1 package net.sf.openrocket.aerodynamics.barrowman;
3 import static net.sf.openrocket.aerodynamics.AtmosphericConditions.GAMMA;
4 import static net.sf.openrocket.util.MathUtil.pow2;
5 import net.sf.openrocket.aerodynamics.AerodynamicForces;
6 import net.sf.openrocket.aerodynamics.BarrowmanCalculator;
7 import net.sf.openrocket.aerodynamics.FlightConditions;
8 import net.sf.openrocket.aerodynamics.WarningSet;
9 import net.sf.openrocket.rocketcomponent.BodyTube;
10 import net.sf.openrocket.rocketcomponent.RocketComponent;
11 import net.sf.openrocket.rocketcomponent.SymmetricComponent;
12 import net.sf.openrocket.rocketcomponent.Transition;
13 import net.sf.openrocket.util.BugException;
14 import net.sf.openrocket.util.Coordinate;
15 import net.sf.openrocket.util.LinearInterpolator;
16 import net.sf.openrocket.util.MathUtil;
17 import net.sf.openrocket.util.PolyInterpolator;
22 * Calculates the aerodynamic properties of a <code>SymmetricComponent</code>.
24 * CP and CNa are calculated by the Barrowman method extended to account for body lift
25 * by the method presented by Galejs. Supersonic CNa and CP are assumed to be the
26 * same as the subsonic values.
29 * @author Sampo Niskanen <sampo.niskanen@iki.fi>
31 public class SymmetricComponentCalc extends RocketComponentCalc {
33 public static final double BODY_LIFT_K = 1.1;
35 private final SymmetricComponent component;
37 private final double length;
38 private final double r1, r2;
39 private final double fineness;
40 private final Transition.Shape shape;
41 private final double param;
42 private final double area;
44 public SymmetricComponentCalc(RocketComponent c) {
46 if (!(c instanceof SymmetricComponent)) {
47 throw new IllegalArgumentException("Illegal component type "+c);
49 this.component = (SymmetricComponent) c;
52 length = component.getLength();
53 r1 = component.getForeRadius();
54 r2 = component.getAftRadius();
56 fineness = length / (2*Math.abs(r2-r1));
58 if (component instanceof BodyTube) {
62 } else if (component instanceof Transition) {
63 shape = ((Transition)component).getType();
64 param = ((Transition)component).getShapeParameter();
65 area = Math.abs(Math.PI * (r1*r1 - r2*r2));
67 throw new UnsupportedOperationException("Unknown component type " +
68 component.getComponentName());
73 private boolean isTube = false;
74 private double cnaCache = Double.NaN;
75 private double cpCache = Double.NaN;
79 * Calculates the non-axial forces produced by the fins (normal and side forces,
80 * pitch, yaw and roll moments, CP position, CNa).
82 * This method uses the Barrowman method for CP and CNa calculation and the
83 * extension presented by Galejs for the effect of body lift.
85 * The CP and CNa at supersonic speeds are assumed to be the same as those at
89 public void calculateNonaxialForces(FlightConditions conditions,
90 AerodynamicForces forces, WarningSet warnings) {
92 // Pre-calculate and store the results
93 if (Double.isNaN(cnaCache)) {
94 final double r0 = component.getForeRadius();
95 final double r1 = component.getAftRadius();
97 if (MathUtil.equals(r0, r1)) {
103 final double A0 = Math.PI * pow2(r0);
104 final double A1 = Math.PI * pow2(r1);
106 cnaCache = 2 * (A1 - A0);
107 System.out.println("cnaCache = "+cnaCache);
108 cpCache = (component.getLength() * A1 - component.getFullVolume()) / (A1 - A0);
114 // If fore == aft, only body lift is encountered
116 cp = getLiftCP(conditions, warnings);
118 cp = new Coordinate(cpCache,0,0,cnaCache * conditions.getSincAOA() /
119 conditions.getRefArea()).average(getLiftCP(conditions,warnings));
123 forces.CNa = cp.weight;
124 forces.CN = forces.CNa * conditions.getAOA();
125 forces.Cm = forces.CN * cp.x / conditions.getRefLength();
127 forces.CrollDamp = 0;
128 forces.CrollForce = 0;
133 // Add warning on supersonic flight
134 if (conditions.getMach() > 1.1) {
135 warnings.add("Body calculations may not be entirely accurate at supersonic speeds.");
143 * Calculate the body lift effect according to Galejs.
145 protected Coordinate getLiftCP(FlightConditions conditions, WarningSet warnings) {
146 double area = component.getComponentPlanformArea();
147 double center = component.getComponentPlanformCenter();
150 * Without this extra multiplier the rocket may become unstable at apogee
151 * when turning around, and begin oscillating horizontally. During the flight
152 * of the rocket this has no effect. It is effective only when AOA > 45 deg
153 * and the velocity is less than 15 m/s.
