Contact geometry is violated in simulation (bug?)
Posted: Mon Oct 11, 2021 3:55 am
Hello list,
I created a simple model via python with 5 bodies and 4 joints. Using Windows 10 and Opensim 4.3.
There is a contacthalfspace to represent the ground and a number of contactspheres fixed to the bodies. The picture below shows the model in its initial state. Please note the ground contact under the large box and the contactsphere attached to the boxes.
Initially the box, connected to the blue surface with a freeJoint, is hovering above "the ground".
When starting a simulation the model collapes to the ground as it should.
But the contact spheres of the large box penetrate the ground level during the simulation as shown in the next image.
This should not happen! Is this a bug in the simulation?
Thanks for any advice,
Sietse
PS. Here, for competeness, the python code
.
I created a simple model via python with 5 bodies and 4 joints. Using Windows 10 and Opensim 4.3.
There is a contacthalfspace to represent the ground and a number of contactspheres fixed to the bodies. The picture below shows the model in its initial state. Please note the ground contact under the large box and the contactsphere attached to the boxes.
- opensim_snapshot_0.png (297.69 KiB) Viewed 268 times
When starting a simulation the model collapes to the ground as it should.
But the contact spheres of the large box penetrate the ground level during the simulation as shown in the next image.
- opensim_snapshot_1.png (302.06 KiB) Viewed 268 times
Thanks for any advice,
Sietse
PS. Here, for competeness, the python code
Code: Select all
import opensim as osim
import sys
import math
pi = math.pi
bbaan = osim.Model()
bbaan.setName("Pusher")
bbaan.setGravity(osim.Vec3(0, -9.90665, 0))
""" The bodies with geometry """
theCourse = osim.Body("The_rowing_course",
1.0,
osim.Vec3(0, 0, 0),
osim.Inertia(0, 0, 0))
theCourseGeometry = osim.Brick(osim.Vec3(20, 0.05, 2))
theCourse.attachGeometry(theCourseGeometry)
theCourseGeometry.setColor(osim.Vec3(0,0,1))
theBoat = osim.Body()
theBoat.setName('TheBoat')
theBoat.setMass(1)
theBoat.setInertia(osim.Inertia(1,1,1,0,0,0))
# boot voorlopig een brick, later een meshfile van een boot
theBoatGeometry = osim.Brick(osim.Vec3(6, 0.3, 0.8))
theBoat.attachGeometry(theBoatGeometry)
theBoatGeometry.setColor(osim.Vec3(0,1,1))
# Lower leg
upper = osim.Body("The_upper_leg",
1.0,
osim.Vec3(0, 0, 0),
osim.Inertia(0, 0, 0))
upperGeometry = osim.Cylinder(0.1, 1)
upper.attachGeometry(upperGeometry)
upperGeometry.setColor(osim.Vec3(0.5,0.5,1))
# Lower leg
lower = osim.Body("The_lower_leg",
1.0,
osim.Vec3(0, 0, 0),
osim.Inertia(0, 0, 0))
lowerGeometry = osim.Cylinder(0.1, 1.5)
lower.attachGeometry(lowerGeometry)
lowerGeometry.setColor(osim.Vec3(1,0,1))
# the foot
blade = osim.Body()
blade.setName('TheBlade')
blade.setMass(1)
blade.setInertia(osim.Inertia(1,1,1,0,0,0))
# boot voorlopig een brick, later een meshfile van een boot
bladeGeometry = osim.Brick(osim.Vec3(0.03, 0.6, 0.6))
