diff --git a/core/src/net/sf/openrocket/aerodynamics/barrowman/FinSetCalc.java b/core/src/net/sf/openrocket/aerodynamics/barrowman/FinSetCalc.java
index 96abf7a62..293a04dd8 100644
--- a/core/src/net/sf/openrocket/aerodynamics/barrowman/FinSetCalc.java
+++ b/core/src/net/sf/openrocket/aerodynamics/barrowman/FinSetCalc.java
@@ -17,15 +17,21 @@ import net.sf.openrocket.util.LinearInterpolator;
import net.sf.openrocket.util.MathUtil;
import net.sf.openrocket.util.PolyInterpolator;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
public class FinSetCalc extends RocketComponentCalc {
+
+ private final static Logger logger = LoggerFactory.getLogger(FinSetCalc.class);
+
private static final double STALL_ANGLE = (20 * Math.PI / 180);
/** Number of divisions in the fin chords. */
protected static final int DIVISIONS = 48;
-
-
+
+
protected double macLength = Double.NaN; // MAC length
protected double macLead = Double.NaN; // MAC leading edge position
protected double macSpan = Double.NaN; // MAC spanwise position
@@ -42,7 +48,7 @@ public class FinSetCalc extends RocketComponentCalc {
protected double[] chordTrail = new double[DIVISIONS];
protected double[] chordLength = new double[DIVISIONS];
-
+
protected final WarningSet geometryWarnings = new WarningSet();
private double[] poly = new double[6];
@@ -84,7 +90,7 @@ public class FinSetCalc extends RocketComponentCalc {
public void calculateNonaxialForces(FlightConditions conditions,
AerodynamicForces forces, WarningSet warnings) {
-
+
if (span < 0.001) {
forces.setCm(0);
forces.setCN(0);
@@ -98,28 +104,28 @@ public class FinSetCalc extends RocketComponentCalc {
return;
}
-
+
// Add warnings (radius/2 == diameter/4)
if (thickness > bodyRadius / 2) {
warnings.add(Warning.THICK_FIN);
}
warnings.addAll(geometryWarnings);
-
-
+
+
//////// Calculate CNa. /////////
// One fin without interference (both sub- and supersonic):
double cna1 = calculateFinCNa1(conditions);
-
-
+ // logger.debug("Component cna1 = {}", cna1);
+
// Multiple fins with fin-fin interference
double cna;
double theta = conditions.getTheta();
double angle = baseRotation;
-
+
// Compute basic CNa without interference effects
if (finCount == 1 || finCount == 2) {
// Basic CNa from geometry
@@ -134,7 +140,8 @@ public class FinSetCalc extends RocketComponentCalc {
cna = cna1 * finCount / 2.0;
}
-
+ // logger.debug("Component cna = {}", cna);
+
// Take into account fin-fin interference effects
switch (interferenceFinCount) {
case 1:
@@ -215,7 +222,7 @@ public class FinSetCalc extends RocketComponentCalc {
break;
}
*/
-
+
// Body-fin interference effect
double r = bodyRadius;
double tau = r / (span + r);
@@ -223,21 +230,26 @@ public class FinSetCalc extends RocketComponentCalc {
tau = 0;
cna *= 1 + tau; // Classical Barrowman
// cna *= pow2(1 + tau); // Barrowman thesis (too optimistic??)
+ // logger.debug("Component cna = {}", cna);
+
+
-
-
// TODO: LOW: check for fin tip mach cone interference
// (Barrowman thesis pdf-page 40)
// TODO: LOW: fin-fin mach cone effect, MIL-HDBK page 5-25
-
-
- // Calculate CP position
- double x = macLead + calculateCPPos(conditions) * macLength;
-
-
+
+ // Calculate CP position
+ // logger.debug("Component macLead = {}", macLead);
+ // logger.debug("Component macLength = {}", macLength);
+ //FIXME - macLength is incorrect!