156 if ((conditions.getMach() < 0.05) && (conditions.getAOA() > Math.PI/4)) {
157 mul = pow2(conditions.getMach() / 0.05);
160 return new Coordinate(center, 0, 0, mul*BODY_LIFT_K * area/conditions.getRefArea() *
161 conditions.getSinAOA() * conditions.getSincAOA()); // sin(aoa)^2 / aoa
166 private LinearInterpolator interpolator = null;
169 public double calculatePressureDragForce(FlightConditions conditions,
170 double stagnationCD, double baseCD, WarningSet warnings) {
172 if (component instanceof BodyTube)
175 if (!(component instanceof Transition)) {
176 throw new BugException("Pressure calculation of unknown type: "+
177 component.getComponentName());
180 // Check for simple cases first
184 if (length < 0.001) {
186 return stagnationCD * area / conditions.getRefArea();
188 return baseCD * area / conditions.getRefArea();
193 // Boattail drag computed directly from base drag
197 double cd = baseCD * area / conditions.getRefArea();
200 return cd * (3-fineness)/2;
204 assert(r1 < r2); // Tube and boattail have been checked already
207 // All nose cones and shoulders from pre-calculated and interpolating
208 if (interpolator == null) {
209 calculateNoseInterpolator();
212 return interpolator.getValue(conditions.getMach()) * area / conditions.getRefArea();
218 * Experimental values of pressure drag for different nose cone shapes with a fineness
219 * ratio of 3. The data is taken from 'Collection of Zero-Lift Drag Data on Bodies
220 * of Revolution from Free-Flight Investigations', NASA TR-R-100, NTRS 19630004995,
223 * This data is extrapolated for other fineness ratios.
226 private static final LinearInterpolator ellipsoidInterpolator = new LinearInterpolator(
227 new double[] { 1.2, 1.25, 1.3, 1.4, 1.6, 2.0, 2.4 },
228 new double[] {0.110, 0.128, 0.140, 0.148, 0.152, 0.159, 0.162 /* constant */ }
230 private static final LinearInterpolator x14Interpolator = new LinearInterpolator(
231 new double[] { 1.2, 1.3, 1.4, 1.6, 1.8, 2.2, 2.6, 3.0, 3.6},
232 new double[] {0.140, 0.156, 0.169, 0.192, 0.206, 0.227, 0.241, 0.249, 0.252}
234 private static final LinearInterpolator x12Interpolator = new LinearInterpolator(
235 new double[] {0.925, 0.95, 1.0, 1.05, 1.1, 1.2, 1.3, 1.7, 2.0},
236 new double[] { 0, 0.014, 0.050, 0.060, 0.059, 0.081, 0.084, 0.085, 0.078}
238 private static final LinearInterpolator x34Interpolator = new LinearInterpolator(
239 new double[] { 0.8, 0.9, 1.0, 1.06, 1.2, 1.4, 1.6, 2.0, 2.8, 3.4},
240 new double[] { 0, 0.015, 0.078, 0.121, 0.110, 0.098, 0.090, 0.084, 0.078, 0.074}
242 private static final LinearInterpolator vonKarmanInterpolator = new LinearInterpolator(
243 new double[] { 0.9, 0.95, 1.0, 1.05, 1.1, 1.2, 1.4, 1.6, 2.0, 3.0},
244 new double[] { 0, 0.010, 0.027, 0.055, 0.070, 0.081, 0.095, 0.097, 0.091, 0.083}
246 private static final LinearInterpolator lvHaackInterpolator = new LinearInterpolator(
247 new double[] { 0.9, 0.95, 1.0, 1.05, 1.1, 1.2, 1.4, 1.6, 2.0 },
248 new double[] { 0, 0.010, 0.024, 0.066, 0.084, 0.100, 0.114, 0.117, 0.113 }
250 private static final LinearInterpolator parabolicInterpolator = new LinearInterpolator(
251 new double[] {0.95, 0.975, 1.0, 1.05, 1.1, 1.2, 1.4, 1.7},
252 new double[] { 0, 0.016, 0.041, 0.092, 0.109, 0.119, 0.113, 0.108}
254 private static final LinearInterpolator parabolic12Interpolator = new LinearInterpolator(
255 new double[] { 0.8, 0.9, 0.95, 1.0, 1.05, 1.1, 1.3, 1.5, 1.8},
256 new double[] { 0, 0.016, 0.042, 0.100, 0.126, 0.125, 0.100, 0.090, 0.088}
258 private static final LinearInterpolator parabolic34Interpolator = new LinearInterpolator(
259 new double[] { 0.9, 0.95, 1.0, 1.05, 1.1, 1.2, 1.4, 1.7},
260 new double[] { 0, 0.023, 0.073, 0.098, 0.107, 0.106, 0.089, 0.082}
262 private static final LinearInterpolator bluntInterpolator = new LinearInterpolator();
264 for (double m=0; m<3; m+=0.05)
265 bluntInterpolator.addPoint(m, BarrowmanCalculator.calculateStagnationCD(m));
269 * Calculate the LinearInterpolator 'interpolator'. After this call, if can be used
270 * to get the pressure drag coefficient at any Mach number.
