompute the mass curve. Having this precomputed will ensure multiple calls to getMass()
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// or getThrust() during the same time step don't accidentally decrement the mass multiple times.
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// Having a lookup table will ensure consistent mass values, as well as speed up the simulation,
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// just at the cost of some extra space
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// Most motor data in the RASP format has a limitation of 32 data points. We're not going to
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// match that, so we can pick whatever we want and just interpolate values. We can have 128
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// for example
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massCurve.reserve(128);
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double timeStep = data.burnTime / 127.0;
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double t = 0.0;
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double propMass{data.propWeight};
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for(std::size_t i = 0; i < 127; ++i)
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{
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massCurve.push_back(std::make_pair(t + i*timeStep, propMass));
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propMass -= thrust.getThrust(t + i*timeStep) * timeStep * data.propWeight / data.totalImpulse;
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}
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massCurve.push_back(std::make_pair(data.burnTime, 0.0));
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}
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void MotorModel::moveMetaData(MetaData&& md)
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{
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data = std::move(md);
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}
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} // namespace model
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