From 4954099b403911cb0feae0719b9d7fd8b3120eb9 Mon Sep 17 00:00:00 2001
From: JoePfeiffer <joseph@pfeifferfamily.net>
Date: Fri, 21 Apr 2023 16:30:49 -0600
Subject: [PATCH] incorporate adaptive time step in tumble stepper

---
 .../simulation/BasicLandingStepper.java          |  9 ++++-----
 .../simulation/BasicTumbleStepper.java           | 16 +++++++++++++++-
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/core/src/net/sf/openrocket/simulation/BasicLandingStepper.java b/core/src/net/sf/openrocket/simulation/BasicLandingStepper.java
index bdd92d8dd..909871732 100644
--- a/core/src/net/sf/openrocket/simulation/BasicLandingStepper.java
+++ b/core/src/net/sf/openrocket/simulation/BasicLandingStepper.java
@@ -1,5 +1,8 @@
 package net.sf.openrocket.simulation;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import net.sf.openrocket.models.atmosphere.AtmosphericConditions;
 import net.sf.openrocket.rocketcomponent.InstanceMap;
 import net.sf.openrocket.rocketcomponent.RecoveryDevice;
@@ -9,9 +12,6 @@ import net.sf.openrocket.util.GeodeticComputationStrategy;
 import net.sf.openrocket.util.MathUtil;
 import net.sf.openrocket.util.WorldCoordinate;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
 public class BasicLandingStepper extends AbstractSimulationStepper {
 	private static final Logger log = LoggerFactory.getLogger(BasicLandingStepper.class);
 	
@@ -77,8 +77,6 @@ public class BasicLandingStepper extends AbstractSimulationStepper {
 		Coordinate coriolisAcceleration = status.getSimulationConditions().getGeodeticComputation().getCoriolisAcceleration(
 				status.getRocketWorldPosition(), status.getRocketVelocity());
 		linearAcceleration = linearAcceleration.add(coriolisAcceleration);
-		
-
 
 		// Select tentative time step
 		double timeStep = RECOVERY_TIME_STEP;
@@ -88,6 +86,7 @@ public class BasicLandingStepper extends AbstractSimulationStepper {
 		if (jerk > MathUtil.EPSILON) {
 			timeStep = Math.min(timeStep, 1.0/jerk);
 		}
+
 		// but don't let it get *too* small
 		timeStep = Math.max(timeStep, MIN_TIME_STEP);
 		log.trace("timeStep is " + timeStep);
diff --git a/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java b/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java
index c22c327dc..a378b1529 100644
--- a/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java
+++ b/core/src/net/sf/openrocket/simulation/BasicTumbleStepper.java
@@ -4,6 +4,9 @@ import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.Map;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import net.sf.openrocket.rocketcomponent.FinSet;
 import net.sf.openrocket.rocketcomponent.FlightConfiguration;
 import net.sf.openrocket.rocketcomponent.InstanceContext;
@@ -20,6 +23,7 @@ import net.sf.openrocket.util.MathUtil;
 import net.sf.openrocket.util.WorldCoordinate;
 
 public class BasicTumbleStepper extends AbstractSimulationStepper {
+	private static final Logger log = LoggerFactory.getLogger(BasicTumbleStepper.class);
 	
 	private static final double RECOVERY_TIME_STEP = 0.5;
 	
@@ -124,8 +128,18 @@ public class BasicTumbleStepper extends AbstractSimulationStepper {
 		
 
 
-		// Select time step
+		// Select tentative time step
 		double timeStep = MathUtil.min(0.5 / linearAcceleration.length(), RECOVERY_TIME_STEP);
+
+		// adjust based on change in acceleration (ie jerk)
+		final double jerk = Math.abs(linearAcceleration.sub(status.getRocketAcceleration()).multiply(1.0/status.getPreviousTimeStep()).length());
+		if (jerk > MathUtil.EPSILON) {
+			timeStep = Math.min(timeStep, 1.0/jerk);
+		}
+		
+		// but don't let it get *too* small
+		timeStep = Math.max(timeStep, MIN_TIME_STEP);
+		log.trace("timeStep is " + timeStep);
 		
 		// Perform Euler integration
 		Coordinate newPosition = status.getRocketPosition().add(status.getRocketVelocity().multiply(timeStep)).