+ double x = macLead + calculateCPPos(conditions) * macLength;
+ // logger.debug("Component x = {}", x);
+
+
+
// Calculate roll forces, reduce forcing above stall angle
// Without body-fin interference effect:
@@ -246,9 +258,9 @@ public class FinSetCalc extends RocketComponentCalc {
// With body-fin interference effect:
forces.setCrollForce(finCount * (macSpan + r) * cna1 * (1 + tau) * cantAngle / conditions.getRefLength());
-
-
-
+
+
+
if (conditions.getAOA() > STALL_ANGLE) {
// System.out.println("Fin stalling in roll");
forces.setCrollForce(forces.getCrollForce() * MathUtil.clamp(
@@ -257,8 +269,8 @@ public class FinSetCalc extends RocketComponentCalc {
forces.setCrollDamp(calculateDampingMoment(conditions));
forces.setCroll(forces.getCrollForce() - forces.getCrollDamp());
-
-
+
+
// System.out.printf(component.getName() + ": roll rate:%.3f force:%.3f damp:%.3f " +
// "total:%.3f\n",
// conditions.getRollRate(), forces.CrollForce, forces.CrollDamp, forces.Croll);
@@ -285,7 +297,7 @@ public class FinSetCalc extends RocketComponentCalc {
forces.setCside(0);
forces.setCyaw(0);
-
+
}
@@ -304,7 +316,7 @@ public class FinSetCalc extends RocketComponentCalc {
}
-
+
/**
* Pre-calculates the fin geometry values.
*/
@@ -329,7 +341,7 @@ public class FinSetCalc extends RocketComponentCalc {
}
}
-
+
// Calculate the chord lead and trail positions and length
Arrays.fill(chordLead, Double.POSITIVE_INFINITY);
@@ -342,7 +354,9 @@ public class FinSetCalc extends RocketComponentCalc {
double x2 = points[point].x;
double y2 = points[point].y;
- if (MathUtil.equals(y1, y2))
+ // Don't use the default EPSILON since it is too small
+ // and causes too much numerical instability in the computation of x below
+ if (MathUtil.equals(y1, y2, 0.001))
continue;
int i1 = (int) (y1 * 1.0001 / span * (DIVISIONS - 1));
@@ -388,7 +402,7 @@ public class FinSetCalc extends RocketComponentCalc {
}
}
-
+
/* Calculate fin properties:
*
* macLength // MAC length
@@ -412,6 +426,7 @@ public class FinSetCalc extends RocketComponentCalc {
double y = i * dy;
macLength += length * length;
+ logger.debug("macLength = {}, length = {}, i = {}", macLength, length, i);
macSpan += y * length;
macLead += chordLead[i] * length;
area += length;
@@ -427,6 +442,7 @@ public class FinSetCalc extends RocketComponentCalc {
}
macLength *= dy;
+ logger.debug("macLength = {}", macLength);
macSpan *= dy;
macLead *= dy;
area *= dy;
@@ -516,8 +532,8 @@ public class FinSetCalc extends RocketComponentCalc {
}
-
-
+
+
private double calculateDampingMoment(FlightConditions conditions) {
double rollRate = conditions.getRollRate();
@@ -527,7 +543,7 @@ public class FinSetCalc extends RocketComponentCalc {
double mach = conditions.getMach();
double absRate = Math.abs(rollRate);
-
+
/*
* At low speeds and relatively large roll rates (i.e. near apogee) the
* fin tips rotate well above stall angle. In this case sum the chords
@@ -548,8 +564,8 @@ public class FinSetCalc extends RocketComponentCalc {
return MathUtil.sign(rollRate) * finCount * sum;
}
-
-
+
+
if (mach <= CNA_SUBSONIC) {
// System.out.println("BASIC: "+
// (component.getFinCount() * 2*Math.PI * rollRate * rollSum /
@@ -594,8 +610,8 @@ public class FinSetCalc extends RocketComponentCalc {
}
-
-
+
+
/**
* Return the relative position of the CP along the mean aerodynamic chord.
