Rigidification problem - Constraint rigidified part

[bmauze]

Hi everyone,

I am currently working on the deformation of a bloc in SOFA. I want to simulate a bloc clamped at both end where on side is totally fixed and the other side is clamped to a rigid part that can move. I am struggling to model the rigid moving part (modeled as a box). I tried to use the rigidify function but it is not working as I want. The thing is the rigidication constrain the rigid part such as it cannot move anymore. The thing I want is a moving part acting as a rigid component (such as I could apply forces and displacements on it and get a uniform response).

I looked on the example of rigidication with the liver. It is exactly what I want to do (without the fixedConstraint function). I do not see why the top part of my block is totally constraint. Please, could you help me to understand and solve my problem?

Here is the code that I am currently running:
https://github.com/bmauze/3PP2F_study/blob/dcaa2936940780716edac4e7b9f9570c7c27becc/Sft_D_Ccpt_v2ElemDefSansPreset.py
The .vtk file is in the same folder.

Best regards,
Benjamin Mauzé

[damienmarchal]

Hi @bmauze

Thanks for your question.

As the yours scene is using the SofaPython2 binding and that this binding is now deprecated I prefered to translate it to SofaPython3. Which leads to the following simulation.

The scene used is the following

import Sofa
import numpy
from splib3.constants import Key
from math import sin, cos, sqrt
from stlib3.physics.constraints import *
from stlib3.physics.deformable import ElasticMaterialObject
from stlib3.physics.mixedmaterial import Rigidify
from splib3.objectmodel import SofaPrefab, SofaObject, setData

PI = 3.14159265359
meshRobot='bloc_v2_mesh1.vtk'

def createScene(rootNode):
    # Root node
    rootNode.dt = 0.05
    rootNode.gravity =[0, 0, -9.81]
    rootNode.addObject('VisualStyle', displayFlags='showBehaviorModels showCollision showVisualModels showForceFields showInteractionForceFields hideCollisionModels hideBoundingCollisionModels hideWireframe')
    rootNode.addObject('OglSceneFrame', style="Arrows", alignment="TopRight")

    #Required plugin
    rootNode.addObject('RequiredPlugin', pluginName=' SoftRobots SoftRobots.Inverse SofaPython3 SofaPreconditioner SofaSparseSolver')
    rootNode.addObject('FreeMotionAnimationLoop')
    rootNode.addObject('DefaultPipeline', verbose=0)
    rootNode.addObject('DefaultContactManager', response='FrictionContactConstraint')
    rootNode.addObject('LocalMinDistance', name="Proximity", alarmDistance=3, contactDistance=0.5)

    modelling = rootNode.addChild("Modelling")
    elasticobject = ElasticMaterialObject(volumeMeshFileName=meshRobot, translation=[0.0, 0.0, 0.0], rotation=[0.0, 0.0, 0.0],
                                          youngModulus=180.0, poissonRatio=0.45, totalMass=0.050, solverName="")
    modelling.addChild(elasticobject)
    modelling.init()
    
    # Fixed box
    FixedBox(elasticobject, atPositions=[[-2.51, -0.01, -11.01],[2.51, 1.01, -10.00]], doVisualization=True)

    # Selection box
    selection = modelling.addChild("Selection")
    commandBox=selection.addObject('BoxROI', name="box",
                                   position=elasticobject.dofs.position.getLinkPath(),
                                   box=[[-2.51, -0.01, 0.701], [2.51, 1.01,  1.01]], drawBoxes=True)
    #commandBox.init()

    # Rigidification management
    rigidifiedstruct = Rigidify(modelling, elasticobject ,
                                groupIndices=[selection.box.indices.value.tolist()],
                                frames=[[0,0.5,1,0,0,0,1]],
                                name="RigidifiedStructure")
    rigidifiedstruct.DeformableParts.addObject("UncoupledConstraintCorrection")
    rigidifiedstruct.RigidParts.RigidifiedParticules.addObject("UncoupledConstraintCorrection")
    rigidifiedstruct.RigidParts.addObject("UncoupledConstraintCorrection")

    setData(rigidifiedstruct.RigidParts.RigidifiedParticules.dofs, showObject=True, showObjectScale=0.1, drawMode=1, showColor=[1., 1., 0., 1.])
    setData(rigidifiedstruct.DeformableParts.dofs, showObject=True, showObjectScale=0.1, drawMode=2)
    setData(rigidifiedstruct.RigidParts.dofs, showObject=True, showObjectScale=1, drawMode=1)


    simulationNode = rootNode.addChild("Simulation")
    simulationNode.addObject("EulerImplicitSolver")
    simulationNode.addObject("CGLinearSolver")
    simulationNode.addChild(rigidifiedstruct)
    return rootNode

[bmauze]

Hi @damienmarchal ,

First, I would like to apologies to the lack of comments inside my code to explain what I want to do.

Thank for your kind response. I still have questions to understand more where were my mistakes and some other points.

1- Considering your changes, the main problem was the missing link between the box “selection” and the mechanical object “elasticobject” isn’t it? You added this link by adding the position field.

2- What is the purpose/meaning of the frames of the rigidify function? I tried to implement it but there is a mismatch between the size of “groupIndices” and “frames”. But it seems to work for you, maybe it is the fact that you are using Python3.

3- I used it because, I sew it in one of your response in the forum but I do not understand the purpose of the init() function of the modelling node. Could you explain to me why we are doing it, please.

I’m trying to change my version of SOFA (currently I’m working on the v19.06) but I’m struggling with the detection/installation of the STLIB plugging. It is not at the same place as the other installed pluggings. When I added it manually, SOFA still does not recognized functions like “fixedbox”. But I will open another discussion for this point.

Best regards,
Benjamin

[hugtalbot]

poke @damienmarchal