--- /dev/null
+package net.sf.openrocket.aerodynamics.barrowman;
+
+import static net.sf.openrocket.aerodynamics.AtmosphericConditions.GAMMA;
+import static net.sf.openrocket.util.MathUtil.pow2;
+import net.sf.openrocket.aerodynamics.AerodynamicForces;
+import net.sf.openrocket.aerodynamics.BarrowmanCalculator;
+import net.sf.openrocket.aerodynamics.FlightConditions;
+import net.sf.openrocket.aerodynamics.WarningSet;
+import net.sf.openrocket.rocketcomponent.BodyTube;
+import net.sf.openrocket.rocketcomponent.RocketComponent;
+import net.sf.openrocket.rocketcomponent.SymmetricComponent;
+import net.sf.openrocket.rocketcomponent.Transition;
+import net.sf.openrocket.util.Coordinate;
+import net.sf.openrocket.util.LinearInterpolator;
+import net.sf.openrocket.util.MathUtil;
+import net.sf.openrocket.util.PolyInterpolator;
+
+
+
+/**
+ * Calculates the aerodynamic properties of a <code>SymmetricComponent</code>.
+ * <p>
+ * CP and CNa are calculated by the Barrowman method extended to account for body lift
+ * by the method presented by Galejs. Supersonic CNa and CP are assumed to be the
+ * same as the subsonic values.
+ *
+ *
+ * @author Sampo Niskanen <sampo.niskanen@iki.fi>
+ */
+public class SymmetricComponentCalc extends RocketComponentCalc {
+
+ public static final double BODY_LIFT_K = 1.1;
+
+ private final SymmetricComponent component;
+
+ private final double length;
+ private final double r1, r2;
+ private final double fineness;
+ private final Transition.Shape shape;
+ private final double param;
+ private final double area;
+
+ public SymmetricComponentCalc(RocketComponent c) {
+ super(c);
+ if (!(c instanceof SymmetricComponent)) {
+ throw new IllegalArgumentException("Illegal component type "+c);
+ }
+ this.component = (SymmetricComponent) c;
+
+
+ length = component.getLength();
+ r1 = component.getForeRadius();
+ r2 = component.getAftRadius();
+
+ fineness = length / (2*Math.abs(r2-r1));
+
+ if (component instanceof BodyTube) {
+ shape = null;
+ param = 0;
+ area = 0;
+ } else if (component instanceof Transition) {
+ shape = ((Transition)component).getType();
+ param = ((Transition)component).getShapeParameter();
+ area = Math.abs(Math.PI * (r1*r1 - r2*r2));
+ } else {
+ throw new UnsupportedOperationException("Unknown component type " +
+ component.getComponentName());
+ }
+ }
+
+
+ private boolean isTube = false;
+ private double cnaCache = Double.NaN;
+ private double cpCache = Double.NaN;
+
+
+ /**
+ * Calculates the non-axial forces produced by the fins (normal and side forces,
+ * pitch, yaw and roll moments, CP position, CNa).
+ * <p>
+ * This method uses the Barrowman method for CP and CNa calculation and the
+ * extension presented by Galejs for the effect of body lift.
+ * <p>
+ * The CP and CNa at supersonic speeds are assumed to be the same as those at
+ * subsonic speeds.
+ */
+ @Override
+ public void calculateNonaxialForces(FlightConditions conditions,
+ AerodynamicForces forces, WarningSet warnings) {
+
+ // Pre-calculate and store the results
+ if (Double.isNaN(cnaCache)) {
+ final double r0 = component.getForeRadius();
+ final double r1 = component.getAftRadius();
+
+ if (MathUtil.equals(r0, r1)) {
+ isTube = true;
+ cnaCache = 0;
+ } else {
+ isTube = false;
+
+ final double A0 = Math.PI * pow2(r0);
+ final double A1 = Math.PI * pow2(r1);
+
+ cnaCache = 2 * (A1 - A0);
+ System.out.println("cnaCache = "+cnaCache);
+ cpCache = (component.getLength() * A1 - component.getFullVolume()) / (A1 - A0);
+ }
+ }
+
+ Coordinate cp;
+
+ // If fore == aft, only body lift is encountered
+ if (isTube) {
+ cp = getLiftCP(conditions, warnings);
+ } else {
+ cp = new Coordinate(cpCache,0,0,cnaCache * conditions.getSincAOA() /
+ conditions.getRefArea()).average(getLiftCP(conditions,warnings));
+ }
+
+ forces.cp = cp;
+ forces.CNa = cp.weight;
+ forces.CN = forces.CNa * conditions.getAOA();
+ forces.Cm = forces.CN * cp.x / conditions.getRefLength();
+ forces.Croll = 0;
+ forces.CrollDamp = 0;
+ forces.CrollForce = 0;
+ forces.Cside = 0;
+ forces.Cyaw = 0;
+
+
+ // Add warning on supersonic flight
+ if (conditions.getMach() > 1.1) {
+ warnings.add("Body calculations may not be entirely accurate at supersonic speeds.");
+ }
+
+ }
+
+
+
+ /**
+ * Calculate the body lift effect according to Galejs.