* Below mach 0.5 it is at the quarter chord, above mach 2 calculated using an
@@ -606,6 +622,7 @@ public class FinSetCalc extends RocketComponentCalc {
*/
private double calculateCPPos(FlightConditions cond) {
double m = cond.getMach();
+ // logger.debug("m = {} ", m);
if (m <= 0.5) {
// At subsonic speeds CP at quarter chord
return 0.25;
@@ -624,7 +641,7 @@ public class FinSetCalc extends RocketComponentCalc {
val += poly[i] * x;
x *= m;
}
-
+ // logger.debug("val = {}", val);
return val;
}
@@ -689,7 +706,7 @@ public class FinSetCalc extends RocketComponentCalc {
//
// }
-
+
@Override
public double calculatePressureDragForce(FlightConditions conditions,
double stagnationCD, double baseCD, WarningSet warnings) {
@@ -727,7 +744,7 @@ public class FinSetCalc extends RocketComponentCalc {
}
// Airfoil assumed to have zero base drag
-
+
// Scale to correct reference area
drag *= finCount * span * thickness / conditions.getRefArea();
@@ -743,7 +760,7 @@ public class FinSetCalc extends RocketComponentCalc {
double lead = component.toRelative(Coordinate.NUL, parent)[0].x;
double trail = component.toRelative(new Coordinate(component.getLength()),
- parent)[0].x;
+ parent)[0].x;
/*
* The counting fails if the fin root chord is very small, in that case assume
@@ -768,8 +785,8 @@ public class FinSetCalc extends RocketComponentCalc {
}
if (interferenceFinCount < component.getFinCount()) {
throw new BugException("Counted " + interferenceFinCount + " parallel fins, " +
- "when component itself has " + component.getFinCount() +
- ", fin points=" + Arrays.toString(component.getFinPoints()));
+ "when component itself has " + component.getFinCount() +
+ ", fin points=" + Arrays.toString(component.getFinPoints()));
}
}
diff --git a/core/src/net/sf/openrocket/util/MathUtil.java b/core/src/net/sf/openrocket/util/MathUtil.java
index 982d1b86f..434792a84 100644
--- a/core/src/net/sf/openrocket/util/MathUtil.java
+++ b/core/src/net/sf/openrocket/util/MathUtil.java
@@ -11,9 +11,9 @@ import org.slf4j.LoggerFactory;
public class MathUtil {
private static final Logger log = LoggerFactory.getLogger(MathUtil.class);
-
+
public static final double EPSILON = 0.00000001; // 10mm^3 in m^3
-
+
/**
* The square of x (x^2). On Sun's JRE using this method is as fast as typing x*x.
* @param x x
@@ -22,7 +22,7 @@ public class MathUtil {
public static double pow2(double x) {
return x * x;
}
-
+
/**
* The cube of x (x^3).
* @param x x
@@ -31,11 +31,11 @@ public class MathUtil {
public static double pow3(double x) {
return x * x * x;
}
-
+
public static double pow4(double x) {
return (x * x) * (x * x);
}
-
+
/**
* Clamps the value x to the range min - max.
* @param x Original value.
@@ -50,7 +50,7 @@ public class MathUtil {
return max;
return x;
}
-
+
public static float clamp(float x, float min, float max) {
if (x < min)
return min;
@@ -58,7 +58,7 @@ public class MathUtil {
return max;
return x;
}
-
+
public static int clamp(int x, int min, int max) {
if (x < min)
return min;
@@ -66,8 +66,8 @@ public class MathUtil {
return max;
return x;
}
-
-
+
+
/**
* Maps a value from one value range to another.
*
@@ -90,8 +90,8 @@ public class MathUtil {
}
return (value - fromMin) / (fromMax - fromMin) * (toMax - toMin) + toMin;
}
-
-
+
+
/**
* Maps a coordinate from one value range to another.
*
@@ -115,8 +115,8 @@ public class MathUtil {
double a = (value - fromMin) / (fromMax - fromMin);
return toMax.multiply(a).add(toMin.multiply(1 - a));
}
-
-
+
+
/**
* Compute the minimum of two values. This is performed by direct comparison.
* However, if one of the values is NaN and the other is not, the non-NaN value is
@@ -127,7 +127,7 @@ public class MathUtil {
return x;
return (x < y) ? x : y;
}
-
+
/**
* Compute the maximum of two values. This is performed by direct comparison.
* However, if one of the values is NaN and the other is not, the non-NaN value is
@@ -138,7 +138,7 @@ public class MathUtil {
return y;
return (x < y) ? y : x;
}
-
+
/**
* Compute the minimum of three values. This is performed by direct comparison.
* However, if one of the values is NaN and the other is not, the non-NaN value is
@@ -151,9 +151,9 @@ public class MathUtil {
return min(y, z);
}
}
-
-
-
+
+
+
/**
* Compute the minimum of three values. This is performed by direct comparison.
