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Merge pull request #2432 from JoePfeiffer/more-accurate-thrust

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More accurate thrust
This commit is contained in:
Joe Pfeiffer 2024-01-04 20:27:38 -07:00 committed by GitHub
commit b03c31f230
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4 changed files with 58 additions and 73 deletions
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14
core/src/net/sf/openrocket/simulation/AbstractSimulationStepper.java
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@ -157,20 +157,18 @@ public abstract class AbstractSimulationStepper implements SimulationStepper {
/**
* Calculate the average thrust produced by the motors in the current configuration, allowing
* listeners to override. The average is taken between <code>status.time</code> and
* <code>status.time + timestep</code>.
* Calculate the thrust produced by the motors in the current configuration, allowing
* listeners to override. The thrust is calculated at time <code>status.time</code>.
* <p>
* TODO: HIGH: This method does not take into account any moments generated by off-center motors.
*
* @param status the current simulation status.
* @param timestep the time step of the current iteration.
* @param acceleration the current (approximate) acceleration
* @param atmosphericConditions the current atmospheric conditions
* @param stepMotors whether to step the motors forward or work on a clone object
* @return the average thrust during the time step.
* @return the thrust at the specified time
*/
protected double calculateAverageThrust(SimulationStatus status, double timestep,
protected double calculateThrust(SimulationStatus status,
double acceleration, AtmosphericConditions atmosphericConditions,
boolean stepMotors) throws SimulationException {
double thrust;
@ -182,11 +180,9 @@ public abstract class AbstractSimulationStepper implements SimulationStepper {
}
thrust = 0;
final double currentTime = status.getSimulationTime() + timestep;
Collection<MotorClusterState> activeMotorList = status.getActiveMotors();
for (MotorClusterState currentMotorState : activeMotorList ) {
thrust += currentMotorState.getAverageThrust( status.getSimulationTime(), currentTime );
//thrust += currentMotorState.getThrust( currentTime );
thrust += currentMotorState.getThrust( status.getSimulationTime() );
}
// Post-listeners

9
core/src/net/sf/openrocket/simulation/BasicEventSimulationEngine.java
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@ -12,6 +12,7 @@ import net.sf.openrocket.logging.WarningSet;
import net.sf.openrocket.l10n.Translator;
import net.sf.openrocket.motor.MotorConfiguration;
import net.sf.openrocket.motor.MotorConfigurationId;
import net.sf.openrocket.motor.ThrustCurveMotor;
import net.sf.openrocket.rocketcomponent.AxialStage;
import net.sf.openrocket.rocketcomponent.DeploymentConfiguration;
import net.sf.openrocket.rocketcomponent.FlightConfiguration;
@ -412,6 +413,14 @@ public class BasicEventSimulationEngine implements SimulationEngine {
continue;
}
// Queue an altitude event for every point in the thrust curve to set the RK4 simulation time
// steps
ThrustCurveMotor motor = (ThrustCurveMotor) motorState.getMotor();
double[] timePoints = motor.getTimePoints();
for (double point : timePoints) {
addEvent(new FlightEvent(FlightEvent.Type.ALTITUDE, point, event.getSource(), motorState));
}
// and queue up the burnout for this motor, as well.
double duration = motorState.getBurnTime();
double burnout = currentStatus.getSimulationTime() + duration;

