Resolve tire loads in an orthonormal road frame

BobLib/Chassis/Suspension/Tires/BaseTire.mo

@@ -47,9 +47,6 @@ model BaseTire
   Modelica.Blocks.Sources.RealExpression realExpressionFy(y = 0) annotation(
     Placement(transformation(origin = {-90, -70}, extent = {{-10, -10}, {10, 10}})));
 
-  Modelica.Blocks.Sources.Constant constantZero(k = 0) annotation(
-    Placement(transformation(origin = {-90, -90}, extent = {{-10, -10}, {10, 10}})));
-
   // Torque expressions
   Modelica.Blocks.Sources.RealExpression realExpressionMx(y = 0) annotation(
     Placement(transformation(origin = {-90, 54}, extent = {{-10, -10}, {10, 10}})));
@@ -61,17 +58,23 @@ model BaseTire
     Placement(transformation(origin = {-90, 26}, extent = {{-10, -10}, {10, 10}})));
 
   Modelica.Mechanics.MultiBody.Forces.WorldForceAndTorque forceAndTorque(
-    resolveInFrame = Modelica.Mechanics.MultiBody.Types.ResolveInFrameB.frame_b,
+    resolveInFrame = Modelica.Mechanics.MultiBody.Types.ResolveInFrameB.world,
     animation = not headless) annotation(
     Placement(transformation(origin = {-30, -50}, extent = {{-10, -10}, {10, 10}})));
 
 protected
+  SI.Force contactForceWorld[3]
+    "Contact-patch cut force resolved in the world frame";
+  SI.Force tireForceWorld[3]
+    "Tire shear force resolved in the road plane";
+  SI.Torque tireTorqueWorld[3]
+    "Tire moment resolved about the road-plane axes";
   Real[3] e_xw "Unit vector along wheel x-axis, resolved in world frame";
   Real[3] e_yw "Unit vector along wheel y-axis, resolved in world frame";
   Real[3] e_spin "Unit vector along wheel spin axis, resolved in world frame";
   Real[3] e_zw "Unit vector along wheel z-axis, resolved in world frame";
   Real[3] e_xg "e_xw projected on the xy-plane (ground) and normalized";
-  Real[3] e_yg "e_yw projected on the xy-plane (ground) and normalized";
+  Real[3] e_yg "Road-plane lateral axis orthogonal to e_xg";
 
   // Velocity quantities (for slip calculation)
   Real[3] v_cp "Contact patch velocity in world frame";
@@ -82,7 +85,9 @@ protected
 equation
 
   // Normal load
-  Fz = noEvent(max(0, cpFrame.f[3]));
+  contactForceWorld =
+    Modelica.Mechanics.MultiBody.Frames.resolve1(cpFrame.R, cpFrame.f);
+  Fz = noEvent(max(0, contactForceWorld[3]));
 
   // World basis (from cpFrame)
   e_xw = Modelica.Mechanics.MultiBody.Frames.resolve1(cpFrame.R, {1, 0, 0});
@@ -92,7 +97,7 @@ equation
 
   // Ground-projected tire basis
   e_xg = normalize({e_xw[1], e_xw[2], 0});
-  e_yg = normalize({e_yw[1], e_yw[2], 0});
+  e_yg = {-e_xg[2], e_xg[1], 0};
 
   // Inclination angle
   gamma = Modelica.Math.asin(noEvent(max(-1.0, min(1.0, e_zw[2]))));
@@ -103,6 +108,19 @@ equation
   Vx = v_g[1]*e_xg[1] + v_g[2]*e_xg[2];
   Vy = v_g[1]*e_yg[1] + v_g[2]*e_yg[2];
 