* However, if one of the values is NaN and the other is not, the non-NaN value is
@@ -162,8 +162,8 @@ public class MathUtil {
public static double min(double w, double x, double y, double z) {
return min(min(w, x), min(y, z));
}
-
-
+
+
/**
* Compute the maximum of three values. This is performed by direct comparison.
* However, if one of the values is NaN and the other is not, the non-NaN value is
@@ -176,7 +176,7 @@ public class MathUtil {
return max(y, z);
}
}
-
+
/**
* Calculates the hypotenuse sqrt(x^2+y^2). This method is SIGNIFICANTLY
* faster than Math.hypot(x,y).
@@ -184,7 +184,7 @@ public class MathUtil {
public static double hypot(double x, double y) {
return Math.sqrt(x * x + y * y);
}
-
+
/**
* Reduce the angle x to the range 0 - 2*PI.
* @param x Original angle.
@@ -194,7 +194,7 @@ public class MathUtil {
double d = Math.floor(x / (2 * Math.PI));
return x - d * 2 * Math.PI;
}
-
+
/**
* Reduce the angle x to the range -PI - PI.
*
@@ -207,8 +207,8 @@ public class MathUtil {
double d = Math.rint(x / (2 * Math.PI));
return x - d * 2 * Math.PI;
}
-
-
+
+
/**
* Return the square root of a value. If the value is negative, zero is returned.
* This is safer in cases where rounding errors might make a value slightly negative.
@@ -225,20 +225,22 @@ public class MathUtil {
}
return Math.sqrt(d);
}
-
-
-
- public static boolean equals(double a, double b) {
+
+
+ public static boolean equals(double a, double b, double epsilon) {
double absb = Math.abs(b);
-
- if (absb < EPSILON / 2) {
+
+ if (absb < epsilon / 2) {
// Near zero
- return Math.abs(a) < EPSILON / 2;
+ return Math.abs(a) < epsilon / 2;
}
- return Math.abs(a - b) < EPSILON * absb;
+ return Math.abs(a - b) < epsilon * absb;
}
-
-
+
+ public static boolean equals(double a, double b) {
+ return equals(a, b, EPSILON);
+ }
+
/**
* Return the sign of the number. This corresponds to Math.signum, but ignores
* the special cases of zero and NaN. The value returned for those is arbitrary.
@@ -251,20 +253,20 @@ public class MathUtil {
public static double sign(double x) {
return (x < 0) ? -1.0 : 1.0;
}
-
+
/* Math.abs() is about 3x as fast as this:
public static double abs(double x) {
return (x<0) ? -x : x;
}
*/
-
-
+
+
public static double average(Collection values) {
if (values.isEmpty()) {
return Double.NaN;
}
-
+
double avg = 0.0;
int count = 0;
for (Number n : values) {
@@ -273,12 +275,12 @@ public class MathUtil {
}
return avg / count;
}
-
+
public static double stddev(Collection values) {
if (values.size() < 2) {
return Double.NaN;
}
-
+
double avg = average(values);
double stddev = 0.0;
int count = 0;
@@ -289,12 +291,12 @@ public class MathUtil {
stddev = Math.sqrt(stddev / (count - 1));
return stddev;
}
-
+
public static double median(Collection values) {
if (values.isEmpty()) {
return Double.NaN;
}
-
+
List sorted = new ArrayList(values);
Collections.sort(sorted, new Comparator() {
@Override
@@ -302,7 +304,7 @@ public class MathUtil {
return Double.compare(o1.doubleValue(), o2.doubleValue());
}
});
-
+
int n = sorted.size();
if (n % 2 == 0) {
return (sorted.get(n / 2).doubleValue() + sorted.get(n / 2 - 1).doubleValue()) / 2;
@@ -322,36 +324,36 @@ public class MathUtil {
* @param t domain value at which to interpolate
* @return returns Double.NaN if either list is null or empty or different size, or if t is outsize the domain.
