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[Chareyre <question680145@xxxxxxxxxxxxxxxxxxxxx>]

Question #680145 on Yade changed:
https://answers.launchpad.net/yade/+question/680145

    Status: Open => Answered

Chareyre proposed the following answer:
Hi, first of all you could have inconsistent restitution due to collisional
error (late detection of contact). Try decreasing the timestep and see if
it's better.

Second, contact viscosity is not very accurately integrated with centered
scheme, again decreasing timestep shoul help.

Finally, Cundall damping should be null for consistent results.

Le mar. 9 avr. 2019 18:08, Alessandro Finazzi <
question680145@xxxxxxxxxxxxxxxxxxxxx> a écrit :

> New question #680145 on Yade:
> https://answers.launchpad.net/yade/+question/680145
>
> Hi everybody,
>
> I have to simulate the behaviour of some spheres in a moving cylinder
> varying the tangential and normal restitution coefficients of the material.
> What seems strange to me is that I get a kinetic Energy increasing with
> lower restitution coefficients.
> >From the definition of coefficient of restitution I would expect the
> contrary.
>
> I am wondering if I'm making a silly conceptual mistake or if there is an
> error in my code.
> Do you see any error in the following code?
> I work with yadedaily, xenial version.
> Many thanks
>
>
>
> from yade import pack,utils,plot,ymport,export,qt,timing
>
> ## Physical Parameters
> density=7950
> cyl_r = 12.7e-3
> cyl_h = 24.6e-3
> sp_p_r = 1.5e-3
> young = 200e9
> poisson = 0.305
>
> ## Parameters to be varied
> #en = 0.1
> #es = 0.1
> en = 0.78
> es = 0.78
>
> ## Creation Cylinder
> facetMat=O.materials.append(ViscElMat(density=density,young=young,
> poisson=poisson,en=en,et=es))
>
> Cylinder=O.bodies.append(geom.facetCylinder((0,0,cyl_h/2),cyl_r,height=cyl_h,segmentsNumber=15,wallMask=7,material=facetMat))
>
> ## Creation Sphere
>
> sphereMat=O.materials.append(ViscElMat(density=density,young=young,poisson=poisson,en=en,et=es))
>
> s=utils.sphere((0,0,12e-3),radius=3e-3,material=sphereMat)
> O.bodies.append(s)
>
> sp=pack.SpherePack()
> sp.makeCloud((-9e-3,-9e-3,1.5e-3),(9e-3,9e-3,8e-3),rMean=sp_p_r,num=20)
> sp.toSimulation(material=sphereMat)
>
> ## Engine
> O.engines=[
>    ForceResetter(),
>    InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Facet_Aabb()]),
>    InteractionLoop(
>    [Ig2_Sphere_Sphere_ScGeom(),Ig2_Facet_Sphere_ScGeom()],
>       [Ip2_ViscElMat_ViscElMat_ViscElPhys()],
>       [Law2_ScGeom_ViscElPhys_Basic()]
>    ),
>
>  GlobalStiffnessTimeStepper(timeStepUpdateInterval=1,label='tss',timestepSafetyCoefficient=0.8,viscEl=True),
>    NewtonIntegrator(gravity=(0,0,-9.81),damping=0.2),
>    PyRunner(command='checkUnbalanced()',realPeriod=1,label='checker')
>    ]
>
> def checkUnbalanced():
>         if O.iter<100000: return
>
> O.engines=O.engines+[HarmonicMotionEngine(A=[0,0,6e-3],f=[0,0,60.0],fi=[0,0,pi],ids=Cylinder),
> PyRunner(command='addPlotData()',realPeriod=1)]
>         checker.command='nothing()'
>
> def nothing():
>         return
>
> def addPlotData():
>         Ek=kineticEnergy()
>
> plot.addData(i=O.iter,t=O.time,Ninter=O.interactions.countReal(),total=O.energy.total(),Ek=kineticEnergy(),**O.energy)
>
>
> O.trackEnergy=True
> O.saveTmp()
>
> plot.plots={'t':('Ek',)}
>
> plot.plot()
>
> qt.Controller()
> qt.View()
>
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