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[Rohit John <question692613@xxxxxxxxxxxxxxxxxxxxx>]

New question #692613 on Yade:
https://answers.launchpad.net/yade/+question/692613

Hello all,

I am new to yade. I have tried the basic tutorial scripts and in them the objects are defined first followed by the engines. In an advanced script (cylinderconnection-roots.py) I saw that the objects were defined after the engines. 

Now I tried writing a script for a ball interacting with a beam made of cylinders. I defined the objects (cylinders and sphere) first and then the engines. When I ran the code, the beam sort of fell apart. I modified the code by defining the cylinder after the engines. It fixed the problem. I want to know what is causing this or if we are required to define the bodies after the engines. 

I am using Ubuntu 20.04 

Please find the bare minimum script that showed this issue.

###################################################################################
from yade.gridpfacet import *


#### params
young = 1e6
poiss = 3
dens  = 1e3
sp_r  = 0.05 
fr_a  = radians(10)



## cylinder
no_cyl = 5
dl_cyl = 0.1

#### materials

O.materials.append(
	FrictMat(
		young         = young,
		poisson       = poiss,
		density       = dens,
		frictionAngle = fr_a,
		label            = 'cyl_ext_mat'
	)
)

O.materials.append(
	CohFrictMat(
		young        = young,
		poisson      = poiss,
		density      = dens,
		frictionAngle= fr_a,
		normalCohesion = 1e40,
		shearCohesion  = 1e40,
		momentRotationLaw = True, 
		label        = 'cyl_int_mat'
	)
 )


#### cylinder
nodesIds=[]
cylIds=[]
verts = []
for i in range(no_cyl):
	verts.append([0.1 + dl_cyl*i,	0.5, 	0.8])


cylinderConnection( # Defining the beam here is causing the issue
	verts,
	nodesIds = nodesIds,
	cylIds   = cylIds,
	radius   = 0.03,
	color    = [1,0,0],
	extMaterial = 'cyl_ext_mat',
	intMaterial = 'cyl_int_mat'
)
O.bodies[nodesIds[-1]].state.blockedDOFs='xyzXYZ'


####
O.engines = [
	ForceResetter(),
	InsertionSortCollider([
		Bo1_GridConnection_Aabb(),
	]),
	InteractionLoop(
		[
			Ig2_GridNode_GridNode_GridNodeGeom6D(),
			Ig2_GridConnection_GridConnection_GridCoGridCoGeom(),
		],
		[
			Ip2_FrictMat_FrictMat_FrictPhys(),
			Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(setCohesionNow=True,setCohesionOnNewContacts=False)
		],
		[
			Law2_ScGeom_FrictPhys_CundallStrack(),
			Law2_ScGridCoGeom_FrictPhys_CundallStrack(),
			Law2_ScGeom6D_CohFrictPhys_CohesionMoment(),
			Law2_GridCoGridCoGeom_FrictPhys_CundallStrack(),
		]
	),
	GlobalStiffnessTimeStepper(timestepSafetyCoefficient=0.1,label='ts'), 
	NewtonIntegrator(gravity = (0,0,9.1))
]

# if I define the beam here, it fixes everything


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