*/
- public static double interpolate( List domain, List range, double t ) {
-
- if ( domain == null || range == null || domain.size() != range.size() ) {
+ public static double interpolate(List domain, List range, double t) {
+
+ if (domain == null || range == null || domain.size() != range.size()) {
return Double.NaN;
}
-
+
int length = domain.size();
- if ( length <= 1 || t < domain.get(0) || t > domain.get( length-1 ) ) {
+ if (length <= 1 || t < domain.get(0) || t > domain.get(length - 1)) {
return Double.NaN;
}
-
+
// Look for the index of the right end point.
int right = 1;
- while( t > domain.get(right) ) {
- right ++;
+ while (t > domain.get(right)) {
+ right++;
}
- int left = right -1;
-
+ int left = right - 1;
+
// Points are:
double deltax = domain.get(right) - domain.get(left);
double deltay = range.get(right) - range.get(left);
-
+
// For numerical stability, if deltax is small,
- if ( Math.abs(deltax) < EPSILON ) {
- if ( deltay < -1.0 * EPSILON ) {
+ if (Math.abs(deltax) < EPSILON) {
+ if (deltay < -1.0 * EPSILON) {
// return neg infinity if deltay is negative
return Double.NEGATIVE_INFINITY;
}
- else if ( deltay > EPSILON ) {
+ else if (deltay > EPSILON) {
// return infinity if deltay is large
return Double.POSITIVE_INFINITY;
} else {
@@ -360,8 +362,8 @@ public class MathUtil {
}
}
- return range.get(left) + ( t - domain.get(left) ) * deltay / deltax;
-
+ return range.get(left) + (t - domain.get(left)) * deltay / deltax;
+
}
-
+
}
diff --git a/core/test/net/sf/openrocket/rocketcomponent/FinSetTest.java b/core/test/net/sf/openrocket/rocketcomponent/FinSetTest.java
index 9febe3256..58dc0a440 100644
--- a/core/test/net/sf/openrocket/rocketcomponent/FinSetTest.java
+++ b/core/test/net/sf/openrocket/rocketcomponent/FinSetTest.java
@@ -3,6 +3,10 @@ package net.sf.openrocket.rocketcomponent;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
+import net.sf.openrocket.aerodynamics.AerodynamicForces;
+import net.sf.openrocket.aerodynamics.FlightConditions;
+import net.sf.openrocket.aerodynamics.WarningSet;
+import net.sf.openrocket.aerodynamics.barrowman.FinSetCalc;
import net.sf.openrocket.material.Material;
import net.sf.openrocket.material.Material.Type;
import net.sf.openrocket.rocketcomponent.ExternalComponent.Finish;
@@ -124,6 +128,45 @@ public class FinSetTest extends BaseTestCase {
}
+ @Test
+ public void testWildmanVindicatorShape() throws Exception {
+ // This fin shape is similar to the aft fins on the Wildman Vindicator.
+ // A user noticed that if the y values are similar but not equal,
+ // the compuation of CP was incorrect because of numerical instability.
+ //
+ // +-----------------+
+ // \ \
+ // \ \
+ // + \
+ // / \
+ // +---------------------+
+ //
+ FreeformFinSet fins = new FreeformFinSet();
+ fins.setFinCount(1);
+ Coordinate[] points = new Coordinate[] {
+ new Coordinate(0, 0),
+ new Coordinate(0.02143125, 0.01143),
+ new Coordinate(0.009524999999999999, 0.032543749999999996),
+ new Coordinate(0.041275, 0.032537399999999994),
+ new Coordinate(0.066675, 0)
+ };
+ fins.setPoints(points);
+ Coordinate coords = fins.getCG();
+ assertEquals(0.00130, fins.getFinArea(), 0.00001);
+ assertEquals(0.03423, coords.x, 0.00001);
+ assertEquals(0.01427, coords.y, 0.00001);
+
+ BodyTube bt = new BodyTube();
+ bt.addChild(fins);
+ FinSetCalc calc = new FinSetCalc(fins);
+ FlightConditions conditions = new FlightConditions(null);
+ AerodynamicForces forces = new AerodynamicForces();
+ WarningSet warnings = new WarningSet();
+ calc.calculateNonaxialForces(conditions, forces, warnings);
+ System.out.println(forces);
+ assertEquals(0.023409, forces.getCP().x, 0.0001);
+ }
+
@Test
public void testFreeFormCGWithNegativeY() throws Exception {
// This particular fin shape is currently not allowed in OR since the y values are negative