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[Jan Stránský <question253399@xxxxxxxxxxxxxxxxxxxxx>]

Question #253399 on Yade changed:
https://answers.launchpad.net/yade/+question/253399

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hi Raphael,
I tried your script and it worked without any problem. I am using Ubuntu
14.04 and yade compiled from source, version 1.11.0-1-g9bafd30
cheers
Jan



2014-08-21 15:07 GMT+02:00 Raphaël Maurin <
question253399@xxxxxxxxxxxxxxxxxxxxx>:

> New question #253399 on Yade:
> https://answers.launchpad.net/yade/+question/253399
>
> Hi all,
>
> I am simulating flows of particles due to an external fluid force. Then,
> the phenomenon is dynamic, I use periodic boundary condition in the
> streamwise direction and I have particles with velocity as high as 0.5m/s.
>
> I noticed a problem of stability when considering small periodic cell.
> After some times to isolate the problem, I found out that the problem
> arises when a particle travel for more than 10 times the size of the
> periodic cell. This does not seem to depend on the contact law, neither on
> the time step or the velocity of the particle, but only on the number of
> time the particle is crossing the periodic cell. I am not sure but I think
> this problem was not present some times ago.
>
> Have you already heard about such a bug ? What can I do to fix that ?
> It is a real problem for me as I would be interested to study the effect
> of the reduction of the size of the periodic cell and reduce it if possible.
>
> Raphaël
>
> I am using Ubuntu 12.04 and yade daily 1.10.0-72-d9ab58c~precise
> Here is a simple  script to reproduce the bug :
>
> O.dt = 1e-7
> lengthCell = 10 #Streamwise length of the periodic cell in diameter
> slope = 0.5     #Angle of the slope in radian
>
> #Particles parameters
> diameterPart = 6e-3     #Diameter of the particles, in meter, 6mm here.
> densPart = 2500 #density of the particles, in kg/m3
> #Contact law
> cnPart = 0.0    #Normal viscous damping coefficient.
> knPart = 1e4    #Normal stiffness of the particle
> partFrictAngle = 0.0 #28 *pi/180 #friction angle of the particles, in
> radian
> csPart = 0   #tangential viscous damping coefficient (=0)
> ksPart = 0.5*knPart #tangential stiffness of the contact
>
> ##Definition of the materials
> O.materials.append(ViscElMat(cn=cnPart, cs=csPart, kn=knPart, ks=ksPart,
> density=densPart, frictionAngle=partFrictAngle, label='sphereMat'))
>
> #
> #Geometrical configuration
> #
> length = lengthCell*diameterPart
> width = length/2.0
> height = length/3.0
> g = Vector3(9.81*sin(slope),0,-9.81*cos(slope))
> groundPosition = height/3.0
> #Definition of the semi-periodic cell
> O.periodic = True
> O.cell.setBox(length,width,height)
> # build the ground
> lowPlane = box(center=
> (length/2.0,width/2.0,groundPosition),extents=(length*10,width*10,0),fixed=True,wire=False,color
> = (0.8,0.8,0.8),material = 'sphereMat')
>
> #Send the ground box and the particle to simulation
> O.bodies.append(lowPlane)
> O.bodies.append(sphere((length/2.0,width/2.0,groundPosition+diameterPart),radius
> = diameterPart*0.5, material = 'sphereMat'))
>
> #########################
> #### SIMULATION LOOP#####
> #########################
>
> O.engines = [
>         # Reset the forces
>         ForceResetter(),
>         # Detect the potential contacts
>         InsertionSortCollider([Bo1_Sphere_Aabb(),
> Bo1_Wall_Aabb(),Bo1_Facet_Aabb(),Bo1_Box_Aabb()],label='contactDetection',allowBiggerThanPeriod
> = True),
>         # Calculate the different interactions
>         InteractionLoop(
>         [Ig2_Sphere_Sphere_ScGeom(), Ig2_Box_Sphere_ScGeom()],
>         [Ip2_ViscElMat_ViscElMat_ViscElPhys()],
>         [Law2_ScGeom_ViscElPhys_Basic()]
>         ),
>         # Integrate the equation and calculate the new
> position/velocities...
>         NewtonIntegrator(damping=0.0, gravity=g, label='newton')
>         ]
>
> O.saveTmp()
>
>
>
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