Object Collision behaviour

[Anonymous]

I am making two objects collide with each other (Triangle Topology Object with Triangle collision model, and a sphere collision model) , but when I do that my object which is .obj format when collided, it creates some form of spikes on the surface. Is this normal behaviour?

[mbarrow]

Hi Fayad.

I saw something similar when I had inappropriate values for ContactStiffness set, only I have to qualify this with the fact I was using only the Triangle Collision model.

Good luck!

[Binesh]

Hi @fayad
Do you have any FEM in your scene?

[Anonymous]

Yes I played with the stiffness to get rid of that behaviour, here is the code to have a better idea:

<!-- Add a mechanical model : Elasticity -->
<Node name="root" dt="0.01" gravity="0 0 0">

    <VisualStyle displayFlags="showCollisionModels hideVisualModels" />
    <DefaultAnimationLoop />
    <CollisionPipeline verbose="0" draw="0"/>
    <BruteForceDetection name="N2"/>
    <NewProximityIntersection name="Proximity" alarmDistance="0.005" contactDistance="0.0025"/>
    <CollisionResponse name="Response" response="default"/>

    <MeshObjLoader name="meshLoader" filename="/Users/fayad/Documents/hamad-work/sofa-work/Models/OBJ/LP/Prostate_02.obj" />

    <Node name="Prostate">
        <EulerImplicitSolver />
        <CGLinearSolver iterations="200" tolerance="1e-06" threshold="1e-06"/>

        <TriangleSetTopologyContainer name="topo" src="@../meshLoader" />
        <TriangleSetGeometryAlgorithms template="Vec3d" name="GeomAlgo" />

        <MechanicalObject template="Vec3d" name="myProstate" position="0 0 0" showObject="1"/>
        <TriangleFEMForceField name="FEM" youngModulus="1000" poissonRatio="0.4"  method="large" />

        <UniformMass totalmass="0" />
        <ConstantForceField force="0 0 0" />

        <Node name="Visu" >
            <OglModel  name="VisualModel" fileMesh="/Users/fayad/Documents/hamad-work/sofa-work/Models/OBJ/LP/Prostate_02.obj" texturename="/Users/fayad/Documents/hamad-work/sofa-work/virtualLabco/prostate.png"/>
            <BarycentricMapping name="VMapping" input="@../myProstate" output="@VisualModel" />
        </Node>

        <Node name="TriangularSurface">
            <TriangleSetTopologyContainer src="@../topo" name="Container" />
            <TriangleSetTopologyModifier   name="Modifier" />

            <Triangle name="CollisionModel" contactStiffness="1"/>

        </Node>

    </Node>

     <Node name="Sphere">
        <EulerImplicitSolver rayleighStiffness="0"/>
        <CGLinearSolver iterations="200" tolerance="1e-06" threshold="1e-06"/>
        <MechanicalObject template="Rigid" name="myParticle" position="2 10 0    0 0 0 0" showObject="1" showObjectScale="0.5" />
        <UniformMass totalmass="20" />
        <ConstantForceField force="0 -1 0 0 1 0" />
        <Sphere name="Floor" listRadius="1" simulated="1" moving="1" contactStiffness="3" />
    </Node>

</Node>

[Hugo]

Hi @fayad

I tested your scene with the “liver.obj” mesh from SOFA, since you did not share your Prostate mesh. It is actually working.

So, as @mjbarrow suggested, it should be due to an issue of numerical settings / parameters. Have you tested the contactStiffness? the time step might also be decreased ?

Best

Hugo

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