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[Jan Stránský <question240275@xxxxxxxxxxxxxxxxxxxxx>]

Question #240275 on Yade changed:
https://answers.launchpad.net/yade/+question/240275

Jan Stránský proposed the following answer:
Hello Zhu,

you can achive it (as you mentioned) by setting groupMask. Let me explain
on your example:

O.bodies[0].mask = 1 # 0b0001
O.bodies[1].mask = 2 # 0b0010
O.bodies[2].mask = 1 # 0b0001
O.bodies[3].mask = 2 # 0b0010

where 0bXXXX stands for number binary representation. The interaction of
two bodies is avoided, if mask1&mask2==0, see [1], section "AND". You can
play e.g. in IPython:

a = 0b0001
b = 0b0010
a&b
# etc..

so in your case, 1&1 = 1, 2&2 = 2, 1&2 = 0, so body pairs 0-2 and 1-3 will
interact and no other pair. To achieve what you want, do something like

O.bodies[0].mask = 0b11 # 3
O.bodies[1].mask = 0b01 # 1
O.bodies[2].mask = 0b11 # 3
O.bodies[3].mask = 0b10 # 2

in this case 3&1=1, 3&2=2, 3&3=3, 2&1=0, 2&2=2, 1&1=1. So all particles
will interact witch each other, except the pairs with mask1=1 and mask2=2,
as 1&2=0. I.e. particles 1 and 3 in your example will not interact with
each other.

Maybe we could improve the documentation about mask attribute a little..

