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[chiara modenese <c.modenese@xxxxxxxxx>]

Hello Bruno,

I wrote a simple script which might be helpful to test contact laws in order
to see if granular ratcheting has any effect, as you suggest below. Please
could you have a quick look at the attached script? Try to run it, I just
attempted to follow the way you suggest below (the four steps of
displacements). There must be something strange in my script because also in
the case of preventGranularRatcheting==True I have got a shear force
(numerical approximations?) and anyway if I try to change that bool from
True to False nothing appears to change.

thanks, Chiara



On 26 May 2010 08:51, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:

> For those interested, I elaborated the comment a little in ScGeom.cpp
> (possible wiki paragraph in the future), as this "granular ratchetting"
> needed explanation.
> We could put a simple py script to simulate the cycle explained below, and
> test any law in Yade to see if it generates ratchetting.
>

      1. translation "dx" in the normal direction
>       2. rotation "a"
>       3. translation "-dx" (back to initial position)
>       4. rotation "-a" (back to initial orientation)
>

#!/usr/local/bin/yade-trunk -x
# -*- coding: utf-8 -*-
# -*- encoding=utf-8 -*-

#__________________________________________________________________
# scrpt to demonstrate the effect of granular ratcheting

from yade import utils

#__________________________________________________________________
# geometry
r1,r2=0.007,0.007 # radii
p1,p2=[0,0,0],[r1+0.9*r2,0,0] # center positions 

#__________________________________________________________________
# material
young=600.0e4 
poisson=0.6 
density=2.60e3 
frictionAngle=26 

# append geometry and material
O.materials.append(FrictMat(young=young,poisson=poisson,density=density,frictionAngle=frictionAngle))
O.bodies.append(utils.sphere(p1,r1,dynamic=False,wire=True)) # body id=0 
O.bodies.append(utils.sphere(p2,r2,dynamic=False,wire=True)) # body id=1

SFixed=O.bodies[0]
SMoving=O.bodies[1]

#__________________________________________________________________
# list of engines
O.engines=[
	StepDisplacer(subscribedBodies=[1],setVelocities=True,label='translation'),
	RotationEngine(subscribedBodies=[1],rotationAxis=[0,0,1],rotateAroundZero=True,label='rotation'),

	PeriodicPythonRunner(iterPeriod=1,command='displ()'),

	ForceResetter(),
	BoundDispatcher([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()]),
	InsertionSortCollider(),

	InteractionGeometryDispatcher([Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()]),
	InteractionPhysicsDispatcher([Ip2_FrictMat_FrictMat_FrictPhys()]),
	LawDispatcher([Law2_ScGeom_FrictPhys_Basic(label='contact')]),

	PeriodicPythonRunner(iterPeriod=1,command='data()'),
]

#__________________________________________________________________
# setting of some attributes
contact.preventGranularRatcheting=True
contact.useShear=True

#__________________________________________________________________
# time step
O.dt=.2*utils.PWaveTimeStep()
O.saveTmp('init')

#__________________________________________________________________
from yade import qt
qt.View()
qt.Controller()

def displ():
	i=O.interactions[0,1]
	if O.iter==2: 
		translation.deltaSe3=(-0.001*i.geom.normal,Quaternion.Identity) # apply displacement
		rotation.angularVelocity=0.0 
	elif O.iter==3: 
		translation.deltaSe3=(Vector3(0,0,0),Quaternion.Identity) 
		rotation.angularVelocity=1500. # apply rotation
	elif O.iter==4:
		translation.deltaSe3=(0.001*i.geom.normal,Quaternion.Identity) # apply displacement (come back to initial position)
		rotation.angularVelocity=0.0 
	elif O.iter==5: 
		translation.deltaSe3=(Vector3(0,0,0),Quaternion.Identity) 
		rotation.angularVelocity=-1500. # apply rotation (come back to initial position)
	else:
		translation.deltaSe3=(Vector3(0,0,0),Quaternion.Identity)
		rotation.angularVelocity=0.0 

def data():
	i=O.interactions[0,1]
	if O.iter==2:		
		it=O.iter; us=i.geom.shear.norm(); un=i.geom.penetrationDepth; Fn=i.phys.normalForce.norm(); Fs=i.phys.shearForce.norm()
		print 'it = %i; us = %e; un = %e; Fn = %e; Fs = %e' % (it, us, un, Fn, Fs), '\n\n--- plus dx ---'
	elif O.iter==3:
		it=O.iter; us=i.geom.shear.norm(); un=i.geom.penetrationDepth; Fn=i.phys.normalForce.norm(); Fs=i.phys.shearForce.norm()
		print 'it = %i; us = %e; un = %e; Fn = %e; Fs = %e' % (it, us, un, Fn, Fs), '\n\n--- plus dteta ---'
	elif O.iter==4:
		it=O.iter; us=i.geom.shear.norm(); un=i.geom.penetrationDepth; Fn=i.phys.normalForce.norm(); Fs=i.phys.shearForce.norm()	
		print 'it = %i; us = %e; un = %e; Fn = %e; Fs = %e' % (it, us, un, Fn, Fs), '\n\n--- minus dx ---'
	elif O.iter==5:
		it=O.iter; us=i.geom.shear.norm(); un=i.geom.penetrationDepth; Fn=i.phys.normalForce.norm(); Fs=i.phys.shearForce.norm()
		print 'it = %i; us = %e; un = %e; Fn = %e; Fs = %e' % (it, us, un, Fn, Fs), '\n\n--- minus dteta ---'
	else: 
		it=O.iter; us=i.geom.shear.norm(); un=i.geom.penetrationDepth; Fn=i.phys.normalForce.norm(); Fs=i.phys.shearForce.norm()
		print 'it = %i; us = %e; un = %e; Fn = %e; Fs = %e' % (it, us, un, Fn, Fs), '\n'

O.run(7,True)