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Prevent RK4 simulation timestep from extending past next scheduled event.

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Calculate thrust at sample points instead of averaged across timestep
This commit is contained in:
JoePfeiffer 2024-01-04 09:52:01 -07:00
parent 6b01afcd67
commit e51b76e176
3 changed files with 41 additions and 59 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(),