blade.attachGeometry(bladeGeometry)
bladeGeometry.setColor(osim.Vec3(1,1,1))
""" The joints """
courseJoint = osim.WeldJoint("courseJoint",
bbaan.getGround(),
osim.Vec3(0, 0.025, 0),
osim.Vec3(0, 0, 0),
theCourse,
osim.Vec3(0, 0, 0),
osim.Vec3(0, 0, 0))
boatJoint = osim.FreeJoint("boatJoint",
theCourse,
osim.Vec3(0, 0.5, 0),
osim.Vec3(0, 0, 0),
theBoat,
osim.Vec3(0, 0, 0),
osim.Vec3(0, 0, 0))
baseJoint = osim.PinJoint("baseJoint",
theBoat,
osim.Vec3(5, 0.3, 0),
osim.Vec3(0, 0, 0),
upper,
osim.Vec3(0, -1, 0),
osim.Vec3(0, 0, 0))
coord_1 = baseJoint.updCoordinate()
coord_1.setName('baseangle')
coord_1.set_range(0, -1.4)
coord_1.set_range(1, 1.0)
act_1 = osim.CoordinateActuator('baseangle')
act_1.setName('act_1')
bbaan.addForce(act_1)
controller = osim.PrescribedController()
controller.addActuator(act_1)
controller.prescribeControlForActuator('act_1', osim.Constant(0.0))
lowerJoint = osim.PinJoint("lowerJoint",
upper,
osim.Vec3(0, 1, 0),
osim.Vec3(0, 0, 0),
lower,
osim.Vec3(0, -1.5, 0),
osim.Vec3(0, 0, pi/2))
coord_2 = lowerJoint.updCoordinate()
coord_2.setName('lowerangle')
coord_2.set_range(0, -1.2)
coord_2.set_range(1, pi/2)
act_2 = osim.CoordinateActuator('lowerangle')
act_2.setName('act_2')
bbaan.addForce(act_2)
controller.addActuator(act_2)
controller.prescribeControlForActuator('act_2', osim.Constant(0.0))
bladeJoint = osim.PinJoint("bladeJoint",
lower,
osim.Vec3(0, 1.6, 0),
osim.Vec3(0, 0, 0),
blade,
osim.Vec3(0, 0, 0),
osim.Vec3(0, 0, 0))
coord_3 = bladeJoint.updCoordinate()
coord_3.setName('bladeangle')
coord_3.set_range(0, 0)
coord_3.set_range(1, pi/2)
act_3 = osim.CoordinateActuator('bladeangle')
act_3.setName('act_3')
bbaan.addForce(act_3)
controller.addActuator(act_3)
controller.prescribeControlForActuator('act_3', osim.Constant(0.0))
bbaan.addController(controller)
""" contact geometry """
theCourseContactSpace = osim.ContactHalfSpace(osim.Vec3(0, 0.1, 0),
osim.Vec3(0, 0, -pi/2), #-pi/2),
theCourse)
theCourseContactSpace.setName("baantje")
bbaan.addContactGeometry(theCourseContactSpace)
# voorlopig 4 spheres op de onderste hoekpunten
# een vlak beter? maar hoe?
corner_1 = osim.ContactSphere()
corner_1.setRadius(0.1)
corner_1.setLocation(osim.Vec3(6, -0.3, -0.8))
corner_1.setFrame(theBoat)
corner_1.setName('corner_1')
bbaan.addContactGeometry(corner_1)
corner_2 = osim.ContactSphere()
corner_2.setRadius(0.1)
corner_2.setLocation(osim.Vec3(-6, -0.3, -0.8))
corner_2.setFrame(theBoat)
corner_2.setName('corner_2')
bbaan.addContactGeometry(corner_2)
corner_3 = osim.ContactSphere()
corner_3.setRadius(0.1)
corner_3.setLocation(osim.Vec3(6, -0.3, 0.8))
corner_3.setFrame(theBoat)
corner_3.setName('corner_3')
bbaan.addContactGeometry(corner_3)
corner_4 = osim.ContactSphere()
corner_4.setRadius(0.1)
corner_4.setLocation(osim.Vec3(-6, -0.3, 0.8))
corner_4.setFrame(theBoat)
corner_4.setName('corner_4')
bbaan.addContactGeometry(corner_4)