77
core/src/net/sf/openrocket/simulation/RK4SimulationStepper.java
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@ -93,26 +93,12 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
RK4SimulationStatus status2;
RK4Parameters k1, k2, k3, k4;
/*
* Start with previous time step which is used to compute the initial thrust estimate.
* Don't make it longer than maxTimeStep, but at least MIN_TIME_STEP.
*/
store.timestep = MathUtil.max(MathUtil.min(store.timestep, maxTimeStep), MIN_TIME_STEP);
checkNaN(store.timestep);
/*
* Get the current atmospheric conditions
*/
calculateFlightConditions(status, store);
store.atmosphericConditions = store.flightConditions.getAtmosphericConditions();
/*
* Compute the initial thrust estimate. This is used for the first time step computation.
*/
store.thrustForce = calculateAverageThrust(status, store.timestep, store.longitudinalAcceleration,
store.atmosphericConditions, false);
/*
* Perform RK4 integration. Decide the time step length after the first step.
@ -162,48 +148,38 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
limitingValue = i;
}
}
log.trace("Selected time step " + store.timestep + " (limiting factor " + limitingValue + ")");
// If we have a scheduled event coming up before the end of our timestep, truncate step
// else if the time from the end of our timestep to the next scheduled event time is less than
// minTimeStep, stretch it
double minTimeStep = status.getSimulationConditions().getTimeStep() / 20;
FlightEvent nextEvent = status.getEventQueue().peek();
if (nextEvent != null) {
double nextEventTime = nextEvent.getTime();
if (status.getSimulationTime() + store.timestep > nextEventTime) {
store.timestep = nextEventTime - status.getSimulationTime();
log.trace("scheduled event at " + nextEventTime + " truncates timestep to " + store.timestep);
} else if ((status.getSimulationTime() + store.timestep < nextEventTime) &&
(status.getSimulationTime() + store.timestep + minTimeStep > nextEventTime)) {
store.timestep = nextEventTime - status.getSimulationTime();
log.trace("Scheduled event at " + nextEventTime + " stretches timestep to " + store.timestep);
}
}
// If we've wound up with a too-small timestep, increase it avoid numerical instability even at the
// cost of not being *quite* on an event
if (store.timestep < minTimeStep) {
log.trace("Too small time step " + store.timestep + " (limiting factor " + limitingValue + "), using " +
minTimeStep + " instead.");
store.timestep = minTimeStep;
} else {
log.trace("Selected time step " + store.timestep + " (limiting factor " + limitingValue + ")");
}
checkNaN(store.timestep);
/*
* Compute the correct thrust for this time step. If the original thrust estimate differs more
* than 10% from the true value then recompute the RK4 step 1. The 10% error in step 1 is
* diminished by it affecting only 1/6th of the total, so it's an acceptable error.
*/
double thrustEstimate = store.thrustForce;
store.thrustForce = calculateAverageThrust(status, store.timestep, store.longitudinalAcceleration,
store.atmosphericConditions, true);
log.trace("Thrust = " + store.thrustForce);
double thrustDiff = Math.abs(store.thrustForce - thrustEstimate);
// Log if difference over 1%, recompute if over 10%
if (thrustDiff > 0.01 * thrustEstimate) {
if (thrustDiff > 0.1 * thrustEstimate + 0.001) {
log.debug("Thrust estimate differs from correct value by " +
(Math.rint(1000 * (thrustDiff + 0.000001) / thrustEstimate) / 10.0) + "%," +
" estimate=" + thrustEstimate +
" correct=" + store.thrustForce +
" timestep=" + store.timestep +
", recomputing k1 parameters");
k1 = computeParameters(status, store);
} else {
log.trace("Thrust estimate differs from correct value by " +
(Math.rint(1000 * (thrustDiff + 0.000001) / thrustEstimate) / 10.0) + "%," +
" estimate=" + thrustEstimate +
" correct=" + store.thrustForce +
" timestep=" + store.timestep +
", error acceptable");
}
}
//// Second position, k2 = f(t + h/2, y + k1*h/2)
status2 = status.clone();
@ -345,8 +321,9 @@ public class RK4SimulationStepper extends AbstractSimulationStepper {
store.dragForce = store.forces.getCDaxial() * dynP * refArea;
double fN = store.forces.getCN() * dynP * refArea;
double fSide = store.forces.getCside() * dynP * refArea;
double forceZ = store.thrustForce - store.dragForce;
store.thrustForce = calculateThrust(status, store.longitudinalAcceleration, store.flightConditions.getAtmosphericConditions(), false);
double forceZ = store.thrustForce - store.dragForce;
store.linearAcceleration = new Coordinate(-fN / store.rocketMass.getMass(),
-fSide / store.rocketMass.getMass(),

