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[Jeffrey Knowles <question694548@xxxxxxxxxxxxxxxxxxxxx>]

New question #694548 on Yade:
https://answers.launchpad.net/yade/+question/694548

I am using Yade 2020.01a. The MWE below simulates the collision of two PFacets. After PFacet 1 (on the left) collides with PFacet 2 (on the right)  unrealistic physical behavior is observed. I would expect PFacet 2 to rotate clockwise about the y-axis. However, it appears that PFacet 2 has a tendency to rotate counter-clockwise about the z-axis with some angular momentum about the y-axis (but in the counter-clockwise direction). I have tried smaller and smaller time steps, but observe the same behavior.

I am not sure if this is a bug, or if I have a misconception about PFacets. At any rate, I would appreciate any time that could be allocated in addressing this issue.


MWE: 

import sys
p = os.getcwd() # current working directory
sys.path.append(p)  
from yade import pack, geom, PyRunner, qt
from yade.gridpfacet import *

############################################# engines ###########################################
O.engines=[

	ForceResetter(),
	InsertionSortCollider(

		[
		Bo1_PFacet_Aabb(),
		Bo1_GridConnection_Aabb()
		]),

	InteractionLoop(

		[
		Ig2_GridConnection_PFacet_ScGeom(),
		Ig2_Sphere_PFacet_ScGridCoGeom(),
		Ig2_GridNode_GridNode_GridNodeGeom6D(),
		Ig2_Sphere_GridConnection_ScGridCoGeom(),
		Ig2_GridConnection_GridConnection_GridCoGridCoGeom(),
		Ig2_PFacet_PFacet_ScGeom()
		],


		[
		Ip2_FrictMat_FrictMat_FrictPhys(),
		Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(setCohesionNow=True,setCohesionOnNewContacts=False),
		],
		

		[
		Law2_ScGeom_FrictPhys_CundallStrack(),
		Law2_ScGeom6D_CohFrictPhys_CohesionMoment(useIncrementalForm = True),
		Law2_ScGridCoGeom_FrictPhys_CundallStrack(), 
		Law2_ScGridCoGeom_CohFrictPhys_CundallStrack(), 
		Law2_GridCoGridCoGeom_FrictPhys_CundallStrack(),
		]),
			
		NewtonIntegrator(gravity=(0,0,0), damping=0.0)
		]

O.dt = 1.0e-9 # times step

############################################# materials ###########################################
cmatName = 'cmat'
fmatName = 'fmat'

O.materials.append( CohFrictMat( young=1.0e14,poisson=0.3,density=1000.0, normalCohesion=1.0e12 ,shearCohesion=1.0e12, fragile = False, momentRotationLaw=True, isCohesive = True, etaRoll=1000.0, etaTwist = 1000.0, frictionAngle=0.0, alphaKr = 100.0, alphaKtw = 100.0,  label=cmatName ) ) 

O.materials.append( FrictMat( young=1.0e14,poisson=0.3,density=1000.0,frictionAngle=0.0,label=fmatName ) )

############################################## pfacets #############################################

# pfacet 1 
gnh1_0 = O.bodies.append( gridNode([0.0, 0.0, 0.3],radius = 0.1,fixed=False,material=cmatName,color=[0, 0, 0]) )
gnh1_2 = O.bodies.append( gridNode([-1.0, 1.0, 0.3],radius = 0.1,fixed=False,material=cmatName,color=[0, 0, 0]) )
gnh1_3 = O.bodies.append( gridNode([-1.0, -1.0, 0.3],radius = 0.1,fixed=False,material=cmatName,color=[0, 0, 0]) )

O.bodies.append( gridConnection(gnh1_2,gnh1_3,radius = 0.1,color=[0, 0, 0],material=fmatName, wire=False) )
O.bodies.append( gridConnection(gnh1_0,gnh1_2,radius = 0.1,color=[0, 0, 0],material=fmatName, wire=False) )
O.bodies.append( gridConnection(gnh1_0,gnh1_3,radius = 0.1,color=[0, 0, 0],material=fmatName, wire=False) )

O.bodies.append( pfacet(gnh1_0, gnh1_2, gnh1_3,material=fmatName,color=[1, 0, 0]) )

# assign initial velocity to pfacet 1
vi = Vector3(10.0, 0.0, 0.0)
for b in O.bodies:
	b.state.vel = vi


# pfacet 2
gnh2_0 = O.bodies.append( gridNode([0.21, 0.0, 0.0],radius = 0.1,fixed=False,material=cmatName,color=[0, 0, 0]) )
gnh2_1 = O.bodies.append( gridNode([0.21, 1.0, 1.0],radius = 0.1,fixed=False,material=cmatName,color=[0, 0, 0]) )
gnh2_2 = O.bodies.append( gridNode([0.21, -1.0, 1.0],radius = 0.1,fixed=False,material=cmatName,color=[0, 0, 0]) )

O.bodies.append( gridConnection(gnh2_0,gnh2_1,radius = 0.1,color=[0, 0, 0],material=fmatName, wire=False) )
O.bodies.append( gridConnection(gnh2_0,gnh2_2,radius = 0.1,color=[0, 0, 0],material=fmatName, wire=False) )
O.bodies.append( gridConnection(gnh2_1,gnh2_2,radius = 0.1,color=[0, 0, 0],material=fmatName, wire=False) )

O.bodies.append( pfacet(gnh2_0, gnh2_1, gnh2_2,material=fmatName,color=[1, 0, 0]) )


#################################### appearance and view ##########################################
qtr = qt.Renderer()
qt.Controller()
v = qt.View()

qtr.bgColor = [1,1,1]

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