How to erase GridConnection

Hi,

I never tried to erase a GridConnection, so not sure what's going on here. Also, without seeing your script it is difficult to guess.

Anyway, wouldn't it be easier to make the initial rope shorter and then apply the pretension to get to a desired length by moving the last node?

HTH
Klaus

Hi Klaus,

Thank you for your answer, I'll post a simplified script of my problem as soon as possible.

I made a script which apply tension by this way and it works well if the cable is linear. But in my case it is not and I can't (or don't find the way to) apply this method.

Anyway, the final goal of this model is to be able to modify the tension during the simulation to get the right equilibrium state.

Thank you,
Loïc

Here you can find my script

#-*- coding: utf-8 -*-
from yade import qt, plot
from yade.gridpfacet import *
import gts, os, locale, sys
import numpy as np

################ Engine ############

O.engines=[
 ForceResetter(),
 InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_GridConnection_Aabb(),]),
 InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom(),Ig2_GridNode_GridNode_GridNodeGeom6D(),Ig2_Sphere_GridConnection_ScGridCoGeom(),Ig2_GridConnection_GridConnection_GridCoGridCoGeom(),],
  [Ip2_WireMat_WireMat_WirePhys(),Ip2_FrictMat_FrictMat_FrictPhys(),Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(setCohesionNow=True,setCohesionOnNewContacts=False),],
  [ Law2_ScGeom_WirePhys_WirePM(),Law2_ScGeom6D_CohFrictPhys_CohesionMoment(),Law2_ScGridCoGeom_CohFrictPhys_CundallStrack(),Law2_GridCoGridCoGeom_FrictPhys_CundallStrack(),Law2_ScGridCoGeom_FrictPhys_CundallStrack(),Law2_ScGeom_FrictPhys_CundallStrack(),]
 ),
 NewtonIntegrator(gravity=(0,0,-9.81),damping=0.9,label='newton'),
 PyRunner(initRun=True,iterPeriod=200,command='Force()'),
 PyRunner(virtPeriod=0.05, virtLast = 3, command='MEP_Pret()'),
]

################## Material & geometry ##########
youngc = 60e9
strenruptc=1400e9
densityc=7850.
poissonc = 0.3
shearCohc = 1e100
Rc = 0.008
cablemat = O.materials.append(CohFrictMat(young=youngc,poisson=poissonc,density=densityc,frictionAngle=radians(10),normalCohesion=pi*strenruptc,isCohesive=True,shearCohesion=shearCohc,momentRotationLaw=False, alphaKr = 1.0))
cablecomat = O.materials.append(FrictMat(young=youngc,poisson=poissonc,density=densityc,frictionAngle=radians(10)))

####################### Adding cable ##############
def Cable_droit_spheres(start, end, lseg, mtxnode, rayon): #just the meshing function

 lenght = end-start
 vecunit = lenght/(abs(lenght))
 lfinal = abs(lenght)
 cable = []
 nbseg = int(lfinal/lseg)
 for i in range(nbseg+1):
  x = start[0] + (vecunit*lfinal)[0]*i/nbseg
  y = start[1] + (vecunit*lfinal)[1]*i/nbseg
  z = start[2] + (vecunit*lfinal)[2]*i/nbseg
  cable.append(O.bodies.append(gridNode([x,y,z],rayon,wire=False,fixed=False,material=mtxnode)))

 return [cable]

#mapping the spheres of the cable
[c2a_1] = Cable_droit_spheres(start = Vector3(-1,0,0) , end = Vector3(-0.25, 0, 0), lseg = 0.1, mtxnode = cablemat,rayon = Rc)
[c2a_2] = Cable_droit_spheres(start = Vector3(-.20,0,-0.1), end = Vector3(0.20,0,-0.1), lseg = 0.1,mtxnode = cablemat,rayon = Rc)
[c2a_3] = Cable_droit_spheres(start = Vector3(0.25,0,0), end = Vector3(1,0,0), lseg = 0.1,mtxnode = cablemat,rayon = Rc)

cable = c2a_1 + c2a_2 + c2a_3

#and the link
concable = []
for i,j in zip(cable[:-1],cable[1:]):
 concable.append(O.bodies.append(gridConnection(O.bodies[i].id,O.bodies[j].id,Rc,wire=False, material = cablecomat) ))

