[Csp-commits] svn:csp r2169 - trunk/csp/cspsim/test

[<sv...@ww...>]

Author: mkrose
Date: 2007-08-12 01:13:48 -0700 (Sun, 12 Aug 2007)
New Revision: 2169

Modified:
   trunk/csp/cspsim/test/test_PhysicsModel.cpp
Log:
Test time dependenent inertia for a spinning body.  Changes to inertia are made
between timesteps such that angular velocity remains constant.  This covers the
common case of stores release, for which angular momentum of the primary
vehicle is not conserved, but neglects internal configuration changes such as
fuel redistribution and variable geometry.

Browse at: https://www.zerobar.net/viewcvs/viewcvs.cgi?view=rev&rev=2169

Modified: trunk/csp/cspsim/test/test_PhysicsModel.cpp
===================================================================
--- trunk/csp/cspsim/test/test_PhysicsModel.cpp	2007-08-10 12:46:55 UTC (rev 2168)
+++ trunk/csp/cspsim/test/test_PhysicsModel.cpp	2007-08-12 08:13:48 UTC (rev 2169)
@@ -315,6 +315,49 @@
 		CSP_EXPECT_FEQ(0, vdiff(object->angularVelocity(), Vector3(1, 2, 3)));
 	}
 
+	CSP_TESTCASE(ForceFreeTop) {
+		// force free motion of a symmetric top, with I3 / I12 = sqrt(7) / 2.
+		object->setInertia(Matrix3(1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.5 * sqrt(7)));
+		// w(0) is 30 degrees from z, in the x-z plane.
+		object->setAngularVelocity(Vector3(0.5, 0, 1) * sqrt(5));
+		// w should precess about z with angular frequency omega, and |w|
+		// should remain constant.
+		double omega = (0.5 * sqrt(7) - 1.0) * sqrt(5);
+
+		const double dt = 5.0 / 1000.0;
+		double t = 0.0;
+		for (int i = 0; i < 1000; ++i) {
+			physics->doSimStep(dt); t += dt;
+			Vector3 w = object->angularVelocityBody();
+			double phase = atan2(w.y(), w.x());
+			CSP_ENSURE_GT(0.00001, fabs(fmod(phase - omega * t, 2*PI)));
+			CSP_ENSURE_GT(0.00001, fabs(w.z() - sqrt(5)));
+		}
+	}
+
+	CSP_TESTCASE(ScratchSpin) {
+		object->setInertia(Matrix3(1, 0, 0, 0, 1, 0, 0, 0, 1));
+		object->setAngularVelocity(Vector3(0, 0, 1));
+
+		// force-free spin, with decreasing moment of inertia.  angular
+		// momentum should decrease as well, since PhysicsModel treats all
+		// inertia changes as external (i.e., as a result of shedding or
+		// gaining mass as opposed to internal reconfigurations of mass).  this
+		// is appropriate, for example, to the release of external stores, but
+		// not correct for mass reconfigurations such as fuel redistribution or
+		// geometry changes.  the latter are effects tend to be small compared
+		// to typical forces, and are thus neglected in the simulation.
+
+		const double dt = 5.0 / 1000.0;
+		double t = 0.0;
+		for (int i = 0; i < 1000; ++i) {
+			double Iz = 1.0 / (1.0 + t);  // Iz reduction over time.
+			object->setInertia(Matrix3(1, 0, 0, 0, 1, 0, 0, 0, Iz));
+			physics->doSimStep(dt); t += dt;
+			CSP_ENSURE_GT(0.00001, vdiff(object->angularVelocity(), Vector3(0, 0, 1)));
+		}
+	}
+
 private:
 	Ref<PhysicsModel> physics;
 	Ref<SystemsModel> systems;