31
core/test/net/sf/openrocket/simulation/FlightEventsTest.java
View File

@ -56,8 +56,8 @@ public class FlightEventsTest extends BaseTestCase {
new FlightEvent(FlightEvent.Type.EJECTION_CHARGE, 2.0, stage),
new FlightEvent(FlightEvent.Type.RECOVERY_DEVICE_DEPLOYMENT, 2.001, parachute),
new FlightEvent(FlightEvent.Type.APOGEE, 2.48338, rocket),
new FlightEvent(FlightEvent.Type.GROUND_HIT, 43.1, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 43.1, null)
new FlightEvent(FlightEvent.Type.GROUND_HIT, 43.076, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 43.076, null)
};
checkEvents(expectedEvents, sim, 0);
@ -99,18 +99,18 @@ public class FlightEventsTest extends BaseTestCase {
new FlightEvent(FlightEvent.Type.LAUNCH, 0.0, rocket),
new FlightEvent(FlightEvent.Type.IGNITION, 0.0, boosterMotorTubes),
new FlightEvent(FlightEvent.Type.IGNITION, 0.0, coreBody),
new FlightEvent(FlightEvent.Type.LIFTOFF, 0.1225, null),
new FlightEvent(FlightEvent.Type.LAUNCHROD, 0.125, null),
new FlightEvent(FlightEvent.Type.APOGEE, 1.867, rocket),
new FlightEvent(FlightEvent.Type.LIFTOFF, 0.1275, null),
new FlightEvent(FlightEvent.Type.LAUNCHROD, 0.130, null),
new FlightEvent(FlightEvent.Type.BURNOUT, 2.0, boosterMotorTubes),
new FlightEvent(FlightEvent.Type.EJECTION_CHARGE, 2.0, boosterStage),
new FlightEvent(FlightEvent.Type.STAGE_SEPARATION, 2.0, boosterStage),
new FlightEvent(FlightEvent.Type.BURNOUT, 2.0, coreBody),
new FlightEvent(FlightEvent.Type.EJECTION_CHARGE, 2.0, coreStage),
new FlightEvent(FlightEvent.Type.STAGE_SEPARATION, 2.0, coreStage),
new FlightEvent(FlightEvent.Type.TUMBLE, 2.38, null),
new FlightEvent(FlightEvent.Type.GROUND_HIT, 13.2, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 13.2, null)
new FlightEvent(FlightEvent.Type.APOGEE, 2.12, rocket),
new FlightEvent(FlightEvent.Type.TUMBLE, 2.202, null),
new FlightEvent(FlightEvent.Type.GROUND_HIT, 14.12, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 14.12, null)
};
break;
// Core stage
@ -120,8 +120,10 @@ public class FlightEventsTest extends BaseTestCase {
new FlightEvent(FlightEvent.Type.BURNOUT, 2.0, coreBody),
new FlightEvent(FlightEvent.Type.EJECTION_CHARGE, 2.0, coreStage),
new FlightEvent(FlightEvent.Type.STAGE_SEPARATION, 2.0, coreStage),
new FlightEvent(FlightEvent.Type.GROUND_HIT, 5.9, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 5.9, null)
new FlightEvent(FlightEvent.Type.APOGEE, 2.1, rocket),
new FlightEvent(FlightEvent.Type.TUMBLE, 2.15, null),
new FlightEvent(FlightEvent.Type.GROUND_HIT, 7.26, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 7.26, null)
};
break;
// Booster stage
@ -131,9 +133,10 @@ public class FlightEventsTest extends BaseTestCase {
new FlightEvent(FlightEvent.Type.BURNOUT, 2.0, boosterMotorTubes),
new FlightEvent(FlightEvent.Type.EJECTION_CHARGE, 2.0, boosterStage),
new FlightEvent(FlightEvent.Type.STAGE_SEPARATION, 2.0, boosterStage),
new FlightEvent(FlightEvent.Type.TUMBLE, 3.428, null),
new FlightEvent(FlightEvent.Type.GROUND_HIT, 10.3, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 10.3, null)
new FlightEvent(FlightEvent.Type.TUMBLE, 2.05, null),
new FlightEvent(FlightEvent.Type.APOGEE, 2.06, rocket),
new FlightEvent(FlightEvent.Type.GROUND_HIT, 12.0, null),
new FlightEvent(FlightEvent.Type.SIMULATION_END, 12.0, null)
};
break;
default:
@ -147,7 +150,7 @@ public class FlightEventsTest extends BaseTestCase {
private void checkEvents(FlightEvent[] expectedEvents, Simulation sim, int branchNo) {
FlightEvent[] actualEvents = sim.getSimulatedData().getBranch(branchNo).getEvents().toArray(new FlightEvent[0]);
// Test event count
assertEquals("Branch " + branchNo + " invalid number of events ", expectedEvents.length, actualEvents.length);