[SOLVED] Applying force to an arbitrary node

[minj]

Hello All!
I would like to apply force to a node and obtain the position of it.
I used pythonController to print the position of node, but I have no idea how to apply force on the mesh.
I guess it is possible because it is possible with mouse input, but I want to make a program that applies force as a function of time.

I am using the v19.06.99_custom_Linux_v5.1, which I downloaded from the SoftRobotics workshop page.

Any ideas of how to do it?
I’d be grateful if you could help me.
Thanks a lot!

[Noura]

Hello minj,

You can apply a constant force field to a certain node in your mesh (let say on the node with index 5), you supply the force direction and value (for instance 7 N. in the positive direction of Y axis), I included the “arrowSizeCoef” parameter which is optional just to help visualizing the force direction.

  <ConstantForceField indices="5" totalForce="0 7 0" arrowSizeCoef="0.1"/>

Hope this helps,

Noura

[Hugo]

Hi @minj Hi Noura !

Since I was already preparing some files for you Minj I am posting them.
Find here an example with a deformable liver on which we apply a constant force and this constant force is applied on a random point of the mesh.

The scene :

<Node name="root" dt="0.05" gravity="0 -9.81 0">
    <!-- Constant force for a deformable -->
    <VisualStyle displayFlags="showBehaviorModels showForceFields" />
    <PythonScriptController name="randomForce" filename="randomForce.py" classname="randomize" listening="1"/>

    <MeshObjLoader name="VisualLoader" filename="mesh/liver-smooth.obj" />
    <MeshGmshLoader name="MecaLoader" filename="mesh/liver.msh" />

    <Node name="Liver" >
        <EulerImplicitSolver name="cg_odesolver"   rayleighStiffness="0.1" rayleighMass="0.1" />
        <CGLinearSolver name="linear solver" iterations="25" tolerance="1e-09" threshold="1e-09" />
        <TetrahedronSetTopologyContainer name="topo" src="@../MecaLoader" />
        <MechanicalObject name="dofs" src="@../MecaLoader" />
        <TetrahedronSetGeometryAlgorithms template="Vec3d" name="GeomAlgo" />
        <DiagonalMass  name="computed using mass density" massDensity="1" />
        <TetrahedralCorotationalFEMForceField template="Vec3d" name="FEM" method="large" poissonRatio="0.3" youngModulus="3000" computeGlobalMatrix="0" />
        <FixedConstraint  name="FixedConstraint" indices="3 39 64" />

        <ConstantForceField name="CFF" indices="14" forces="0 -10 0" />

        <Node name="Visu" tags="Visual" gravity="0 -9.81 0">
            <OglModel  name="VisualModel" src="@../../VisualLoader" />
            <BarycentricMapping name="visual mapping" input="@../dofs" output="@VisualModel" />
        </Node>

    </Node>
</Node>

The python script (randomForce.py):

import Sofa
import sys    
import random

class randomize(Sofa.PythonScriptController):
    
    # optionnally, script can create a graph...
    def initGraph(self,node):
        self.nodeLiver = node.getChild('Liver')
        self.activeRandomize=0

        #save a pointer to the ConstantForceField
        self.RandomForce = self.nodeLiver.getObject('CFF')
        return 0

    def bwdInitGraph(self,node):
        #count the number of points
        self.nbPoints = self.nodeLiver.getObject('dofs').findData("size").value
        print "nbPoints = "+str(self.nbPoints)
        return 0

    def onBeginAnimationStep(self,dt):
        # if active, randomly change the indice on which the force is applied
        if self.activeRandomize==1 :
            newIndice = random.randint(1,self.nbPoints)
            self.nodeLiver.getObject('CFF').findData("indices").value = newIndice
            print "Randomizing force on point = "+str(newIndice)
        return 0

    def onKeyPressed(self, c):
        if c=="L" :
            if self.activeRandomize==1 :
                self.activeRandomize=0
                print "Randomizing inactive"
            else:
                self.activeRandomize=1
                print "Randomizing active"
        return 0;

I hope this helps.
Best

Hugo

[minj]

Hi Hugo Hi Noura!
Thanks y’all for your replies.
It helped me so much.

Best,
Minji

[Hugo]

you are very welcome @minj
Do not hesitate to close the topic if it is solved.
Best

Hugo

[Author]

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