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[Jan Stránský <question211358@xxxxxxxxxxxxxxxxxxxxx>]

Question #211358 on Yade changed:
https://answers.launchpad.net/yade/+question/211358

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hello Christian,

how do you measure the force in your experiment? how looks ground in your
experiment?

I would say that the simulation is much stiffer than reality (the ground
sphere is perfectly fixed, which is not present in reality), therefore you
get higher force in simulation. Also note that FrictMat.young differs from
real Young modulus of material, but this is not the source of such huge
error. To obtain better results in the contact phase, I would decrease the
time step.

So in my opinion the problem is in assumption of equivalency between the
experiment and simulation (I did some simple analytical solution of your
simulation and the force was 440N, so the simulation itself is ok).

good luck
Jan


2012/10/16 Christian Sommerfeld <question211358@xxxxxxxxxxxxxxxxxxxxx>

> New question #211358 on Yade:
> https://answers.launchpad.net/yade/+question/211358
>
> Hi,
>
> i want to validate a simple test with 2 balls. But i get a force in my
> simulation which is so much higher than the force of the real test. So i
> take a look in my code for 2 days but i can't find any mistake.
>
> The experiment: The first ball has the material porcelain and this ball
> falls down from a high of 0,1 m with the normal gravity 9,81. At the point
> (0,0,0) is the second ball which has teh material steel and this ball is
> fixed. In the real experimentr i get for the approach a force of 6 N in the
> direction of movement. For the simulazion i  use the SI- units for all of
> my parameters to make it as easy as possible. But i get a force of 350 N
> and i do know why?
>
>
> from yade import  plot, geom, utils
>
> O.materials.append(FrictMat(young=210e9,poisson=0.3,frictionAngle=.5,density=7900,
> label='mat_ground'))
>
> O.materials.append(FrictMat(young=90e9,poisson=0.14,frictionAngle=.5,density=2500,
> label='mat_spheres'))
>
> O.bodies.append(utils.sphere([0,0,0.103],0.003,color=[1,1,0],
> material='mat_spheres'))
>
> O.bodies.append(utils.sphere([0,0,0.003],0.003,color=[1,1,1], fixed=True,
> material='mat_ground'))
>
> O.engines=[
>    ForceResetter(),
>    InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Facet_Aabb()]),
>    InteractionLoop(
>       [Ig2_Sphere_Sphere_ScGeom(),Ig2_Facet_Sphere_ScGeom()],
>       [Ip2_FrictMat_FrictMat_FrictPhys()],
>       [Law2_ScGeom_FrictPhys_CundallStrack()]
>
>    ),
>   NewtonIntegrator(damping=0.2, gravity=(0,0,-9.81)),
>  PyRunner(iterPeriod=5,command="myAddPlotData()")
> ]
>
> O.dt=1*utils.PWaveTimeStep()
>
> def myAddPlotData():
>         force=plot.addData(t=O.time,F=O.forces.f(0).norm())
>
> plot.plots={'t':('F')}
> plot.plot()
>
> from yade import qt
> v=qt.View()
>
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