272 * First, the transonic/supersonic region is computed. For conical and ogive shapes
273 * this is calculated directly. For other shapes, the values for fineness-ratio 3
274 * transitions are taken from the experimental values stored above (for parameterized
275 * shapes the values are interpolated between the parameter values). These are then
276 * extrapolated to the current fineness ratio.
278 * Finally, if the first data points in the interpolator are not zero, the subsonic
279 * region is interpolated in the form Cd = a*M^b + Cd(M=0).
281 @SuppressWarnings("null")
282 private void calculateNoseInterpolator() {
283 LinearInterpolator int1=null, int2=null;
286 interpolator = new LinearInterpolator();
288 double r = component.getRadius(0.99*length);
289 double sinphi = (r2-r)/MathUtil.hypot(r2-r, 0.01*length);
292 * Take into account nose cone shape. Conical and ogive generate the interpolator
293 * directly. Others store a interpolator for fineness ratio 3 into int1, or
294 * for parameterized shapes store the bounding fineness ratio 3 interpolators into
295 * int1 and int2 and set 0 <= p <= 1 according to the bounds.
299 interpolator = calculateOgiveNoseInterpolator(0, sinphi); // param==0 -> conical
303 interpolator = calculateOgiveNoseInterpolator(param, sinphi);
307 int1 = ellipsoidInterpolator;
312 int1 = bluntInterpolator;
313 int2 = x14Interpolator;
315 } else if (param <= 0.5) {
316 int1 = x14Interpolator;
317 int2 = x12Interpolator;
319 } else if (param <= 0.75) {
320 int1 = x12Interpolator;
321 int2 = x34Interpolator;
324 int1 = x34Interpolator;
325 int2 = calculateOgiveNoseInterpolator(0, 1/Math.sqrt(1+4*pow2(fineness)));
332 int1 = calculateOgiveNoseInterpolator(0, 1/Math.sqrt(1+4*pow2(fineness)));
333 int2 = parabolic12Interpolator;
335 } else if (param <= 0.75) {
336 int1 = parabolic12Interpolator;
337 int2 = parabolic34Interpolator;
340 int1 = parabolic34Interpolator;
341 int2 = parabolicInterpolator;
347 int1 = vonKarmanInterpolator;
348 int2 = lvHaackInterpolator;
353 throw new UnsupportedOperationException("Unknown transition shape: "+shape);
360 // Check for parameterized shape and interpolate if necessary
362 LinearInterpolator int3 = new LinearInterpolator();
363 for (double m: int1.getXPoints()) {
364 int3.addPoint(m, p*int2.getValue(m) + (1-p)*int1.getValue(m));
366 for (double m: int2.getXPoints()) {
367 int3.addPoint(m, p*int2.getValue(m) + (1-p)*int1.getValue(m));
372 // Extrapolate for fineness ratio if necessary
374 double log4 = Math.log(fineness+1) / Math.log(4);
375 for (double m: int1.getXPoints()) {
376 double stag = bluntInterpolator.getValue(m);
377 interpolator.addPoint(m, stag*Math.pow(int1.getValue(m)/stag, log4));
383 * Now the transonic/supersonic region is ok. We still need to interpolate
384 * the subsonic region, if the values are non-zero.
387 double min = interpolator.getXPoints()[0];
388 double minValue = interpolator.getValue(min);
389 if (minValue < 0.001) {
390 // No interpolation necessary
394 double cdMach0 = 0.8 * pow2(sinphi);
395 double minDeriv = (interpolator.getValue(min+0.01) - minValue)/0.01;
397 // These should not occur, but might cause havoc for the interpolation
398 if ((cdMach0 >= minValue-0.01) || (minDeriv <= 0.01)) {
402 // Cd = a*M^b + cdMach0
403 double a = minValue - cdMach0;
404 double b = minDeriv / a;
406 for (double m=0; m < minValue; m+= 0.05) {
407 interpolator.addPoint(m, a*Math.pow(m, b) + cdMach0);
412 private static final PolyInterpolator conicalPolyInterpolator =
413 new PolyInterpolator(new double[] {1.0, 1.3}, new double[] {1.0, 1.3});
415 private static LinearInterpolator calculateOgiveNoseInterpolator(double param,
417 LinearInterpolator interpolator = new LinearInterpolator();
419 // In the range M = 1 ... 1.3 use polynomial approximation
420 double cdMach1 = 2.1*pow2(sinphi) + 0.6019*sinphi;
422 double[] poly = conicalPolyInterpolator.interpolator(
424 4/(GAMMA+1) * (1 - 0.5*cdMach1), -1.1341*sinphi
427 // Shape parameter multiplier
428 double mul = 0.72 * pow2(param-0.5) + 0.82;
430 for (double m = 1; m < 1.3001; m += 0.02) {
431 interpolator.addPoint(m, mul * PolyInterpolator.eval(m, poly));
434 // Above M = 1.3 use direct formula
435 for (double m = 1.32; m < 4; m += 0.02) {
436 interpolator.addPoint(m, mul * (2.1*pow2(sinphi) + 0.5*sinphi/Math.sqrt(m*m - 1)));