hongshaorou/openrocket
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

eliminate SymmetricComponent::integrateInertiaSurface()

Browse Source 
Previously, the code calculated the volume of a component, and if that volume was too small calculated its moments of inertia based on the surface instead of the volume. The decision wasn't based on the thickness of the shell (which might have made sense to me), it was the actual volume. The result is any really small component had its moments of inertia calculated using this surface method, no matter how "solid" the object was.

The cause of #2403 was that this method was used to calculate the moments of inertia in the .ork that failed, but the actual CG was used in the parallel axis theorem. This put the CG in a different place than a "surface CG" would have, so the longitudinal moment of inertia ended up less than 0 triggering the crash.

Now, if a component is so small that's volume is 0 it is assumed its contribution to moment of inertia must also be negligible, so the moments of inertia are set to 0 in this case.
This commit is contained in:
JoePfeiffer 2023-11-21 16:01:41 -07:00
parent 9fec2af7a8
commit 4b1c6a4f4b
1 changed files with 6 additions and 70 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

76
core/src/net/sf/openrocket/rocketcomponent/SymmetricComponent.java
View File

@ -314,10 +314,7 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
@Override
public double getLongitudinalUnitInertia() {
if (Double.isNaN(longitudinalInertia)) {
if (getComponentVolume() > 0.0000001) // == 0.1cm^3
integrateInertiaVolume();
else
integrateInertiaSurface();
integrateInertiaVolume();
}
return longitudinalInertia;
}
@ -326,10 +323,7 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
@Override
public double getRotationalUnitInertia() {
if (Double.isNaN(rotationalInertia)) {
if (getComponentVolume() > 0.0000001) // == 0.1cm^3
integrateInertiaVolume();
else
integrateInertiaSurface();
integrateInertiaVolume();
}
return rotationalInertia;
}
@ -497,9 +491,11 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
r1 = r2;
x += l;
}
// a part so small it has no volume can't contribute to moment of inertia
if (MathUtil.equals(vol, 0)) {
integrateInertiaSurface();
rotationalInertia = 0;
longitudinalInertia = 0;
return;
}
@ -509,66 +505,6 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
// Shift longitudinal inertia to CG
longitudinalInertia = longitudinalInertia - pow2(getSymmetricComponentCG().x);
}
/**
* Integrate the longitudinal and rotational inertia based on component surface area.
* This method may be used only if the total volume is zero.
*/
private void integrateInertiaSurface() {
double x, r1, r2;
longitudinalInertia = 0;
rotationalInertia = 0;
if (getLength() <= 0) return;
final double l = getLength() / DIVISIONS;
r1 = getRadius(0);
x = 0;
double surface = 0;
for (int n = 1; n <= DIVISIONS; n++) {
/*
* r1 and r2 are the two radii, outer is their average
* x is the position of r1
* hyp is the length of the hypotenuse from r1 to r2
* height if the y-axis height of the component if not filled
*/
r2 = getRadius(x + l);
final double hyp = MathUtil.hypot(r2 - r1, l);
final double outer = (r1 + r2) / 2;
final double dS = hyp * (r1 + r2) * Math.PI;
rotationalInertia += dS * pow2(outer);
longitudinalInertia += dS * ((6 * pow2(outer) + pow2(l)) / 12 + pow2(x + l / 2));
surface += dS;
// Update for next iteration
r1 = r2;
x += l;
}
if (MathUtil.equals(surface, 0)) {
longitudinalInertia = 0;
rotationalInertia = 0;
return;
}
longitudinalInertia /= surface;
rotationalInertia /= surface;
// Shift longitudinal inertia to CG
longitudinalInertia = longitudinalInertia - pow2(getSymmetricComponentCG().x);
}
/**
* Invalidates the cached volume and CG information.