Add unit test

core/src/net/sf/openrocket/aerodynamics/barrowman/RailButtonCalc.java

@@ -47,8 +47,8 @@ public class RailButtonCalc extends RocketComponentCalc {
 	@Override
 	public double calculatePressureCD(FlightConditions conditions,
 									  double stagnationCD, double baseCD, WarningSet warnings) {
+
 		// grab relevant button params
-		
 		final int instanceCount = button.getInstanceCount();
 		final Coordinate[] instanceOffsets = button.getInstanceOffsets();
 
@@ -65,10 +65,10 @@ public class RailButtonCalc extends RocketComponentCalc {
 			// compute boundary layer height at button location.  I can't find a good reference for the
 			// formula, e.g. https://aerospaceengineeringblog.com/boundary-layers/ simply says it's the
 			// "scientific consensus".
-			double x = (button.toAbsolute(instanceOffsets[i]))[0].x;  // location of button
+			double x = (button.toAbsolute(instanceOffsets[i]))[0].x;   // location of button
 			double rex = calculateReynoldsNumber(x, conditions);       // Reynolds number of button location
 			double del = 0.37 * x / Math.pow(rex, 0.2);                // Boundary layer thickness
-			
+
 			// compute mean airspeed over button
 			// this assumes airspeed changes linearly through boundary layer
 			// and that all parts of the railbutton contribute equally to Cd,
@@ -96,6 +96,7 @@ public class RailButtonCalc extends RocketComponentCalc {
 			// add to CDmul
 			CDmul += cd;
 		}
-		return CDmul*stagnationCD * refArea / conditions.getRefArea();
+		
+		return CDmul * stagnationCD * refArea / conditions.getRefArea();
 	}
 }

core/test/net/sf/openrocket/aerodynamics/RailButtonCalcTest.java

@@ -0,0 +1,101 @@
+package net.sf.openrocket.aerodynamics;
+
+import static org.junit.Assert.assertEquals;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import com.google.inject.Guice;
+import com.google.inject.Injector;
+import com.google.inject.Module;
+
+import net.sf.openrocket.ServicesForTesting;
+import net.sf.openrocket.aerodynamics.BarrowmanCalculator;
+import net.sf.openrocket.aerodynamics.barrowman.RailButtonCalc;
+import net.sf.openrocket.plugin.PluginModule;
+import net.sf.openrocket.rocketcomponent.FlightConfiguration;
+import net.sf.openrocket.rocketcomponent.BodyTube;
+import net.sf.openrocket.rocketcomponent.RailButton;
+import net.sf.openrocket.rocketcomponent.LaunchLug;
+import net.sf.openrocket.rocketcomponent.Rocket;
+import net.sf.openrocket.rocketcomponent.position.AxialMethod;
+import net.sf.openrocket.startup.Application;
+import net.sf.openrocket.util.MathUtil;
+import net.sf.openrocket.util.TestRockets;
+import net.sf.openrocket.util.Transformation;
+
+public class RailButtonCalcTest {
+	protected final double EPSILON = 0.0001;
+	
+	private static Injector injector;
+	@BeforeClass
+	public static void setup() {
+		Module applicationModule = new ServicesForTesting();
+		Module pluginModule = new PluginModule();
+		
+		injector = Guice.createInjector( applicationModule, pluginModule);
+		Application.setInjector(injector);
+	}
+		
+	@Test
+	public void testRailButtons() {
+
+		Rocket rocket = TestRockets.makeEstesAlphaIII();
+		FlightConfiguration config = rocket.getSelectedConfiguration();
+
+		// Get the body tube...
+		BodyTube tube = (BodyTube)rocket.getChild(0).getChild(1);
+
+		// Replace the launch lug with a (single) railbutton
+		LaunchLug lug = (LaunchLug)tube.getChild(1);
+		rocket.removeChild(lug);
+
+		RailButton button = new RailButton();
+		tube.addChild(button);
+		
+		// Button parameters from Binder Design standard 1010
+		button.setOuterDiameter(0.011);
+		button.setInnerDiameter(0.006);
+		
+		button.setBaseHeight(0.002);
+		button.setFlangeHeight(0.002);
+		button.setTotalHeight(0.008);
+
+		button.setAxialMethod(AxialMethod.ABSOLUTE);
+		button.setAxialOffset(1.0);
+
+		// Set up flight conditions
+		FlightConditions conditions = new FlightConditions(config);
+		conditions.setMach(1.0);
+
+		BarrowmanCalculator barrowmanObj = new BarrowmanCalculator();
+		RailButtonCalc calcObj = new RailButtonCalc(button);
+		
+		// Calculate effective CD for rail button
+		// Boundary layer height
+		double rex = calcObj.calculateReynoldsNumber(1.0, conditions);      // Reynolds number of button location
+		double del = 0.37 * 1.0 / Math.pow(rex, 0.2);                       // Boundary layer height
+
+		// Interpolate velocity at midpoint of railbutton
+		double mach = MathUtil.map(0.008/2.0, 0, del, 0, 1.0);
+
+		// Interpolate to get CD
+		double cd = MathUtil.map(mach, 0.2, 0.3, 1.22, 1.25);
+
+		// Reference area of rail button
+		final double outerArea = button.getTotalHeight() * button.getOuterDiameter();
+		final double notchArea = (button.getOuterDiameter() - button.getInnerDiameter()) * button.getInnerHeight();
+		final double refArea = outerArea - notchArea;
+
+		// Get "effective" CD
+		double calccd = cd * MathUtil.pow2(mach) * barrowmanObj.calculateStagnationCD(conditions.getMach()) * refArea / conditions.getRefArea() ;
+
+		// Now compare with value from RailButtonCalc
+		WarningSet warnings = new WarningSet();
+		AerodynamicForces assemblyForces = new AerodynamicForces().zero();
+		AerodynamicForces componentForces = new AerodynamicForces();
+
+		double testcd = calcObj.calculatePressureCD(conditions, barrowmanObj.calculateStagnationCD(conditions.getMach()), 0, warnings);
+
+		assertEquals("Calculated rail button CD incorrect", calccd, testcd, EPSILON);
+	}
+}