O.bodies[cable[0]].state.blockedDOFs='xyzXYZ'
O.bodies[cable[-1]].state.blockedDOFs='xyzXYZ'

plot.plots={'t':('Fcable'),}
plot.plot(noShow=False, subPlots=False)
O.dt = 1e-6
#O.run()
################### Functions ####################

def MEP_Pret():

 Lcable = 0
 for i in range(len(cable)-1):
  Lcable += np.linalg.norm(O.bodies[cable[i]].state.pos-O.bodies[cable[i+1]].state.pos)

 if O.time > 0.6 :
  O.pause()
  pos1 = O.bodies[cable[-1]].state.pos

  for i in O.bodies[cable[-1]].intrs(): #deleting interaction with the extremity of the cable
   O.interactions.erase(i.id1,i.id2)
  for i in O.bodies[concable[-1]].intrs():
   O.interactions.erase(i.id1,i.id2)

  O.bodies.erase(concable[-1]) #deleting the cylinder (the crash comes from here)

  O.bodies[cable[-1]].state.pos = Vector3(pos1[0]-0.10,pos1[1],pos1[2])
  concable.append(O.bodies.append( gridConnection(cable[-2],cable[-1], Rc,material = cablecomat) ))
  O.bodies[cable[-1]].state.pos = pos1
  O.run()

def Force():

 Fcable = np.linalg.norm(O.forces.f(cable[0]))
 t = O.time
 plot.addData(
 Fcable = Fcable/1000,
 t = O.time)
 if t> 3.0 :
  O.pause()

Hi Loic,

I played a bit with it myself and the trick is to also delete the non real interaction. Also, I would first delete the body and then the interaction because in theory erasing the body should also erase the interaction. The latter is however not implemented yet but I will probably do it in the future. Anyway, here my MWE. You can delete the cylinder and create one as many times as you want. This works for me.

# encoding: utf-8
from yade.gridpfacet import *

#### Parameters ####
L=2. # minimum length
r=0.5 # radius of the cylinder element
phi=30. # friction angle
E=1e6 # Young's modulus

#### Engines ####
O.engines=[
 ForceResetter(),
 InsertionSortCollider([
  Bo1_GridConnection_Aabb(),
  Bo1_Sphere_Aabb(),
  Bo1_Wall_Aabb(),
 ]),
 InteractionLoop([
  Ig2_GridNode_GridNode_GridNodeGeom6D(),
  Ig2_GridConnection_GridConnection_GridCoGridCoGeom(),
  Ig2_Wall_Sphere_ScGeom(),
 ],
 [
  Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(setCohesionNow=True,setCohesionOnNewContacts=False),
  Ip2_FrictMat_FrictMat_FrictPhys()
 ],
 [
  Law2_ScGeom6D_CohFrictPhys_CohesionMoment(), # contact law for "internal" cylider forces
  Law2_ScGridCoGeom_FrictPhys_CundallStrack(), # contact law for Cylinder-pFacet interaction
  Law2_GridCoGridCoGeom_FrictPhys_CundallStrack() # contact law for cylinder-cylinder interaction
 ]
 ),
 GlobalStiffnessTimeStepper(timestepSafetyCoefficient=0.1,label='ts'),
 NewtonIntegrator(gravity=(0.,0,-10),damping=0.5,label='newton'),
]

#### Creat materials ####
O.materials.append( CohFrictMat( young=E,poisson=0.3,density=1000,frictionAngle=radians(phi),normalCohesion=1e10,shearCohesion=1e10,momentRotationLaw=True,label='cMat' ) ) # material to create the gridConnections
O.materials.append( FrictMat( young=E,poisson=0.3,density=1000,frictionAngle=radians(phi),label='fMat' ) ) # material for general interactions

#### Create cylinders ####
nodesIds=[]
cylIds=[]
cylinder((0,0,2*r),(0,0,L+2*r),radius=r,nodesIds=nodesIds,cylIds=cylIds,fixed=False,intMaterial='cMat',extMaterial='fMat')