blade_1 = osim.ContactSphere()
blade_1.setRadius(0.1)
blade_1.setLocation(osim.Vec3(0.05, 0.6, 0.6))
blade_1.setFrame(blade)
blade_1.setName('blade_1')
bbaan.addContactGeometry(blade_1)
blade_2 = osim.ContactSphere()
blade_2.setRadius(0.1)
blade_2.setLocation(osim.Vec3(0.05, 0.6, -0.6))
blade_2.setFrame(blade)
blade_2.setName('blade_2')
bbaan.addContactGeometry(blade_2)
blade_3 = osim.ContactSphere()
blade_3.setRadius(0.1)
blade_3.setLocation(osim.Vec3(0.05, -0.6, 0.6))
blade_3.setFrame(blade)
blade_3.setName('blade_3')
bbaan.addContactGeometry(blade_3)
blade_4 = osim.ContactSphere()
blade_4.setRadius(0.1)
blade_4.setLocation(osim.Vec3(0.05, -0.6, -0.6))
blade_4.setFrame(blade)
blade_4.setName('blade_4')
bbaan.addContactGeometry(blade_4)
elbow_0 = osim.ContactSphere()
elbow_0.setRadius(0.1)
elbow_0.setLocation(osim.Vec3(0.0, 1.0, 0.0))
elbow_0.setFrame(upper)
elbow_0.setName('elbow_0')
bbaan.addContactGeometry(elbow_0)
""" forces, actuators """
# Define Contact Force Parameters
stiffness = 1000000;
dissipation = 0.2 #2.0;
staticFriction = 0 #0.8;
dynamicFriction = 0 #0.4;
viscousFriction = 0 #0.4;
transitionVelocity = 0 #0.2;
# Make a Hunt Crossley Force
cornerforce_1 = osim.HuntCrossleyForce()
cornerforce_1.setName('BoatForce_1')
cornerforce_1.addGeometry('corner_1')
cornerforce_1.addGeometry('baantje')
cornerforce_1.setStiffness(stiffness)
cornerforce_1.setDissipation(dissipation)
cornerforce_1.setStaticFriction(staticFriction)
cornerforce_1.setDynamicFriction(dynamicFriction)
cornerforce_1.setViscousFriction(viscousFriction)
cornerforce_1.setTransitionVelocity(transitionVelocity)
bbaan.addForce(cornerforce_1)
# Make a Hunt Crossley Force
cornerforce_2 = osim.HuntCrossleyForce()
cornerforce_2.setName('BoatForce_2')
cornerforce_2.addGeometry('corner_2')
cornerforce_2.addGeometry('baantje')
cornerforce_2.setStiffness(stiffness)
cornerforce_2.setDissipation(dissipation)
cornerforce_2.setStaticFriction(staticFriction)
cornerforce_2.setDynamicFriction(dynamicFriction)
cornerforce_2.setViscousFriction(viscousFriction)
cornerforce_2.setTransitionVelocity(transitionVelocity)
bbaan.addForce(cornerforce_2)
# Make a Hunt Crossley Force
cornerforce_3 = osim.HuntCrossleyForce()
cornerforce_3.setName('BoatForce_3')
cornerforce_3.addGeometry('corner_3')
cornerforce_3.addGeometry('baantje')
cornerforce_3.setStiffness(stiffness)
cornerforce_3.setDissipation(dissipation)
cornerforce_3.setStaticFriction(staticFriction)
cornerforce_3.setDynamicFriction(dynamicFriction)
cornerforce_3.setViscousFriction(viscousFriction)
cornerforce_3.setTransitionVelocity(transitionVelocity)
bbaan.addForce(cornerforce_3)
# Make a Hunt Crossley Force
bladeforce_1 = osim.HuntCrossleyForce()
bladeforce_1.setName('BladeForce_1')
bladeforce_1.addGeometry('blade_1')
bladeforce_1.addGeometry('baantje')
bladeforce_1.setStiffness(stiffness)
bladeforce_1.setDissipation(dissipation)
bladeforce_1.setStaticFriction(staticFriction)
