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Pin CP to axis when calculating in BarrowmanCalculator.calculateNonAxialForces()

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It turns out that the assumption of radial symmetry is absolutely pervasive in our CP calculations.  Looking at FinSetCalc.calculateNonAxialForces(), we don't actually compute the CP of a fin -- we calculate its X value, and pin it to Y=Z=0.

The only exception to this is in BarrowmanCalculator.calculateNonAxialForces(), where the pinning only takes place if there are three or more fins in a FinSet.  If we remove the test for number of fins in the FinSet, we are in essence making the assumption that there are more fins *somewhere* which will end up being radially symmetric.
This commit is contained in:
JoePfeiffer 2020-05-06 16:57:04 -06:00
parent 73dd6b7e7a
commit f0e5902e00
2 changed files with 2 additions and 10 deletions
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3
core/src/net/sf/openrocket/aerodynamics/BarrowmanCalculator.java
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@ -204,8 +204,7 @@ public class BarrowmanCalculator extends AbstractAerodynamicCalculator {
Coordinate cp_inst = instanceForces.getCP();
Coordinate cp_abs = context.transform.transform(cp_inst);
if ((comp instanceof FinSet) && (((FinSet)comp).getFinCount() > 2))
cp_abs = cp_abs.setY(0.0).setZ(0.0);
cp_abs = cp_abs.setY(0.0).setZ(0.0);
// if( 1e-6 < cp_inst.weight) {
// System.err.println("_________ cp:inst: (rel): " + cp_inst.toString());

9
core/test/net/sf/openrocket/aerodynamics/BarrowmanCalculatorTest.java
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@ -338,20 +338,13 @@ public class BarrowmanCalculatorTest {
// results with and without it
// cpNoPods (0.34125,0.00000,0.00000,w=16.20502) -- interference disabled
// cpNoPods (0.34797,0.00000,0.00000,w=19.34773) -- interference enabled
// another note: the fact that this is seen as three one-fin
// FinSets instead of a single three-fin FinSet means the CP
// will be off-axis (one of the fins is taken as having an
// angle of 0 to the airstream, so it has no contribution).
// This doesn't turn out to cause a problem in an actual
// simulation.
final Coordinate cpNoPods = calcNoPods.getCP(configNoPods, conditionsNoPods, warningsNoPods);
final Coordinate cpPods = calcPods.getCP(configPods, conditionsPods, warningsPods);
System.out.printf("with pods %s\n", cpPods.toString());
System.out.printf("without pods %s\n", cpNoPods.toString());
assertEquals(" Alpha III With Pods rocket cp x value is incorrect:", cpNoPods.x - 0.002788761352, cpPods.x, EPSILON);
assertEquals(" Alpha III With Pods rocket cp y value is incorrect:", cpNoPods.y - 0.005460218430206499, cpPods.y, EPSILON);
assertEquals(" Alpha III With Pods rocket cp y value is incorrect:", cpNoPods.y, cpPods.y, EPSILON);
assertEquals(" Alpha III With Pods rocket cp z value is incorrect:", cpNoPods.z, cpPods.z, EPSILON);
assertEquals(" Alpha III With Pods rocket CNa value is incorrect:", cpPods.weight, cpNoPods.weight - 3.91572, EPSILON);
}