+ */
+ protected Coordinate getLiftCP(FlightConditions conditions, WarningSet warnings) {
+ double area = component.getComponentPlanformArea();
+ double center = component.getComponentPlanformCenter();
+
+ /*
+ * Without this extra multiplier the rocket may become unstable at apogee
+ * when turning around, and begin oscillating horizontally. During the flight
+ * of the rocket this has no effect. It is effective only when AOA > 45 deg
+ * and the velocity is less than 15 m/s.
+ */
+ double mul = 1;
+ if ((conditions.getMach() < 0.05) && (conditions.getAOA() > Math.PI/4)) {
+ mul = pow2(conditions.getMach() / 0.05);
+ }
+
+ return new Coordinate(center, 0, 0, mul*BODY_LIFT_K * area/conditions.getRefArea() *
+ conditions.getSinAOA() * conditions.getSincAOA()); // sin(aoa)^2 / aoa
+ }
+
+
+
+ private LinearInterpolator interpolator = null;
+
+ @Override
+ public double calculatePressureDragForce(FlightConditions conditions,
+ double stagnationCD, double baseCD, WarningSet warnings) {
+
+ if (component instanceof BodyTube)
+ return 0;
+
+ if (!(component instanceof Transition)) {
+ throw new RuntimeException("Pressure calculation of unknown type: "+
+ component.getComponentName());
+ }
+
+ // Check for simple cases first
+ if (r1 == r2)
+ return 0;
+
+ if (length < 0.001) {
+ if (r1 < r2) {
+ return stagnationCD * area / conditions.getRefArea();
+ } else {
+ return baseCD * area / conditions.getRefArea();
+ }
+ }
+
+
+ // Boattail drag computed directly from base drag
+ if (r2 < r1) {
+ if (fineness >= 3)
+ return 0;
+ double cd = baseCD * area / conditions.getRefArea();
+ if (fineness <= 1)
+ return cd;
+ return cd * (3-fineness)/2;
+ }
+
+
+ assert(r1 < r2); // Tube and boattail have been checked already
+
+
+ // All nose cones and shoulders from pre-calculated and interpolating
+ if (interpolator == null) {
+ calculateNoseInterpolator();
+ }
+
+ return interpolator.getValue(conditions.getMach()) * area / conditions.getRefArea();
+ }
+
+
+
+ /*
+ * Experimental values of pressure drag for different nose cone shapes with a fineness
+ * ratio of 3. The data is taken from 'Collection of Zero-Lift Drag Data on Bodies
+ * of Revolution from Free-Flight Investigations', NASA TR-R-100, NTRS 19630004995,
+ * page 16.
+ *
+ * This data is extrapolated for other fineness ratios.