+  // MF52 shear forces are defined in the road plane, using the same
+  // ground-projected axes as the slip kinematics.  Tire moments follow the
+  // corresponding road axes, with aligning moment about the road normal.
+  tireForceWorld =
+    realExpressionFx.y*e_xg +
+    realExpressionFy.y*e_yg;
+  tireTorqueWorld =
+    realExpressionMx.y*e_xg +
+    realExpressionMy.y*e_yg +
+    realExpressionMz.y*{0, 0, 1};
+  forceAndTorque.force = tireForceWorld;
+  forceAndTorque.torque = tireTorqueWorld;
+
   // Slip model
   slipModel.Vx = Vx;
   slipModel.Vy = Vy;
@@ -117,18 +135,6 @@ equation
     Line(points = {{-100, 0}, {-30, 0}}));
   connect(wheelModel.cpFrame, cpFrame) annotation(
     Line(points = {{0, -30}, {0, -100}}, color = {95, 95, 95}));
-  connect(realExpressionFx.y, forceAndTorque.force[1]) annotation(
-    Line(points = {{-78, -56}, {-42, -56}}, color = {0, 0, 127}));
-  connect(realExpressionFy.y, forceAndTorque.force[2]) annotation(
-    Line(points = {{-78, -70}, {-60, -70}, {-60, -56}, {-42, -56}}, color = {0, 0, 127}));
-  connect(constantZero.y, forceAndTorque.force[3]) annotation(
-    Line(points = {{-78, -90}, {-50, -90}, {-50, -56}, {-42, -56}}, color = {0, 0, 127}));
-  connect(realExpressionMx.y, forceAndTorque.torque[1]) annotation(
-    Line(points = {{-78, 54}, {-50, 54}, {-50, -44}, {-42, -44}}, color = {0, 0, 127}));
-  connect(realExpressionMy.y, forceAndTorque.torque[2]) annotation(
-    Line(points = {{-78, 40}, {-60, 40}, {-60, -44}, {-42, -44}}, color = {0, 0, 127}));
-  connect(realExpressionMz.y, forceAndTorque.torque[3]) annotation(
-    Line(points = {{-78, 26}, {-70, 26}, {-70, -44}, {-42, -44}}, color = {0, 0, 127}));
   connect(forceAndTorque.frame_b, wheelModel.cpFrame) annotation(
     Line(points = {{-20, -50}, {0, -50}, {0, -30}}, color = {95, 95, 95}));
   connect(wheelModel.hubFlange, hubFlange) annotation(

Tests/BobLibTest/Regression/TireForceFrameSmoke.mo

@@ -0,0 +1,70 @@
+within BobLibTest.Regression;
+
+model TireForceFrameSmoke
+
+  import SI = Modelica.Units.SI;
+
+  inner parameter Real linkDiameter = 0.02;
+  inner parameter Boolean headless = true;
+
+  parameter
+    BobLib.Records.VehicleRecord.Chassis.Suspension.Templates.Tire.Templates.PartialWheelRecord
+    pWheel(
+      R0 = 0.3,
+      rimR0 = 0.2,
+      rimWidth = 0.2,
+      staticAlpha = 15,
+      staticGamma = 10);
+
+  model InclinedTire
+
+    parameter
+      BobLib.Records.VehicleRecord.Chassis.Suspension.Templates.Tire.Templates.PartialWheelRecord
+      pTestWheel;
+
+    extends BobLib.Chassis.Suspension.Tires.BaseTire(
+      pPartialWheel = pTestWheel,
+      realExpressionFy(y = 1000),
+      realExpressionMz(y = 100));
+
+    output SI.Force appliedForceWorld[3] = tireForceWorld;
+    output SI.Torque appliedTorqueWorld[3] = tireTorqueWorld;
+
+  initial equation
+    assert(
+      abs(e_xg*e_yg) < 1e-12,
+      "Ground-projected tire axes must be orthogonal");
+    assert(
+      abs(sqrt((600*e_xg + 800*e_yg)*(600*e_xg + 800*e_yg)) - 1000) < 1e-8,
+      "Combined road-plane force magnitude must be basis invariant");
+  end InclinedTire;
+
+  output SI.Force appliedForceWorld[3] = tire.appliedForceWorld;
+  output SI.Torque appliedTorqueWorld[3] = tire.appliedTorqueWorld;
+
+  inner Modelica.Mechanics.MultiBody.World world(
+    n = {0, 0, -1},
+    enableAnimation = false);
+
+  Modelica.Mechanics.MultiBody.Parts.Fixed chassis(
+    r = {0, 0, 0.3});
+
+  InclinedTire tire(pTestWheel = pWheel);
+
+initial equation
+  assert(
+    abs(appliedForceWorld[3]) < 1e-8,
+    "Tire shear force must remain in the road plane");
+  assert(
+    abs(sqrt(appliedForceWorld[1]^2 + appliedForceWorld[2]^2) - 1000) < 1e-8,
+    "Road-plane force magnitude must be preserved");
+  assert(
+    abs(appliedTorqueWorld[3] - 100) < 1e-8,
+    "Aligning moment must act about the road normal");
+
+equation
+  connect(chassis.frame_b, tire.chassisFrame);
+
+  annotation(
+    experiment(StartTime = 0, StopTime = 0.001, Tolerance = 1e-6, Interval = 0.001));
+end TireForceFrameSmoke;