bladeforce_1.setDynamicFriction(dynamicFriction)
bladeforce_1.setViscousFriction(viscousFriction)
bladeforce_1.setTransitionVelocity(transitionVelocity)
bbaan.addForce(bladeforce_1)
# Make a Hunt Crossley Force
bladeforce_2 = osim.HuntCrossleyForce()
bladeforce_2.setName('BladeForce_2')
bladeforce_2.addGeometry('blade_2')
bladeforce_2.addGeometry('baantje')
bladeforce_2.setStiffness(stiffness)
bladeforce_2.setDissipation(dissipation)
bladeforce_2.setStaticFriction(staticFriction)
bladeforce_2.setDynamicFriction(dynamicFriction)
bladeforce_2.setViscousFriction(viscousFriction)
bladeforce_2.setTransitionVelocity(transitionVelocity)
bbaan.addForce(bladeforce_2)
# Make a Hunt Crossley Force
bladeforce_3 = osim.HuntCrossleyForce()
bladeforce_3.setName('BladeForce_3')
bladeforce_3.addGeometry('blade_3')
bladeforce_3.addGeometry('baantje')
bladeforce_3.setStiffness(stiffness)
bladeforce_3.setDissipation(dissipation)
bladeforce_3.setStaticFriction(staticFriction)
bladeforce_3.setDynamicFriction(dynamicFriction)
bladeforce_3.setViscousFriction(viscousFriction)
bladeforce_3.setTransitionVelocity(transitionVelocity)
bbaan.addForce(bladeforce_3)
# Make a Hunt Crossley Force
bladeforce_4 = osim.HuntCrossleyForce()
bladeforce_4.setName('BladeForce_4')
bladeforce_4.addGeometry('blade_4')
bladeforce_4.addGeometry('baantje')
bladeforce_4.setStiffness(stiffness)
bladeforce_4.setDissipation(dissipation)
bladeforce_4.setStaticFriction(staticFriction)
bladeforce_4.setDynamicFriction(dynamicFriction)
bladeforce_4.setViscousFriction(viscousFriction)
bladeforce_4.setTransitionVelocity(transitionVelocity)
bbaan.addForce(bladeforce_4)
# Make a Hunt Crossley Force
elbow_force_0 = osim.HuntCrossleyForce()
elbow_force_0.setName('elbow_force_0')
elbow_force_0.addGeometry('elbow_0')
elbow_force_0.addGeometry('baantje')
elbow_force_0.setStiffness(stiffness)
elbow_force_0.setDissipation(dissipation)
elbow_force_0.setStaticFriction(staticFriction)
elbow_force_0.setDynamicFriction(dynamicFriction)
elbow_force_0.setViscousFriction(viscousFriction)
elbow_force_0.setTransitionVelocity(transitionVelocity)
bbaan.addForce(elbow_force_0)
bbaan.addBody(theCourse)
bbaan.addBody(theBoat)
bbaan.addBody(upper)
bbaan.addBody(lower)
bbaan.addBody(blade)
bbaan.addJoint(courseJoint)
bbaan.addJoint(boatJoint)
bbaan.addJoint(baseJoint)
bbaan.addJoint(lowerJoint)
bbaan.addJoint(bladeJoint)
reporter = osim.ConsoleReporter()
reporter.set_report_time_interval(1.0)
bbaan.addComponent(reporter)
bbaan.finalizeConnections()
bbaan.printToXML("Pusher.osim")
# uncomment the rest to directly get the simulation
"""
bbaan.setUseVisualizer(True)
state = bbaan.initSystem()
print(state.getY())
finalState = osim.simulate(bbaan, state, 10)
# Analyze a simulation.
print(coord.getValue(finalState))
model.realizePosition(finalState)
print(model.calcMassCenterPosition(finalState))
model.realizeAcceleration(finalState)
print(joint.calcReactionOnParentExpressedInGround(finalState))
"""