+ */
+
+ private static final LinearInterpolator ellipsoidInterpolator = new LinearInterpolator(
+ new double[] { 1.2, 1.25, 1.3, 1.4, 1.6, 2.0, 2.4 },
+ new double[] {0.110, 0.128, 0.140, 0.148, 0.152, 0.159, 0.162 /* constant */ }
+ );
+ private static final LinearInterpolator x14Interpolator = new LinearInterpolator(
+ new double[] { 1.2, 1.3, 1.4, 1.6, 1.8, 2.2, 2.6, 3.0, 3.6},
+ new double[] {0.140, 0.156, 0.169, 0.192, 0.206, 0.227, 0.241, 0.249, 0.252}
+ );
+ private static final LinearInterpolator x12Interpolator = new LinearInterpolator(
+ new double[] {0.925, 0.95, 1.0, 1.05, 1.1, 1.2, 1.3, 1.7, 2.0},
+ new double[] { 0, 0.014, 0.050, 0.060, 0.059, 0.081, 0.084, 0.085, 0.078}
+ );
+ private static final LinearInterpolator x34Interpolator = new LinearInterpolator(
+ new double[] { 0.8, 0.9, 1.0, 1.06, 1.2, 1.4, 1.6, 2.0, 2.8, 3.4},
+ new double[] { 0, 0.015, 0.078, 0.121, 0.110, 0.098, 0.090, 0.084, 0.078, 0.074}
+ );
+ private static final LinearInterpolator vonKarmanInterpolator = new LinearInterpolator(
+ new double[] { 0.9, 0.95, 1.0, 1.05, 1.1, 1.2, 1.4, 1.6, 2.0, 3.0},
+ new double[] { 0, 0.010, 0.027, 0.055, 0.070, 0.081, 0.095, 0.097, 0.091, 0.083}
+ );
+ private static final LinearInterpolator lvHaackInterpolator = new LinearInterpolator(
+ new double[] { 0.9, 0.95, 1.0, 1.05, 1.1, 1.2, 1.4, 1.6, 2.0 },
+ new double[] { 0, 0.010, 0.024, 0.066, 0.084, 0.100, 0.114, 0.117, 0.113 }
+ );
+ private static final LinearInterpolator parabolicInterpolator = new LinearInterpolator(
+ new double[] {0.95, 0.975, 1.0, 1.05, 1.1, 1.2, 1.4, 1.7},
+ new double[] { 0, 0.016, 0.041, 0.092, 0.109, 0.119, 0.113, 0.108}
+ );
+ private static final LinearInterpolator parabolic12Interpolator = new LinearInterpolator(
+ new double[] { 0.8, 0.9, 0.95, 1.0, 1.05, 1.1, 1.3, 1.5, 1.8},
+ new double[] { 0, 0.016, 0.042, 0.100, 0.126, 0.125, 0.100, 0.090, 0.088}
+ );
+ private static final LinearInterpolator parabolic34Interpolator = new LinearInterpolator(
+ new double[] { 0.9, 0.95, 1.0, 1.05, 1.1, 1.2, 1.4, 1.7},
+ new double[] { 0, 0.023, 0.073, 0.098, 0.107, 0.106, 0.089, 0.082}
+ );
+ private static final LinearInterpolator bluntInterpolator = new LinearInterpolator();
+ static {
+ for (double m=0; m<3; m+=0.05)
+ bluntInterpolator.addPoint(m, BarrowmanCalculator.calculateStagnationCD(m));
+ }
+
+ /**
+ * Calculate the LinearInterpolator 'interpolator'. After this call, if can be used
+ * to get the pressure drag coefficient at any Mach number.
+ *
+ * First, the transonic/supersonic region is computed. For conical and ogive shapes
+ * this is calculated directly. For other shapes, the values for fineness-ratio 3
+ * transitions are taken from the experimental values stored above (for parameterized
+ * shapes the values are interpolated between the parameter values). These are then
+ * extrapolated to the current fineness ratio.
+ *
+ * Finally, if the first data points in the interpolator are not zero, the subsonic
+ * region is interpolated in the form Cd = a*M^b + Cd(M=0).
+ */
+ @SuppressWarnings("null")
+ private void calculateNoseInterpolator() {
+ LinearInterpolator int1=null, int2=null;
+ double p = 0;
+
+ interpolator = new LinearInterpolator();
+
+ double r = component.getRadius(0.99*length);
+ double sinphi = (r2-r)/MathUtil.hypot(r2-r, 0.01*length);
+
+ /*
+ * Take into account nose cone shape. Conical and ogive generate the interpolator
+ * directly. Others store a interpolator for fineness ratio 3 into int1, or
+ * for parameterized shapes store the bounding fineness ratio 3 interpolators into
+ * int1 and int2 and set 0 <= p <= 1 according to the bounds.