Tests/BobLibTest/Regression/package.order

@@ -1,2 +1,3 @@
 MF52PureSlipSmoke
+TireForceFrameSmoke
 VehicleSimAnimationOn

Tests/modelica_initialization_baseline.csv

@@ -1,5 +1,6 @@
 model,numeric_count,finite_count,nonfinite_count,names_sha256,sum,sum_abs,max_abs,values_sha256
 BobLibTest.Regression.MF52PureSlipSmoke,8,8,0,a0fa6bc905c8ec7862790f47844443e6b3d0fbc901c2ddba34402dac7b1c9ed6,1291.2252864882239,1442.9166355632356,1367.049907523304,602021d8f6960ca5b5fdbb9d57887c8eca559b89200569fc13037adaa1b71c30
+BobLibTest.Regression.TireForceFrameSmoke,496,496,0,d71a3728741fa3d149b2dc7fc96ae2e63fcc4cf37c1cea25690d94fecdc8e781,4626.3120793459366,25075.180061240306,1000,9561bb1105f95f48ccf875f5c5edad7d08820527d9c746e63f938e2c8736506d
 BobLibTest.Regression.VehicleSimAnimationOn,1018,1018,0,bcf17a741d234b4273f3519e9a77fa72a0a2ad04dd966908a7d168f024cf4385,17285096.54280192,17286075.114064306,8400000,091bf5ae4529665cb8ecb40f00759f21bf3999ca31ebcb2aa707679ac743a332
 BobLibTest.TestUtilities.TestMechanics.TestMultiBody.TestContactMechanics.TestGroundPhysics,75,75,0,494136a7a7c0f8b792cb3b044f96e92127a93c7eb042f412e4683ed40b67a423,138.2500000500003,139.25000015000086,128,0019557349df1e442f79cce3d2e75ecafdd8c2918ba114af267a7076af9b5afe
 BobLibTest.TestUtilities.TestMechanics.TestMultiBody.TestContactMechanics.TestGroundPhysicsRotatedFrame,3,3,0,fdf3ffca9af5c7e9474527b0256e59a25dd21d67d978aa439bb1d807f53d30f2,-1000.000252499937,1000.000252499937,1000.000252499937,825340ecd2192a9ad74b04f65e256164f0ee47c735ee73b57c5efc0205b460fa

Tests/modelica_physics_baseline.csv

@@ -7,6 +7,8 @@ BobLibTest.Regression.MF52PureSlipSmoke,0.01,Mz,-28.781188544190439,1e-6,1e-9,MF
 BobLibTest.Regression.MF52PureSlipSmoke,0.01,pneumaticTrail,0.021053502425769931,1e-9,1e-9,MF52 pure slip smoke pneumatic trail
 BobLibTest.Regression.MF52PureSlipSmoke,0.01,residualScrub,0,1e-9,1e-9,MF52 pure slip smoke residual scrub
 BobLibTest.Regression.MF52PureSlipSmoke,0.01,MzReconstructed,-28.781188544190439,1e-6,1e-9,MF52 aligning moment reconstruction
+BobLibTest.Regression.TireForceFrameSmoke,0.001,appliedForceWorld[3],0,1e-9,1e-9,Tire shear force remains in the road plane
+BobLibTest.Regression.TireForceFrameSmoke,0.001,appliedTorqueWorld[3],100,1e-9,1e-9,Tire aligning moment acts about the road normal
 BobLibTest.TestUtilities.TestMechanics.TestMultiBody.TestContactMechanics.TestGroundPhysicsRotatedFrame,0.01,contactForceWorld[1],0,1e-9,1e-9,rotated contact-frame force has no world x component
 BobLibTest.TestUtilities.TestMechanics.TestMultiBody.TestContactMechanics.TestGroundPhysicsRotatedFrame,0.01,contactForceWorld[2],0,1e-9,1e-9,rotated contact-frame force has no world y component
 BobLibTest.TestUtilities.TestMechanics.TestMultiBody.TestContactMechanics.TestGroundPhysicsRotatedFrame,0.01,contactForceWorld[3],-1000.000252499937,1e-6,1e-9,rotated contact-frame force remains world vertical

Tests/modelica_runtime_baseline.csv

@@ -1,5 +1,6 @@
 model,budget_s,description
 BobLibTest.Regression.MF52PureSlipSmoke,8,MF52 smoke physical baseline simulation
+BobLibTest.Regression.TireForceFrameSmoke,15,Tire road-frame force regression simulation
 BobLibTest.TestUtilities.TestMechanics.TestMultiBody.TestContactMechanics.TestGroundPhysicsRotatedFrame,5,rotated contact-frame physical baseline simulation
 BobLibTest.TestVehicle.TestAero.TestCFDAeroMap,5,CFD aero map physical baseline simulation
 BobLibTest.TestVehicle.TestPowertrain.TestPowerLimitedMotor,25,Motor power and torque sign physical baseline simulation