#### For viewing ####
from yade import qt
qt.View()
Gl1_Sphere.stripes=True

#### Delete and create cylinder/gridConnection ####
def delcylinder():
 O.bodies.erase(cylIds[0]) # first delete the cylinder
 O.interactions.erase(nodesIds[0],nodesIds[1]) # then delete the real interaction between the gridNodes
 O.interactions.eraseNonReal() # finally delete non real interactions

def createcylinder():
 O.bodies.append(gridConnection(nodesIds[0],nodesIds[1],r,wire=False, material = 'cMat') )

HTH
Klaus

Hi Klaus,

Thank you for your help, this is working, I can now delete and replace the cylinder. But there is a new problem, the new cylinder is here but it seems that the new interaction is not activated. I modify a little your script to show this problem. I think this comes from the fact that the new interaction is not taken into account but I don't know how to deal with it. Any idea ?

In the script if you don't change the cylinder, the node1 is falling as expect but if you change the cylinder, the interaction don't hold it:

############

# encoding: utf-8
from yade.gridpfacet import *

#### Parameters ####
L=2. # minimum length
r=0.5 # radius of the cylinder element
phi=30. # friction angle
E=1e6 # Young's modulus

#### Engines ####
O.engines=[
 ForceResetter(),
 InsertionSortCollider([
  Bo1_GridConnection_Aabb(),
  Bo1_Sphere_Aabb(),
  Bo1_Wall_Aabb(),
 ]),
 InteractionLoop([
  Ig2_GridNode_GridNode_GridNodeGeom6D(),
  Ig2_GridConnection_GridConnection_GridCoGridCoGeom(),
  Ig2_Wall_Sphere_ScGeom(),
 ],
 [
  Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(setCohesionNow=True,setCohesionOnNewContacts=False),
  Ip2_FrictMat_FrictMat_FrictPhys()
 ],
 [
  Law2_ScGeom6D_CohFrictPhys_CohesionMoment(), # contact law for "internal" cylider forces
  Law2_ScGridCoGeom_FrictPhys_CundallStrack(), # contact law for Cylinder-pFacet interaction
  Law2_GridCoGridCoGeom_FrictPhys_CundallStrack() # contact law for cylinder-cylinder interaction
 ]
 ),
 GlobalStiffnessTimeStepper(timestepSafetyCoefficient=0.1,label='ts'),
 NewtonIntegrator(gravity=(0.,-10,0),damping=0.5,label='newton'),
 PyRunner(initRun=True,iterPeriod=200,command='delcylinder()'),
 PyRunner(initRun=True,iterPeriod=200,command='createcylinder()')
]

#### Creat materials ####
O.materials.append( CohFrictMat( young=E,poisson=0.3,density=1000,frictionAngle=radians(phi),normalCohesion=1e10,shearCohesion=1e10,momentRotationLaw=True,label='cMat' ) ) # material to create the gridConnections
O.materials.append( FrictMat( young=E,poisson=0.3,density=1000,frictionAngle=radians(phi),label='fMat' ) ) # material for general interactions

#### Create cylinders ####
nodesIds=[]
cylIds=[]
cylinder((0,0,2*r),(0,0,L+2*r),radius=r,nodesIds=nodesIds,cylIds=cylIds,fixed=False,intMaterial='cMat',extMaterial='fMat')

O.bodies[nodesIds[0]].state.blockedDOFs='xyzXYZ' #fixe the sides
O.bodies[nodesIds[1]].state.blockedDOFs='xyzXYZ'

#### For viewing ####
from yade import qt
qt.View()
Gl1_Sphere.stripes=True

#### Delete and create cylinder/gridConnection ####
def delcylinder():
 O.bodies.erase(cylIds[0]) # first delete the cylinder
 O.interactions.erase(nodesIds[0],nodesIds[1]) # then delete the real interaction between the gridNodes
 O.interactions.eraseNonReal() # finally delete non real interactions

def createcylinder():
 O.bodies.append(gridConnection(nodesIds[0],nodesIds[1],r,wire=False, material = 'cMat') )
 O.bodies[nodesIds[1]].state.blockedDOFs='' #release one side after changing the cylinder

Hi Klaus,

This is working nicely and solving my problem,

Thank you for your time,

Loïc

Thanks Klaus Thoeni, that solved my question.