+ */
+ switch (shape) {
+ case CONICAL:
+ interpolator = calculateOgiveNoseInterpolator(0, sinphi); // param==0 -> conical
+ break;
+
+ case OGIVE:
+ interpolator = calculateOgiveNoseInterpolator(param, sinphi);
+ break;
+
+ case ELLIPSOID:
+ int1 = ellipsoidInterpolator;
+ break;
+
+ case POWER:
+ if (param <= 0.25) {
+ int1 = bluntInterpolator;
+ int2 = x14Interpolator;
+ p = param*4;
+ } else if (param <= 0.5) {
+ int1 = x14Interpolator;
+ int2 = x12Interpolator;
+ p = (param-0.25)*4;
+ } else if (param <= 0.75) {
+ int1 = x12Interpolator;
+ int2 = x34Interpolator;
+ p = (param-0.5)*4;
+ } else {
+ int1 = x34Interpolator;
+ int2 = calculateOgiveNoseInterpolator(0, 1/Math.sqrt(1+4*pow2(fineness)));
+ p = (param-0.75)*4;
+ }
+ break;
+
+ case PARABOLIC:
+ if (param <= 0.5) {
+ int1 = calculateOgiveNoseInterpolator(0, 1/Math.sqrt(1+4*pow2(fineness)));
+ int2 = parabolic12Interpolator;
+ p = param*2;
+ } else if (param <= 0.75) {
+ int1 = parabolic12Interpolator;
+ int2 = parabolic34Interpolator;
+ p = (param-0.5)*4;
+ } else {
+ int1 = parabolic34Interpolator;
+ int2 = parabolicInterpolator;
+ p = (param-0.75)*4;
+ }
+ break;
+
+ case HAACK:
+ int1 = vonKarmanInterpolator;
+ int2 = lvHaackInterpolator;
+ p = param*3;
+ break;
+
+ default:
+ throw new UnsupportedOperationException("Unknown transition shape: "+shape);
+ }
+
+ assert(p >= 0);
+ assert(p <= 1.001);
+
+
+ // Check for parameterized shape and interpolate if necessary
+ if (int2 != null) {
+ LinearInterpolator int3 = new LinearInterpolator();
+ for (double m: int1.getXPoints()) {
+ int3.addPoint(m, p*int2.getValue(m) + (1-p)*int1.getValue(m));
+ }
+ for (double m: int2.getXPoints()) {
+ int3.addPoint(m, p*int2.getValue(m) + (1-p)*int1.getValue(m));
+ }
+ int1 = int3;
+ }
+
+ // Extrapolate for fineness ratio if necessary
+ if (int1 != null) {
+ double log4 = Math.log(fineness+1) / Math.log(4);
+ for (double m: int1.getXPoints()) {
+ double stag = bluntInterpolator.getValue(m);
+ interpolator.addPoint(m, stag*Math.pow(int1.getValue(m)/stag, log4));
+ }
+ }
+
+
+ /*
+ * Now the transonic/supersonic region is ok. We still need to interpolate
+ * the subsonic region, if the values are non-zero.
+ */
+
+ double min = interpolator.getXPoints()[0];
+ double minValue = interpolator.getValue(min);
+ if (minValue < 0.001) {
+ // No interpolation necessary
+ return;
+ }
+
+ double cdMach0 = 0.8 * pow2(sinphi);
+ double minDeriv = (interpolator.getValue(min+0.01) - minValue)/0.01;
+
+ // These should not occur, but might cause havoc for the interpolation
+ if ((cdMach0 >= minValue-0.01) || (minDeriv <= 0.01)) {
+ return;
+ }
+
+ // Cd = a*M^b + cdMach0
+ double a = minValue - cdMach0;
+ double b = minDeriv / a;
+
+ for (double m=0; m < minValue; m+= 0.05) {
+ interpolator.addPoint(m, a*Math.pow(m, b) + cdMach0);
+ }
+ }
+
+
+ private static final PolyInterpolator conicalPolyInterpolator =
+ new PolyInterpolator(new double[] {1.0, 1.3}, new double[] {1.0, 1.3});
+
+ private static LinearInterpolator calculateOgiveNoseInterpolator(double param,
+ double sinphi) {
+ LinearInterpolator interpolator = new LinearInterpolator();
+
+ // In the range M = 1 ... 1.3 use polynomial approximation
+ double cdMach1 = 2.1*pow2(sinphi) + 0.6019*sinphi;
+
+ double[] poly = conicalPolyInterpolator.interpolator(
+ 1.0*sinphi, cdMach1,
+ 4/(GAMMA+1) * (1 - 0.5*cdMach1), -1.1341*sinphi
+ );
+
+ // Shape parameter multiplier
+ double mul = 0.72 * pow2(param-0.5) + 0.82;
+
+ for (double m = 1; m < 1.3001; m += 0.02) {
+ interpolator.addPoint(m, mul * PolyInterpolator.eval(m, poly));
+ }
+
+ // Above M = 1.3 use direct formula
+ for (double m = 1.32; m < 4; m += 0.02) {
+ interpolator.addPoint(m, mul * (2.1*pow2(sinphi) + 0.5*sinphi/Math.sqrt(m*m - 1)));
+ }
+
+ return interpolator;
+ }
+
+
+
+}
projects / debian / openrocket / blobdiff