cheers
Jan

[1] http://en.wikipedia.org/wiki/Bitwise_operation



2013/12/4 ZHU Huaxiang <question240275@xxxxxxxxxxxxxxxxxxxxx>

> Question #240275 on Yade changed:
> https://answers.launchpad.net/yade/+question/240275
>
> Description changed to:
> Hello all,
>
> I am doing a special biaxial test which only content Four particles laying
> to be a rhombus, like this
>
>                          1
>                          o
>                  2 o       o 0
>                          o
>                          3
>
> how can I avoid interaction between axial line particles 1 and 3 if they
> contact?
>
> I already tried the 'mask' and 'avoidSelfInteractionMask' to cooperate,
> as
>
> O.bodies[0].groupMask=1;O.bodies[2].groupMask=1
> O.bodies[1].groupMask=2;O.bodies[3].groupMask=2
> [engines]collider.avoidSelfInteractionMask=2
>
> but when the 1,3 interaction is avoided it is also impossible to
> establish interactions between two different mask's particles, then all
> interaction will lose by using 'avoidSelfInteractionMask'.
>
> Do you have any idea to achieve that? thank you.
>
>
> Huaxiang
>
>
> here is my code
>
> -------------------------------------------------------------------------------------------------------
>
> import math
> from yade import plot
>
> conf=100000
> poisson=0.5
> kn=1.0e8
> E=kn/1.0
> ks=poisson*kn
> rate=5e-4
> status=[0.0,0.0,0.0,0.0]
>
>
> O.materials.append(FrictMat(young=E,poisson=poisson,frictionAngle=radians(99.0),density=2600,label='spheres'))
>
> O.materials.append(FrictMat(young=1.0e3*kn,poisson=0.3,frictionAngle=radians(99.0),density=0,label='walls'))
>
>
> mn,mx=Vector3(-math.sqrt(2)-1,-math.sqrt(2)-1,-1.1),Vector3(math.sqrt(2)+1,math.sqrt(2)+1,1.1)
> walls=utils.aabbWalls([mn,mx],thickness=0.001,material='walls')
> wallIds=O.bodies.append(walls)
>
> O.bodies.append([
>
>  utils.sphere(center=(math.sqrt(2),0.0,0.0),radius=1.0,material='spheres'),
>
>  utils.sphere(center=(0.0,math.sqrt(2),0.0),radius=1.0,material='spheres'),
>
>  utils.sphere(center=(-math.sqrt(2),0.0,0.0),radius=1.0,material='spheres'),
>    utils.sphere((0.0,-math.sqrt(2),0.0),1.0,material='spheres')
> ])
>
>
> for k in O.bodies:
>    if isinstance(k.shape, Sphere): k.state.blockedDOFs='zXY'
>
> O.dt=.5*utils.PWaveTimeStep()
> O.usesTimeStepper=True
>
>
> O.engines=[
>  ForceResetter(),
>  InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Box_Aabb()]),
>  InteractionLoop(
>   [Ig2_Sphere_Sphere_ScGeom(),Ig2_Box_Sphere_ScGeom()],
>   [Ip2_FrictMat_FrictMat_FrictPhys()],
>   [Law2_ScGeom_FrictPhys_CundallStrack()]
>  ),
>  GlobalStiffnessTimeStepper(active=1,timeStepUpdateInterval=100,timestepSafetyCoefficient=0.8,
> defaultDt=4*utils.PWaveTimeStep()),
>  NewtonIntegrator(damping=0.01),
> ]
>
> O.dt=.5e-3*utils.PWaveTimeStep()
>
> def setVel(velX,velY):
>   O.bodies[0].state.vel=Vector3(velX,0.0,0.0)
>   O.bodies[1].state.vel=Vector3(-velX,0.0,0.0)
>   O.bodies[2].state.vel=Vector3(0.0,velY,0.0)
>   O.bodies[3].state.vel=Vector3(0.0,-velY,0.0)
>
> rateTmp=rate
> while 1:
>   meanS=(abs(O.forces.f(1)[0])+abs(O.forces.f(3)[1]))
>   unb=unbalancedForce()
>   if rateTmp>0.0 and meanS>conf:
>      print 'convert'
>      rateTmp=-0.5*rateTmp
>   elif rateTmp<0.0 and meanS<conf:
>      print 'convert'
>      rateTmp=-0.5*rateTmp
>   setVel(rateTmp,rateTmp)
>   O.run(1, True)
>   unb=unbalancedForce()
>   meanS=(abs(O.forces.f(1)[0])+abs(O.forces.f(3)[1]))*0.5
>   print 'unbalanced force:',unb,' mean stress: ',meanS
>   if unb<0.001 and abs(meanS-conf)/conf<0.005:
>     break
>
> plot.plots={'e2':'q'}
> plot.plot()
> raw_input('confining finish')
>
> '''
> ini=O.bodies[7].state.se3[0][1]
> e22=0.0
> e11=0.0
> #rate=1e2*rate
> while 1:
>    setVel(0.0,rate);e22+=rate
>    O.run(1,True)
>    while unbalancedForce()>0.001:
>        setVel(0.0,0.0)
>        O.run(1,True)
>    rateTmp=-0.5*rate
>    lateralS=(abs(O.forces.f(0)[0])+abs(O.forces.f(1)[0]))*0.5
>    while abs(lateralS-conf)/conf>0.001:
>        lateralS=(abs(O.forces.f(0)[0])+abs(O.forces.f(1)[0]))*0.5
>        if rateTmp>0.0 and lateralS>conf:
>           rateTmp=-0.5*rateTmp
>        elif rateTmp<0.0 and lateralS<conf:
>           rateTmp=-0.5*rateTmp
>        setVel(rateTmp,0.0)
>        O.run(1, True);e11+=rateTmp
>        lateralS=(abs(O.forces.f(0)[0])+abs(O.forces.f(1)[0]))*0.5
>    print
> O.forces.f(3)[1]-O.forces.f(1)[0],O.forces.f(1)[0],(ini-O.bodies[7].state.se3[0][1])/ini
>    plot.addData(e2=e22,e1=e11,q=O.forces.f(3)[1]-O.forces.f(1)[0],i=O.iter)
> '''
>
> rate=10.0*rate
> adjust=math.cos(75.0*pi/180.0)/math.sin(75.0*pi/180.0)*rate*1e-1
> ini=O.bodies[7].state.se3[0][1]
> e22=0.0
> e11=0.0
> rateX=0.0
> while 1:
>    lateralS=(abs(O.forces.f(0)[0])+abs(O.forces.f(1)[0]))*0.5
>    if lateralS>conf:
>        adjust=-abs(adjust)
>    elif lateralS<conf:
>        adjust=abs(adjust)
>    rateX+=adjust
>    setVel(rateX,rate);e22+=rate
>    O.run(1,True)
>    while unbalancedForce()>0.01:
>        setVel(0.0,0.0)
>        O.run(1,True)
>    print
> O.forces.f(3)[1]-O.forces.f(1)[0],O.forces.f(1)[0],(ini-O.bodies[7].state.se3[0][1])/ini,unbalancedForce()
>    plot.addData(e2=e22,e1=e11,q=O.forces.f(3)[1]-O.forces.f(1)[0],i=O.iter)
>
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