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Merge pull request #1068 from JoePfeiffer/fix-1063

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Fix 1063 -- correct subsonic nose cone drag interpolation
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SiboVG 2022-01-11 12:38:05 +01:00 committed by GitHub
commit 06c02cdd1f
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2 changed files with 59 additions and 5 deletions
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25
core/src/net/sf/openrocket/aerodynamics/barrowman/SymmetricComponentCalc.java
View File

@ -18,7 +18,8 @@ import net.sf.openrocket.util.MathUtil;
import net.sf.openrocket.util.PolyInterpolator; import net.sf.openrocket.util.PolyInterpolator;
import net.sf.openrocket.util.Transformation; import net.sf.openrocket.util.Transformation;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/** /**
* Calculates the aerodynamic properties of a <code>SymmetricComponent</code>. * Calculates the aerodynamic properties of a <code>SymmetricComponent</code>.
@ -32,6 +33,8 @@ import net.sf.openrocket.util.Transformation;
*/ */
public class SymmetricComponentCalc extends RocketComponentCalc { public class SymmetricComponentCalc extends RocketComponentCalc {
private final static Logger log = LoggerFactory.getLogger(SymmetricComponentCalc.class);
public static final double BODY_LIFT_K = 1.1; public static final double BODY_LIFT_K = 1.1;
private final double length; private final double length;
@ -375,7 +378,16 @@ public class SymmetricComponentCalc extends RocketComponentCalc {
interpolator.addPoint(m, stag * Math.pow(int1.getValue(m) / stag, log4)); interpolator.addPoint(m, stag * Math.pow(int1.getValue(m) / stag, log4));
} }
} }
// dump transonic/supersonic knots, in a format easily imported into python
String vel = "vel = [ ";
String cd = "cd = [ ";
for (double m : interpolator.getXPoints()) {
vel = vel + m + ", ";
cd = cd + interpolator.getValue(m) + ", ";
}
log.debug(vel + "]");
log.debug(cd + "]");
/* /*
* Now the transonic/supersonic region is ok. We still need to interpolate * Now the transonic/supersonic region is ok. We still need to interpolate
@ -391,6 +403,9 @@ public class SymmetricComponentCalc extends RocketComponentCalc {
double cdMach0 = 0.8 * pow2(sinphi); double cdMach0 = 0.8 * pow2(sinphi);
double minDeriv = (interpolator.getValue(min + 0.01) - minValue) / 0.01; double minDeriv = (interpolator.getValue(min + 0.01) - minValue) / 0.01;
log.debug("cdMach0 = " + cdMach0);
log.debug("minDeriv = " + minDeriv);
// These should not occur, but might cause havoc for the interpolation // These should not occur, but might cause havoc for the interpolation
if ((cdMach0 >= minValue - 0.01) || (minDeriv <= 0.01)) { if ((cdMach0 >= minValue - 0.01) || (minDeriv <= 0.01)) {
@ -398,10 +413,10 @@ public class SymmetricComponentCalc extends RocketComponentCalc {
} }
// Cd = a*M^b + cdMach0 // Cd = a*M^b + cdMach0
double a = minValue - cdMach0; final double b = min * minDeriv / (minValue - cdMach0);
double b = minDeriv / a; final double a = (minValue - cdMach0) / Math.pow(min, b);
for (double m = 0; m < minValue; m += 0.05) { for (double m = 0; m < min; m += 0.05) {
interpolator.addPoint(m, a * Math.pow(m, b) + cdMach0); interpolator.addPoint(m, a * Math.pow(m, b) + cdMach0);
} }
} }

39
core/test/net/sf/openrocket/aerodynamics/SymmetricComponentCalcTest.java
View File

@ -103,4 +103,43 @@ public class SymmetricComponentCalcTest {
assertEquals(" SymmetricComponentCalc produces bad C_m: ", 0.0, forces.getCm(), EPSILON); assertEquals(" SymmetricComponentCalc produces bad C_m: ", 0.0, forces.getCm(), EPSILON);
} }
@Test
public void testEllipseNoseconeDrag() {
Rocket rocket = TestRockets.makeEstesAlphaIII();
NoseCone nose = (NoseCone)rocket.getChild(0).getChild(0);
// use an ellipsoidal nose cone with fineness ratio 5
nose.setType(Transition.Shape.ELLIPSOID);
nose.setLength(nose.getAftRadius() * 5.0);
SymmetricComponentCalc calcObj = new SymmetricComponentCalc( nose );
FlightConfiguration config = rocket.getSelectedConfiguration();
FlightConditions conditions = new FlightConditions(config);
conditions.setAOA(0.0);
WarningSet warnings = new WarningSet();
double frontalArea = Math.PI * nose.getAftRadius() * nose.getAftRadius();
// vvv TEST vvv
// these values from a reimplementation of the pressure cd calculation in python
// values at M = 0, 0.05, ... , 1.15
double cd[] = {
8.000392024269301e-07, 2.422001414621988e-06, 2.0098855921838474e-05,
8.295843903984836e-05, 0.000230425812213129, 0.0005104254351619708,
0.0009783566607446353, 0.0016963974152150677, 0.0027329880483111142,
0.004162427611715722, 0.006064546184601524, 0.008524431611715306,
0.011632196831399358, 0.01548277847481293, 0.020175760185344116,
0.02581521589534269, 0.032509569500239276, 0.04037146820686186,
0.04951766743137877, 0.06006892556095394, 0.07214990722137526,
0.08588909394291767, 0.10141870131021756, 0.11887460183385967 };
for (int i = 0; i < cd.length; i++) {
double m = i/20.0;
String buf = "SymmetricComponentCalc produces bad Cd at index " + i + "(m=" + m +")";
conditions.setMach(m);
double testcd = calcObj.calculatePressureDragForce(conditions, 0.0, 0.0, warnings) *
conditions.getRefArea() / frontalArea;
assertEquals(buf, cd[(int) Math.round(m*20)], testcd, EPSILON);
}
}
} }