hongshaorou/openrocket
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Instead of incrementing through the slices of the component, multiply to recalculate each slice (from some comments in the code I suspect there were some problems with floating point error accumulating).

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Increase the number of divisions to 128, so division is just an exponent change and won't cause floating point error

a little tidying
This commit is contained in:
JoePfeiffer 2023-11-21 17:47:17 -07:00
parent ff6b23f366
commit e92e2bc3a9
1 changed files with 15 additions and 29 deletions
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44
core/src/net/sf/openrocket/rocketcomponent/SymmetricComponent.java
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@ -23,7 +23,7 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
public static final double DEFAULT_RADIUS = 0.025; public static final double DEFAULT_RADIUS = 0.025;
public static final double DEFAULT_THICKNESS = 0.002; public static final double DEFAULT_THICKNESS = 0.002;
private static final int DIVISIONS = 100; // No. of divisions when integrating private static final int DIVISIONS = 128; // No. of divisions when integrating
protected boolean filled = false; protected boolean filled = false;
protected double thickness = DEFAULT_THICKNESS; protected double thickness = DEFAULT_THICKNESS;
@ -332,9 +332,6 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
* Performs integration over the length of the component and updates the cached variables. * Performs integration over the length of the component and updates the cached variables.
*/ */
private void integrate() { private void integrate() {
double x, r1, r2;
double cgx;
wetArea = 0; wetArea = 0;
planArea = 0; planArea = 0;
planCenter = 0; planCenter = 0;
@ -343,6 +340,8 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
cg = Coordinate.NUL; cg = Coordinate.NUL;
longitudinalInertia = 0; longitudinalInertia = 0;
rotationalInertia = 0; rotationalInertia = 0;
double cgx = 0;
// Check length > 0 // Check length > 0
if (getLength() <= 0) { if (getLength() <= 0) {
@ -350,27 +349,18 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
} }
// Integrate for volume, CG, wetted area, planform area, and moments of inertia // Integrate for volume, CG, wetted area, planform area, and moments of inertia
for (int n = 0; n < DIVISIONS; n++) {
final double l = getLength() / DIVISIONS;
final double pi3 = Math.PI / 3.0;
final double pil = Math.PI * l;
final double pil3 = Math.PI * l / 3;
r1 = getRadius(0);
x = 0;
cgx = 0;
for (int n = 1; n <= DIVISIONS; n++) {
/* /*
* r1 and r2 are the two radii * x1 and x2 are the bounds on this section
* x is the position of r1
* hyp is the length of the hypotenuse from r1 to r2 * hyp is the length of the hypotenuse from r1 to r2
* height is the y-axis height of the component if not filled * height is the y-axis height of the component if not filled
*/ */
final double x1 = n * getLength() / DIVISIONS;
// Further to prevent round off error from the previous statement, final double r1 = getRadius(x1);
// we clamp r2 to length at the last iteration. final double x2 = (n + 1) * getLength() / DIVISIONS;
r2 = getRadius((n==DIVISIONS) ? getLength() : x + l); final double r2 = getRadius(x2);
final double l = x2 - x1;
final double xmean = (x1 + x2) / 2;
final double outer = (r1 + r2) / 2; final double outer = (r1 + r2) / 2;
final double hyp = MathUtil.hypot(r2 - r1, l); final double hyp = MathUtil.hypot(r2 - r1, l);
@ -381,7 +371,7 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
final double dV; final double dV;
final double dFullV; final double dFullV;
dFullV = pi3 * l * (r1 * r1 + r1 * r2 + r2 * r2); dFullV = Math.PI * l * (r1 * r1 + r1 * r2 + r2 * r2) / 3.0;
if ( filled || r1 < height || r2 < height ) { if ( filled || r1 < height || r2 < height ) {
inner = 0; inner = 0;
@ -405,7 +395,7 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
// Add to the volume-related components // Add to the volume-related components
volume += dV; volume += dV;
fullVolume += dFullV; fullVolume += dFullV;
cgx += (x + l / 2) * dV; cgx += xmean * dV;
// Wetted area ( * PI at the end) // Wetted area ( * PI at the end)
wetArea += hyp * (r1 + r2); wetArea += hyp * (r1 + r2);
@ -413,14 +403,10 @@ public abstract class SymmetricComponent extends BodyComponent implements BoxBou
// Planform area & center // Planform area & center
final double p = l * (r1 + r2); final double p = l * (r1 + r2);
planArea += p; planArea += p;
planCenter += (x + l / 2) * p; planCenter += xmean * p;
rotationalInertia += dV * (pow2(outer) + pow2(inner)) / 2; rotationalInertia += dV * (pow2(outer) + pow2(inner)) / 2;
longitudinalInertia += dV * ((3 * (pow2(outer) + pow2(inner)) + pow2(l)) / 12 + pow2(x + l / 2)); longitudinalInertia += dV * ((3 * (pow2(outer) + pow2(inner)) + pow2(l)) / 12 + pow2(xmean));
// Update for next iteration
r1 = r2;
x += l;
} }
wetArea *= Math.PI; wetArea *= Math.PI;